cenomanian turonian facies succession in the guerrero morelos basin southern mexico abstract the cenomanian turonian succession of southern mexico is characterized by an abrupt change from shallow marine to pelagic facies the drowning of the platform coincides with the widely documented cenomanian turonian oceanic anoxic event ctoae a proper understanding of the drowning event and the effects of the oae requires as an essential first step the construction of a detailed stratigraphic framework this has been achieved and utilizes sedimentological data as well as a combination of benthic and planktonic biostratigraphic schemes deposition of the cenomanian turonian sedimentary rocks of the guerrero morelos basin was controlled by tectonic and oceanographic factors resulting in depositional environments ranging from a semi restricted shelf ramp pelagic and prodelta deposits facies analysis indicates that shallow marine limestones of the morelos formation lower upper cenomanian were deposited in intertidal shallow supratidal and subtidal environments in a semi restricted shelf peloidal bioclastic packstone wackestones with minor grainstones are the predominant texture of these rocks abundant large benthic foraminifers calcareous algae dasycladacean and mollusks gastropods and rudists characterize the fossil assemblage the cuautla formation uppermost cenomanian turonian represents sedimentation on a low energy wave dominated carbonate ramp the inner ramp accumulated bioclastic banks and shoals composed of peloidal benthic foraminifer grainstone calcareous red and green algae rudists and minor solitary corals the middle ramp is represented by nodular packstones with a diverse assemblage of echinoderms green and red algae bryozoan rudists solitary corals roveacrinids calcisphaerulids and non keeled planktonic foraminifers the outer ramp is dominated by argillaceous wackestone packstone characterized by calcisphaerulids roveacrinids and non keeled planktonic foraminifers an increase in terrigenous clastic material towards the eastern part of the area indicates progradation of a deltaic system while the mexcala formation uppermost cenomanian turonian was deposited in a pelagic setting the drowning of the platform is at the contact between the morelos and cuautla or mexcala formations and is dated as latest cenomanian the drowning is a hiatus in most sections and it began before the end of the cenomanian by a minimum of 150 ky if the top of the morelos is not eroded

missing aragonitic biota and the diagenetic evolution of heterozoan carbonates a case study from the oligo miocene of the central mediterranean abstract several previous studies have addressed the diagenetic evolution of heterozoan carbonate assemblages generally it is assumed that early diagenetic processes in heterozoan settings are mainly destructive including abrasion and dissolution on the sea floor constructive diagenesis cementation is delayed to later stages in the burial environment with pressure solution of calcitic grains acting as a cement source this paper presents a study of oligo miocene inner to outer ramp heterozoan carbonates from the central mediterranean maltese islands and sicily indicating that early diagenetic processes are more important than previously assumed four to five different cement types including fibrous two types of epitaxial bladed and blocky cement are distinguished based on transmitted light microscopy cathodoluminescence microscopy allowed a differentiation between primary high mg calcitic fibrous and epitaxial cement i and primary low mg calcitic epitaxial cement ii bladed and blocky cements stable isotope data indicate cement precipitation from marine marine derived and meteoric waters trace element analyses point to cementation in an open system maltese islands and a closed system sicily our investigations show that the majority of constructive diagenetic processes in these rocks occurs rather early in the shallow marine burial environment which is transitional between the marine seafloor and the deep burial diagenetic environment the main cement source in this environment is assumed to be aragonite we suggest careful consideration of the importance of aragonitic components in fossil heterozoan settings which seem to be more abundant than previously assumed and can act as a major early cement source due to the low preservation potential of these components detailed geochemical studies are necessary to detect aragonite as the cement source our findings also have implications when considering the reservoir qualities of these rocks because primary porosity can be occluded early and secondary porosity is not preserved

karst bauxite deposits in the zagros mountain belt iran more than 190 occurrences of bauxitic lateritic deposits were investigated in seven areas within the zagros simply folded mountain belt in southwestern of iran the bauxitic horizons are situated in eroded major nw se trending anticlines and occur in karst cavities near or at the boundary between the sarvak and ilam formations uplift in the cenomanian turanian period had exposed the sarvak limestone to karst weathering and during a period of unconformity layers of ferruginous argillaceous limestone debris developed and accumulated on its surface the ferruginous argillaceous debris was partly converted to bauxite folding and faulting in oligocene miocene time with ensuing erosion exposed the bauxitic horizons on the limbs and cores of anticlines the karst bauxite deposits are probably of authigenic origin as evidenced by their lithologic associations textural and mineralogy

