calcified microbial reefs in cambrian series 2 north china platform implications for the evolution of cambrian calcified microbes abstract this study focuses on the microbial reefs of the zhushadong formation cambrian series 2 in shandong province china in order to understand the evolution of calcified microbes in the north china platform during the cambrian series 2 and 3 the microbial reefs occur in a thin unit ca 3 m thick over an area of 1 km 2 they consist of three types of thrombolite based on their mesostructures rimmed grainstone patch and dendritic the thrombolites mainly occur in various coarse grained carbonate facies including crudely stratified oolitic grainstone stromatolitic grainstone and disorganized limestone conglomerate calcified microbes in the thrombolites include epiphyton kordephyton a tubiform microbe bija tarthinia renalcis amgaina and razumovskia the zhushadong thrombolites were formed within a grainstone shoal and experienced repeated burial and exposure the rimmed thrombolite and grainstone patch thrombolite experienced abundant input of carbonate grains forming grainstone patches in contrast the dendritic thrombolite formed solely by calcification of microbes that mainly include epiphyton tarthinia and the tubiform microbe the outer crusts of the rimmed thrombolite were formed by amgaina under high energy conditions the diverse calcified microbes of the zhushadong formation form the earliest assemblage of their type in the north china platform their descendants mostly epiphyton subsequently thrived forming a ca 180 m thick microbialite oolite dominated succession during the cambrian series 3 zhangxia formation although the reefs in the zhushadong formation are much smaller than those of the overlying zhangxia formation their calcified microbes are more diverse this most likely reflects changes in depositional environments e g abundant siliciclastic input and tidal effects vs those of a stable carbonate platform and or global changes within reef environments e g end cambrian series 2 extinction of archaeocyaths and calcified microbes a decrease in diversity of calcified microbes in the north china platform where archaeocyaths were absent may help to account for evolutionary trends in calcified microbes that occurred independently of archaeocyath influence

marine oxygenation lithistid sponges and the early history of paleozoic skeletal reefs abstract microbial carbonates were major components of early paleozoic reefs until coral stromatoporoid bryozoan reefs appeared in the mid ordovician microbial reefs were augmented by archaeocyath sponges for 15 myr in the early cambrian by lithistid sponges for the remaining 25 myr of the cambrian and then by lithistid calathiid and pulchrilaminid sponges for the first 25 myr of the ordovician the factors responsible for mid late cambrian microbial lithistid sponge reef dominance remain unclear although oxygen increase appears to have significantly contributed to the early cambrian explosion of marine animal life it was followed by a prolonged period dominated by greenhouse conditions as sea level rose and co2 increased the mid late cambrian was unusually warm and these elevated temperatures can be expected to have lowered oxygen solubility and to have promoted widespread thermal stratification resulting in marine dysoxia and hypoxia greenhouse conditions would also have stimulated carbonate platform development locally further limiting shallow water circulation low marine oxygenation has been linked to episodic extinctions of phytoplankton trilobites and other metazoans during the mid late cambrian we propose that this tendency to dysoxia hypoxia in shallow marine environments also limited many metazoan reef builders in contrast during the mid late cambrian the ability of lithistid sponges to withstand low oxygen levels allowed them to create a benthic association with microbial carbonates that dominated global reefs these conditions ameliorated during the ordovician as temperature decline promoted ocean ventilation the prolonged time gap occupied by low diversity reefs between the cambrian explosion and the great ordovician biodiversification event reflects elevated temperatures and reduced marine oxygenation that limited metazoan diversification in shallow marine environments

late archaean synorogenic basins of the eastern goldfields superterrane yilgarn craton western australia part ii kurnalpi terrane abstract the penny dam belches yilgangi white hills granny royal lucky brock and wallaby supersequences of the kurnalpi terrane crop out in synclines that are the erosional remnants of basins that developed as linear zones of subsidence between approximately north trending compartment bounding faults dominant sedimentary facies range from gravel rich and sand rich concentrated density flow deposits to thickly and thinly bedded bouma type turbidites background deposits are black shales or laminated green mudstones and banded iron formation is preserved in some condensed sections periods of non deposition are recorded by bedded chert which is the product of early diagenetic sea floor silicification the basins were separate deep marine canyon to linear fan systems that were linked laterally and distally by mud rich deposits there is only minor evidence for fault anchored canyon margin slope aprons basin development occurred during two stages separated by a period of deformation uplift and erosion sparse palaeocurrents establish sediment dispersal was to the south or southeast indicating that uplift to the north or northwest controlled palaeoslopes stacking of lithofacies is aggradational and consistent with deposition in fault bound basins tectonostratigraphic equivalence with siliciclastic supersequences of the kalgoorlie and gindalbie terranes is established by common depositional systems stratigraphic styles and stratigraphic responses to tectonic forcing consequently the siliciclastic supersequences represent overlap or late stage basins that tied together arc related terranes following terrane amalgamation similar depositional facies aggradational styles of facies stacking and two stage development characterise the syncollisional plio pleistocene coastal range basin of taiwan modern analogues are the deep marine southern longitudinal and taitung troughs off southeastern taiwan that are being filled by synorogenic sediments derived from the taiwan orogen

paleolatitude distribution of phanerozoic marine ooids and cements opdyke b n and wilkinson b h 1990 paleolatitude distribution of phanerozoic marine ooids and cements palaeogeogr palaeoclimatol palaeoecol 78 135 148 data on 493 phanerozoic marine ooid and cement occurrences indicate that the dominance of calcite versus aragonite in tropical marine settings has changed in response to variation in atmospheric co2 and or oceanic temperature gradient holocene ooid and cement precipitation occurs over similar latitudes with means centered around 24 and 28 respectively aragonite and calcite also display roughly comparable distributions with average occurrences between 25 and 28 surface seawater saturation values requisite for ooid cement carbonate precipitation are at least 3 8 rs for aragonite and 3 4 a s for calcite ancient ooid cement occurrences vary in space and time with depositional zones generally closer to the equator during continental emergence greatest extent correlates with periods of maximum transgression aragonite formation is favored in more equatorial localities than calcite when cement ooid distributions are narrow and continents are emergent similarity of latitude distribution of marine ooids cement and biogenic carbonate suggests that physicochemical processes that control levels of carbonate saturation were more important in predicating sites of limestone accumulation in phanerozoic seas than biological processes related to net productivity of various carbonate platform communities continental position and tropical shelf area available for carbonate accumulation dictates the relative abundance of shallow water inorganic carbonate precipitates in space and time

an oscillating trend in phanerozoic non skeletal carbonate mineralogy textural and compositional data on ancient ooids and cements suggest the existence of an oscillating phanerozoic temporal trend in non skeletal carbonate mineralogy the trend shows good correlation with eustatic climatic oscillations proposed by others the most likely mechanism appears to be plate tectonically influenced oscillations in pco2 the vapour pressure of co2 rather than change in oceanic mg ca ratio

