GEOSCIENCE CANADA Volume 41 2014 105

COLUMNThe Tooth of Time: Conrad Gebelein

Paul F. Hoffman

1216 Montrose Ave.Victoria, BC, Canada, V8T 2K4

I had been in Baltimore less than aweek, long enough to be asked to leavethe home of my foreign-student host(for suggesting that some good mightcome from the Cuban Revolution andthat not all the bad could be blamedon Fidel Castro). The eviction provedto be of little inconvenience: in thelow-occupancy zone a few blockssouth of the university, where urbanwhite “BALL-mer” met inner-cityblack “Bal-TEE-more”, they wouldrent to anyone. Eager to get runningagain after the field season, I hadsigned up for a locker at HomewoodField, the Johns Hopkins Universitylacrosse and football stadium. The var-sity cross-country squad was going outfor a “long” run, so I decided to jointhem to learn a route. With conceit, Inoted that they did nothing withoutexplicit instructions from a coach: atMcMaster University, Ron Wallingford(3rd in the Boston marathon the year Igraduated) had encouraged us to trainindependently, each according to theiracademic schedule. We had feasted oncross-border competition and wereCIAU champions the previous Fall.The run took us on a flat loop aroundthe industrial east side of Baltimore, anold port city at the head of Chesa-peake Bay where “the rocket’s redglare” and “bombs bursting in air”memorialize the Colonies’ war over

taxes. Accustomed to the NiagaraEscarpment in Hamilton, I chafed atthe pace and when, after less than anhour, the team turned back towardHomewood Field, I moved up to signalthat I was going around again. Toemphasize the point, I took off at aserious clip before turning hard rightto repeat the loop. After 10 minutes ofsolitude, I was startled by what sound-ed like footfalls not my own. I doubtedthat any of the varsity squad had fol-lowed me, let along caught up, butwithout turning I knew there wassomeone on my tail. Sensing his pres-ence was known, the mystery runnercame up alongside, looked over, andgrinned. His thick neck and slopingshoulders were those of an athlete; theclipped stride was all runner. Long-jawed, with a broad freckled foreheadand reddish hair, already in retreat, hissmall mouth bore a trumpet player’sdistinctive callouses. We finished theloop, first one leading and then theother, before introducing ourselves byname after returning to HomewoodField. Conrad D. (Connie) Gebelein,was a Baltimore native who had cap-tained the varsity cross-country andtrack teams before graduating the pre-vious Spring in biology and biochem-istry. He was staying on at Hopkins todo graduate work in oceanography, astrong department linked with theChesapeake Bay Institute (since dis-solved). Conrad had the idea, uncom-mon in 1964, that microbes weregrossly understudied relative to theirimportance in the balance of marinelife. He thought that microbial mats incoastal settings were a good place tostart because high cell densities wereaccessible without the need of a

research vessel. Gebelein had deep Hopkins

connections, but not in science. I nevermet his father, Conrad G. Gebelein, amusician-in-residence, but his grandfa-ther was a Hopkins institution. ConradGebelein Sr was born in 1894 in north-ern Bavaria, close to Nüremburg, oneof ten children of a produce broker.At nine, he began music lessons paidfor by working in an instrument repairshop. As a teenager, he emigrated witha sister to Baltimore, where he workedin a foundry, played in dance bands,and eventually graduated in music fromthe Peabody Conservatory. He was thefirst musician to perform live onWBAL-AM radio and in 1924 hefounded the BMO, Baltimore Man-dolin Orchestra. As composer,arranger, conductor, music director andfeatured soloist—on banjo and Hawai-ian guitar—“Gebby” Gebelein’s 19-piece ensemble, plus a featured banjoquartet, nearly doubled in size duringits five-year existence, cut short by theGreat Depression. The mandolin fami-ly of instruments covers the full tonalrange of a bowed-string orchestra, per-mitting voiceings that are impossiblefor a guitar ensemble. The popularityof Hawaiian-style guitar in the early20th century lives on in the pedal-steelguitar of country & western music, theslide guitar of the blues, and the legacyof Jimi Hendrix. Gebelein revived theBMO in 1938, only to be cut downagain when the U.S. entered WW-II.The present BMO, a thriving andviable orchestra, was reconstituted in1975 and directed by Gebelein until ayear before his death at 86 in 1981.During his long life, he taught music atmany prestigious Baltimore prep

Geoscience Canada, v. 41, http://dx.doi.org/10.12789/geocanj.2014.41.044 © 2014 GAC/AGC®

106

schools, had a financially successfulprivate teaching practice, and was theinstrumental and vocal music directorand adored band leader at Johns Hop-kins for 50 years. In 1967, I joined thethrong attending the official naming ofthe main grandstand at HomewoodField, the “Yankee Stadium ofLacrosse”, in his honour.

Events during our first year ingrad school caused our interests toconverge beyond running and music.After the 1965 field season with JohnMcGlynn, southeast of Great SlaveLake, GSC gave me some days of heli-copter time to conduct a feasibilitycheck of my proposed thesis projecton early Paleoproterozoic (Orosirian)stratigraphy and paleocurrents. Fluvialclastics were the primary targets forpaleocurrent work, but I had beendeeply impressed on Appalachian fieldtrips by the exquisite presentation ofsedimentary structures in natural out-crops (cow pastures) of early Paleozoiccarbonates. Sedimentology was in theprocess of rediscovering sedimentarystructures and outcrops after decadesof catering to the petroleum industry’sneed for analysis of drill-cores and cut-tings. Carbonates are intrinsically moreinformative than clastic sedimentsbecause they are products of biologi-cal, physical and chemical processescombined, resulting in a distinct car-bonate record for every geologicalperiod. For months, I had wondered ifthe nearly two-billion-year-old carbon-ates in the east arm fold belt of GreatSlave Lake would preserve primarystructures. Now I was about to findout. “Algal structures” were reportedon the gently-dipping north side of thefold belt (Lausen 1929; Stockwell 1932)and the east end of Blanchet Islandwas singled out for good exposure inthe marginal notes on Stockwell’s map(Stockwell 1936). As the pilot circledfor a landing I began to see them, reg-ularly-spaced columns, reef-like clus-ters, here in oblique cross-section,there on a glaciated bedding plane,occasionally in synoptic growth mor-phology. When the blades stopped, Iwas out and running through the thinbush shouting, “They’re everywhere!”The pilot later said he feared he mighthave to fly to Snowdrift and fetch theConstable.

Analogous structures (Fig. 1)

were first described and named, Crypto-zoon proliferum, in the Hoyt limestone(Furongian) near Saratoga Springs inupstate New York (Hall 1883).Although well-laminated, the structuresproved to lack cellular preservation andthe study of crudely similar laminatedencrustations in modern freshwaterlakes and rivers led to their interpreta-tion as tufa-like precipitates, inducedby vital processes (CO2 consumption)of “blue-green algae” (Walcott 1914;Roddy 1915; Bradley 1929), whichwere reclassified as cyanobacteria inthe 1980’s. Walcott, discoverer of theBurgess Shale fauna in 1909, inferredthat the Cambrian “explosion” was notan explosive radiation at all, but simplyan expression of the first marine trans-gression of the continents (Walcott1914). He pointed to the abundance ofstromatolites in the Belt-Purcell andother “Algonkian” (Proterozoic) car-bonates as evidence that pre-Cambrianepicontinental basins were non-marineand thereby incapable of recording agradual emergence of animal life in the(permanent) ocean. However inEurope, where the term “stromatolite”(Kalkowsky 1908) was introduced forbenthic (attached) laminated structuresof microbial origin (Riding 1999), Tri-assic examples occur in marine as wellas terrestrial formations.

