sequence stratigraphy of the precambrian rooihoogte–timeball...
TRANSCRIPT
Sequence stratigraphy of the Precambrian Rooihoogte–Timeball
Hill rift succession, Transvaal Basin, South Africa
Octavian Catuneanu a,*, Patrick G. Eriksson b
aDepartment of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, Alberta, Canada T6G 2E3bDepartment of Earth Sciences, University of Pretoria, Pretoria 0002, South Africa
Received 31 December 2000
Abstract
Third-order sequence stratigraphic analysis is performed on the Rooihoogte–Timeball Hill second-order rift succession of
the Paleoproterozoic Transvaal Basin, South Africa. This provides a case study for systems tract and sequence development
during a time of glacio-eustatic fall, when accommodation was generated by subsidence related to syn-rift and post-rift tectonic
processes. Two third-order depositional sequences have been identified, separated by a basin-wide subaerial unconformity. The
lower third-order sequence includes the complete succession of lowstand, transgressive, and highstand systems tracts (LST,
TST, and HST), whereas the upper third-order sequence only preserves lowstand and transgressive systems tracts. This indicates
that the fall in base level associated with the upper second-order boundary of the Rooihoogte–Timeball Hill sequence was of
higher magnitude relative to the third-order subaerial unconformity, which is in agreement with the principles of boundary
hierarchy based on the magnitude of base-level changes. The position of the lower boundary of the Rooihoogte–Timeball Hill
second-order sequence has been revised from the base of the chert breccias to the contact between the breccias and the overlying
chert conglomerates. This is because a major tilting event occurred between the deposition of the two facies, which are
genetically unrelated, and which are separated by a subaerial unconformity. The lithostratigraphic contact between the
Rooihoogte and Timeball Hill formations is interpreted as a diachronous transgressive surface of erosion. In this interpretation,
the Polo Ground Member of the Rooihoogte Formation may be coeval with the basal black shales of the Timeball Hill
Formation, the two facies (fluvial and marine, respectively) forming together a transgressive systems tract. D 2002 Elsevier
Science B.V. All rights reserved.
Keywords: Precambrian sequence stratigraphy; Second-order rift sequence; Third-order systems tracts; Transvaal Basin
1. Introduction
Sequence stratigraphy, which developed as a meth-
odology for explaining the relationships of allostrati-
graphic units that fill a sedimentary basin, is currently
one of the most actively evolving disciplines in sedi-
mentary geology. Through the recognition of bounding
surfaces, genetically related facies (systems tracts) can
be identified. Lithofacies can then be correlated accord-
ing to where each unit is positioned along an inferred
curve that represents base-level fluctuations. The con-
cepts of sequence stratigraphy have primarily been
perfected from the study of Phanerozoic successions,
which provide better preservation potential and time
control for detailed stratigraphic analyses and correla-
0037-0738/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.
PII: S0037-0738 (01 )00188 -9
* Corresponding author. Tel.: +1-780-492-6569.
E-mail address: octavian@ualberta ca (O. Catuneanu).
www.elsevier.com/locate/sedgeo
Sedimentary Geology 147 (2002) 71–88
tions (Vail, 1987; Posamentier et al., 1988, 1992; Van
Wagoner et al., 1990; Hunt and Tucker, 1992; Miall,
1997; Plint and Nummedal, 2000). More recently, the
principles of sequence stratigraphy have also been
applied to genetic interpretations of Precambrian suc-
cessions (e.g., Christie-Blick et al., 1988; Catuneanu
and Eriksson, 1999; Catuneanu and Biddulph, in
press).
1.1. Concepts of sequence stratigraphy
Comprehensive discussions of sequence strati-
graphic concepts and their application to the Precam-
brian rock record are provided by Christie-Blick et al.
(1988) and Catuneanu and Eriksson (1999). Briefly
summarized below are key concepts relevant to this
study. The various systems tracts and stratigraphic
surfaces are defined relative to the base-level and
transgressive–regressive curves (Fig. 1). The two
curves are offset by a time period equivalent to the
duration of sediment-driven (‘‘normal’’) regressions,
which depends on the ratio between the rates of base-
level rise and the sedimentation rates (see Catuneanu
and Eriksson, 1999 for a more detailed discussion).
Lowstand systems tracts form during early stages
of base-level rise, when the rates of base-level rise are
outpaced by sedimentation rates. As a result, a ‘‘nor-
mal’’ regression of the shoreline occurs. Typical
products for lowstand systems tracts (LST) include
amalgamated channel fills overlying subaerial uncon-
formities, and lowstand deltaic deposits. Protected
from subsequent erosion by the aggradation of over-
lying transgressive and highstand deposits, these LST
deposits have a high preservation potential.
Transgressive systems tracts form during acceler-
ated base-level rise, when rates of base-level rise out-
pace sedimentation rates. As a result, a transgressive
shift of the shoreline occurs, and retrogradation and
vertical aggradation in both fluvial and shallow marine
environments results.
Fig. 1. Types of sequences, bounding surfaces and systems tracts defined in relation to the base-level and transgressive– regressive curves
(modified from Catuneanu et al., 1998). Abbreviations: TST—transgressive systems tract; RST—regressive systems tract; LST—lowstand
systems tract; HST—highstand systems tract; FSST—falling stage systems tract; SU—subaerial unconformity; c.c.—correlative conformity;
MRS—maximum regressive surface; MRS-c—MRS-correlative (i.e., the nonmarine correlative of the marine MRS); MTS—maximum
transgressive surface; (A)—positive accommodation; NR—normal (sediment supply-driven) regression; FR—forced (base-level fall-driven)
regression.