relative precipitation rates of aragonite and mg calcite from seawater temperature or carbonate ion control the temperature and degree of carbonate mineral supersaturation co3 2 ion concentration of seawater are the two most likely controlling variables on the compositions of recent marine carbonate cements the relative importance of these variables is difficult to assess in nature because they have similar trends with depth 0 1500 m and latitude in modern oceans we carried out laboratory experiments to investigate the relative growth rates of calcite mg calcite and aragonite in seawater as functions of both temperature 5 25 and 37 c and of carbonate ion concentration 2 5 to 15 times supersaturated with respect to calcite the precipitation rates of aragonite relative to those of calcite increase strongly with increasing temperature and are not affected greatly by changes in saturation state at 5 c calcite precipitation rates are nearly equivalent to those of aragonite regardless of the degree of saturation at both 25 and 37 c aragonite precipitation rates are much more rapid than those of calcite up to a factor of 4 except at very low saturation states calcite compositions vary from less than 5 mol mgco3 at 5 c to 14 mol mgco3 at 37 c our results suggest that the well documented shift toward precipitation of lower mol mg calcite and the decrease in abundance of aragonite cements with increasing oceanic depth and latitude can be attributed largely to lower temperatures

late archaean deep marine volcaniclastic sedimentation in an arc related basin the kalgoorlie sequence of the eastern goldfields superterrane yilgarn craton western australia abstract the kalgoorlie sequence 2658 ma is a 3000 m thick succession of volcaniclastic sedimentary rocks and subordinate rhyolite dacite andesite and basalt spatially and temporally associated with subvolcanic sills and dykes of rhyolite and dacite gabbro sills and i type granitoids although basalts are tholeiitic the felsic rocks have ttd affinity the sequence comprises mostly deep marine channel levee turbidite complexes and hemipelagites resedimented syneruptive volcaniclastic deposits are associated with coherent lavas but almost all of the sedimentary fill was recycled from prior cycle volcanic and volcaniclastic sources provenance was mainly dacitic rhyolitic with minor andesitic basaltic and polymictic compositions volcano bound and fault bound architectures and two styles of basin filling are identified progradational or aggradational transverse fans and slope aprons and retrogradational longitudinal fans of a linear trough retrogradation in longitudinal systems is consistent with basin lengthening and deepening six depositional sequences are grouped in four unconformity bounded tectonic stages that record uplift subsidence cycles coeval mafic and felsic magmatism indicate that the tectonic stages represent extensional tectonic settings whereas volcanogenic provenance spatially linked volcanism and plutonic magmatism and deep marine environments support an intra arc site cyclic uplift subsidence and basin lengthening are more consistent with strike slip controls on basin formation than with orthogonal extension the tectonic setting is interpreted to have been a pull apart basin associated with strike slip faulting and amalgamating arc related terranes similar to the modern philippines archipelago the strong similarity between archaean volcaniclastic and modern arc related volcaniclastic environments implies comparable tectonic settings and therefore comparable controlling tectonic factors

depauperate skeletonized reef dwelling fauna of the early cambrian insights from archaeocyathan reef ecosystems of western mongolia abstract reef dwelling organisms in the early cambrian include typical members of the cambrian fauna such as trilobites chancelloriids and hyoliths however in comparison to later ordovician reefs cambrian reefs often do not appear as diverse here we investigate early cambrian microbial archaeocyathan reefs of the salaagol formation in the zavkhan basin of mongolia as well as perform a literature survey of 40 early paleozoic reefs to understand the timing of reef biodiversity by using point count analysis we can quantify the carbonate contribution of framework builders and reef dwelling organisms in these ecosystems we find that mongolian reefs contained several genera of framework building archaeocyaths 5 0 by volume and associated microbial forms 5 4 but are unevenly distributed through the formation archaeocyathan contribution increases are potentially concurrent with negative shifts in carbon isotopic composition similar to other localities in gondwana however reef dwelling biota was minimal 0 3 throughout the salaagol formation and did not correlate to changes in framework builders or geochemical proxies such as u v and carbon isotopes a literature survey of ediacaran through ordovician reefs suggests that there is a trend of increasing reef dweller abundance functional richness and skeletonization through time the changes in abundance 17 9 to 28 8 considered frequent and functional richness 3 7 to 6 0 functional groups could be due to an increase in productivity in the oceans during the cambrian thereby expanding the base of the food web during the lead up to the ordovician radiation the trend of increasing skeletonization could be due to the evolution of more robust skeletons among reef dwellers in order to protect themselves from increased predation in reef environments these trends suggest that at least during the early paleozoic increases in biological diversity are not necessarily concurrent with the establishment of a framework reef

the ecology of lower cambrian buildups from zuune arts mongolia implications for early metazoan reef evolution reefal buildups in western mongolia of mid early cambrian late atdabanian age flourished during a period when shelf seas were globally widespread the succession at zuune arts records the transition from shallow marine siliciclastic sediments bayan gol formation to shallow marine but still clastic influenced carbonates salaany gol formation the salaany gol formation is interpreted as having been deposited as a series of shallowing upwards cycles on a shallow gently inclined shelf in a rapidly subsiding epicontinental sea cycles commenced with the growth of subtidal metazoan calcimicrobe aggregative communities on an open shelf the resultant buildups were commonly engulfed by extensive massive microbial stromatolites when they grew in agitated intertidal conditions latterly they were smothered by ooid shoals in response to rapid sea level rise four types of reefal buildup are distinguished 1 green coloured calcimicrobe tarthinia epiphyton gordonophyton and renalcis boundstones 2 red or green coloured cambrocyathellus tarthinia epiphyton bafflestones 3 red coloured okulitchicyathus bindstones and 4 red coloured radiocyath archaeocyath cribricyath bioherms each is interpreted as having grown at increasing depths and possibly sedimentation rates the buildups are commonly enclosed within graded and planar bedded bioclastic grainstones and packstones and are best developed towards the top of the formation when sea level was high thickets of large solitary archaeocyaths are also inferred in the deeper interbiohermal areas these buildups had synoptic relief and constructed porous structures with growth framework cavities housing diverse coelobiontic communities extensive synsedimentary cements are present including pseudomorphed aragonitic fans and possible pseudomorphed aragontic botryoids these early reefs thus have geological fabrics similar to later phanerozoic representatives it is proposed however that this ecosystem was largely composed of generalist and opportunistic filter and suspension feeders which were dependent upon a far higher input of nutrients than modern day reefal developments bacteria were probably the main primary producers from both planktic and benthic cyanobacterial communities the diversity of each buildup assemblage appears to be controlled by primary cavity size the richest fauna belonging to the highly tiered radiocyath dominated community inferred to have lived in the deepest waters the communities at zuune arts can be compared with other buildups from the early cambrian and with lower ordovician receptaculid calcimicrobe solitary sponge bioherms known from the usa and siberia

the xigaze forearc basin evolution and facies architecture cretaceous tibet abstract the mid cretaceous to eocene flysch deposits of the xigaze forearc basin in southern tibet were investigated in a 120 km segment along the indus yarlung suture zone the basin evolved south of the magmatic arc gangdise belt of the lhasa block on top of trapped oceanic or transitional crust remnants of shelf carbonates are preserved along the northern edge of the basin the mapped segment was shortened by about 65 metamorphism reached low grade conditions along the northern margin of the basin the flysch sequence reaches a thickness of at least 5 km and consists to a large degree of volcaniclastic andesitic to dacitic material shed from the magmatic arc gangdise belt particularly in the western part of the study area plutonic and sedimentary rocks from deep erosion levels and or more distal sources contributed to the basin fill rivers from the lhasa block acted as point sources and fed five major deep sea channel systems turbidity currents in the channels were directed towards the growing accretionary wedge of the subduction zone thus indicating that the basin was continuously filled up to outer ridge level and gradually shallowing the forearc flysch is subdivided into at least three megasequences which begin with wide up to several km incised 10 to 50 m coarse grained channel fills and their associated fan deposits the upper parts of the megasequences contain hemipelagic dark shales and marls deposited above the calcite compensation depth lateral channel migration channel lobe switching but also volcanic pulses generated a predominantly fining upward high frequency cyclicity after continental collision the marine sedimentation in the forearc basin was replaced by fluvial deposits of the eocene oligocene qiuwu formation which is time equivalent to the kailas and indus molasses farther west and rich in coarse gravel derived from the gangdise belt both forearc flysch and qiuwu formation were deformed simultaneously during the miocene we assume that the molasse type qiuwu formation represents the final continental facies of the forearc basin filling