The epic investigation ofAndros Island (Great Bahama Bank)by Maurice Black of Cambridge Uni-versity in 1930, part of Richard M.Field’s visionary geological oceanogra-phy mega-project, confirmed thatmodern stromatolites grow under theinfluence of biologically heterogeneousmats of “blue-green algae”, in condi-tions ranging from seasonally fresh tofully marine, and that growth in marinewaters is dominated by entrapment ofpre-existing grains, rather than by insitu carbonate precipitation (Black1933). In the 1960’s, interest in stroma-tolites was re-energized by the discov-ery of impressive Holocene examplesin Shark Bay, a hypersaline embaymentin Western Australia, which wereinferred to be diagnostic of the inter-tidal zone (Logan 1961; Logan et al.1964). Geologists were quick to adopta paleoenvironmental diagnostic. Yet,as Conrad pointed out at Friday beerhour, no controlled experiment hadbeen conducted to prove that livingcells were responsible for stromatolitegrowth, not the mere presence ofcopious, mucilagenous, extracellular,sheath material. Nor, I chimed in, hadthe growth rate or the temporal signifi-cance of the characteristic laminationbeen measured in any actively growingstromatolite.

Figure 1. Cryptozoön proliferum (Hall 1883), low-relief columnar stromatolites in theHoyt limestone (Furongian), exposed on a glaciated bedding-plane (43°05’32.5”N,73°50’54”W) near Saratoga Springs, New York. 500 million years ago, Laurentiawas encircled by vast areas of shallow-water carbonate sediments.

GEOSCIENCE CANADA Volume 41 2014 107

Fortuitously, carbonate sedi-mentologist Bob Ginsburg (formerlywith Shell Development Company, theresearch arm of Shell Oil, in CoralGables, Florida) was appointed to ajoint professorship in geology andoceanography at Hopkins in 1965 (Pet-tijohn 1988). With him came theknowledge (Ginsburg 1955) that mod-ern stromatolites, like those studied byMaurice Black in the Bahamas, couldalso be found in south Florida (Fig. 2).With him as well came the ability toconvince a biologist-biochemist likeConrad that the paramount signifi-cance of microbially mediated sedi-mentary processes was geological.Conrad’s thesis on “Dynamics ofRecent carbonate sedimentation andecology” (Gebelein 1977) focused onCape Sable (Fig. 3), the south-west tipof mainland Florida, deep in the Ever-glades. There, a formerly brackish tofreshwater lake and complex of pondsare protected from the sea by barrierbeaches. When mapped by the USCoast Survey a few years before theAmerican Civil War, the lake (nowLake Ingraham, unchanged in outline)was “ankle-deep in winter but over sixfeet deep in summer, and connected toall the ponds by trails worn by the alli-gators in their migrations” (Dorr1857). The only outlet to the sea wasnorthward through Little Sable Creek.In the early 1900’s, hundreds ofdrainage canals were cut all across thestate for land development, loweringthe freshwater table by up to 2 metersand diverting runoff away from CapeSable. In 1922-26, canals were cut atboth ends of Lake Ingraham (Fig. 3)by the Model Land Company, exposingthe lake and connected ponds to openmarine, tidal conditions (Tebeau 1968).“The opening of the canals brought about amarked change in sedimentation style andrate. This change is clearly recorded in the sed-iments and provides a baseline from whichcalculations of thicknesses and rates of depo-sition under the present marine regime can bemade” (Gebelein 1977).

Following the stromatoliteextravaganza in Great Slave Lake, Itook a bus from Calgary to Laramie(Wyoming) and hitch-hiked to theGrand Tetons in hopes of meeting upwith Baltimore apartment mate PeteGeiser and his climbing associates.Unable to find them, I bought an

International Scout (4x4) in GreenRiver and spent two glorious weekstouring Wyoming and Utah geologyuntil a September snowstorm in theWind River Range chased me back toBaltimore. Thanks to the vehicle, Ibecame Conrad’s first field assistant atCape Sable. Oceanographers carrymore gear than geologists and thetruck was crammed with sedimenttraps, current velocity meters, levelingrods, boxes and tubes of all sizes forsediment coring, and endless samplesbags and bottles of various liquids andpowders. There was barely room forour personal gear, Conrad’s trumpetcase, an alto sax I picked up at a pawnshop, two lacrosse sticks and a bag ofballs. Field work with Conrad was lotsof fun. At Cape Sable, we confirmedGinsburg’s observation that uncement-ed proto-stromatolites, composed ofparticulate carbonate mud trapped bymicrobial mats, occur on the cut banksof levees along the tidal channels ofLake Ingraham. Their immediate loca-tion was not propitious for immortality

in the stratigraphic record. However,fields of laminated proto-stromatolitesthe size of cow flaps occur around themargins of the many ponds adjacent toLake Ingraham, where microbial matscolonize desiccation polygons (Figs. 4,5).

As a geologist used to passiveobjects of study, Conrad’s ingenuity inmaking measurements (all manual) andconducting controlled experiments inthe field was an eye-opener. Currentvelocities, for instance, were measuredby timing the travel of a black man-grove pneumatophore, which floatsbelow the surface, unaffected by wind,but shallow enough to be seen. Therewere many experiments, but the onesmost interesting to me concerned stro-matolite accretion rates. Conrad stakedscores of square-meter size plots onmicrobial surfaces at different levels(flooding frequencies) and flowregimes. He sprinkled non-toxic ironoxide paint pigment on the surface ofeach plot, lightly so as not to impedemicrobial growth, but enough to iden-

Figure 2. Oblique satellite image of south Florida, showing Conrad Gebelein’s the-sis area at Cape Sable in relation to the Everglades and Florida Bay. Florida Straitsand Great Bahama Bank lie to the right out of view. The middleground is ~200km wide.

tify the horizon later in a core. At mostsites there were two plots, one for con-trol and one in which the mats werekilled without mechanical disruption byemersion in concentrated formalin.The plots were revisited and cored,weekly, monthly or seasonally as appro-priate. As a back-up, and out of impa-tience, we measured accretion rates inthe field by simply cutting the sedimentwith a knife.

Given short winter days andthe transit time in a skiff from ourcampsite on the marl prairie, it wasnearly two weeks before we had timeto revisit the first of the sedimentationrate experiment sites. “Yes!”, shoutedConrad as the skiff felt bottom. Thepigment could still be seen at the poi-soned plots—excepting those at high-velocity locations where the pigmentwas moved by currents—but the con-trols were covered by new sediment.We soon had field data from a suffi-cient vertical range to show that indi-vidual sediment laminae (~0.5-mmlight-dark couplets) within the mat-bound structures corresponded rough-ly with submergence events duringhigh tides. But when Conrad comparedour field data with the USGS tidetables for the East Cape Canal (Fig. 3),two new relations emerged. First, eachsemi-diurnal submergence was record-ed (depending on elevation) only ifsome part of the submergenceoccurred in daylight. Strictly nocturnalsubmergences went unrecorded. Sec-ond, the thickness of the sediment-richlaminae at any given site correlatedroughly with the duration of submer-gence during daylight hours. I wasdumbfounded. We had ourselves acoupled record of diurnal and tidalforcings. “Biology can do anything,”said Conrad, one of his favouriteexpressions. We had a couple of extrarounds that night at the FlamingoLounge. Walking back to camp after-wards under moonlight, we dared todream of a Precambrian record ofplanetary spin-reduction and lunarretreat, modulated by time-dependenttidal friction, constrained by data fromstromatolite laminology (Pannella 1972;see also Jones 1981).

The next morning over break-fast and many glasses of orange juice,nocturnal processing revealed a prob-lem with our sedimentation rates. If

108

Figure 3. Oblique satellite image of Cape Sable at the southwest tip of mainlandFlorida. Lake Ingraham, a former freshwater lake, as well as adjacent ponds,became fully marine tidal environments after the East Cape and Middle Capecanals (ECC and MCC) were cut in 1922–26. Before that time, Lake Ingrahamdrained northward through Little Sable Creek. The Flamingo Lounge lies to theright out of view. The middleground is ~30 km wide.

