the road river group of northern yukon canada early paleozoic deep water sedimentation within the great american carbonate bank cambrian devonian sedimentary rocks of the northern canadian cordillera record both the establishment and demise of the great american carbonate bank a widespread carbonate platform system that fr

carbonate platforms of passive extensional continental margins types characteristics and evolution abstract carbonate platforms of extensional margins may be grouped into several major categories homoclinal ramps have gentle slopes into deep water may have skeletal or ooid pellet sand shoal complexes that grade without break in slope into deep ramp nodular limestone and then into pelagic hemipelagic basin facies they generally lack significant slump and sediment gravity flow deposits in the deeper water facies distally steepened ramps differ from the above in having a marked increase in slope at the seaward edge of the deep ramp and abundant slumps slope breccias and turbidites however clasts of shallow platform margin facies are generally absent from breccias rimmed shelves have linear trends of shelf edge lime sands and reefs a marked increase in slope into deep water and foreslope and slope sands breccias with clasts of platform margin rocks and turbidites grading seaward into basin hemipelagic pelagic muds they may be divided into accretionary bypass and erosional margins isolated platforms are broad flat topped shallow platforms surrounded by deeper water few hundred meters to 4 km deep many are bypass margins but accretionary and erosional margins also occur finally incipiently to completely drowned or open platforms may develop by rapid submergence of ramps shelves or isolated platforms shallow platform margin facies are shifted landward and the earlier shallow water platform is covered with transgressive lags and deeper water blankets of hemipelagic or pelagic facies or open marine whole fossil wackestone the carbonate prisms commonly develop above a basal clastic phase ramps develop early and evolve into rimmed shelves however with drowning rimmed shelves may evolve up into ramps rimmed shelves may also develop into ramps where miogeoclinal faces prograde into filling marginal basins carbonate miogeocline deposition terminates when the shelf becomes a prograding clastic shelf or where it becomes part of a collisional orogen the various platform types may be recognized from continental margin sequences ranging from proterozoic to holocene in age

controls on facies and sequence stratigraphy of an upper miocene carbonate ramp and platform melilla basin ne morocco abstract upwelling of cool seawater paleoceanographic circulation paleoclimate local tectonics and relative sea level change controlled the lithofacies and sequence stratigraphy of a carbonate ramp and overlying platform that are part of a temporally well constrained carbonate complex in the melilla basin northeastern morocco at melilla from oldest to youngest a third order depositional sequence within the carbonate complex contains 1 a retrogradational transgressive warm temperate type rhodalgal ramp 2 an early highstand progradational bioclastic platform composed mainly of a temperate type bivalve rich molechfor facies and 3 late highstand progradational to downstepping subtropical tropical type chlorozoan fringing porites reefs the change from rhodalgal ramp to molechfor platform occurred at 7 0 0 14 ma near the tortonian messinian boundary during a late stage in the development of the bioclastic platform a transition from temperate type molechfor facies to subtropical tropical type chlorozoan facies occurred and is bracketed by chron 3an 2n 6 3 6 6 ma comparison to a well dated carbonate complex in southeastern spain at cabo de gata suggests that upwelling of cool seawater influenced production of temperate type limestone within the ramp and platform at melilla during postulated late tortonian early messinian subtropical tropical paleoclimatic conditions in the western paleo mediterranean region the upwelling of cool seawater across the bioclastic platform at melilla could be related to the beginning of siphoning of deep cold atlantic waters into the paleo mediterranean sea at 7 17 ma the facies change within the bioclastic platform from molechfor to chlorozoan facies may be coincident with a reduction of the siphoning of atlantic waters and the end of upwelling at melilla during chron 3an 2n the ramp contains one retrogradational parasequence and the bioclastic platform three progradational parasequences minor erosional surfaces that bound the upper surface of the ramp and upper surface of the oldest platform parasequence are related to relative falls in sea level induced by local volcanism and associated tectonic uplift these local relative falls had little influence on a broader scale rise to stillstand in relative sea level that controlled development of the transgressive and early highstand systems tracts represented in the ramp and platform respectively

metallic ion binding by bacillus subtilis implications for the fossilization of microorganisms the silicification of bacterial cells has been followed in a laboratory simulation by electron microscopy and energy dispersive x ray spectroscopy structural degradation of the bacteria was not influenced by silica availability but the remains of degraded cells did promote the precipitation of silica in contrast cells reacted with ferric iron before aging remained intact and structures conforming to the original morphology of the bacteria were preserved by silicification the binding of metallic ions by microbial cells in particular the retention of iron is therefore considered to be an important contributing factor to the fossilization of microorganisms

facies associations and evolution of pelagic carbonate platform basin systems examples from the italian jurassic abstract during the structural and sedimentological evolution of rifted continental margins in carbonate dominated settings a characteristic stage is commonly reached when pelagic carbonate sedimentation occurs in association with complex fault block systems an integrated study of the ammonite biostratigraphy and sedimentology of jurassic pelagic rocks in the umbria marche apennines central italy and in the sila mountains north east calabria southern italy has revealed three distinctive facies associations which can be related to specific structural and depositional settings the condensed pelagic facies association is the constituent of condensed usually discontinuous sequences with numerous hiatal surfaces the normal and resedimented pelagic facies association is typical of thicker sequences comprising gravity flow and rockfall deposits the composite pelagic facies association is one in which rockfall deposits are found associated with condensed sequences containing minor or no gravity flow deposits palaeotopographical highs are dominated by the condensed pelagic facies association and constitute the pelagic carbonate platform pcp structurally the pcp can be coincident with the top of a horst or central high block or the crestal area of a tilted block in the latter case the sediment surface of the pcp slopes gently maximum of 1 3 in this the shallowest area of a pelagic carbonate ramp pcps can have erosional bypass rare and depositional margins stepped margins also exist as subparallel rows of erosional and bypass margins trends from erosional to depositional margins are usually seen as a response to basin filling and burial of submarine tectonic escarpments by pelagic deposits in late synrift or early post rift times this is apparent from progradation of pcp facies deposits beyond the structural boundaries of the pcp palaeoenvironmental analysis in pelagic carbonate platform deposits of the umbria marche apennines suggests that drowning of ancestral peritidal carbonate platforms in pliensbachian time was followed first by a moderate deepening and then by shallowing in the tithonian