middle ordovician chazy group cavity dwelling boring sponges microcavities in lower middle ordovician bryozoan mounds from the laval formation chazy group near montreal quebec contain evidence that endolithic boring sponges were present ramose borings with scalloped walls and swellings resembling endolithic sponge galleries faceted carbonate grains similar to modern sponge chips and siliceous spicules both in situ on the cavity wall or roof and in the sediment all point to the activities of endolithic sponges in the hard substrate of the wall and roof coelobiontic cavity dwelling endolithic sponges therefore infested cavities in skeletal mounds and reefs in the middle ordovician and appear to have exploited the cavity habitat very soon after the appearance of metazoan skeletal reefs in the ordovician

relationships between charcoal particles in air and sediments in west central siberia production and size of charred particles determine transport and deposition in lakes lack of such data is a principal obstacle to interpretation of past fire from charcoal profiles our two part a

structure and diversity of oldest sponge microbe reefs lower cambrian aldan river siberia the oldest sponge reef is a small early cambrian bioherm at the base of the tommotian stage 535 540 ma in southeast siberia the mainly archaeocyath construction may be a response to turbid conditions cambrocyathellus bowls fused to create a rigid cavernous frame colonized by cryptic archaeolynthus and calcified microbes renalcis in addition to these constructors and binders other reef guilds are present bafflers other archaeocyaths spiculate sponges and hyoliths and dwellers hyoliths mollusks and many others this is the oldest known reef possessing an open skeletal frame structure built by animals and a mixed animal autotroph composition it provides a blueprint for younger phanerozoic reefs

primary aragonite and high mg calcite in the late cambrian furongian potential evidence from marine carbonates in oman acknowledgements fieldwork and sampling was funded by petroleum development oman during s al marjibis s ph d their help is gratefully acknowledged we also thank colleagues at the university of aberdeen julie dougans suerc for assisting with stable isotope analysis and dr richard hinton eimf for assistance with ion microprobe analysis profs kiessling tucker bosence coleman dr dickson and an anonymous reviewer are thanked for their helpful and encouraging comments

giant subtidal stromatolites forming in normal salinity waters we report here the discovery of giant lithified subtidal columnar stromatolites 2 m high growing in 7 8 m of clear oceanic water in current swept channels between the exuma islands on the eastern bahama bank they grow by trapping ooid and pelletal carbonate sand and synsedimentary precipitation of carbonate cement within a field of giant megaripples the discovery is important to geologists and biologists because similar organo sedimentary structures built by a combination of cementation and the trapping of sediment by microbes were the dominant fossil types during the precambrian stromatolites are thought to have been responsible for the production of free oxygen and thus the evolution of animal life1 2 until the discovery of small lithified subtidal columnar stromatolites in the bahamas3 the only subtidal marine examples known to be living while undergoing lithification were in the hypersaline waters of hamelin pool at shark bay western australia4 7 shark bay stromatolites range from intertidal to the shallow subtidal with the larger columns reaching 1 m in height the shark bay stromatolites have strongly influenced geological interpretation by analogy many ancient stromatolites have been considered to have grown in intertidal and or hypersaline conditions8 although hypersalinity was not a necessity for growth during the precambrian because grazing metazoan life had not then evolved

a braided distributary system on the orinoco deep sea fan abstract a long range side scan sonar gloria survey has been made of part of the orinoco deep sea fan that abuts against the deformation front of the barbados outer ridge i e in a pre orogenic setting immediately east of the deformation front sinuous channels up to 65 m deep and 3 km wide extend downslope and become very shallow a few metres or less deep and branch into a pattern that resembles stream braiding near the foot of the slope here there is a possible suprafan lobe and an almost flat perched sediment pond dammed by a buried basement ridge in this locality many of the acoustic contrasts on the sonographs are primarily due to differences in sediment type and small scale roughness rather than to variations in slope angle possible debris flows aligned along some of the braided channels have been identified from high resolution profiles this braided system of shallow channels then converges into a single channel that overtops the dam because of their braided nature the internal structure of the resulting deposits is likely to be complex these deposits should eventually be incorporated into the barbados ridge complex in contrast to this pre orogenic setting gloria sonographs also suggest that some orinoco sediment moves down along synclinical axes of folds on the barbados ridge complex i e in a syn orogenic setting

middle late cambrian rankenella girvanella reefs of the mila formation northern iran following the collapse of the early cambrian archaeocyathan calcimicrobial reef consortium the middle late cambrian furongian was an interval dominated by purely microbial dendrolite and stromatolite reefs however among these latter a few exceptional occurrences of metazoan reefs are known one such reef complex occurs in the late middle early late cambrian furongian portion of the mila formation of northern iran in the otherwise low energy interval of this formation the anthaspidellid demosponge rankenella hamdii sp nov is associated with encrusting girvanella eocrinoid plates rhynchonelliformean brachiopod valves and subordinate hyoliths and trilobites in tempestite shell beds these beds underwent synsedimentary cementation on the seafloor to form hardgrounds in the succeeding higher energy interval a complex of metre scale bioherms and or taphoherms incorporates toppled or transported rankenella hamdii in association with brachiopods echinoderm plates trilobites and some red arg

was phanerozoic reef history controlled by the distribution of non enzymatically secreted reef carbonates microbial carbonate and biologically induced cement throughout most of the phanerozoic reef rigidity resulted as much or more from early lithification by microbial carbonates and biologically induced cements non enzymatic carbonates than from biological encrustation of or by large enzymatically secreted metazoan skeletons reef framework is divided into four categories 1 skeletal metazoan 2 non skeletal microbialite stromatolite and thrombolite 3 calcimicrobe and 4 biocementstone in which small or delicate organisms serve as scaffolds for rigid cement crusts the last three categories are dominated by non enzymatic carbonates skeletal framework and non skeletal microbialite framework were the most abundant framework types through the phanerozoic the composition and abundance of skeletal framework was controlled largely by mass extinction events but most reefs consisted of both microbialite and skeletal organisms in a mutually beneficial relationship microbialite framework was abundant throughout the palaeozoic and early mesozoic but declined after the jurassic calcimicrobe framework was important during the cambrian early ordovician and devonian and biocementstone framework was important from the late mississippian to the late triassic the phanerozoic history of reefs does not correlate well with the stratigraphic distribution of large skeletal reef builders or with a variety of physicochemical parameters including sea level history wilson cycle or global climate cycles because non enzymatic carbonates result from induction by non obligate calcifiers and not enzymatic precipitation by obligate calcifiers the distribution of these carbonates was controlled to a larger extent by temporal changes in physicochemical parameters affecting the saturation state of sea water with respect to carbonate minerals changes in pco ca mg ratios cation concentrations and temperature may have affected the abundance of non enzymatic carbonates and hence reefs independently from the effects of these same parameters and mass extinction events on skeletal reef biota the decline in abundance of reefal microbialite and absence of calcimicrobe and biocementstone reef framework after the jurassic may be a result of relatively low saturation states of sea water owing to increased removal and sequestration of finite marine carbonate resources by calcareous plankton since the jurassic reef history is difficult to correlate with temporal changes in specific global parameters because these parameters affect skeletal biota and biologically induced carbonate precipitation independently hence reef history was regulated not just by skeletal reef biota but by parameters governing non enzymatic carbonates

