development of equatorial delta-front patch reefs …searg.rhul.ac.uk/pubs/wilson_2005 borneo patch...
TRANSCRIPT
JOURNAL OF SEDIMENTARY RESEARCH, VOL. 75, NO. 1, JANUARY, 2005, P. 114–133Copyright q 2005, SEPM (Society for Sedimentary Geology) 1527-1404/05/075-114/$03.00 DOI 10.2110/jsr.2005.010
DEVELOPMENT OF EQUATORIAL DELTA-FRONT PATCH REEFS DURING THE NEOGENE, BORNEO
MOYRA E.J. WILSONDepartment of Geological Sciences, Durham University, South Road, Durham, DH1 4EL, U.K.
email: [email protected]
ABSTRACT: Miocene patch reefs formed in turbid waters associatedwith high siliciclastic input at the seaward margin of the equatorialMahakam Delta in eastern Borneo, SE Asia. Patch reefs were initiatedon unstable substrates on localized low-relief bathymetric highs asso-ciated with delta-front channels or distributary mouthbars in the pro-cess of abandonment. Patch reefs developed only in shallow waters,formed low-relief buildups, lacked rigid frameworks, and had gentlysloping margins. Although the biodiversity of the patch reefs may becomparable with that of clear-water systems, all the organisms presentwere adapted to turbid-water areas associated with siliciclastic, andsometimes nutrient, influx. The patch reefs were transient features, andtheir demise was influenced by increased siliciclastic and nutrient in-put, perhaps at times associated with deepening.
Carbonate production and bioherm or patch-reef development canoccur in turbid-water delta-front areas as localized or more regionallyextensive units during any phases of eustatic sea level. However, de-velopment and preservation of turbid-water carbonates is most likelyduring relative transgression or perhaps late lowstand periods. This isin contrast with common highstand carbonates from clear-watershelves, where nearly pure carbonates interdigitate with siliciclastics.It is the interplay between factors such as tectonics, eustasy, delta lobeswitching, shelf currents, and amount and size fraction of siliciclasticinflux that ultimately controlled carbonate development and preser-vation.
INTRODUCTION
There is growing recognition that shallow-water carbonate productioncan and does occur in areas of coeval siliciclastic input (Mount 1984; Doyleand Roberts 1988; Woolfe and Larcombe 1998, 1999; Wilson and Lokier2002). Between 5 and 25% of coral reefs at any time throughout theirgeological history are known to have developed in siliciclastic, coastal, orrestricted settings, with the greatest abundances known from the Cretaceousand Tertiary (Kiessling 2002; Sanders and Baron-Szabo in press). However,previous detailed documented geological examples of mixed carbonate–siliciclastic systems tend to concentrate on successions in which nearly purecarbonates are interbedded with nearly pure siliciclastics (e.g., Dutton 1982;Santisteban and Taberner 1988; Braga et al. 1990). There is limited datafrom sections, particularly of Tertiary or Miocene age (Sanders and Baron-Szabo in press), in which coral-rich deposits contain a significant admixedsiliciclastic component, i.e., the in situ mixing category of Mount (1984).In particular there is a paucity of sections where detailed lateral and verticalfacies changes have been documented from siliciclastic-influenced reefs,and little quantification of deposit components and characteristics. Wheredata is available from siliciclastic coral deposits, such as from Jurassicsuccessions (Insalaco 1996, 1998; Leinfelder 2001; Dupraz and Strasser2002), the deposits are often highly localized, patchy, and of limited size(few meters). Sedimentological and morphological characteristics of turbid-water reefs are rarely described, and there is limited discussion of factorsinfluencing their local initiation, development, and demise. There is a finebalance between siliciclastic input and in situ mixed carbonate–siliciclasticdevelopment, with the actual responses of carbonate producers dependenton a range of factors including rates and frequency of clastic influx, grainsizes, energy, and the presence of nutrients (Wilson and Lokier 2002).
On a larger scale, although there is growing discussion of mixed car-
bonate–siliciclastic sequence development (Rankey et al. 1999), particular-ly for Cenozoic successions, most descriptions are of those with limited insitu admixing of components where highstand carbonates commonly de-velop (e.g., Ferro et al. 1999; Cunningham et al. 2003; Yang and Kominz2002). To date there is little discussion of influences on sequence devel-opment where in situ mixed carbonate–siliciclastic reefs developed, andlittle from delta-front areas with nearly constant siliciclastic input.
This study reveals that shallow-water carbonate production can occur inan apparently inhospitable environment; that of a proximal delta-front set-ting contemporaneous with high, constant siliciclastic input. Studies ofmodern patch reefs and their ancient equivalents from outcrop, core, andseismic from the Mahakam Delta, Borneo (Figs. 1, 2), allow evaluation ofsmall-scale temporal and spatial variations in facies and biotic distribution.These properties were influenced by local water depth, siliciclastic input,and water clarity. Regional development of delta-front patch reefs was con-trolled by a range of factors including intrinsic changes in the activity ofthe delta lobes, and by extrinsic relative variations in sea level, amountsof siliciclastic input related to tectonic uplift and climate, and changes inshelf currents.
The aims of this paper are threefold. (1) To describe the deposits, andevaluate the depositional environment, of patch reefs containing abundantadmixed siliciclastics that formed in a delta-front setting. (2) To evaluatethe depositional morphology and evolution of the patch reef deposits. (3)To evaluate the influences of local and regional factors on patch-reef anddelta-front sequence development from turbid-water areas. This is one ofthe first detailed geological studies of shallow-water reefs that were influ-enced by siliciclastic influx throughout their history. The study has impli-cations for siliciclastic–carbonate interactions, sequence development, andthe survival of comparable modern reefs forming in siliciclastic-impactedenvironments.
CARBONATE DEVELOPMENT AND THE MAHAKAM DELTA
Cenozoic plate-tectonic convergence in SE Asia and weathering in ahumid equatorial climate have resulted in high rates of Neogene uplift anderosion of the landmass of Borneo (Hall and Nichols 2002). Sedimentderived from this eroding landmass resulted in delta progradation and sig-nificant siliciclastic input into basinal areas to the north and east of Borneo(Hamilton 1979; Hutchison 1989; Wilson and Moss 1999; Hall and Nichols2002). The Mahakam Delta has been actively prograding eastwards andcontributing towards infilling the Tertiary Kutai Basin (Fig. 1) with around9 (Hamilton 1979; Hall and Nichols 2002) to 14 (Chambers and Daley1995) km of sediment since at least the early Miocene (van de Weerd andArmin 1992; Allen and Chambers 1998; Moss and Chambers 1999).
The formation of the modern Mahakam Delta has been influenced bymoderate tides of about 3 m, a steady, high fluvial input of between 500and 5000 m3/s, and very low wave energy (Allen and Chambers 1998).The morphology of this fluvially and tidally influenced delta is fan-shapedand lobate (Figs. 1, 3). A network of bifurcating fluvial distributaries radiateout from the Mahakam River and are actively forming mouthbars wherethey meet the sea (Allen and Chambers 1998). Separate highly sinuoustidal channels present on the lower delta plain allow drainage of tidal waterfrom interdistributary areas (Fig. 3). Tidal channels are up to 18 m deep,whereas the distributary channels are generally between 8–13 m deep. It isinferred from outcrop and core studies that the Neogene delta developedunder tide and wave conditions similar to those of the present day (Allen
115DELTA-FRONT PATCH REEF DEVELOPMENT
FIG. 1.—A) Location of Borneo in SE Asia, B) the research area in Borneo, and C) the locations of the patch reefs studied in eastern Borneo. Position of anticlinalstructures from Allen and Chambers (1998) and Alam et al. (1999).
FIG. 2.—Outcrop photograph looking north, showing deposits of the patch reef atAirputih dipping steeply towards the east. Upstanding ridge of the Permasip patch-reef outcrop is arrowed in the background.
and Chambers 1998). However, the development of the Kutai Lakes in theupstream part of the Mahakam River, due to post-Miocene uplift associatedwith growing thrust-top anticlines (Fig. 1C), is thought to have recentlydamped the effects of fluvial floods (Allen and Chambers 1998). Sourcerivers for the Mahakam Delta drain an area of ; 750,000 km2, and annual
rainfall in the drainage basin varies between 3000 and 4000 mm. Theaverage sediment supply to the delta is 8 3 106 m3/yr (Allen et al. 1976).Deposits of the Mahakam Delta are predominantly fine-grained with clay-and silt-size particles constituting ; 70% of the material and sand theremainder (Allen et al. 1976).
Despite high siliciclastic input to the Mahakam Delta, modern and Pleis-tocene carbonates are known from two settings in the delta front. Theseare proximal patch reefs and more distal shelfal buildups developed inwater depths of , 10 m and between 30–100 m, respectively (Fig. 3;Roberts and Sydow 1996). Delta-front reefs are not just a recent phenom-enon, in that outcrop (Figs. 1, 2) and subsurface (Figs. 3, 4; Alam et al.1999; Hook and Wilson 2003) carbonates within the Neogene deltaics areanalogous to modern deposits.
Miocene onshore carbonate outcrops (Figs. 1C, 2) are the subject of thisstudy. Using the lithostratigraphic scheme of Land and Jones (1987), theseare classified as the Batih Putih Limestone (equivalent to the Bebulu Car-bonates; Moss and Chambers 1999). The Batu Putih Limestone was orig-inally interpreted as being older than the deltaics and deep-water shalesthat entomb them (Land and Jones 1987). However, these carbonates arein fact transitional shelf deposits that accumulated contemporaneously be-tween deep marine deposits and deltaics (Fig. 5; Allen and Chambers1998).
The Pleistocene and Recent distal carbonates, imaged using shallow seis-mic, occur mainly on the northern part of the shelf, forming mounds, plat-forms, and buildups (Figs. 3, 4; Roberts and Sydow 1996). Bioherms of
116 M.E.J. WILSON
FIG. 3.—Composite plan view showing the location of modern and Holocenecarbonate buildups (identified on seismic; from Roberts and Sydow 1996) and SLARimage of the modern Mahakam Delta (from Magnier et al. 1975). Extent of Holocenedeltaic units (H1 and H2) are shown (see also Fig. 4). On SLAR image, typicaldistributary (D) and tidal (T) channels are highlighted.
the inner and middle shelf are commonly 15–25 m thick but may be up to40 m thick. These bioherms are inactive and have been covered with aclay-rich siliciclastic layer 0.5–2 m thick. Roberts and Sydow (1996) reportthat shallow vibracores from the upper few meters of the bioherms retrievedabundant Halimeda plates together with common coralline algal rhodoliths
and formainifera in a micritic to clay matrix. Their radiocarbon dates re-vealed that these uppermost bioherm deposits accumulated less than 12 kaago. Along the shelf margin, buildups with 40–120 m relief proved difficultto core. The well-sorted sediments retrieved by Roberts and Sydow (1996)contained common foraminifera, coralline algal rhodoliths, molluscs, andsolitary corals. These shelf carbonates were inferred to have developed ontransgressive ravinement surfaces with the thin mud layer draping the bioh-erms on the inner and middle shelf interpreted as late highstand to lowstanddeposits (Roberts and Sydow 1996). The recent concentration of carbonatesaround the northern part of the delta is related to two factors. The southerndelta lobe is currently more active than the northern lobe, and the Indo-nesian Throughflow Current flowing southwards with velocities of up to90 cm/s both result in less-turbid waters to the north (Roberts and Sydow1996). Neogene carbonates were also concentrated in the north, althoughthere was variation through time. Nutrient loading has been suggested asa factor contributing to abundant Halimeda development on the inner-shelfbioherms (Roberts and Sydow 1996).
METHODOLOGY
Sedimentary outcrop logging, sample collection, and facies mappingwere undertaken on seven patch-reef complexes in eastern Borneo (Fig. 1).The carbonates are interbedded with Miocene deposits of the proto–Ma-hakam delta, and are exposed in the limbs of NNE–SSW trending rolloveranticlines associated with Miocene and younger basin inversion (Chambersand Daley 1995; Allen and Chambers 1998). Excellent two- to three-di-mensional outcrops (Fig. 2), with up to 90% exposure, allowed sectioncorrelation through individual patch reefs. Dip directions are towards theESE or WNW, and dip angles vary from ten degrees to nearly vertical.The carbonates crop out as isolated areas of upstanding modern karst, 200m to 4 km across, and up to 200 m high (Fig. 2). Outcrops were studiedin active quarries (Figs. 2, 6A), disused, often densely vegetated quarries,and on unquarried karst. Despite the low-tech ‘‘sledgehammer’’ method ofquarrying, many of the sections were being rapidly removed and no longerexist.
Twenty-three sections through the seven reef complexes were logged,and of the 250 samples collected, 130 were studied petrographically. Thinsections were half stained with Alizarin Red S and potassium ferricyanideto highlight different carbonate phases. Point counting of thin sections pro-vided additional quantitative data. Micropaleontology, larger benthic fora-minifera (BouDagher-Fadel and Wilson 2000), and coral analysis of handspecimens, thin sections, and sieved samples was undertaken to obtain ad-ditional biostratigraphic and environmental data. Fifty samples were dis-solved in 10% hydrochloric acid to determine the percentages of carbonateand siliciclastics present. Analysis of the mineralogical components of theclay-size fraction from 20 samples was undertaken by X-ray diffraction.
