PRECAMBRIAN CARBONATES EVOLUTION OF UNDERSTANDING

JOHN P GROTZINGER MA 02139 U SA Department ofEarth Atmospheric and Planetary Sciences Massachusetts Institute ofTechnology Cambridge AND NOEL P JAMES K7L 3N6 Canada Department ofGeological Sciences Queen s University Kingston Ontario

a of abiotic and ABSTRAcr In the Precambrian world devoid of higher organisms except near its end carbonate sediments formed by variety and climatic These ancient rocks demonstrate that the microbial processes with patterns of deposition determined by tectonic eustatic processes were initiated in earth with the basic attributes of carbonate sedimen fundamental tenets of carbonate production and accumulation early history tation well established by Neoproterozoic time evolution of the earth The broad temporal patterns of Precambrian carbonate facies composition and disposition parallel the long term s oceans sea whereas the record and atmosphere Archean and Paleoproterozoic carbonates commonly contain abundant floor precipitates Neoproterozoic are transitional and is dominated by clastic textured facies and abundant carbonate mudstones Mesoproterozoic carbonates Mesoproterozoic structure Grainstones dominated ooids early Neoproterozoic carbonates also contain abundant quantitites of the enigmatic molar tooth by giant unusual carbonates a of with centimeter scale diameters are characteristic of many Neoproterozoic carbonates Texturally featuring reprise Archean style sea floor precipitates often cap glacial deposits of middle Neoproterozoic age Precambrian reefs Archean reefs are The influence of biology on sediment texture is best expressed in the history of through Mesoproterozoic of and calcite the dominantly stromatolite based Lamination textures reveal the progressive shift from in situ precipitation aragonite encrusting and stromatolites to textures consistent with accretion of loose sediment trapping binding sea floor in Archean through Paleoproterozoic through of abiotic factors and the concomittant increase of in Neoproterozoic stromatolites This trend is interpreted to reflect the progressive decrease reefs witness the of more textures that benthic microbial mats on controlling stromatolite growth Neoproterozoic appearance complex likely in the seafloor its surface and involve the participation of calcified microbes and noncalcified higher algae colonizing increasing complexity Terminal Proterozoic thrombolitic reefs contain the first resulting in highly porous frameworks for the first time in geologic history additionally calcified metazoans

most carbonates such as INTRODUCTION simple question asked of Phanerozoic Were the sediments produced biologicallyand answered af Precambrian carbonate rocks have within them a legible rec firmatively in scores of introductory level textbooks and sum ord of earth history that spans more than three billion years articles is not so easily resolved for the Precambrian rec From the period of first continental accretion to the advent of mary ord For rocks of this age the absence of coarse skeletal debris ecologically diverse biomineralizing metazoans these sedimen in all but terminal Proterozoic carbonates does notprovide an tary rocks contain chemical and proxies biological physical that are vast and the easy for the many platforms as for past tectonic regimes environmental change and evo explanation diverse as any of Phanerozoic age The prob lution of life Their physical attributes reflect tectonic subsi compositionally lem of the of Phanerozoic carbonate mud so easily ex dence and sea level fluctuation their chemical variability pro origin through the post mortem disintegration of green algae vides insight into carbon burial rates continental growth and plained does notfind much basis in accounting for the mudstones pres surficial redox their paleontology illustrates how microorgan ent across the 600 000 km2 late Archean Transvaal platform isms have evolved and how the structure of early ecosystems at least 1 5 billion older than the first direct evidence for developed years in the fossil record Precambrian carbonate sedi Studies of Precambrian carbonates like analyses of their green algae have thus had to rely on a number of different younger counterparts generally fall into two categoriesone mentologists to to address some of these essen in which the former sedimentary facies their constituentgrains approaches begin simple yet tial and so the of sedimentological trace and the platforms they form are of primary interest and the questions integration element biomarker and data has be other in which the sediments are viewed principally as carriers isotopic paleobiological more even for studies devoted to the e is come widespread origin of a geochemical record g C and Sr isotopes which itself of the sediment itself the object of study In the first case investigations are motivated it was notclear what facies Pre by the desire to interpret sedimentation patterns that result from Thirty years ago comprised in the cambrian carbonates if they formed differentiated platforms physical chemical and biological processes whereas and if were well for detailed study The second studies are oriented more toward understanding biogeo they enough preserved view was and to some extent still is that Precam chemical cycles and the ancient ocean atmosphere system prevailing fall into either brian carbonate rocks were endless hectares of stromat In this volume we have assembled papers that simply dolostone in an is olites and fabric destructive Several key papers category Having done so emerging trend obvious however answers to these several of these studies accomplish both This degree of inte the mid 1970s provided distinct and demonstrated the clear for additional gration is motivated by the realization that the clearest records questions potential more detailed Hoffman 1974 Serebryakov and Semik of biogeochemical events are elucidated through careful study study hatov Beukes 1977 and 1978 These of sedimentary and diagenetic patterns Conversely sedimen 1974 Cecile Campbell combination with the ofextensive fields of tation patterns are being explored in the context of the local studies in disovery in a effort to better un and global microbiological and physicochemical variability that stromatolites Shark Bay ignited major and might influence textures and accumulations rates derstand the paleoenvironmental paleobiological signifi Walter The study of Precambrian carbonate platforms necessitates cance of stromatolites in platform carbonates 1976 effort in turn to a of studies in such integrated approaches to problem solving An apparently This led second generation

Carbonate Sedimentationand Diagenesis in the Evolving Precambrian World Copyright @ 2000 SEPM Society for Sedimentary Geology Special Publication 67 ISBN 1 56576 072 7 4 PRECAMBRIAN CARBONATES EVOLUTION OF UNDERSTANDING

which platforms were mapped facies were interpreted in the velopment of Precambrian carbonate platforms is identical to context of modern and analogs complementary diagenetic modern ones Important controls on platform geometry include studies aimed at were trying to unravel primary mineralogy and patterns of differential subsidence eustatic fluctuations silici carbonate precipitation mechanisms Kerans 1982 Grotzinger clastic sediment flux and paleoclimate Ramps and rimmed and Read Bertrand 1983 Sarfati and Moussine Pouchkine shelves are both present although Neoproterozoic rocks show 1983 Tucker 1983 Teitz and Mountjoy 1985 Grey and a dominance of ramps over rimmed shelves The reasons for Thorne 1985 1986a 1986b Hofmann and Jack this trend Grotzinger of abundant Neoproterozoic ramps are unclear but son Beukes Fairchild and 1987 1987 Spiro 1987 Zempolich may be related to the abundance of grainstones in some systems et aI 1988 Syntheses of Precambrian carbonates at the close e g Knoll and Swett 1990 Clough and Goldhammer this of the decade Grotzinger 1988 1989b summarized existing volume the general decline of stromatolites that might have data and demonstrated that to a first order approximation the formed effective barriers Grotzinger 1988 1990 and the rise of their a geometries carbonate platforms primary mineralogies of higher algae Butterfield et 1988 that might have com and the distribution of since at least the late general facies Ar peted effectively for substrate space Knoll and Swett 1990 chean similar were to those present in Paleozoic through Recent Nevertheless many platforms beginning with the late Ar carbonates chean Campbellrand Malmani structure Beukes 1980 1987 This of research however also out that show phase pointed large morphologic development from an initial ramp that un the parts of Precambrian record were non actualistic with no dergoes progressive transition to a rimmed shelf Fig 1 analogues in the modern or for that matter in the Phanerozoic Younger examples include the Paleoproterozoic Pethei and The last ten years has been a watershed in our understanding Rocknest platforms Hoffman 1974 Grotzinger 1986b Sami in this regard as Precambrian carbonates have been interpreted and James 1993 the Neoproterozoic Yellowhead platform on own and not their merits viewed simply as variants on Phan Teitz and Mountjoy 1985 1989 and terminal Proterozoic car erozoic models Furthermore new analytical techniques have bonates of the Gourma basin Bertrand Sarfati and Moussine allowed heretofore unimagined correlation and thus revealed Pouchkine 1983 and the central Oman basin Mattes and Con unknown attributes of sediment previously dynamics Finally way Morris 1990 In these cases basin development is the fresh have geochemical techniques permitted different proxies dominant control on transitions from ramp to rimmed shelf to about speak the compositions of the Precambrian oceans and with intial flooding of antecedent topography and rapid rates atmospheres Important papers on Precambrian carbonates that of accommodation giving way to slower long term subsidence facies andor identify potentially age dependent processes in and attendant reduced accommodation This pattern is charac clude Archean a carbonates Simonson et 1993 Sumner and teristic of many Phanerozoic transitions 1 Grotzinger 1996a 996b Simonson and Jarvis 1996 Sumner The sequence architecture of all well studied Precambrian a 1997a 1997b Paleoproterozoic carbonates Burdett et platforms Fig 2 shows patterns that are identical to Phaner 1990 Kah and 1992 Karhu 1993 Sami and James ozoic a Grotzinger platforms e g Grotzinger 1986b Christie Blick et 1993 1994 1996 Grotzinger and Rothman 1996 Mesopro 1988 Sami and James 1993 1994 Knoll et a 1995a Saylor terozoic carbonates Pelechaty and James 1991 Pelechaty et et aI 1995 Pelechaty et a 1 996a Sami et a this volume a a a 1991 Buick et 1995 Sergeev et 1995 Knoll et aI Clough and Goldhammer this volume Jackson et aI this vol a 1995b Kah and Knoll 1996 Frank et 1997 Furniss et a that ume implying the ratio of accommodation space creation 1998 and James a Narbonne 1996 Xiao et 1997 Knoll and to sediment flux was not significantly different In most cases Semikhatov 1998 and carbonates Neoproterozoic Aitken sediment production rates were higher than what was required 1988 Aitken and Narbonne 1989 Southgate 1989 Peryt et so that the meter scale shallowing upward paradigm is as a ubiq 1990 et a a Wright 1990 Fairchild 1991 1993 Knoll and uitous in Archean Martin et 1980 Sumner and Grotzinger a a Swett 1990 Kaufman et 1991 Knoll et 1993 1995a this volume and Proterozoic Grey and Thorne 1985 Grot Sumner and Grotzinger 1993 Grotzinger and Knoll 1995 zinger 1986a Southgate 1989 Sami and James 1994 Jackson et a 1997 a a Fairchild 1989 1990 Saylor et 1995 1998 et this volume carbonates Fig 3 as it is in Phanerozoic a Pelechaty et 1 996a 1996b Hoffman et a 1998a 1998b carbonates Pratt et a 1992 a a Kennedy 1996 Kennedy et 1998 Turner et 1993 The architecture of Precambrian carbonates alone provides 1997 The papers in this volume represent a milestone of that powerful evidence that sediment accumulation rates have al effort and strive to extract some of the most important issues ways been anomalously high in comparison to shallow marine that make Precambrian carbonates so fascinating The goal of siliciclastic systems with sediment production easily matching this is to review some of the and introductory paper briefly progress typically exceeding available accommodation space High that has been made over the decade and past to identify the sediment production rates should not be viewed as a special Not we important outstanding problems surprisingly find that attribute of Phanerozoic carbonate producing systems im of these are not to many problems unique Precambrian carbon parted through the advent of biocalcifying higher organisms at ates rather the record of Precambrian carbonate sedimentation the dawn of Cambrian time cf Riding 1982 Knoll et a simply illustrates the fundamental nature of these problems 1993 It seems likely that the calcium carbonate saturation state a on carbonates of providing fresh perspective Phanerozoic seawater has always been at least as high as that in the Phan erozoic and the reason for this is straightforward carbon on earth is between PLATFORM GEOMETRY AND ARCHITECTURE Inorganic distributed the atmo sphere the ocean and the crust Precipitation of calcium car The studies of individual many detailed late Archean and bonate biologically or inorganically represents transfer from confirm that the younger platforms general structure and de ocean to crust Over long periods of time millions of years JOHN P GROTZINGER AND NOEL P JAMES 5