microstructures textures and deformation mechanisms in hematite abstract deformation and recrystallization of hematite in iron formations and high grade ore bodies of the caue formation from the quadrilatero ferrifero district minas gerais brazil resulted in several types of fabrics depending on the tectonic and metamorphic imprint the fabrics vary from randomly oriented granoblastic to strongly oriented lepidoblastic mylonitic with local development of cataclastic features complete pole figures of the crystallographic planes 003 basal plane 110 prism and 104 rhombohedron were measured on several samples from different areas by means of neutron diffraction revealing a typical crystallographic preferred orientation for the different fabric types the configuration and intensity of the maxima are directly related to the magnitude of the deformation and the type of response of the ore the analysis of the textures and microstructures of the iron ores and comparison with experimental deformation data lead us to the conclusion that three main mechanisms are active basal slip diffusion processes and anisotropic grain growth post tectonic recrystallization and secondary grain growth did not affect the textures developed during deformation

equatorial rain forest lateritic mantles a geomembrane filter the superimposed weathering layers in equatorial rain forest lateritic mantles from gabon atxca function as interactive compartments forming a dynamic semipermeable geomembrane filter selectivity of the filter is controlled by a progressive downward disappearance of connected macropore pathways created by bioturbation and dissolution the natural balance of root activity translocation dissolution deformation and pore evolution leads to the development of porous and permeable mature open geochemical weathering systems at the expense of the lithosphere these conclusions can be useful in modeling the fate of lateritic soils which cover one third of the emerged area of the world and which are economically important both as metal deposits and agricultural soils

role of the tectonic facies concept in orogenic analysis and its application to tethys in the eastern mediterranean region abstract the purpose of this paper is to advocate the use of a tectonic facies concept which aids systematic and objective analysis of orogenic belts the tectonic facies concept as discussed here focuses on the recognition of discrete tectonic settings mainly those exposed at high crustal levels in orogenic belts application of the tectonic facies concept can help field geologists to relate plate scale processes to outcrop geology tectonic facies are recognised based on knowledge of the modern oceans and margins and well constrained land settings tectonic facies analogous to sedimentary facies can be identified from integrated sets of field data and related laboratory studies a number of tectonic facies models can be recognised in this way their identification aids interpretation and comparisons of orogenic belts palinspastic reconstructions require additional information particularly age kinematic and palaeomagnetic data in this paper the tectonic facies concept is tested by application to a well documented mainly high level orogenic segment tethys in the eastern mediterranean area and is found to be an effective way both of the describing and interpreting this region other methods of tectonic analysis e g recognition of tectono stratigraphic terranes may also be found useful in certain settings and can be used in conjunction with the tectonic facies concept

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

40ar 39ar geochronological constraints on the evolution of lateritic iron deposits in the quadrilatero ferrifero minas gerais brazil weathering profiles overlying the sapecado pico and andaime iron ore deposits quadrilatero ferrifero qf minas gerais brazil reach depths of 150 400 m and host world class supergene iron orebodies in addition to hosting supergene ore bodies of global economic significance weathered banded iron formations at the quadrilatero ferrifero and elsewhere e g carajas hamersley are postulated to underlie some of the most ancient continuously exposed weathering profiles on earth laser incremental heating 40ar 39ar results for 69 grains of hollandite group manganese oxides extracted from 23 samples collected at depths ranging from 5 to 150 m at the sapecado pico and andaime deposits reveal ages ranging from ca 62 to 14 ma older mn oxides occur near the surface while younger mn oxides occur at depth however many samples collected at the weathering bedrock interface yield ages in the 51 41 ma range suggesting that the weathering profiles in the quadrilatero ferrifero had already reached their present depth in the paleogene the antiquity of the weathering profiles in the quadrilatero ferrifero is comparable to the antiquity of dated weathering profiles on banded iron formations in the carajas region brazil and the hamersley province western australia the age versus depth distributions obtained in this study but not available for other regions containing similar supergene iron deposits suggest that little further advance of the weathering front has occurred in the quadrilatero ferrifero lateritic profiles during the neogene the results suggest that weathering in some of these ancient landscapes is not controlled by the steady state advance of weathering fronts through time but may reflect climatic and geomorphological conditions prevailing in a remote past the geochronological results also confirm that the ancient landsurfaces in the quadrilatero ferrifero probably remained immune to erosion for tens of millions of years deep weathering mostly in the paleogene combined with low erosion rates account for the abundance and widespread distribution of supergene iron manganese and aluminum orebodies in this region