SHALLOW-WATER PATCH REEFS
Locations, Ages, and Dimensions of Patch Reefs
The locations, ages, and characteristics of the seven patch reefs studiedare shown in Figures 1 and 7, and in Table 1. The western patch-reefoutcrops at Senoni and Kota Bangun are older (early Miocene) than thoseexposed to the east at Airputih, DPR, Permasip, Badak, and Bontang (earlyto predominantly middle Miocene; BouDagher-Fadel and Wilson 2000) onthe basis of larger benthic foraminifera and nannofossil biostratigraphy (Ta-ble 1). Individual patch-reefs are up to 2–4 km across and have post-compactional thicknesses of up to 40 m. Patch-reef thickness may varyconsiderably along strike, with variations from 201 m to less than 10 mseen over lateral distances of 200–300 m at Airputih and Permasip. Car-bonate and mixed carbonate–siliciclastic facies of the patch reefs, overlie,interdigitate with, and are overlain by fine-grained siliciclastic deposits ofthe delta (Figs. 6B, C, D). An area where a patch reef has developed may
117DELTA-FRONT PATCH REEF DEVELOPMENT
FIG. 4.—A) Schematic stratigraphic summary of the Mahakam shelf and B) high-resolution D21 seismic line across bioherms from the mid-shelf (from Roberts andSydow 1996). Seismic facies, important units of Holocene (H) and Pleistocene (P) ages, and surfaces (DL—Downlap) are shown together with the locations of shallowvibracores V25 and V26. Inset map shows lines of section.
FIG. 5.—Simplified lithostratigraphic relationship diagram (from Allen and Chambers 1998) showing the position of the Batu Putih Limestone relative to the adjacentdeltaics (Loa Kulu Formation) and deeper-water shales (Loa Duri Formation). Alluvial flood-plain facies are represented by the Prangat and Kambola Formations.
be the location for later patch reefs to form. This relationship is seen atSenoni and Permasip, where the older patch reefs are separated from youn-ger patch reefs by 15–20 m and 75–100 m of deltaic siliciclastics respec-tively.
Patch-Reef and Associated Deltaic Facies and Successions
Twelve facies were identified, based on their constituent components,textural and lithologic characteristics (Table 2). These facies were subdi-vided into three facies associations, on the basis of weight % insoluble non
carbonate material. These are siliciclastic facies (. 95% siliciclastics),mixed carbonate–siliciclastic facies, or mixed facies (35–90% siliciclastics),and carbonate facies (6–35% siliciclastics). Throughout the reefal succes-sion there is consistently greater than 6% by weight of insoluble siliciclasticmaterial, most of which consists of clays and silts.
The carbonate and mixed facies are classified on the basis of the texturalschemes of Dunham (1962) and Insalaco (1998). The latter is an expansion,and modification, of the Embry and Klovan system (1971), and is suitedto describing coral growth fabrics with subdivisions based on dominantgrowth forms. The subdivisions are domestone (domal and massive colo-
118 M.E.J. WILSON
119DELTA-FRONT PATCH REEF DEVELOPMENT
FIG. 7.—Simplified diagram showing ages, dimensions, and characteristics of the patch-reef deposits. The predominantly siliciclastic facies of the proto–Mahakam Deltapresent between the patch reefs are not shown. Lateral distances between patch reefs are not drawn to scale. The Bontang, Permasip, Airputih, and Senoni localities werecharacterized by multiple measured sections, whereas the Badak, Dibelakan Parliament, and Kota Bangun localities have limited lateral extent and were studied in singlemeasured sections.
←
FIG. 6.—Representative outcrop photographs and thin-section photomicrographs of lithologies from the Miocene siliciclastic influenced delta-front patch reefs of Borneo.A) Quarried outcrop of patch reef carbonates at Senoni. The piles of carbonate rocks under the shelter have been broken by hand for use mainly as roadstone. B) Basaldeposit of the patch reef at Senoni showing bedded and laminated silts and clays passing gradationally upwards into platy coral sheetstones (p). C) Close-up photographof part B showing interlaminated silts and clays at base of patch reef at Senoni (Section SB). D) Plane-polarized-light (PPL) photomicrograph of sandy packstone fromAirputih (sample AE2). Fragmented bioclasts are mainly larger benthic foraminifera. Field of view 1 cm 3 1.7 cm. E) Platy coral sheetstone from the base of patch reefat Airputih (Section AA) containing about 60% insoluble fine-grained siliciclastics. F) In situ recrystallized head coral from coral domestone at Airputih. Surroundingmatrix is gray and contains 10% fine-grained siliciclastics. G) PPL photomicrograph of branching coral float–rudstone with recrystallized corals (c) encrusted by foraminifera(f) from Airputih. Field of view 2 cm 3 3.2 cm. H) Larger benthic-foraminifera packstones capping the patch reef at Airputih; the PPL photomicrograph shows Miogypsina.Field of view 1 cm 3 1.7 cm. I) PPL photomicrograph of Halimeda wackestone from top of patch reef section at Permasip. Field of view 1 cm 3 1.7 cm.
nies), pillarstone (vertical branches), platestone and sheetstone (flattenedhorizontal forms with a width-to-height ratio of between 30:1–5:1 and .30:1, respectively) and mixstone (no one growth form dominates). Al-though corals dominate through much of the patch-reef deposits, largerbenthic foraminifera, coralline algae, molluscs, and Halimeda are locallyabundant, particularly in the mixed facies.
Patch reefs show distinct vertical and lateral variations in facies and biotaassociated with siliciclastic content (Figs. 7, 8, 9, 10). Characteristic reefalsuccessions consist of lithologies recording an up-section trend in coralmorphologies dominated successively by platy, branching, head, branching,and platy forms (Figs. 8, 6E, F, G). Associated with these changes in biotathere is a marked decrease in siliciclastic content from up to 80% in sheet-stones to less than 20% in domestones. Carbonate facies in the ‘‘core’’ of
the patch reefs pass gradationally vertically and laterally into basal, upper,and marginal mixed facies, which in turn are surrounded by siliciclasticfacies of the delta. Siliciclastic facies pinch out into, or onlap onto, mixedfacies of the patch-reef margins. Complete vertical successions of silici-clastics, then mixed and carbonate facies, passing back into mixed andsiliciclastic facies, with characteristic facies development of sheetstones,pillarstones, domestones–mixstones, then back into pillar and sheetstonesas described below, occur only where sections cut through patch-reef cen-ters. Some sections with just mixed facies, such as at Badak, probably cutthrough the margins of a patch reef. However, ‘‘full’’ patch-reef devel-opment with accumulation of carbonate facies may not have occurred inall areas. Although vertical and lateral changes in facies are generally gra-dational, vertical successions may be truncated and capped by another fully
120 M.E.J. WILSON
or partially developed succession, or mixed facies may sharply overlie car-bonate facies. The upper to middle parts of meter-scale units of siliciclasticfacies at the margins of the patch reefs often correspond with boundariesbetween two stacked successions towards the reef center.
Siliciclastic Facies
Two siliciclastic facies were encountered: a shale–clay facies, and aninterlaminated silty sand and clay facies (Table 2). These facies underlie,overlie, and are interbedded with deposits from the margins of the patchreefs, with the shale–clay facies usually adjacent to, and passing grada-tionally into, mixed facies (Fig. 6B). Dark gray shale–clay deposits maybe massive, bioturbated, or laminated on a millimeter scale and includecross-laminated stringers of silty sand. Clays, such as kaolinite and smec-tite, are the main components of this facies. Most units contain a fewpercent of unabraded, flattened larger benthic foraminifera, and whole ordisseminated plant material.
The silty to fine or medium-grained sand of the interlaminated silty sandand clay facies is quartz rich, contains abundant clay drapes and laminae,and is often cross-laminated or planar-laminated on a millimeter scale (Fig.6C). Ripples have asymmetric to symmetric form, and facing direction ofasymmetric ripples is unidirectional to more rarely bidirectional with up toa few tens of degrees variability. Bioturbation, although commonly absent,may disrupt some bedding. Load and flame structures are present. Wherepresent, carbonate bioclasts consist of fragmented shelly material and fo-raminifera. Disseminated carbon and well-preserved leaves are common,particularly along laminae surfaces.
Interpretation.—Both facies are inferred to have accumulated underpredominantly low to moderate energy conditions, on the basis of theirsmall constituent grain sizes, and presence of parallel lamination and well-preserved plant material. Fluctuations in energy are suggested for the siltysand, because of the abundance of clay drapes and laminae. The rippleforms are indicative of deposition under low-velocity wave and/or currentflow, with some evidence for both a predominant flow direction and bidi-rectional flows. The influence of tides would be consistent with the vari-ations in current direction and inferred changes in velocity. Both facies areinferred to have accumulated above fair-weather wave base on the basis ofthe presence of wave-formed ripples. The well-preserved larger benthicforaminifera in the shale–clay facies are indicative of deposition in a marinesetting within the photic zone. It is suggested that high influx of clays and/or turbid waters hindered further development of photoautotrophs. Waterdepth is not thought to have been a factor limiting carbonate producers,because these facies are interbedded with the marginal deposits of the patchreef. Rapid sedimentation under waterlogged conditions is inferred for thesilty sands, on the basis of load and flame structures. The siliciclastic grainsmaking up these facies are inferred to have been predominantly terrestriallyderived, judging by abundant reworked material from land plants. Thisinterpretation is supported by the occurrence of kaolinite, a clay mineralmost commonly formed in equatorial terrestrial settings. Because marinebioclasts were absent from some of the silty sand facies, it may be thatsome of this facies developed under brackish conditions. A shallow, delta-front depositional environment is inferred for these facies on the basis ofthe combined evidence of wave activity, high sedimentation rates, a ter-restrial influx, and the suggestion of tidal activity in a marine to perhapsbrackish environment.
Through comparison with cored deposits of the modern Mahakam Delta(Carbonel and Moyes 1987; Gastaldo and Huc 1992; Allen and Chambers1998), it is possible to more accurately define likely depositional environ-ments for the two siliciclastic facies. Medium- to fine-grained sand and siltare localized in channels and at the delta front (Allen and Chambers 1998;Gastaldo and Huc 1992). The interlaminated silty sand and clay facies mostclosely resembles the muddy sand facies of Allen and Chambers (1998)and the bioturbated sand–mud couplet facies of Gastaldo and Huc (1992).
These modern facies are most commonly observed in the lower reaches ofthe distributary channels with a tidal influence, in subaqueous channels atthe delta front adjacent to mouth bars, and as an infill to abandoned chan-nels at the delta front, or sometimes in interdistributary areas. The shale–clay facies of this study is comparable with gray to black muds found ininterdistributary areas, in abandoned channel fills at the delta front, and atthe periphery of distributary mouth bars (Gastaldo and Huc 1992; Allenand Chambers 1998). Some of the more massive, homogeneous clays maybe prodelta muds, which in the modern delta are accumulating in waterdepths of 5 to 70 m (Allen et al. 1976; Allen and Chambers 1998). Theoverall succession at the base of the patch reefs of interlaminated silty sandsand muds, passing upwards into shale–clay facies is most consistent withabandonment and then colonization of: (1) a tidally influenced distributarychannel, (2) a tidal channel, or (3) the margins of a distributary mouthbaradjacent to a channel (cf. Allen and Chambers 1998).
Mixed Carbonate–Siliciclastic Facies
The four facies in this association all contain 35–90% siliciclastics aswell as common to abundant skeletal bioclasts (Table 2). Three facies (theplaty coral sheetstone, the clayey wackestone, and the larger benthic fo-raminifera packstone) contain a dark gray, predominantly clay matrix. Thematrix of the bioclastic sand is a muddy fine to medium quartz-rich sand(Fig. 6D).
The platy coral sheetstones invariably form the basal few meters of thepatch reefs (Fig. 6B), and are also common towards their top and margins.The shales–clays below the patch-reef deposits pass gradationally upwardsinto the sheetstones containing abundant laminar and platy corals, such asPachyseris and Leptoseris (Fig. 6E). The sheetstones contain up to 80%clayey matrix, although there is a general trend up section for platy coralsto become larger and thicker associated with a decreased siliciclastic con-tent (; 40%), resulting in sheetstone–platestone textures. Other bioclastspresent are pectens, solitary corals, such as Cycloseris, and flattened largerbenthic foraminifera up to 2.5 cm across. Although uncommon, encrusta-tion by coralline algae and larger benthic foraminifera is present on boththe upper and lower surfaces of corals.
Deposits of the clayey wackestone facies are common along patch-reefmargins closest to siliciclastic input, and may also be present in the upperparts of the reefs. This facies includes a comparable siliciclastic content(50–70%) and similar bioclastic components to the platy coral sheetstonefacies. However, instead of platy corals, delicate branching Tubastrea upto a few millimeters in diameter are dominant, and are preserved bed par-allel and compacted.
The larger benthic foraminifera facies predominantly forms the upper-most unit capping earlier patch-reef deposits. Characteristic of this faciesis an abundance of well-preserved, curved, flattened, to robust larger ben-thic foraminifera (Fig. 6H), aligned parallel to bedding. Miogypsina, Am-phistegina, and, in Serravallian Tf2 deposits, Katacycloclypeus are abun-dant, with less common Lepidocyclina and Cycloclypeus (BouDagher-Fadeland Wilson 2000). Rhodoliths may be common, and are formed by cor-alline algae encrusting the larger benthic foraminifera. Other componentsin the clayey micritic matrix are pectens, gastropods, and echinoid spines.
Bioclastic sands are interbedded with siliciclastic facies at the marginsof the patch reefs and may cap reef deposits. This facies is predominantlyhomogeneous, although it may be burrowed along bed surfaces. Bioclastsmake up to 20% by weight and include larger benthic foraminifera, pectens,shelly fragments, and echinoid spines (Fig. 6D). Disseminated plant ma-terial is common (5%).
