stratigraphic architecture palaeogeography and sea level changes of a third order depositional sequence the late turonian early coniacian in the northern iberian ranges and central system spain abstract this paper reports a high resolution stratal palaeogeographical and quantitative analysis of a late turonian early coniacian carbonate ramp the northern iberian ranges and its siliciclastic coastal margin the central system the analyzed succession comprises a complete 3rd order depositional sequence with a shelf margin wedge a transgressive systems tract and a highstand systems tract based on the existence of a subaerial exposure evidences and early diagenetic overprints b stratal relationships onlap offlap toplap regarding underlying and overlying sequences and c changes in the vertical facies evolution the depositional sequence was bounded by two major sequence boundaries these indicate that a major fall in relative sea level occurred in these boundaries the comparative study of the internal stratal surfaces and the vertical facies succession allowed the identification of superimposed higher order depositional parasequences sets and parasequences 4th to 5th order which record short term changes in the relative sea level thus when vertical facies trends in the parasequences are arranged in the framework of a parasequence set a clearer palaeogeographic picture is obtained and palaeogeographic maps can more clearly show the evolutionary trend of the basin each parasequence set was composed of a basal lowstand transgressive systems tract in turn composed of fringing siliciclastic shoreface deposits and offshore muds older sequences were partially exposed further landwards the sedimentation of these sands resulted in the progradation of the coastal systems during times of low relative sea level during which the basal parasequence set boundary was also generated subsequent transgression remobilised underlying lowstand sands the early highstand was composed of carbonate sediments in platform areas and mixed siliciclastic carbonate sediments landwards separated by a narrow fringe of muddy marl offshore sediments the late highstand showed a progressive shallowing trend with carbonate littoral and tidal sediments covering broad areas of the basin and lagoon facies were restricted to the northern outcrops during late highstand underlying transgressive systems tract and older highstand deposits were exposed landwards sea level and accommodation curves have been obtained from paleogeographical sedimentological and sequence stratigraphical data the mean sea level curve for the entire 3rd order sequence shows a rise of the sea level and then an overall stillstand but accommodation curve shows a positive trend along the sequence the 3rd order sea level cycle has a mean amplitude of 52 m and high frequency cycles have amplitudes of 20 40 m 4th order and about 1 5 4 m 5th order the mean final rise in the sea level 46 6 m is quite similar to the total accommodation deduced from fischer plot 45 75 m the sea level cycles are considered to be eustatic in origin and driven by orbital forcing in the milankovitch band based on the estimated 4th order 400 kyr and 5th order cycle lengths 80 kyr

origin of phosphatic stromatolites in the upper cretaceous condensed sequence of the polish jura chain abstract the turonian stromatolite bearing condensed sequence in the polish jura chain the european epicontinental basin provides good insight into the environment of formation of cretaceous phosphatic stromatolites owing to their purely phosphatic development and negligible post depositional alteration the sequence developed as a result of slow pelagic sedimentation and microbial mat phosphatization on a submarine swell surrounded by local basins with non condensed carbonate deposition diagenesis of organic matter and dissolution of biogenic apatite were the major sources of reactive phosphorus for the microbial mat phosphatization stromatolite growth occurred due to pulses of amorphous or poorly ordered calcium phosphate precipitation followed by crystallization of carbonate fluorapatite cfa the phosphogenic environment left an imprint on the isotopic composition of limestone carbon and lattice bound carbon and sulphur in cfa and on the light rare earth element lree distribution in cfa the 13c of the stromatolite bearing sequence shows a negative excursion 1 to 3 standing in marked contrast to positive carbon values of the surrounding basinal carbonate most of the 34s values of cfa 20 to 21 fit the value range of the coeval seawater sulphate and the lree distribution shows a well defined seawater pattern this geochemical signature is indicative of intense diagenesis of organic matter at the seafloor pelagic carbonate dissolution and prolonged exposure of the deposited phosphate towards the water column the enhanced deposition and diagenesis of organic phosphorus in the stromatolitic environment reflects elevated levels of the epicontinental basin nutrification related to sea level rises and the associated oceanographic and geochemical changes

microbial mats as bioreactors populations processes and products microbial mats are dynamic and complex ecosystems exhibiting spatial and temporal heterogeneity the physical chemical environment is typified by steep gradients and distinct microenvironments these microenvironments support a great diversity of species with a wide range of metabolic processes these processes often result in coupled reactions and biogeochemical cycles and produce important end products such as trace gases and mineral precipitates the latter can impact the composition and character of the sediment imparting a biosignature these biosignatures can be preserved in the rock record and are useful in the interpretation of fossil record on earth and possibly as an indication of life on other planetary bodies the modern marine stromatolites of the exuma cays bahamas provide an ideal system for studying the populations processes and products in a microbial ecosystem using a multidisciplinary approach in order to acquire redox energy microbial populations need to carry out metabolic reactions at rates faster than the equivalent chemical abiotic reactions as such microbes can be viewed as bioreactors that preferably oxidize carbon to co2 to maximize the energy yield the study of the microbial role in carbonate sedimentation and lithification in these stromatolites provides a picture of microbial mats as bioreactors producing a biosignature