regional stratigraphy of the zagros fold thrust belt of iran and its proforeland evolution the latest neoproterozoic through phanerozoic stratigraphy of the zagros fold thrust belt of iran has been revised in the light of recent investigations the revised stratigraphy consists of four groups of rocks each composed of a number of unconformity bounded megasequences representing various tectonosedimentary settings in the lowest group ranging in age from latest precambrian to devonian the uppermost neoproterozoic to middle cambrian rocks constitute a megasequence of evaporites siliciclastic deposits and interlayered carbonates which were deposited in pull apart basins that developed by the najd strike slip fault system this megasequence is overlain by a second one middle to late cambrian in age which consists of shallow marine siliciclastic and carbonate rocks representing deposition in an epicontinental platform the overlying shales siltstones and partly volcanogenic sandstones of ordovician silurian and devonian age are local remnants of stratigraphic units that were extensively eroded during development of several major unconformities the second group consists of two megasequences one permian and the other triassic composed of widespread transgressive basal siliciclastic rocks and overlying evaporitic carbonates of an equatorial epi pangean very shallow platformal sea the third group is composed of four megasequences formed of shallow and deep water carbonates with some siliciclastic and evaporite deposits which accumulated on a neo tethyan continental shelf during earliest jurassic through late turonian time the fourth group comprises siliciclastic and carbonate deposits of a largely underfilled nw to se trending forward and backward migrating late cretaceous to recent proforeland basin which has evolved as an integral part of the zagros orogen this last group consists of three megasequences ix x and xi with distinctive lateral and vertical facies variations which reflect specific tectonic events megasequence ix comprises uppermost turonian to middle maastrichtian prograding and retrograding siliciclastic and carbonate deposits whose accumulations reflect emplacement obduction of ophiolite slivers and subsequent collisional events in the zagros orogen megasequence x consists of uppermost maastrichtian to upper eocene siliciclastic and carbonate rocks which deposited first progradationally in front of the zagros orogenic wedge with reduced contractional tectonic activity and then retrogradationally due to intensified thrust stacking in the interior parts of the orogen megasequence xi consists of oligocene and lower miocene carbonate strata deposited retrogradationally shortly after a period of intensified late eocene thrust faulting in the deformational wedge and an overlying succession of upward coarsening northeasterly derived siliciclastic deposits of lower miocene to recent age which are composed of erosional byproducts of the southwest vergent zagros thrust sheets

microfacies and depositional environment of the cenomanian of the bangestan anticline sw iran abstract the sarvak formation albian to turonian in age of the zagros basin is a thick sequence of shallow water carbonates this work focuses on the microfacies and sedimentary environment of the margin of the cenomanian intrashelf basin in the study area southwest of iran the sarvak formation is subdivided into 12 microfacies that are distinguished by petrographic analysis on the basis of their depositional textures and fauna in addition four major depositional environments were identified in the sarvak formation these include shelf lagoon platform margin slope and basin environmental settings which are interpreted as a carbonate shelf without an effective barrier separating the platform from the open ocean

depositional environment sequence stratigraphy and geochemistry of lower cretaceous carbonates fahliyan formation south west iran abstract the fahliyan formation is a carbonate sequence of lower cretaceous berriasian hauterivian age and was deposited in the zagros sedimentary basin iran in this investigation the fahliyan formation at the type section and in the subsurface has been studied facies analysis and petrographic studies led to the recognition of 10 microfacies that were deposited in three facies belts lagoon shoal and open marine the observed facies patterns indicate a carbonate rimmed shelf depositional environment based on field observations microfacies analysis and sequence stratigraphic concepts two third order sequences in the type section and three third order sequences in the subsurface section were identified the transgressive deposits display a predominance of deep subtidal facies while highstand deposits show shallow subtidal facies some petrographic evidence such as an abundance of aragonite skeletal and non skeletal components shows that this formation was deposited in a sub tropical environment with original aragonite mineralogy geochemical evidence such as high sr na ratios also support original aragonite mineralogy 18o and 13c values suggests that alteration occurred during burial diagenesis in a closed system with low water rock interaction palaeotemperature calculation based on the heaviest oxygen isotope value in micritic samples of the fahliyan limestone shows that ambient water temperature was around 24 c during the deposition of this formation

a critical assessment of mollusk 18 o 16 o mg ca and 44 ca 40 ca ratios as proxies for cretaceous seawater temperature seasonality seasonal temperature fluctuations of tethyan coastal water are recorded in a pristine 80 my old rudist shell from turkey in order to critically assess factors other than seawater temperature that might have influenced the shell geochemical record three different paleo temperature proxies 18o mg ca and 44ca were applied in a qualitative manner all three proxies reflect the same cyclical trends and thus yield robust evidence for seasonal fluctuations in late cretaceous surficial seawater temperature this suggests the successful application of the new 44ca temperature proxy to fossil mollusk calcite the direct comparison of the three data sets however demonstrates that all proxies are fraught with problems similar to other studies 18o 16o ratios point to warmer summer temperature maxima than those in comparable costal settings today nevertheless the 18o 16o proxy is subject to environmental factors that might lead to an overestimation of peak temperatures moreover mg ca molar ratios are less sensitive to environmental factors but were strongly affected by the ion regulating capability of the rudist bivalve that responded to the low mg ca ratio of cretaceous seawater similarly uncertainties of the 44ca composition of cretaceous seawater and the complex bio calcification of mollusks presently limit the interpretation of 44ca values in terms of absolute seawater temperature the multiproxy approach applied here however documents that these limitations do not obscure the dominant patterns of seasonal sea surface temperature variations recorded in the biogeochemical rudist archive

testing the cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the turonian tropics on demerara rise glassy turonian foraminifera preserved in clay rich sediments from the western tropical atlantic yield the warmest equivalent 18o sea surface temperatures ssts yet reported for the entire cretaceous cenozoic we estimate turonian ssts that were at least as warm as conservative mean 30 c to significantly warmer warm mean 33 c than those in the region today however if independent evidence for high middle cretaceous pco2 is reliable and resulted in greater isotopic fractionation between seawater and calcite because of lower sea surface ph our conservative and warm sst estimates would be even higher 32 and 36 c respectively our new tropical ssts help reconcile geologic data with the predictions of general circulation models that incorporate high cretaceous pco2 and lend support to the hypothesis of a cretaceous greenhouse our data also strengthen the case for a turonian age for the cretaceous thermal maximum and highlight a 20 40 m y mismatch between peak cretaceous cenozoic global warmth and peak inferred tectonic co2 production we infer that this mismatch is either an artifact of a hidden turonian pulse in global ocean crust cycling or real evidence of the influence of some other factor on atmospheric co2 and or ssts a hidden pulse in crust cycling would explain the timing of peak cretaceous cenozoic sea level also turonian but other factors are needed to explain high frequency 10 100 k y instability in middle cretaceous ssts reported elsewhere