early visean paleogeography of northern siberia new evidence of rift to drift transition along the eastern margin of siberia abstract in the late devonian early carboniferous the eastern part of siberia was affected by multi stage rifting which led to formation of a late paleozoic mesozoic passive margin four sections of the lower visean strata were studied in the northern part of the kharaulakh ridge along the lena river and bykov channel north east of siberia the studied sedimentary succession comprises two lithologically contrasting units coarse grained turbidites and hemipelagic cherts deposition occurred in a marine basin bounded by steep slopes which is a key geomorphological feature facilitating deposition of coarse grained turbidites within the studied sandy turbidites several different zones of submarine sand rich fans have been recognized integrated sedimentological and petrographical analyses allow us to interpret that the nearby uplifts composed of proterozoic middle paleozoic rocks were the main provenance areas for the visean clastic rocks those uplifts were formed as a result of the latest stages of rifting in the study region that occurred in the earliest visean following termination of much of the tectonic activity during the tournaisian a similar rock association has been described previously from the central and southern part of the eastern margin of siberia suggesting that the rift to drift transition occurred approximately at the same time across east siberia and is of early visean age

lowstand slope channels of the itilli succession maastrichtian lower paleocene nuussuaq west greenland abstract the maastrichtian lower paleocene itilli slope succession of nuussuaq west greenland consists of an at least 2 5 km thick turbidite succession composed of mudstone thinly interbedded sandstone and mudstone chaotic beds amalgamated sandstone and giant scale cross bedded sandstone the amalgamated and giant scale cross bedded sandstones were deposited in 1 2 km wide slope channels draining basin margin source areas the chaotic beds invariably underlie undisturbed channel fill sandstones suggesting that initially channels were excavated largely by retrogressive slumping of unstable slope mudstones retrogressive slumping was followed by intense channel excavation with continued scouring of channel base and walls before deposition of channel fills from high density turbidity currents it is suggested that destabilisation of the slope mudstones was triggered by drops in relative sea level associated with increased sediment deposition on the slope sequence stratigraphic concepts have been applied to the itilli slope succession the chaotic beds are related to the forced regressive wedge systems tract the sequence boundary is placed at the erosional unconformity separating the chaotic beds from the overlying channel sandstone turbidites and it represents the lowest point of relative sea level fall the channel fill represents the lowstand prograding wedge systems tract and the transgressive systems tract poorly developed highstand systems tract deposits include thinly interbedded sandstones and mudstones and are probably also represented in the redeposited material in the chaotic beds

comparison of turbidite facies associations in modern passive margin mississippi fan with ancient active margin fans abstract our comparison of the modern passive margin mississippi fan dsdp leg 96 with ancient active margin fans e g eocene hecho group spain reveals major differences in turbidite facies associations mutti and ricci lucchi scheme and in seismic characteristics in the lower fan area the lower outer mississippi fan is composed of channel facies b and f and non channel facies c and d whereas ancient fans are characterized by non channelized thickening upward depositional lobe facies c and d an absence of depositional lobes in the lower mississippi fan is also suggested by a lack of convex upward mounded seismic reflections with bidirectional downlap continuous seismic reflections of the lower mississippi fan may represent sheet sands but not those of true depositional lobes with mounded character extensive channelization in modern passive margin fans appears to be a product of the lateral shifting of a major sinuous distributary system developed as a consequence of low gradients and the transport of sediment with a relatively low sand mud ratio in contrast channels in active margin fans are short and of low sinuosity as a result of high gradients and the transport of sediment with a relatively high sand mud ratio the turbidite facies association scheme which was developed exclusively from ancient active margin fans should be applied to mature passive margin fans with qualifications because of the differences in spatial distribution of turbidite facies and their associations

archaeocyathan buildups within an entirely siliciclastic succession new discovery in the toyonian lalun formation of northern iran the proto paleotethys passive margin of northern gondwana abstract meter scale buildups constructed exclusively by archaeocyaths have been recognized within the uppermost lower cambrian siliciclastic succession of eastern alborz in northern iran they are the only known toyonian reefs in iran and adjacent countries and occur in the lower part of the shale unit of the lalun formation the reefs are of limited lateral extent reach a maximum thickness of 2 5 m and consist of several reef complexes containing cabbage or sack shaped buildups surrounded by well bedded colored shale each reef complex in the main reef zone consists of meter scale individual and kalyptrate compound buildups that are overgrown by laminated stromatolite the individual buildups are 12 to 75 cm thick and 5 to 50 cm in diameter but the compound buildups are up to 2 m thick and their diameter ranges from 75 to 120 cm in contrast to most lower cambrian reefs these compound buildups demonstrate a complete ecological succession including pioneer and climax phases archaeocyaths in the buildups are solitary and colonial types showing great diversity of growth forms with vase bowl and cup shaped and cylindrical forms present the cups range from less than 1 mm to 1 5 cm in diameter and are up to 4 cm tall in the majority of the skeletons but they may reach up to 4 cm in diameter in the massive colonial forms or in the branching forms of the upper outer part of the compound bioherms the limited lateral extent of the reef horizons and lateral facies changes in the colored shale toward various reefs supports deposition in drowned tidal channels in an estuarine depositional environment a change of the individual bioherms to larger compound buildups suggests lateral depth variation of the tidal channels partial infilling of the primary inter biohermal cavities by large reef clasts and cross laminated siltstone to very fine sandstone suggests occasional disturbances by storms and periodic influx of coarse siliciclastics in striking contrast to other lower cambrian reefs the archaeocyathan buildups of the alborz flourished in a completely siliciclastic setting and lack the skeletal calcimicrobes which dominated the lower cambrian reefs abrupt lateral and vertical facies changes to colored shale and fluvial red beds the presence of infiltrated shale between the skeletons and in central cavities and the intervallum of the archaeocyaths suggest highly turbulent and turbid incoming water with abnormally high concentrations of fine siliciclastic material during reef development high concentrations of fine suspended siliciclastics could well have prevented the light penetration which was necessary for calcimicrobial growth in addition the relatively small size of the archaeocyaths and absence of reef dwellers is very likely a consequence of the high terrigenous mud content and perhaps below normal salinity of the ambient sea water in the absence of calcimicrobes and suspension feeder metazoans in the dark and muddy water of the mid estuarine setting archaeocyathans became the only bioconstructors of the iranian buildups abnormally high concentration of nutritious fine siliciclastics suggests that photosymbionts and oligotrophic conditions were not needed by archaeocyaths particular hydrodynamic conditions along with high nutrient flux rather than light were essential for archaeocyathan communities