50 km JJ JJ J J J J J

e e e

e n n n e n n

rV rV fV rv rvI rvI rvI rvI

I rvI rvI rvI rvI rvI rvI rvI rvI rvI rvI rvI rvI rvI rvI rvI rvI J n n n n n n n n rvI n rvI rvI rvI rvI n n n n n n n n n n n n n n n n n n n rvI rvI rvI rvI rvI rvI rvI rvI rvI n n o Lagoonal o Shallow Subtidal I Intertidal II Supratidal II Banded Iron Formation 1 I Slope Basin Facies 1 1 Giant Elongate Stromatolites IT Deep Subtidal Microbialite o Grainstone Shoal

facies differentiation and transition from FIG I Late Archean 2 5 Ga Campbell rand platform northern Cape Province South Africa Note well defined shelf After Beukes and Sumner and this volume ramp to rimmed morphology 1987 Grotzinger

NW SE accommodation space creation

@ @@ @

o

B

A II

IIIIII11 Microdigitate stromatolites 00 Stromatolite bioherms Fenestral microbial laminite Domal stromatolites Wavy microbial laminite intraclast Prone microbial laminite Oncoid grainstone

@ Limestone @ Oolite rhythmite

Pethei northwest Canada Note accentutation of rim FIG 2 Sequence stratigraphic development of Paleoproterozoic 18 Ga platform geometry during times of accommodation increase similar to Phanerozoic platforms After Sami and James 1994 6 PRECAMBRIAN CARBONATES EVOLUTION OF UNDERSTANDING

w E term of the continents than to the advent of biocalci 150 200 km flooding fication The transgression that started with the breakup of the late Proterozoic supercontinent and culminated in late Cam I brian time was responsible for the deposition and therefore REEFAL into the crust of of carbonate BOUNDSTONE rn GRAINSTONE E TIDAL FLAT lAMINITES partitioning great volumes over all the continents Bond et a As a much aPERITIDAL STROMATOLiTES D DOlOSllTlTE lAGOONAL SHALE 1989 consequence inorganic carbon was buried and removed from the oceanic realm 5 tom A

CHEMOSTRATIGRAPHIC CORRELATION TECHNIQUES

Correlation techniques based on carbon and strontium have revolutionized Precambrian carbonate stratigraphy Veizer and B colleagues Veizer and Compston 1976 Veizer and Hoefs 1976 first suggested that primary variations in the 813C and FIG 3 Facies architecture A and inferred relation chronostratigraphic 87Sr 86Sr composition of Precambrian carbonates reflect ships B in a single meter scale platform cycle Paleoproterozoic 19 Ga might differences in the of seawater Rocknest platform northwest Canada A Note that the shallowing upward composition contemporaneous motif is best middle section of Focus on of the record the developed across cycle To the west near the the Neoproterozoic part confirmed shelf consist of platform edge cycles unconformity bounded tidal flat facies potential magnitude and form of these major isotopic excur whereas to the east consist of conformable successions of shale a cycles lagoonal sions Knoll et 1986 Fairchild et aI 1989 Fairchild and and dolosiltites B Note that cycles nucleated near therim and then prograded Spiro 1987 The decade resulted in a effort to dominantly eastward Downlapping shales were supplied by an eastern source ensuing major the of the excursions in a region and are in turn downlapped by prograding carbonates After Grotzinger prove utility providing Neoprotero I986a zoic chronostratigraphy useful in global correlation of other wise poorly fossiliferous strata Fairchild et aI 1990 Knoll 1991 Kaufman et aI 1991 Kaufman et aI 1993 Knoll and Walter 1992 Pell et aI 1993 Burns and Matter 1993 Brasier the only way to decrease the oceanic inventory of inorganic et aI 1992 1997 Narbonne et aI 1994 Kaufman and Knoll carbon is to allow long term partioning of carbonate minerals 1995 1996 et a 1998 Knoll et aI 1995a into the crust Walker 1985 In this a new state is Kennedy Kennedy way steady a Knoll et 1995b Pelechaty et aI 1996b et aI 1998 reached in which the oceanic reservoir becomes progressively Saylor Hoffman et aI 1998a 1998b Most the carbon smaller The concentration of carbonate in seawater would recently global curve has been used to subvide strata for the therefore decrease other factors being equal isotope purpose of resolution intrabasinal correlation et aI Prior to the advent of calcareous microplankton in Jurassic high Pelechaty 1 996a Smith 1998 when used in combination with time carbonates were precipitated abundantly only in shallow sequence and data this approach promises marine environments Precipitation of shallow water carbon stratigraphic biostratigraphic a level of resolution for terminal Proterozoic strata that may ates is limited to the space created as a result of sea level rising rival that of Paleozoic time relative to the land surface accommodation space Unlike sil The conclusion ofthese studies is that correlation iciclastic sediments carbonate sediments cannot be deposited techniques based on carbon and strontium are a tremendous asset above sea level because they are produced in the marine envi isotopes in subdivision of Neoproterozoic age strata the ter ronment except for volumetrically trivial amounts oflacustrine particularly minal Proterozoic part of the record Initial studies of the iso carbonate Transgression and onlap commonly result in net topic variability of Mesoproterozoic and car carbonate deposition whereasregression and offtap lead to sub Paleoproterozoic bonates however show that the signal may be of much lower aerial exposure and net carbonate dissolution Consequently and thus the for resolution correlation the maximum amount of carbonate that could have been ex amplitude prospect high seems less promising Veizer and Hoefs 1976 Buick et aI tracted from pre Jurassic oceans is directly proportional to the 1995 Knoll et aI 1995b Frank and this volume Frank accommodation space over the continents As has been shown Lyons et aI 1997 Kah this volume A possible exception may be previously Grotzinger 1989b 1994 Grotzinger and Kasting the Paleoproterozoic Event when the 1993 carbonates have been able to fill the available accom Lomagundi amplitude of carbon anomalies seems to have been similar to that modation space since at least the late Archean In other words isotope present in Neoproterozoic time Schidlowski 1988 Karhu their growth potential has been enough to effec always high 1993 tively fill the space created by eustatic rises in sea level or accelerations in subsidence Therefore it is not clear that the of SECULAR CHANGES IN FACIES inception benthic biocalcification would have had an impor tant effect on the saturation state seawater the of amount pre The past decade of research has confirmed that significant cipitated would still have been restricted by the available ac differences exist between Precambrian carbonate facies of dif commodation space Biocalcification acts only as a catalyst ferent ages It is necessary to view the record of Precambrian restrained in its potential to sequester any more carbonate than carbonate sedimentation in discrete intervals marked by impor by inorganic means because of the impositions of subsidence tant differences in the style and mode of carbonate production and eustasy Considered collectively the progression of facies types pro that there Indeed it seems if was a decrease in the saturation vides the record of the long term chemical evolution of sea state of Paleozoic seawater it would be more attibutable to long water and to a lesser extent biological evolution JOHN P GROTZINGER AND NOEL P JAMES 7

Fairchild 1991 et aI In some cases facies types are distinctly bounded in time Read 1983 Grotzinger 1989b Bartley volume and this volume Winefield this however in most cases the transitions are gradual Fig 4 this Pope Grotzinger the not Thus unlike the Phanerozoic record where abrupt changes in volume with striking difference that they do simply but are as direct on the sea carbonate facies often coincide with major evolutionary pulses fill voids widespread precipitates include fans e floor itself Facies large divergent crystal in carbonate secreting organisms g Ordovician radiation upward of calcite and dolomite 1 with radii com the Precambrian record appears to have been influenced mostly replaced aragonite on the order of many tens to hundreds of centimeters by inorganic processes that evolved over much longer time monly 5A 2 much smaller upward divergent forming scales Indeed supposedly biologic parameters such as diver Fig aragonite 3 encrust taxa actual microdigitate stromatolites Fig 5B isopachously sity of stromatolite show little correlation with the micron to millimeter thick of former high mag record of fossil microbes instead correlation with the broader ing layers nesium 4 of term calcite Fig 5C isopachously encrusting layers range of carbonate facies supports the possibility that long calcite 5D and rarely 5 marine tufas with environmental change has influenced all carbonate facies in herringbone Fig branching dendritic morphologies Figure 5E cluding stromatolites Grotzinger and Knoll 1999 Combined The abundance of sea floor calcite and aragonite precipita with the ofPrecambrian likely misrepresented history evaporite a tion shows to a first order approximation monotonic de sedimentation Grotzinger 1989b Grotzinger and Kasting crease from late Archean through Mesoproterozoic time Grot 1993 Pope and this volume these changes in the Grotzinger zinger 1989b 1993 1994 Grotzinger and Kasting 1993 record of carbonate sedimentation provide the warrant for non Grotzinger and Knoll 1995 Sumner and Grotzinger this vol uniformitarian models of earth evolution and accounts of en ume Decimeter to meter scale fans offormer aragonite occur vironmental secular change late Archean carbonate in virtually every well preserved plat form and occur in open marine subtidal environments includ Archean Sea Floor Encrusting Precipitates ing storm dominated shelves and reefal rims fronting major Sumner and Grotzinger this volume Sea floor en Nature of the Precipitates platforms crusting precipitates form discrete beds up to several meters trends is the One of the most conspicuous age dependent thick and cements beds as thin as 20 centimeters can be traced long term decrease in the volume of carbonate precipitated di laterally for over 100 kilometers Sumner 1995 Individual have on the rectly on the sea floor Fig 4 These precipitates in the form aragonite botryoids now calcite typically radii of aragonite and calcite pseudomorphs are present as discrete order of tens of centimeters Fig 5A and in some cases were and 1989 sea floor encrustations of both inorganic and microbial origin as great as 150 centimeters Grotzinger Friedman Abiotic precipitates are morphologically and mineralogically Grotzinger et aI 1993 Sumner and Grotzinger 1996a Sumner identical to marine cements of Phanerozoic age Grotzinger and 1997a Sumner and Grotzinger this volume

S13C Sea Tidal II Ice Iron Floor H bone CaS04 Flat Molar Giant 5 0 A e Fm Fans Calcite Eva s Tufas Tooth Ooids 0 53

0 Q Z t 1 0 I 0 Jl o Q NE 1 5 e Q 0 0 I 2 0 a Q a a

2 5

0 Q c Z

3 0 aj Q o Jl Q E

3 5

iron formation and carbon FIG 4 Temporal evolution of Archean and Proterozoic carbonate facies calcium sulfate evaporites glacial deposits isotope and dolomite beds in excess of I meter composition of carbonates Sea Floor Fans include mesoscopic peudomorphs of calcite replaced aragonite forming associated with the carbonates rocks not thick The few occurrences of this facies in the Neoproterozoic record are specifically capping glaciogenic including calcite the sea floor Tidal Rat Tufas includes the exceptions mentioned in the text H bone Calcite includes beds of herringbone precipitated directly on thin crusts and stromatolites in restricted tidal flat environ calcite and dolomite replaced pseudomorphs of aragonite and calcite precipitated as microdigitate ments 8 PRECAMBRIAN CARBONATES EVOLUTION OF UNDERSTANDING

FIG 5 Textures created of carbonate on the sea floor by precipitation directly A Large calcite replaced aragonite fans interbedded with rippled ooid mudstone grainstonelime Late Archean 2 7 Ga Cheshire Formation Belingwe greenstone belt Zimbabwe Scale in centimeters B Microdigitate stromatolites 97 Ga Paleoproterozoic 1 Kimerot platform Kilohigok Basin northwest Canada Coin is 2 centimeters in diameter C Isopachous laminites Late Archean 2 5 Ga Malmani Subgroup Transvaal Province South Africa D Herringbone calcite late Archean 25 Ga Gamohaan Formation northern Cape Province South Africa Scale in millimeters E Dendriticany branching tufa Paleoproterozoic 18 Ga Hearne Formation Pethei platform northwest Canada Scale in centimeters