gravity slide and resedimentation processes in a miocene carbonate ramp hyblean platcau southeastern sicily abstract more than twenty sharp based channel form structures occur in the miocene palazzolo formation carbonates within a distally steepened se sicilian miocene carbonate ramp contemporaneous biota indicate deposition in water depths of 70 150 m fully exposed structures commonly exceed one kilometre along palacostrike their bases are concordant with the host strata but these steepen to 15 in proximity of their margins internal bedding planes generally are concordant with the basal truncation surface the lithologies of the channel fills are similar to the host sediment there is little evidence that these structures are erosional since they contain neither breccias nor turbidites rather they are interpreted as the product of gravitational sliding involving thin detached sheets of consolidated ramp carbonates the resulting irregular topography was draped by redeposited fine grained carbonate sediments once healed and further oversteepened renewed gravity sliding occurred this resulted in a 250 m thick slide dominated succession in a zone 4 km wide located between the outer ramp apron comprised of coralline algal and foraminifera rich sediments and basin margin pelagic marls this phenomenon although unusual in shallow water settings is well known from modern continental slope environments sliding was probably triggered by seismicity in the region associated with two known mesozoic basement faults an alternative hypothesis involving pressure gradient build up along distally steepened ramp zones during storm surges is dismissed as a cause although this mechanism may have facilitated resedimentation of seafloor sediments over the slide zone

breccia hosted manganese rich minerals of alpi apuane italy a marine redox generated deposit mn rich beds occur within the brecce di seravezza formation bsfm intercalated between norian metadolostone megalodontic marble and hettangian marble in the alpi apuane italy the bsfm is a rockfall talus deposit that accumulates at the base of the footwall scarp of normal faults bordering extensional marine coastal basins the type sequence of metabreccia ends with a bed of chloritoid schist interpreted as the metamorphic equivalent of lateritic soils the four main types of mn mineral assemblages are 1 braunite piemontite and rare hausmannite 2 piemontite braunite hollandite and minor rhodochrosite and kutnahorite 3 braunite hollandite and rare piemontite the other minerals are quartz calcite muscovite phlogopite baryte and minor hematite rutile and apatite during the alpine orogeny pressures of 4 6 kb and temperatures of 350 380 c were attained mn assemblages with hematite and phlogopite indicate o2 10 8 for t 350 c and o2 10 6 when braunite appears on the mn rich rocks ti fe nb sn ta hf th ga rb pr k na nd were identified as detrital in origin and are positively correlated with al u is positively correlated with co pb bi mo the rare earth element patterns normalized to seawater show a negative slope towards the heavy rare earth elements with positive ce anomalies in some samples positive ce and eu anomalies in other samples and negative ce and positive eu anomalies in a third group the eu concentrations are nearly constant and the eu anomalies reflect differences in the concentration of other rare earth elements for ce a positive correlation with al2o3 sio2 indicate that a detrital signature prevails on that produced by duration of seawater exposure but a significant good correlation of la tm lu with mg could indicate at least for these elements a seawater signature only in some samples ba eu sr show anomalously high concentrations likely of hydrothermal origin however generally in all the chemical variation diagrams the bsfm samples fall outside the field of hydrothermal and hydrogenous deposits as defined in the literature for other mn deposits in addition metabasites and metavolcaniclastic beds are absent from the bsfm sequence and bsfm coastal basins were for the most part separated from the open ocean and related streams that must be excluded as possible mn sources owing to the arid climate of late triassic the runoff was negligible and the groundwater oxidizing and alkaline were unable to mobilize mn the bsfm basins are then the most suitable depositional environment for mn the water column was stagnant and stratified only where bottom of the basin was deeper than the oxic anoxic boundary reducing marine bottom waters percolated within the fractured basement and leached mn from disseminated minerals of metamorphic rocks and then rising along fault and fractures supplied mn to the bottom waters afterwards when tectonic uplift and sealevel drop brought the bottom into the oxic field mn precipitated and formed the mn rich matrix of the bsfm deposits

soft sediment deformation in a tectonically active area the plio pleistocene zarzal formation in the cauca valley western colombia abstract the plio pleistocene zarzal formation corresponds to fluvio lacustrine sediments deposited in an intramontane depression within the colombian andes associated with the cauca romeral fault system it crops out mainly in the cauca valley where numerous field sections have permitted the mapping of the vertical and lateral lithological variations lacustrine deposits of sands silts clays and diatomites are interbedded with fluvial sand and gravel beds and fluvio volcanic mass flows derived from the volcanic central cordillera numerous soft sediment deformation structures are encountered in this formation particularly in fine to medium grained sands silts and clays load structures load casts flame structures pseudonodules water escape structures water escape cusps dish and pillar and pocket and pillar structures soft sediment intrusions clastic sills and dykes disturbed laminites convolute laminations slumps and synsedimentary faulting deformation mechanisms and driving forces are related essentially to gravitational instabilities dewatering liquidization and brittle deformations field and regional geological data show that most of these deformations are related to seismicity and can be interpreted as seismites this area has a geological and recent seismic history and outcrops show both syn and post depositional faulting related to the transpressional regime of this part of the colombian andes which generates strike slip faults and associated local normal faults the drainage pattern within the zarzal formation shows the signature of neotectonics moreover the fine to coarse grained sands of the zarzal formation are lithologies prone to liquefaction when affected by seismic waves the intercalation of the deformed intervals within undisturbed strata confirms the catastrophic nature of the events finally the large areal extent of the deformations and the type of structures are compatible with seismites consequently the existence of seismites in the zarzal formation represents corroboration of tectonic activity in this area during the pleistocene earthquakes with a magnitude higher than 5 can be postulated based upon the proximity of active faults and the types of deformations

