structure and composition of organic reefs and carbonate mud mounds concepts and categories defined here as essentially in place calcareous deposits created by sessile organisms organic reefs are diverse and complex structures with a long geological history their classification has been the subject of fierce debate often characterized by reliance on subjective features such as wave resistance and qualitative attempts to discriminate between first and second class reefs in contrast emphasis is here placed on the objective characteristic of the type of sedimentary support which largely determines the sedimentary composition of the deposit constructional and depositional processes result in three principal sedimentary components matrix m essentially in place skeletons s and cavity cement c whose proportions can be represented on msc triangular plots separately or together these components also provide the structural support for the reef on these compositional and structural bases three main categories of organic reef are recognized 1 matrix supported reefs agglutinated microbial reefs cluster reefs segment reefs 2 skeleton supported reefs frame reefs 3 cement supported reefs cement reefs agglutinated microbial reefs possess laminated clotted or aphanitic fabrics created by microbial trapping of particulate sediment in place skeletons and large primary cavities are rare early cementation may provide added support topographic relief is limited by the need for currents to provide sediment to accreting surfaces cluster reefs skeletal reefs in which essentially in place skeletons are adjacent but not in contact resulting in matrix support characterized by relatively high matrix skeleton ratios and low volumes of extra skeletal early cement sediment trapping is an important corollary of skeletal growth and cluster reef organisms are tolerant of loose sediment absence of framework limits the topographic relief that cluster reefs can attain relative to spatial extent and may permit bedding to develop within the reef close cluster reefs have skeletons up to 1 unit distance apart spaced cluster reefs have skeletons more than 1 and up to 2 unit distances apart with increasing separation of skeletons they grade to level bottom communities segment reefs matrix supported reefs in which skeletons are adjacent and may be in contact but are mostly disarticulated and mainly parauthochtonous matrix abundance is high and early cement relatively low moderate relief can develop in response to intense on reef sediment production frame reefs skeletal reefs in which essentially in place skeletons including calcified microbes are in contact characterized by relatively high skeleton matrix ratio skeletal support enables them to raise themselves above the substrate independently of cementation and particulate sedimentation simultaneously by creating partly open shelter cavities skeletal support may facilitate early cementation both relief and early lithification promote marginal talus formation skeletal shape and orientation distinguish conical stick like dendritic domical and laminar frames each of these may be open or filled open frame reefs

giant holocene freshwater microbialites laguna bacalar quintana roo mexico with more than 10 km of total length holocene microbialites in laguna bacalar mexico belong to the largest freshwater microbialite occurrences microbialites include domes ledges and oncolites domal forms can grow to diameters and heights of 3 m microbialites are composed of low magnesium calcite which is to a large extent precipitated due to the metabolic activity of the cyanobacteria homeothrix and leptolyngbya and associated diatoms photosynthesis removes carbon dioxide and triggers carbonate precipitation also an elevated carbonate concentration in lagoon waters derived from dissolution of cenozoic limestone in a karst system supports carbonate precipitation trapping and binding of detrital grains is also observed but is not as common as precipitation bacalar microbialites are largely thrombolitic however stromatolitic sections occur as well the bulk of bacalar microbialites probably formed in the late holocene ca 1 kyr bp until present according to 14c dating microbialites accreted 9 to 8 cal kyr bp however these ages may be too old as a result of a strong hard water effect this effect is seen in 14c ages of living bivalve and gastropod mollusc shells from bacalar lagoon which are 8 to 7 cal kyr bp the modern associated fauna of microbialites is characterized by low diversity and high abundance of the bivalve mollusc dreissena sp and the gastropod pomacea sp the abundant grazing gastropods presumably hamper modern microbialite formation a comparison of bacalar microbialites with other modern microbialite occurrences worldwide shows only a few patterns sizes shapes microbial taxa mineralogy type of accretion and settings including water properties of microbialite occurrences exhibit high variability a trend may be seen in the grazing metazoa which are rare to absent in the marine and brackish examples but apparently present in all the freshwater occurrences of microbialites also freshwater examples are usually characterized by elevated concentrations of carbonate and or calcium ions in the surrounding waters