These facies are of marine representative open rather than are rare in younger rocks Grotzinger 1989b with these ex restricted and conditions Sumner Grotzinger this volume in ceptions often marking unusual local conditions in sea water contrast to most early interpretations which assumed that the chemistry Grotzinger and Knoll 1995 One particularly well crystal fans were replaced gypsum and therefore deposited in developed instance occurs in the Paleoproterozoic Teena Do restricted e Martin et aI environments g 1980 see summary lomite where the fans form continuous sheets within a re in Grotzinger 1989b Occurrences of crystal fans of this scale stricted likely anoxic basin Winefield this volume Another JOHN P GROTZINGER AND NOEL P JAMES 9 exception includes thin sheets within foreland basin siliciclastic sediments of Paleoproterozoic age formed along the maximum flooding surfaces of individual sequences where siliciclastic se dimention rates were greatly reduced Grotzinger and Fried mann 1989 Herringbone calcite was a common sea floor precipitate in Archean carbonates that declined sharply in abundance at the end of early Paleoproterozoic time Fig 4 Sumner and Grot zinger 1996a 1996b The constituent crystals of herringbone calcite have textures Fig 5D that may indicate preferential growth of crystal faces forced by the presence of an inhibitor possibly FeH or MnH Sumner and Grotzinger 1996a Thus its abundance in Archean carbonates has been explained in the context of environmental models in which lower oxygen con centrations in seawater lead to greater solubility of iron and manganese which in turn interfered with calcite precipitation to the extent that calcite was precipitated with highly distorted crystals that recrystallized to form the distinctive herringbone texture Herringbone calcite is rare in Phanerozoic rocks where it may reflect locally dysaerobic to anaerobic pore fluids and seawater Sumner and Grotzinger 1996b Implications

The trend in declining sea floor precipitates is considered to be only a first order relationship and does not rule outtransient reversals in response to short term events There are late Ar chean platforms that are dominated by muds intraclasts ooids andor nonprecipitated stromatolites and lack the abundant en crusting precipitates that define the late Archean norm Simi larly the Neoproterozoic record contains exceptions to the gen eral dearth of macroscopic seafloor encrustations and other carbonates The occurin the so called precipitated exceptions FIG 6 Archean clastic carbonate sediments A Ripple cross stratified cap carbonates that overlie Neoproterozoic glaciogenic rocks ooid intraclast grainstone late Archean 2 5 Ga Cheshire Formation Be belt Zimbabwe Hand lens is 2 cm wide B Thin bedded see discussion below lingwe greenstone dolomitic lime mudstone Late Archean 2 5 Ga Frisco Formation Transvaal In an attempt to highlight this distinctive trend it should not Province South Africa Hammer is 30 cmlong be overlooked that all of these facies are associated with many conventional clastic carbonate facies Large sea floor fans of the late Archean carbonate platforms are often associated with The simplest interpretation is that Precambrian surface sea wave rippled ooid grainstones and wavy bedded interstratified water was substantially oversaturated with respect to calcium rippled limestones with dolomitic lime mudstone drapes Fig carbonate well above the factor of 3 5 that is typical of the 6A These facies are identical in terms of their primary bedding oceans today Li et a 1969 so that the sea floor was directly textures and diagenesis coarse grains calcite mudstones do encrusted with prolific marine carbonate precipitates Grotzin lomite to the ubiquitous ribbon limestones of early Paleozoic ger 1989b Grotzinger and Kasting 1993 The only known age Demicco 1983 In other cases the sea floor fans are as Holocene analogs are nonmarine thermal spring and alkaline sociated with broad expanses or thick buildups of stromatolites lake deposits in which extreme levels of oversaturation result although the stromatolites themselves may also be constructed in massive precipitation at the sediment water interface Chaf at least in part of laminae that were precipitated in situ In other etz and Folk 1984 Bensen 1994 Jones and Renaut 1995 a cases successions of micritic limestones and dolostones may Fouke et 1999 Counter to intuition extreme oversaturation be present Fig 6B with uncommon development of fans does notresult in spontaneous micritic whitings in these set Consequently the development of the sea floor fan facies is tings waters are generally clear and sediment is uncommon in characterized by a high degree of variability with some plat the precipitated crusts Instead the precipiated crusts commonly forms apparently containing a smaller volume of sea floor pre feature growth of large crystals and in extreme cases with non cipitates e g Carawine Dolomite Simonson et aI 1993 and crystallographic and dendritic textures Accordingly the satu others constituting 50 or more by volume e g Cheshire and ration state of Precambrian surface seawater is inferred to have Gamohaan Formations Grotzinger et a 1993 Sumner 1997a been highest in the Archean declining through the Paleopro Sumner and Grotzinger this volume The important point is terozoic and Mesoproterozoic and reaching near Phanerozoic that in addition to the usual association of stromatolites grain values only during the the Neoproterozoic Grotzinger 1989b stones and mudstones the late Archean seafloor commonly Knoll and Swett 1990 Fairchild et aI 1990 Grotzinger and precipitated calcite and aragonite directly on the seafloor Kasting 1993 Grotzinger and Knoll 1995 Grotzinger and sometimes in remarkable abundance Kasting 1993 noted that this interpretation is consistent with 10 PRECAMBRIAN CARBONATES EVOLUTION OF UNDERSTANDING

observations that the partial pressure of atmospheric carbon di ozoic Kotuikan Formation it is clear that these primary min oxide may have been much greater early in Earth history Kast eralogies were contemporaneous Grotzinger 1986a Bartley et ing 1987 and that the total alkalinity in sea water may have aI this volume been much higher as a result Other theoretical arguments have been presented Kempe and Degens 1985 Kempe and Kaz Implications mierczak 1994 that also favor elevated in alkalinity early When combined with the data from late Archean platforms oceans albeit at extreme levels a substantial soda geologic seem where sea floor precipitates of both calcite and aragonite database on and carbonate however refutes evaporite deposits to have developed it is not clear that any long term trends in of such extreme and the conditions Young Long are interpretation the primary mineralogy of shallow marine carbonates pres 1977 Jackson and Ianelli 1981 Muir 1987 Buick and Dun ent for this time interval Similarly primary mineralogy as in 1987 1990 and 1993 and Grot lop Grotzinger Kasting Pope ferred from ooids does not show any obvious trends Simonson this volume The term decrease in the saturation zinger long and Jarvis 1996 Thus there is no evidence through this time state of seawater is to be related to at least two factors thought interval for a first order trend in mineralogy similar to that seen 1 term carbon from the long transfer of inorganic atmosphere for the Phanerozoic Sandberg 1983 Wilkinson et aI 1985 and ocean to the continents as a result of the formation 2 5 by Macroscopically visible precipitate structures are rare in 2 0 Ga of and stable continents of large capable preserving Neoproterozoic rocks Fig 4 In fact the only significant oc substantial limestone and dolostone and 2 a deposits major currences are associated with the cap carbonates discussed decrease in concentration of reduced and therefore more sol below One occurrence not associated with a cap carbonate uble iron and in seawater as a resultof a manganese Paleopro comprises calcite replaced aragonite botryoids associated with terozoic increase in levels in the and surface oxygen atmsophere stromatolites in the circa 900 Ma Atar Group Mauritania Fair seawater Sumner and 1996b It is that a Grotzinger postulated child et 1990 In another occurrence dolomite pseudo FeH and MnH acted in the does in as same manner as MgH cm are morphs ofaragonite fans up to 25 in diameter interpreted calcium carbonate precipitation Berner 1975 Mucci inhibiting to have been deposited in hypersaline low energy ponds rep and Morse and The 1983 Sumner Grotzinger I996b major sented by the Katakturuk Dolomite northern Alaska Clough decline of seafloor both and precipitates inorganic microbial and Goldhammer this volume The size ofthe Katakturukfans occurred hundreds of millions of before the Precambrian years are comparable to those seen in Archean carbonates and are Cambrian and thus cannot be related to the advent boundary anomalous with respect to other Neoproterozoic carbonates of carbonate secreting metazoans and higher algae In terms of is constrained Unfortunately the age of the Katakturuk poorly its effects on carbonate facies and textures this decline is as 543 Ma 800 Ma so it is difficult to place these carbonates as the significant Cambrian radiation of skeletonized organisms within a broader framework of secular evolution and the Mesozoic evolution of calcareous microplankton

Neoproterozoic Cap Carbonates Proterozoic Sea Floor Precipitates Attributes Nature ofthe Precipitates

Seafloor precipitates are widespread in Paleoproterozoic suc Tillites and associated glaciogenic facies have long been cessions but individual crystal fans and sheets more commonly known to occur in middle Neoproterozoic successions e g have thicknesses measured in millimeters to centimeters rather Harland 1965 and from the time they were first recognized than decimeters and often form microdigitate stromatolites their intimate stratigraphic association with carbonates was con formed of radiating crystal fans Fig 5B Furthermore in con sidered paradoxical e g Schermerhorn 1974 Particularly unusual com trast to the Archean sea floor precipitates these precipitated puzzling are the cap carbonates texturally buff dolo that facies are mostly limited to restricted often peritidal environ monly pink or stones less commonly limestones ments Grotzinger and Read 1983 Grey and Thorne 1985 form distinctive beds several meters thick above many Neopro Grotzinger 1986a 1989b Hofmann and Jackson 1987 Sami terozoic tillites The cap carbonates are extraordinary in that and James 1996 By Mesoproterozoic time precipitated mi they were globally deposited directly on top of the glacial de that carbonate occurred world crodigitate stromatolites and laminar crusts were more limited posits implying sedimentation in development although they are locally abundant in peritidal wide at the onset of transgression over previously glaciated strata that are associated with evaporites such as in the Society landscapes In most cases cap carbonates are remarkably pure Kah and Knoll Other as laminated 7A Cliffs Formation e g 1996 peritidal they commonly appear dolomicrospar Fig evidence lithification but strata generally lack these structures except for occasional in showing of rapid locally they include tervals that represent only a small fraction of the overall plat seafloor cements of originally aragonitic centimeter to deci form e g Bartley et aI this volume meter scale crystal fans Fig 7 B C Recently cap carbonates Petrographic studies indicate that the microdigitate stromat have been characterized as thin deep water deposits Kennedy olites and smaller scale botryoidal fans were precipitated as 1996 Although some cap carbonates may fit the deep water aragonite Grotzinger and Read 1983 Hofmann and Jackson description it is also clear that in other cases the thin deep 1987 Kah and Knoll 1996 Bartley et aI this volume In water facies pass laterally into much thicker platformal facies a contrast the micron to millimeter scale laminated crusts Fig associations Williams et aI 1974 Cloud et 1974 Hegen a 5C have textures more consistent with a calcite precursor berger 1993 Hoffman et 1998a 1998b Thus it seems that Grotzinger 1986a Bartley et aI this volume In carbonates despite potentially rapid sea level rise associated with degla of the Paleoproterozoic Rocknest Formation and Mesoproter ciation sediment production rates were high enough to match JOHN P GROTZINGER AND NOEL P JAMES 11

cordance between tillites and carbonates can be explained in terms of stromatolite accretion in cold lakes as occurs today in Antarctica this mechanism however cannot account for either the texture or the distribution of most cap carbonates or the observation that stromatolites are a minor facies in most cap carbonates In contrast Tucker 1986 Singh 1987 and Fair child 1993 suggested that the carbonates might have been precipitated during warm interglacial intervals implying that Neoproterozoic ice ages were terminated rapidly This model invokes the thermodynamic relation between warming of sea water and its decreasing solubility of carbonate Warming of seawater in shallow environments would have triggered car bonate precipitation An additional mechanism would include turnover of a previously stratified ocean driven by rapid melt ing of glacial ice which would have forced upwelling of an eft oxic isotopically depleted alkaline deep water Kaufman et aI 1991 Grotzinger and Knoll 1995 This latter model can ac 1 count for the strongly negative o13C isotopic values that are r l characteristic of virtually all cap carbonates Kaufman and Knoll 1995 The sedimentology of cap carbonates is consis JttI tr j tent with this hypothesis and independent evidence for deep r r f ocean anoxia comes from the found in associ J iron formations ation with some Neoproterozoic tillites Beukes and Klein ft L rllilll I J c 1993 The evidence for ocean stratification I iI strongest sequential 0 j and turnover is however carbon data o13C f provided by isotope l values for later Neoproterozoic platform carbonates deposited