Interpretation.—Marine depositional conditions are inferred for allthese facies, on the basis of the common occurrence of well-preservedstenohaline biota. There is minimal breakage and abrasion of bioclasts,particularly in facies containing the clayey matrix, and most of the bioclastsare inferred to be in situ, or very close to in situ. Because a number of the
121DELTA-FRONT PATCH REEF DEVELOPMENT
TABLE 1.—Locations, ages, and characteristics of patch reefs.
Patch Reef Latitude Longitude Age Lateral Continuity Thickness and Notes
Kota Bangun (KB) - 1 section 00824917.710 S 116845939.620 E Early Miocene 2001 m One patch reef (KB, 20 m thick), composed of 1fully developed succession
Senoni (S) - 3 sections (SA-SC) 00819953.450 S 116850944.350 E Early Miocene (Lower Tfl orolder)
5001 m Two stacked patch reefs, each composed of onefully to partially developed succession. Lowerpatch-reef deposits (SA and SC, 30 m) separatedfrom upper (SB, 101 m) by 15–20 m of poorlyexposed shales and interbedded fine sandstonesand siltstones.
Airputih (A) - 11 sections (AA-AL)
00828904.780 S 117807901.350 E Early to predominantly MiddleMiocene (Tfl-2 and NN4-NN5).
2500 m One patch reef (up to 30 m thick) composed oftwo fully to partially developed amalgamatedsuccessions. 1–2 m thick beds of shales and in-terbedded fine sandstones to siltstones interdigi-tate with the patch-reef deposits at their margins.
Dibelakan Parliament (DPR) - 1section
00830929.790 S 117806906.500 E Early to predominantly MiddleMiocene (NN4-NN5)
1001 m One patch reef (10 m thick), composed of 2 par-tially developed stacked successions, separatedby 2 m of laminated shale.
Permasip (P) - 5 sections (PA-PE)
00825936.080 S 117808903.260 E Early to predominantly MiddleMiocene (middle to upper Tfland NN3-NN5)
4000 m Two stacked patch reefs, separated by 75–100 mof shales and interbedded fine sandstones to silt-stones. Lower patch reef (PA-PD, up to 36 mthick) is composed of 2 amalgamated fully topartially developed successions. Upper patchreef (PE, 17 m) is composed of 1 to 2 fully topartially developed succession(s).
Badak (BA) - 1 section 00818937.940 S 117817922.470 E Middle Miocene 1001 m At least 1 patch reef with 1 partially developedsuccession (BA, 51 m thick). outcrop veryheavily disturbed by bulldozing, originally moreextensive.
Bontang (BB) - 2 sections 00801905.350 S 117821902.100 E Early to Middle Miocene (NN3-NN5)
1501 m One patch reef (15–20 m thick), composed of onepartially to fully (BB1–15) developed succes-sion.
skeletal components are photoautotrophs, production occurred in the photiczone. The abundance of clay-size particles, and good preservation of del-icate bioclasts, in the platy coral sheetstones and clayey wackestone isindicative of their formation under low energy conditions. Moderate energyconditions are inferred for the larger benthic foraminifera packstones andsandy packstones on the basis of the occurrence of sand-size particles, someabrasion of bioclasts, and the robust, lenticular shapes of some of the largerbenthic foraminifera present (cf. Hallock and Glenn 1986). All the faciesformed under moderate to high siliciclastic input. The presence of commondisseminated plant material in the sandy packstone facies is indicative ofa terrestrial input and nutrient influx during deposition of this facies. Thecommon occurrence of coralline algae and disseminated carbon in the larg-er benthic foraminifera packstone facies is also suggestive of accumulationunder high nutrient conditions.
Among photoautotrophs, thin and flattened shapes, with a high surfacearea to volume ratio, are an adaptation to production in environments withlow incident irradiation (Hallock and Glenn 1986). Deposits containingpredominantly thin platy corals form in marine environments with littlelight penetration, either in clear, deep-water settings towards the base ofthe photic zone, or in turbid waters, where suspended material hinders lightpenetration (Rosen et al. 2002). The platy coral sheetstones are inferred tohave formed in the later turbid-water setting, because they contain abundantclay-size material. In life, at least some of the platy corals grew projectingabove the sediment surface, as inferred from encrustation on their under-side. Angled, tiered, or whorled growth forms of platy corals facilitate theshedding of sediment (Rosen et al. 2002). Whorled platy corals have beenrecorded from modern turbid environments where only the outer marginshave live tissue and the central portion is covered in fine-grained silici-clastics (Riegl et al. 1996; Tomascik et al. 1997).
A low-energy, turbid depositional setting is also inferred for the clayeywackestone facies. Being azooxanthellate, Tubastrea does not require sun-light and is today reported in abundance from cryptic reef habitats, under-hangs, cave walls, deep reef slopes, and very turbid environments in In-donesia (Tomascik et al. 1997). It is here suggested from the presence oflarger benthic foraminifera co-occurring with Tubastrea that the clayeywackestone facies developed under low light levels rather than in the dark.
Tomascik et al (1997) noted that where Tubastrea is present in modernturbid waters, the environment is commonly current-swept. During accu-mulation of the clayey wackestone facies, currents may have been a factorin breakage of the Tubastrea and maintaining low water clarity, hinderingabundant development of photoautotrophs. However, it is inferred that ve-locities of any currents were not high, judging by the delicate growth formsof corals and the abundance of clay-size material.
The depositional setting of the larger benthic foraminifera packstone fa-cies is constrained from the life habits and paleoecology of the highlyabundant foraminifera present (BouDagher-Fadel and Wilson 2000). Mio-gypsina has a median layer composed of many convex cubiculae, whichact as lenses focusing sunlight and providing a ‘‘greenhouse environment’’for the development of symbiont diatoms. It is likely that Miogypsina, andKatacycloclypeus (Rottger 1971), relied on their symbionts to provide nu-trients, with their pseudopodia little used for food gathering. Because theseforaminifera were reliant on their symbionts for energy, they occurred onlyin shallow-water environments with high incident light. The irregular shapeof many of the Miogypsina in this facies result from a sedentary life habiton a strongly curved substrate, such as seagrass. The larger benthic fora-minifera deposits therefore formed in shallow seagrass beds, under low tomoderate energy conditions associated with fine siliciclastic input, possiblyin areas of high nutrient input.
The bioclastic sand units are comparable with the modern bioclastic sandfacies of Gastaldo and Huc (1992), and are inferred to have formed asdelta-front or distributary-mouth-bar deposits. Allen and Chambers (1998)note that similar deposits are forming where an inactive mouthbar at theentrance to an abandoned distributary channel is currently being colonizedby marine fauna.
Carbonate Facies
The six facies in this association (Table 2) contain 6–35% predominantlyclay-size siliciclastic material. Four of the facies—the branching coral pil-larstone, the head coral mixstone–domestone (mix–domestone), the coralrud–floatstone, and the coralline algae and coral floatstone include 20–60%corals. Although corals are present (, 30%) in the bioclastic wacke–pack–
122 M.E.J. WILSONTA
BLE
2.—
Asso
ciat
ions
,des
crip
tions
,and
infe
rred
depo
sitio
nale
nvir
onm
ents
offa
cies
.
Faci
esA
ssoc
iatio
nan
dFa
cies
Lith
olog
ies
Loca
tion
and
Occ
urre
nce
Bed
Thic
knes
sB
edC
onta
cts
Late
ralC
ontin
uity
Com
pone
nts
Sedi
men
tary
Stru
ctur
es%
Non
carb
onat
eEn
viro
nmen
tal
Inte
rpre
tatio
n
Silic
icla
stic
faci
esas
soci
atio
n( .
95%
silic
icla
stic
s)
Shal
e-cl
ayfa
cies
Lam
inat
edsh
ale,
lam
inat
-ed
silty
shal
e,sh
ale-
clay
.
Bas
eof
succ
essi
on:o
verla
inby
plat
yco
ralp
late
-she
etst
ones
.Mar
gins
ofpa
tch
reef
:int
erbe
dded
with
plat
yco
rals
heet
ston
esan
dco
ralli
neal
gae
and
cora
lfloa
tsto
nes.
Top
ofsu
cces
-si
on:o
verli
espl
aty
cora
lpla
te-
shee
tsto
nes
orla
rger
bent
hic
fora
mi-
nife
rapa
ckst
ones
.
dm/m
Plan
aror
undu
lose
and
grad
atio
nal.
Met
res
to10
sm
etre
sPr
edom
inan
tly( .
95%
)cl
ays
(kao
linite
&sm
ectit
e),s
ilt(q
uartz
)and
min
orm
icrit
e.Fl
atte
ned
larg
erbe
nthi
cfo
ram
inife
ra( ,
1%),
smal
lben
thic
fora
min
ifera
,bar
ren
ofna
nnof
ossi
ls.D
isse
min
ated
carb
onan
dle
aves
(2–4
%).
Fiss
ile,m
mpa
ralle
lla
min
atio
n,ho
-m
ogen
eous
orbi
otur
bate
d.So
me
cros
s-la
mi-
nate
dsi
ltysa
ndst
ringe
rs.
.95
%Lo
w-e
nerg
yde
posi
ts,
abov
efa
ir-w
eath
erw
ave
base
.Loc
ally
aero
bic.
Silty
sand
and
clay
faci
esLa
min
ated
silty
sand
and
clay
.B
ase
ofsu
cces
sion
:ove
rlain
bysh
ale–
clay
.Top
ofsu
cces
sion
:ove
rlies
shal
e-cl
ay.
cm/d
mPl
anar
and
shar
por
grad
a-tio
nal.
Met
res
to10
sm
etre
sQ
uartz
-ric
hsi
ltysa
ndw
ithof
ten
abun
dant
clay
lam
inae
.Abu
ndan
tdis
sem
inat
edca
r-bo
n,an
dw
ell-p
rese
rved
leav
esal
ong
lam
-in
ae.F
ragm
ente
dsh
ells
(3–4
%).
mm
para
llela
ndcr
oss-
lam
inat
ion.
Load
and
flam
est
ruct
ures
.Bio
-tu
rbat
ion.
Som
em
assi
vesa
nds.
.95
%Lo
wto
mod
erat
e-en
ergy
abov
efa
irw
eath
erw
ave
base
.Sig
nific
ants
ilici
-cl
astic
inpu
t.
Mix
edca
rbon
ate-
silic
icla
stic
faci
esas
soci
atio
n(3
5–80
%si
licic
last
ics)
Plat
yco
rals
heet
ston
efa
-ci
esPl
aty
cora
lshe
et-p
late
-st
one.
Bas
eof
succ
essi
onan
dm
argi
nsof
patc
hre
ef:o
verli
essh
ale
faci
es,i
n-te
rdig
itate
sw
ith,a
ndov
erla
inby
bioc
last
icw
acke
-floa
tsto
nes
and
bran
chin
gco
ralp
illar
ston
e.To
pof
succ
essi
on:o
verla
inby
larg
erbe
n-th
icfo
ram
inife
rapa
ckst
ones
,int
er-
digi
tate
sw
ithbi
ocla
stic
wac
ke-fl
oat-
ston
es.
dm/m
Plan
aror
undu
lose
and
grad
atio
nal.
Met
res
to10
sm
etre
sW
ell-p
rese
rved
,abu
ndan
tpla
tyco
rals
(20–
40%
),up
tofe
wcm
thic
kan
d40
cmac
ross
.Fra
gmen
ted
unab
rade
dpl
aty
and
bran
chin
gco
rals
.Dis
c-sh
aped
solit
ary
cora
ls(1
–2%
),fe
wcm
acro
ss.F
latte
ned
larg
erbe
nthi
cfo
ram
inife
ra(2
–3%
).Pe
c-te
nsan
dga
stro
pods
(1–2
%).
Hal
imed
a( ,
10%
).C
oral
line
alga
een
crus
tatio
nat
top
ofse
ctio
n.A
bund
antc
lay,
min
orsi
ltan
dm
icrit
em
atrix
(20–
45%
).
Plat
yco
rals
bed
para
llel.
Atb
ase
ofsu
cces
sion
in-
crea
sein
thic
k-ne
ssan
dsi
zeof
plat
yco
rals
up-
war
ds.F
riabl
e.
40–8
0%Lo
w-e
nerg
yde
posi
tsin
phot
iczo
ne.I
nsi
tugr
owth
ofpl
aty
cora
lsin
turb
idw
ater
sw
ithhi
ghin
flux
offin
esi
licic
las-
tics.
Cla
yey
wac
kest
one
faci
esB
ranc
hing
cora
lcla
yey
wac
kest
one,
Bra
nchi
ngco
rala
ndfo
ram
inife
racl
ayey
wac
kest
one.
Top
ofsu
cces
sion
and
mar
gins
ofpa
tch
reef
:int
erbe
dded
with
wac
ke-
float
ston
esan
dco
ralr
ud-fl
oats
tone
s.
dm/m
Plan
aror
undu
lose
and
shar
por
grad
atio
nal.
Met
res
to10
sm
etre
sD
ark
gray
clay
mat
rix(4
0–70
%).
Abu
ndan
tfla
ttene
dbr
anch
ing
cora
ls,f
ewm
mdi
am-
eter
(30–
40%
),fla
ttene
dla
rger
bent
hic
fo-
ram
inife
ra( ,
5%),
disc
-sha
ped
solit
ary
cora
ls(1
–2%
),fe
wcm
acro
ss.
Elon
gate
larg
erbe
nthi
cfo
ram
i-ni
fera
mos
tlybe
dpa
ralle
l.