precambrian crustal evolution of the eastern north china craton as revealed by u pb ages and hf isotopes of detrital zircons from the proterozoic jing eryu formation abstract simultaneous in situ u pb dating trace element and hf isotopic analyses have been carried out on detrital zircons obtained from sandstones in the neoproterozoic jing eryu formation from the eastern block north china craton ncc with the aim of constraining the ages of magmatic and metamorphic events and hence the precambrian crustal evolution of the ncc two groups of zircons i e magmatic and metamorphic in origin have been identified based on cathodoluminescence images zircon ti temperatures and th u ratios zircon u pb dating shows two main magmatic events with ages of 2 55 2 47 ga and 1 80 1 70 ga and four metamorphic events with ages of 2 51 2 48 ga 1 96 1 90 ga 1 87 1 85 ga and 1 80 ga in the ncc no zircons with ages of 3 8 ga have been identified in this study indicating either these were covered at the time of deposition or the limited presence of 3 8 ga rocks in the ncc the hf isotopic data show the 2 5 ga magmatic zircons have variable hf t values including both positive and negative values and with crustal model ages of 2 7 2 9 ga which can be interpreted to indicate mixed sources for their parental rocks i e ancient crust 3 8 ga or 3 3 ga and depleted mantle implying significant continental crustal growth at 2 5 ga however paleoproterozoic magmatic zircons all have negative hf t and archean hf model ages suggesting that their parental rocks were formed from recycled archean materials the widespread 2 5 ga metamorphism in the eastern block coupled with extensive 2 5 ga magmatism and crustal growth are consistent with a mantle plume beneath the eastern block of the ncc during the neoarchean whereas a progressive increase in 1 85 ga metamorphic zircon westward across the eastern block toward the trans north china orogen is best explained by collision between the eastern and western blocks at this time

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

sedimentary pyrite a window into the microbial past early diagenetic pyrite forms as a result of microbial processes in sediments but has received little attention as a potential source of microbial fossils sedimentary pyrite grains archean to jurassic in age were examined by scanning and transmission electron microscopy tem ion milling was essential for the preparation of electron transparent tem samples most pyrite grains revealed coccoid rod shaped and even filamentous features that are interpreted as microbial identification of microbial remains in sedimentary pyrite may greatly expand our knowledge of microbial life in the sedimentary record combined with geochemical characterization the study of pyritized microbes in the geologic record may in the future enable us to interpret changes in geochemical signatures more realistically in terms of different sulfate reducing communities sedimentary pyrite grains may also represent a good prospect to further our knowledge of past life on mars

steep microbial boundstone dominated plaform margins abstract seaward progradation of several kilometers has been documented mostly for leeward margin low angle carbonate slope systems with a dominant platform top sediment source however steep and high relief margins fronting deep basins can also prograde and as such are somewhat perplexing characteristics of two prograding carboniferous examples provide a model which may apply elsewhere 1 outcrops in asturias northern spain serve as important analogs for 2 hydrocarbon reservoirs in steep sided isolated platforms of the north caspian basin kazakhstan such as tengiz seismic and well data from tengiz corroborate outcrop patterns for slope development showing progradation of up to 5 and more than 10 km respectively despite the high relief up to 600 m and steep 20 35 nature of these margins the two examples share a highly productive microbial boundstone factory extending from the platform break down the slope to nearly 300 m or more depth and a lower slope dominated by mega breccias and grain flow deposits derived from the margin and slope itself the broad depth range of microbial boundstone increases the potential for production during both lowstands and high stands of sea level and thereby facilitates progradation independent from platform top derived sediment rapid in situ lithification of the boundstone provides stability to the steep slopes but also leads to readjustment through shearing and avalanching what controls the microbial cement boundstone formation remains a debate but its presence is a key factor controlling the progradational geometry of these and possibly other margins this new model of slope shedding has implications for slope readjustment processes and resulting architecture sequence stratigraphic interpretation reservoir characterization and reservoir modeling especially the isotropic character of microbial boundstone will reduce the potential for coherent seismic reflections to develop and possibly invoke under certain stress regimes shattering and fracturing thereby generating significant non matrix permeability key considerations are the contrasts with the bahamian high stand shedding depositional model slope progradation rates that range from 450 to 1500 m my and net growth rates of in situ boundstone of 1000 m my comparable to or higher than accretion rates for metazoan skeletal reef growth