segmentation and supercycles a catalog of earthquake rupture patterns from the sumatran sunda megathrust and other well studied faults worldwide abstract after more than 100 years of earthquake research earthquake forecasting which relies on knowledge of past fault rupture patterns has become the foundation for societal defense against seismic natural disasters a concept that has come into focus more recently is that rupture segmentation and cyclicity can be complex and that a characteristic earthquake model is too simple to adequately describe much of fault behavior nevertheless recognizable patterns in earthquake recurrence emerge from long high resolution spatially distributed chronologies researchers now seek to discover the maximum minimum and typical rupture areas the distribution variability and spatial applicability of recurrence intervals and patterns of earthquake clustering in space and time the term supercycle has been used to describe repeating longer periods of elastic strain accumulation and release that involve multiple fault ruptures however this term has become very broadly applied lumping together several distinct phenomena that likely have disparate underlying causes we divide earthquake cycle behavior into four major classes that have different implications for seismic hazard and fault mechanics 1 quasi periodic similar ruptures 2 clustered similar ruptures 3 clustered complementary ruptures rupture cascades and 4 superimposed cycles segmentation is likewise an ambiguous term we identify master segments and asperities as defined by barriers to fault rupture these barriers may be persistent rarely or never traversed frequent occasionally traversed or ephemeral changing location from cycle to cycle we compile a catalog of the historical and paleoseismic evidence that currently exists for each of these types of behavior on major well studied faults worldwide due to the unique level of paleoseismic and paleogeodetic detail provided by the coral microatoll technique the sumatran sunda megathrust provides one of the most complete records over multiple earthquake rupture cycles long historical records of earthquakes along the south american and japanese subduction zones are also vital contributors to our catalog along with additional data compiled from subduction zones in cascadia alaska and middle america as well as the north anatolian and dead sea strike slip faults in the middle east we find that persistent and frequent barriers rupture cascades superimposed cycles and quasi periodic similar ruptures are common features of most major faults clustered similar ruptures do not appear to be common but broad overlap zones between neighboring segments do occur barrier regions accommodate slip through reduced interseismic coupling slow slip events and or smaller more localized ruptures and are frequently associated with structural features such as subducting seafloor relief or fault trace discontinuities this catalog of observations provides a basis for exploring and modeling root causes of rupture segmentation and cycle behavior we expect that researchers will recognize similar behavior styles on other major faults around the world

abiological origin of described stromatolites older than 3 2 ga the three well documented occurrences of three dimensional stromatolites older than 3 2 ga meet most criteria for biogenicity except the presence of fossil bacteria however they also show features more consistent with nonbiological origins small conical structures in the strelley pool chert in the upper part of the warrawoona group 3 5 3 2 ga western australia lack the structure typical of stromatolites and probably formed mainly through evaporitc precipitation a domal structure from the north pole chert warrawoona group formed by soft sediment deformation or originally flat layers laminated chert containing domal and pseudocolumnar structures in the onverwacht group 3 5 3 3 ga barberton greenstone belt south africa extends downward into veins and cavities where it formed through inorganic precipitation although bacterial communities were widespread on earth prior to 3 2 ga these particular three dimensional structures are probably abiotic in origin and do not provide information on the paleobiology or paleoecology of early organisms the paucity of archean stromatolites older than 3 2 ga probably reflects the paucity of known and possibly extant carbonate deposits of this age

evaporitic subtidal stromatolites produced by in situ precipitation textures facies associations and temporal significance abstract the transition between carbonate platforms or isolated carbonate buildups and overlying evaporites commonly is marked by assemblages of stromatolites and interlaminated carbonates and evaporites stromatolites display lamination textures that vary from peloidal and discontinuous on a scale of a millimeter to a few centimeters to isopachous and continuously laminated on a scale of a centimeter to a few meters the isopachous lamination texture may be composed of either 1 micritic or radial fibrous calcite or 2 dolomite isopachous stromatolitic laminae are remarkably uniform varying little in thickness over a given lateral distance in contrast to stromatolites formed of peloidal laminae which show marked variation in thickness over an equivalent lateral distance these isopachous textures are uncommon on most open marine carbonate platforms and apparently developed in transitional carbonate to evaporite settings because of increasing temperature salinity and anoxia related to water stratification which would have created ecologic restriction and an opportunity for stromatolite growth stromatolites with isopachous lamination are here interpreted to have formed as a result of in situ precipitation of sea floor encrusting calcite and possibly dolomite whereas the stromatolites composed of peloidal discontinuous lamination are inferred to have formed by trapping and binding of loose carbonate sediment in microbial mats while the presence of microbes in almost all near surface environments nullifies use of the term abiotic to describe most precipitated minerals we interpret growth of the isopachous stromatolites to have been dominated by chemogenic precipitation in the absence of microbial mats and the growth of peloidal stromatolites to have been controlled by sedimentation in the presence of microbial mats these transitional stromatolite facies are best developed atop proterozoic and paleozoic carbonate platforms that underlie major evaporite successions however inspection of jurassic and younger evaporite basins such as the messinian of the mediterranean region shows that stromatolites with thin isopachous lamination and radial fibrous textures though present are rare instead these facies may have been replaced by stromatolites with peloidal clastic textures and by low diversity diatomaceous and coccolith mudstones accumulation of the mudstones would have imposed two important effects 1 production of coccoliths would have helped extract calcium carbonate from seawater thus lowering the growth potential for precipitation of sea floor encrusting stromatolites 2 settling of both coccoliths and diatoms would have created a sediment flux to the sea floor which would have served to impede growth of precipitated stromatolites because of smothering of growing crystals