1 8 to and 1 prior to glaciation are unusally high 9 0 locally higher whereas cap carbonates have values of 2 to 6 Kaufman and Knoll 1995 Co occurring organic carbon shows the same secular variation supporting petrological geochemical imd geographic data that the isotopic signatures faithfully record secular changes in the isotopic composition of the surface ocean The surface waters of stratified oceans are typically en riched in I3C because large volumes of I3C depleted organic matter are exported to anoxic bottom waters and the sediments beneath them Deuser 1970 Bacterial sulfate reduction of organic matter in the deep anoxic water column produces HCO and C03 that are depleted in 13c The magnitude and inferred duration of pre glacial carbon isotope excursions in Neoproterozoic successions are unusual implying a pro tracted build up of isotopically light deep ocean water Re mixing of this alkalinity laden deep water into the surface ocean would have resulted in the precipitation of carbonates whose isotopic composition would be determined primarily by the composition of the large deep alkalinity reservoir Ar thur 1979 Holser 1984 FIG 7Cap carbonate facies A Thinly laminated dolomite mudstone Alternatively the isotopic composition of cap carbonates southern Namibia Coin is 2 in diameter B Neoproterozoic Gariep Group cm could be explained by a model involving cessation of primary Calcite replaced aragonite fans interbedded with shaly lime mudstones ter in the ocean thus down the minal Proterozoic Buschmannsklippe Formation central Namibia Coin is 2 productivity shutting biological carbon cmin diameter C Calcite replaced aragonite fans interbedded with lime mud pump and driving ocean carbon isotope compositions a stone terminal Proterozoic Ravensthroat cap carbonate Mackenzie Mountains to riverine values of approximately 4 0 Hoffman et Canada Scale in centimeters 1998a Eliminating primary productivity in the surface oceans for a time sufficiently long enough to drive carbon consistent with sources or exceed accommodation production with resulting strong isotopic values to those nonbiologic platform to basin differentiation requires dramatic causal mechanisms cf Hsti and McKenzie 1985 such as covering the entire globe with ice Kirschvink Origin 1992 Hoffman et a 1998a The differences between the Models for the origin of these enigmatic carbonates are di ocean upwelling model and the snowball earth model predict verse Walter and Bauld 1983 proposed that the apparent dis fundamental differences in the regularity of carbon isotope 12 PRECAMBRIAN CARBONATES EVOLUTION OF UNDERSTANDING

compositions and the duration of the negative anomalies With may have increased relative to younger and older periods be the upwelling model substantial variability in the carbon iso cause of climate fluctuations associated with the waxing and tope composition of cap carbonates is expected and the du waning ofthe extensive Neoproterozoic icesheets Many giant ration of anomalies should be short probably equal to or less ooid beds see tabulation in Sumner and Grotzinger 1993 than the residence time of carbon in the oceans or about 105 occur stratigraphically below tillites deposited during glacia years Broecker and Peng 1982 In terms of isotopic com tion Tucker 1983 Herrington and Fairchild 1989 Swett and position it has been noted Kennedy 1996 that the diverse Knoll 1989 or between glacial deposits Singh 1987 In range of values in the global inventory of cap carbonates is either case increased agitation cannot be the sole catalyst for consistent with this upwelling hypothesis In the snowball development of giant ooids because they are absent in similar earth model the carbon isotope composition ofcap carbonates settings of Phanerozoic age including the Neogene icehouse should be stable near riverine and mantle input values of 4 and could be for much 0 maintained continuously longer Molar Tooth Structure a than 105 years Hoffman et I 998a suggest 107 years for Attributes isotopically depleted carbonates of northern Namibia based on inferences of sediment rates Thus far direct accumulation age Lack of body fossils means that any sedimentary features constraints on the duration of carbonates are non in carbonates for any cap Precambrian are inordinately important pa existent and proper calibration is required before any of these leoenvironmental interpretation One such group of annoy hypotheses are rejected ingly enigmatic features is molar tooth structure Molar tooth structure Fig 8B comprises mainly vertical Neoproterozoic Giant Ooids ptygmatically folded sheets of finely crystalline calcite sparin dolomitic or argillaceous lime mudstone Smith 1968 Ooids are one of the basic platform building components O Connor 1972 Horodyski 1976 The calcite spar filling is of both Phanerozoic and Precambrian carbonates For Phan erozoic carbonates variability in their abundance and miner alogy through time has provided insight into changes in en vironmental regimes and ocean chemistry Sandberg 1983 1985 Wilkinson et a 1985 The potential variability in the primary mineralogy of Precambrian ooids has only recently been summarized Simonson and Jarvis 1996 It is also instructive to consider variations in the size of ooids Sumner and Grotzinger 1993 In general modern ooids tend to be less than I mm in diameter Bathurst 1975 This is true of most Phanerozoic oolites although there are exceptions Swett and Knoll 1989 Archean and Proterozoic ooids tend to be slightly larger but are still dominantly less than 2 mm in diameter During early and middle Neoproter ozoic time Fig 4 however there were extreme exceptions to this size limit and significant deposits of 2 mm sized ooids are found in diverse areas Sumner and Grotzinger 1993 For example Fig 7A in the Akademikerbreen Group Spitsbergen 400 m of a 2000 m section are dominated by ooids with 4 0 9 0 mm diameters reaching a maximum size of 14 mm Swett and Knoll 1989 Knoll and Swett 1990 Why were such great volumes of giant ooids formed during Neoproterozoic time and what environmental changes could have generated these deposits Sumner and Grotzinger 1993 concluded that the combi nation of lower nucleation rate imparted by the lower flux of nuclei higher growth rate due to higher carbonate saturation of seawater and increased storminess due to the prevalence of ramps and possibly stormier climate are all suggested to have conspired to produce the giant ooids of the Neoproter ozoic Of these environmental agitation was likely the most important An increase in environmental energy of deposits in late Pro terozoic platforms could have been due to the predominance FIG 8 Giant ooids of Akademikerbreen Svalbard of ramps over rimmed shelves Grotzinger 1989b Unlike Neoproterozoic Group Scale in centimeters Photograph by A H Knoll B Molar tooth structure in rimmed shelves ramps feel the full force of storm events Bur finely crystalline dolostone Neoproterozoic Little Dal Group Mackenzie chette and Sumner and 1993 Wright 1992 Grotzinger sug Mountains northwest Canada Scale in centimeters Photograph by G M Nar gested that the absolute level of Neoproterozoic storminess bonne JOHN P GROTZINGER AND NOEL P JAMES 13 peculiar The crystals are pure uniform equant polygonal In an alternative model based on innovative experimental tightly packed blocky calcite crystals 5 15 mm across and in evidence Furniss et al 1998 visualize the formation of mo sharp contact with surrounding sediment Such crystals are lar tooth structure as a two stage process Biogenic gas gen unusual in carbonate rocks They are neither obvious cement erated by decaying organic matter creates a series of cracks cf Bathurst 1975 a precipitate filling a void nor microspar fissures and bubbles filled with H2S CO2 and CH4 within a cf Folk 1965 a neomorphic product of preexisting carbon meter or so of the depositional surface Experimental evidence ate Fairchild et al 997 report that some crystals contain shows that as the gas generated fissures develop water is a luminescent rhomb shaped core drawn from the sediment promoting compaction The gas Molar tooth structure is globally distributed but temporally cannot escape because the surface is sealed perhaps by mi restricted to rocks mostly of Mesoproterozoic and early Neo crobial mats cf James et aI 1998 Calcite spar probably a proterozoic age Fig 4 James et 1998 Molar tooth struc microbially mediated precipitates in the open voids prior to ture is also facies dependent with most occurrences in shal compaction 13C isotopic data Frank and Lyons 1998 how low platform and inner mid ramp paleoenvironments James ever do not show any difference between the sediment and et aI 1998 More specifically molar tooth structure is a dis the crack filling tinctly subtidal feature Herrington and Fairchild 1989 Knoll Unfortunately all current hypotheses fail to explain the and Swett 1990 Fairchild et aI 1997 and is particularly scarcity of molar tooth structure in older Proterozoic and Ar abundant in the lower parts of shallowing upward cycles chean carbonate rocks The ubiquity of both earthquakes and O Connor 1972 Frank and Lyons 1998 Pratt 1998 Molar microbes ensures that such processes should have been active tooth structure is not usually found in either basinal or peri throughout the geologic history of Precambrian carbonates tidal facies suggesting that as yet unrecognized factors must have been operative Origin

The origin of molar tooth structure has been debated for REEFS more than a century and continues to be highly contentious recent interpretations include subaqueous shrinkage or syn General Attributes aeresis Horodyski 1976 Knoll and Swett 1990 microbial The robust of stromatolites to build reefs that are growth Smith 1968 O Connor 1972 replacement of evap capacity identical in many respects to the diversity of Phanerozoic orites Eby 1975 microbially induced gas bubble expansion reefs et aI 1988 has been addressed in Furniss et aI 1998 and earthquake induced dewatering Geldsetzer previous 1988 data Fairchild et aI 1997 Pratt 1998 The problem resembles studies Grotzinger 1989b 1990 1994 Existing demonstrate that stromatolite a of dif that of stromatactis in Phanerozoic carbonates the struc reefs occupied variety ferent niches similar to their These in tures have no obvious modern counterpart they are composed younger counterparts been clude barrier reefs 9A to large seaways of calcite spar they may have open spaces originally major Fig adjacent 1986b 1989a Beukes 1987 and Gold and while organisms may have been involved physical pro Grotzinger Clough hammer this volume reefs and reefs Fig 9B cesses were clearly important patch pinnacle located on seaways The cracks seem to belong to a of structures that C gentle ramps facing open Grotzinger family a and Khetani 1994 et aI 1995 Narbonne et include synaeresis cracks in terrigenous clastic rocks and di Grotzinger this volume and even bioherms that astasis cracks in earliest Phanerozoic carbonates They are not downslope grew entirely within Aitken 1988 Kerans desiccation cracks Recent thought points to the geotechnical a deeper quieter water setting and Donaldson 1988 Turner et aI 1993 Narbonne and properties of the sediment as playing an important role in the James 1996 Turner et aI this volume development of both diastasis and molar tooth cracks Dias Research over the three decades has established that tasis cracks from Phanerozoic carbonates superficially resem past stromatolite are true reefs sensu James and ble molar tooth but they are clearly voids filled with grains many buildups 1992 Stromatolitic reefs could from from the overlying bed not finely crystalline calcite as in mo Bourque grow deeper water into the shallow zone of contin lar tooth The process of crack formation may involve the quiet settings upwards ual wave to resist and continue in the zone action of waves diastasis Cowan and James 1992 or seis agitation growth wave action and to sizes so as micity molar tooth Fairchild et aI 1997 Pratt 1998 Al of expand laterally significant a to influence their circulation salin ternatively and perhaps most likely Furniss et 1998 pro surroundings by affecting vide compelling experimental evidence to show that ity and sediment production Precambrian reefs commonly show the catch and of biological particularly microbial processes are fundamental up keep up give up phases develop associated with in the genesis of the cracks ment commonly younger Phanerozoic reefs Pratt 1998 envisages the sediment as an original clay lime Construction mud sediment mixture Seismic shaking I compacts the sed Reef iment and generates a of sheet like cracks and variety pockets Stromatolites and 2 segregates the lime mud which is granular in character from the clay and the lime mud is carried into the fissures and Having established that Precambrian stromatolite reefs cracks as a slurry Continued shaking consolidates and shears possess all the properties of true ecologic reefs a first order the host sediment The lime mud in the fissures starts to lithify question remains What serves as the basic frame building almost immediately by grain growth with CaC03 coming constituent For Phanerozoic reefs rigid metazoan skele from seawater tons supercalcifiers of Stanley and Hardie 1999 allow 14 PRECAMBRIAN CARBONATES EVOLUTION OF UNDERSTANDING