Figure 4. Conrad Gebelein at Cape Sable in early 1967, examining desiccationpolygons in marine aragonitic pelleted mud, deposited in the rarely-exposed centralpart of a large pond near Lake Ingraham. The following year, the cracks had healedwithout a trace (Gebelein 1977).

true, they implied that the total thick-ness of microbially laminated mudaccumulated since 1922-26 (~0.3 m)represents only a few months of accre-tion. Stumped, we continued collectingdata. During his second field season atCape Sable, Conrad stayed on past theequinoctial start of the rainy season.Caught on an exposed mud flat duringa heavy rainstorm, he was unsettled tosee the proto-stromatolites beingactively eroded. The mucilagenoussheath material, so efficient at trappingand binding particulate grains borne bytidal currents, was vulnerable tomechanical attack by wind-driven rain-drops. Evidently, the microbially-lami-nated mud unit, including the proto-stromatolites, accretes every winterduring the dry season and degrades insummers when it pours every after-noon. Uninterrupted lengthy timeseries of Precambrian intertidal stro-matolites looked like a long-shot.

The reason Conrad stayed lateat the Cape was that in February(1967), Ginsburg had convened a con-ference at Hopkins on algal stromato-lites. Among the invited speakers wereSteve Golubiç (Boston) on freshwatermicrobial carbonates, Claude Monty

(Liège) on the Bahamian microbialstructures, David Kinsman and ChrisKendall (London) on the coastalsabkhas and microbial mats on theTrucial Coast of the Persian Gulf, andBrian Logan (Perth) on the modernstromatolites in Shark Bay, WesternAustralia. As a result of the confer-ence, I would visit each of these areasthe following year. At the conference, Ihad presented results from my first fullfield season in Great Slave Lake. Withassistants Tom Tourek (Hopkins) andWayne Shepheard (Calgary), we hadmeasured the orientations of elongatestromatolites (Fig. 6) and current-relat-ed structures in hundreds of beds ofthe Pethei Group, which is exposed for~160 km along strike and undergoes amajor shelf-to-basin facies changeacross the narrow fold belt (Hoffman1974, 1989). We found that elongatestromatolites are oriented parallel topaleocurrents and perpendicular to themajor facies zones. Furthermore, theyare consistently oversteepened in theoff-shore direction, due to excessaccretion toward the source of carbon-ate sediment. Stromatolite shape andorientation offered a simple means ofdetermining shoreline orientations and

facing-directions in ancient carbonatesequences, not a trivial aid in Precam-brian shields where structural basins ofpreservation cannot be assumed tomimic depositional basins. Logan but-ton-holed me after my talk and said Ineeded to come to Shark Bay (Fig. 7).Buoyed by the conference, I immedi-ately finalized and submitted my firstever paper (Hoffman 1967)—Conradhaving already published, on cyanobac-terial pigmentation, as an undergradu-ate. The galley proofs arrived on theplane with Conrad and Ginsburg whenthey visited Great Slave Lake that sum-mer.

Their visit was both a reunionwith Conrad and a farewell. Conradand I had another trait in common Ihaven’t mentioned—a distaste formathematics. We shared a belief thatwith so many exciting things to dowhich we were good at, a lengthystruggle to gain base-level proficiencyin a skill we had little need for seemeda poor investment. Unfortunately forConrad, the oceanography departmentincluded physical oceanographers,whereas the geology department (atthat time) had no geophysicist (nor hadMcMaster). I had passed my orals, onthe second try, because my co-advisorand geology chairman Francis Petti-john, as well as his predecessor ErnstCloos, had risked a schism in thedepartment on my behalf. Conrad wasnot so lucky. I never understood whyGinsburg didn’t allow Conrad to trans-fer over into geology. Perhaps it wasbecause delicate negotiations werealready underway to unite geology andgeophysical fluid mechanics in a newdepartment of Earth and PlanetarySciences (Pettijohn 1988). Perhaps itwas because the Ginsburgs alreadysensed how much they missed southFlorida, that their stay in Baltimorewould not be for long. Perhaps hethought that the move to Brown Uni-versity (Providence, Rhode Island)would be good for Conrad. My pre-ferred explanation is that a transfer togeology was offered and Conrad choseto go to Brown on its merits. In 1967,the arrival of oceanographer JohnImbrie made Brown better positionedfor the future (e.g. Hays et al. 1976)than was Hopkins.

With no Precambrian fieldwork scheduled, 1968 was my opportu-

GEOSCIENCE CANADA Volume 41 2014 109

Figure 5. “Cow-flap” stromatolites formed where microbial mats colonized desic-cation polygons at the margin of a pond adjacent to Lake Ingraham, Cape Sable.Hat for scale. The calyx-like structures are internally laminated and consist ofmicrobially-bound marine pellet-mud. The structures are flooded only at high tides,unlike the mat-free polygons in the center of the pond (Fig. 4), which are rarelyexposed.

nity to compare modern shallow-watercarbonates beyond south Florida andmeasure stromatolite accretion rates inother settings. Conrad had shown dur-ing the previous summer that lamina-couplets in sublittoral stromatolites ofthe Bermuda Islands are strictly diur-nal, not tidal, sediment-rich layersaccreting in daylight and organic-richones at night (Gebelein 1969). My firststop was the northwest coast ofAndros Island (Fig. 8), where Ginsburgand colleagues Lawrie Hardy andOwen Bricker were beginning a four-year study of sedimentation in thetidal-channel belt and adjacent suprati-dal “algal” marsh (Shinn et al. 1969;Hardie 1977; Monty and Hardie 1977).Like South Florida, microbial matswere limited to the upper intertidal andsupratidal zones. Mapping showed thisto result from grazing below mean tidelevel by snails (Fig. 9), rendering mostmodern tidal flats poor analogs forperitidal carbonates deposited beforeanimals evolved (Garrett 1970). Thesupratidal marshes, flooded by rainwa-ter in summer, are carpeted by vari-ably-calcified “pincushions” of tuftedfilamentous cyanobacteria (Fig. 10). Ierroneously compared this facies with

Precambrian “microdigitate” stromato-lites (Hoffman 1975), a forced mod-ern-ancient comparison. JohnGrotzinger later demonstrated petro-graphically that most microdigitatestromatolites are actually sea-floorcements, composed of pseudomor-phosed aragonite crystal-fans, a majorPrecambrian carbonate facies not rep-resented in the modern (Grotzingerand Read 1983; Grotzinger and Knoll1995). Understanding the Holocenedynamics of the Andros tidal-channelbelt would require intensive coring anddating (e.g. Maloof and Grotzinger2012).

Flying halfway round theworld was easier in 1968 than today:landings and walks were obligatoryevery five or six hours for refueling. Ihad plenty of time to read up on SharkBay between Andros Town and Perth.From Logan’s work, I knew that graz-ing by snails would not be a problemin Hamelin Pool (Fig. 11), whererestricted circulation due to seagrassbanks and strong net evaporation drivesalinities up to nearly twice normal sea-water, above the tolerance of cerithidgastropods and all but one molluscanspecies, the button-size pelecypod

Fragum erugatum, which lives in suchextraordinary abundance that sawedblocks of Fragum coquina (both eolianand shoreface) were used to build thepub in Denham. In the absence ofgrazing by snails, microbial mats colo-nize the lower intertidal zone, subjectto the action of refracted waves. Incontrast, grazing by snails prevents matformation in the lower intertidal zoneof the metahaline parts of Shark Bay,outside Hamelin Pool, where no high-relief stromatolites occur. In summer,Shark Bay experiences sustained gale-force southerly winds (Fig. 11), whichsuppress tides and create wave-domi-nated coastal sand flats, unlike the tide-dominated mud flats of Lake Ingra-ham and western Andros Island. High-relief circular (Fig. 12) and seaward-seeking elongate stromatolites (Fig. 13)are found on exposed headlands andunprotected bights, respectively, on theeast side of Hamelin Pool (Fig. 11).Early cementation by cryptocrystallinearagonite provides lithified crusts onwhich the microbial mats becomeestablished; early cementation makeseven the high-relief microbial struc-tures wave resistant.