O. Catuneanu, P.G. Eriksson / Sedimentary Geology 147 (2002) 71–8872
Highstand systems tracts form during late stages of
base-level rise, when sedimentation rates outpace
rates of base-level rise. ‘‘Normal’’ regression of the
shoreline occurs, resulting in aggradation and progra-
dation of both fluvial and marine deposits. Highstand
deltaic deposits, bounded above by subaerial uncon-
formities, are typical products. Highstand strata may
have a low preservation potential due to erosion
accompanying subsequent base-level falls.
Subaerial unconformities develop in the nonmarine
portion of the basin due to fluvial or wind degradation
during stages of base-level fall. They may overlie
fluvial or marine strata, but are overlain by nonmarine
deposits.
Transgressive surfaces of erosion, also known as
‘‘ravinement surfaces’’, are scours cut by shoreface
waves during the transgression of a shoreline. They
are highly diachronous surfaces, separating fluvial
strata below from shallow marine facies above. In
areas of high preservation potential, ravinement sur-
faces may be entirely developed within transgressive
systems tracts, which is why they are not represented
in Fig. 1 (see Catuneanu and Eriksson, 1999, for
discussion and illustration).
Maximum regressive surfaces represent the boun-
dary between a lowstand systems tract and an over-
lying transgressive systems tract. They are also known
as ‘‘conformable transgressive surfaces’’ (Embry,
1995; Catuneanu et al., 1998).
Maximum transgressive surfaces represent the
boundary between a transgressive systems tract and
an overlying highstand systems tract. A synonymous
term is ‘‘maximum flooding surfaces’’.
1.2. Aim of research
This paper focuses on the Transvaal Basin of South
Africa (Fig. 2), which preserves a � 650-My record
of Late Archaean to Early Proterozoic sedimentation.
Previous work equated the sedimentary fill of the
Transvaal Basin, that is, the Transvaal Supergroup,
with a first-order depositional sequence bounded by
subaerial unconformities generated in relation to
major changes in the tectonic setting (Catuneanu
and Eriksson, 1999; Fig. 3). The inferred curve of
base-level changes for the Transvaal Basin allowed
the further subdivision of the Transvaal first-order
sequence into five second-order depositional sequen-
ces, that is, the Protobasinal, Black Reef, Chunies-
poort, Rooihoogte–Timeball Hill, and Boshoek–
Houtenbek sequences (Fig. 3). The purpose of this
research is to increase the resolution of sequence
stratigraphic analysis to the third-order level of cyclic-
ity, for the case study of the Rooihoogte–Timeball
Hill second-order sequence. The motivation for doing
this work is twofold: (1) no third-order sequence
stratigraphic analyses have been performed so far on
the Transvaal succession, and (2) the accumulation of
the Rooihoogte–Timeball Hill strata took place dur-
ing a time of global glacio-eustatic fall (Young, 1995;
Eriksson et al., 1998; Martin, 1999; Young et al., in
press; Fig. 3), which provides a case study for systems
tract and sequence development with accommodation
generated by tectonic processes. This is particularly
relevant in view of the core debate of sequence
stratigraphy over the eustatic versus tectonic controls
on accommodation and sequence development.
2. Geological background
2.1. Tectonic setting
The Transvaal Supergroup overlies the c. 3.0- to
2.7-Ga Witwatersrand Supergroup in the stratigraphic
record and constitutes the sedimentary floor to the
Bushveld igneous complex (Fig. 3). It should be noted
here, that the c. 2.7-Ga Ventersdorp Supergroup,
which unconformably succeeds the Witwatersrand
strata, is approximately coeval with the lowermost
portion of the Transvaal Supergroup (e.g., Eriksson et
al., in press). The 2714-Ma boundary between the
Witwatersrand and Transvaal (Ventersdorp) Super-
groups marks a significant change in the structural
style of the receiving sedimentary basins. The Witwa-
tersrand succession accumulated within a retroarc
foreland basin developed in relation to the supra-
crustal loading associated with the initial phases of
the Limpopo Orogeny (Winter, 1987; Stanistreet and
McCarthy, 1991; Robb and Meyer, 1995), and prob-
ably also associated with collision of arc systems with
the emerging Kaapvaal craton (Catuneanu, in press).
In contrast, sedimentation within the Transvaal Basin
was controlled by cycles of extensional and/or thermal
subsidence separated by stages of uplift or glacio-
eustatic base-level fall (Catuneanu and Eriksson,
O. Catuneanu, P.G. Eriksson / Sedimentary Geology 147 (2002) 71–88 73
Fig. 2. Outcrop distribution of the Transvaal lithostratigraphic units within the confines of the Transvaal Basin. Modified from Eriksson and Reczko (1995).
O.Catuneanu,P.G.Eriksso
n/Sedimentary
Geology147(2002)71–88
74
1999). The upper boundary of the Transvaal Super-
group, that is, the 2050-Ma contact with the Bushveld
complex, corresponds to another first-order tectonic
event that terminated the evolutionary history of the
Transvaal Basin. Bounded by these two 2050- and
2714-Ma contacts, the Transvaal Supergroup is inter-
preted as a first-order sequence related to the accu-
mulation of sediment within the tectonic setting of the
Transvaal and correlative basins.
The five second-order depositional sequences of
the Transvaal Supergroup correspond to distinct
cycles of extensional and/or thermal subsidence, and
are separated by second-order subaerial unconform-
ities. Important to note is the cyclic repetition of
tectonic settings within the succession of second-order
sequences, indicating no major shifts in structural
styles during the evolution of the Transvaal Basin.
The accumulation of the Rooihoogte–Timeball Hill
second-order sequence took place during a full rifting
cycle, with accommodation provided by syn-rift
extensional subsidence (Rooihoogte time) followed
by post-rift thermal subsidence (Timeball Hill time;
Catuneanu and Eriksson, 1999; Fig. 3).