tation sediment infiltration and bioerosion James and Bo urque 1992 In this context individual stromatolites can be considered the frame building element of stromatolite reefs Grotzinger 1986b 1988 1989b This interpretation is based on the assumption that because stromatolites may have been produced primarily through the trapping and bind ing and or precipitation inducing activity of benthic micro bial communities they can be regarded as having had the same function as individual metazoans had during the devel opment of Phanerozoic reefs they are directly responsible for the vertical accretion of the structure This view however nec essarily ignores the microscopic aspects of stromatolite growth in particular the specific roles of microorganisms in the accre tionary process This may no longer be justifiable for several reasons In the first case recent studies of sediment mat interactions in both modern and ancient stromatolites underscore the highly vari able role of the organisms themselves in the generation of stro matolitic laminae Grotzinger and Knoll 1999 New data sug gest that in addition to the well established mechanism of trapping and binding Black 1933 Ginsburg and Lowenstam 1958 Gebelein 1974 stromatolites formed in mineralizing systems are dominated by in situ calcification of cyanobacteria Golubic 1991 Cady and Farmer 1996 and by precipitation nucleation triggered by heterotrophic bacteria below the sedi ment water interface Canfield and Raiswell 1991 Chafetz and Buczynski 1992 In extreme cases the microbes behave passively with accretion resulting from largely abiotic precipi tation from highly oversaturated waters Cady and Farmer 1996 Fouke et a 1999 These new studies of modern min eralizing systems provide better analogs for the Precambrian stromatolite textures which represent growth not through pro cesses related to sediment trapping by mats but rather by crys tal precipitation regulated by abiotic processes or mat degra dation by heterotrophic bacteria Grotzinger and Read 1983 Hofmann and Jackson 1987 Kah and Knoll 1996 Grotzinger and Rothman 1996 Sami and James 1996 Bartley et a this volume Pope and Grotzinger this volume Seong Joo and Go lubic this volume Although most stromatolites were likely formed through the precipitation inducing andor trapping and binding activities of a diverse range of microbes it is no longer clear exactly what specific role these microorganisms had inthe construction of stromatolites particularly for early Precambrian stromatolites What is now clear is that the unique influences of biology be best at scales but difficult to FIG 9 Reefs A Prograding barrier reef of accretionary rimmed shelf may expressed microscopic Paleoproterozoic 18 Ga Abner Formation northern Quebec Canada Large distinguish from abiotic processes at macroscopic scales Grot reefal mounds overlie reefal foreslope facies in progradational stacking pattern zinger and Rothman 1996 Grotzinger and Knoll 1999 Future mound in center of is 5 meters wide B Ag Large photograph approximately advances in the study of stromatolite accretion processes are gradational reef about 100 m in height background developed on bedded strongly dependent on the interpretation of the textures that slope ribbon and parted limestones in gorge foreground Mesoproterozoic define individual stromatolitic laminae and thus the true frame 12 Ga Victor Bay Formation Baffin Island Canada C Thrombolitic pin nacle reef developed on platform as part ofdrowning succesion covering deep building processes Grotzinger and Knoll 1999 In the most are on of water shales have been mostly exhumed but still visible right side abiotic cases microbes likely resided at the sediment water in photograph Terminal Proterozoic Nama Group southern Namibia terface and therefore probably exerted some passive control on the accretion process Seong Joo and Golubic this volume on the other hand the most obviously biological textures provide the reef to grow in any environment from tranquil to wave no evidence for the role of obligate calcifiers in the active con dominated settings and thereby influence other environ struction of accretion textures Grotzinger and Khetani 1994 ments A framework results from a combination of the Grotzinger and Knoll 1999 Thus unlike metazoan reefs in intertwining growth by calcified benthic organisms cemen which the biochemistry of enzymatic secretion depends little JOHN P GROTZINGER AND NOEL P JAMES 15 on the local physical environment Precambrian microbial reefs were always critically dependent on the physical environment either through providing a source of sediment to be trapped and bound or in providing a high degree of oversaturation to enable local precipitation

Thrombolites

A second problem in identifying the basic frame building constituent of inferred microbial reefs arises from the occur rence of thrombolites Fig lOA in addition to stromatolites in some Proterozoic reefs Aitken and Narbonne 1989 Kah and Grotzinger 1992 Turner et a 1993 Turner et aI this vol ume Although known from Paleoproterozoic reefs thrombo lites are not important reef building components until Neopro terozoic time Fig 4 For these reefs the basic frame building element is considered to be the thrombolitic mesoclot Kennard and James 1986 Because the growth of the irregular clots imparts a higher degree of irregularity to the actively accreting sediment water interface the final structure contains a greater number of large primary pores as compared to stromatolites The oldest thrombolites appearto derive their distinctive tex ture from early lithification of mats with high surface rough ness probably composed of coccoid cyanobacteria Kah and Grotzinger 1992 Evidence for this is provided by well pre servea fossil Entophysalis mats showing rough surface mor phology in sediments of similar age Golubic and Hofmann 1976 Hofmann 1975 In comparison the high initial porosity ofNeoproterozoic thrombolites also is likelyrelated to the early lithification of coccoid dominated mats however the complex ity and surface roughness of the mats may also have been in creased through the additional presence of green algae Feld mann and McKenzie 1998 Grotzinger and Knoll 1999 This is supported by the presence of algae in rocks of this age Fig 4 Butterfield et aI 1988 Grant et a 1991 Xiao et a 1998

Calcified Microbes The other important development in later Precambrian time is the calcification of microbial filaments of many different types calcimicrobes James and Gravestock 1990 Although the taxonomic and phylogenetic affinities are ambiguous and many are products of diagenesis morphologically they resem ble Fig lOB early Phanerozoic taxa such as Girvanella and 101 Renalcis Turner et aI 1993 These taxa are recognized as critical elements of early and middle Paleozoic reefs James and Bourque 1992 These calcimicrobes because oftheir var ied architecture sometimes resulted in porous reef highly FIG 1O Biolic elements of Neoprolerozoic reefs A Outcrop photograph frameworks in became sites for Cavities produced this way of thrombolitic mesoc1ots dark forming framestone within pinnacle reef of growth of cavity dwelling biotas cement precipitation and in Figure 9C Primary pore space is infilled by geopetal lime mudstone light Coin is ternal geopetal sediment accumulation gray and void filling marine cement and blocky spar white 2 5 cm in diameter B Filamentous calcimicrobes preserved as tubules and threads Neoproterozoic Little Dal reefs Canada Interstitial porosity is filled with fi Evolution the of ReefArchetype brous calcite cement Scale bar 500 microns C Calcified metazoan fossils associated with thrombolitic reefal facies terminal Proterozoic Nama Group there a secular in the nature of Predictably just as is change Namibia sedimentary facies so there is a parallel change in the nature of Precambrian reefs Grotzinger 1989b Paleoproterozoic buildups are constructed by cement rich stromatolites in tegrated into platforms and ramps as biostromes because abi which the influence of synsedimentary carbonate precipitation otic precipitation is so extensive and widespread exceeds that of microbes There is little variability in stromat Mesoproterozoic reefs record a long period of stasis with olite form mostly hemispherical columnar laminated and stromatolites broadly similar to older growth forms They are conical types Isolated buildups are notabundant most are in however more muddy and display increasing diversity in 16 PRECAMBRIAN CARBONATES EVOLUTION OF UNDERSTANDING

stromatolite form It appears that the role of synsedimentary Late Archean and Paleoproterozoic carbonate deposition abiotic precipitation and microbial influence were roughly formed mostly rimmed platforms in which a large proportion equal in importance Knoll and Semikhatov 1998 Increased of the carbonate was precipitated directly onto the seafloor as stromatolite diversity relates more to environmental than bio aragonite fans microdigitate stromatolites and beds of mag logic evolution Grotzinger and KnoIl 1999 nesian calcite The decreasing abundance of such precipitates The Neoproterozoic 1 00 54 Ga was a period of dramatic with time through the Paleoproterozoic suggests gradual deple global change The appearance of calcimicrobes and thrombo tion of the highly oversaturated Archean seawater The sedi lites in the Tonian 1 00 85 Ga coincides with the decline of ments are otherwise grainy reefs are composed of cement rich conical elements and decline in stromatolites It seems that the stromatolites and even though glaciation occurred there are role of microbes became more important than that of synsedi surprisingly no cap carbonates mentary cement in overaIl reef structure at this time In deep The Mesoproterozoic long regarded as a time of stasis was water buildups their activities led to rapid upward accretion and a period in which ramps as well as rimmed platforms are seen the formation of growth cavities containing both internal geo in the record Seafloor cement precipitation was greatly dimin petal sediment and synsedimentary cement The importance of ished except in platforms where contemporaneous evaporites calcimicrobes appears to be less in shaIlow water reefs where were deposited and stromatolites show greater textural diver they are mostly spar fiIled filament molds sity than in older rocks The platforms are somewhat muddier The first calcified metazoans appear in thrombolite reefs to and molar tooth calcite is a significant part ofthe sediment with ward the end of Neoproterozoic post glacial Vendian time Fig spar clasts 10caIly forming carbonate sands 4 further adding to their ecologic complexity Grotzinger and The Neoproterozoic is a period of dramatic changes in global Khetani 1994 Grotzinger et aI 1995 Calcified fossils are tectonics oceanography and sedimentation Carbonate plat abundant in thombolitic facies of the Nama Group Namibia forms are mostly ramps there is vanishingly little seafloor ce and occur within both clotted domal and columnar structures ment precipitation sediments are commonly muddy molar that make up individual reefs as weIl as within the intrachannel tooth carbonate is abundant and shoals formed of giant ooids fiIl between domes and columns This fiIl consists of trough are 10caIly important Although stromatolites still formed reefs cross bedded skeletal packstone and grainstone of simple tubes the appearance of thrombolites and calcified microbes in abun more complex cups and goblets Cloudina and their bioclastic dance dramatically altered their internal structure creating void detritus Fig 1OC The thrombolitic cores of domes and col spaces that enabled both rapid vertical accretion and provided umns contain fossils and fossil fragments up to 1 centimeter internal spaces for cement precipitation sediment accumula wide whereas the stromatolitic rinds of domes and columns tion and the growth of coelobites Cap carbonates occur di contain millimeter scale fossils and fragments The thromboli rectly above glacigene sediments and although their structure tic reefal facies are considered to have developed within unre is reminiscent of Archean carbonates dominated by seafloor stricted shaIlow subtidal environments that during platform precipitation they contain their own distinctive facies motifs drowning developed pinnacle geometries Fig 9C In this en We have only just begun to appreciate the holdings in this vironmental context the development of the Nama thrombolite vast repository of information about the young earth and it is calcified fossil facies is analogous to younger Cambrian reefal clear that many unresolved problems still exist The most im facies dominated by thrombolites and other microbialites with portant of these problems such as the role of microbes in in associated calcified higher organisms Soja 1994 Kruse et aI fluencing precipitation mechanisms and sediment textures 1995 Riding and Zhuravlev 1995 must be approached carefully with regard to the potential role of modern analogs based on thermal springs and alkaline lakes rather than marine In other cases there be no SUMMARY AND CONCLUSIONS systems may suitable modern analog and research must utilize a non actu The last decade has seen a surge in research on Precambrian alistic approach letting the rocks dictate the conditions for anal carbonate rocks These studies have been driven the reali by ysis Only in this way will we be able to identify processes that zation that Precambrian and many platforms ramps despite may have changed overtime or even have been unique in the their antiquity are composed of beautifuIly preserved sedimen history of carbonate sedimentation tary rocks The most important advances have been achieved by searching out these exceptionaIly well preserved localities ACKNOWLEDGMENTS documenting them in detail and applying new geochemical techniques to resolve problems of stratigraphy composition This work was supported by NSF Grant EAR 9628257 and and paleoceanography NASA Astrobiology Institute grant NCC2 l053 to JPG and Precambrian platforms and ramps are strikingly similar to NSERC grant 2028 99 to NPJ A KnoIl and G Narbonne re Phanerozoic structures with similar facies belts bothparticulate viewed the manuscript and provided numerous helpful and muddy sediment ooids reefs seafloor cement precipita comments tion and recurring patterns of stratigraphic packaging Yet set this most against uniformitarian background perhaps the im REFERENCES portant advance in the last decade has been the realization that J 1988 Giant reefs middle Proterozoic Little different periods of the Precambrian have discrete carbonate AITKEN D algal upper Dal Group 770 1200 Ma Mackenzie Mountains N W T Canada in Just as and depositional systems Cambrian Cretaceous carbon Geldsetzer H James N P and Tebbutt G eds ReefsCanada and Ad ates are different so and Neo distinctively Paleoproterozoic jacent Areas Canadian Society of Petroleum Geologists Memoir 13 p 13 proterozoic carbonates are quite dissimilar 23 JOHN P GROTZINGER AND NOEL P JAMES 17