The first “algal reef ” was dis-covered near Flagpole Landing inHamelin Pool (Fig. 11) in January 1955by Richard L. (Dick) Chase, a Universi-

110

Figure 7. Holocene microbialites in the wave-dominatedintertidal zone (pustular mat zone) south of Carbla Point,Hamelin Pool, Shark Bay, Western Australia (see Fig. 11).Elongation direction is parallel to currents generated bybreaking waves and perpendicular to the shoreline because ofwave refraction. Shovel handle (left center) is graduated in10ths of feet (~3 cm). Photographed from step-ladder.

Figure 6. Synoptic morphology of ~1.87-Ga columnar stro-matolites in the Pethei Group, Utsingi Point, Christie Bay,Great Slave Lake. A glaciated bedding-parallel surface hasspalled parallel to the internal stromatolitic lamination. Theelongation direction is parallel to paleocurrents determinedfrom current ripples and perpendicular to the major plat-form-to-basin facies zones (Hoffman 1974, 1989). The sur-face is in the upper part of an unbroken 15-m-thick stroma-tolite biostrome at the top of the Taltheilei Formation. Viewlooks southwest; hammer (arrow) for scale.

ty of Western Australia (UWA) under-graduate working for Wapet (WestAustralian Petroleum) as an assistant toPhillip E. (Phil) Playford. Chase hadseen ancient stromatolites on a classfield trip to the Moora Group (Meso-proterozoic) led by Rhodes Fairbridge.The next year, Chase and Brian Logandid a joint Honours thesis (Logan andChase 1961) on the Moora Group,which dips off the Yilgarn cratonalong the Darling Escarpment, northof Perth. Dick Chase went off toPrinceton University for his PhD andhas been professor (now emeritus) ofmarine geology at UBC Vancouversince the advent of plate tectonics.Logan went on to do his PhD on thegeology of Shark Bay, after which heconducted a major study of moderncarbonate sediments and reefs on theYucatán Shelf of eastern Mexico

(Logan et al. 1969), while at TexasA&M. He had returned to UWA tomount a research program in carbon-ate sedimentology, ecology and diagen-esis, in and around Shark Bay (Loganet al. 1970, 1974; Logan 1987). Amonghis PhD students at the time of myvisit were Graham Davies and FredRead, who would achieve notable suc-cess in North America as industry andacademic carbonate sedimentologists,respectively. My job was to describe thebasic microbial mat zonation and stro-matolite morphotypes on the east sideof Hamelin Pool (Hoffman 1976), col-lect samples for taxonomic study byConrad at Brown (Logan et al. 1974),and carry out stromatolite accretionrate studies. “Blue-green algal”(cyanobacterial) taxonomy was in acontinual state of flux (Golubiç1976b). The study was limited to a sin-

gle season and time of year (winter),but it would set a basemark for laterwork (e.g. Playford 1980; Golubiç1985; Burne and Moore 1987; Reid etal. 2003; Burne and Johnson 2012; Jah-nert and Collins 2013). Conrad hadtrained me well.

Trading summer in theBahamas for winter in Perth, WesternAustralia, was shocking and after twoweeks at the University of WesternAustralia, I was glad to turn my facetoward the Sun and head northwardfor two months alone in Shark Bay.Logan’s approach to modern carbonatesedimentation impressed me greatly.He embraced the dynamic stratigraphicimplications of Quaternary andHolocene base-level changes. He wasparticularly obsessed by a mysterious1-2 m late Holocene (<5 kyr) base-level fall, evidence for which occurswidely on the coast of Western Aus-tralia and elsewhere around the IndianOcean (Fairbridge 1961). The muchphotographed stromatolites aroundCarbla Point are largely inactivethrough Recent emergence and desic-cation (Fig. 12). The cause of the rela-tive sea-level fall was then unknown: ifeustatic, it implied net growth of polarice sheets nearly equivalent to a secondWest Antarctic Ice Sheet. Two proba-ble explanations were subsequentlyconceived and quantitatively investigat-ed in numerical simulations. The first isthat the slow collapse of flexuralbulges peripheral to the Laurentide andScandinavian ice sheets syphonedwater from the tropical ocean to fill thesubsiding boreal areas of the seafloor(Mitrovica and Peltier 1991). The sec-ond is that the addition of a globalaverage ~125 m of meltwater duringthe last deglaciation caused isostaticsubsidence of the seafloor and conse-quent upward levering of all continen-tal margins (Mitrovica and Milne 2002).

The obvious fact of coastalemergence in Hamelin Pool turned myattention seaward, where on calm daysat low tide I could see rows of ghostlyfree-standing structures on the sublit-toral platform off Carbla Point, atdepths of a meter or more at lowspring tide. I had a diving mask,snorkle and underwater camera, but nowet suit, having been advised not toswim alone because of sea snakes.Dead ones were washed up on the

GEOSCIENCE CANADA Volume 41 2014 111

Figure 8. Oblique satellite image of the Loggerhead Point (Triple Goose Creek)area (Shinn et al. 1969; Hardie 1977; Maloof and Grotzinger 2012), northwestAndros Island, Bahamas. On the left in blue is the shallow sublittoral platform ofthe Great Bahama Bank. In the center is the belt of tidal channels (dark green)with levees (grey), colonized by microbial mats, and ponds (white), in which matsare not developed due to grazing by cerithid gastropods (Fig. 9). Irregular greysplotches in the center foreground are cloud shadows. On the right is the supratidaland seasonally freshwater “algal” marsh (Fig. 10). The prominent creek in the cen-ter of the image was informally named Triple Goose Creek by R.N. Ginsburg, forthree Grumman G-21(“Goose”) seaplanes that moored there on field trips. Themiddleground is ~12 km wide.

beaches, but I never saw a live one inthe water, expecting that like freshwa-ter snakes they would swim at the sur-face. I later learned that sea snakes hugthe bottom in coastal waters and oftenswim in schools. Their bites are usuallypainless and no symptoms appear forhours, after which progressive paraly-sis, renal failure and cardiac arrest mayoccur. The West Australian Currentmakes Shark Bay waters painfully coldin July, but I was too dazzled by myfirst dive to care. Freestanding colum-nar stromatolites and stromatolite clus-ters, some with branches, rose up to ameter above the wave-rippled sand(Fig. 14). Given the water depth, theirtips were never exposed at low springtide. They had a distinctive colloformsurface morphology and a glisteningepiflora of Acetabularia, a macroscopicgreen alga, accounts for their ghostlyappearance. In the excitement of tak-ing photographs and samples underwa-ter, I lost track of time. Back in mytent on the beach, I was barely able tostart the Optimus to heat some soup,before retreating into my sleeping bagand shivering uncontrollably for hours.

Driving back to Perth, Irecalled that some intertidal stromato-lites in Hamelin Pool had colloform-like interior structure. I began to won-der if they had originated in the shal-low sublittoral and became intertidalduring the mysterious late Holoceneregression. I anticipated that Loganwould be excited by the new develop-

ment, but instead it made him gloomy.He insisted that the sublittoral stroma-tolites were relict intertidal structuresformed during early Holocene trans-gression. He seemed wedded to theidea that stromatolites were strictlyintertidal in origin. I thought an earlyHolocene age for the sublittoral stro-matolites was far-fetched and, althoughConrad’s marking technique was not sosuccessful underwater, I had markedsome of them for growth rate study. Iowed my entire Shark Bay experienceto Logan, so I let the matter drop.