2.2. Lithostratigraphy
The Transvaal Supergroup comprises four main
lithostratigraphic units, that is, the protobasinal (a
nondescriptive term) rocks, Black Reef Formation,
Chuniespoort Group, and Pretoria Group (Eriksson
and Reczko, 1995; Fig. 3). Our stratigraphic objective
is represented by the two lowermost formations of the
Pretoria Group, that is, the Rooihoogte and Timeball
Hill (Fig. 3).
A generalized lithostratigraphic profile for the
Rooihoogte and Timeball Hill formations is presented
in Fig. 4. The basal contact of the Rooihoogte
Formation, as well as the top contact of the Timeball
Hill Formation, are both marked by major angular
unconformities. These unconformities have been
identified as second-order depositional sequence
boundaries (Catuneanu and Eriksson, 1999), and their
features are described in detail by Eriksson et al. (in
press).
The Rooihoogte Formation consists of three lith-
ostratigraphic members, with a total thickness in
excess of 400 m in the northwestern part of the
Transvaal Basin. The lower Bevets Member includes
coarse products of in situ weathering and alluvial
sedimentation represented by chert breccias and con-
glomerates, respectively. The chert breccias have been
traditionally considered as the basal part of the Pre-
toria Group, but they have been recently reassigned to
the underlying Chuniespoort Group (Eriksson et al., in
press). The revised contact between the Chuniespoort
and Pretoria Groups is now taken at the unconform-
able limit between the Bevets breccias and conglom-
erates (Fig. 4). More details on the reasons for this
suggested change are presented in Section 3 of this
paper. Fig. 4 accommodates both old and new inter-
pretations, preserving at the same time the integrity of
the ‘‘Bevets Member’’ as defined in current literature.
Overlying these basal coarse facies are the shale and
Polo Ground sandstone members (Fig. 4), represent-
ing the products of lacustrine and fluvial sedimenta-
tion, respectively.
The Timeball Hill Formation, with a thickness in
excess of 1100 m in the northern part of the Transvaal
Basin, also comprises three sedimentary members;
these include the lower and upper shale members
separated by a sandstone unit, the Klapperkop quartz-
ite Member (Eriksson et al., 1994a; Fig. 4). Minor
lenses of poorly sorted diamictites and wackes,
ascribed to reworking of periglacial detritus have also
been identified in the upper shale member (Visser,
1971). A variety of genetic facies associations are
recognized in the formation: pelagic suspension
deposits, distal and proximal turbidites, contourites,
and lower and upper tidal flat deposits (Eriksson and
Reczko, 1998). The close association between deeper
marine and coastal facies is explained by a significant
stratigraphic break that separates the lower mudstones
from the overlying Klapperkop quartzite Member
(Fig. 4). Thin stromatolitic carbonate interbeds in
the Timeball Hill mudstones suggest that sedimenta-
tion took place within the photic zone (Eriksson and
Reczko, 1998).
In the southern part of the basin, the contact
between the Rooihoogte and Timeball Hill formations
is marked by a localized occurrence of highly altered
lavas (i.e., the Bushy Bend lava Member, Eriksson et
al., 1994b; Fig. 4). With an average thickness of about
30 m, these lavas are interpreted to reflect the eruption
episode related to the transition from Rooihoogte
rifting, to subsequent post-rift subsidence (Eriksson
et al., in press).
O. Catuneanu, P.G. Eriksson / Sedimentary Geology 147 (2002) 71–88 75
Fig. 4 infers the relative chronologies of the
lithostratigraphic members that build together the
Rooihoogte and Timeball Hill Formations. Although
this generalized vertical profile reflects the true rela-
tionships for individual data points, temporal overlaps
between the timing of sedimentation of the various
facies within the basin are most likely (Catuneanu and
Eriksson, 1999).
2.3. Palaeoclimatic background
The available age constraints of the Rooihoogte
and Timeball Hill formations indicate deposition
within the span of the c. 2.4- to 2.2-Ga global gla-
ciation (Young, 1995; Eriksson et al., 1998; Martin,
1999; Young et al., in press; Fig. 3). As evidence for
extensive ice cover on the Kaapvaal craton is limited,
sea levels were likely low and freeboard high (emer-
gent, glaciated continents; Eriksson et al., in press). In
addition, the cold temperatures would also have
lowered the rates of weathering processes. In view
of the low syn-glacial eustatic levels, subsidence to
accommodate aggradation and epeiric drowning dur-
ing the Rooihoogte–Timeball Hill times must have
been significant. This provides a case study where
accommodation and sequence development were
apparently primarily controlled by tectonic processes.
3. Sedimentary facies
This section presents genetic interpretations for the
sedimentary facies that comprise the Rooihoogte and
Timeball Hill Formations. The outcrop distribution of
the Rooihoogte–Timeball Hill succession is illus-
trated in Fig. 5.
3.1. Rooihoogte Formation
Fig. 6 shows the location of the main data points
and the associated vertical profiles for the Rooihoogte
Formation. Sedimentary facies with regional extent
include chert breccias, chert conglomerates, shales,
and the ‘‘Polo Ground’’ sandstones.
3.1.1. Chert breccias
The chert breccias form a discrete, wedge-shaped
lithological unit that develops at the limit between the
Chuniespoort and Pretoria Groups. This unit was
originally assigned to the Rooihoogte Formation,
and more recently re-interpreted as the time equivalent
of the Duitschland Formation, at the top of the
Chuniespoort Group (Eriksson et al., in press; Fig.