the bouma sequence and the turbidite mind set abstract conventionally the bouma sequence bouma a h 1962 sedimentology of some flysch deposits a graphic approach to facies interpretation elsevier amsterdam 168 pp composed of ta tb tc td and te divisions is interpreted to be the product of a turbidity current however recent core and outcrop studies show that the complete and partial bouma sequences can also be interpreted to be deposits formed by processes other than turbidity currents such as sandy debris flows and bottom current reworking many published examples of turbidites most of them hydrocarbon bearing sands in the north sea the norwegian sea offshore nigeria offshore gabon gulf of mexico and the ouachita mountains are being reinterpreted by the present author as dominantly deposits of sandy debris flows and bottom current reworking with only a minor percentage of true turbidites i e deposits of turbidity currents with fluidal or newtonian rheology in which sediment is suspended by fluid turbulence this reinterpretation is based on detailed description of 21 000 ft 6402 m of conventional cores and 1200 ft 365 m of outcrop sections the predominance of interpreted turbidites in these areas by other workers can be attributed to the following 1 loose applications of turbidity current concepts without regard for fluid rheology flow state and sediment support mechanism that result in a category of turbidity currents that includes debris flows and bottom currents 2 field description of deep water sands using the bouma sequence an interpretive model that invariably leads to a model driven turbidite interpretation 3 the prevailing turbidite mind set that subconsciously forces one to routinely interpret most deep water sands as some kind of turbidites 4 the use of our inability to interpret transport mechanism from the depositional record as an excuse for assuming deep water sands as deposits of turbidity currents 5 the flawed concept of high density turbidity currents that allows room for interpreting debris flow deposits as turbidites 6 the flawed comparison of subaerial river currents fluid gravity flows dominated by bed load transport with subaqueous turbidity currents sediment gravity flows dominated by suspended load transport that results in misinterpreting ungraded or parallel stratified deep sea deposits as turbidites and 7 the attraction to use obsolete submarine fan models with channels and lobes that require a turbidite interpretation although the turbidite paradigm is alive and well for now the turbidites themselves are becoming an endangered facies

lower cambrian shelf and shelf margin buildups flinders ranges south australia1 carbonate buildups in the flinders ranges of mid early cambrian age grew during a period of high archaeocyath diversity and are of two types 1 low energy archaeocyath sponge spicule mud mounds and 2 high energy archaeocyath calcimicrobe calcified microbial microfossil bioherms mud mounds are composed of red carbonate mudstone and sparse to abundant archaeocyath floatstone have a fenestral fabric display distinct stromatactis contain abundant sponge spicules and form structures up to 150m wide and 80 m thick bioherms are either red or dark grey limestone and occur as isolated small structures 2 20 m in size surrounded by cross bedded calcarenites and calcirudites or as complexes of mounds and carbonate sands several hundreds of metres across red bioherms comprise masses of white epiphyton with scattered archaeocyaths and intervening areas of archaeocyath rich lime mudstone grey bioherms are complex intergrowths of archaeocyaths encrusting dark grey renalcis and thick rinds of fibrous calcite cement the bioherms were prone to synsedimentary fracturing and exhibit large irregular cavities up to 1 5 m across lined with fibrous calcite the buildups are isolated or in contiguous vertical succession mud mounds occur alone in low energy frequently nodular limestone facies individual bioherms and bioherm complexes occur in high energy on shelf and shelf margin facies the two types also form large scale shallowing upward sequences composed of basal deep water mud mounds grading upward into archaeocyath calcimicrobe bioherm complexes and bioherms in cross bedded carbonate sands the uppermost sequence is capped by ooid grainstone and or fenestral to stromatolitic mudstone the calcimicrobe and metazoan associations form the two major biotic elements which were to dominate reefs throughout much of subsequent phanerozoic time

early ordovician lithistid sponge calathium reefs on the yangtze platform and their paleoceanographic implications lithistid sponge calathium microbial reefs were widespread on the yangtze platform during the early ordovician and are well studied however the biological affinity and the role of calathium in these reefs have remained unclear up to now we document lithistid sponge calathium reefs from the upper hunghuayuan formation early floian at huanghuachang in hubei south china these reefs have a three dimensional skeletal framework that is mostly produced by calathium and lithistid sponges calathium had a critical role in reef construction as demonstrated by well developed lateral outgrowths which connected individuals of the same species and with lithistid sponges bryozoans stromatoporoids and microbial components were secondary reef builders morphological constructional and functional analyses provide evidence that calathium was a sponge grade metazoan rather than a receptaculitid alga as previously thought at the dawn of the ordovician radiation these small scaled patch reefs thus represent the initial rebound of metazoan dominated reefs after the late early cambrian archaeocyath reef crisis gradual global cooling through the early ordovician may have been a key driver for the return of metazoan reefs

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

early cambrian reefs reef complexes and associated lithofacies of the shackleton limestone transantarctic mountains the shackleton limestone formed a carbonate platform that bordered part of the greater antarctic craton in middle and late early cambrian time in the holyoake range of the central transantarctic mountains this unit records deposition on a stable shelf on which flourished ecological reefs composed of microorganisms and archaeocyathans burrow mottled lime mudstone wackestone and packstone with patch reefs represent accumulation in shelf areas of relatively low to moderate energy thick ooidal grainstone units reflect deposition in higher energy shoals and as sand sheets that were associated with extensive reef complexes the framework of these reefs was principally the product of micro organisms by inference mostly cyanobacteria archaeocyathans constitute as much as 30 of some reefs but commonly they form less than 10 and are absent from some on the basis of microbial composition three reef types are recognized the first type is a renalcis boundstone that lacks archaeocyathans within these abundant upward directed thalii of renalcis formed a framework that trapped fine grained sediment the second type which forms the core of some larger reefs is composed of stromatactis bearing microbial boundstone the third yet most common reef type is variable in composition it is characterized by the presence of abundant epiphyton but may include archaeocyathans and the microbial microfossils girvanella and renalcis as well as cryptomicrobial clotted micrite in this type of reef frame building organisms typically constructed highly porous structures that had small interparticle and fenestral pores and large growth framework cavities as well as rare metre sized caverns within these spaces epiphyton and less commonly renalcis encrusted framework elements fine grained sediments accumulated and pervasive sea floor cements were precipitated boundstone fabrics in the shackleton limestone are highly complex with fabrics analogous to younger more metazoan rich reefs as well as deep water stromatactis bearing mud mounds the epiphyton girvanella archaeocyathan frameworks and stromatactis bearing boundstones both of which seemingly first appeared in the middle early cambrian are regarded as the precursors in structure composition and preferred hydrologic setting of the more extensive reefs and complex framework styles of later phanerozoic time

types of submarine fan lobes models and implications different lobe models imply significantly different reservoir geometries thus one must apply the proper lobe model to ancient fan sequences braided suprafan lobes are characterized by stacked channel sand bodies with good lateral and vertical communication and they constitute excellent reservoir facies depositional lobes composed of sheet like sand bodies with good lateral and moderate vertical communication exhibit properties of good reservoir facies fanlobes which refer to meandering channels and associated levee facies of large mud rich submarine fans such as the mississippi fan are characterized by offset stacked sand bodies with poor lateral and vertical communication these lenticular sands have the potential to be moderately good reservoir facies ponded obes which represent mud rich slump facies of slope environments comprise poor reservoir facies because of low sand content and poor sand body connectivity furthermore the presence of contorted mud layers in ponded lobes is expected to hinder fluid flow external mounded reflections in seismic profiles often are interpreted as lobes however there are no definite seismic criteria to delineate mud rich lobes from sand rich lobes