The existence of sublittoralstromatolites in Hamelin Pool wouldnot remain secret for long. Withinweeks of my departure, Phil Playfordand Tony Cockbain of the GeologicalSurvey of Western Australia foundsmaller but otherwise homologousstromatolites on the sublittoral plat-form off Flagpole Landing (Playfordand Cockbain 1976; Playford et al.2013). Later, the full extent of sublit-toral stromatolites in Hamelin Pool,ten times the area of intertidal forms,would be documented as would theiractive sublittoral growth (Jahnert andCollins 2011, 2012). Playford andLogan had a difficult relationship. DickChase had been working for Phil whenthe Hamelin Pool stromatolites were

first discovered. Playford had suggest-ed Shark Bay as a thesis area for Logan(encouraged presumably also by DickChase) and he retained an active inter-est in the area, although his primaryfocus was on the Devonian reef com-plexes of the Canning Basin (Playfordand Lowry 1966, Playford et al. 2009),work which established his internation-al reputation. Playford had the abilityto describe complex relationships insimple terms. Too simple for Brian,who sternly insisted that readers beimpressed by real complexity. When Isubmitted a draft manuscript to Logan,it would come back three times longer.Brian clearly resented what he consid-ered Phil’s interference, if not propri-etary interest, in Shark Bay.

A short while after my visit,Logan came under the influence ofsedimentologist Victor Semeniuk,newly arrived from Adelaide. Brian,whose experience with ancient carbon-ates was limited, came to believe thatmany so-called “primary” structuresare actually products of dissolution(stylolitization) and other burial-diage-netic and metamorphic alterations. Heeven went so far as to disavow theexcellent work on ancient carbonatesof his own students (e.g. Read 1973).He published a major critique of Play-

112

Figure 10. “Pincushions” of the tufted filamentouscyanobacterium Scytonema, characteristic of the supratidalmarshes on the west side of Andros Island (Black 1933;Hardie 1977; Monty and Hardie 1977). The cushions aremostly 5–10 cm in diameter (note mangrove roots) and areintermittently flooded in summer by rainwater. Sedimentbeneath the surface is well-laminated and partially lithified,with upstanding filament moulds. This semi-arid supratidalfacies contasts with the evaporitic supratidal facies of SharkBay (Fig. 11) and the Trucial Coast (Fig. 14).

Figure 9. Cerithid gastropod shell lag in the intertidal zoneon Andros Island, Bahamas. Grazing by these snails effective-ly limits microbial mat development on modern marine tidalflats to the upper intertidal and supratidal zones (Garett1970), excepting hypersaline areas like Hamelin Pool (Fig. 11)uninhabitable by gastropods.

ford’s Devonian reef complex model(Playford and Lowrie 1966), claimingthat the entire forereef – reef – back-reef zonation and geometry in theCanning Basin are products of styloliti-zation and related postdepositionalprocesses (Logan and Semeniuk 1976).Brian’s career never fully recoveredfrom this débacle, nor did he everrelinquish the view that primary struc-tures are rarely preserved in ancientcarbonates.

Flying from Perth to the Tru-cial Coast (now United Arab Emirates)in early August was a reverse climateshock. August is the hottest month ofthe year on the Trucial Coast and agentle onshore wind maintains highhumidity to go along with 42°C(109°F) daily high temperatures in AbuDhabi, hotter inland. David Kinsman’screw bunked in a trailer in the Industri-al Area—residential areas for citizens(Bedouin), commercial workers (SouthAsian), manual labourers (East African)and minority westerners were strictlysegregated. Even then, Aramco (Arabi-an-American Oil Company) and geo-

logical circumstance gave Abu Dhabicitizens the world’s highest averageearnings. When BOAC flights arrivedfrom London, they would dip theirwing toward the Royal Palace beforelanding. Kinsman, who was centrallyinterested in sabka evaporites, hadbeen working on the Trucial Coastsince the early 1960’s, a senior protégéof Doug Shearman (Imperial CollegeLondon), who gave a spellbindingshort-course on evaporite petrographyin Calgary, hosted by the Alberta Soci-ety of Petroleum Geologists, in 1970.The daily routine in Abu Dhabi was toget up in the middle of the night, driveout of the city to a marked spot on thesabkha, and walk seaward across thetidal flats before first light ~5:20 am.Conditions were quite pleasant until~7:30 am, after which our voices gotprogressively lower and slower until~9:30 am, when we start walking slow-ly back across the flats. Entering thetrailer at midday, where the tempera-ture was maintained at 35°C (95°F),was like walking into a fridge.

Unlike the confines of Cape

Sable and Hamelin Pool, the vast scaleof the coastal sabkha and adajcent“algal” flats (Kinsman 1964; Kendalland Skipwith 1968; Purser and Evans1973; Kinsman and Park 1976) is morecomparable to the Pethei Group ofGreat Slave Lake. The Cambro-Ordovician carbonate bank encirclingLaurentia has no modern counterpart.Microbial mats are mainly developedabove mean sea-level, limited bycerithid gastropod grazing. No high-relief (lower intertidal) stromatolitesoccur. The mats are best developed inupper intertidal ponds, despite beingtoo hot to wade across by late morn-ing. The supratidal zone is a desolatesalt crust (sabkha), overlying wind-blown sediment in which nodularanhydrite precipitates by evaporativepumping (Fig. 15). Given the gypsifer-ous supratidal of Shark Bay, the occur-rence of anhydrite on the TrucialCoast was consistent with LawrieHardie’s experimentally-determinedgypsum-anhydrite equilibrium tempera-tures (Hardie 1967), a potential paleo-climate proxy. Since the early Holocenetransgression, the Abu Dhabi tidal flatshave prograded seaward at a rate ofnearly 1.0 m per year, hastened by lateHolocene base-level fall of 1.2±0.1 m(Kinsman and Park 1976). A few yearsago, I went to Google Earth forimagery of the tidal flats I saw withKinsman outside Abu Dhabi. They aretotally obliterated by condominiumdevelopments, roadways and jetties.

GEOSCIENCE CANADA Volume 41 2014 113

Hamelin

Pool

Wooramel Delta

I ndian

Ocean

Freycinet

Basin

Hopeless Reach

Carbla Pt

Flagpole Landing

Denham

Naturaliste Passage

Denham

Sound

Toolonga Plateau (Cretaceous)

N

26oSseagrass sill

Tamala Eolianite

(Pleistocene)

Figure 11. Oblique satellite image of Shark Bay, WesternAustralia. Net evaporation, restricted circulation due to sea-grass sills, and persistent southerly gales in summer (blackarrows) cause hypersalinity (<65‰) in Hamelin Pool andmetahaline conditions (<50‰) in Freycinet Basin and Hope-less Reach. Note blowouts in the coastal Pleistocene eolianlimestone (Edel Land). Hypersalinity excludes grazing bysnails in Hamelin Pool, allowing microbial mats and stromato-lites to develop on wave-dominated lower intertidal sand flatsand shallow sublittoral platforms.

Figure 12. Progressive emergence of unoriented columnarstromatolites at Carbla Point (Fig. 11), due to late Holoceneregression (see text). The structures have <0.8 m of reliefand are mostly 1–2 m in diameter. They originated in the sub-littoral and lower intertidal zone (background), but those withblue, black and orange tops (foreground) now project into thesupratidal and are inactive.