an upper turonian fine grained shallow marine stromatolite bed from the munecas formation northern iberian ranges spain abstract a fine grained stromatolite bed laterally continuous on the kilometer scale and with small synoptic relief crops out in the munecas formation in the northern iberian ranges the munecas fm was deposited during the late turonian on a shallow water platform in the upper cretaceous intracratonic iberian basin the stromatolite bed has a tabular to domed biostromal macrostructure its internal mesostructure consists of planar wavy to hemispherical stromatoids that display a broad spectrum of microstructures including dense micrite bahamite peloids peloidal to clotted microfabrics irregular micritic wall tubes which are suggestive of algae and filamentous microframeworks which are suggestive of filamentous cyanobacteria various stromatolite growth stages have been linked to the dominance of different accretion processes the accretion of the entire fine grained stromatolite involves a complex mosaic of processes trapping and binding of quartz silt grains and bahamites which form the agglutinated parts of some laminae and microbially induced precipitation which forms spongiostromic and micritic laminae tubiform and filamentous microframeworks resembling porostromatate or skeletal stromatolitic growth were also recognized laser icp ms measurements of al si mg mn sr s and fe were analyzed to detect the influence of siliciclastic inputs and major trends during stromatolite accretion carbon and oxygen isotopic compositions from the stromatolite and associated facies were used to identify possible microbial signatures these data describes a unique and well preserved example of a shallow marine upper turonian fine grained stromatolite

hardened subtidal stromatolites bahamas hardened high relief stromatolites have been discovered along the margins of some bahamian platforms they occur in high energy tidal oolitic sand environments in waters ranging in depth from about 1 to 5 meters physical stress produced by actively migrating bed forms of oolitic sand appears to exclude grazing gastropods and subsequent community successions permitting stromatolite growth

compilation and time series analysis of a marine carbonate δ18o δ13c 87sr 86sr and δ34s database through earth history abstract the sr s o and c isotope database of marine carbonates contains over 55 000 published isotope values of low mg calcite from diagenetically little altered phanerozoic fossil shells as well as samples of whole rocks and calcite cements of ordovician to archean age carbon and oxygen isotope data for the shell material are divided into habitat subsets high mid low latitude and deep sea and whole rock data are separated by mineralogy into calcite dolomite subsets trend correlation wavelet and spectral analyses on gaussian filtered isotope records were applied to detect and quantify similarities and patterns in temporal records with the following results 1 oxygen isotope trends from the high latitude and deep sea habitats are almost indistinguishable through the last 115 ma consistent with the existence of the oceanic conveyor belt throughout this interval 2 all oxygen isotope habitat records show a strong coherent 30 45 ma 38 ma cyclicity throughout the cretaceous and the cenozoic 3 up to 70 of the multi million year variability in the 18o record of the last 115 ma can be simulated by the following equation 18 o 0 64 sin 2 t 120 ma 0 9 x sin 2 t 38 3 ma 1 1 with x ranging from 0 4 0 6 for the low high latitude and deep sea habitats to 0 8 for the mid latitude realm 1 a 120 20 ma cycle occurs in the paleozoic and neoproterozoic 18o record consistent with paleoclimate variability as interpreted from sedimentological and faunal records 2 the offset of 13c values between deep water and high latitude vs surficial habitats at lower latitudes is consistent with the operation of a biological pump in the oceans since at least the cretaceous 3 sr and s isotope records exhibit a 60 70 ma cyclicity throughout the phanerozoic