calcification of cyanobacterial filaments girvanella and the origin of lower paleozoic lime mud the origin of lime mud in ancient shallow marine carbonate platforms is one of the most vexing mysteries in sedimentary geology possible sources previously suggested include the physical and biological disintegration of animal and algal bioclasts mineralizing pelagic organisms and spontaneous whitings from either abiotic precipitation or calcification of suspended picoplankton and organic matter the styles of occurrence of micrite walled tubes referred to girvanella in lower paleozoic limestones argue that occasional permineralization of mucilaginous sheaths of the benthic filamentous cyanobacteria precursor could have produced lime mud when the tubes fell apart estimated volumes are comparable to those calculated for the modern bahama platform the copious growth of cyanobacteria typical in shallow marine settings indicates that this mechanism could account for a considerable amount of lime mud especially in the early paleozoic

characteristics distribution and morphogenesis of subtidal microbial systems in shark bay australia abstract the distribution nature and extent of microbial deposits in hamelin pool shark bay have been investigated and mapped with emphasis on the occurrence external morphologies internal fabrics constructional mechanisms microbial communities growth rates and sediment associations in the intertidal and previously little researched subtidal zone detailed georeferenced substrate mapping revealed extensive subtidal microbial deposits occupying approximately 300 km 2 of the total holocene 1400 km 2 area of hamelin pool the microbial pavement covers 227 km 2 of the subtidal substrate that together with columnar structures reveals a subtidal microbial habitat which occupies an area 10 times larger than the area of the intertidal deposits microbial carbonate is composed of aragonite 80 98 that reveals high positive values of 13 c 4 46 to 5 88 and 18 o 3 06 to 3 88 as a characteristic of the highly evaporative environment with extensive microbial activity oldest dated heads are 1915 and 1680 14 c years bp and the overall system was deposited in two stages the first between 2000 and 1200 and the last from 900 years bp to the present slow growth rates vary from less than 0 1 mm year to 0 5 mm year different internal fabrics were constructed according to their position in relation to the littoral zone by distinct microbial communities and lateral fabric relations have been established evidence of shallowing upward fabric sequences of microbial origin reflects relative falling sea levels during the late holocene and is likely useful in ancient environmental interpretation a sequence of events and mechanisms are described emphasizing differences between the stromatolitic thrombolitic and cryptomicrobial deposits in shark bay the new substrate map and depositional history for this distinctive and peculiar microbial habitat establish the significance of subtidal structures and emphasize the geoscientific importance of hamelin pool especially with respect to early life studies and ancient analogues for understanding microbial activity deposit characteristics fenestral fabrics and distribution

cyanobacterial tufa calcification in two freshwater streams ambient environment chemical thresholds and biological processes abstract calcareous freshwater streams near bad urach southwest germany were studied to determine the environmental limits to cyanobacterial calcification daily variations in temperature ph calcium concentration and alkalinity were measured at seasonal intervals from september 1993 to january 1995 in two small woodland streams with lengths of 1 0 and 1 5 km the principal cause of supersaturation in these fast flowing streams is inorganic carbon dioxide outgassing from resurging groundwater locally enhanced by turbulence at waterfalls and cascades photosynthetic uptake of carbon dioxide and temperature effects are negligible nonetheless organic substrates particularly cyanobacteria dominated microbial mats and biofilm significantly localize precipitation by providing suitable nucleation sites precipitation rates on artificial substrates up to 2 2 mm yr on limestone correlate with high saturation index values copper substrates inhibited microbial colonization and received negligible encrustation tufa formation and external calcium carbonate encrustation of cyanobacteria are conspicuous where the annual wateq4f saturation index exceeds 0 8 and are slightly below 0 7 calcium carbonate impregnation of cyanobacterial sheaths has not been observed we infer that in these fast flowing streams cyanobacteria utilize co2 in photosynthesis whereas elsewhere in sluggish freshwater cyanobacteria utilize hco3 leading to sheath impregnation by calcium carbonate even where saturation index is only 0 2 0 3 thus photosynthetic influence on cyanobacterial calcification appears to be negligible in fast flowing co2 rich streams and cyanobacterial calcification takes the form of external encrustation in slow flowing co2 poor streams and lakes cyanobacteria preferentially utilize bicarbonate and sheath impregnation can result modern tropical marine carbonate shelves have saturation indices commonly in the range 0 62 0 82 and cyanobacterial calcification is negligible extrapolation suggests that cyanobacterial calcification could occur in present day seas if saturation index exceeded 0 8 this level corresponding with heavy calcification in the freshwater streams studied may have been widespread in marine environments in the geological past at times when calcified cyanobacteria and environmentally influenced non skeletal calcium carbonate precipitates were abundant