structural framework of the zagros fold thrust belt iran abstract data gleaned from the literature on the zagros have been compiled and used in conjunction with new interpretations to provide a better picture of the structures sedimentation history and deformation of this hydrocarbon rich mountain belt the belt parallel mountain front the n s trending kazerun izeh and e w trending bala rud fault zones are defined as the master structural elements of the belt these fault zones divide the zagros basin into zones with different stratigraphic successions and different rheological profiles this resulted in different structural styles developing along the belt during the subsequent collision the kazerun and izeh fault zones acted as the depositional system transition zone between the lurestan and fars regions in jurassic cretaceous time and partly controlled the distribution of the kazhdumi formation one of the major source rocks by the end of the cretaceous the nw se trending mountain front fault divided the present folded belt of the zagros into a major foreland basin to the southwest and a piggyback basin to the northeast activity along other major transfer fault zones including the izeh kazerun and bala rud fault zones occurred at this time and controlled the sedimentation and subsidence of the dezful embayment the main target region for hydrocarbon exploration these fault zones controlled the thickness of the asmari formation one of the main reservoirs and also the considerable thickness and facies changes of the gachsaran formation the major seal to the asmari formation the present morphology of the mountain belt is interpreted as being mainly related to the pinning of the mountain front fault to the northwest of the dezful embayment and to the north of the strait of hormuz

variation of structural style and basin evolution in the central zagros izeh zone and dezful embayment iran abstract structural style and its relationship to sedimentary facies and the evolution of sedimentary depocenters since late cretaceous times have been studied on the basis of one regional balanced transect and several updated isopach maps in the izeh zone and the dezful embayment central zagros this study relies on fieldwork data existing geological maps seismic data and well information a new structural classification for part of the zagros sedimentary cover is presented to highlight the different mechanical behavior of the formations in the stratigraphic column it shows the existence of several local decollement levels activated during folding these decollement levels separate lithotectonic units which accommodate shortening in different ways the lower paleozoic is the basal decollement level throughout the studied area triassic evaporites albian shales eocene marls and miocene evaporites can act as intermediate decollement levels and present variable facies in the central zagros lateral facies and thickness variations the sedimentary overburden and the close relationship with inherited fault patterns influenced the wavelength amplitude and style of folding in the study area furthermore surface structures do not necessarily coincide with deeper objectives where these disharmonic levels are involved in folding the evolution of sedimentary depocenters from the late cretaceous obduction episode until early miocene collision is described based on updated isopach maps and tectonic subsidence curves this analysis shows continuous compression and movements along n s and nw se trending faults in the zagros basement which predate the neogene zagros folding and influence sedimentation history it also indicates a southwestward migration of the depocenters through time in addition to the basement involvement below some folds during the zagros orogeny

chemical diagenesis of a multicomponent carbonate system 2 stable isotopes abstract this study examines the oxygen and carbon isotopic distribution in the brachiopods crinoids rugose corals and matrix cement from the mississippian burlington limestone iowa and missouri and the silurian read bay formation arctic canada the isotopic data can be reconciled with textural and trace element observations only if the 18o content of ancient oceans differed from that of the present oceans this postulated secular variation in the 18o content of seawater requires a separate evaluation of the mississippian and silurian carbonate components examination of the 18o content of the least altered low mg calcite fossil components of the two formations suggests that the 18o of mississippian seawater was on average about 1 5 lighter and that of silurian seawater was about 5 5 lighter than the 18o of present day ocean water the average diagenetic shift in 18o for the read bay formation which stabilized in a partly closed diagenetic phreatic meteoric system is about 1 for the original low mg calcite and about 2 for the original high mg calcite and aragonite components conversely for the burlington limestone which stabilized in an open diagenetic phreatic meteoric system the average diagenetic shift in 18o is about 3 for the original low mg calcite and about 4 f r the original high mg calcite components the 13c values of the originally low mg calcite or high mg calcite with less than 7 mole mgco3 brachiopods and rugose corals the originally high mg calcite crinoids and the originally aragonite lime mud of the burlington limestone and read bay formation are bimodally distributed this bimodal 13c distribution is independent of geologic age inferred original mineralogy of the component degree of diagenetic alteration and the type of diagenetic meteoric system with components from both the read bay formation and burlington limestone contributing to both 13c groups the mode of the light 13c group is 0 25 and for the heavy 13c group it is 3 25 pdb both 13c groups also show a decrease in 13c of about 1 with increasing diagenetic alteration stabilization

kinetic control of morphology composition and mineralogy of abiotic sedimentary carbonates abstract conventional thinking has long held that the abiotic precipitation of calcium carbonate occurs with a causal relationship between fluid my ca ratios and crystal morphology crystal composition and carbonate mineralogy resulting in the formation of meteoric equant low magnesium calcite and marine acicular high magnesium calcite and aragonite problematically calcites with varying amounts of incorporated magnesium occur either as equant or acicular crystals and aragonite may coexist with calcite in either environment commonly however a systematic relation exists between crystal morphology composition mineralogy and rates of reactant supply to growing crystal surfaces for example equant rather than acicular crystals of calcite form in modern deep and or cold marine meteoric phreatic and deep burial settings where the degree of carbonate saturation and or rates of fluid flow are low in areas of higher saturation and or fluid flow such as in warm shallow marine and meteoric vadose environments acicular calcite may predominate this relation is also seen in systems in which aragonite and calcite form in intimate association aragonite precipitation is favored when rates of reactant supply are high calcite forms when rates are low such relations suggest that crystal morphology composition and mineralogy are controlled by the kinetics of surface nucleation and the amount of reactants principally carbonate ions at growth sites precipitating phases are the ones which can best accommodate such excess reactants ambient mg ca ratios only indirectly control the nature of inorganically precipitated carbonate phases