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

microbial biomineralization processes forming modern ca mg carbonate stromatolites abstract modern ca mg carbonate stromatolites form in association with the microbialmat in the hypersaline coastal lagoon lagoa vermelha brazil thestromatolites although showing diversi ed fabrics characterized by thin orcrude lamination and or thrombolitic clotting exhibit a pervasive peloidalmicrofabric the peloidal texture consists of dark micritic aggregates of veryhigh mg calcite and or ca dolomite formed by an iso oriented assemblage ofsub micron trigonal polyhedrons and organic matter limpid acicular crystalsof aragonite arranged in spherulites surround these aggregates unlike thearagonite crystals organic matter is present consistently in the dark micriticcarbonate comprising the peloids this organic matter is observed as sub micron at and lamentous mucus like structures inside the interspaces of thehigh mg calcite and ca dolomite crystals and is interpreted as the remains ofdegraded extracellular polymeric substances moreover many fossilizedbacterial cells are associated strictly with both carbonate phases these cellsconsist mainly of 0ae2to4lm in diameter sub spherical rod like and lamentous forms isolated or in colony like clusters the co existence offossil extracellular polymeric substances and bacterial bodies associated withthe polyhedrons of ca mg carbonate implies that the organic matter andmicrobial metabolism played a fundamental role in the precipitation of theminerals that form the peloids by contrast the lack of extracellular polymericsubstances in the aragonitic phase indicates an additional precipitationmechanism the complex processes that induce mineral precipitation in themodern lagoa vermelha microbial mat appear to be recorded in the studiedlithi ed stromatolites sub micron polyhedral crystal formation of high mgcalcite and or ca dolomite results from the coalescence of carbonatenanoglobules around degraded organic matter nuclei sub micron polyhedralcrystals aggregate to form larger ovoidal crystals that constitute peloids subsequent precipitation of aragonitic spherulites around peloids occurs asmicro environmental water conditions around the peloids change keywords bacterial fossils biomineralization microbialite nanoglobules peloids stromatolites

measurement of differential rupture duration as constraints on the source finiteness of deep focus earthquakes 2 synthetic tests to estimate errors in rupture vectors and their effect on fault plane identification 1 the directivity method of warren and silver 2006 has been used to distinguish the fault planes of deep earthquakes in the tonga and middle america subduction zones these studies identified exclusively subhorizontal fault planes between 100 and 300 km depth raising the question of whether the observations represent new constraints on the physical mechanism of the earthquakes or a bias in the methodology here the strengths weaknesses and biases of the method are investigated through the comprehensive analysis of 120 synthetic earthquakes with varying depth rupture vector orientation rupture complexity signal to noise ratio and station distribution these synthetic tests which allow the evaluation of the effect of each of the varied parameters on the rupture vector determination show that fault planes can be identified for a wide variety of conditions the method underestimates rupture velocities by 76 94 but this does not affect the determination of the orientation of the rupture vector the most important parameter for determining the orientation of the rupture vector and thereby allowing identification of the fault plane is the distribution of stations recording the earthquake better coverage around the earthquakes results in tighter constraints on the rupture vector the broader distribution of recording stations for deeper earthquakes results in tighter constraints on the rupture vectors for deeper earthquakes and therefore more ease in identifying the fault plane however the difference in resolution does not systematically prohibit the identification of certain orientations of fault planes at shallower depths and suggests that previous observations of exclusively subhorizontal fault planes between 100 and 300 km depth are not the result of systematic bias in the methodology instead the observed dominance of subhorizontal fault planes provides important constraints on the physical mechanism of intermediate depth earthquakes the observed subhorizontal fault orientation is inconsistent with the reactivation of the dominant trenchward dipping outer rise normal faults

combined textural and stable isotopic data as proxies for the mid cretaceous paleoclimate a case study of lacustrine stromatolites in the gyeongsang basin se korea abstract microbial interference of the prevailing sedimentary dynamics during stromatolite growth records vital biogeochemical information which reflects the prevailing paleoclimatic conditions this study documents the simultaneous geochemical and textural changes in mid cretaceous lacustrine stromatolites gyeongsang basin se korea deposited in a semi arid setting fibrous calcite micrite couplets in the stromatolites occurring in the sinyangdong hwasan and banyawol formations constitute the basic growth cycles and can be divided into first second and third order cycles second order cycles show couplets with gradual textural changes from fibrous calcite to micrite laminae and three different types of micrite are present sometimes one type of micrite evolves into another within the second order cycle in the sinyangdong stromatolites consistent enrichments in 18o and depletion in 13c towards micrites within the sinyangdong and hwasan stromatolite couplets and a concomitant depletion of both isotopes from fibrous calcite to micrite in the banyawol sample can be observed these shifts reflect paleohydrological changes in the lake water related to paleoproductivity and paleosalinity fluctuations relatively higher paleosalinity values within the sinyangdong lake water system is registered by higher 18o values of fibrous calcite and micrite in the sy 3 than in the sy 1 and sy 2 stromatolites the consistent shifts in 18o and 13c isotopes in different textural growth fabrics indicate that paleohydrological factors could play a significant role in the formation of these primary lacustrine carbonates textural changes shown by the frequency of the growth cycles also corresponds with oxygen and carbon isotopic values these results appear to have been influenced by climate related paleohydrological changes