stomatolite reefs AITKEN J D AND NARBONNE G M 1989 Two occurrences drPrecambrian M P AND CAMPBELL FH A 1978 Regressive thrombolites from the Mackenzie Mountains Northwestern Canada Palaios and associated facies middle Goulburn Group lower Proterozoic in Ki Basin N W T of environmental control of stromatolite v 4 p 384388 lohigok an example Bulletin v 26 237 ARTHUR M A 1979 Paleoceanographic events recognition resolution and form Canadian Society of Petroleum Geologists p reconsideration Review of Geophysics and Space Physics v 17 p 1474 267 lithification 1494 CHAFETZ H S AND BUCZYNSKI c 1992 Bacterially induced BATHURST R G c 1975 Carbonate Sediments and Their Diagenesis Am of microbial mats Palaios v 7 p 277 293 sterdam Elsevier 658 p CHAFETZ H S AND FOLK R L 1984 Travertines depositional morphology BENSEN J 1994 Carbonate deposition Pyramid Lake subbasin Nevada I and the bacterially constructed constituents Journal of Sedimentary Petrol Sequence of formation and elevational distribution of carbonate deposits ogy v 54 p 289 316 tufas Palaeogeography Palaeoclimatology Palaeoecology v 109 p 55 CHRISTIE BLICK N GROTZINGER J P AND VON DER BORCH C c 1988 87 Sequence stratigraphy in Proterozoic successions Geology v 16 p 100 BERNER R A 1975 The role of magnesium in the crystal growth of calcite 104 and aragonite from sea water Geochimica et Cosmochimica Acta v 39 p CLOUD PE WRIGHT L A WILLIAMS E G DIEHL P AND WALTER M 489 504 R 1974 Giant stromatolites and associated vertical lubes from the upper BERTRAND SARFATI J AND MOUSSINE POUCHKINE A 1983 Platform to Proterozoic Noonday Dolomite Death Valley Region eastern California Proterozoic Vendian Gourma basin facies evolution the carbonates of late Geological Society of America Bulletin v 85 p 1869 1882 v 53 275 293 west Africa Journal of Sedimentary Petrology p CONWAY MORRIS S MATTES B W AND MENGE c 1990 The early skel siliciclastic to carbonate sedimentation BEUKES N J 1977 Transition from etal organism Cloudina new occurrences from Oman and possibly China near the base of the Transvaal Supergroup northern Cape Province South American Journal of Science v 290 A 245 260 v 18 201 221 Africa Sedimentary Geology p COWAN C A AND JAMES N P 1992 Diastasis cracks mechanically gen en litofasies van die BEUKES N J 1980 Stratigrafie Campbellrand subgrop erated synaeresis like cracks in Upper Cambrian shallow water oolitic and noord of vandie Proterofitiese Ghaap groep Kaapland Geological Society ribbon carbonates Sedimentology v 39 p 1101 1118 Africa Transactions v 83 141 170 South p DEMICCO R V 1983 Wavy and lenticular bedded carbonate ribbon rocks of BEUKES N J 1987 Facies relations environments and depositional diagen the upper Cambrian Conococheague Limestone central Appalachians Jour esis in a Proterozoic stromatolitic carbonate to basinal major early platform nal of Sedimentary Petrology v 53 p 1121 1132 Transvaal southern Africa sequence Campbellrand Subgroup Supergroup DEUSER W c 1970 Carbon I 3 in Black Seawaters and implications for the Geology v 54 146 Sedimentary p origin of hydrogen sulfide Science v 268 p 1575 1577 N J KLEIN c 1993 Models for iron formation in BEUKES AND deposition EBY D E 1975 Carbonate sedimentation under elevated salinities and im

J W and Klein c eds The Proterozoic Cambridge car Schopf Biosphere plications for the origin of molar tooth structure in the middle Belt UK Press 147 151 Cambridge University p bonate interval late Precambrian northwestern Montana abstract Geo Bahamas So BLACK M 1933 The sediments of Andros Island Royal v algal logical Society of America Abstracts With Program 7 p 1063 London Transactions Series B v 222 165 192 ciety Philosophical FAIRCHILD I J 1991 Origins of carbonate in Neoproterozoic stromatolites BOND G c KOMINZ M A STECKLER M S AND GROTZINGER J P 1989 and the identification of modem analogues Precambrian Research v 53 p Role of thermal subsidence flexure and in the evolution of eustasy early 281 299 Paleozoic carbonate platforms in Crevello P D Wilson J passive margin FAIRCHILD I J 1993 Balmy shores and icy wastes the paradox of carbonates L J F and Read J F eds Controls on Carbonate Platform and Sarg associatedwith glacial deposits in Neoproterozoic times Sedimentology Re Basin Development SEPM Special Publication 44 p 3961 view v I p 1 15 BRASIER M GREEN 0 AND SHIELDS G 1997 Ediacaran sponge spicule FAIRCHILD I J EINSELE G AND SONG T 1997 Possible seismic origin of clusters from southwestern Mongolia and the origins of the Cambrian fauna molar tooth structures in Neoproterozoic carbonate ramp deposits north Geology v 25 303 306 China Sedimentology v 44 p 611636 BRASIER M D ANDERSON MM AND CORFIELD R M 1992 Oxygen and FAIRCHILD I J HAMBREY M J JEFFERSON T H AND SPIRO B 1989 carbon isotope stratigraphy of early Cambrian carbonates in southeastern Proterozoic carbonates in NE new into the v Late glacial Spitsbergen insights Newfoundland and England Geological Magazine 129 265 297 carbonate tillite association Geological Magazine v 126 p 469490 BROECKER W S AND PENG T H 1982 Tracers in the Sea Palisades New FAIRCHILD I J MARSHALL J D AND BERTRAND SARFATI J 1990 Strati York Lamont Doherty Geological Observatory 690 p shifts in carbon from Proterozoic stromatolitic carbonates BUICK R DES MARAIS D J AND KNOLL AH 1995 Stable isotopic com graphic isotopes Mauritania influence of primary mineralogy and diagenesis American positions of carbonates from the Mesoproterozoic Bangemall Group north Journal of Science v 290 A p 4679 western Australia Chemical Geology v 123 153 171 FAIRCHILD I J AND SPIRO B 1987 Petrological and isotopic implications BUICK R AND DUNLOP JS R 1987 Early Archean evaporitic sediments of some Late Precambrian carbonates NE Sedi from the Warrawoona Group North Pole Western Australia abstract Geo contrasting Spitsbergen v 34 973 989 v mentology p logical Society of America Abstracts with Program 19 p 604 FELDMANN M AND McKENZIE J 1998 Stromatolite thrombolite associa BUICK R AND DUNLOP JS R 1990 Evaporitic sediments of early Archean tions in a modern environment Lee Stocking Island Bahamas Palaios v age from the Warrawoona Group North Pole Western Australia Sedimen 13 p 201 212 tology v 37 p 247 278 FOLK R L 1965 Some of recrystallization in ancient limestones In BURCHETTE T P AND WRIGHT V P 1992 Carbonate ramp depositional aspects Dolomitization and Limestone ill Lc and R C systems Sedimentary Geology v 79 p 3 57 Diagenesis Pray Murray eds of Economic and p 1448 BURDETT J W GROTZINGER JP AND ARTHUR M A 1990 Did major Society Paleontologists Mineralogists FOUKE B w FARMER J D DES MARAIS D J PRATT L STURCHIO N changes in the stable isotope composition of Proterozoic seawater occur c BURNS P c AND DISCIPULO M K 2000 facies and Geology v 18 p 227 230 Depositional solid of travertine hot Ter BURNS SJ AND MATTER A 1993 Carbon isotope record of the latest aqueous geochemistry depositing springs Angel Mammoth Hot Yellowstone National Park U S A Journal Proterozoic from Oman Eclogae Geologicae Helvetiae v 86 p 595607 race Springs of Research in BUTfERFIELD N J KNOLL A H AND SWETT K 1988 Exceptional pres Sedimentary press FRANK T D AND LYONS T W 1998 Molar tooth structures a ervation of fossils in an Upper Proterozoic shale Nature v 334 p 424 geochem v 427 ical perspective on a Proterozoic enigma Geology 26 p 683 686 D LYONS T W c L K 1997 evidence for the CADY S L AND FARMER J 1996 Fossilization processes in siliceous FRANK T AND tsotopic D evolution of the Helena Formation thermal springs trends in preservation along thermal gradients in Walter paleoenvironmental Mesoproterozoic USA Geochimica et Cosmochimica Acta v 61 M R ed Evolution of Hydrothermal Ecosystems on Earth and Mars Belt Supergroup Montana 5023 5041 Chichester U K Wiley p 150 173 p 1998 Gas bubble and CANFIELD D E AND RAISWELL R 1991 Carbonate precipitation and dis FURNISS G RITTEL J F AND WINSTON D expansion Middle Proterozoic solution its relevance to fossil preservation in Allison P A and Briggs crack origin of molar tooth calcite structures in the D E ed Taphonomy Releasing the Data Locked in the Fossil Record Belt Supergroup Western Montana Journal of Sedimentary Research v 68 104 114 New York Plenum Press p 411453 CECILEp 18 PRECAMBRIAN CARBONATES EVOLUTION OF UNDERSTANDING

GEBELEIN C D 1974 control of stromatolite microstructure Biologic impli HARLAND W B 1965 Critical evidence fora great Infra Cambrian glaciation cations for Precambrian time American of v stratigraphy Journal Science Geologische Rundschau v 54 p 4561 274 p 575 598 HEGENBERGER W 1993 Stratigraphy and sedimentology of theLate Precam GELDSETZER HH J JAMES N P AND TEBBUTf G E 1988 Reefs brian Witvlei and Nama Groups east of Windhoek Geological Survey of Canada and Adjacent Areas Canadian Society of Petroleum Geologists Namibia Memoir 17 82 p Memoir 13 775 p HERRINGTON P M AND FAIRCHILD 1 J 1989 Carbonate shelf and slope GINSBURG R N AND LOWENSTAM HA 1958 The influence of marine facies evolution prior to Vendian glaciation central East Greenland in bottom communities on the depositional environment of sediments Journal Gayer R ed The Caledonide Geology of Scandinavia London Graham v of Geology 66 p 310318 Trotman p 263 273 GOLUBIC S 1991 Modern stromatolites a review in Riding R ed Cal HOFFMAN P F 1974 Shallow and deep water stromatolites in lower Prote careous Algae and Stromatolites Heidelberg Springer Verlag p 541 561 rozoic platform to basin facies change Great Slave Lake Canada American GOLUBIC S HOFMANN AND H J 1976 Comparison of modern and mid Association of Petroleum Geologists Bulletin v 58 p 856867 Precambrian Entophysalidaceae Cyanophyta in stromatolitic algal mats HOFFMAN P F KAUFMAN A J HALVERSON G P AND SCHRAG D P cell division and of degradation Journal Paleontology v 50 p 1074 1082 1998a A Neoproterozoic snowball earth Science v 281 p 1342 1346 GRANT S WF KNOLL AH AND GERMS G J B 1991 Probable calcified HOFFMAN P F KAUFMAN A J AND HALVERSON G P 1998b Comings metaphytes in the latest Proterozoic Nama Group Namibia Journal of Pa and goings of global glaciation on a Neoproterozoic tropical platform in leontology v 65 p 1 18 Namibia GSA Today v 8 no 5 p 1 9 GREY K AND THORNE A M 1985 Biostratigraphic significance of stro HOFMANN H J 1975 Stratiform Precambrian stromatolites Belcher Islands matolites in upward shallowing sequences of the early Proterozoic Duck Canada relations between silicified microfossils and microstructure Amer Creek Dolomite Western Australia Precambrian Research v 29 p 183 ican Journal of Science v 275 p 1121 1132 206 HOFMANN H J 1985 The mid Proterozoic Little Dal macrobiota Mackenzie