introduction to tectonics of china abstract the continental crust of china is a mosaic of cratonic blocks and orogenic belts containing small cratons and terranes with various tectonic settings they have diverse origins and complex histories of amalgamation and often suffered repeated reworking after multiple episodes of amalgamation in the last three decades extensive geological geochemical and geophysical investigations have been carried out on these cratonic blocks and intervening orogenic belts producing an abundant amount of new data and competing interpretations this provides important insights into understanding the formation and evolution of the chinese continents the papers assembled in this volume present a timely and comprehensive overview on major advancements and controversial issues related to the formation and evolution of continental crust in china complex tectonic histories were experienced not only by the large scale cratonic blocks and orogenic belts but also by small scale terranes and orogens between and inside these blocks nevertheless our understanding of lithotectonic units and geological processes has been greatly advanced by recent studies of zirconology and geochemistry for various rock types from major petrotectonic units in china it has been further advanced from integrated interpretations of geochemical and petrological data for petrogenesis of magmatic rocks an overview of these observations and interpretations provides new insights into understanding the continental plate tectonics and the chemical geodynamics of subduction zones

depositional processes of the zhushadong and mantou formations early to middle cambrian shandong province china roles of archipelago and mixed carbonate siliciclastic sedimentation on cycle genesis during initial flooding of the north china platform to understand the depositional processes and environmental changes during the initial flooding of the north china platform this study focuses on the lower to middle cambrian zhushadong and mantou formations in shandong province china the succession in the jinan and laiwu areas comprises mixed carbonate and siliciclastic deposits composed of limestone dolostone stromatolite thrombolite purple and grey mudstone and sandstone a detailed sedimentary facies analysis of seven well exposed sections suggests that five facies associations are the result of an intercalation of carbonate and siliciclastic depositional environments including local alluvial fans shallowing upward carbonate siliciclastic peritidal cycles oolite dominant shoals shoreface and lagoonal environments these facies associations successively show a transition from an initially inundated tide dominated carbonate platform to a wave dominated shallow marine environment in particular the peritidal sediments were deposited during a large number of depositional cycles these sediments consist of lime mudstone dolomite stromatolite and purple and grey mudstones these shallowing upward cycles generally resulted from carbonate production in response to an increase of accommodation during rising sea level the carbonate production was however interrupted by frequent siliciclastic input from the adjacent emergent archipelago the depositional cycles thus formed under the influence of both autogenetic changes including sediment supply from the archipelago and allogenic control of relative sea level rise in the carbonate factory a low relief archipelago with an active tidal regime allowed the development of tide dominated siliciclastic and carbonate environments on the vast platform siliciclastic input to these tidal environments terminated when most of the archipelago became submerged due to a rapid rise in sea level this study provides insights on how a vast cambrian carbonate platform maintained synchronous sedimentation under a tidal regime forming distinct cycles of mixed carbonates and siliciclastics as the system kept up with rising relative sea level during the early stage of basin development in the north china platform

development of middle cambrian leiolitic bioherms dominated by calcified microbes a case study of the xinji section north china platform abstract among the varieties of microbial carbonate rocks leiolites are rare in ancient rock records and have only few examples in the modern environment which makes them difficult to study this study documents the sedimentary environment characteristics and composition of microbial carbonates dominated by calcified microbes which developed in the cambrian miaolingian xuzhuang formation on the north china platform the upper part of the formation in the xinji section of lushan city henan province is bounded by a drowning unconformity surface of a third order depositional sequence beside the development of an ooid shoal in response to sea level fall a bioherm dominated by leiolite also developed in the upper part of the xuzhuang formation these leiolites represent special sedimentary phenomena due to their occurrence with high energy ooid shoals microscopically they are characterized by abundant calcified cyanobacteria fossils such as dichotomous branching epiphyton and filamentous cyanobacteria thus showing the diversity and complexity of the cyanobacterial microbial mats that predominate the leolitic bioherm four groups are confirmed for epiphyton based on the morphological characteristics of calcified filaments the filamentous cyanobacteria can be divided into girvanella and subtifloria and their possible forming mechanisms are discussed the macroscopic and microscopic characteristics of the current leiolites provide important research clues and typical examples for understanding the origin of the miaolingian leiolitic bioherm and its paleoenvironmental significance