the fabrics and origins of peloids immediately after the end permian extinction guizhou province south china abstract peloids are major contributors to modern and ancient limestones although their origins are not yet comprehensively understood upper permian to lower triassic carbonate successions are well preserved at the bangeng area in guizhou province south china where microbialites thrombolites coccoidal microbes and peloids are preserved together these peloids are classified into three types peloid a b c that typically occur together along with coccoidal microbes and restricted bioclasts in a variety of microenvironments peloid a is most common and exhibits close relationship with coccoidal microbes peloid a1 has spherical grain and a size range typical for coccoidal microbes 10 60 m in diameter whereas peloid a2 is marked by larger spherical and subrounded grains with diffuse margins ranging from 70 to 200 m in diameter peloid a1 is in part produced by the complete micritic filling in coccoidal microbes by their metabolic activities whereas peloid a2 is related to the calcification of a colony of coccoidal microbes by their metabolic activities or simply to the aggregation of individual peloids and coccoidal microbes peloids of this type might also originate from other carbonate precipitation processes peloid b is derived merely by micrite filling in ostracodes and gastropods skeletons whereas peloid c is of micritized bioclast origin these peloidal origins do not explain those of all environments and ages peloids are polygenetic in origin irrespective of the presence of coccoidal microbes however it is emphasized that the peloids formed after the end permian extinction are dominated by microbes related ones those kinds of peloids might have occurred repeatedly and predominantly especially in severely deteriorated environments such as those after the end permian mass extinction

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 effect of subaerial exposure on the morphology and microstructure of stromatolites in the cretaceous sinyangdong formation gyeongsang supergroup korea1 stromatolite morphology is usually controlled by a number of biological and environmental factors in the south eastern part of the korean peninsula three stromatolite units of the cretaceous sinyangdong formation have been studied with regard to the effect of diagenesis on their morphology here it is proposed that subaerial exposure and meteoric diagenesis are the most significant factors in shaping the stromatolites of the cretaceous sinyangdong formation most previous palaeontological and sedimentological studies on stromatolites have concentrated on the environmental and biogenic controls on stromatolite morphology these include extrinsic factors such as sedimentation rates or current velocities the main controlling factor on the morphology of the stromatolites in the sinyangdong formation is apparently transient subaerial exposure and related meteoric diagenesis textural examination of stromatolite samples from three stratigraphic horizons shows a characteristic repetitive pattern of cycles with gradual transition from fibrous calcite to micrite layers reflecting changes in the hydrological cycle of the lake in which the stromatolites grew stromatolite growth was terminated by corroded surfaces indicative of subaerial exposure related to a fall in lake level the growth pattern of the stromatolites was mostly determined by the morphology of the corroded substrates during subaerial exposure furthermore the internal stromatolite structure was strongly modified by the process of leaching as a result growth forms mostly changed from stratiform to columnar mesostructure this study strongly implies that diagenesis could make a very significant influence on the morphogenesis of lacustrine stromatolites in the geological past

environmental controls on perennial and ephemeral carbonate lakes the central palaeo andean basin of bolivia during late cretaceous to early tertiary times abstract in the central palaeo andean basin potosi basin of bolivia the up to 450 m thick el molino formation campanian maastrichtian to early tertiary includes two main carbonate lacustrine episodes each of different extent and duration these episodes are separated by an extensive development of alluvial facies floodplain deposits and limestones deposited in playa lakes or isolated ponds the el molino formation has been investigated in six different areas of the potosi basin and affords the opportunity to document climatic and tectonic controls on the development of perennial and ephemeral carbonate lacustrine systems the first lacustrine episode originated predominantly in perennial lakes with wave dominated low gradient ramp type margins outer marginal lacustrine facies include winnowed oolitic grainstones ostracod packstones and microbialite bioherms more agitated areas were characterized by nearshore oolitic bars with associated thrombolite mounds the fossil content and the lack of significant precipitation of evaporites indicate that the lake waters were of low salinity probably oligohaline during most of this period after the first lacustrine episode the widespread development of terrigenous alluvial facies floodplain deposits with interspersed playa lakes or isolated ponds in depressions on the floodplain may indicate a change in the net water budget the second lacustrine episode is dominated by dark micritic limestones and to a lesser extent microbialite bioherms which developed under semiarid climatic conditions this episode includes the deposits of ephemeral saline locally alkaline shallow lakes which were characterized by low energy low gradient ramp type margins the stable isotopic analysis of 163 carbonate samples covering the different facies and depositional settings displays a wide range of values 14 2 18 o and 12 9 13 c that is typical of nonmarine environments the distribution of the values indicates that during the deposition of the el molino formation the basin was hydrologically closed and experienced no strong hydrogeographical changes except for variations in the palaeolake level related to fluctuations in the regional p e ratio these are recorded by two main isotopic trends related to changes between perennial and ephemeral lacustrine conditions lacustrine sedimentation was controlled predominantly by climatically driven hydrological changes with repeated oscillations of the water level expansion and contraction and subsequent fluctuations in the width of lacustrine facies belts

stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks stromatolites are attached lithified sedimentary growth structures accretionary away from a point or limited surface of initiation though the accretion process is commonly regarded to result from the sediment trapping or precipitation inducing activities of microbial mats little evidence of this process is preserved in most precambrian stromatolites the successful study and interpretation of stromatolites requires a process based approach oriented toward deconvolving the replacement textures of ancient stromatolites the effects of diagenetic recrystallization first must be accounted for followed by analysis of lamination textures and deduction of possible accretion mechanisms accretion hypotheses can be tested using numerical simulations based on modern stromatolite growth processes application of this approach has shown that stromatolites were originally formed largely through in situ precipitation of laminae during archean and older proterozoic times but that younger proterozoic stromatolites grew largely through the accretion of carbonate sediments most likely through the physical process of microbial trapping and binding this trend most likely reflects long term evolution of the earth s environment rather than microbial communities

marine peloids a product of bacterially induced precipitation of calcite high magnesian calcite peloids are a common constituent of cemented marine carbonate accumulations they are abundant and well developed within both isolated microcavities and surface crusts the nuclei of marine peloids are composed of fossil bacterial clumps encased within anhedral submicron to micron sized high magnesian calcite crystals the marine peloids are similar to silt sized particles found in travertine deposits that also are composed of fossil bacterial clumps and their surrounding calcite coronas these similarities include size 20 60 mu m a cloudy brown nucleus and rims of clear euhedral crystals in addition previous studies have established the presence of fatty acids of bacterial origin within peloidal deposits and enriched stable isotopic signatures have been interpreted as recording organic fractionation concomitant with calcite precipitation these characteristics all indicate that the nuclei of many peloids originate as calcite precipitates within and around clumps of bacteria and that this precipitation was induced by the vital activity of bacterial colonies

the oldest record of microbial caddisfly bioherms from the early cretaceous jinju formation korea occurrence and palaeoenvironmental implications abstract fossil microbial caddisfly bioherms have been recently discovered in the early cretaceous lacustrine deposits jinju formation at jahyeri korea the jahyeri deposits consist of shallow to marginal lake deposits in which medium to fine grained sandstone beds and silty mudstone beds are alternated and small scale wave ripples and polygonal desiccation cracks are common the microbial caddisfly bioherms occur on and within oolitic sandstone and are also covered by oolitic sandstone suggesting that the bioherms formed in shallow and turbulent water the depositional condition of jahyeri caddisfly bioherms is thus correspondent with the wave washed and well oxygenated biotope of modern lentic trichoptera by comparing the habitat size and shape of cases the composition of case building particles and case construction way it seems likely that the jahyeri caddisfly cases were those of the family leptoceridae the jahyeri microbial caddisfly bioherms are all that have been discovered throughout the jinju formation and the jahyeri bioherms are very small compared with the tall growth of the eocene little mesa bioherms the limited growth and occurrence of microbial caddisfly bioherms in the jinju formation might have resulted from the predominance of clastic deposition in the jinju lake the occurrence of jahyeri microbial caddisfly bioherms may reflect the development of a drought stage which resulted in a limited supply of clastic sediments into the jahyeri lake the jahyeri microbial caddisfly bioherms have common features with modern and tertiary microbial caddisfly bioherms in that the colonial caddis cases constructed bioherms in cooperation with a benthic microbial mat the similarity between the jahyeri microbial caddisfly bioherms and those from the tertiary and modern deposits suggests that the physical environments of microbial caddisfly symbiosis has changed little throughout the geologic time and space and thus indicates that the microbial caddisfly bioherms can be used to interpret paleohydrological conditions this finding is the first report of fossil microbial caddisfly bioherms in asia and represents the oldest occurrence of microbial caddisfly bioherms in the geological records

peloidal fabrics in upper jurassic reefal limestones weald basin southern england abstract coraliferous limestones from the corallian group upper jurassic of subsurface of the weald basin southern england record the localized development of superimposed patch reefs and banks the reefal limestones exhibit a variety of peloidal fabrics in particular well sorted peloids 10 60 m in diameter with a well developed euhedral rim of fibrous sparry calcite around a micritic anhedral nucleus they occur in confined intraskeletal pores corals molluscs and borings growth cavities between framebuilders and as stromatolitic crusts the peloids in interskeletal cavities and as crusts resemble microbial precipitates and merge into spongiostromate fabrics the distribution of these peloidal fabrics seems to be facies related and is best developed in zones which had relatively low framework growth rates low sedimentation rates and moderate energy levels the peloids are identical in form and occurrence to those in some ancient and quaternary reefs the association of the peloids with stromatolitic coatings and spongiostromate fabrics leads us to interpret the peloids as microbial precipitates either by direct precipitation or by induction the abundance of microbial carbonate in these reefal limestones places them in an intermediate category between frame built reefs and microbial mud mounds