carbonate platform evolution and conodont stratigraphy during the middle silurian mulde event gotland sweden evidence from sedimentology and conodont biostratigraphy is used to reinterpret the mid homerian late wenlock succession on gotland sweden a new conodont zonation includes from below the ozarkodina bohemica longa zone including five subzones the kockelella ortus absidata zone and the ctenognathodus murchisoni zone two taxa are named ozarkodina bohemica longa and pseudooneotodus linguicornis these new zones are integrated with facies in order to correlate strata and infer the major depositional environments and the controls on deposition during the mid homerian mulde event reef associated and skeletal carbonate deposition predominated before and after the event i e during the uppermost o s sagitta zone and again in the c murchisoni zone these periods are characterized by the expansion of reefs and shoal facies across marls in the topmost slite group on eastern gotland and in the lower parts of the klinteberg formation on western gotland respectively the intervening o b longa and k o absidata zones are initially characterized by rapid facies changes including siliciclastic deposition and later stabilisation of a carbonate depositional system the composition of sediments and depositional rates are closely related to the creation and destruction of accommodation space and reflects a classical case of depositional bias of the carbonate and siliciclastic depositional systems based on coastline migration stratal boundaries and the stratigraphic position of major reef belts several facies associations can be fitted into a sequence stratigraphic model for platform evolution a highstand systems tract hst situation prevailed prior to and during the early part of the event the upper slite group including the lower frjel formation this hst was characterized by prolific skeletal production and regional reef development except for during the latest stage when carbonate production declined at the onset of the mulde event platform growth was inhibited during a following regressive systems tract rst when regional siliciclastic deposition predominated the gannarve member the subsequent lowstand resulted in regional emersion and karstification i e a complete termination of the platform the post extinction transgressive systems tract tst is exclusively composed of non skeletal carbonates the bara member of the halla formation re occurrence of reefs and a prolific skeletal production marks platform recovery during a second hst the remaining halla and the lower klinteberg formations integration of high resolution biostratigraphy and sequence stratigraphy reveals that the major physical control on platform evolution was a 5th order eustatic sea level change during an early part of the mulde event and that the bulk of the strata accumulated when the platform aggraded and prograded during the highstand systems tracts thus silurian oceanic events and associated sea level changes had profound impact on the neritic carbonate system the gotland based middle and late homerian sea level curve shows two rapid regressions both leading to truncation of highstand systems tracts the first lowstand occurred at the very end of the c lundgreni chron and the second at the end of the co ludensis chron the intervening interval was characterized by stillstand or possibly slow transgression

early proterozoic gold placers of the moeda formation within the gandarela syncline minas gerais brazil gold bearing placer conglomerates dated between 2 2 and 2 8 ga have been identified at the base of the moeda formation in the gandarela syncline intensive investigation of outcrop and underground exposures both old and new and borehole intersections around the western and southern margin of the syncline has defined a paleoenvironment consisting of an upland fluvial drainage system in the north leading southward to an alluvial fan and braided plain depository heavy mineral concentrates composed predominantly of coarse rounded pyrite are concentrated in the matrix of cobble conglomerates that occur in the form of discrete bars and sheets the mineralogy and geochemistry of the ore closely resembles that of witwatersrand placers as does the composition of the gold gold concentrations are equal to those of the average witwatersrand gold deposit and therefore these deposits may make a significant contribution to brazil9s future gold production

evidence for reversal of basin polarity during carbonate ramp development in the mesoproterozoic borden basin baffin island distribution of facies in the lower half of the bylot supergroup suggests overall westward deepening of the mesoproterozoic borden basin in marked contrast the upper half of the succession records a reversal in the overall bathymetric trend such that the eastern portion underwent relative deepening as the west experienced relative shallowing strata deposited during this reversal belong to the victor bay formation a ramp composed predominantly of limestone karsting of carbonate strata and development of an angular unconformity in the west contrast with back stepping and drowning of the ramp in the east followed by mantling by deep water limestone carbonaceous carbonate and turbidites increased accommodation space during this time via both tectonic subsidence and eustatic sea level rise led to a profusion of stromatolite pinnacle reefs and large biostromes the reversal of basin polarity is best reconciled with development of a distal foreland basin superimposed on the borden aulacogen crustal rethickening and uplift occurred along reactivated basement faults during an eastward directed compressional event and could be related to thrusting of similar age and vergence in the coppermine river group of northwestern canada

the platiniferous au pd belt of minas gerais brazil and genesis of its botryoidal pt pd aggregates we delineate an approximately 240 km long north trending au pd pt belt in minas gerais brazil which hosts hydrothermal pd pt bearing gold mineralization in its southern part quadrilatero ferrifero and itabira district and alluvial pd pt au mineralization in its northern part southern serra do espinhaco the hydrothermal pd pt bearing gold mineralization locally known as jacutinga occurs as late orogenic quartz hematite talc kaolinite veins which truncate the brasiliano regional tectonic foliation of the itabiritic host rocks of the paleoproterozoic itabira iron formation the alluvial pd pt au mineralization occurs as botryoidal pd pt nuggets and delicate palladiferous gold aggregates in clastic and organic rich valley infill on quartzite and hematitic rocks of the paleo to mesoproterozoic espinhaco supergroup the au pd pt belt follows the regional trend of major thrust faults related to the 0 6 ga brasiliano orogeny and the hydrothermal jacutinga mineralization could be regarded as an oxidized variant of the orogenic gold deposit spectrum secondary botryoidal and arborescent pt pd aggegates and primary detrital au pd grains are peculiar to the alluvial platiniferous deposits of the northern part of the belt in the serra do espinhaco we suggest that their source was jacutinga style vein mineralization as deduced from abundant detrital hematite and rutile and the discovery of detrital hongshiite a pt cu alloy that forms bonanza pockets within jacutinga at itabira reconnaissance laser ablation inductively coupled plasma mass spectrometry analyses for trace metals in the botryoidal pt pd grains show that they have elevated tl and se contents of 0 9 to 354 and 54 to 2 700 ppm respectively these elements correlate positively with a tl se ratio of about 0 08 a value that contrasts with tl se 1 for hongshiite from the hydrothermal jacutinga system at itabira the low and roughly constant tl se ratios of the alluvial samples are close to the average value of 0 12 for fluvial waters we suggest that the botryoidal pt pd aggregates grew in situ by electrochemical metal accretion from dilute solutions carrying pt and pd from the dissolution of detrital pt pd minerals from jacutinga the connection between jacutinga and platiniferous alluvia indicates that there is a prospective trend of about 240 km for pd pt bearing gold mineralization reaching from ouro preto to diamantina the very high oxidation state required for efficient low temperature aqueous mobilization of pt pd and au was apparently controlled by the quartzitic and hematitic rocks in the serra do espinhaco but not in the southern belt where greenstone rocks buffered fluids to moderate ph and lower oxidation states