extensive recession of cordillera darwin glaciers in southernmost south america during heinrich stadial 1 abstract the geographic expression and phasing of events during the last termination are important for isolating mechanisms that caused earth to emerge from the last ice age heinrich stadial 1 hs1 14 600 18 000 yr bp is a key because of the central role that its far field effects had on the last termination in the southern hemisphere here we present new data from cordillera darwin that show rapid glacier recession in southern south america during hs1 this retreat was coeval with ice recession elsewhere in south america and new zealand with increased upwelling in the southern ocean with warming of ssts offshore of chile and with a rise in atmospheric co2 together these data indicate a coherent and rapid response to the effects of hs1 in the middle and high latitudes of the southern hemisphere

growth morphologies of modern marine stromatolites a case study from highborne cay bahamas abstract stromatolites are a uniquely coupled geo biosphere system which potentially records important paleoenvironmental and biological information characterizing and distinguishing between the biological and physical factors that control stromatolite morphogenesis therefore has important implications for the understanding of modern stromatolites and the interpretation of ancient systems this paper documents the occurrence and distribution of stromatolites with distinct growth morphologies in the highborne cay reef system and other locations in exuma cays bahamas and explores the relative contributions of physical and biological environmental factors controlling stromatolite shape our observations suggest that macro scale growth morphologies of exuma stromatolites are primarily controlled by accommodation space hydrodynamics and sedimentation patterns the latter are critical for the stromatolite ecosystem in that the suspended sediment provides grains for trapping and binding and thus stromatolite accretion furthermore sediment burial removes macroalgae allowing the prokaryotic community to dominate changes in sedimentation patterns and frequency allow for the colonization of stromatolites by macroalgae and boring macrofauna which in time destroy and degrade the stromatolite structure

the late early cambrian microbial reefs immediately after the demise of archaeocyathan reefs hunan province south china abstract the archaeocyath bearing reefs that first appeared in south china in the atdabanian were last seen in the lower toyonian e g in the tianheban and jindingshan formations the upper toyonian lower amgan qingxudong formation of hunan province examined in this study includes large sized reefs formed solely by calcimicrobes of epiphyton kordephyton girvanella hedstroemia and renalcis during the middle and upper cambrian small scale stromatolite reefs were formed the qingxudong reefs are therefore interpreted to be the most well developed microbial reefs of the post archaeocyath bearing reefs in the late early cambrian the transition from archaeocyath bearing to purely microbial reefs was caused by a decline in the diversity of metazoans and was accompanied by a reduction in the abundance of reefs possibly related in part to late early cambrian regression the late early cambrian reefs of south china contain a well preserved record of reef succession and provide important insights into the factors that led to the demise of archaeocyath bearing reefs and the subsequent long lasting hindrances to the development of skeletal dominated reefs during the middle and late cambrian

sequence sequence stratigraphy sea level changes and depositional systems in the cambro ordovician of the north china carbonate platform abstract the cambro ordovician strata in north china were deposited over a very extensive craton extending some 1500 km east west and 1000 km north south the dominantly shallow water carbonate succession reaches up to 2000 m in thickness and two megasequences transgressive regressive cycles can be distinguished lower cambrian through lower ordovician strata and middle through upper ordovician strata separated by a major palaeokarst the first megasequence consists of nine sequences which are generally 50 150 m in thickness the lower cambrian sediments consist of phosphorites and phosphatic sandstones deposited during the flooding of the craton carbonates mudrocks and evaporites were deposited in the early cambrian under an arid climate laying the foundation for the subsequent long period of shallow water carbonate deposition which lasted some 70 m y the middle and lower upper cambrian sequences consist predominantly of mudrocks and storm deposits tempestites in the lower part and oolitic grainstones and tidal flat lime mudstones in the upper part these represent outer mid and mid inner ramp depositional systems respectively of the transgressive and highstand systems tracts these sequences have strong similarities with the grand cycles in the cambro ordovician successions of north america in the upper cambrian there is a distinctive unit of glauconitic purple red mudstone several metres thick which is interpreted as the deposits of the maximum flooding of the first megasequence in the upper cambrian there was a phase of tilting of the north china carbonate platform to the north and storm deposits especially intraclastic conglomerates and hummocky cross stratified grainstones packstones were very common at this time also common in upper middle and lower upper cambrian strata are stromatolitic thrombolitic bioherms several metres in diameter the upper upper cambrian through lower ordovician strata are dominantly fine grained limestones and dolomites deposited in shallow subtidal and inter to supra tidal environments on a low energy epeiric sea platform this part of the succession is the regressive part of the first megasequence so that overall the platform shows an evolution from platform initiation to platform foundation to a ramp depositional system and then an extensive epeiric platform on a small scale the succession is composed of metre scale shallowing upward cycles parasequences arranged into cycle sets of 10 30 m thick the middle upper ordovician megasequence consists mostly of shallow water carbonates with several thick evaporite units minor palaeokarsts and palaeosoils separate the sequences which are composed of metre scale cycles regional uplift affected the north china platform in the ordovician and sedimentation did not resume until the carboniferous there is a good correlation of the two transgressive regressive megasequences described here with the global 2nd order relative sea level curve for the cambro ordovician