50–7
0%Lo
w-e
nerg
y,hi
ghin
flux
ofcl
ays
inph
otic
zone
.Bi-
otic
prod
uctio
nin
turb
idw
ater
s.
Sand
ypa
ckst
one
faci
esB
iocl
astic
sand
ypa
ck-
ston
e.To
pof
succ
essi
onan
dm
argi
nsof
patc
hre
ef:o
verli
espl
aty
cora
lsh
eets
tone
s,ov
erla
inby
mud
ston
es.
dmPl
anar
and
shar
por
grad
a-tio
nal.
Met
res
Qua
rtz-r
ich
(30%
)pa
ckst
one,
with
clay
eym
atrix
.Dis
sem
inat
edpl
antm
ater
ialc
om-
mon
(5%
).Fl
atte
ned
larg
erbe
nthi
cfo
ra-
min
ifera
(10%
),pe
cten
s(2
–4%
)an
dec
hi-
noid
spin
es(2
–3%
).
Fria
ble.
Bur
row
sco
mm
onal
ong
bed
surf
aces
.
60%
Mod
erat
een
ergy
influ
xof
fine
sand
and
nutri
ents
abov
efa
ir-w
eath
erw
ave
base
.Som
ebi
otic
pro-
duct
ion.
Larg
erbe
nthi
cfo
ram
inif-
era
pack
ston
efa
cies
Larg
erbe
nthi
cfo
ram
inif-
era
wac
ke-p
acks
tone
,rh
odol
ithan
dla
rger
-be
nthi
c-fo
ram
inife
rabi
ocla
stic
pack
ston
e.
Top
ofsu
cces
sion
:Ove
rlies
plat
yco
ral
shee
tsto
nes,
over
lain
bysh
ale-
clay
faci
es,c
oral
line
alga
ean
dco
ral
float
ston
es,o
rco
ralr
ud-fl
oats
tone
s.
dmPl
anar
orun
dulo
sean
dsh
arp.
Met
res
to10
0sm
etre
sA
bund
antl
arge
rbe
nthi
cfo
ram
inife
ra,u
pto
1.5
cmac
ross
,thi
n,fla
tand
mor
ero
bust
form
s(2
5–50
%).
Som
efr
agm
enta
tion
and
encr
usta
tion
byco
ralli
neal
gae
ofro
bust
fora
min
ifera
.Rar
epl
ankt
onic
fora
min
if-er
a.W
ell-p
rese
rved
pect
ens
and
gast
ro-
pods
(2–3
%).
Fria
ble
clay
–silt
mat
rix.
Elon
gate
larg
erbe
nthi
cfo
ram
i-ni
fera
mos
tlybe
dpa
ralle
l.
20–5
0%Lo
wto
mod
erat
een
ergy
inph
otic
zone
.Uns
tabl
esh
iftin
gsu
bstra
te,p
ossi
-bl
yw
ithse
agra
ssin
tur-
bid
wat
erw
ithco
nsid
er-
able
fine
silic
icla
stic
inpu
t.
123DELTA-FRONT PATCH REEF DEVELOPMENT
TAB
LE2.
—C
ontin
ued.
Faci
esA
ssoc
iatio
nan
dFa
cies
Lith
olog
ies
Loca
tion
and
Occ
urre
nce
Bed
Thic
knes
sB
edC
onta
cts
Late
ralC
ontin
uity
Com
pone
nts
Sedi
men
tary
Stru
ctur
es%
Non
carb
onat
eEn
viro
nmen
tal
Inte
rpre
tatio
n
Car
bona
tefa
cies
asso
ciat
ion
(6– ,
35%
silic
icla
stic
s)
Bra
nchi
ngco
ralp
illar
-st
one
faci
es.
Bra
nchi
ngco
ralp
illar
-st
one,
Bra
nchi
ngan
dpl
aty
cora
lpill
ar-fl
oat-
ston
e,
Low
erto
mid
dle
part
ofsu
cces
sion
:in
terb
edde
dw
ithbr
anch
ing
and
head
cora
lmix
–dom
esto
nes
and
plat
yco
rals
heet
-pla
test
ones
.
dm/m
Plan
aror
undu
lose
and
shar
por
grad
atio
nal
Met
res
to10
sm
etre
sPr
edom
inan
tlyin
situ
bran
chin
gco
rals
(20–
50%
,som
ebo
red
&en
crus
ted)
.Fra
gmen
t-ed
unab
rade
dbr
anch
ing
cora
ls( ,
25%
),he
adco
rals
( ,15
%),
and
plat
yco
rals
( ,15
%).
Mic
ritic
orsh
aley
wac
ke-p
ack-
ston
em
atrix
incl
udes
echi
noid
spin
es(1
–2%
),pe
cten
s(1
–2%
).En
crus
tatio
nof
cor-
als
byco
ralli
neal
gae
(5–1
0%)
and
fora
min
ifera
( ,3%
).
Insi
tubr
anch
ing
cora
lsco
mm
on.
Frag
men
ted
cor-
als
alig
ned
bed
para
llelt
ora
n-do
mly
25–3
5%Lo
wto
mod
erat
een
ergy
insh
allo
wpa
rtof
phot
iczo
ne.I
nsi
tugr
owth
ofbr
anch
ing
cora
lsin
area
ofm
oder
ate
fine
silic
i-cl
astic
inpu
t.So
me
top-
plin
gof
near
insi
tuco
r-al
s.
Cor
alru
d-flo
atst
one
faci
esB
ranc
hing
cora
lrud
-floa
t-pa
ckst
one,
Hea
dco
ral
rud-
float
-pac
ksto
ne,
Hea
dan
dbr
anch
ing
cora
lrud
-floa
tsto
ne
Tow
ards
base
and
top
ofsu
cces
sion
:in
terb
edde
dw
ithpl
aty
cora
lshe
et–
plat
esto
nean
dbr
anch
ing
cora
lpil-
lars
tone
s.To
pof
succ
essi
on:a
lso
inte
rbed
ded
with
rhod
olith
and
cora
lflo
atst
ones
.
dm/m
Plan
aror
undu
lose
and
shar
por
grad
atio
nal.
Met
res
to10
sm
etre
s,m
ayfo
rmlo
wan
gle
lens
,fe
w-m
etre
acro
ss
Cor
als
(20–
60%
frag
men
ted,
unab
rade
dbr
anch
ing
and
head
cora
ls).
Min
orpl
aty
cora
ls.M
icrit
icor
shal
eyw
acke
-pac
ksto
nem
atrix
incl
udes
echi
noid
spin
es(1
–2%
),pe
cten
s(1
–2%
).En
crus
tatio
nof
cora
lsby
cora
lline
alga
e(5
–10%
)an
dfo
ram
inife
ra( ,
3%).
Elon
gate
bioc
last
sal
igne
dbe
dpa
r-al
lel.
15–3
0%Lo
wto
mod
erat
een
ergy
insh
allo
wpa
rtof
phot
iczo
ne.
Topp
ling
ofin
situ
bran
ch-
ing
orhe
adco
rals
.Som
efin
esi
licic
last
icin
put.
Cor
allin
eal
gae
and
cora
lflo
atst
one
faci
esR
hodo
lith
and
cora
lpac
k-flo
at-m
ix-r
udst
one,
Rho
dolit
han
dbr
anch
-in
gco
ralfl
oat-p
illar
-pa
ckst
one,
Cor
allin
eal
-ga
ean
dco
ral
float
-rud
ston
e
Tow
ards
top
ofsu
cces
sion
:ove
rlies
head
cora
lmix
-dom
esto
nes,
inte
r-be
dded
with
cora
lfloa
t-rud
ston
esan
dpl
aty
cora
lshe
etst
ones
.Rar
eat
base
ofsu
cces
sion
:int
erbe
dded
with
plat
yco
rals
heet
ston
esan
dco
ral
rud-
float
ston
es.
dm/m
Plan
aror
undu
lose
and
grad
atio
nal.
Met
res
to10
sm
etre
sB
ranc
hing
and
head
cora
ls(2
0–40
%fr
ag-
men
ted
and
insi
tu,b
ored
and
encr
uste
d).
Rho
dolit
hs,u
pto
6cm
,bra
nchi
ngan
den
-cr
ustin
gco
ralli
neal
gae
(10–
15%
).M
icri-
ticsh
aley
wac
ke-p
acks
tone
mat
rixin
-cl
udes
echi
noid
spin
es(2
–4%
),pe
cten
s( ,
1%)
and
diss
emin
ated
Hal
imed
apl
ates
( ,2%
).
Insi
tuco
rals
and
rand
omto
bed-
para
llela
lign-
men
tof
elon
gate
bioc
last
s
10–3
0%Lo
wto
mod
erat
een
ergy
insh
allo
wpa
rtof
phot
iczo
ne.I
nsi
tugr
owth
ofco
ralli
neal
gae
and
cora
lsin
area
ofm
oder
ate
fine
silic
icla
stic
and
nutri
ent
inpu
t.So
me
topp
ling
ofne
arin
situ
cora
ls.
Bio
clas
ticw
acke
-pac
k-flo
atst
one
Bio
clas
ticw
acke
-pac
k-flo
atst
one,
Cor
albi
o-cl
astic
pack
-floa
tsto
ne
Bas
eof
succ
essi
on:I
nter
bedd
edw
ithpl
aty
cora
lshe
et-p
late
ston
es.
dmPl
anar
orun
dulo
sean
dsh
arp
orgr
adat
iona
l.M
etre
sto
10s
met
res
Wel
l-pre
serv
edpl
aty
cora
ls( ,
20%
),up
tofe
wcm
thic
kan
d40
cmac
ross
,som
ebo
red
and
frag
men
ted.
Min
orbr
anch
ing
and
head
cora
ls,u
pto
10cm
acro
ss( ,
10%
).La
rger
bent
hic
fora
min
ifera
( ,5%
).Ec
hino
idsp
ines
(1–2
%),
pect
ens
and
gast
ropo
ds(1
–2%
).C
oral
line
alga
e,br
anch
ing
orm
men
crus
tatio
n(2
–3%
).C
lay,
min
orsi
ltan
dm
icrit
em
atrix
.
Som
eal
ignm
ento
fel
onga
tebi
ocla
sts
15–2
5%Lo
wen
ergy
with
inph
otic
zone
.Som
ein
flux
offin
esi
licic
last
icm
ater
ial.
Hal
imed
aan
dfo
ram
inif-
era-
cora
lwac
kest
one
faci
es
Hal
imed
aan
dla
rger
ben-
thic
fora
min
ifera
bio-
clas
ticpa
ckst
one,
Hal
i-m
eda
and
plat
yco
ral
shee
tsto
ne,H
alim
eda
and
bran
chin
gco
ral
pack
-floa
tsto
ne
Top
ofsu
cces
sion
and
mar
gins
ofpa
tch
reef
:ove
rlies
plat
yco
ral
shee
tsto
nes,
over
lain
bysh
ale-
clay
.
dmPl
anar
and
shar
por
grad
a-tio
nal
Met
res
to10
sm
etre
sW
ell-p
rese
rved
Hal
imed
apl
ates
(15–
40%
).Fl
atte
ned
larg
ebe
nthi
cfo
ram
inife
ra(u
pto
20%
).Th
inpl
aty
orbr
anch
ing
cora
ls(u
pto
30%
).Fr
agm
ente
dbr
anch
ing
cora
lline
alga
e(2
-15%
),ec
hino
idsp
ines
( ,2%
)an
dpe
cten
s( ,
3%).
Mic
ritic
tosh
aley
-si
ltym
atrix
(30–
50%
).D
isse
min
ated
plan
tm
ater
ial(
upto
4%).
Elon
gate
bioc
last
sal
igne
dbe
dpa
r-al
lel.
10–2
5%Lo
wen
ergy
,hig
hin
flux
ofcl
ays
and
poss
ibly
nutri
-en
tsin
phot
iczo
ne.B
iot-
icpr
oduc
tion
intu
rbid
wat
ers.
Hea
dco
ralm
ix-d
ome-
ston
efa
cies
Hea
dco
ralm
ix-d
ome-
rud-
ston
e,H
ead
and
bran
chin
gco
ralp
illar
-m
ixst
one.
Mid
dle
ofsu
cces
sion
:int
erbe
dded
with
bran
chin
gco
ralp
illar
ston
esan
dco
ralr
ud-fl
oats
tone
s.
mPl
anar
orun
dulo
sean
dsh
arp
orgr
adat
iona
lM
etre
sto
10s
met
res
Pred
omin
antly
(50–
60%
)in
situ
head
and
bran
chin
gco
rals
,hea
dco
rals
upto
60–
100
cmac
ross
.Som
ebo
ring
and
encr
usta
-tio
nof
cora
l,pa
rticu
larly
frag
men
ted
cor-
als
byco
ralli
neal
gae.
Mic
ritic
wac
ke-p
acks
tone
mat
rixin
clud
esec
hino
idsp
ines
(1–2
%),
pect
ens
(1–2
%),
and
Hal
i-m
eda
plat
es( ,
2%).
Mas
sive
beds
,in
situ
head
and
bran
chin
gco
rals
com
mon
.Fra
g-m
ente
dco
rals
bed
para
llelt
ora
ndom
alig
n-m
ent.
,10
–15%
Low
tom
oder
ate
ener
gyin
shal
low
part
ofph
otic
zone
.In
situ
grow
thof
head
and
bran
chin
gco
r-al
sin
area
oflim
ited
fine
silic
icla
stic
inpu
t.So
me
topp
ling
ofne
arin
situ
cora
ls.