3). The sheet-like nature of the Chuniespoort carbo-
nate and iron-rich units (Malmani Subgroup and
Penge Formation, respectively, in Fig. 3) enables
estimation of the stratigraphic loss related to the basal
Pretoria unconformity, which is shown as a contour
map of denudation in Fig. 7. Preserved thickness of
the chert breccias, when superimposed on Chunies-
poort denudation contours, exhibits a good correlation
(Fig. 7), as expected for such residual products of in
situ weathering. The in situ nature of the breccias, as
borne out by their compositional similarity to varying
underlying chemical sedimentary strata, was first
observed by Button (1973). As shown by Eriksson
et al. (in press), the Duitschland Formation largely
comprises weathered Chuniespoort detritus that has
been transported northwards from the uplifted south-
ern area of the basin, and reworked to produce mainly
fine marly facies. Possibly, formation of the Duitsch-
land basin, presumably restricted to the northeast of
the preserved Transvaal depository, was coeval with
uplift of the southern Chuniespoort rocks. Chert
breccias overlying the Chuniespoort chemical sedi-
ments in the south, and the Duitschland lithologies,
may thus be time equivalents in addition to their
inferred proximal–distal relationship. If the chert
breccias and Duitschland rocks may be correlated,
then these strata represent the entire time gap (possi-
bly up to 80 My; Eriksson and Reczko, 1995; Fig. 3)
between the end of Chuniespoort chemical sedimen-
tation and the onset of Pretoria Group deposition
(beginning with the Rooihoogte conglomerates).
Fig. 3. Lithostratigraphy, chronology, tectonic settings, paleoenvironments and inferred base-level changes for the Transvaal Supergroup. 1) from
Armstrong et al. (1991); 2) from Eriksson and Reczko (1995); 3 – 5) from Walraven and Martini (1995); 6) from Eriksson and Reczko (1995); 7)
from Walraven and Martini (1995); 8) from Harmer and von Gruenewaldt (1991). Wavy lines suggest unconformable contacts. Modified from
Catuneanu and Eriksson (1999).
O. Catuneanu, P.G. Eriksson / Sedimentary Geology 147 (2002) 71–88 77
Fig. 4. Lithostratigraphic profile of the Rooihoogte and Timeball Hill Formations (Pretoria Group). Modified from Eriksson and Reczko (1995).
Wavy lines indicate unconformable contacts.
Fig. 5. Outcrop distribution of the Rooihoogte–Timeball Hill succession in the context of the Transvaal Basin. Modified from Eriksson and
Reczko (1998).
O. Catuneanu, P.G. Eriksson / Sedimentary Geology 147 (2002) 71–8878
3.1.2. Chert conglomerates
The chert conglomerates represent alluvial fan and
fan-delta deposits sourced from the north, which pro-
gressively downlap onto the underlying lithologies in a
southward direction. The major occurrence (up to 250
m thick) of the chert conglomerate facies in the west of
the basin is lobate in preserved geometry, and thickens
northwards towards the source (Fig. 8). Amuch thinner
lobe occurs in the northeast, where it overlies both
Duitschland and older rocks. There is also a partial
overlap between the areas of occurrence of chert
breccias and chert conglomerates in the central part
of the Transvaal Basin (Fig. 8). The conglomerates
contain mostly chert pebbles, are matrix- and clast-
supported (thus indicating, respectively, gravity flow
and streamflow transport processes), and with pebbles
that vary in size up to about 10–15 cm, with sizes of 7
cm or less being most common (Fig. 6). The matrix of
the conglomerates is generally sand-sized and sili-
ceous, and the roundness of clasts varies between
poorly rounded, subrounded, and well rounded.
A very significant aspect is the change in topo-
graphic tilt at the boundary between the chert breccias
and the overlying chert conglomerates (Fig. 8). The
direction of tilt during the latest Chuniespoort times
was from south to north, which explains the more
pronounced weathering (thicker chert breccias) in the
south. The progradation of the younger chert con-
glomerates took place on a topographic slope dipping
to the south, which marks a change of approximately
180� in the direction of topographic tilt. This shows
that the second-order sequence boundary that sepa-
rates the Chuniespoort and Pretoria groups is related
to a significant tectonic event that led to the reorgan-
ization of the Transvaal Basin. The chert breccias and
the chert conglomerates preceded and succeeded this
tectonic event, respectively, which indicates that they
belong to sedimentary packages that are unrelated
Fig. 6. Lithological field profiles of the Rooihoogte Formation.
O. Catuneanu, P.G. Eriksson / Sedimentary Geology 147 (2002) 71–88 79
Fig. 7. Contour map showing the correlation between the occurrence of chert breccias and the thickness loss of the underlying Chuniespoort
chemical deposits. Modified from Eriksson et al. (in press).
Fig. 8. Isopach maps of the chert breccias (uppermost Chuniespoort Group) and chert conglomerates (lowermost Pretoria Group), showing the
contrast in the direction of topographic tilt between the timing of deposition of the two facies. Modified from Eriksson et al. (in press).
O. Catuneanu, P.G. Eriksson / Sedimentary Geology 147 (2002) 71–8880
genetically (i.e., different depositional sequences sep-
arated by a subaerial unconformity).
3.1.3. Rooihoogte shales
The shales of the Rooihoogte Formation exhibit
horizontal stratification, graded laminae, ripple marks
(siltstone interbeds), flaser lamination, and varve
structures (Eriksson, 1988; Eriksson et al., 1991).