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

microfacies and geochemistry of the middle cretaceous sarvak formation in zagros basin izeh zone sw iran abstract the sarvak formation albian to cenomanian forming part of the bangestan group comprises a thick succession of carbonate rocks in the zagros basin of southern iran the sarvak formation forms one of the main hydrocarbon reservoirs of this region three sections in the northern 252 m thickness and southern flanks 348 m thickness of the mish and anneh anticlines 245 m thickness in the izeh zone of sw iran were selected for this study petrographic analysis led us to define 10 microfacies units deposited in four facies belts i tidal flat ii lagoonal iii shoal and iv open marine all of these form part of a platform ramp environment geochemical investigations limited to outcrops of the mish anticline aided in understanding geochemical and diagenetic characteristics of carbonate rocks from the sarvak formation variations of oxygen and carbon isotope data from limestones of the sarvak formation indicate near primary marine phreatic and partially meteoric digenesis for both flanks of the mish anticline respectively lower abundances of mn and fe suggest that the carbonates at both sites appear to have stabilized under mainly oxic conditions the sarvak carbonates from the north flank of the mish anticline indicate higher rock water interaction and a closed diagenetic system in comparison to the south flank of the mish anticline vertical and lateral variations in stratigraphic thicknesses in selected outcrops can be related to the presence of syn sedimentary faults in the zagros basin that resulted in regional instability or due to rates of sedimentation with lower rates of deposition in the basin during middle cretaceous times

mid cretaceous albian santonian sea surface temperature record of the tropical atlantic ocean paleoclimate records of geologic time periods characterized by extreme global warmth such as the mid cretaceous are important for a better understanding of the earth9s climate system operating in an exceptionally warm mode here we applied an organic geochemical proxy tex 86 on organic matter rich albian santonian sediments recovered from ocean drilling program leg 207 sites 1258 and 1259 on demerara rise to reconstruct sea surface temperatures ssts in the western equatorial atlantic preceded by a stepwise cenomanian warming trend 31 35 c the onset of the cretaceous thermal maximum coincided here with the cenomanian turonian boundary event once established this extreme warm climate regime characterized by averaged tropical ssts close to 35 c lasted up to the turonian coniacian transition two pronounced cooler intervals 2 3 c interrupt this otherwise remarkably stable record providing the first 18 o independent evidence for middle turonian cooling that previously has been attributed to glacioeustatic sea level lowering coniacian ssts decline stepwise reaching a minimum in the santonian 32 33 c where cooling is most pronounced presumably concomitant with the first progressive opening of a deep water passage through the equatorial atlantic gateway

isotopic evidence for late jurassic early cretaceous climate change abstract strontium oxygen and carbon isotope ratios have been determined from late jurassic early cretaceous belemnites from the volga basin russia and kawhia harbour new zealand 87sr 86sr ratios derived from well preserved belemnites from the volga basin support a middle tithonian age derived from the analysis of the endemic ammonite fauna the kawhia harbour section records a gradual rise in 87sr 86sr values and in comparison with the published 87sr 86sr curve suggests that the lower part of the section is latest oxfordian in age whilst the upper part of the section correlates well with the biostratigraphic correlation suggestion of an early middle tithonian age although the published strontium calibration curve shows a degree of scatter our new data confirm the uniform rise in 87sr 86sr values from the late jurassic into the early cretaceous such an increase may result from either a decrease in mid oceanic ridge spreading and or an increase in weathering rates and flux of radiogenic strontium although a eustatic drop in sea level and concurrent western cordillera uplift suggests that weathering may have been the controlling factor of late jurassic seawater strontium isotope composition palaeotemperatures derived from the well preserved belemnite 18ocarb values from the volga basin indicate that the middle volgian late kimmeridgian was warm 14 20 c followed by a slight cooling and a subsequent gradual increase to the jurassic cretaceous boundary the 18ocarb values from new zealand located at a palaeolatitude of 80 s if interpreted in terms of palaeotemperature indicate a high degree of variability such variability may not be related to palaeotemperature but to changes in oceanic chemistry resulting from the formation and dissolution of an ice sheet and or snow during the oxfordian kimmeridgian carbon isotope trends for the late jurassic show a fall in values from the oxfordian with lowest values occurring in the early middle tithonian before rising but without reaching values obtained in the oxfordian the overall low 13ccarb may be related to a global increase in continental weathering and or upwelling of cooler oceanic water enriched in oxidised organic carbon 12c enriched

structures of the zagros fold thrust belt in iran the zagros fold thrust belt in iran forms the external part of the zagros active orogenic wedge it includes a sequence of heterogeneous latest neoproterozoic phanerozoic sedimentary cover strata 7 to 12 km thick and composed of alternating incompetent and competent layers overlying precambrian crystalline basement with a complex pre zagros structural fabric balancing structures of the cover statigraphic units in the zagros fold thrust belt requires in sequence and out of sequence involvement of the precambrian basement in the deformation six detailed balanced and retrodeformable cross sections which are constructed based on geological and geophysical data across various sectors of the belt show fault bend and fault propagation folds interpreted to have formed by slip on their subjacent thrusts out of sequence basement rooted thrusts as the interpretations in the constructed cross sections suggest have breached the cover basement interface and using incompetent cover strata for propagation cut across the cover structures and have created associated new folds superimposed upon the pre existing structures this style of deformation which has resulted in structural complexity of the belt characterizes a 200 to 300 km wide zone of distributed partly synchronous deformation with along strike and across strike variations it also implies that the zagros fold thrust belt as the external part of the orogenic wedge is still in its subcritical condition with internal deformation to achieve a critical taper in creating structural complexity in addition to out of sequence thrusting mechanically weak layers evaporites and mudstones of the cover strata have played a significant role by providing several detachment horizons shortening estimates across the belt are variable based on the constructed cross sections and their restorations minimum shortening estimates range from 16 percent to 30 percent in different sectors of the belt