A week late for the start ofclasses, I returned to North Americaand moved my belongings to Lancast-er, Pennsylvania, armed to teach com-parative modern-ancient sedimentologyat Franklin and Marshall College, while

writing up my thesis chapters directlyfor publication (then innovative, nowroutine). I delivered the biological sam-ples to Conrad and reported that stro-matolite growth rates at Shark Baywere slow—the red markings were still

clearly visible when I left. Subsequentwork supported Logan’s interpretationthat the lamination is basically season-al, with grainy layers (ooids andforams) accreted during winter hightides and micritic layers produced dur-ing wind-driven summer lowstands,through textural obliteration of preex-isting grains by microbial enterolithicboring and precipitation of void-fillingmicrocrystalline aragonite (Chivas et al.1990; Reid et al. 2003; Burne and John-son 2012; Jahnert and Collins 2012).Stromatolite lamination—tidal at CapeSable, diurnal in Bermuda and annualat Shark Bay—was not a reliable clock.Nevertheless, measured stromatoliteaccretion rates were geologically swift,raising interesting questions regardingthe pair of 15-m-thick columnar stro-matolite beds in the Pethei Group ofGreat Slave Lake (Hoffman 1974; Samiand James 1994).

Conrad described the biologi-cal make-up of my seven basic mattypes (Hoffman 1976) from the smallsamples I brought back in my checkluggage—“No, officer, they are not soilsamples.” Each mat type represents acomplex consortium of microbial taxa,but each is dominated by a small num-ber of characteristic cyanobacteria.Allowing for the fluidity of taxonomicnomenclature, Conrad’s identificationsand characterizations of the basic mat

114

Figure 15. Coastal sabkha (supratidal salt flat) bordering Khor al Bazam, AbuDhabi (UAE). Inset shows meter-deep trench wall exposing a regressive Holocenesequence: (1) organic-rich microbial mud deposited in upper intertidal ponds, (2)nodular “chicken-wire” anhydrite precipitated in the vadose zone from marinegroundwater pumped landward by net evaporation, (3) windblown supratidal siltand fine-grained sand. Tidal flats in the area have prograded seaward <10 km inthe Holocene, hastened by late Holocene base-level fall (see text). Spade for scale.

Figure 14. Branching stromatolites ~2.5 m below mean sea-level on the sublittoral platform at Carbla Point (Fig. 11). Thestructure in the foreground has ~0.4 m of relief and is neversubaerially exposed. The epiflora is dominated by glisteningcapped-stalks and hairs of the macroscopic green alga, Acetab-ularia.

Figure 13. Seaward-tilted columnar stromatolites and rippledooid-foram sand in the lower intertidal zone of the bightsouth of Carbla Point (Fig. 11). Stromatolite inclination is dueto a combination of excess accretion and basal ablation in theoff-shore direction. Elongate stromatolites (parallel to shovelhandle) are oriented parallel to wave scour (normal to thestrandline) but occur in rows (upper left) that parallel theshoreline. The same geometry is observed in the PetheiGroup (1.87 Ga), Great Slave Lake.

types stood up well under subsequentscrutiny (Golubiç 1976a, 1982, 1985).This was remarkable because the maincrate of samples rested at the Port ofPhiladelphia for two years, while bro-ker’s invoices chased me around thecontinent. It would have made for afragrant episode of “Storage Wars.”

I last saw Conrad in StonyBrook on Long Island, where he hadbeen promoted to associate professorafter obtaining his PhD from Brown in1971. I met his wife, Nancy Maynard,their daughter Jennifer, then an infant,and their semi-domesticated pet crow,Corvus. Conrad later served as assis-tant director at the Bermuda BiologicalStation before being appointed associ-ate professor at UCSB (University ofCalifornia, Santa Barbara), in 1974 atthe young age of 28 (Fig. 16). Heobtained funding and began alongterm ecology-sedimentologyresearch program on the unstudied andremote southwest coast of AndrosIsland, where the tidal-channel belt isfar wider than in the classic TripleGoose Creek area (Fig. 8) to the north(Gebelein 1974). He had long had hiseye on this area. I was teaching at theUniversity of Texas near Dallas in early1978 when I heard that Conrad hadunexpectedly died under mysteriouscircumstances in the Bahamas. Con-flicting stories circulated about thecause of his death, some suggestinghomicide. I won’t add to them here.Last year at the GSA Annual Meetingin Denver, I ran into Dave Pierce, whowas the imaging technician in PrestonCloud’s Geobiology Lab at UCSBwhen I was a lecturer there, three yearsbefore Conrad arrived. After the meet-ing, it occurred to me to ask Dave ifhe had any knowledge about what hadhappened to Conrad. Indeed he did.He knew Conrad well and they wereworking to have Dave admitted asConrad’s graduate student. While con-ducting research on Andros, Conradtook time off to work on a water proj-ect in Haiti, where he contractedmeningitis (undiagnosed). Feeling ill, hereturned to the Bahamas but died in ahotel room before reaching hisresearch station. No coroner, mindfulof the tourist industry, would wish to

see “meningitis” on a Bahamian deathcertificate, so what happened after theautopsy is anyone’s guess. For Conrad’sparents, family, colleagues and friends,he left a hole that time would nevercompletely infill.

Today, geobiologist TanjaBosak (Massachusetts Institute ofTechnology) has taken the experimen-tal approach to stromatolite genesis toa new level—she grows them in thelab. The results are provocative andtimely. On the one hand, she hasgrown ordinary stromatolites withmetabolically-ancient, anoxygenic bacteri-al phototrophs, proving that stromato-lites per se are not diagnostic ofcyanobacteria (Bosak et al. 2007). Onthe other hand, she has replicated thedisturbed apical zone characteristic ofcertain conical stromatolites (Conophy-ton) by the inflation and bursting ofbubbles of dioxygen, produced strictlyby cyanobacteria (Bosak et al. 2009,2010). The significance of this discov-ery for the problematic origin of oxy-genic photosynthesis now depends onthe range of Conophyton in the Archeanstratigraphic record.

REFERENCESBlack, M., 1933, The algal sediments of

Andros Island, Bahamas: Philosophi-cal Transactions of the Royal Society,London, ser. B, v. 222, p. 165–192.

Bosak, T., Greene, S.E., and Newman,D.K., 2007, A likely role for anoxy-genic photosynthetic microbes in theformation of ancient stromatolites:Geobiology, v. 5, p. 119–126,http://dx.doi.org/10.1111/j.1472-4669.2007.00104.x.

Bosak, T., Liang Biqing, Sim Min-Sub, andPetroff, A.P., 2009, Morphologicalrecord of oxygenic photosynthesis inconical stromatolites: Proceedings ofthe National Academy of Sciences(USA), v. 106, p. 10939–10943,http://dx.doi.org/10.1073/pnas.0900885106.

Bosak, T., Bush, J.W.M., Flynn, M.R.,Liang, B., Ono, S., Petroff, A.P., andSim, M.S., 2010, Formation and stabil-ity of oxygen-rich bubbles that shapephotosynthetic mats: Geobiology, v. 8,p. 45–55, http://dx.doi.org/10.1111/j.1472-4669.2009.00227.x.

Bradley, W.H., 1929, Algae reefs and oolitesof the Green River formation: UnitedStates Geological Survey, ProfessionalPapers, 154, p. 165–192.

Burne, R.V., and Johnson, K., 2012, Sea-level variation and the zonation of

GEOSCIENCE CANADA Volume 41 2014 115

Figure 16. Conrad Gebelein (1945–1978) in Santa Barbara, California, around 1975.

microbialites in Hamelin Pool, SharkBay, Western Australia: Marine andFreshwater Research, v. 63, p.994–1004,http://dx.doi.org/10.1071/MF12184.

Burne, R.V., and Moore, L.S., 1987, Micro-bialites: Organosedimentary depositsof benthic microbial communities:Palaios, v. 2, p. 241–254,http://dx.doi.org/10.2307/3514674.

Chivas, A.R., Torgersen, T., and Polach,H.A., 1990, Growth rates andHolocene development of stromato-lites from Shark Bay, Western Aus-tralia: Australian Journal of Earth Sci-ences, v. 37, p. 113–121,http://dx.doi.org/10.1080/08120099008727913.