GROTZINGER J P 1986a Cyclicity and paleoenvironmental dynamics Rock Mountains north west Canada Paleontology v 28 p 331 354 nest platform northwest Canada Geological Society of America Bulletin HOFMANN H J AND JACKSON GD 1987 Proterozoic ministromatolites v with radial fibrous fabric v 97 p 1208 1231 Sedimentology 34 p 963 971 GROTZtNGER J P 1986b Evolution of early Proterozoic passive margin car HOLSER W T 1984 Gradual and abrupt shifts in ocean chemistry during bonate platform Rocknest Formation Wopmay Orogen NWT Canada Phanerozoic time in Holland HD and Trendall A F eds Berlin 123 143 Journal of Sedimentary Petrology v 56 p 831 847 Springer Verlag p GROTZINGER J P 1988 Introduction to Precambrian reefs in Geldsetzer H HORODYSKI R J 1976 Stromatolites of the upper Siyeh Limestone Middle James N P and Tebbutt G eds Reefs Canada and Adjacent Areas Proterozoic Belt Supergroup Glacier National Park Montana Precambrian Canadian of Research v 3 517 536 Society Petroleum Geologists Memoir 13 p 9 12 p HsO K J MCKENZIE 1985 GROTZINGER J P 1989a Construction of early Proterozoic 1 9 Ga barrier AND J A A Strangelove ocean in theearliest reef complex Rocknest platform Northwest Territories in Geldsetzer H Tertiary in Sundquist E T and Broecker W S eds The Carbon Cycle and CO Natural Variations Archean to Present American James N P and Tebbutt G eds ReefsCanada and Adjacent Areas Atmospheric Union 32 487492 Canadian Society of Petroleum Geologists Memoir 13 p 3037 Geophysical Geophysical Monograph p JACKSON GD AND IANELLI T R 1981 Rift related sedimentation GROTZINGER J P 1989b Facies and evolution of Precambrian carbonate dep cyclic in the Neohelikian Borden Basin northern Baffin Island in FH ositional systems emergence ofthe modern platform archetype in Crevello Campbell A ed Proterozoic Basins of Canada of Canada P D Wilson J L Sarg J F and Read J F eds Controls on Carbonate Geological Survey Paper 81 10 269 302 Platform and Basin Development SEPM Special Publication 44 p 79 106 p GROTZINGER J P 1990 Geochemical model for Proterozoic stromatolite de JAMES N P AND BOURQUE P A 1992 Reefs and mounds in Walker R G and James N P eds Facies Models to Sea Level cline American Journal of Science v 290 A p 80103 Response Change Association of Canada 323 348 GROTZINGER J P 1993 New views of old carbonate sediments Geotimes v Geological p JAMES N P AND GRAVESTOCK D 1990 Lower Cambrian shelf and shelf 38 p 12 15 Flinders GROTZINGER J P 1994 Trends in Precambrian carbonate sediments and their margin buildups Ranges South Australia Sedimentology v 37 p 455480 implication for understanding evolution in Bengtson S ed Early Life on JAMES N P NARBONNE G M AND SHERMAN A G 1998 Molar tooth Earth New York Columbia University Press Nobel Symposium No 84 p carbonates shallow subtidal facies of the Mid to Late Proterozoic Journal 245 258 of Research v 68 716722 GROTZINGER J P BOWRING BZ SAYLOR BZ AND KAUFMAN A J Sedimentary p JONES B AND RENAUT R 1995 calcite dendrites from 1995 Biostratigraphic and geochronologic constraints on early animal evo Noncrystallographic hot spring deposits at Lake Journal of Re lution Science v 270 p 598604 Bogoria Kenya Sedimentary search v A65 154 169 GROTZINGER J P AND FRIEDMANN JS 1989 Occurrence of thick crusts p KAH L C AND GROTZINGER J P 1992 Proterozoic 19 Ga throm of former Rifle and Formations 197 Ga Early botryoidal aragonite Beechey bolites of the Rocknest Formation Northwest Territories Canada Palaios Kilohigok Basin N W T abstract Geological Association of Canada v 7 p 305 315 Program with Abstracts v 14 p A77 KAH Lc AND KNOLL A H 1996 Microbenthic distribution of Proterozoic GROTZINGER J P AND KASTING J F 1993 New constraints on Precambrian tidal flats environmental and taphonomic considerations Geology v 24 p ocean Journal of v 101 235 243 composition Geology p 79 82 GROTZINGER J P AND KHETANI A 1994 Facies and diagenesis of late KARHU J A 1993 Paleoproterozoic evolution of the carbon isotope ratios of Vendian thrombolite shelly Cloudina invertebrate reefs Nama pinnacle sedimentary carbonates in the Fennoscandian Shield Geological Survey of Group Namibia abstract Geological Society of America Northeast Sec Finland Bulletin 371 87 p tion Abstracts with Program p 56 KASTING J F 1987 Theoretical constraints on oxygen and carbon dioxide GROTZINGER J P AND KNOLL AH 1995 Anomalous carbonate precipi concentrations in the Precambrian atmosphere Precambrian Research v 34 tates Is the Precambrian the to thePermian Palaios v 10 p 578 596 key p 205 229 GROTZINGER J P AND KNOLL AH 1999 Stromatolites in Precambrian KAUFMAN A J HAYES J M KNOLL A H AND GERMS G J B 1991 carbonates or Environmental Annual Evolutionary Mileposts Dipsticks Isotopic compositions of carbonates and organic carbon from upper Prote Review of Earth and Science v 27 313 358 Planetary p rozoic successions in Namibia stratigraphic variation and theeffects of dia GROTZINGER J P AND READ J F 1983 Evidence for primary aragonite genesis and metamorphism Precambrian Research v 49 p 301 327 lower Proterozoic 19 Ga dolomite north precipitation Wopmay orogen KAUFMAN A J JACOBSEN S B AND KNOLL AH 1993 The Vendian v west Canada Geology II p 710713 record of Sr and C isotopic variations in seawater Implications for tectonics GROTZINGER J P AND ROTHMAN D R 1996 An abiotic model for stro and paleoclimate Earth and Planetary Science Letters v 120 p 409430 matolite morphogenesis Nature v 383 p 423425 KAUFMAN A J AND KNOLL AH 1995 Neoproterozoic variations in the GROTZINGER J P SUMNER DY AND BEUKES N J 1993 Archean car C isotope composition of seawater stratigraphic and biogeochemical impli bonate sedimentation in an active extensional basin Belingwe Greenstone cations Precambrian Research v 73 p 27 50 Belt Zimbabwe abstract Geological Society of America Abstracts with KEMPE S AND DEGENS ET 1985 An early sodaocean ChemicalGeology Program p A64 v 53 p 95 108 JOHN P GROTZINGER AND NOEL P JAMES 19