diversity of neomorphic fabrics in new zealand plio pleistocene cool water limestones insights into aragonite alteration pathways and controls abstract many ancient cool water carbonates include little or no evidence for aragonite being present in their primary sediment composition and consequently that they inherited a low diagenetic potential however despite differences in skeletal assemblages age and depositional settings plio pleistocene cool water limestones from eastern north island of new zealand are characterized by locally abundant aragonite remains typically c 20 range 60 either directly as variably altered skeletons or indirectly as biomolds oversized pores and detrital material resulting from collapse of dissolved shells specifically five types of aragonite preservation are evident a skeletons with original aragonite b skeletons with original aragonite but with leaching cavities c skeletons with aragonite relics encased in either dirty or pale brown neomorphic calcite spar d skeletons neomorphically altered to calcite preserving relic shell structures and e dissolved out skeletons leaving an empty or calcite cement filled cavity all these types of preservation including transitions between them can occur within the same sample these observations motivate a conceptual model for the timing and complex pathways of neomorphism in these plio pleistocene cool water limestones related to their diagenetic evolution from shallow marine to burial to uplift related meteoric environments in this the aragonite alteration pathways suggest that the different neomorphic fabrics formed at any stage during the diagenetic history of the host carbonates and are likely not unequivocal indicators of specific diagenetic environments instead differing alteration pathways can potentially produce similar fabrics the observations are consistent with the interpretation that shell microstructures controlling the nature of the intraskeletal neomorphic front and the degree of openness of the diagenetic system were of greater importance in determining the neomorphic fabrics and relic preservation of aragonite than was the general diagenetic environment be it marine meteoric or burial also important were external controls linked to the types of depositional settings that dictated the composition of carbonate factories the morpho tectonic evolution of the host basin and the influence of relative sea level fluctuations on sediment production accumulation and condensation these results illustrate that factors controlling ultimate preservation of carbonate biofacies are multifarious and complex moreover they suggest that the importance of aragonitic components could be underestimated for many ancient cool water carbonate deposits thereby compromising estimation of original skeletal assemblages depositional environments and sediment budgets

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

the cenomanian turonian oceanic anoxic event ii palaeoceanographic controls on organic matter production and preservation correlation of the 13c spike with the well dated occurrences of strata rich in organic carbon detailed in schlanger et al this volume indicates that a global episode of intense organic carbon orgc burial took place during the latest cenomanian earliest turonian oceanic anoxic event oae a plenus through i labiatus macrofossil zones and upper r cushmani trz through w archecretacea prz foraminiferal zones over a period of no more than 1 million years m y the shape of the 13c curve indicates that rates of orgc burial gradually increased in the early part of the late cenomanian increased more rapidly in the later cenomanian and levelled off at peak values in latest cenomanian early turonian time during the maximum rate of orgc burial the 13c values decreased nearly to pre late cenomanian levels in the early to middle turonian the decrease in 13c reflects decreasing rates of orgc burial following the cenomanian turonian oceanic anoxic event as well as the probable oxidation and return of significant amounts of orgc to the oceans following regression and re oxygenation of much of the deeper water masses in contact with the seafloor

petrographic and geochemical evidence for original aragonite mineralogy of upper jurassic carbonates mozduran formation sarakhs area iran abstract diverse skeletal and non skeletal grains with abundant red and blue green calcareous algae evaporites and early diagenetic dolomites in the mozduran carbonates are similar to those of modern warm water shallow marine carbonates isopachous and fibrous intragranular sparry calcite cements resemble modern aragonite morphologies concentric and radial ooids are like modern aragonitic forms which are formed in turbulent and in low energy environments respectively deformed ooids shattered micritic envelopes and spalled ooids indicate aragonite dissolution during meteoric diagenesis meteoric cements are equant mosaic to drusy calcites burial cements only occur as vein fillings sr and na covariance with mn supports evidence of inversion of aragonite to calcite with subsequent open phreatic diagenesis fe concentrations are a magnitude higher than mn due to a reducing phreatic environment high sr na ratios suggest original aragonite mineralogy the 18 o and 13 c field of mozduran limestone lies at the edge of the modern shallow marine field indicating a range from marine to meteoric cements differences in 18 o values between marine calcites and meteoric derived calcites is similar to that in the modern tropics the surface marine diagenetic trend line that passes through shallow marine modern whole carbonates cuts the mozduran limestone isotope field due to their formation in warm shallow marine waters given that atmospheric co 2 levels were similar to those at present increasing mn and fe values decreasing na and uniform sr values with increasingly lighter values of both 18 o and 13 c are exlained by extensive meteoric diagenesis the least altered marine calcite 18 o value of 2 6 pdb corresponds to 29 or 24 c depending on whether 0 of present seawater and 1 2 of ancient seawater with no ice caps are taken as a base an original calcite mineralogy postulated for some jurassic limestones is related to a non tropical origin