Dorr, F.W., 1857, Report to the Superinten-dent of the United States Coast Sur-vey: United States Coast Survey, Exec-utive Documents, 33, p. 383–387.

Fairbridge, R.W., 1961, Eustatic changes insea level, in Physics and Chemistry ofthe Earth, v. 4: Pergamon Press, NewYork, p. 99–185.

Garrett, P., 1970, Phanerozoic stromato-lites: Noncompetitive ecologic restric-tion by grazing and burrowing ani-mals: Science, v. 169, p. 171–173,http://dx.doi.org/10.1126/sci-ence.169.3941.171.

Gebelein, C.D., 1969, Distribution, mor-phology and accretion rate of recentsubtidal algal stromatolites, Bermuda:Journal of Sedimentary Petrology, v.39, p. 46–69.

Gebelein, C.D., 1974, Guidebook for mod-ern Bahamian platform environments:Geological Society of America, Annu-al Meeting, 1974, Field Trip Guide-books, 97 p.

Gebelein, C.D., 1977, Dynamics of RecentCarbonate Sedimentation and Ecolo-gy, Cape Sable, Florida: E.J. Brill, Lei-den, 120 p., 52 figs., 8 plates.

Ginsburg, R.N., 1955, Recent stromatoliticsediments from south Florida(abstract): Journal of Paleontology, v.29, p. 723–724.

Golubiç, S., 1976a, Organisms that buildstromatolites, in Walter, M.R., ed.,Developments in Sedimentology: Stro-matolites: Elsevier, Amsterdam, v. 20p.113–126, http://dx.doi.org/10.1016/S0070-4571(08)71132-4.

Golubiç, S., 1976b, Taxonomy of extantstromatolite-building cyanophytes, inWalter, M.R., ed., Developments inSedimentology: Stromatolites: Elsevi-er, Amsterdam, v. 20, p. 127–140,http://dx.doi.org/10.1016/S0070-4571(08)71133-6.

Golubiç, S., 1982, Microbial ecology ofalgal mats and recent stromatolites in

Shark Bay, Western Australia: NationalGeographic Society, Research Reports,v. 14, p. 277–286.

Golubiç, S., 1985, Microbial mats andmodern stromatolites in Shark Bay,Western Australia, in Caldwell, D.E.,Brierley, J.A., and Brierley, C.L., eds.,Planetary Ecology: Van NorstrandReinhold Co., New York, p. 3–16.

Grotzinger, J.P., and Knoll, A.H., 1995,Anomalous carbonate precipitates: Isthe Precambrian the key to the Permi-an?: Palaios, v. 10, p. 578–596,http://dx.doi.org/10.2307/3515096.

Grotzinger, J.P., and Read, J.F., 1983, Evi-dence for primary aragonite precipita-tion, lower Proterozoic (1.9 Ga) Rock-nest dolomite, Wopmay orogen,northwest Canada: Geology, v. 11, p.710–713, http://dx.doi.org/10.1130/0091-7613(1983)11<710:EFPAPL>2.0.CO;2.

Hall, J., 1883, Cryptozoon, N. G., and Crypto-zoon proliferum n. sp.: New York StateMuseum, Annual Reports, 36, 6 platesand explanation.

Hardie, L.A., 1967, The gypsum-anhydriteequilibrium at one atmosphere pres-sure: American Mineralogist, v. 52, p.171–200.

Hardie, L.A., ed., 1977, Sedimentation onthe Modern Carbonate Tidal Flats ofNorthwest Andros Island, Bahamas:The Johns Hopkins University Press,Baltimore, 202 p.

Hays, J.D., Imbrie, J., and Shackleton, N.J.,1976, Variations in the Earth’s orbit:pacemaker of the ice ages: Science, v.194, p. 1121–1132, http://dx.doi.org/10.1126/science.194.4270.1121.

Hoffman, P., 1967, Algal stromatolites: usein stratigraphic correlation and pale-ocurrent determination: Science, v.157, p. 1043–1045, http://dx.doi.org/10.1126/science.157.3792.1043.

Hoffman, P., 1974, Shallow and deepwaterstromatolites in lower Proterozoicplatform-to-basin facies change, GreatSlave Lake, Canada: American Associ-ation of Petroleum Geologists Bul-letin, v. 58, p. 856–867.

Hoffman, P., 1975, Shoaling-upward shale-to-dolomite cycles in the RocknestFormation (Lower Proterozoic),Northwest Territories, Canada, inGinsburg, R.N., ed., Tidal Deposits, aCasebook of Recent Examples andFossil Counterparts: Springer-Verlag,New York, p. 257–265.

Hoffman, P., 1976, Stromatolite morpho-genesis in Shark Bay, Western Aus-tralia, in Walter, M.R., ed., Develop-ments in Sedimentology: Stromato-lites: Elsevier, Amsterdam, v. 20, p.261–271, http://dx.doi.org/

10.1016/S0070-4571(08)71139-7.Hoffman, P.F., 1989, Pethei reef complex

(1.9 Ga), Great Slave Lake, N.W.T., inGeldsetzer, H.H., James, N.P., andTebbutt, G.E., eds., Reefs, Canada andAdjacent Areas: Canadian Society ofPetroleum Geologists, Memoirs, 13, p.38–54.

Jahnert, R.J., and Collins, L.B., 2011, Signif-icance of subtidal microbial depositsin Shark Bay, Australia: Marine Geolo-gy, v. 286, p. 106–111,http://dx.doi.org/10.1016/j.mar-geo.2011.05.006.

Jahnert, R.J., and Collins, L.B., 2012, Char-acteristics, distribution, and morpho-genesis of subtidal microbial systemsin Shark Bay, Australia: Marine Geolo-gy, v. 303-306, p. 115–136,http://dx.doi.org/10.1016/j.mar-geo.2012.02.009.

Jahnert, R.J., and Collins, L.B., 2013, Con-trols on microbial activity and tidal flatevolution in Shark Bay, Western Aus-tralia: Sedimentology, v. 60, p.1071–1099,http://dx.doi.org/10.1111/sed.12023.

Jones, C.B., 1981, Periodicities in stromato-lite lamination from the early Protero-zoic Hearne Formation, Great SlaveLake, Canada: Palaeontology, v. 24,Part 2, p. 231–250.

Kalkowsky, E., 1908, Oolith und Stromatolithim norddeutschen Bundsandstein:Zeitschrift der Deutschen Geologis-chen Gesellschaft, v. 60, p. 68–125.

Kendall, C.St.C., and Skipwith, Sir P.A.d’E.,Bt., 1968, Recent algal mats of a Per-sian Gulf lagoon: Journal of Sedimen-tary Petrology, v. 38, p. 1040–1058.

Kinsman, D.J.J., 1964, The recent carbon-ate sediments near Halal al Bahrani,Trucial Coast, Persian Gulf, in vanStraaten, L.M.J.U., ed., Developmentsin Sedimentology: Deltaic and ShallowMarine Deposits: Elsevier, Amster-dam, v. 1, p. 189–192,http://dx.doi.org/10.1016/S0070-4571(08)70485-0.

Kinsman, D.J.J., and Park, R.K., 1976, Algalbelt and coastal sabkha evolution, Tru-cial Coast, Persian Gulf, in Walter,M.R., ed., Developments in Sedimen-tology: Stromatolites: Elsevier, Ams-terdam, v. 20, p. 421–433,http://dx.doi.org/10.1016/S0070-4571(08)71149-X.

Lausen, C., 1929, A geological reconnais-sance of the east end of Great SlaveLake: Bulletin of the Canadian Insti-tute for Mining and Metallurgy, v. 22,no. 209, p. 361–392.

Logan, B.W., 1961, Cryptozoon and associatestromatolites from the Recent, SharkBay, Western Australia: The Journal of

116

Geology, v. 69, p. 517–533,http://dx.doi.org/10.1086/626769.