depositional architecture of a rimmed carbonate platform albian gorbea western pyrenees a lower cretaceous carbonate platform depositional system with a rimmed margin and an adjacent oversteepened slope was analysed in order to determine its depositional architecture and major depositional controls the platform is made up of coral rudist orbitolinid and algal limestones and in a 12 km dip transect there is a gradation from lagoon to platform margin slope and basin environments each characterized by distinctive sedimentological features and facies associations the rimmed platform is an aggradational system developed during approximately 4 2 million years of fluctuating relative sea level rise and it is bounded by unconformities at its base and top internal cyclicity in the construction of the system is evident mainly in platform interior and slope settings the seven recognized sequences average 0 6 million years in duration and are related to minor relative sea level changes carbonate deposition occurred in shallow and deep water settings during periods of high relative sea level reduced rates of sea level rise led to the development of shallowing upward sequences and eventually to the exposure of the shallowest parts of the platform during relative sea level falls during low relative sea level erosion surfaces developed on the slope and gravitational resedimentation occurred at the toe of slope basinwards resedimented units pinch out over distances of a few hundred metres active faults controlled sedimentation at the platform margin promoting the development of steep slopes up to 35 and preventing progradation of the shallow water platform despite high sediment production rates the development of sequences is interpreted to be related to tectonic activity

stromatolite provinces of hamelin pool physiographic controls on stromatolites and associated lithofacies recent studies recognized distinct stromatolite provinces in hamelin pool western australia each with morphologically distinct stromatolite structures paired with characteristic shelf physiography in the present paper we couple detailed lithofacies mapping with hamelin pool bathymetry and consider physiography as a control of sedimentation processes including stromatolite development bathymetric transects derived from a high resolution bathymetry map with depths from 0 to 11 meters allow calculation of slope gradients in the provinces as in other settings bathymetry is linked to energy regimes which in turn appear to be coupled with variations in stromatolite morphologies and associated lithofacies as follows 1 low gradient ramps with low energy settings are associated with sheet mats and elongate clustered stromatolites that exhibit regular spatial patterns possibly indicative of self organization 2 low gradients coupled with high energy settings resulting from strong winds result in seif stromatolites with pronounced directional bands 3 medium to steep gradients coupled with medium to high energy are associated with individual and merged stromatolites often with thin basal necks 4 headlands and promontories where the topography deflects currents are associated with elongate nested stromatolites and 5 medium to high energy slopes typically found at promontory edges and shelf margins are dominated by blocky pavement observations linking stromatolite morphology to physiography in a modern microbial system provide insight into the long lived debate about biology versus environment in controlling stromatolite morphology when physiography leads to a high energy regime environmental controls are the main factor determining stromatolite morphology in contrast when physiography promotes a low energy environment the response of biological communities becomes the main driver of macroscale stromatolite morphology

trace element characteristics of different pyrite types in mesoarchaean to palaeoproterozoic placer deposits a comparative in situ la icp ms trace element study on pyrite from three different variably auriferous archaean to palaeoproterozoic palaeoplacer deposits in the ouro fino syncline quadrilatero ferrifero brazil the elliot lake area north of lake huron se canada and several deposits within the witwatersrand basin south africa revealed systematic differences between morphologically different pyrite types and between the various palaeoplacer deposits especially the ni and au concentrations as well as co ni and mo ni ratios were found to be systematically different in detrital compact detrital porous and post sedimentary hydrothermal pyrite grains from different source areas high co ni ratios and low au concentrations are typical of post sedimentary pyrite which is hydrothermal in origin in contrast relatively low co ni ratios and high au contents characterise detrital porous banded and concentric pyrite grains au 1 ppm which are syn sedimentary in origin in the elliot lake area and the witwatersrand basin detrital compact rounded pyrite is characterised by high co ni ratios which is in agreement with derivation from a hydrothermal source low au concentrations in this pyrite type support the contention of the gold and the pyrite in these deposits coming from different source rocks in contrast derivation from an originally diagenetic pyrite is suggested for the detrital compact pyrite in the ouro fino syncline because of low to intermediate co ni ratios high au contents may indicate a genetic relationship between pyrite and gold there systematic differences exist between the three areas with respect to au ni co mo and cu distributions in detrital pyrite which reflects differences in the provenance a predominantly mafic ultramafic source is indicated for the ouro fino a felsic source for the elliot lake and a mixed felsic mafic provenance for the witwatersrand pyrite populations independently of pyrite type the higher au endowment of the studied witwatersrand and ouro fino conglomerates are also reflected by an overall higher au concentration in the respective pyrite grains compared to the relatively au poor samples from elliot lake in general a strong positive correlation between au and pb levels in the various pyrite grains is noted analogous to pb which is well known for not being easily accommodated in the pyrite crystal lattice but occurring as discrete pbs phases au is considered to be present mainly in the form of discrete au phases in minute pores and interstices of the pyrite grains rather than within the pyrite lattice