stable isotope sclerochronology of rudist bivalves growth rates and late cretaceous seasonality the almost complete translation of shell accretion to vertical growth was a successful morphogenetic adaptation of rudist bivalves which replaced coral algal hydrozoan communities in most tethyan shallow marine environments during the cretaceous growth rates of rudist shells are therefore important in reconstructions of cretaceous shallow marine benthic communities carbon and oxygen isotopic compositions were analyzed in sclerochronological profiles through the shells of two late cretaceous rudist bivalves from greece and turkey values of 13 c vary between 0 8 and 2 2 in the hippuritid vaccinites ultimus and between 0 8 and 2 6 in the radiolitid gorjanovicia cf costata ranges in 18 o are 5 3 to 2 9 and 4 6 to 2 1 respectively a distinct cyclicity of 13 c and 18 o in both shells reflects late cretaceous seasonality and indicates annual vertical growth increments of 45 mm in v ultimus and 54 mm in gorjanovicia the concentrations of minor elements are similar to those of extant bivalves with low mg calcite shells

possible atmospheric co2 extremes of the middle cretaceous late albian turonian 1 atmospheric carbon dioxide co2 estimates for the middle cretaceous mk have a range of 4000 ppm which presents considerable uncertainty in understanding the possible causes of warmth for this interval this paper examines the problem of mk greenhouse forcing from an inverse perspective we estimate upper ocean water temperatures from oxygen isotope measurements of well preserved late albian turonian planktonic foraminifera and compare these against temperatures predicted by general circulation model gcm experiments with co2 concentrations of 500 7500 ppm at least 4500 ppm co2 is required to match maximum temperatures inferred from well preserved planktonic foraminifera approximately 900 ppm co2 produces a good match between the model and the minimum temperature estimates for the mk an ocean model forced by these two extremes in surface conditions brackets nearly all available bottom water temperature estimates for this interval the climate model results support nearly the entire range of mk co2 estimates from proxy data the ocean model suggests possible mk oceanographic changes from deep water formation in the high latitude region of one hemisphere to the other hemisphere in response to changes in atmospheric temperatures and hydrologic cycle strength we suggest that rather than contradicting one another the various proxy co2 techniques especially those with high temporal resolution may capture true variability in co2 concentrations and that mk co2 could have varied by several thousand ppm through this interval

comparison of carbonate c and o stable isotope records across the jurassic cretaceous boundary in the tethyan and boreal realms abstract carbon and oxygen stable isotope records were compared for jurassic cretaceous j k boundary sections located in the tethyan realm brodno western slovakia and puerto escano southern spain bulk limestones and the boreal realm nordvik peninsula northern siberia belemnites since a detailed biostratigraphic correlation of these tethyan and boreal sections is impossible due to different faunal assemblages correlation of the isotope records was based on paleomagnetic data this novel approach can improve our understanding of the synchroneity of individual isotope excursions in sections where detailed biostratigraphic correlation is impossible no significant excursions in either the carbon or oxygen isotope records to be used for future boreal tethyan correlations were found around the j k boundary the upper tithonian and lower berriasian magnetozones m20n to m18n in the studied sections at the nordvik section where a much longer section middle oxfordian basal boreal berriasian was documented the transition from the middle oxfordian to the kimmeridgian and further to the volgian is characterized by a decrease in belemnite 18 o values from 18 o values up to 1 6 vs v pdb in the oxfordian to values between 0 3 and 0 8 in the late volgian and earliest boreal berriasian this trend which has previously been reported from the russian platform and tethyan realm sections corresponds either to gradual warming or a decrease in seawater 18 o supposing that the oxygen isotope compositions of seawater in the arctic boreal and tethyan realms were similar then the differences between oxygen isotope datasets for these records indicate differences in temperature the boreal tethyan temperature difference of 7 9 c in the middle and late oxfordian decreases towards the j k boundary indicating a significant decrease in latitudinal climatic gradients during the late jurassic two positive carbon isotope excursions recorded for the middle oxfordian and upper kimmeridgian in the nordvik section can be correlated with a similar excursion described earlier for the russian platform minor influence of biofractionation at the carbon isotopes and the influence of migration of belemnites to deeper slightly cooler water at the oxygen isotopes cannot be excluded for the obtained belemnite data

microfacies and geochemistry of the ilam formation in the tang e rashid area izeh s w iran abstract the ilam formation santonian campanian in age part of the bangestan group is disconformably overlain by the sarvak formation and underlain by the gurpi formation in the tang e rashid peyon area izeh zagros southwest of iran facies analyses indicate that the ilam carbonates formed in four microfacies belts tidal flat lagoon shoal and open marine in a platform ramp environment major and minor elements and carbon and oxygen isotope values were used to determine the original carbonate mineralogy of the ilam formation petrographic evidence and elemental and oxygen and carbon isotope values indicate that aragonite was the original carbonate mineralogy in the ilam formation the elemental and isotopic compositions of the ilam carbonates also illustrate that they have stabilized in the marine phreatic environment variations of sr ca and 18 o values versus mn suggest that diagenetic alteration occurred in a closed system temperature calculation based on the oxygen isotope value of the least altered sample indicates that the very early shallow burial fluid temperature was around 28 c recognition of the exact boundary between the ilam and sarvak formations is difficult due to similar lithologies and the absence of the surgah formation in the study area however elemental and oxygen and carbon isotope analysis were used to determine the boundary between these formations the 18 o and 13 c values along with elemental results clearly indicate a subaerial exposure surface below which meteoric diagenesis affected the sediments