124 M.E.J. WILSON
125DELTA-FRONT PATCH REEF DEVELOPMENT
←
FIG. 8.—Simplified section, biotic zonation, and siliciclastic content through two measured sections from different delta-front patch reef at Airputih (AK) and DPR. Analmost complete, ‘‘ideal’’ reefal succession (as described in the text) can be found in the lower part of section AK. In the grain-size column the dominant grain size(whether carbonate or siliciclastic grains) is shown as a solid line. For carbonate and mixed carbonate facies the siliciclastic component of clay or silt size is not illustrated,and if the carbonate components have a bimodal distribution, the more minor grain-size fraction is shown as a dashed line.
floatstone and the Halimeda and foraminifera–coral wackestone, other bio-clasts dominate.
Bioclastic wacke–pack–floatstone beds are present throughout the patchreefs, but are most commonly found interbedded with platy coral sheet–platestones. The bioclasts present (, 40%) include corals, larger benthicforaminifera, echinoid spines, pectens, and gastropods.
The platy coral sheetstones and clayey wackestone units forming thebasal and marginal deposits of the patch reefs are interbedded with, andpass up-section and laterally into, branching coral pillarstones and coralrud–floatstones. Siliciclastic content within the pillarstones and float–rud-stones is 15–35%. These facies contain abundant branching corals, such asPorites and Stylophora, together with possible hydrozoans (Heliopora),which are commonly delicate but may become more robust up-section. Thepillarstones and float–rudstones pass up-section and along strike into headcoral mix–domestones (Fig. 6F), and coral float–rudstones. The mix–dome-stones contain a variety of recrystallized branching and head corals, in-cluding Favia, Porites, and Goniopora, showing minimal evidence for frag-mentation and abrasion, with colony sizes up to 1–2 m across. The micriticor shaly wackestone matrix to these facies contains echinoid spines, largerbenthic foraminifera, pectens, and minor Halimeda. As the succession be-comes richer in in situ branching and then head corals, there is a decreasein the siliciclastic content to around 20% and 6–10%, respectively. Al-though these are the general trends in corals and lithologies along beds,there is considerable local variation, particularly in the mix–domestonesand float–rudstones. Lateral changes in lithologies from sheetstones throughto domestones along strike of individual beds may be accompanied by astratigraphic difference of just a few meters, with the mix–domestones de-veloped in slightly elevated positions.
Coralline algae and coral floatstone facies are common in the upper partsof the patch reefs. Siliciclastic content within these deposits at 10–30% ishigher than in the head-coral mix–domestones, which they commonly over-lie. Coralline algae is present as branching fragments and loosely laminarrhodoliths up to 6 cm in diameter. Fragmented and in situ branching andhead corals are heavily bored and encrusted with coralline algae, commonlyMesophyllum, and Acervulinid foraminifera. Coral pillarstones and float–rudstones are also common towards the top of the patch reefs, but in con-trast to deposits lower in the section, corals are commonly bored and en-crusted (Fig. 6G). Lithologies towards the top of the patch reefs tend to berich in carbonaceous material together with echinoid plates and flattenedlarger benthic foraminifera.
The Halimeda and foraminifera–coral wackestone facies was only seencapping, or forming marginal deposits to, the patch reefs. This facies con-tains 15–40% unabraded, recrystallized Halimeda plates (Fig. 6I) and upto 4% disseminated plant material. Other bioclasts present include thinplaty or branching corals, flattened larger benthic foraminifera, echinoidspines, pectens, and fragmented branching coralline algae.
Interpretation.—As in the mixed facies, there is minimal breakage andabrasion of bioclasts and most skeletal components accumulated in situ, orvery close to in situ. The occurrence of well-preserved stenohaline photo-autotrophs throughout these facies is indicative of marine conditions withinthe photic zone. Formation under low to moderate energy conditions ishere suggested, on the basis of on the presence of clay-size particles in allfacies, general absence of abrasion of bioclasts, and the delicate to robustgrowth forms of skeletal components. All facies contain a siliciclastic com-ponent, and only the head-coral mix–domestone with 6–15% insoluble ma-terial is inferred to have formed during periods of low siliciclastic influx.
The remaining deposits, particularly from the upper parts of patch reefs,accumulated under high nutrient conditions associated with moderate sili-ciclastic input.
The diversity and robust growth forms of the branching and massivecorals in the pillarstones, rud–floatstones, and mix–domestones is sugges-tive of development in shallow waters. Despite this diversity, Acropora,one of the most abundant corals in modern SE Asian reefs, is rare, perhapsbecause of its known modern preference for moderate to high energy, gen-erally clear-water settings (Tomascik et al. 1997). Many of the corals pre-sent in the assemblages, such as Porites and Goniopora, are known fortheir sediment shedding ability and have been documented in low-energy,turbid environments today (Tomascik et al. 1997). Facies containingbranching corals generally contain a higher siliciclastic component thanthose with massive corals, perhaps related to the sediment shedding abilityof the former (Scoffin 1997).
The coralline alga Mesophyllum is reported from low-light environmentsand is commonly found in clear waters at depths of 20–801 m (Adey1979; Minnery et al. 1985; Perrin et al. 1995). Acervulinid foraminifera area common component in reefal environments where ecological conditions,most frequently related to a decrease in light intensity, lead to the reductionof competition for substrate encrustation (Perrin 1992). Increased nutrientavailability may be the explanation for the positive correlation betweenincreased organic matter, siliciclastic content and degree of bioerosion andencrustation by algae and infaunal suspension feeders (Hallock and Schla-ger 1986; Perrin et al. 1995; Edinger et al. 2000) in the upper parts of thepatch reefs. It is here inferred that the coralline algae facies accumulatedduring periods of high turbidity associated with nutrient input.
In Indonesia, Halimeda associated with a stenohaline fauna is commonon lower reef slopes or platforms in 20–40 m water depth (Tomascik et al.1997). An environment with low light penetration is inferred for the Hal-imeda and foraminifera–coral wackestone facies on the basis of the com-monly flattened growth forms of photoautotrophs. Although Halimeda istolerant of siliciclastic and nutrient input (Gussman and Smith 2002), waterclarity may have been moderate during accumulation of this facies becauseit contains a low to moderate concentration of fine siliciclastic material(10–25%). In Borneo, some beds of this Halimeda-rich facies occur at themargins of the patch reef, and would have formed in slightly deeper waterdepths than along strike patch reef ‘‘core’’ facies (see below). On the basisof the combined evidence it is here suggested that this facies accumulatedpredominantly in deeper, perhaps nutrient-rich waters, similar to the Hal-imeda bioherms offshore today (Roberts et al. 1987, 1988; Phipps andRoberts 1988; Roberts and Sydow 1996).
DEVELOPMENT OF PATCH REEFS
Initiation and Growth of Patch Reefs
Patch reefs initially developed on a soft, muddy substrate either at themargins of a distributary-mouth bar or in abandoned tidal or distributarychannels. Although corals are good colonizers of rubble (Hayward 1985;Braga et al. 1990) there is less documentation that corals colonize soft,fine-grained substrates. During an early coring study, deposits of a fringingreef developed in turbid waters bordering Sumatra were found to rest en-tirely on a muddy substrate (Sluiter 1890; Umbgrove 1947). Subsequentstudies in Java, Sulawesi, Borneo, and Thailand have shown that reefalinitiation on soft substrates is common in SE Asia (Umbgrove 1947; Neth-erwood and Wight 1992; Tudhope and Scoffin 1994; Tomascik et al. 1997).
126 M.E.J. WILSON
FIG.9
.—D
etai
led
log
corr
elat
ion
ofm
easu
red
sect
ions
from
the
Airp
utih
patc
hre
ef.C
olor
edco
rrel
atio
ntie
lines
show
nar
eba
sed
ona
com
bina
tion
ofw
alki
ngou
tbed
surf
aces
inth
efie
ld,b
iost
ratig
raph
icag
eda
ting,
and
chan
ges
insi
licic
last
icco
nten
t.N
ote
that
the
colo
red
corr
elat
edsu
rfac
essh
own
gene
rally
corr
espo
ndto
patc
h-re
ef‘‘
sequ
ence
boun
darie
s’’
rela
ted
toch
ange
sin
silic
icla
stic
cont
ent.
The
depo
sits
ofth
eA
irput
ihpa
tch
reef
are
inte
rpre
ted
astw
om
ajor
amal
gam
ated
patc
h-re
efsu
cces
sion
s.R
ough
corr
elat
ion
ofun
itsis
also
poss
ible
thro
ugh
late
rala
ndve
rtica
ltra
cing
ofth
esi
licic
last
icco
nten
t(w
hite
,gra
y,an
dst
ippl
edba
ckgr
ound
effe
cts)
.How
ever
,bec
ause
ther
eis
som
eov
erla
pin
silic
icla
stic
cont
entb
etw
een
carb
onat
ean
dm
ixed
carb
onat
e–si
licic
last
icfa
cies
,som
ebe
dsof
carb
onat
esfa
cies
with
a.
30%
silic
icla
stic
cont
enta
ppea
rin
the
gray
,pr
edom
inan
tlym
ixed
carb
onat
e–si
licic
last
icfa
cies
field
.
127DELTA-FRONT PATCH REEF DEVELOPMENT
FIG. 10.—Depositional model of Miocene delta-front patch reefs, highlighting key features.
Mechanisms for coral colonization of soft substrates include settling andgrowth of planulae on any loose solid fragments of rocks or bioclasts(Umbgrove 1947; Tomascik et al. 1997), or through laminar growth formsspreading out over the substrate (Martin et al. 1989). It is inferred that bothof these mechanisms were important during early colonization by platycorals, with larger benthic foraminifera, solitary corals, or molluscs perhapsacting as suitable initial substrates. The Agariciidae, which includes thePachyseris and Leptoseris found in abundance in the platy-coral sheet-stones, are known to be one of the early colonizers in Indo-Pacific reefsfollowing environmental disturbance (Tomascik et al. 1997). A furthermechanism for soft substrate colonization through breakage and regrowthof fragmented corals, such as Porites (Tudhope and Scoffin 1994; Tomas-cik et al. 1997) may have been locally important within the patch reefs ortowards their margins.
Once the corals were established, rigid frameworks did not form in thepatch-reef deposits. This is due to the growth forms of the biota present,the contemporaneous deposition of fine siliciclastic material surroundingbioclasts, and the common occurrence of bioerosion. The lack of rigidframeworks and limited depth range inhabitable by photoautotrophs hin-dered development of steep margins, and the patch reefs slope gently intodeeper water (Figs. 10, 11). The susceptibility of turbid-water reefs to earlyreworking (Tudhope and Scoffin 1994) due to the combined lack of rigidframeworks, paucity of marine cements, the high proportion of unconsol-idated matrix, and the presence of structurally delicate, often bioerodedskeletons, affects their preservation potential (see below).
Morphology and Differential Compaction of Patch Reefs
The dimensions of the patch reefs preserved at outcrop gives some ideaof their original low-relief morphology during development, albeit with aprofile accentuated by differential compaction (Figs. 7, 9). Dewatering andburial of shales may result in 80–90% compaction (Tucker 1992). In themodern delta, prodelta clays in areas of mouth-bar formation have com-pacted by 5–7 m, resulting in greater accommodation space and thickeningof delta-front deposits (Allen and Chambers 1998). In the patch reefs car-bonate facies containing more abundant clays show progressively greatercompaction effects. On the basis of measuring the profile of crushed bio-clasts in the clayey wackestones and platy-coral sheetstones, it is inferredthat these clay-rich facies underwent 60–80% compaction. Compaction ofcarbonate-rich lithologies has taken place through a combination of me-chanical and chemical compaction, the later resulting in dissolution seamsand minor sutured grain contacts. Judging by draping of units over com-petent uncompacted massive corals and petrographic studies of dissolutionseams, compaction of 20–30% is suggested for the head-coral mix–dome-stone. Using these rough values all patch reefs are inferred to have hadlow depositional relief, on the order of a few meters, prior to compaction(Fig. 10). The patch-reef surface would have been irregular, with slopeangles no higher than a few degrees.
Demise of Patch Reefs
All the patch reefs studied were transient and met their demise in dif-ferent ways:
128 M.E.J. WILSON
129DELTA-FRONT PATCH REEF DEVELOPMENT
←
FIG. 11.—Summary diagram showing influences on local and regional accumulation, and sequence development, of in situ mixed carbonate–siliciclastic deposits developedin delta-front areas. Illustrations show a low-energy depositional setting, similar to the Mahakam Delta patch reefs.
Increase in Siliciclastic Input and/or Nutrient Input in Very ShallowWater.—Most of the patch-reef deposits have an increasing siliciclastic,and carbonaceous, component associated with shallow-water biota in theirupper parts. Many successions are capped by foraminifera-rich depositstogether with plant-rich clays and rippled silty sands, all of which accu-mulated in shallow, high-nutrient waters. It is inferred that increased sili-ciclastic and nutrient input due to renewed delta front progradation resultedin demise of patch-reef production through a combination of physicalsmothering by sediment, decreased light levels, and increased nutrient lev-els.
Increase in Siliciclastic Input and/or Nutrient Input in ModerateWater Depths, Perhaps Associated with Deepening.—Because all thereef sections studied are overlain by shallow-water siliciclastics, the overallmechanism for their demise is inferred to be via increased siliciclastic inputas described above. However, for the larger patch reefs such as Permasip,as the areas closer to siliciclastic input were ‘‘smothered,’’ more distal,perhaps moderate-water-depth areas might have experienced increased nu-trients. The deposits rich in Halimeda, formed at the margins and cappingsome of the patch-reef sections, are inferred to have formed under theseconditions of high nutrient input. A relative rise in sea level, perhaps as-sociated with increased nutrient input, might also result in Halimeda-richdeposits capping patch reefs, as may be the case for bioherms on the mod-ern shelf.