microbial silicification in iodine pool waimangu geothermal area north island new zealand implications for recognition and identification of ancient silicified microbes silicified microbes provide evidence for some of the earliest life forms on earth they are extremely important to understanding the early development of life and the conditions that allowed its development such discussions commonly rely on comparisons with extant taxa and therefore depend upon the preservation style of the microbes and in particular the preservation of the taxonomically important features silicified microbes are deceptive they commonly appear to be well preserved even though their taxonomically critical features have been destroyed by silicification an understanding of the early taphonomic processes that influence microbial silicification can be obtained by studying extant microbes that are being silicified in modern hot spring pools iodine pool located in the waimangu geothermal area on the north island of new zealand is ideal for this purpose the spring water has a temperature of 69 100 c a ph of 8 3 9 0 and 440 457 ppm sio 2 glass slides left in the shallow marginal waters of this pool for 90 h became covered with thin layers of opaline silica discrete opal a spheres unsilicified microbes pseudofilaments partly silicified microbes and silicified microbes the rapidly silicified microbes appear well preserved with their general morphology diameter length and presence or absence of septa being readily apparent most of the silicified microbes however lack the key features that would allow accurate comparisons with extant taxa only two of the silicified microbes can be tentatively allied with the unsilicified forms despite being found side by side on the same glass slide these problems in identifying modern rapidly silicified microbes suggest that identifications of ancient silicified microbes can be problematic and must be treated with caution

carbonate ramp to deeper shale shelf transitions of an upper cambrian intrashelf basin nolichucky formation southwest virginia appalachians the nolichucky formation 0 300 m thick formed on the cambrian pericratonic shelf in a shallow intrashelf basin bordered along strike and toward the regional shelf edge by shallow water carbonates and by nearshore clastics toward the craton lateral facies changes from shallow basinal rocks to peritidal carbonates suggest that the intrashelf basin was bordered by a gently sloping carbonate ramp peritidal facies of the regional shelf are cyclic upward shallowing stromatolitic carbonates these grade toward the intrashelf basin into shallow ramp cross bedded ooid and oncolitic intraclast grain stones that pass downslope into deeper ramp subwave base ribbon carbonates and thin limestone conglomerate ribbon limestones are layers and lenses of trilobite packstone parallel and wave ripple laminated quartzose calcisiltite and lime mudstone arranged in storm generated fining upward sequences 1 5 cm thick that may be burrowed shallow basin facies are storm generated upward coarsening and upward fining sequences of green calcareous shale with open marine biota parallel to hummocky laminated calcareous siltstone and intraformational flat pebble conglomerate there are also rare debris flow paraconglomerate 10 60 cm thick and shaly packstone wackestone with trace fossils glauconite horizons and erosional surfaces hardgrounds a 15 m thick tongue of cyclic carbonates within the shale package contains subtidal digitate algal bioherms which developed during a period of shoaling in the basin understanding the nolichucky facies within a ramp to intrashelf basin model provides a framework for understanding similar facies which are widely distributed in the lower palaeozoic elsewhere the study demonstrates the widespread effects of storm processes on pericratonic shelf sedimentation finally recognition of shallow basins located on pericratonic shelves is important because such basins influence the distribution of facies and reservoir rocks whose trends may be unrelated to regional shelf edge trends

the tectonic evolution of the quadrilatero ferrifero minas gerais brazil abstract the structural framework of the quadrilatero ferrifero is the result of two main deformational events the first is an extensional event of palaeoproterozoic age between 2 100 and 1700 ma the transamazonian event which resulted in the formation of archaean granite gneiss domes and the nucleation of regional synclines in the overlying rio das velhas and minas supergroups strata such regional synclines are continuous with each other and are bordered by structural granite gneiss highs at the contact between these units ductile brittle to ductile extensional shear zones are developed representing the dislocation surfaces of archaean blocks this tectonism is probably related to the evolution of a metamorphic core complex formed in the hinterland to the west of a transamazonian collision zone which structured the paramirim craton the second event is compressive and associated with the closure of the pan african brasiliano proto ocean 650 500 ma situated to the east of quadrilatero ferrffero qf during this event a west verging fold and thrust belt ftb developed causing inversion amplification translation and rotation of the basinal synclines the ftb affected mainly the eastern portion of qf and obliterated many of the tectonic features of the extensional event

depositional environments along a carbonate shelf to basin transect in the silurian of nevada u s a abstract during the llandovery silurian in central nevada foundering of the shelf margin and drowning of a homoclinal carbonate ramp produced a rimmed carbonate shelf westward the shelf was bordered by a slope which passed into a deep water basin at the shelf margin carbonate sand shoals lone mountain dolomite aggraded and prograded westwards over the slope the spatial and temporal facies variation in a transect across the slope roberts mountains formation records the history of a prograding shelf margin initial slope sedimentation adjacent to the carbonate shelf margin was lime mudstone hemipelagically derived from the shelf westwards and downslope dilute carbonate turbidites and hemipelagic lime mudstone laminated facies were deposited contemporaneous slope rise sediments fourmile canyon formation consist primarily of siliciclastic mudstone with minor dilute carbonate turbidites and turbiditic siliciclastic siltstone the latter essentially being part of the deep water basin subsequent shelf margin progradation and increasing slope differentiation is reflected in the downslope introduction of calcarenite and conglomerate derived from the shelf margin slope sedimentation records an overall coarsening and thickening upwards cycle superimposed on this in some areas are small scale coarsening and thickening upwards cycles reflecting deposition on carbonate debris aprons abandonment and subsequent build out of the aprons reflects the pulsatory and uneven progradation of the outer shelf margin simultaneous with these depositional patterns the immediate shelf margin periphery top of slope received hemipelagic lime mudstone sediments many rotational slides some generating debris flows indicate upper slope instability most allochthonous carbonate debris from the shelf margin by passed the top of slope and was deposited further downslope with the westward progradation of the shelf margin the fringing facies migrated basinward