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

influence of a major exposure surface on the development of microporous micritic limestones example of the upper mishrif formation cenomanian of the middle east microporous platform top limestones of the cenomanian mishrif formation offshore qatar were studied in order to investigate the diagenetic processes associated with the top mishrif subaerial unconformity and its influence on the development of microporosity in underlying carbonates petrographical and stable isotope results indicate that complex diagenetic changes occurred during subaerial exposure of the mishrif formation including pervasive dissolution and meteoric cementation as well as neomorphism of the micritic matrix micrites at the top of the mishrif formation are coarse i e 2 m sub rounded and very dull luminescent under cathodoluminescence in this uppermost part of the studied interval the limestone matrix first underwent dissolution of unstable grains in the vadose zone with subsequent precipitation of low magnesium calcite lmc overgrowths within an oxidising phreatic setting this process explains the poor luminescence of the micrite crystals and their relatively coarse crystallometry which results in the present day in relatively good reservoir properties 13c ratios within the microporous limestones are negative up to 4 v pdb due to the incorporation of isotopically light carbon derived from palaeosols which developed during exposure by contrast fine i e 2 m polyhedral and bright luminescent micritic matrix with higher 13c values up to 4 v pdb and lower permeability are dominant within the underlying carbonate interval these fine micrites are likely to be the product of early neomorphic recrystallisation in the lowermost part of the palaeo aquifer associated with the top mishrif unconformity and were precipitated from meteoric or mixed dysoxic waters which were slightly supersaturated with respect to calcite

stratigraphic organization of carbonate ramps and organic rich intrashelf basins natih formation middle cretaceous of northern oman the middle cretaceous carbonate deposits in the middle east are among the most productive oil bearing stratigraphic intervals in the world containing numerous giant fields in for instance the united arab emirates mauddud and mishrif formations iran sarvak formation and oman natih formation one of the main reasons for this concentration of hydrocarbons is a geological factor the coexistence of both reservoir facies and source rocks in the same depositional sequences due to the repeated creation of organic rich intrashelf basins this is demonstrated in a high resolution sequence stratigraphic study of the natih formation in oman which shows distinct and predictive patterns in the distribution and geometries of reservoir source rock and seal facies the sequence stratigraphic model presented here may serve as a reference for time equivalent deposits in the middle east the sedimentological analysis showed that the natih formation was formed by the alternation of two types of depositional systems 1 a flat bedded mixed carbonate clay ramp dominated by benthic foraminifera and 2 a carbonate dominated ramp bordering an intrashelf basin with abundant rudists in the mid ramp environment and organic rich basinal facies three fully developed third order sequences are distinguished showing a similar evolution of the depositional system with a mixed carbonate clay ramp system at the base followed by a carbonate dominated ramp system in the upper part variations occur on this pattern however depending on the relative influence of eustasy environmental factors and tectonism the late albiannearly cenomanian sequence i shows an evolution from a mixed flat ramp to a carbonate dominated ramp and organic rich intrashelf begin page 22 basin and sedimentation is predominantly controlled by eustatic sea level in the middle cenomanian sequence ii the evolution from a mixed ramp to a carbonate ramp is also observed but no intrashelf basin topography was developed in the studied area this may be due to the high influx of clay that influenced the environment in this sequence inhibiting the carbonate production probably in combination with the lack of sufficient creation of accommodation space the late cenomaniannearly turonian transgressive part of sequence iii shows a similar evolution to that observed in sequence i with the development of an organic rich intrashelf basin during highstand however a tectonically controlled sedimentation pattern is observed with the development of forced regressive wedges due to the flexural bulge of the foreland basin intrashelf basin formation occurred twice in the transgressive part of the third order depositional sequences of the natih formation our study shows that this is mainly the result of differential sedimentation rates that is the dynamics of the carbonate sedimentary system itself in response to rapid rises in relative sea level probably of eustatic origin tectonism was only a minor factor in the creation of the basin topography possibly through the creation of small initial relief the accumulation of the organic matter is not only a result of the creation of a sufficiently deep water column to guarantee dysaerobic conditions for its preservation the late albian and late cenomaniannearly turonian were also periods of generally favorable conditions worldwide for high organic matter productivity the time lines and stratigraphic architecture of the third order sequences presented here have an application potential at the scale of the arabian plate the general sedimentation pattern is predicted by our model but modifications due to different local conditions are likely to occur

missing organic carbon in eocene marine sediments is metabolism the biological feedback that maintains end member climates 1 ocean chemistry is affected by pco2 in the atmosphere by increasing the dissolution of solid calcium carbonate and elevating the dissolved inorganic carbon concentrations in seawater positive feedbacks between the ocean and atmosphere can maintain high atmospheric pco2 and affect global climate we report evidence for changes in the oceanic carbon cycle from the first high quality organic carbon corg data set of eocene sediments beneath the equatorial pacific upwelling region leg 199 of the ocean drilling program eocene corg mass accumulation rates mars are 10 times lower than holocene rates even though expected corg mars estimated from biogenic barium mars an indicator of biological production equal or exceed modern fluxes what happened to the missing corg recent advances in ecology and biochemical kinetics show that the metabolism of nearly all animals marine and terrestrial is positively correlated by first principles to environmental temperatures the approximately 10 c abyssal temperature difference from eocene to holocene should have radically reduced pelagic corg burial as we observe we propose that higher basal metabolism and nutrient utilization recycling rates in the eocene water column and surface sediments precluded corg sediment burial in the pelagic ocean increased rates of metabolism nutrient utilization and lowered corg sedimentation caused by increased temperature may have acted as a biological feedback to maintain high atmospheric pco2 and hothouse climates conversely these same parameters would reverse sign to maintain low pco2 when temperatures decrease thereby maintaining icehouse conditions during cold climate regimes