genesis of stromatactis cavities between submarine crusts in palaeozoic carbonate mud buildups it is concluded that the sedimentary structure stromatactis is a calcite cement fill of a swarm of labyrinthine cavities developed in marine carbonate muds of palaeozoic bioherms commonly with geopetal sediment field and petrographic evidence is examined from the ordovician of dalarna sweden the devonian of the canning basin australia and of belgium and the carboniferous of lancashire u k in all four occurrences the host microspar encloses masses of radiaxial fibrous calcite with sub horizontal floors following other workers radiaxial fibrous calcite is regarded as an altered marine cement a conclusion supported by the presence of overlying geopetal sediments with marine fossils widespread evidence of early submarine cementation in palaeozoic mud mounds isotopic analyses and the presence of microdolomites the stromatactis masses are separated from each other by laminae of host biomicrospar which show discontinuities resembling fractures which are healed with the early marine cement or filled with marine internal sediments the fractures are therefore of submarine origin the evidence points to episodic submarine lithification of the carbonate muds yielding successive crusts between which cavities were eroded and then filled the crusts were broken and rotated during bioturbation differential compaction or shearing during burial

a new post early cambrian archaeocyath from antarctica a new species of archaeocyath sponge dictyocyathus neptunensis is described from the lower third of the nelson limestone of the neptune range antarctica based on the presence of the trilobites nelsonia schesis and amphoton oatesi these strata are interpreted to be mid to late middle cambrian in age d neptunensis shows a branching low integration modular form and a very simple skeletal type such an organization is predicted from known morphological trends within the early cambrian archaeocyatha specimens are not in life position and probably form part of a storm deposit the absence of dictyocyathus from latest early cambrian toyonian strata worldwide suggests a convergent nature for this highly simplified skeletal type in archaeocyaths

climatic tectonic and volcanic controls of sediment supply to an oligocene foredeep basin the val d aveto formation northern italian apennines abstract the val d aveto formation is a turbidite sequence deposited in the northern apennines during the oligocene 32 29 ma the occurrence of calcareous siliciclastic volcaniclastic and carbonatoclastic deposits makes the val d aveto formation a natural laboratory to study the interplay among climate tectonics and volcanism in a subduction related context eight logs have been studied in order to reconstruct the stratigraphic architecture of the succession ten different facies one limestone senso lato facies four siliciclastic facies four volcaniclastic facies and one carbonatoclastic facies have been recognized on the basis of their different sedimentary features microtextures and matrix compositions through thin section analysis and x ray powder diffraction for the first time syn volcanic facies pyroclastic density current and epiclastic deposits have been distinguished from post volcanic facies in the volcaniclastic facies compositional trends of sandy to muddy detritus together with image analyses on gravel dimensions highlight spatial and temporal persistence of the syn depositional volcanic activity across the source to sink system lithological and petrographic analyses on the gravel size fraction of the siliciclastic and volcaniclastic detritus point out a se france provenance and reveal the strong influence that tectonics has on sediment production the comparison between the geodynamic evolution of the source area and the stratigraphic evolution of the val d aveto formation can help unravel the importance of climate on the redistribution of tectonically produced sediments and shaping of the resulting submarine fan

eve of biomineralization controls on skeletal mineralogy carbonate mineralogies have oscillated between aragonite and calcite seas through geological time proposed to be due mainly to secular variation in the magnesium calcium ratio driven by changing rates of ocean crust production a quantitative compilation of inorganic and biominerals from the onset of biomineralization late ediacaran middle ordovician reveals a correspondence between seawater chemistry and the first adopted mineralogy of skeletal clades ediacaran tommotian skeletons and inorganic precipitates were composed exclusively of aragonite or high mg calcite but these were replaced by low mg calcite mineralogies during the early atdabanian implying the onset of a calcite sea this transition is empirically constrained by fluid inclusion data late atbadanian botoman inorganic precipitates returned to aragonite with high mg calcite echinoderms and solitary tabulaconids and massive aragonitic tabulaconids originating during this interval middle cambrian ordovician inorganic precipitates were low mg calcite and the ordovician radiation in skeletal expression was due mostly to groups with low mg calcite mineralogies these short lived transitions can be most parsimoniously explained by minor oscillations of mmg ca around 2 during this period possibly combined with the progressive onset of greenhouse conditions during the mid late cambrian

late archaean synorogenic basins of the eastern goldfields superterrane yilgarn craton western australia abstract siliciclastic supersequences of the kalgoorlie and gindalbie terranes post date 2660 ma deformation uplift and erosion associated with the amalgamation of arc related terranes but were tectonically buried to greenschist or amphibolite facies during the orogenic shortening that accreted the eastern goldfields superterrane to the yilgarn craton the supersequences are synclinal remnants of late stage basins that were linear zones of subsidence adjacent to north trending strike slip faults fluvial facies merougil navajo jones creek scotty creek and yandal basins are dominated by sheet sandstones that represent the deposits of medial braid plains but proximal channel and bar complexes of cobble and boulder conglomerates are also preserved submarine facies kurrawang basin range from boulder to pebble conglomerates but are dominantly bouma turbidites with rare black shales and record the filling of a proximal canyon that fed a distal submarine fan axial depositional systems are preferentially preserved in all basins but transverse systems are preserved at the base of some fluvial deposits the gross vertical succession in all basins is from proximal up to distal the basins developed during two tectonic stages separated by an intervening period of uplift tilting and erosion with the southern kalgoorlie terrane recording change from a stage i fluvial to a stage ii deep marine basin stage ii fluvial deposits are preserved in the northern kalgoorlie terrane and in the gindalbie terrane sparse palaeocurrents establish sediment dispersal was to the south or southeast implying uplift to the north or northwest controlled palaeoslopes stacking of lithofacies is aggradational and is consistent with limited lateral migration of facies tracts in fault confined basins similar lithofacies and aggradational styles of facies stacking characterise syncollisional sequences of the cenozoic coastal range basin of taiwan and the present day syncollisional basins of southeastern taiwan are good analogues of late stage basins of the kalgoorlie and gindalbie terranes

synsedimentary seismic activity in an immature passive margin basin lower member of the katrol formation upper jurassic kutch india abstract seismites are difficult to identify in a sedimentary sequence that has been exposed to a number of other synsedimentary disturbances the paper identifies some possible signatures of earthquakes in a lower submarine fan complex that formed in an extensional basin at the northwestern margin of the indian plate dying growth faults preferential basal brecciation of shale beds frequent local intraformational unconformities reverse grading attributed to mechanical sieving and intrabasinal mass flows through sand volcanoes bear the distinctive records of seismicity abundant synsedimentary grabens and horsts and profuse signs of liquifaction are suggestive in this association the thinning and fining up channel fill sequences with evidence of gradually declining mass flow regimes also corroborate

early cambrian bioconstructions in the zavkhan basin of western mongolia the neoproterozoic cambrian succession in the zavkhan basin of western mongolia preserves early cambrian bioconstructions of nemakit daldynian to botomian age as elsewhere siberia morocco the nemakit daldynian bioconstructions in the upper tsagaan oloom formation to lower bayan gol formation interval were purely calcimicrobial spectacular calcimicrobial patch reefs of presumed tommotian age are present in the lower bayan gol formation in contrast late atdabanian early botomian bioconstructions are varied and well developed in the upper salaany gol formation including in addition to calcimicrobial bioherms gordonophyton razumovskia crusts radiocyathan archaeocyathan bioherms and thickets of the ramose archaeocyath cambrocyathellus these latter zavkhan basin buildups show some ecological and sedimentological features in common with coeval bioconstructions in south australia which also developed under a tectonically active regime