sequence stratigraphy of the taebaek group cambrian ordovician mideast korea abstract this study focuses on the sequence stratigraphic implications of the taebaek group cambrian ordovician a mixed carbonate siliciclastic sequence ca 1200 m thick in the mideastern part of the korean peninsula the group contains 11 lithologic units formations that can be partitioned into four packages supersequences i iv each package comprises alternation of siliciclastic and carbonate successions corresponding to the second order sequence supersequence formed in a period of 10 100 m y supersequence i jangsan myeonsan myobong and daegi fms represents the initial inundation and subsequent drowning during the late early to middle middle cambrian it experienced the drowning between the middle and late middle cambrian forming type 3 sequence boundary supersequence ii sesong and hwajeol fms was formed by prolonged marine flooding during the late middle and late cambrian it was terminated by a large supply of siliciclastics due to the rejuvenation of the drainage basin and the subsequent shallowing at the cambrian ordovician boundary type 2 sequence boundary supersequence iii dongjeom dumugol and makgol fms comprises the lowstand coarse grained siliciclastics transgressive shale by marine flooding and shallow platform carbonates by highstand progradation in the early ordovician following the large scale eustatic fall of sea level in the earliest middle ordovician supersequence iv jigunsan and duwibong fms formed on the subaerial exposure surface type 1 sequence boundary by resumed marine flooding in the middle ordovician this study provides basis for basin scale correlation with the coeval sequences in northeastern china

the late cambrian spice δ13c event and the sauk ii sauk iii regression new evidence from laurentian basins in utah iowa and newfoundland carbon isotope data from upper cambrian sections in three laurentian basins in northern utah central iowa and western newfoundland record a large positive d 13 c excursion spice event of up to 1 5 peak d 13 c ratios are well dated by trilobite collections to the middle of the steptoean stage dunderbergia zone and occur during maximum regression associated with formation of the sauk ii sauk iii subsequence boundary on the north american craton max imum regression was marked by an influx of quartz sand into carbon ate platform settings in all three widely separated basins in northern utah this quartz sand formed a thick sequence known as the worm creek quartzite which marks a conspicuous interruption of carbonate deposition during the middle to late cambrian in the region in west ern newfoundland the thickness of the quartz sand unit is much re duced but still marks a brief shutdown of the carbonate factory that is unique to the cambrian shelf succession of the area in the central iowa area of the cratonic interior an upward shallowing carbonate succession culminates in cross stratified trilobite grainstones at the peak of the spice in dunderbergia zone time and the lowest point on the relative sea level curve is associated with the occurrence of coarse quartz sand derived from the encroaching shoreface although it is difficult to determine precisely the departure from baseline d 13 c that marks the beginning of the spice excursion in the stratigraphic successions analyzed our results are consistent with a rise and subsequent fall in d 13 c tracking a major regressive transgressive event recorded across northern laurentia the correlation of a major d 13 c excursion with regression is similar to that described for the late ordovician for which the pattern has been attributed to either in creased carbonate relative to terrigenous weathering rates as ice sheets covered up organic matter containing silicates at high latitudes or high productivity and organic carbon burial driven by oceanic overturn the lack of known steptoean age ice sheets that could have affected the ratio of carbonate to silicate weathering rates suggests that organic carbon burial was the likely cause of the spice event we suggest that increased weathering and erosion rates during relative sea level fall sauk ii iii increased the burial fraction of organic carbon in an expanded region of fine grained siliciclastic deposits in shelf and upper slope environments during the steptoean