cephalopod limestone deposition on a shallow pelagic ridge the tafilalt platform upper devonian eastern anti atlas morocco as a result of early variscan tectonic movements and of differential subsidence a platform and basin topography was created along the northern margin of the sahara craton during the late devonian in the moroccan anti atlas mountains the tafilalt platform is an approximately n s running ridge which developed since the late middle devonian it separated a slowly subsiding shallow basin in the east tafilalt basin from a rapidly subsiding furrow in the west mader basin platform deposits are characterized by highly reduced thicknesses shallow subtidal to supratidal deposits in the late frasnian and by unconformities at the lower upper frasnian and the frasnian famennian boundaries after a local transgression over emergent areas in the north water depth probably never reached more than several tens to about 100 m in the lower famennian cephalopod limestones of this age deposited on the platform represent a very diverse facies pattern comprising quartz rich brachiopod coquinas crinoidal limestones thick bedded cephalopod limestones and nodular limestones sedimentation rates ranged from 1 to 5 mm 1000 yr in the late famennian more uniform marl and nodular limestone facies suggest slightly deeper environments platform margins are characterized by higher rates of subsidence debris flow deposits and slump structures in the relatively shallow tafilalt basin marls with intercalated nodular limestones were deposited in the mader basin sandy and calcareous turbidites suggest deeper water conditions in the late devonian during the strunian tournaisian the whole area was overwhelmed by a thick deltaic sequence the general facies distribution is in agreement with depositional models of other upper devonian and lower carboniferous cephalopod limestones in the european variscan orogenic belts in all these cases condensed cephalopod limestones occupy a distinct palaeogeographic position in predictable facies sequences that reflect pre orogenic phases in the variscan geodynamic cycle moreover close parallels exist with condensed sequences in the triassic and jurassic that occur in a very similar position within the alpine orogenic cycle

late triassic to late jurassic evolution of the adriatic carbonate platform and budva basin southern montenegro abstract southeastern montenegro is the only part of the adriatic carbonate platform adcp that bears record of its evolution from a ramp through a distally steepened ramp to a platform in this paper we present the sequence stratigraphy of the late triassic to late jurassic rocks from this part of tethys for the first time in the literature we discovered and described three new facies hardground and cerebroid oolites of the livari supersequence and black pebble conglomerate of the tejani supersequence the mid ramp and lower ramp cherty oolite wackestone and mudstone facies of the livari supersequence as well as oolite conglomerate facies of the stari bar supersequence were partially or completely reinterpreted the middle and late triassic rifting separated the adcp from the other south tethyan carbonate platforms and created the intraplatform budva basin the adcp evolved through three morphologic stages a detached ramp livari supersequence rhaetian early toarcian a distally steepened ramp tejani supersequence early toarcian middle callovian and an accretionary rimmed platform stari bar supersequence oxfordian to neogene the rhaetian regression is marked by a regional unconformity surface that represents a type s sequence boundary at the base of the livari supersequence lowstand wedge of the halobia limestone was the oldest sediment in the budva basin tst and hst of the livari supersequence include supratidal and intertidal inner ramp sediments ooid shoals and cyclic shallowing up parasequences of the mid ramp sedimentation rates were high in the inner ramp while budva basin received relatively thin accumulation of siliceous plankton a brief exposure of supratidal flats and ooid bars represents a type p sequence boundary between the livari and the tejani supersequences which was flooded by the early toarcian transgression tst and hst of the tejani supersequence consist of supratidal lagoon and shoal sediments in the inner ramp and deeper water carbonates of the mid and outer ramp highstand shedding of the sediment from the steepened ramp left thick deposits in the budva basin the bathonian regression is marked by a regional unconformity that represents a type s sequence boundary between the tejani and stari bar supersequences stari bar oolite conglomerate is a lowstand wedge of the stari bar supersequence the middle callovian transgression induced aggradation of ooid shoals deep into the platform interior oxfordian coral reefs created a rimmed platform and restricted export of the shallow carbonates into the budva basin

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

seismic interpretation of carbonate depositional environments most seismic stratigraphic or seismic lithologic interpretations have been applied to clastic depositional systems because of their unique sedimentologic and mineralogic characteristics carbonate rocks are more difficult to study using seismic data increased knowledge of carbonate deposits and their petrophysical parameters and higher quality geophysical tools now permit a better understanding of carbonate rocks using seismic images in this paper seismic facies of carbonate rocks are characterized step by step from the basin to the supratidal environment 1 pelagic deposits shales and micritic limestone layers exhibit continuous parallel reflections with an apparently high frequency chalk deposits display continuous high amplitude reflections at the top and base with an internal reflection free zone 2 talus deposits are characterized by discontinuous oblique reflections of high amplitude carbonate debris flow generates chaotic reflections with hummocky surfaces channels exhibit erosional truncations 3 reef barriers are mound shaped biogenic deposits that display marginal onlapping reflections overlying reflections drape the reefs and underlying reflections exhibit pull up or pull down effects hyperbolic diffractions also may occur 4 platform border sands are mound shaped oblique reflections of moderately high amplitude 5 inner shelf strata are characterized by parallel continuous reflections typically displaying low frequency patch reefs may be distinguished within the inner shelf system mound shape drape of overlying reflections velocity anomalies and spurious events 6 where dolomitized the intertidal to supratidal facies exhibit a marbled zone a practically reflection free zone with a few discontinuous reflections diagenetic events such as paleokarst zones may be delineated using special analyses involving amplitude offset variations the study of carbonate depositional environments and petrophysical characteristics provides a more complete geologic insight including relative changes in sea level within a sedimentary basin such studies are fundamental in analyzing carbonate reservoirs and their paleogeographic settings