This facies is interpreted to represent periglacial la-
custrine sedimentation, with the depocenter in the
western part of the Transvaal Basin (Eriksson and
Reczko, 1995). The Rooihoogte shale Member dis-
plays a variable thickness, ranging from about 18 up
to 250 m (Eriksson, 1988; Fig. 6). The boundary
between the shales and the underlying chert conglom-
erates is a diachronous facies contact, as the two facies
are partly age equivalent (Catuneanu and Eriksson,
1999). The conglomerates and shales together form a
fining-upward genetic package that led to the pene-
planation of the pre-existing karst topography. Paleo-
geographic reconstructions show the progradation of
chert conglomerates via alluvial fans and fan-delta
systems towards the south, into the standing body of
water of the lacustrine environment (Eriksson and
Reczko, 1995). The balance between fan progradation
and lacustrine aggradation gradually shifted in the
favor of the latter, in parallel with the denudation of
the northern sediment source areas, which explains the
overall fining-upward profile of the alluvial–deltaic–
lacustrine systems tract (Catuneanu and Eriksson,
1999).
3.1.4. Polo Ground quartzite Member
This lithofacies is thin, generally varying from 6 to
10 m in thickness (Fig. 6). It comprises fine- to
medium-grained ferruginous quartz wackes, with
locally abundant lenses of very coarse pebbly lithic
wackes, 10–50 cm thick and 1–5 m wide. The
pebbles consist of siltstone and silty, very fine sand-
stone, indicating erosion of the underlying lithofacies
(Eriksson, 1988). These intraformational pebbles may
be interpreted as rip-up clasts preserved at the base of
braided channel fills, generated as the unconfined
fluvial systems shifted laterally across their own over-
bank areas. The high-energy character of the inter-
preted braided systems is also confirmed by the
observed sedimentary structures and textures. The
sandstones exhibit common planar and trough cross-
bedding organized in macroforms up to 8 m wide and
70 cm thick, indicating the manifestation of down-
stream accretion processes, typical for multiple-chan-
nel, low-sinuosity systems. The sandstones are
commonly granular in the far west of the basin, and
contain both chert grains and feldspar. They are
coarsest and most immature in the northwest of the
basin, which was probably where they were most
proximal (Eriksson, 1988). The contact between the
Polo Ground sandstones and the underlying lacustrine
shales appears to be conformable, locally represented
by channel base scours. Taking the top contact of the
underlying alluvial–deltaic–lacustrine systems tract
as a time-line datum, the deposition of the Polo
Ground fluvial sands in the west of the basin appears
to be concomitant with the transgression recorded in
the east by the basal black shales of the Timeball Hill
Formation.
3.2. Timeball Hill Formation
The Timeball Hill Formation is the product of
dominantly marine and marginal marine sedimenta-
tion, being represented by fine-grained sedimentary
strata (lower and upper shale members), and subordi-
nate sandstones (medial Klapperkop Member). The
regional distribution of these facies is illustrated in
Fig. 9. The three members can be recognized around
the preserved basin, and tend to have a sheet-like
geometry (Eriksson and Reczko, 1998). The contact
with the underlying Rooihoogte Formation is sharp,
being represented by the ravinement surface at the
base of the lowermost Timeball Hill transgressive
black shales.
3.2.1. Lower shale Member
The Lower Shale Member consists of a widespread
basal black shale lithofacies, succeeded by rhythmical-
ly interbedded mudstones, siltstones, and fine-grained
sandstones, often termed the ‘‘rhythmite lithofacies’’, or
‘‘lower mudstones’’, by previous researchers (Eriksson
et al., 1994b).
The marine black shales are inferred to have trans-
gressed approximately from east to west (Eriksson
and Reczko, 1998). This facies is typically laminated,
with subordinate lenses of silty material with planar
cross-laminations and current ripples. The black pig-
mentation is due predominantly to pervasive micro-
O. Catuneanu, P.G. Eriksson / Sedimentary Geology 147 (2002) 71–88 81
scopic iron minerals (mainly limonite after pyrite),
with subordinate thin beds and laminae more intensely
pigmented by flakes of carbonaceous material (Eriks-
son et al., 1994b).
Above the transgressive black shale, the ‘‘lower
mudstones’’ consist of a shallowing-upward succes-
sion of pelagic, distal delta-fed turbidites, and con-
tourites, interpreted by Eriksson and Reczko (1998) as
being deposited under highstand conditions. Domi-
nant lithofacies include laminated and graded mud-
stones, and sheets of laminated and cross-laminated
siltstones and fine-grained sandstones. These are
compatible with the Te, Td, and Tc subdivisions of
the low-density turbidity current systems (Eriksson
and Reczko, 1998). Thin interbeds of stromatolitic
carbonates support photic water depths up to about
100 m. Small lenses of coarse siltstone to very fine-
grained sandstone, analogous to modern continental
rise contourite deposits, occur within the suspension
and distal turbidite sediments, and also form local
wedges of inferred contourites at the transition from
suspension to lowermost turbidite deposits (Eriksson
and Reczko, 1998).
3.2.2. Klapperkop quartzite Member
The arenaceous Klapperkop Member (Fig. 9) con-
sists of an erosively based, generally upward-coarsen-
ing succession of tidally reworked braid-delta
deposits, interpreted as lowstand facies by Eriksson
and Reczko (1998). Eriksson and Reczko (1998)
recognized two separate facies within the Klapperkop
Member: (1) mature cross-bedded sandstone sheets,
interpreted as lower tidal flat deposits; and (2) inter-
bedded lenticular immature sandstones and mud-
stones, interpreted as medial to upper tidal flat
deposits.
The lower tidal flat deposits consist of sandstone
beds with lateral extents of tens to hundreds of
meters, and bed thicknesses of up to 5 m. These
rocks are mostly fine- to medium-grained, and com-
prise quartz arenites with subordinate sublithic are-
nites, quartz wackes, and lithic wackes (Schreiber,
1990). Minor, thin mudstone interbeds are also found
(Eriksson and Reczko, 1998). The sandstone sheets
display planar and trough cross-bedding with varying
proportions around the basin (Button, 1973; Key,
1983; Van der Neut, 1990; Schreiber, 1990). A few
Fig. 9. Fence diagram illustrating the distribution, thickness, and sheet-like geometry of the lithofacies identified by previous workers in the
Timeball Hill Formation. Modified from Eriksson et al. (1994b) and Eriksson and Reczko (1998). The position of all localities in the context of
the Transvaal Basin is indicated in Fig. 5.