Subaerial Exposure.—This is not thought to have resulted in the demiseof any of the reefs studied, but it may have caused a temporary cessationin production at Senoni. At Senoni an irregular, possibly karstified horizon(Fig. 7) with up to 20 cm relief is overlain by a head-coral mix–domestone.If subaerial exposure occurred, carbonate production was reestablished asrelative sea level rose. In turbid settings renewed photoautotroph productionis likely only if the magnitude of relative rise was low, allowing coloni-zation in a reduced-depth photic zone.
DISCUSSION
Siliciclastic–Carbonate Interactions
The results from this study and other recent studies indicate that reefaldevelopment, although modified by siliciclastic input, is a natural, if tran-sient, phenomenon in many turbid-water equatorial areas. Of the four cat-egories of mixed carbonate–siliciclastic successions recognized by Mount(1984) only ’’in situ mixing’’ is applicable to the delta-front reefs of Bor-neo. However, Mount (1984) suggested that in situ mixing is favored intemperate settings with foramol deposits rather than warm-water equatorialsettings. The apparent paucity of in situ mixing in warm-water settings wasattributed to the inhibiting effects of increased turbidity, unstable substrates,and the clogging of feeding mechanisms, all factors thought to hinder de-velopment of chlorozoan–chloralgal assemblages (Mount 1984). However,these Miocene patch reefs contain a diverse chlorozoan and chloralgal as-semblage; they formed in turbid waters, on unstable substrates, with theorganisms present using a variety of feeding strategies despite contempo-raneous siliciclastic input. Recent results from this, and other similar Ce-nozoic (Netherwood and Wight 1992; Saller and Vijaya 2002; Wilson2002) and modern (Tomascik et al. 1997; Larcombe et al. 2001) examplesin Australasia reveal that if conditions are suitable, siliciclastic input andturbid waters do not always limit equatorial reef development.
Using the Miocene patch reefs of Borneo as one example, Wilson and Lokier(2002) evaluated the influences of siliciclastic and volcaniclastic input on car-bonate development in different climatic or depositional settings. They recog-
nized that in humid equatorial settings high rainfall is associated with high ratesof weathering, erosion, terrestrial runoff, and onshore organic productivity.Consequently, nearshore carbonate producers in equatorial areas were subjectedto high levels of terrestrially derived fine-grained clastic input associated withfreshwater and high nutrient influxes.
This study corroborates the findings of Wilson and Lokier (2002) thatclastic influx has three major influences on carbonate development: (1)changes in types of biota, (2) changes in morphology of biota, and (3)influences on deposit characteristics and sequence development. Wilsonand Lokier (2002) did not document the third point, and sequence devel-opment and influencing factors are discussed in more detail below and inFigure 11. To briefly summarize the findings on the first two points, avariety of carbonate-producing biota, including larger benthic foraminifera,coralline algae, echinoderms, molluscs, and platy and branching coralscould tolerate nearly continuous siliciclastic influx approximately equal totheir production rates. These organisms adopted various strategies for cop-ing with clastic input, including a degree of mobility, some heterotrophicfeeding, morphologies adapted to unstable substrate inhabitation or sedi-ment shedding, and shapes adapted to low light levels (Wilson and Lokier2002). A commonly held view is that carbonates developed in areas ofsiliciclastic input would have low biotic diversity. As shown herein, al-though low diversities may occur in deposits such as the platy coral sheet-stones, for the patch reefs as a whole diversities are considered moderateto high, with at least ten coral genera and a wide range of other biotapresent. This is consistent with other turbid-water reefs where coral diver-sity may be similar to or up to around two thirds that of clear-water reefs(McClanahan and Obura 1997; Larcombe et al. 2001; Sanders and Baron-Szabo in press).
Influences on Patch-Reef and Sequence Development
A range of commonly interlinked factors, operating on a variety ofscales, influence the development of turbid-water mixed carbonate–silici-clastic successions (Fig. 11). On a local scale, changes in siliciclastic input,environmental conditions, and presence of slight basement highs were themain influences on trophic levels and light penetration, and consequentlythe biota and stratigraphy of individual patch reefs. Locally, accommoda-tion space for individual patch reefs could be created through a decreasein siliciclastic supply, together with compaction, although distinguishingthis from a gradual rise in relative sea level is problematic. On a regionalscale carbonate development within the delta is related to autogenic chang-es in lobe activity or sediment supply, or rises in relative sea level due toeustasy or tectonics.
Local Siliciclastic Input.—Reduced water clarity resulting from turbid-ity, associated with siliciclastic input or resuspension events (Larcombe etal. 2001), is interpreted as the dominant influence on local development ofpatch reefs rather than fluctuations in relative water depth. Reasons for thisinterpretation include that the biota and sedimentary structures presentthroughout the deposits are indicative of shallow waters. There is no evi-dence, such as plankton-rich flooding surfaces or abundant subaerial ex-posure surfaces, that relative changes in sea level had a major affect onpatch-reef development. Changes in photoautotrophs towards forms betteradapted to low light levels, which in clear-water reefs would be interpretedas a response to deepening, are instead associated with periods of increasedsiliciclastic content (Fig. 8). Although morphology of biota can also berelated to changes in energy, low to moderate energies are inferred for alldeposits. The patch reefs developed in shallow waters over a bathymetric
130 M.E.J. WILSON
range of a few meters, yet these deposits show all the common zonationof clear-water reefs normally spread over many tens of meters (Pomar2001). On the basis of their morphology and depth zonation these patchreefs are inferred to have formed in an area where light penetration wasrestricted to around the upper ten meters of the water column. In turbidwaters the depth at which light penetration drops below that required forhermatypic corals (2–0.5% of incident surface radiation) is typically up to,or significantly shallower than, 20 m (Acevedo et al. 1989; Titlyanov andLatypov 1991).
In initial patch-reef deposits siliciclastic content is high, and it is inferredthat turbid waters resulting in low water clarity allowed colonization onlyby opportunistic photoautotrophs in very shallow water (Figs. 10, 11). Assiliciclastic content decreases, organisms adapted to lower siliciclastic inputand higher light levels dominate the very shallow-water assemblages. Dur-ing periods of fine-grained siliciclastic onlap onto the gently sloping mar-gins, siliciclastic content increases in patch-reef deposits. At these times ofonlap, the area of carbonate production shrinks to the central, shallowest-water area of the patch reef (Fig. 10). There is also vertical contraction ofthe carbonate zonation, and assemblages adapted to low light levels andhigh siliciclastic input moved into bathymetrically elevated positions (cf.Acevedo et al. 1989). Any subsequent decrease in siliciclastic content wasassociated with an increase in areal extent of carbonate production, andpatch-reef, or seagrass, deposits spread out over, or downlap onto, the fine-grained siliciclastics at their margins. There is also a reexpansion of thelight-dependent depth zonation of biota within the patch reef.
Other Local Environmental Influences.—In addition to turbidity otherfactors that influenced local patch-reef development are nutrient influx, de-positional energy, and presence of slight bathymetric highs (Fig. 11). Nu-trient input is often associated with increased siliciclastic input, and organ-isms adapted to eutrophic conditions such as algae, associated grazers, andinfaunal suspension feeders become common in the upper parts of succes-sions. Some photoautotropic organisms, such as Leptoseris, may be able toswitch to more heterotropic feeding mechanisms in turbid, high-nutrientwaters (Insalaco 1996). Development of low-light-level assemblages, inwhich organisms produce thin or structurally lighter skeletons (Tomasciket al. 1997), would have been feasible only in shallow waters under theinferred predominantly low-energy conditions. In higher-energy, turbid wa-ters, robust corals may develop, but only within the upper few meters ofthe water column (Larcombe et al. 2001). The depositional topography atthe delta front affects the highly localized distribution of carbonates. Patchreefs were preferentially developed on slight bathymetric highs inferred tobe elevated into the photic zone and bypassed or shielded from some sil-iciclastic influx.
Autogenic Factors, such as Deltaic Switching, or Current Activity.—On the modern shelf, high sedimentation rates of the southern delta lobeand southward-flowing shelf currents result in less turbid waters, and aconcentration of carbonates, on the northern part of the shelf (Roberts andSydow 1996). On a smaller scale, individual distributary channels and as-sociated mouthbars may be abandoned, convert to tidal channels, and be-come sites of local carbonate colonization, as seen in the northern part ofthe delta today (Allen and Chambers 1998). In Miocene outcrops, inter-digitation of plant-rich siliciclastics, containing bidirectional-facing asym-metric ripples, with patch-reef marginal deposits suggests that these envi-ronments were prone to fluvial flooding and renewed influx of siliciclasticsin a tidal environment. Delta lobe switching, distributary abandonment, andshelf currents are all factors that may alter local siliciclastic supply andwater turbidity independently of any relative sea-level change. Fossiliferousintervals from Spanish Eocene, and Texan Carboniferous, fan deltas werealso highly localized and developed during local abandonment of individualfan-delta lobes and distributary-channel mouthbars (Dutton 1982; Molenaarand Martinius 1996).
Effects of Base-Level Change, Compaction and Subsidence.—Sedi-ment supply to the Kutai Basin has been variable with time, with intervals
of rapid sedimentation associated with periods of uplift and erosion of oldersediments (Allen and Chambers 1998). Compaction effects are known tobe considerable in many deltas, with the original ‘‘soupy,’’ water-rich pro-delta muds and delta-front shales of the Mahakam reducing in thicknessby 50% or more (Allen and Chambers 1998). Given that individual pro-gradational deltaic units are typically on the order of tens of meters thick,compaction of the shale sequence could generate enough accommodationspace for the thickness of carbonates seen in many of the outcrops. Overallthe Miocene deposits of the Mahakam Delta are several kilometers to overten kilometers in thickness. Regionally, tectonic subsidence during the Mio-cene has been considerable, with suggested long-term subsidence rates of200–300 m/Myr. On a local scale, gravitational collapse and shale diapirismmay also have been important in generating accommodation space. Re-gional subsidence would have provided accommodation space for carbonateand siliciclastic deposition and resulted in likely burial of carbonates. Sinceturbid-water reefs are generally uncemented and lack rigid frameworks,subsidence and burial is considered necessary for their preservation (Tud-hope and Scoffin 1994).
Relative Sea-Level Changes.—Relative changes in sea level, with or with-out linked variations in siliciclastic input, may have a number of potentialeffects on the development of individual turbid-water patch reefs. Evidence ofemergence associated with sea-level fall is not commonly seen in the patchreefs studied, perhaps because of the overall regime of subsidence, and thelikelihood of erosion of the unconsolidated deposits (Johnson and Risk 1987;Tudhope and Scoffin 1994). Falling sea level is commonly associated withincreased siliciclastic input, causing compaction of underlying prodelta claysand likely burial of carbonates. Gradual relative rise in sea level, whetherthrough subsidence or eustasy, appears to have been instrumental in creatingaccommodation space and allowing carbonates to develop (see below). How-ever, a rapid relative sea-level rise has the potential to result in deepening-upwards successions if carbonate production is unable to keep pace (Holland1993; Choi et al. 1999; Yang and Kominz 2002; Rankey et al. 1999). Thiswould be particularly important if siliciclastic input is not reduced in associationwith any relative rise, because carbonate producers may become submergedbelow the depth of a shallow photic zone. The production rates of uppermostHalimeda-rich deposits from offshore bioherms are inferred to have decreasedrapidly because of increasing water depths (Phipps and Roberts 1988). It issuggested here that the shallow-water coral-rich reefs may convert to deeper-water Halimeda banks if they are unable to ‘‘keep-up’’ with relative sea-levelrise in the nutrient-rich waters of the delta front. A sea-level stillstand duringthe current relative highstand period has allowed renewed progradation of theMahakam Delta. This high siliciclastic input has limited carbonate productionto distal areas of the shelf, or areas of moderate to low delta-lobe activityfollowing local reduction of siliciclastic input along a broadening delta front(Roberts and Sydow 1996; Allen and Chambers 1998).
Sequence Development
Many of the internal changes observed within individual patch reefs canbe attributed to variations in siliciclastic input, with accommodation spaceresulting from decreased siliciclastic input together with subsidence and/orrelative changes in sea level. Additional data on larger-scale sequence de-velopment of turbid mixed carbonates–siliciclastics is gleaned from re-gional and published studies, and it remains for many of the ideas discussedhere and summarized in Figure 11 to be fully tested. In turbid delta-frontareas, although regional development and preservation of extensive car-bonates is most likely under specific conditions, if local conditions aresuitable they may develop during any stage of eustatic sea level (aboveand Fig. 11).
Similar to the extensive Holocene and earlier shelfal or subsurface car-bonates from the Mahakam Delta (Roberts and Sydow 1996), the outcrop-ping patch reefs developed at the lower to middle Miocene boundary (DPR,Airputih, Permasip and Bontang) are also interpreted as transgressive de-
131DELTA-FRONT PATCH REEF DEVELOPMENT
posits. Formation of these extensive carbonates is inferred to be related toa landward shift of siliciclastic depocenters during flooding of the deltatop. This is directly comparable with the mechanism of extensive trans-gressive carbonate development on other mixed carbonate–siliciclasticshelves (Mack and James 1985; Holland 1993; Woolfe and Larcombe,1999; Rankey et al. 1999; Olszewski and Patzkowsky 2003).