microbial carbonate abundance compared with fluctuations in metazoan diversity over geological time abstract secular variation in microbial carbonate abundance may be reflected by stromatolite morphotype diversity and reefal microbial carbonate abundance these datasets reveal long term changes over the past 3000 myr that include a peak of abundance 1250 myr ago late proterozoic decline cambrian resurgence and fluctuating decline during the remainder of the phanerozoic it is conceivable that proterozoic metazoan diversification coincided with inception of stromatolite decline 1250 myr ago but microbial carbonate increase during cambrian metazoan radiation together with failure of microbial carbonates to increase in the aftermaths of the end ordovician end triassic and end cretaceous mass extinctions suggest that factors in addition to metazoan competition significantly influenced long term changes in microbial carbonate abundance

growth patterns of the cambrian microbialite phototropism and speciation of epiphyton abstract microbes started constructing shallow marine stromatolitic bioherms in the archean but they transferred their role as a major buildup maker to metazoans in phanerozoic microbial buildups often recovered their predominance in the carbonate platform when reefal metazoan communities collapsed epiphyton an extinct taxon of calcified microbe that possessed branching filamentous trichomes was an important reef builder in the shallow marine carbonate platform during middle cambrian aftermath of an extinction of archaeocyath sponges which were major reef building sessile organisms in the early cambrian here we present direct evidence of phototropism of epiphyton found from fossilized behavior in micro and macro structures of meter scale microbial bioherms of the zhangxia formation middle cambrian north china platform shandong province china the bioherms consist of stacked growth layers with the inner and outer divisions divided by distinct boundary the inner division of growth layers of the epiphyton bioherm is dominated by dense uniform bush shaped epiphyton thalli whereas the curved outer division has layered texture normal to the surface comprised of elongated and chambered thalli it suggests that photosynthetic epiphyton reacted actively to the spatial changes in intensity of sunlight controlled by angle of illumination on the curved growth surface of the bioherm the inner and the outer divisions comprise different morpho types of epiphyton the spatial distributions of different morpho types in variously illuminated divisions of epiphyton might have caused further speciation of epiphyton

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

formative mechanisms depositional processes and geological implications of furongian late cambrian reefs in the north china platform abstract the cambrian series 3 furongian successions of the north china platform contain various microbial metazoan and microbial reefs this study focuses on furongian reefs of the platform in order to understand formative processes and the evolution of the reefs during cambrian epoch 3 and the furongian three types of furongian reefs were differentiated in the shandong region china maceriate reefs columnar stromatolitic reefs and small scale microbial reefs maceriate reefs show dm to m scale domal or flat bedded geometry and consist of cm scale maze like maceria structures made of siliceous sponges and microbial components microstromatolites girvanella and tarthinia columnar stromatolitic reefs are characterized by stromatolite columns of 10 100 cm in height and 5 50 cm in diameter they consist dominantly of girvanella with less conspicuous poorly preserved sponge spicule networks small scale microbial reefs commonly show cm to dm scale domal macrostructures and were constructed mainly by calcimicrobes girvanella and renalcis these three types of furongian reefs were deposited in various shallow marine settings in response to relative sea level changes the furongian reefs are markedly different in terms of macro and micro fabrics from the cambrian series 3 reefs that are dominated by thrombolites and dendrolites and were constructed mainly by epiphyton in the shandong region this difference is also recognized in the beijing region ca 500 km away the abrupt transition from the cambrian series 3 type to furongian type reefs coincidently with a decrease in calcified microbe diversity was most likely due to global euxinic oceanic conditions and a possible eustatic sea level drop rather than the highly diachronous platform wide drowning event i e drowning of the cambrian series 3 carbonate platform the abundant occurrence of sponge spicule networks in the furongian reefs suggests that metazoan reef builders i e sponges resurged and became actively involved in the reefal systems prior to the great ordovician biodiversification event this study may provide an important basis for further investigation into the evolution of reefal systems during the middle to late cambrian when metazoan reef builders were known to be scarce