a warm equable cretaceous the nature of the problem abstract the nature of the problem of warm equable paleoclimates is defined by investigating the mid cretaceous period the problem consists of three components 1 defining precisely the climatic state during any specified interval of geologic time 2 specifying the external climatic forcing factors which may have been important and 3 understanding the climatic response to any specific modifying influence these components are characterized by limitations of critical importance in understanding paleoclimates the nature of the problem of a warm cretaceous is defined both qualitatively and quantitatively within these limits

structural architecture and tectonic evolution of the cenozoic zhanhua sag along the tan lu fault zone in the eastern north china reconciliation of tectonic models on the origin of the bohai bay basin abstract the zhanhua sag a major depocenter within the larger bohai bay basin bbb along the tan lu fault zone tlfz in the eastern north china developed through two successive phases with different stress regimes during the paleogene the kinematics and the slip history of the nw se and n s striking normal fault systems strongly controlled the internal structure and stratigraphy of the paleocene lower eocene strata in the zhanhua sag during phase 1 isopach maps of the paleocene lower eocene stratigraphy show 4000 m thick clastic rock sequences in these structurally controlled depocenters the average dip slip rates of the nw se and n s striking faults were 78 96 and 50 82 m m y respectively in the paleocene early eocene but decreased to 45 87 and 35 81 m m y in the middle late oligocene the ne sw striking fault systems and their slip history controlled the development of the middle eocene oligocene depocenters and their strata during phase 2 the average dip slip rate of the ne sw striking faults was 10 47 m m y in the paleocene early eocene but increased to 93 49 m m y in the middle late oligocene the ne sw oriented faults cut across and displace the nw se striking faults indicating their relatively younger ages these fault patterns and kinematics recorded in the zhanhua sag reflect an abrupt change in extension directions from ene wsw to nw se before and after the middle eocene that was related to a reversal in the slip direction from sinistral to dextral along the tlfz this slip reversal was in turn a result of a major change in the subduction direction of the pacific plate beneath eastern asia and in the mode of strain partitioning across the tlfz in the continental upper plate

facies sequences on a carbonate ramp the carboniferous limestone of south wales during early carboniferous times a major sea level rise led to the development of an extensive carbonate ramp over what is now south wales differential subsidence and sea level changes resulted in distinctive facies sequences in the ramp succession and a model is offered which recognizes three distinct geomorpho tectonic settings inner mid and outer ramp the inner ramp zone occurs in the more landward part of the province and was an area undergoing little or no subsidence the sequence is dominated by oolitic grainstones and peritidal limestones representing shoal and back shoal environments the peritidal units are transgressive deposits consisting of stacked asymmetrical shallowing up cycles the sequence contains many subaerial breaks and tectonic uplift resulted in base level changes and fluvial incision the mid ramp zone sequence is intermediate in thickness between the inner and outer ramp successions and consists mainly of bioclastic limestones deposited below fairweather wave base sedimentation periodically exceeded sea level rise and subsidence and regressive progradational oolitic sand bodies developed the thickest of which are stacked units with up to four individual sand bodies storm processes were of major importance in this setting the outer ramp zone is represented by a thick sequence of muddy bioclastic limestones deposited below storm wave base and major waulsortian reef mounds also developed none of the shallowing phases seen in the other ramp zones can be detected in this sequence subsidence and eustatic sea level rise seem to have been the major controls on deposition but the recognition of eustatic sea level falls is difficult the detailed facies model for ramp carbonates presented here may be applicable elsewhere in the geological record

effects of early sea floor processes on the taphonomy of temperate shelf skeletal carbonate deposits abstract cool water shelf carbonates differ from tropical carbonates in their sources modes and rates of deposition geochemistry and diagenesis inorganic precipitation marine cementation and sediment accumulation rates are absent or slow in cool waters so that temperate carbonates remain longer at or near the sea bed early sea floor processes occurring between biogenic calcification and ultimate deposition thus take on an important role and there is the potential for considerable taphonomic loss of skeletal information into the fossilised record of cool water carbonate deposits the physical breakdown processes of dissociation breakage and abrasion are mediated mainly by hydraulic regime and are always destructive impact damage reduces the size of grains removes structure and therefore information and ultimately may transform skeletal material into anonymous particles abrasion is highly selective amongst and within taxa their skeletal form and structure strongly influencing resistance to mechanical breakdown dissolution and precipitation are the end members of a two way chemical equilibrium operating in sea water in cool waters inorganic precipitation is rare there is conflicting opinion about the importance of diagenetic dissolution of carbonate skeletons on the temperate sea floor but test maceration and early loss of aragonite in particular are reported dissolution may relate to undersaturated acidic pore waters generated locally by a combination of microbial metabolisation of organic matter strong bioturbation and oxidation of solid phase sulphides immediately beneath the sea floor in otherwise very slowly accumulating skeletal deposits laboratory experiments demonstrate that surface to volume ratio and skeletal mineralogy are both important in determining skeletal resistance to dissolution biological processes on the sea floor include encrustation and bioerosion encrustation a constructive process may be periodic or seasonal and can be reversed it produces both information and material bioerosion in contrast is destructive and permanent in temperate areas bioerosion may destroy even very large shells during their long residence at the sea floor on the order of hundreds to thousands of years overall processes on the temperate sea floor may combine to destroy more carbonate than they produce and the preservation potential of temperate shelf carbonate into the rock record may be significantly affected where preservation does occur in such a destructive regime the effects of early sea floor processes will be key determinants of the deposit resulting in a taphofacies characteristic of temperate shelf carbonate sediments