On a regional scale, transgression of deltaic successions may be causedby eustatic sea-level changes, tectonic subsidence, or a reduction in sedi-ment input together with compaction. Extensive Quaternary delta-frontbioherms are related to a rise in eustatic sea level (Roberts and Sydow1996). A eustatic transgression at the early to middle Miocene boundary(Haq et al. 1987) may have favored reef development, although direct cor-relation is difficult because of the resolution of dating. However, in general,prior to 125,000 years ago there is poor correlation between inferred globaleustatic sea-level changes and sequence development of the Mahakam Del-ta, because of considerable regional tectonic activity (Carbonel and Moyes1987). Intervals of rapid deltaic sedimentation are associated with periodsof uplift and erosion of older sediments during the Pliocene, early, middle,and late Miocene (Tanean et al. 1996; Allen and Chambers 1998). Moreactive progradation due to tectonics, perhaps in combination with eustaticchanges, may therefore have resulted in highly localized patch-reef devel-opment during the early and middle Miocene, compared with more exten-sive reef formation at the early to middle Miocene boundary.
Transgressive carbonates are forming today in the northern, less activepart of the Mahakam Delta during a eustatic highstand. This illustrates thatidentical small-scale regressive–transgressive deltaic sequences can be gen-erated through both external allogenic and internal autogenic processes.Unless high-resolution correlation of strata is possible over large areas, itmay be impossible to distinguish between allogenic and autogenic causalmechanisms. Distributary or delta-lobe abandonment may occur because ofdecreasing sediment flux from the hinterland and/or dispersion effects alongan increasingly broad delta front following highstand, regressive, or low-stand delta progradation (Allen and Chambers 1998). Although a ravine-ment surface was reported at the base of some shelf bioherms (Roberts andSydow 1996), this is not seen on all seismic sections. In all outcrops patch-reef initiation appears to be related to a decrease in siliciclastic input, withno evidence for a depositional hiatus or a change from marine conditions.It is therefore possible that a decrease in siliciclastic input, together withsubsidence allowed transgressive carbonate development rather than a eu-static rise.
Highstand carbonates have been reported from modern (Belize—Ferroet al. 1999; Florida—Cunningham et al. 2003) and ancient (Paleozoic,U.S.A.—Rankey 1997; Rankey et al. 1999; Choi et al. 1999; Yang andKominz 2002) mixed carbonate–siliciclastic systems. In all cases whereextensive highstand carbonates formed, siliciclastic deposition was confinedmainly to coastal areas and the carbonates are predominantly siliciclastic-free. On subsequent emergence, these pure carbonates are prone to disso-lution rather than reworking and may be preserved as karstic remnants inthe rock record (Ferro et al. 1999). These systems are very different fromareas like the modern Mahakam Delta, where a relative stillstand in sealevel during a highstand enabled renewed progradation of siliciclastics ontothe shelf. In these turbid, highstand areas, carbonate development is highlylocalized, restricted to a reduced photic zone, and any carbonates containin situ mixed siliciclastics. Turbid-water stillstand carbonate production ispromoted where earlier or contemporaneous siliciclastic sedimentation ‘‘el-evated’’ the substrate into a reduced photic zone (Johnson and Risk 1987;Tudhope and Scoffin 1994). The presence of a substratum within the photiczone is also important in the modern extensive ‘‘clear’’-water transgressiveto highstand carbonates. It is unlikely that the Belize and Florida exampleswould have developed without the presence of broad shelves formed duringearlier phases of relative sea level (Cunningham et al. 2003). Yang andKominz (2002), suggested that carbonate and siliciclastic parasequencesfrom the Paleozoic of Texas formed during highstands tend to be thick,
and shallowing and coarsening upwards. These were differentiated fromtransgressive parasequences, which tend to be thin and deepen upwards.
CONCLUSIONS
● Carbonate production can and does occur in areas of high, nearly con-stant, fine-grained siliciclastic input, such as delta-front areas in equa-torial regions.
● Turbid-water reefs may have moderate to high biodiversity, but the or-ganisms present are adapted to the local environmental conditions. Asa consequence the assemblages of turbid-water reefs can be quite dif-ferent from their better studied clear-water counterparts.
● Organisms found to be tolerant of siliciclastic input in the Miocene patchreefs include some larger benthic foraminifera, coralline algae, echi-noids, molluscs, together with solitary, platy, and branching corals.Characteristics that enabled these organisms to inhabit areas affected bysiliciclastic input included mobility, heterotropic feeding, and morphol-ogy changes amongst photoautotrophs to maximize surface area avail-able to incident light (Wilson and Lokier 2002).
● Patch-reef development was initiated on soft substrates in shallow waterson slight bathymetric highs. The settings of patch-reef initiation duringthe Miocene were delta-front channels, or distributary-mouth bars, in theprocess of being abandoned. Although siliciclastic input was reducedcompared with active distributary mouths, siliciclastic input was stillconsiderable.
● Carbonate producers, particularly those dependent on light, were able todevelop only in shallow water depths, because of a reduced depth of thephotic zone associated with low light penetration in turbid waters. Thecarbonate producers are surrounded in a clay-rich matrix, and frameworkdevelopment was not observed. The lack of rigid frameworks and limiteddepth range of the photic zone resulted in patch reefs with low relief,and gently sloping margins which interdigitate with the surrounding sil-iciclastics.
● Causes of patch-reef demise are variable, but increased siliciclastic input,sometimes associated with nutrient input and/or deepening, was a majorfactor in termination.
● Variations in siliciclastic input, together with associated changes in tur-bidity and nutrient levels, appear to have been the primary factors influ-encing local development of individual delta-front patch reefs. Otherfactors that influenced local carbonate production were depositional en-ergy, particle size, and presence of slight bathymetric highs.
● Carbonate production and bioherm or patch-reef development may occurin turbid-water, delta-front areas as localized or more regionally exten-sive units during any phase of eustatic sea level. Extensive clear-waterhighstand carbonates may develop where siliciclastic deposition is con-fined to coastal zones. However, in areas of high siliciclastic input suchas the Mahakam Delta extensive turbid-water reef development is mostlikely when terrestrially derived material is confined during transgres-sions, regional decreases in influx, or local lobe abandonment often fol-lowing progradation (Roberts and Sydow 1996; Allen and Chambers1998). It is the interplay between factors such as tectonics, eustasy, deltaswitching, shelf currents, and amount and size fraction of siliciclasticsediment supply that ultimately control carbonate development and pres-ervation (cf. Yang and Kominz 2002; Rankey et al. 1999).
Turbid-water reefs have been a natural phenomenon since at least theTriassic (Sanders and Baron-Szabo in press), and do develop in equatorialregions if the local environmental conditions are suitable. This is at oddswith the suggestion that in situ mixing of carbonate and siliciclastic depositswas favored in cooler-water settings dominated by foramol assemblages(Mount 1984). These turbid reefs may have variable, but close to comparablebiodiversity as clear-water reefs, although their constituent biota, depositcharacteristics, and sequence development often differ considerably.
132 M.E.J. WILSON
ACKNOWLEDGMENTS
This research was predominantly undertaken at Royal Holloway College, Londonas part of postdoctoral studies with the SE Asia Research Group. The work wouldnot have been possible without the help and support of members of the Group, inparticular Robert Hall and Diane Cameron, and the consortium of industrial fundingcompanies. In Indonesia, LASMO, Unocal, and VICO provided logistical support,with John Chambers, Harry Alam, Hans Schwing, and the LASMO field crewswarranting special thanks, terima kasih banyak. Brian Rosen, Marcelle BouDagher-Fadel, and Ted Finch are thanked for their considerable help with coral, foraminifera,and nannofossil work, respectively. Constructive comments from reviewers/editorsSteven Bachtel, David Budd, Evan Franseen and Toni Simo, together with discus-sions with Lisa Burton, Nigel Deeks, Stephen Lokier, James Hook, Dan Bosence,and Oliver Gussman, have helped improve this manuscript.
REFERENCES
ACEVEDO, R., MORELOCK, J., AND OLIVIERI, R.A., 1989, Modification of coral reef zonation byterrigenous sediment stress: Palaios, v. 4, p. 92–100.
ADEY, W.H., 1979, Crustose coralline algae as microenvironmental indicators for the Tertiary,in Gray, J., and Boucot, A.J., eds., Historical Biogeography: Oregon State University Press,p. 459–464.
ALAM, H., PATERSON, D.W., SYARIFUDDIN, N., BUSONO, I., AND CORBIN, S.G., 1999, Reservoirpotential of carbonate rocks in the Kutai Basin region, East Kalimantan, Indonesia: Journalof Asian Earth Sciences, v. 17, p. 203–214.
ALLEN, G.P., AND CHAMBERS, J.L.C., 1998, Sedimentation in the Modern and Miocene MahakamDelta: Indonesian Petroleum Association, Jakarta, Indonesia, 236 p.
ALLEN, G.P., LAURIER, D., AND THOUVENIN, J., 1976, Sediment distribution patterns in the modernMahakam Delta: 5th Annual Convention of the Indonesian Petroleum Association, Proceed-ings, p. 159–177.
BOUDAGHER-FADEL, M.K., AND WILSON, M.E.J., 2000, A revision of some larger Foraminiferafrom the Miocene of East Kalimantan: Micropaleontology, v. 46, p. 153–165.
BRAGA, J.C., MARTIN, J.M., AND ALCALA, B., 1990, Coral reefs in coarse-terrigenous sedimentaryenvironments Upper Tortonian, Granada Basin, southern Spain): Sedimentary Geology, v.66, p. 135–150.
CARBONEL, P., AND MOYES, J., 1987, Late Quaternary paleoenvironments of the Mahakam Delta(Kalimantan, Indonesia): Palaeogeography, Palaeoclimatology, Palaeoecology, v. 61, p.265–284.
CHAMBERS, J.L.C., AND DALEY, T., 1995, A tectonic model for the onshore Kutai Basin, EastKalimantan, based on an integrated geological and geophysical interpretation: 24th AnnualConvention of the Indonesian Petroleum Association, Proceedings, p. 111–130.
CHOI, Y.S., SIMO, J.A., AND SAYLOR, B.Z., 1999, Sedimentologic and sequence stratigraphicinterpretation of a mixed carbonate–siliciclastic ramp, midcontinent epeiric sea, Middle toUpper Ordovician Decorah and Galena Formations, Wisconsin, in Harris, P.M., Saller, A.H.,and Simo, J.A., eds., Carbonate Sequence Stratigraphy: Applications to Reservoirs, Out-crops, and Models: SEPM, Special Publication 63, p. 275–289.
CUNNINGHAM, K.J., LOCKER, S.D., HINE, A.C., BUKRY, D., BARRON, J.A., AND GUERTIN, L.A., 2003,Interplay of late Cenozoic siliciclastic supply and carbonate response on the Southeast Flor-ida Platform: Journal of Sedimentary Research, v. 73, p. 31–46.
DOYLE, L.J., AND ROBERTS, H.H., 1988, Carbonate–Clastic Transitions: Amsterdam, Elsevier,Developments in Sedimentology, 42, 304 p.
DUNHAM, R.J., 1962, Classification of carbonate rocks according to depositional texture, inHam, W.E., ed., Classification of Carbonate Rocks: American Association of PetroleumGeologists, Memoir 1, p. 108–121.
DUPRAZ, C., AND STRASSER, A., 2002, Nutritional modes in coral–microbial reefs (Jurassic, Ox-fordian, Switzerland): Evolution of tropic structure as a response to environmental change:Palaios, v. 17, p. 449–471.
DUTTON, S.P., 1982, Pennsylvanian fan-delta and carbonate deposition, Mobeetie Field, TexasPanhandle: American Association of Petroleum Geologists Bulletin, v. 66, p. 389–407.
EDINGER, E.N., LIMMON, G.V., JAMALUDDIN, J., WIDJATMOKO, W., HEIKOOP, J.M., AND RISK, M.J.,2000, Normal coral growth rates on dying reefs: are coral growth rates good indicators ofreef health?: Marine Pollution, Bulletin, v. 40, p. 404–425.
EMBRY, A.F., AND KLOVAN, J.E., 1971, A Late Devonian reef tract on northeastern Banks Island,Northwest Territories: Bulletin of Canadian Petroleum Geology, v. 33, p. 730–781.
FERRO, C.E., DROXLER, A.W., ANDERSON J.B., AND MUCCIARONE, D., 1999, Late Quaternary shiftof mixed siliciclastic–carbonate environments induced by glacial eustatic sea-level fluctua-tions in Belize, in Harris, P.M., Saller, A.H., and Simo, J.A., eds., Carbonate SequenceStratigraphy: Applications to Reservoirs, Outcrops, and Models: SEPM, Special Publication63, p. 385–411.
GASTALDO, R.A., AND HUC, A.-Y., 1992, Sediment facies, depositional environments, and dis-tribution of phytoclasts in the recent Mahakam Delta, Kalimantan, Indonesia: Palaios, v. 7,p. 574–590.
GUSSMANN, O.A., AND SMITH, A.M., 2002, Mixed siliciclastic–skeletal carbonate lagoon sedi-ments from a high volcanic island, Viti Levu, Fiji, Southwest Pacific: Pacific Science, v.56, p. 169–189.
HALL, R., AND NICHOLS, G., 2002, Cenozoic sedimentation and tectonics in Borneo: climaticinfluences on orogenesis, in Jones, S.J., and Frostick, L.E., eds., Sediment Flux to Basins:Causes, Controls and Consequences: Geological Society of London, Special Publication 191,p. 5–22.