an introductory review on gravitational deformation induced structures fabrics and modeling abstract recent studies have pointed out a similarity between tectonics and slope tectonic induced structures numerous studies have demonstrated that structures and fabrics previously interpreted as of purely geodynamical origin are instead the result of large slope deformation and this led in the past to erroneous interpretations nevertheless their limit seems not clearly defined but it is somehow transitional some studies point out continuity between failures developing at surface with upper crust movements in this contribution the main studies which examine the link between rock structures and slope movements are reviewed the aspects regarding model and scale of observation are discussed together with the role of pre existing weaknesses in the rock mass as slope failures can develop through progressive failure structures and their changes in time and space can be recognized furthermore recognition of the origin of these structures can help in avoiding misinterpretations of regional geology this also suggests the importance of integrating different slope movement classifications based on distribution and pattern of deformation and the application of structural geology techniques a structural geology approach in the landslide community is a tool that can greatly support the hazard quantification and related risks because most of the physical parameters which are used for landslide modeling are derived from geotechnical tests or the emerging geophysical approaches

continental growth and secular evolution constraints from u pb ages and hf isotope of detrital zircons in proterozoic jixian sedimentary section 1 8 0 8 ga north china craton a b s t r a c t in order to understand the precambrian crustal growth and reworking history of the north china craton in situ u pb and lu hf isotope analyses were carried out on the detrital zircons from a well preserved nearly undeformed proterozoic sedimentary section with time interval of 1 8 0 8 ga totally 806 zircons separated from 7 samples collected from each representative stratigraphic unit were measured for upb and lu hf isotopic compositions of which 430 grains yielded concordant u pb ages the concordant zircons show three prominent age groups of 1 6 1 8 ga 1 9 2 2 ga and 2 3 2 6 ga both positive and negative ehf t values were exhibited by zircons from all groups suggesting both juvenile crust addition and crustal reworking for all age groups the hf crustal model ages of zircons reveal that the juvenile materials were continuously added to the crust between 4 0 and 2 0 ga with a prominent peak at 2 7 3 0 ga and a less significant peak at 3 1 3 4 ga the juvenile contributions to the newly formed crust decrease stepwise through time and crustal reworking has dominated over juvenile inputs to the continental crust since 2 6 ga compared with the detrital zircons from modern rivers running within the north china craton the sedimentary rocks contain more older zircons implying the relatively poor preservation of archean crustal rocks in modern river sand and accordingly the weights of archean crystallizations ages and crustal growth inferred from detrital zircons in modern river are significantly underestimated the integrated studies of detrital zircons from both modern river sands and ancient sedimentary rocks are essential to decipher the early crustal growth history more faithfully

geobiology of microbial carbonates metazoan and seawater saturation state influences on secular trends during the phanerozoic abstract microbial carbonates are long ranging essentially bacterial aquatic sediments their calcification is dependent on ambient water chemistry and their growth is influenced by competition with other organisms such as metazoans in this paper these relationships are examined by comparing the geological record of microbial carbonates with metazoan history and secular variations in caco3 saturation state of seawater marine abundance data show that microbial carbonates episodically declined during the phanerozoic eon past 545 myr from a peak 500 myr ago this abundance trend is generally inverse to that of marine metazoan taxonomic diversity supporting the view that metazoan competition has progressively limited the formation of microbial carbonates lack of empirical values concerning variables such as seawater ionic composition atmospheric partial pressure of co2 and ph currently restricts calculation of caco3 saturation state for the phanerozoic as a whole to the use of modeled values these data together with palaeotemperature data from oxygen isotope analyses allow calculation of seawater caco3 saturation trends microbial carbonate abundance shows broad positive correspondence with calculated seawater saturation state for caco3 minerals during the interval 150 545 myr ago consistent with the likelihood that seawater chemistry has influenced the calcification and therefore accretion and preservation of microbial carbonates these comparisons suggest that both metazoan influence and seawater saturation state have combined to determine the broad pattern of marine microbial carbonate abundance throughout much of the phanerozoic in contrast for the major part of the precambrian it would seem reasonable to expect that seawater saturation state together with microbial evolution was the principal factor determining microbial carbonate development interrelationships such as these with feedbacks influencing organisms sediments and the environment are central to geobiology