microbial deposits in upper miocene carbonates mallorca spain the santanyi limestone a 30 35 m thick upper miocene limestone succession cropping out in mallorca contains abundant microbialite deposits the shape microstructure and texture of which was controlled by environmental factors depth energy and salinity three main types of microbialites are distinguished 1 domed dnos and stratiform mostly undulate unos non oolitic stromatolites 2 undulate oolitic laminites uol and 3 domed oolitic thrombolites dots based on lithofacies associations and occurrence of microbialite types the santanyi limestone succession is subdivided into five stratigraphic units i to v separated by sharp surfaces within units ii iii and v the vertical evolution of microbialites was induced by changes in accommodation space depth 1 intertidal very shallow subtidal conditions at the base were induced by flooding over a wide area 2 continued sea level rise caused submergence to subtidal conditions and 3 a significant bathymetric decrease created the sharp surface bounding these units in units ii and iii nos accumulated in variable energy and depth conditions as buildups with thick somewhat discontinuous and mostly non isopachous lamination surrounded by oolitic grainstones with wave and current structures and oolitic intraclasts in contrast thin and generally regular and smooth lamination of nos in unit v suggests along with the absence of oolite grainstones and macrobiota calm and restricted maybe more saline conditions uol consisting of oolitic layers separated by thin micritic laminae developed adjacent to nos in units ii and iii and to dot at the lower part of unit iii in shallow water and low energy conditions both ooids and micrite laminae have evidence for biogenesis micritized ooids containing microbial remains are common micritic laminae in uol and the dark micritic laminae in nos are thought to represent bacterially enhanced calcite precipitation and lithification during periods of low sedimentation oolitic thrombolites containing macrobiota are only present in unit iii they represent deeper and open marine conditions affected by high energy events in which microbially mediated precipitation favoured microbialite accretion and lithification

nature and environmental significance of microbialites in quaternary reefs the tahiti paradox drill cores from the bamer reef edge of tahiti exhibit 85 93 m thick coralgal sequences recording at least 13 500 years of continuous reef growth in optimal environmental conditions the cored reef sequences form an overall shallowingupward succession with assemblages of branching or massive colonies of porires at the base overlain by a robust branching community acropom gr dmmi robirstn heavily encrusted by coralline algae sessile vermetid gastropods and arborescent foraminifers which grew at depths less than 6 m microbialites generally form the last stage of encrustation of coral colonies or more commonly of related encrusting organisms thus appearing as a major structural component of the reef sequence where they may locally form 809 of the rock by volume they developed in an open cavity system of the reef framework with freely circulating normal marine water microbialites include laminated crusts and clotted micritic masses commonly associated in compound crusts probably feflecting differences in the composition of the involved biological communities and in biomineralization processes that controlled the accretion of the crusts the isotopic composition of the microbialites 2 05 to 3 92 i they underwent also indivitlual processes of biominrlali2ation besicles the overall decrease in lizht and enqy conditions rttlecting progressive burial by conil growth the widespread development of microbialites within the reef framework may be related to increased alkalinity and niitrient availability in interstitial waters due to temstrial groundwwr seepage and puiodic runoffs the tlevelopment of micrubialites in the cryptic niches of the reef framework ceased about 6000 years

a global marine sedimentary response to the end permian mass extinction examples from southern turkey and the western united states the end permian mass extinction greatly diminished marine diversity and brought about a whole scale restructuring of marine ecosystems these ecosystem changes also profoundly affected the sedimentary record data presented here attained through facies analyses of strata deposited during the immediate aftermath of the end permian mass extinction southern turkey and at the close of the early triassic southwestern united states in combination with a literature review show that sedimentary systems were profoundly affected by 1 a reduction in biotic diversity and abundance and 2 long term environmental fluctuations that resulted from the end permian crisis lower triassic strata display widespread microbialite and carbonate seafloor fan development and contain indicators of suppressed infaunal bioturbation such as flat pebble conglomerates and wrinkle structures facies considered unusual in post cambrian subtidal deposits our observations suggest that depositional systems too respond to biotic crises and that certain facies may act as barometers of ecologic and environmental change independent of fossil assemblage analyses close investigation of facies changes during other critical times in earth history may serve as an important tool in interpreting the ecology of metazoans and their environment