O. Catuneanu, P.G. Eriksson / Sedimentary Geology 147 (2002) 71–8882
herringbone cross-bed sets occur, as well as minor
interference and bifurcating ripples, and rare mud-
cracked surfaces and preserved megaripples (Button,
1973; Schreiber, 1990). A relatively shallow water
depositional setting is inferred for these cross-bedded
sandstone sheets, supported by uncommon mudcracks
and ripple marks. The presence of minor herringbone
cross-beds, bifurcating, and interference ripples sug-
gests tidal action. The textural and compositional
maturity of these inferred tidal sandstone sheets
points to a lower tidal flat setting where reworking
would have been more prevalent (Eriksson and
Reczko, 1998).
The medial to upper tidal flat deposits are com-
monly interbedded with stacked lower tidal flat sand-
stone sheet successions up to 30 m thick (Eriksson and
Reczko, 1998). The inferred upper tidal flat deposits
comprise lenticular sandstone bodies, from less than 1
m to about 50 m in lateral extent, and up to about 50 cm
thick, interbedded with finely laminated, micaceous
mudstones. The sandstones are compositionally and
texturally immature, mostly fine to medium grained.
Locally, coarse-grained sandstones and even small
pebble conglomeratic basal lags are observed (Eriksson
and Reczko, 1998). The presence of interbedded sand-
stones and mudstones, ladderback and flat-top ripples,
herringbone cross-strata, and mudcracks supports the
varying energy levels and intermittent exposure typical
of middle to upper tidal flats.
3.2.3. Upper shale Member
The Upper Shale Member consists of a deep-
ening-upward succession of suspension deposits and
delta-fed turbidite fan systems interpreted as trans-
gressive facies (Eriksson and Reczko, 1998). Sub-
ordinate occurrences of black shales and diamictites
are recorded in the south of the basin, and arkosic
sandstones in the north (Fig. 9). Typical for these
‘‘upper mudstones’’ are widespread soft sediment
deformation structures (Eriksson et al., in press).
The zone of disturbed mudstones extends over much
of the eastern part of the basin, thinning to both
north and south of an approximately central max-
imum preserved depth (below the upper contact of
the formation) of deformation of c. 160 m (Button,
1973). The soft sediment deformation of the uncon-
solidated upper Timeball Hill facies is likely related
to the tectonic instability that terminated the evolu-
tion of the Timeball Hill seaway. This tectonic event
was interpreted to reflect conditions of pre-rift uplift
that generated the second-order subaerial unconform-
ity that separates the Rooihoogte–Timeball Hill
from the overlying Boshoek–Houtenbek second-
order depositional sequence (Catuneanu and Eriks-
son, 1999).
4. Sequence stratigraphy
Previous sequence stratigraphic analysis of the
Transvaal Supergroup identified the Rooihoogte–
Timeball Hill succession as a second-order depositio-
nal sequence bounded by major subaerial unconform-
ities (Catuneanu and Eriksson, 1999). This sequence
accumulated during a stage of glacio-eustatic fall,
with accommodation provided by syn-rift extensional
and post-rift thermal subsidence. At a second-order
level of stratigraphic cyclicity, the Rooihoogte–Time-
ball Hill succession conforms with the definition of a
depositional sequence, as it groups together a rela-
tively conformable package of strata that are genet-
ically related to one full tectonic cycle of rifting. As
argued in the previous sections of this paper, the
position of the lower second-order sequence boundary
of the Rooihoogte–Timeball Hill sequence should be
revised from the base of the chert breccias to the
contact of these breccias with the overlying chert
conglomerates (Fig. 10). This is because the chert
breccias are likely age equivalent with the Duitsch-
land Formation of the Chuniespoort Group, and the
major tectonic event leading to the basin inversion and
the change in topographic tilt succeeded the timing of
breccia formation and preceded the progradation of
chert conglomerates. For this reason, the chert brec-
cias and conglomerates are unrelated genetically and
belong to different depositional sequences.
The conformable character of the second-order
Rooihoogte–Timeball Hill succession is disrupted
by the basin-wide erosional surface at the base of
the Klapperkop quartzite Member. This basal Klap-
perkop unconformity has a markedly different char-
acter relative to the second-order sequence boundaries
of the Rooihoogte–Timeball Hill succession. The
basal Rooihoogte and basal Boshoek unconformities
(previously identified as second-order sequence boun-
daries: Catuneanu and Eriksson, 1999) are strongly
O. Catuneanu, P.G. Eriksson / Sedimentary Geology 147 (2002) 71–88 83
angular and erosional, being associated with major
tectonic reorganizations of the basin. The amounts of
downcutting are estimated to up to 800 and 250 m,
respectively (Eriksson et al., in press; Button, 1973).
The basal Klapperkop unconformity is not associated
with any significant tectonic reorganization within the
basin, and does not display angular relationships. For
these reasons, although it is still uncertain at this stage
how much downcutting took place due to the lack of
angular relationships, we propose that this unconform-
ity has a lower hierarchical order relative to the basal
Rooihoogte and basal Boshoek surfaces. We therefore
suggest that the basal Klapperkop unconformity is a
third-order sequence boundary, which provides the
basis for the sequence stratigraphic subdivision of the
Rooihoogte–Timeball Hill second-order sequence
into two third-order depositional sequences. These
two third-order sequences are marked as (1) and (2)
in Fig. 10.