1972 Classification and environmental of the KEMPE S AND KAZMIERCZAK J 1994 The role of alkalinity in theevolution O CONNOR M P interpretation molar tooth structure of the Precambrian of ocean chemistry organization of living systems and biocalcification pro cryptalgal organosedimentary Belt Purcell Journal of v 80 592610 cesses in Doumenge F Allemand D and Toulemont A eds Past and Supergroup Geology p Present Biomineralization Processes Considerations about the carbonate cy PELECHATY S M GROTZINGER J P KASHIRTSEV VA AND JERINOVSKY V P 1996a and constraints on cle Institut Oceanographique Monaco p 61 116 Chemostratigraphic sequence stratigraphic stromatolites Two VendianCambrian basin northeast Siberian craton Journal of KENNARD J M AND JAMES N P 1986 Thrombolites and dynamics v 104 543 564 distinct types of microbial structures Palaios v I p 492 503 Geology p middle Proterozoic KENNEDY M J 1996 Stratigraphy sedimentology and isotopic geochemistry PELECHATY S M AND JAMES N P 1991 Dolomitized Ol3C excursions and calcretes Bathurst Inlet Northwest Territories Canada Journal of Sedimen of Australian postglacial cap dolostones deglaciations carbonate precipitation Journal of Sedimentary Research v 66 p 1050 tary Petrology v 6 I p 988 100 I c GROTZINGER J P 1991 1064 PELECHATY S M JAMES N P KERANS AND and associated rocks Elu KENNEDY M J RUNNEGAR B PRAVE AR HOFFMANN K H AND AR A middle Proterozoic paleokarst unconformity v Basin northwest Canada v 38 775 797 THUR M A 1998 Two or four Neoproterozoic glaciations Geology Sedimentology p PELECHATY S M KAUFMAN A J AND GROTZINGER J P 1996b Evalua 26 p 1059 1063 ol3C for intrabasinal correlation Vendian strata KERANS C 1982 Sedimentology and Stratigraphy of the Dismal Lakes tion of isotope stratigraphy Olenek and Kharaulakh Mountains Siberian Russia Group Ph D Dissertation Carleton University Ottawa 304 p of the uplift platform stromatolite of America Bulletin v 108 992 1003 KERANS C AND DONALDSON J A 1988 Deeper waterconical Geological Society p R J F 1993 Edi reef Sulky Formation middle Proterozoic N W T in Geldsetzer H PELL S D McKIRDY D M JANSYN J AND JENKINS of South Australia of James N P and Tebbutt G eds ReefsCanada and Adjacent Areas acaran carbon isotope stratigraphy Royal Society v 117 153 161 Canadian Society of Petroleum Geologists Memoir 13 p 81 88 South Australia Transactions p KIRSCHVINK J L 1992 Late Proterozoic low latitude global glaciation the PERYT T M HOPPE A BECHSTADT T KOSTER J PIERRE c AND RICH Bambui snowball earth in Schopf J W and Klein c eds The Proterozoic Bio TER DK 1990 Late Proterozoic aragonite cement crusts Group 569 581 Minas Gerais Brazil v 37 279 286 sphere Cambridge UK Cambridge University Press p Sedimentology p in Proterozoic carbonate rocks or KNOLL A H 1991 End of the Proterozoic Eon Scientific American v 265 PRATT B R 1998 Molar tooth structure from and for the nature and p 6473 igin synsedimentary earthquakes implications marine sediment of America KNOLL AH FAIRCHILD 1 J AND SWETT K 1993 Calcified microbes in evolution of basins and Geological Society Bulletin v 110 1028 1045 Neoproterozoic carbonates Implications for our understanding of the Pro p N P AND COWAN C A 1992 Peritidal carbonates in terozoic Cambrian transition Palaios v 8 p 512 525 PRATT BR JAMES to Level KNOLL AH GROTZINGER J P KAUFMAN A J AND KOLOSOV P 1995a Walker R G and James N P eds Facies Models Response Sea from Association of Canada 303 322 Integrated approaches to terminal Proterozoic stratigraphy an example Change Geological p in theOlenek uplift northeastern Siberia Precambrian Research v 73 p 251 RIDING R 1982 Cyanophyte calcification and changes ocean chemistry 270 Nature v 299 p 814815 KNOLL AH HAYES J M KAUFMAN A J SWETT K AND LAMBERT 1 RIDING R AND ZHURAVLEV A Y 995 Structure and diversity of oldest v B 1986 Secular variation in carbon isotope ratios from Upper Proterozoic sponge microbe reefs Lower Cambrian Aidan River Siberia Geology successions of Svalbard and East Greenland Nature v 321 p 832 838 23 p 649652 of an Proterozoic foreland KNOLL A H KAUFMAN A J AND SEMIKHATOV M A 1995b The carbon SAMI TT AND JAMES N P 1993 Evolution early Slave Lake northwest isotope composition of Proterozoic carbonates Riphean successions from basin carbonate platform lower Pethei Group Great northwestern Siberia Anabar massif Turukhansk uplift American Journal Canada Sedimentology v 40 p 403430 SAMI TT AND JAMES N P 1994 Perilidal and of Science v 295 p 823 850 platform growth cyclicity in Proterozoic foreland basin Pethei northwest Can KNOLL AH AND SEMIKHATOV M A 1998 The genesis and time distri an early upper Group ada Journal of Research v B64 111 131 bution of two distinctive Proterozoic stromatolite microstructures Palaios Sedimentary p SAMI T T AND JAMES N P 1996 cements as v 13 p 408422 Synsedimentary platform Pethei northwesternCanada Jour KNOLL AH AND SWETT K 1990 Carbonate deposition during the later building blocks Paleoproterozoic Group Research v 66 209 222 Proterozoic Era an example form Spitsbergen American Journal of Science nal of Sedimentary p SANDBERG P A 1983 An trend in Phanerozoic non skeletal car v 290 A p 104132 oscillating Nature v 305 19 22 KNOLL AH AND WALTER M R 1992 Latest Proterozoic stratigraphy and bonate mineralogy P 1985 Nonskeletal and in the Phanerozoic Earth history Nature v 356 p 673 678 SANDBERG A aragonite pC02 Carbon KRUSE P D ZHURAVLEV A Y AND JAMES N P 1995 Primordial meta and Proterozoic in Sundquist E T and Broecker W S eds The Siberian Plat and Natural Variations Archean to Present Amer zoancalcimicrobial reefs Tommotian early Cambrian of the Cycle Atmospheric CO2 ican Union 32 585 594 form Pa aios v 10 p 291 321 Geophysical Geophysical Monograph p J P GERMS G J B 1995 LI T H TAKAHASHI T AND BROECKER W S 1969 The degree of satu SAYLOR BZ GROTZINGER AND Sequence v of the Kuibis and Schwa ration of CaCO in the oceans Journal of Geophysical Research 74 p stratigraphy and sedimentology Neoproterozoic Precambrian Re 5507 5525 rzrand Subgroups Nama Group Southwest Namibia MARTIN A NISBET E G AND BICKLE M J 1980 Archean stromatolites search v 73 p 153 171 URBAN F 1998 A of the Belingwe Greenstone Belt Zimbabwe Rhodesia Precambrian Re SAYLOR B Z KAUFMAN A J GROTZINGER J P AND reference section for terminal Proterozoic strata of southern Na search v 13 p 337 362 composite of Research v 66 1178 1195 MATTES B W AND CONWAY MORRIS S 1990 Carbonate evaporite depo mibia Journal Sedimentary p G 1974 Late Precambrian mixtites Glacial andor sition in the Late Precambrian Early Cambrian Ara Formation of southern SCHERMERHORN L J Oman in Robertson AH F Searle M P and Ries A c eds The nonglacial American Journal of Science v 274 p 673 824 M 1988 A 3 8oo million record of life from Geology and Tectonics of the Oman Region Geological Society of London SCHIDLOWSKI year isotopic carbon in rocks Nature v 333 313 318 Special Publication p 617636 sedimentary p Sr into SEREBRYAKOV S N AND SEMIKHATOV M A 1974 and Recent MUCCI A AND MORSE J W 1983 The incorporation of Mg and Riphean American Journal of Science v 274 556 calcite overgrowths Influences of growth rate and solution composition stromatolites a comparison p Geochimica et Cosmochimica Acta v 47 p 217 233 574 MUIR M D 1987 Facies models for Australian Precambrian evaporites in SERGEEV VN KNOLL A H AND GROTZINGER JP 1995 Paleobiology Anabar northern Siberia Peryt T ed Evaporite Basins Heidelberg Springer Verlag p 5 21 of the Mesoproterozoic Billyakh Group Uplift waterreefs Journal of to No I v 69 1 37 NARBONNE G M AND JAMES N P 1996 Mesoproterozoic deep Paleontology Supplement p 1996 Microfabrics of oolites and from the Borden Penninsula Arctic Canada Sedimentology v 43 p 827 SIMONSON B M AND JARVIS DG pi 848 solites in the 2 5 Ga Carawine Dolomite of western Australia in Rezak R Carbonate Microfabrics Berlin 45 NARBONNE G M KAUFMAN A J AND KNOLL AH 1994 Integrated and Lavoie D eds Springer Verlag p chemostratigraphy and biostratigraphy of the upper Windemere Supergroup 67 1993 Carbonate Neoproterozoic northwestern Canada Implications for Neoproterozoic SIMONSON B M SCHUBEL KA AND HASSLER S W of correlations and the early evolution of animals Geological Society of Amer sedimentology of the early Precambrian Hamersley Group Western Aus tralia Precambrian Research v 60 287 335 ica Bulletin v 106 p 1281 1292 p 20 PRECAMBRIAN CARBONATES EVOLUTION OF UNDERSTANDING

SINGH U 1987 Ooids and cements from the late Precambrian of the Flinders TUCKER M E 1986 Formerly aragonitic limestones associated with tillites South Australia Journal of v 57 Ranges Sedimentary Petrology p 117 in the late Proterozoic of Death Valley California Journal of Sedimentary 127 Petrology v 56 p 818 830 SMITH AG 1968 The and deformation of molar tooth struc origin some TURNER EC JAMES N P AND NARBONNE G M 1997 Growth dynamics tures in the Precambrian Belt Purcell Supergroup Journal of Geology v of Neoproterozoic calcimicrobial reefs Mackenzie Mountains northwest 76 p 426443 Canada Journal of Sedimentary Petrology v 67 p 437450 SMtTH O A 1998 Terminal Proterozoic Carbonate Platform Development TURNER E c NARBONNE G M AND JAMES N P 1993 Neoproterozoic and of the Kuibis ca 550548 Ma Stratigraphy Sedimentology Subgroup reef microstructures from the Little Dal Group northwestern Canada Ge Northern Nama Basin Namibia MSc Thesis Massachusetts Institute of ology v 3 p 259 262 Technology Cambridge Massachusetts 132 p VEIZER J AND COMPSTON W 1976 7Sr16Sr in Precambrian carbonates as SOJA C 1994 M of Silurian stromatolite reefs an Significance sphinctozoan index of crustal evolution Geochimica et Cosmochimica Acta v 40 p v 22 355 358 Geology p 905 914 SOUTHGATE P N 1989 Relationships between and stromatolite form 1 cyclicity VEIZER J AND HOEFS J 1976 The nature of 0 160 and I3C I2C secular in the late Proterozoic Bitter Springs Formation Australia Sedimentology trends in sedimentary carbonate rocks Geochimica et Cosmochimica Acta v 36 p 323 339 v 40 p 1387 1395 STANLEY S M AND HARDIE L A 1999 Hypercalcification paleontology WALKER J C G 1985 Carbon dioxide on the early Earth Origins of Life links plate tectonics and geochemistry to GSA v 9 sedimentology Today v 16 no p 117 127 2 p 1 7 WALTER M R 1976 Stromatolites Amsterdam Elsevier 790 SUMNER DY 1995 Facies Paleogeography and Carbonate Precipitation in p WALTER M R AND BAULD J 1983 The association of the Archean 2520 Ma Campbellrand Malmani Carbonate Platform Trans sulphate evaporites stromatolitic carbonates and sediments vaal Supergroup South Africa Ph D Dissertation Massachusetts Institute glacial examples from the Protero zoic of Australia and the Cainozoic of Antarctica Precambrian Research v of Technology Cambridge Massachusetts 514 p SUMNER 21 129 148 DY 1997a Carbonate precipitation and oxygen stratification in late p WILKINSON Archean seawater as deduced from facies and stratigraphy of theGamohaan BH OWEN R M AND CARROLL A R 1985 Submarine and Frisco formations Transvaal Supergroup South Africa American Jour Iiydrothernal weathering global eustasy and carbonate polymorphism in nal of Science v 297 p 455487 Phanerozoic marine oolites Journal of Sedimentary Petrology v 55 p 171 SUMNER DY 1997b Late Archean calcite microbe interactions Two mor 183 distinct microbial phologically communities that affected calcite nucleation WtLLIAMS E G WRIGIIT L A AND TROXEL B W 1974 The Noonday Palaios v 12 302 differently p 318 Dolomite and equivalent stratigraphic units southern Death Valley region SUMNER DY AND GROTZINGER J P 1993 Numerical modeling of ooid California ill Wright L A and Troxel B eds Guidebook Death Valley size and the of ooids Journal of problem Neoproterozoic giant Sedimentary Region California and Nevada Shoshone California Death Valley Pub Petrology v 63 p 974982 lishing Company p 73 77 SUMNER DY AND GROTZINGER JP 1996a calcite Herringbone Petrog WRIGHT V P RIEs A c AND MUNN S G 1990 Intraplatformal basin fill raphy and environmental significance Journal of Sedimentary Research v deposits from the Infracambrian Huqf Group east Central Oman in Rob 66 p 419429 ertson A HE Searle M P and Ries A c eds The Geology and SUMNER DY AND GROTZINGER J P 1996b Were kinetics of Archean Tectonics of the Oman Region Geological Society of London Special Pub calcium carbonate precipitation related to oxygen concentration Geology lication 49 London p 601616 v 24 p 119 122 XIAO S KNOLL AH KAUFMAN A J YIN L AND YUN Z 1997 Neo SWElT K AND KNOLL AH 1989 Marine from Proterozoic pisolites Upper fossils in rocks resolution carbonates of East Greenland proterozoic Mesoproterozoic Chemostratigraphic and Spitsbergen Sedimentology v 36 p 75 of a conundrum from the North China Platform 93 biostratigraphic Precam brian Research v 84 197 220 TEITZ M AND MOUNTJOY E W 1985 The Yellowheadand Astoria carbon p XIAO S KNOLL A H AND YUAN X 1998 reconstruction ate platforms in the late Proterozoic Upper Miette Group Jasper Alberta Morphological of Canada of Miaohephyton biJurcatum a possible brown alga from Geological Survey Paper 85 lA Current Research Part A p Neoproterozoic DoushantuoFormation 341 348 south China Journal of Paleontology v 72 p 1072 1086 TEITZ M AND MOUNTJOY E w 1989 The late Proterozoic Yellowhead carbonate platform west of Jasper Alberta in Geldsetzer H James N P YOUNG G M AND LONG DG E 1977 Carbonate sedimentation in a late and Tebbutt G eds Reefs Canada and Adjacent Areas Canadian Society Precambrian shelf sea Victoria Island Canadian Arctic Archipelago Journal of Petroleum Geologists Memoir 13 p 129 134 of Sedimentary Petrology v 47 p 943 955 TUCKER M E 1983 Diagenesis geochemistry and origin of a Precambrian ZEMPOLICH W G WILKINSON B H AND LOHMANN K c 1988 Diagenesis dolomite The Beck Spring Dolomite of eastern California Journal of Sed of late Proterozoic carbonates The Beck Spring Dolomite of eastern Cali v 53 1097 imentary Petrology p 1119 fornia Journal of Sedimentary Petrology v 58 p 656672