palaeomagnetism of the bayan gol formation western mongolia oriented samples of the lower cambrian bayan gol formation from salaany gol mongolia were collected at roughly 5 m stratigraphic intervals for palaeomagnetic analysis progressive alternating field and thermal demagnetization isolated two magnetic components a present field overprint typically removed by 10 mt fields and 200 c heating and a high coercivity high unblocking temperature 550 600 c predominantly single polarity component that was imparted to the rocks prior to early or middle palaeozoic deformation single polarity magnetization at salaany gol contrasts with results from lower cambrian rocks on the siberian platform previously considered correlative with the bayan gol formation which show a prominent change in polarity bias near the top of the tommotian stage two hypotheses can explain this discrepancy first the entire bayan gol formation may correlate with the predominantly reversely polarized lower half of the tommotian stage in siberia this model is consistent with plausible interpretations of 13 c profiles for the zavkhan basin and the siberian platform alternatively the characteristic magnetic direction from our samples may be a pre fold overprint if post accretionary then comparison with siberian palaeomagnetic results suggest a silurian devonian remagnetization age and existing bioand chemostratigraphic correlations provide the most reliable spatial and temporal links between the zavkhan basin and the siberian platform if the observed magnetic directions are primary or an immediate overprint then they may be used to constrain the early cambrian palaeogeography of the zavkhan basin and the palaeo pacific ocean mean inclination of 62 4 corresponds to a palaeolatitude of 44 5 several thousand kilometres from the equatorial siberian craton

latest middle cambrian metazoan reef from northern iran middle and late cambrian reefs were built mainly by cyanobacterial communities a few reefs with a metazoan as well as an algal component however are known from this interval a middle cambrian reef formed primarily by spicular demosponges is described here from the mila formation in the elburz mountains northern iran the reef is enclosed within calcareous grainstones which contain terminal middle cambrian late mayan trilobites the mila formation reef was constructed by sponges of the family anthaspidellidae and bacterial algal sheaths and is the earliest metazoan reef to be documented from the interval after the demise of archaeocyath sponges the reefal community is typical of subsequent reefal communities of early middle ordovician age the ordovician examples differ only by the incorporation of additional metazoan elements

cambrian series 3 carbonate platform of korea dominated by microbial sponge reefs abstract metazoans have been considered as negligible components of cambrian series 3 and furongian microbial dominated reefs in contrast to their presence in earlier terreneuvian cambrian series 2 microbial archaeocyath reefs however recent discoveries of sponges in cambrian series 3 furongian reefs of australia china iran usa and korea have raised question regarding their contribution in terms of carbonate platform development which have never been assessed this study examines cambrian series 3 deposits of the daegi formation korea to elucidate this question the 100 m thick middle part of the daegi formation is dominated by boundstone facies which occupies 45 of the study interval as well as bioclastic wackestone to packstone bioclastic grainstone and ooid packstone to grainstone facies the daegi reefs are primarily thrombolitic in composition with 90 n 26 29 of the reefs containing an average of 9 sponges in aerial percentage calculated from thin sections lithistid sponges composed of peloidal fabrics some desma spicules and spicule networks commonly occupy the interstitial space in microbial clusters are encrusted by mesoclots and epiphyton and are surrounded by micrite subordinate non lithistid demosponges occur within clusters of microbial elements the middle daegi formation can be largely subdivided into shoal environment dominated by grainstone to packstone facies and shallow subtidal platform interior environment located behind shoal with wackestone to packstone facies the microbial sponge reefs mainly developed around platform interior as patch reefs the current study indicates that metazoans in the form of lithistid and non lithistid demosponges are nearly ubiquitously incorporated in daegi reefs and contributed greatly to the formation of microbial sponge reefs as well as carbonate platform during the time study of these microbial sponge reefs and their distribution within the carbonate platform may help us to understand how carbonate sedimentary environments responded to the extinction of archaeocyaths

is the turbidite facies association scheme valid for interpreting ancient submarine fan environments although turbidite facies reflect only processes of deposition turbidite facies associations are routinely used to identify ancient submarine fan subenvironments e g upper fan channel lobe etc the assumption that process of deposition also reflects environment of deposition may not be valid for the following reasons 1 mutti and ricci lucchi9s facies association scheme for submarine fans has been developed exclusively from ancient turbidite sequences however the true relationship between such turbidite facies associations and related fan subenvironments has not been confirmed from modern fans 2 individual channel levee systems of many modern submarine fans are in many cases large enough to contain the entire ancient fan systems on which these facies associations are based 3 large channel levee systems comparable to those of modern fans have not been recognized in outcrops consequently the validity of turbidite facies associations for interpreting ancient submarine fan subenvironments must be considered tenuous until confirmed in modern fans

middle cambrian siliceous sponge calcimicrobe buildups daegi formation korea metazoan buildup constituents in the aftermath of the early cambrian extinction event abstract numerous decimetre to metre scale carbonate buildups dominated by siliceous sponges and the calcimicrobe epiphyton are reported from the middle cambrian series 3 daegi formation of korea these siliceous sponge epiphyton buildups consist predominantly of grey micritic boundstones with dark clots and or white clumps the boundstones contain sponge spicule networks interpreted as the calcified remains of siliceous sponges the white clumps and dark clots in the boundstones represent variously preserved epiphyton siliceous sponges form constructional pore space and are commonly encrusted by epiphyton the sponges were probably the primary frame builders providing substrates for the attachment and subsequent growth of epiphyton epiphyton is considered to be a binder when covering the surface of siliceous sponges and a subordinate frame builder when filling depositional voids created by siliceous sponges or growing on top of other epiphyton growth bundles the siliceous sponge epiphyton buildups of the daegi formation show similarities to previously described late cambrian furongian anthaspidellid calcimicrobe buildups from iran and the usa together with recently reported examples from the zhangxia formation of eastern china the sponge epiphyton buildups from korea represent some of the oldest metazoan calcimicrobe buildups after the extinction of most archaeocyaths at the end of the early cambrian series 2 this implies that the incorporation of metazoans in middle cambrian series 3 carbonate buildups occurred much earlier than previously known the buildup forming siliceous sponges described in this study demonstrate that their role in early phanerozoic carbonate buildups has been grossly underestimated

biosedimentology of a silurian thrombolite reef with meter scale growth framework cavities a completely dolomitized silurian reef at maumee ohio u s a is uncommon among early paleozoic reefs in that its framework consists of about 95 thrombolite boundstone and 5 corals the reef lithified syndepositonally as evidenced by centimeter to meter scale growth framework cavities within it that are completely filled with internal sediment the largest cavities 2 3 5 m in diameter are prob ably the largest ever recorded in a thrombolite reef four main types of components are distinguished in the reef frame work 1 dense bushy mesoclots 2 dense rounded to subrounded mesoclots 3 saccate microstructures and 4 crusts mostly struc tureless but also containing dense bushy mesoclots the dense bushy components are abundant rounded to sub rounded mesoclots less so and the remaining components are rare the dense bushy and rounded to subrounded mesoclots are interpreted to represent the calcified re mains of what were initially either aggregates of the probable filamen tous cyanobacterum angulocellularia or aggregates of renalcid calci microbes or both and the saccate mesoclots as the calcimicrobe ren alcis sensu stricto it is speculated that syndepositonal lithification of the reef framework was accomplished by impregnation of unlithified protomesoclots by micrite to create mesoclots along with the formation of micritic cement around and between mesoclots that served to fuse together successive generations of mesoclots the direction of branching of bushy mesoclots in the reef indicates that unlithified protomesoclots were able to grow upward laterally and downward this ability along with syndepositional lithification to create mesoclots and to cement them together enabled the protome soclots and mesoclots to create reef knobs and eventually to roof over spaces that were centimeters to three or more meters in width and height to create growth framework cavities features indicative of rap id deposition including graded bedding poor sorting of bioclasts and textural inversion are common in internal sediment in meter size cav ities these features suggest that storms possibly hurricanes were at least as important and probably more so than everyday wave en ergy in transporting sediment into all cavities in the reef regardless of size