4.1. Sequence (1)
Sequence (1) includes the entire Rooihoogte
Formation, plus the Lower Shale Member of the
Timeball Hill Formation (Fig. 10). It corresponds to
a period of time of continuous base-level rise, when
a succession of lowstand, transgressive, and high-
stand systems tracts accumulated in the Transvaal
Basin.
The lowstand systems tract (LST) consists of a
fining-upward succession of partly coeval lacustrine,
fan-delta, and alluvial fan sediments, which includes
Fig. 10. Sequence stratigraphic interpretation of the Rooihoogte–Timeball Hill succession. Not to scale. The Rooihoogte and Timeball Hill
Formations build together a second-order depositional sequence. This sequence is split by the basal Klapperkop basin-wide subaerial
unconformity into two third-order depositional sequences, marked as (1) and (2) in this diagram. Abbreviations: LST—lowstand systems tract;
TST—transgressive systems tract; HST—highstand systems tract; (1)—lacustrine facies (mudstone Member) of the Rooihoogte Formation;
(2)—Polo Ground sandstone Member of the Rooihoogte Formation; (3)—Lower Shale Member of the Timeball Hill Formation, excluding the
basal black shales; (4)—Klapperkop Member of the Timeball Hill Formation; (5)—Upper Shale Member of the Timeball Hill Formation.
O. Catuneanu, P.G. Eriksson / Sedimentary Geology 147 (2002) 71–8884
all the pre-Polo Ground Member lithofacies of the
Rooihoogte Formation. The progradation of alluvial
fans and fan-deltas into the lacustrine environment
took place from north to south, which indicates the
direction of syn-depositional topographic tilt (Fig. 8).
This initial stage of aggradation in the Pretoria Basin
led to the peneplanation of the pre-existing karst
topography that formed during extensive subaerial
exposure at the top of the Chuniespoort Group. The
lower contact of the LST coincides with the second-
order subaerial unconformity that bounds the Rooi-
hoogte–Timeball Hill succession at the base. The
upper contact of the LST is represented by a max-
imum regressive surface (Fig. 10), which is associated
with a tectonic re-organization of the basin and the
debut of the subsequent transgression.
The transgressive systems tract (TST) includes
two lithostratigraphic units that are inferred to be
partly age equivalent: the Polo Ground fluvial sand-
stones of the Rooihoogte Formation, and the trans-
gressive black shales of the Timeball Hill Formation.
There is a noticeable change in the direction of
topographic tilt between the LST and the TST, as
inferred from the chert conglomerate isopachs (Fig.
8), Polo Ground paleocurrents (Eriksson, 1988), and
the direction of initial Timeball Hill transgression
(Eriksson and Reczko, 1998). The transgression of
the Timeball Hill seaway took place from east to
west, which implies an easterly tilt in the basin. This
in agreement with the paleodrainage patterns of the
Polo Ground fluvial systems, with an overall flow
along the strike of the basin in an easterly direction.
The change in topographic tilt from the LST to the
TST (southerly to easterly, respectively) is most likely
related to differential subsidence in the basin. The
bounding surfaces of the TST are represented by a
maximum regressive surface, at the base, and a
maximum transgressive surface, at the top (Fig. 10).
The latter surface marks the contact with the over-
lying shallowing-upward succession of the lower
Timeball Hill shales.
The highstand systems tract (HST) is built by the
shallowing-upward succession of the Timeball Hill
Lower Shale Member (Fig. 10). This succession of
fine-grained pelagic and low-density gravity flow
facies is interpreted to represent aggradation in a
marine environment during the normal regression of
the shoreline. The HST is bounded at the base by the
maximum transgressive surface (contact with the
underlying transgressive black shales), and at the top
by the third-order subaerial unconformity (contact
with the overlying Klapperkop Member).
4.2. Sequence (2)
Sequence (2) includes the Klapperkop and Upper
Shale members of the Timeball Hill Formation. It is
bounded at the base and top by two basin-wide
subaerial unconformities of third- and second-order,
respectively (Fig. 10). This sequence preserves low-
stand and transgressive systems tracts.
The lowstand systems tract is represented by the
tidally reworked braid-delta deposits of the Klapper-
kop Member (Fig. 10). The shallowing upward tran-
sition from lower tidal flat to medial and upper tidal
flat settings suggests gradual normal regression in the
braid-delta environment. This normal regression
resulted in the aggradation of sandy lowstand deposits
with a sheet-like geometry being developed across the
entire Transvaal Basin. The lowstand aggradation
lasted until the debut of the subsequent transgression,
which is marked by an abrupt facies shift from low-
stand sands to transgressive mudstones and shales.
The contact between the lowstand and the overlying
transgressive facies is represented by a wave-cut
ravinement surface (Fig. 10).
The transgressive systems tract is equated with the
Upper Shale Member of the Timeball Hill Formation.
This is a deepening-upward marine succession of
pelagic and gravity flow deposits, topped by the upper
boundary of the Rooihoogte–Timeball Hill second-
order sequence (Fig. 10). The lack of a preserved
maximum transgressive surface, as well as of an
overlying highstand systems tract, indicates signifi-
cant subaerial erosion and truncation associated with
the upper boundary of the Rooihoogte–Timeball Hill
depositional sequence.
The uppermost deep marine facies of the Timeball
Hill Formation are sharply overlain by the high energy
alluvial fan deposits of the Boshoek Formation (Fig.
3), indicating an abrupt change in the sedimentation
regime across the sequence boundary. This second-
order subaerial unconformity may be related to a stage
of pre-rift uplift that preceded the next second-order
cycle of rifting in the Pretoria Basin (Catuneanu and
Eriksson, 1999).