secular variation in late cretaceous carbon isotopes a new δ13c carbonate reference curve for the cenomanian campanian 99 6 70 6 ma carbon stable isotope variation through the cenomanian santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven chalk successions in england the sections show consistent stratigraphic trends and 13c values that provide a basis for highresolution correlation positive and negative 13cexcursions and inflection points on the isotope profiles are used to define 72 isotope events key markers are provided by positive 13c excursions of up to 2 the albian cenomanianboundary event mid cenomanian event i thecenomanian turonian boundary event the bridgewick hitch wood and navigation events of late turonian age and the santonian campanian boundary event isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons an age calibrated composite 13c reference curve and an isotope event stratigraphy are constructed using data from the english chalk the isotope stratigraphy is applied to successions in germany france spain and italy correlation with pelagic sections at gubbio central italy demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the cenomanian turonian stages confirming established relationships between tethyan planktonic foraminiferal and boreal macrofossil biozonations correlation of the coniacian santonian stages is less clear cut magnetostratigraphic evidence for placing the base of chron 33r near the base of the upper santonian is in good agreement with the carbon isotope correlation but generates significant anomalies regarding the placement of the santonian and campanian stage boundaries with respect to tethyan planktonic foraminiferal and nannofossil zones isotope stratigraphy offers a more reliable criterion for detailed correlation of cenomanian santonian strata than biostratigraphy with the addition of campanian 13c data from one of the english sections a composite cenomanian campanian age calibrated reference curve is presented that can be utilized in future chemostratigraphic studies the cenomanian campanian carbon isotope curve is remarkably similar in shape to supposedly eustatic sea level curves increasing 13c values accompanying sea level rise associated with transgression and falling 13c values characterizing sea level fall and regression the correlation between carbon isotopes and sea level is explained by variations in epicontinental sea area affecting organic matter burial fluxes increasing shallow sea floor area and increased accommodation space accompanying sea level rise allowedmore efficient burial ofmarine organic matter with the preferential removal of 12c from the marine carbon reservoir during sea level fall reduced seafloor area marine erosion of previously deposited sediments and exposure of basin margins led to reduced organiccarbon burial fluxes and oxidation of previously deposited organic matter causing falling 13c values additionally drowning of carbonate platforms during periods of rapid sea level rise may have reduced the global inorganic relative to the organic carbon flux further enhancing 13c values while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition variations in nutrient supply changing rates of oceanic turnover and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon isotope ratios

contribution of microbialites to the development of coral reefs during the last deglacial period case study from vanuatu south west pacific coral reefs have grown continuously during the last 24 ka on the island of espiritu santo vanuatu south west pacific in a setting characterized by frequent tectonic uplifts related to subduction of the australia plate beneath the vanuatu island arc sedimentological and geochemical studies of two neighbouring areas having much different mean uplift rates and environmental settings provides an opportunity to analyze the environmental factors that promoted the widespread development of microbialite crusts from about 24 to 6 ka b p nutrient supplies and probably the rapidity of the sea level rise are critical to an explanation of the distinctive distribution of microbialites in reef cores nutrient flux has been related to terrigenous fluxes in the tasmaloum reef system that fringed the south west uplifting coast of espiritu santo and possibly to upwelling in the urelapa sequence that was isolated from the main island during its growth a peak in microbialite abundance occurred between 16 and 10 ka b p a time window characterized by increasing erosional processes and or more intense upwelling during a very rapid rise in sea level

carbonate stromatolites from a messinian hypersaline setting in the caltanissetta basin sicily petrographic evidence of microbial activity and related stable isotope and rare earth element signatures lower messinian stromatolites of the calcare di base formation at sutera in sicily record periods of low sea level strong evaporation and elevated salinity thought to be associated with the onset of the messinian salinity crisis overlying aragonitic limestones were precipitated in normal to slightly evaporative conditions occasionally influenced by an influx of meteoric water evidence of bacterial involvement in carbonate formation is recorded in three dolomite rich stromatolite beds in the lower portion of the section that contain low domes with irregular crinkly millimetre scale lamination and small fenestrae the dominant microfabrics are i peloidal and clotted dolomicrite with calcite filled fenestrae ii dolomicrite with bacterium like filaments and pores partially filled by calcite or black amorphous matter and iii micrite in which fenestrae alternate with dark thin wispy micrite the filaments resemble beggiatoa like sulphur bacteria under scanning electron microscopy the filaments consist of spherical aggregates of dolomite interpreted to result from calcification of bacterial microcolonies the dolomite crystals are commonly arranged as rounded grains that appear to be incorporated or absorbed into developing crystal faces biofilm like remains occur in voids between the filaments the dolomite consistently shows negative d 13 c values down to 11ae3 and very positive d 18 o mean value 7ae9 that suggest formation as primary precipitate with a substantial contribution of organic co2 very negative d 13 c values down to 31ae6 of early diagenetic calcite associated with the dolomite suggest contribution of co2 originating by anaerobic methane oxidation the shale normalized rare earth element patterns of sutera stromatolites show features similar to those in present day microbial mats with enrichment in light rare earth elements and m type tetrad effects enrichment around pr coupled to a decline around nd and a peak around sm and eu taken together the petrography and geochemistry of the sutera stromatolites provide diverse and compelling evidence for microbial influence on carbonate precipitation