HALLOCK, P., AND GLENN, E.C., 1986, Larger Foraminifera: a tool for paleoenvironmental anal-ysis of Cenozoic carbonate depositional facies: Palaios, v. 1, p. 55–64.
HALLOCK, P., AND SCHLAGER, W., 1986, Nutrient excess and the demise of coral reefs andcarbonate platforms: Palaios, v. 1, p. 389–398.
HAMILTON, W., 1979, Tectonics of the Indonesian Region: U.S. Geological Survey, ProfessionalPaper 1078, 345 p.
HAQ, B.U., HARDENBOL, J., AND VAIL, P.R., 1987, Chronology of fluctuating sea levels sincethe Triassic: Science, v. 235, p. 1156–1165.
HAYWARD, A.B., 1985, Coastal alluvial fans (fan deltas) of the Gulf of Aqaba (Gulf of Eilat),Red Sea: Sedimentary Geology, v. 43, p. 241–260.
HOLLAND, S.M., 1993, Sequence stratigraphy of a carbonate–clastic ramp: The CincinnatianSeries (Upper Oxfordian) in its type area: Geological Society of America, Bulletin, v. 105,p. 306–322.
HOOK, J., AND WILSON, M.E.J., 2003, Stratigraphic relationships of a Miocene mixed carbonate–siliciclastic interval in the Badak field, East Kalimantan, Indonesia: 29th Indonesian Petro-leum Association, Annual Convention, Proceedings, p. 147–161.
HUTCHISON, C.S., 1989, Geological Evolution of South-East Asia: Oxford Monographs on Ge-ology and Geophysics 13, 368 p.
INSALACO, E., 1996, Upper Jurassic microsolenid biostromes of northern and central Europe:facies and depositional environment: Palaeogeography, Palaeoclimatology, Palaeoecology,v. 121, p. 169–194.
INSALACO, E., 1998, The descriptive nomenclature and classification of growth fabrics in fossilscleractinian reefs: Sedimentary Geology, v. 118, p. 159–186.
JOHNSON, D.P., AND RISK, M.J., 1987, Fringing reef growth on a terrigenous mud foundation,Fantome Island, central Great Barrier Reef, Australia: Sedimentology, v. 34, p. 275–287.
KIESSLING, W., 2002, Secular variations in the Phanerozoic reef ecosystem, in Kiessling, W.,Flugel, E., and Golonka, J., eds., Phanerozoic Reef Patterns: SEPM, Special Publication 72,p. 625–690.
LAND, D.H., AND JONES, C.M., 1987, Coal geology and exploration of part of the Tertiary KuteiBasin in East Kalimantan, Indonesia, in Scott, A.C., ed., Coal and Coal-Bearing Strata:Recent Advances: Geological Society of London, Special Publication 32, p. 235–255.
LARCOMBE, P., COSTEN, A., AND WOOLFE, K.J., 2001, The hydrodynamic and sedimentary settingof nearshore coral reefs, central Great Barrier Reef shelf, Australia: Paluma Shoals, a casestudy: Sedimentology, v. 48, p. 811–835.
LEINFELDER, R.R., 2001, Jurassic reef ecosystems, in Stanley, G.D., ed., The History and Sed-imentology of Ancient Reef Systems: Topics in Geobiology, Kluwer Academic Publishers,v. 17, p. 251–309.
MACK, G.H., AND JAMES, W.C., 1985, Cyclic sedimentation in the mixed siliciclastic–carbonateAbo–Hueco transitional zone (Lower Permian), southwestern New Mexico: Journal of Sed-imentary Petrology, v. 56, p. 635–647.
MAGNIER, P.H., OKI, T., AND KARTAADIPUTRA, L.W., 1975, The Mahakam Delta, Kalimantan,Indonesia: 9th World Petroleum Congress Tokyo, Proceedings, p. 239–250.
MARTIN, J.M., BRAGA, J.C., AND RIVAS, P. 1989, Coral successions in Upper Tortonian reefs inSE Spain: Lethaia, v. 22, p. 271–286.
MCCLANAHAN, T.R., AND OBURA, D., 1997, Sedimentation effects on shallow coral communitiesin Kenya: Journal of Experimental Marine Biology and Ecology, v. 209, p. 103–122.
MINNERY, G.A., REZAK, R., AND BRIGHT, T.J., 1985, Depth zonation and growth form of crustosecoralline algae: Flower Garden Banks, North-western Gulf of Mexico, in Toomey, D.F., andNitecki, M.H., eds., Paleoalgology: Contemporary Research and Applications: Berlin,Springer-Verlag, 237–246.
MOLENAAR, N., AND MARTINIUS, A.W., 1996, Fossiliferous intervals and sequence boundaries inshallow marine, fan-deltaic deposits (early Eocene, southern Pyrenees, Spain): Palaeogeog-raphy, Palaeoeclimatology, Palaeoecology, v. 121, p. 147–168.
MOUNT, J.F., 1984, Mixing of siliciclastic and carbonate sediments in shallow shelf environ-ments: Geology, v. 12, p. 432–435.
MOSS, S.J., AND CHAMBERS, J.L.C., 1999, Tertiary facies architecture in the Kutai Basin, Kali-mantan, Indonesia: Journal of Asian Earth Sciences, v. 17, p. 157–181.
NETHERWOOD, R., AND WIGHT, A., 1992, Structurally-controlled, linear reefs in a Pliocene Delta-front setting, Tarakan Basin, Northeast Kalimantan, in Siemers, C.T., Longman, M.W., Park,R.K., Kaldi, J.G., eds., Carbonate Rocks and Reservoirs of Indonesia: Indonesian PetroleumAssociation, Core Workshop Notes 1, Ch. 3.
OLSZEWSKI, T.D., AND PATZKOWSKY, M.E., 2003, From cyclothems to sequences: the record ofeustasy and climate on an icehouse epeiric platform (Pennsylvanian–Permian, North Amer-ican midcontinent): Journal of Sedimentary Research, v. 73, p. 15–30.
PERRIN, C., 1992, Signification ecologique des foraminiferes acervulinides et leur role dans la for-mation de facies recifaux et organogenes depuis le paleocene: Geobios, v. 25, p. 725–751.
PERRIN, C., BOSENCE, D., AND ROSEN, B., 1995, Quantitative approaches to palaeozonation andpalaeobathymetry of corals and coralline algae in Cenozoic reefs, in Bosence, D.W.J., andAllison, P.A., eds., Marine Palaeoenvironmental Analysis from Fossils: Geological Societyof London, Special Publication 83, 181–229.
PHIPPS, C.V.G., AND ROBERTS, H.H., 1988, Seismic characteristics and accretion history of Hal-imeda bioherms on Kalukalukuang Bank, eastern Java Sea (Indonesia): Coral Reefs, v. 6,p. 149–159.
POMAR, L., 2001, Types of carbonate platforms: a genetic approach: Basin Research, v. 13, p.313–334.
RANKEY, E.C., 1997, Relations between relative changes in sea level and climate shifts: Penn-sylvanian–Permian mixed carbonate–siliciclastic strata, western United States: GeologicalSociety of America, Bulletin, v. 109, p. 1089–1100.
RANKEY, E.C., BACHTEL, S.L., AND KAUFMAN, J., 1999, Controls on stratigraphic architecture oficehouse mixed carbonate–siliciclastic systems: a case study from the Holder Formation(Pennsylvanian, Virgillian), Sacramento Mountains, New Mexico, in Harris, P.M., Saller,
133DELTA-FRONT PATCH REEF DEVELOPMENT
A.H., and Simo, J.A., eds., Carbonate Sequence Stratigraphy: Applications to Reservoirs,Outcrops, and Models: SEPM, Special Publication 63, p. 127–150.
RIEGL, B., HEINE, C., AND BRANCH, G.M., 1996, Function of funnel-shaped coral growth in ahigh-sedimentation environment: Marine Ecology, Progress Series, v. 145, p. 87–93.
ROBERTS, H.H., AHARON, P., AND PHIPPS, C.V., 1988, Morphology and sedimentology of Hali-meda bioherms from the eastern Java Sea (Indonesia): Coral Reefs, v. 6, p. 161–172.
ROBERTS, H.H., AND SYDOW, J., 1996, The offshore Mahakam Delta: Stratigraphic response oflate Pleistocene-to-modern sea level cycle: 25th Indonesian Petroleum Association, AnnualConvention, Proceedings, p. 147–161.
ROBERTS, H.H., PHIPPS, C.V., AND EFFENDI, L.L., 1987, Halimeda bioherms of the eastern JavaSea, Indonesia: Geology, v. 15, p. 371–374.
ROSEN, B.R., AILLUD, G.S., BOSELLINI, F.R., CLACK, N., INSALACO, E., VALLDEPERAS, F.X., AND
WILSON, M.E.J., 2002, Platy coral assemblages: 210 million years of response to the limitingeffects of depth, light and turbidity: 9th International Coral Reefs Symposium, 2000, Pro-ceedings, p. 255–264.
ROTTGER, R., 1971, Die Bedeutung der Symbiose von Heterostegina depressa (Foraminifera,Nummulitidae) fur hohe Siedlungsdichte und Karbonatproduction: Deutsche ZoologischeGesellschaft Sonderdruck aus Verhandlungsbericht, v. 65, Jahresversammlung, Gustav Fi-scher Verlag, p. 42–47.
SALLER, A.H., AND VIJAYA, S., 2002, Depositional and diagenetic history of the Kerendan car-bonate platform, Oligocene, central Kalimantan, Indonesia: Journal of Petroleum Geology,v. 25, p. 123–150.
SANDERS, D., AND BARON-SZABO, R.C., in press, Fossil coral assemblages under sediment input:their characterisitcs and relation to the nutirent input concept: Palaeogeography, Palaeocli-matology Palaeoecology.
SANTISTEBAN, C., AND TABERNER, C., 1988, Sedimentary models of siliciclastic deposits and coralreef interactions, in Doyle, L.J., and Roberts, H.H., eds., Carbonate–Clastic Transitions:Amsterdam, Elsevier, Developments in Sedimentology, v. 42, p. 35–76.
SCOFFIN, T.P., 1997, Preservation and CaCO3 budget of reef-flat corals, Phuket, South Thailand:8th International Coral Reef Symposium, Proceedings, v. 2, p. 1795–1800.
SLUITER, C.PH., 1890, Einiges uber die Entstehung der Korallenriffen in der Javasee und Bran-tweinsbai, und uber neue Korallenbildung Krakatau: Natuurkundig Tijdschrift NederlandschIndie, v. 49, p. 360–380.
TANEAN, H., PATERSON, D.W., AND ENDHARTO, M., 1996, Source provenance interpretation of Kuteibasin sandstones and implications for the tectono-stratigraphic evolution of Kalimantan: Indo-nesian Petroleum Association, 25th Annual Convention, Proceedings v. 1, p. 333–345.
TITLYANOV, E.A., AND LATYPOV, Y.Y., 1991, Light-dependence in scleractinian distribution inthe sublittoral zone of South China Sea Islands: Coral Reefs, v. 10, p. 133–138.
TOMASCIK, T., MAH, A.J., NONTJI, A., AND MOOSA, M.K., 1997, The Ecology of the Indonesian Seas:Oxford, U.K., Oxford University Press, The Ecology of Indonesia Series, v. VII, 1388 p.
TUCKER, M.E., 1992, Sedimentary Petrology; An Introduction: Oxford, U.K., Blackwell Sci-entific Publications, 252 p.
TUDHOPE, A.W., AND SCOFFIN, T.P., 1994, Growth and structure of fringing reefs in a muddyenvironment, South Thailand: Journal of Sedimentary Research, v. A64, p. 752–764.
UMBGROVE, J.H.F., 1947, Coral reefs of the East Indes: American Association of PetroleumGeologists, Bulletin, v. 58, p. 729–778.
VAN DE WEERD, A.A., AND ARMIN, R.A., 1992, Origin and evolution of the Tertiary hydrocarbon-bearing basins in Kalimantan (Borneo), Indonesia: American Association of Petroleum Ge-ologists, Bulletin, v. 76, p. 1778–1803.
WOOLFE, K.J., AND LARCOMBE, P., 1998, Terrigenous sediment accumulation as a regional con-trol on the distribution of reef carbonates, in Camoin, G.F., and Davies, P.J., eds., Reefsand Carbonate Platforms in the Pacific and Indian Oceans: International Association ofSedimentologists, Special Publication 25, p. 295–310.
WOOLFE, K.J., AND LARCOMBE, P., 1999, Terrigenous sedimentation and coral reef growth: aconceptual framework: Marine Geology, v. 155, p. 331–345.
WILSON, M.E.J., 2002, Cenozoic carbonates in SE Asia: Implications for equatorial carbonatedevelopment: Sedimentary Geology, v. 147, p. 295–428.
WILSON, M.E.J., AND LOKIER, S.W., 2002, Siliciclastic and volcaniclastic influences on equatorialcarbonates: insights from the Neogene of Indonesia: Sedimentology, v. 49, p. 583–601.
WILSON, M.E.J., AND MOSS, S.J., 1999, Cenozoic evolution of Borneo–Sulawesi: Palaeogeog-raphy, Palaeoclimatology, Palaeoecology, v. 145, p. 303–337.
YANG, W., AND KOMINZ, M.A., 2002, Characteristics, stratigraphic architecture, and time frame-work of multi-order mixed siliciclastic and carbonate depositional sequences, outcroppingCisco Group (Late Pennsylvanian and Early Permian), Eastern Shelf, north-central Texas,U.S.A.: Sedimentary Geology, v. 154, p. 53–87.
Received 6 May 2003; accepted 28 June 2004.