O. Catuneanu, P.G. Eriksson / Sedimentary Geology 147 (2002) 71–88 85
5. Discussion
Precambrian successions are generally character-
ized by a scarce time control, due to the lack of a
usable fossil record and the error margins associated
with the radiometric dating of pre-Phanerozoic rocks.
This impairs sequence stratigraphic analyses at high-
frequency temporal scales. This case study, as well as
the previous lower resolution work in the Transvaal
Basin (Catuneanu and Eriksson, 1999), shows, how-
ever, that sequence stratigraphy can be applied with a
high degree of confidence at second- and third-order
levels of stratigraphic cyclicity. The lack of a high-
resolution time control may be partly compensated by:
(a) careful observations of the facies relationships of
the basin fill, and (b) the study of changes in the
direction of topographic tilt through time. Lateral and
vertical facies changes allow for genetic interpreta-
tions of relative sea-level changes, as well as for the
delineation of systems tracts. In addition, the shifts in
the direction of topographic tilt help to constrain the
age relationships between the various facies in the
absence of other absolute or relative time indicators.
For example, both the Polo Ground sandstones and
the basal black shales of the Timeball Hill Formation
accumulated during the same stage of easterly tilt,
which differentiates them from the underlying systems
tract dominated by a southerly topographic tilt.
The value of applying the methods of sequence
stratigraphy also consists in the better understanding
of the nature and significance of the contacts between
lithostratigraphic units. The most important lithostrati-
graphic contact in this case study is the boundary
between the Rooihoogte and Timeball Hill forma-
tions. As inferred from our analysis, this contact is
represented by a ravinement surface cut by waves in
the upper shoreface during the transgression of the
shoreline. This makes the Rooihoogte–Timeball Hill
contact a diachronous surface, with the rate of shore-
line transgression, which develops within a transgres-
sive systems tract.
It is difficult to quantify the absolute and relative
contributions of the different controls on accommo-
dation, due to subsequent denudation and the intru-
sion of the Bushveld Complex (Eriksson et al., in
press). We do know, however, that at the second-order
level of the Rooihoogte–Timeball Hill rifting episode,
extensional and thermal subsidence rates outpaced the
rates of glacio-eustatic fall to generate the necessary
accommodation for sediment accumulation. It is still
uncertain what caused the relative sea-level fall that
resulted in the subaerial unconformity at the base of
the Klapperkop Member. Temporary slowing down of
subsidence, outpaced by the eustatic fall, or a tempo-
rary increase in the rate of eustatic fall, outpacing the
subsidence rates, may both explain the generation of
the third-order sequence boundary identified at the
base of the Klapperkop Member.
6. Conclusions
(1) The Rooihoogte–Timeball Hill second-order
sequence represents the depositional product of a
rifting cycle in the Transvaal Basin, and accumulated
during a stage of glacio-eustatic fall. This provides a
case study for accommodation and sequence develop-
ment controlled by tectonic processes.
(2) Relative to previous research, the position of
the lower boundary of the Rooihoogte–Timeball Hill
sequence is revised from the base of the chert brec-
cias, to the contact between the breccias and the
overlying chert conglomerates. This is because a
major tilting event occurred between the deposition
of the two facies, which are unrelated genetically and
separated by a subaerial unconformity. The chert
breccias formed through in situ weathering on a
northerly dipping topographic slope, whereas the
chert conglomerates represent the product of alluvial
and delta–fan progradation on a southerly dipping
topographic profile.
(3) The Rooihoogte–Timeball Hill second-order
sequence consists of two third-order depositional
sequences separated by the subaerial unconformity
at the base of the Klapperkop quartzite Member. The
lower third-order sequence preserves lowstand, trans-
gressive, and highstand systems tracts. The upper
third-order sequence includes only a lowstand systems
tract and a partially preserved transgressive systems
tract. The missing highstand systems tract indicates
strong erosional processes associated with the upper
boundary of the Rooihoogte–Timeball Hill second-
order sequence.
(4) Secondary tectonic reorganizations within the
basin, including changes in the direction of topo-
graphic tilt and changes in the subsidence rates,
O. Catuneanu, P.G. Eriksson / Sedimentary Geology 147 (2002) 71–8886
occurred during the Rooihoogte–Timeball Hill sec-
ond-order cycle of rifting. Paleocurrents and stratal
stacking patterns record a change in the direction of
topographic tilt between the lowstand and the trans-
gressive systems tracts of the lower third-order
sequence, likely related to differential subsidence in
the basin. The third-order subaerial unconformity at
the base of the Klapperkop Member also suggests a
shift in the balance between the rates of subsidence
and eustatic fall, leading to a stage of relative sea-level
fall.
(5) The lithostratigraphic contact between the Rooi-
hoogte and Timeball Hill formations is interpreted as a
transgressive surface of erosion (ravinement surface)
in sequence stratigraphic terms. This contact develops
within a third-order transgressive systems tract,
between the inferred coeval Polo Ground fluvial sand-
stones and the transgressive marine black shales, and is
diachronous with the rate of shoreline transgression.
(6) Sequence stratigraphy can be successfully
applied to the analysis of Precambrian successions at
least at the second- and third-order levels of cyclicity.
The scarce time control may be partly compensated by
careful observations of lateral and vertical facies
relationships. Supplementary age constraints may be
added by the changes through time in the direction of
topographic tilt, which may be inferred from paleo-
currents and stratal stacking patterns.
Acknowledgements
O.C. acknowledges financial support from the
University of Alberta and NSERC Canada. P.G.E. is
grateful for generous research support from the
University of Pretoria and the National Research
Foundation, South Africa. We thank Andrew Willis
and John Hancox for their thoughtful reviews of the
manuscript. In addition, we are grateful to the special
issue subeditor, Pradip Bose, for his thorough
handling of the manuscript, guidance, and construc-
tive comments.
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