Logan, B.W., 1987, The McLeod evaporitebasin, Western Australia: AmericanAssociation of Petroleum Geologists,Memoirs, 44, 140 p.

Logan, B.W., and Chase, R.L., 1961, Thestratigraphy of the Moora Group,Western Australia: Journal and Pro-ceedings of the Royal Society ofWestern Australia, v. 44, p. 14–32.

Logan, B.W., and Semeniuk, V., 1976,Dynamic metamorphism; processesand products in Devonian carbonaterocks, Canning Basin, Western Aus-tralia: Geological Society of Australia,Special Publications, 6, 138 p.

Logan, B.W., Rezak, R., and Ginsburg,R.N., 1964, Classification and environ-mental significance of algal stromato-lites: The Journal of Geology, v. 72, p.68–83,http://dx.doi.org/10.1086/626965.

Logan, B.W., Harding, J.L., Ahr, W.M.,Williams, J.D., and Snead, R.G., 1969,Carbonate sediments and reefs,Yucatán Shelf, Mexico: AmericanAssociation of Petroleum Geologists,Memoirs, 11, p. 1–198.

Logan, B.W., Davies, G.R., Read, J.F., andCebulski, D.E., 1970, Carbonate sedi-mentation and environments, SharkBay, Western Australia: AmericanAssociation of Petroleum Geologists,Memoirs, 13, Tulsa, Oklahoma, 223 p.

Logan, B.W., Read, J.F., Hagan, G.M., Hoff-man, P., Brown, R.G., Woods, P.J., andGebelein, C.D., 1974, Evolution andDiagenesis of Quaternary CarbonateSequences, Shark Bay, Western Aus-tralia: American Association of Petro-leum Geologists, Memoirs, 22, Tulsa,Oklahoma, 358 p.

Maloof, A.C., and Grotzinger, J.P., 2012,The Holocene shallowing-upwardparasequence of north-west AndrosIsland, Bahamas: Sedimentology, v. 59,p. 1375–1407, http://dx.doi.org/10.1111/j.1365-3091.2011.01313.x.

Mitrovica, J.X., and Milne, G.A., 2002, Onthe origin of late Holocene sea-levelhighstands within equatorial oceanbasins: Quaternary Science Reviews, v.21, p. 2179–2190, http://dx.doi.org/10.1016/S0277-3791(02)00080-X.

Mitrovica, J.X., and Peltier, W.R., 1991, Onpostglacial geoid subsidence over theequatorial oceans: Journal of Geo-physical Research, v. 96, p.20053–20071, http://dx.doi.org/10.1029/91JB01284.

Monty, C.L.V., and Hardie, L.A., 1977, Thegeological significance of the freshwa-ter blue-green algal calcareous marsh,in Walter, M.R., ed., Developments in

Sedimentology: Stromatolites: Elsevi-er, Amsterdam, v. 20, p. 447–477.

Pannella, G., 1972, Precambrian stromato-lites as palaeontological clocks: 24thInternational Geological Congress,Montreal, Section 1, p. 50–57.

Pettijohn, F.J., 1988, A Century of Geology1885–1985 at The Johns HopkinsUniversity: Gateway Press, Baltimore,316 p.

Playford, P.E., 1980, Environmental con-trols on the morphology of modernstromatolites at Hamelin Pool, West-ern Australia, in Annual Report for1979: Geological Survey of WesternAustralia, p. 73–77.

Playford, P.E., and Cockbain, A.E., 1976,Modern algal stromatolites at HamelinPool, a hypersaline barred basin inShark Bay, Western Australia, in Wal-ter, M.R., ed., Developments in Sedi-mentology: Stromatolites: Elsevier,Amsterdam, v. 20, p. 389–411,http://dx.doi.org/10.1016/S0070-4571(08)71147-6.

Playford, P.E., and Lowry, D.C., 1966,Devonian reef complexes of the Can-ning Basin, Western Australia: Geolog-ical Survey of Western Australia, Bul-letins, 118, 149 p. and supplementaryatlas.

Playford, P.E., Hocking, R.M., and Cock-bain, A.E., 2009, Devonian reef com-plexes of the Canning Basin, WesternAustralia: Geological Survey of West-ern Australia, Bulletins, 145, 444 p.and 8 full-colour geologic maps, scales1:500,000 to 1:25,000.

Playford, P.E., Cockbain, A.E., Berry, P.F.,Roberts, A.P., Haines, P.W., andBrooke, B.P., 2013, The Geology ofShark Bay: Geological Survey ofWestern Australia, Bulletins, 146, 281p.

Purser, B.H., and Evans, G., 1973, Regionalsedimentation along the Trucial Coast,SE Persian Gulf, in Purser, B.H., ed.,The Persian Gulf: Holocene Carbon-ate Sedimentation and Diagenesis in aShallow Epicontinental Sea: Springer-Verlag, New York, p. 211–231,http://dx.doi.org/10.1007/978-3-642-65545-6_13.

Read, J.F., 1973, Paleo-environments andpaleogeography, Pillara Formation(Devonian), Western Australia: Bul-letin of Canadian Petroleum Geology,v. 21, p. 344–394.

Reid, R.P., James, N.P., Macintyre, I.G.,Dupraz, C.P., and Burne, R.V., 2003,Shark Bay stromatolites: microfabricsand reinterpretation of origins: Facies,v. 49, p. 299-324.

Riding, R., 1999, The term stromatolite:towards an essential definition: Letha-

ia, v. 32, p. 321–330,http://dx.doi.org/10.1111/j.1502-3931.1999.tb00550.x.

Roddy, H.J., 1915, Concretions in streamsformed by the agency of blue-greenalgae and related plants: AmericanPhilosophical Society, Proceedings, v.54, p. 246–258.

Sami, T.T., and James, N.P., 1994, Peritidalcarbonate platform growth and cyclic-ity in an early Proterozoic forelandbasin, upper Pethei Group, northwestCanada: Journal of SedimentaryResearch, v. 64, p. 111–131,http://dx.doi.org/10.1306/D4267F6E-2B26-11D7-8648000102C1865D.

Shinn, E.A., Lloyd, R.M., and Ginsburg,R.N., 1969, Anatomy of a moderncarbonate tidal-flat, Andros Island,Bahamas: Journal of SedimentaryResearch, v. 39, p. 1202–1228,http://dx.doi.org/10.1306/74D71DCF-2B21-11D7-8648000102C1865D.

Stockwell, C.H., 1932, Great Slave Lake –Coppermine River area, NorthwestTerritories, in Annual Report, Part C:Geological Survey of Canada, p.37–63.

Stockwell, C.H., 1936, Eastern portion ofGreat Slave Lake: Geological Surveyof Canada, Maps, 377A (west half)and 378A (east half), scale: 4 miles toone inch.

Tebeau, C.W., 1968, Man in the Everglades:University of Miami Press, CoralGables, Florida, 192 p.

Walcott, C.D., 1914, Pre-CambrianAlgonkian algal flora: SmithsonianMiscellaneous Collections, v. 64, p.74–156.

ACKNOWLEGEMENTSWhile these columns have benefitedfrom comments and suggestions ofreaders too numerous to list by name,a few individuals provided detailedinformation that was critical for astory’s veracity. I am endebted toAlfred Kröner (Mainz), Marcus Kunz-mann (Montréal), Roy Miller (Wind-hoek) and Gabi Schneider (Windhoek)re Henno Martin (v. 40, no. 1); KarinSigloch (Munich) re the North AmericanCordillera (v. 40, no. 2); Peter Dawes(Copenhagen) and Tom Frisch(Ottawa) re Lauge Koch (v. 40, no 4),and Bob Burne (Canberra), Dick Chase(Vancouver) and Dave Pierce (SantaBarbara) re Conrad Gebelein (v. 41, no.2).

GEOSCIENCE CANADA Volume 41 2014 117