phosphatized early cambrian archaeocyaths and small shelly fossils ssfs of southwestern mongolia abstract archaeocyaths are an enigmatic group of calcifying sponges prevalent in early cambrian terreneuvian to series 2 successions around the world and preserved predominantly in reefal buildups but also in adjacent reworked deposits here we report exceptionally preserved phosphatized archaeocyaths and small shelly fossils from phosphatized reef flank deposits at the top of the salaagol formation of southwestern mongolia recent chemostratigraphic age models suggest that these archaeocyaths are among the earliest reported in the terreneuvian stage 2 tommotian these fossils provide a window into the mechanisms of archaeocyath phosphatization a generally rare mode of archaeocyath preservation to assess the composition and nature of phosphatization fossil assemblages were examined in insoluble residue and thin section these archaeocyaths are preserved as phosphatic internal molds in residue and both phosphatized and unphosphatized archaeocyaths are present in thin section the occurrence of internal molds and complementary mineralogical data suggest that the decay of organic material within the archaeocyaths created the necessary redox conditions for apatite nucleation we propose that shortly after death this assemblage was transported to a deeper water environment and that the presence of organic matter in a low oxygen setting led to abundant phosphatization of archaeocyaths

submarine fan and channel levee deposits in the lower cretaceous bogota trough colombian andes abstract bogota trough in the cordillera oriental of colombia was an elongate ne sw oriented lower cretaceous basin it was one of the main depocentres in the northern andes during earliest cretaceous time six lithofacies and three facies associations are recognised based on four detailed stratigraphic sections situated in the western portion of the trough sedimentation in the basin comprised channel levee fan lobe and outer fan basin plain depositional environments channel levee complexes without a well developed fan growth pattern were more proximal to the sediment supply in more distal settings the migrating channels evolved into suprafan lobes their sediments were covered by outer fan basin plain deposits at a time of retrogradation of the fan system the evolution in the basin continued with progradation and development of depositional lobes and channel fill middle fan environments the western portion of the trough was situated near to the zone of convergence between the nazca and the south american plates and the main sediment supply derived from the paleo central cordillera which in early cretaceous time consisted of an uplifted jurassic plutonic arc this active margin defined the coexistence of small sand rich radial fans and channel levee complexes in the eastern portion of the basin main source area the stable guayana shield determined the existence of a larger fan system of a hybrid type between radial and elongate fans despite the differences between the two fan systems in eastern and western portions of the trough the observed retrogradational and progradational sequences are similar

cyanobacterial archaeocyathan radiocyathan bioherms in the wirrealpa limestone of south australia the 140 m thick wirrealpa limestone of south australia is an open shelf marine deposit of early middle cambrian botomian or toyonian age bioherms preserved within this unit have a distinctive epiphyton thrombolitic stromatolite framestone core colonized by a low diversity archaeocyathan radiocyathan biota of ajacicyathus sp archaeocyathus abacus n sp and girphanovella gondwana n sp together with other skeletal invertebrates and macroborers the largest bioherm some 3 m in thickness and 36 m in length is enclosed within an interval of thin bedded to nodular silty bioclast limestone but rests directly on a substrate of bioclast intraclast and onkoid packstone floatstone rudstone the archaeocyathan radiocyathan biota represents the youngest known australian occurrence of these groups

turbidite deposition in five miocene bathyal formations along an active plate margin north island new zealand with notes on styles of deposition at the margins of east coast bathyal basins abstract five miocene turbidite formations whakataki oldest greenhollows tanawa pakowhai waihoki youngest in northern wairarapa north island new zealand are described the whakataki formation widespread on the east coast of wairarapa formed at the onset of the kaikoura orogeny earliest miocene to recent on a deep sea plain whereas younger formations were deposited in a part of a long lived slope basin the tawhero basin situated between the greenhill anticline in the west and the tinui fault in the east the whakataki and the mud rich tanawa formations were probably largely fan deposited whereas the greenhollows pakowhai and waihoki formations are largely non fan deposited the mid miocene tanawa formation has turbidites which invariably lack sole structures even in areas close to the mouths of small submarine channels canyons i e in proximal locations and contains sandstone mudstone couplets usually with t b or t c basal this is thought to indicate that the formation was largely deposited from low velocity turbidity currents the early miocene greenhollows formation and the latest miocene waihoki formation are composed of couplets containing thick sandstone parts and they represent sheeted high density turbidity currents features recognised within miocene northern wairarapa deep sea turbidite formations are 1 fan and non fan styles of deposition 2 deposition from high or low velocity turbidity currents 3 thick turbidites having a sheet like distribution in three of the formations 4 deposition of turbidites at mid or upper bathyal depths 5 syndepositional deformation and 6 the small size of the basin in which the four youngest formations were deposited little sediment is deposited at the margin of slope basins where there is substantial syndepositional uplift whereas at the margins of turbidite basins formed in foreare areas there is thick massive upper bathyal slope deposited siltstone

were there framework reefs in the cambrian it is commonly thought that framework reefs did not exist prior to middle ordovician time lower cambrian archaeocyathan algal limestones from several localities suggest that this view may be incorrect in particular limestones in the poleta formation of western nevada and eastern california display a complex branched framework and a biological zonation similar to that described from ordovician and younger rocks these archaeocyathan rich limestones are associated with coarse grained oolite contain tidal channels and are flat topped and laterally continuous rather than biohermal i interpret them to have been wave resistant environment dominating framework reefs

the neoproterozoic to early cambrian in southwest mongolia an introduction in this collection of papers we attempt to document through interdisciplinary studies in southwest mongolia the interlinked evolution of the biosphere and lithosphere over the neoproterozoic cambrian interval in so doing we bring together the fruits of two expeditions to the altay mountains sponsored by igcp project 303 on precambrian cambrian event stratigraphy both expeditions took place during an interval of great socio economic change in the region the first expedition in 1991 was one of the last in a series of joint soviet mongolian palaeontological expeditions organized by a yu rozanov and r barsbold and led by e a zhegallo and a yu zhuravlev scientists from sweden and the uk also participated the second 1993 expedition was one of the first igcp project meetings organized independently by the mongolian academy of sciences and was led by m d brasier and d dorjnamjaa

control of triassic seawater chemistry and temperature on the evolution of post paleozoic aragonite secreting faunas the terminal permian extinction event ended the dominance of calcite secreting benthic faunas that had prevailed during the paleozoic most of those calcite secretors especially brachiopods and corals were replaced during the early and middle triassic by aragonite secreting faunas especially bivalves and scleractinian corals geochemical evidence suggests that a unique combination of elevated sulfate concentrations elevated temperatures and possibly elevated mg ca ratios characterized early and middle triassic seawater these triassic geochemical conditions may have favored evolution of the aragonitic faunas that arose in the aftermath of the permian extinctions and that have subsequently dominated the mesozoic and cenozoic