polymeric substances and biofilms as biomarkers in terrestrial materials implications for extraterrestrial samples organic polymeric substances are a fundamental component of microbial biofilms microorganisms especially bacteria secrete extracellular polymeric substances eps to form slime layers in which they reproduce in the sedimentary environment biofilms commonly contain the products of degraded bacteria as well as allochthonous and autochthonous mineral components they are complex structures which serve as protection for the colonies of microorganisms living in them and also act as nutrient traps biofilms are almost ubiquitous wherever there is an interface and moisture liquid liquid liquid solid liquid gas solid gas in sedimentary rocks they are commonly recognized as stromatolites we also discuss the distinction between bacterial biofilms and prebiotic films the eps and cell components of the microbial biofilms contain many cation chelation sites which are implicated in the mineralization of the films eps biofilms and their related components thus have strong preservation potential in the rock record fossilized microbial polymeric substances fps and biofilms appear to retain the same morphological characteristics as the unfossilized material and have been recognized in rock formations dating back to the early archaean 3 5 b y we describe fps and biofilms from hot spring deep sea volcanic lake and shallow marine littoral environments ranging up to 3 5 b y in age fps and biofilms are more commonly observed than fossil bacteria themselves especially in the older part of the terrestrial record the widespread distribution of microbial biofilms and their great survival potential makes their fossilized remains a useful biomarker as a proxy for life with obvious application to the search for life in extraterrestrial materials

facies analysis and depositional environments of permian carbonates of the venezuelan andes palaeogeographic implications for northern gondwana abstract upper palaeozoic strata in south america were deposited over cratonic areas and in intracratonic basins e g solimoes amazonas parana however in many areas such as venezuela and colombia they are rarely exposed through dense vegetation and the nature of the terrain so that the strata are poorly documented however these strata do have significant implications for the palaeogeography of the time this article reports on a study of the permian carbonates of the palmarito formation exposed throughout the venezuelan andes and discusses the succession of palaeoenvironments and the palaeogeography resulting from detailed field and lab work deposition took place on an extensive ramp which probably dipped gently northwards towards the open ocean much of the palmarito succession shows a general transgressive trend with a few thinner more regressive intervals likely a response to glaciation deglaciation cycles towards the end of the permian in the venezuelan andes region a major sea level fall led to extensive uplift and erosion resulting in a major disconformity between the upper guadalupian carbonates and overlying jurassic red beds the early palmarito tidal flat facies are noteworthy for their sub metre scale mud to sand cycles with incipient palaeosoil fabrics overlying mid outer ramp carbonate facies are characterised by thin storm beds and bioclastic lenses arranged into metre scale coarsening upward cycles succeeding shallow marine inner mid ramp bioclastic grain wacke stones are dominated by an open marine fauna of fusulinids calcareous algae crinoids bryozoans and brachiopods outer ramp facies are wacke mud stones with sponge spicules radiolarians and brachiopod fragments there are similarities between the permian deposits of venezuela and those recorded from guatemala and mexico to the north and from colombia and peru bolivia to the west and southwest where carbonate systems also dominate these facies were all part of a tropical foreland basin setting the mucuchachi basin which contrasts with the other late palaeozoic intracratonic basins in south america evidence provided here demonstrates that a seaway existed between laurentia and gondwana from the early permian through to the late early permian

early diagenetic ree phosphate minerals florencite gorceixite crandallite and xenotime in marine sandstones a major sink for oceanic phosphorus

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

short paper a standardized model for tethyan tertiary carbonate ramps low latitude carbonates in massive and clinoform bedded sheets termed ramps occur throughout the tertiary tethyan realm and are characterized by recurring biofacies usually including large foraminifera rhodolithic algae coralgal patch reef and gastropod dominated sequences all can be interpreted broadly within a standardized tertiary carbonate ramp model biota can be used to define precise palaeobathymetric zones which have a predictive utility in palaeoenvironmental modelling especially where data are limited the carbonate ramp model of earlier authors has been elaborated by read 1982 and ramp formation occurs mostly in passive margin and extensional tectonic settings ramps are characterized by slope gradients of less than 1 degree and once established are conservative to change much use has been made of the ramp model for palaeozoic and mesozoic lithofacies modelling in contrast published work on cenozoic ramps is limited however tethyan ramps are particularly widespread and extend tens to hundreds of kilometres along strike and occupy tens of kilometres of slope many studies have dealt with cenozoic ramp associations and sequences e g pedley 1983 reiss hottinger 1984 purser 1973 and have demonstrated the diversity of biotal and sediment detail but without ascribing them to a ramp model biota were quick to adapt to the tertiary environments left vacant after the k t boundary extinction events new genera of foraminifera mollusca bryozoa and echinoder mata rapidly replaced the extinct forms in bursts of innovative opportunism codiacean algae rhodophyta and marine angiosperms were equally adaptive colonizers of the carbonate platforms novel biofacies associations were derived from

xenotime hematite aggregates on opaline filaments evidence for biomineralization in weathered siliciclastic rocks capanema quadrilatero ferrifero of minas gerais brazil dissolution cavities in weathered pebbly quartzite of the 2 5 ga moeda formation at capanema quadrilatero ferrifero of minas gerais brazil are decorated with suspended filaments of opaline silica the filaments sustain xenotime hematite aggregates in the open space xenotime occurs as inclusions in buds and botryoidal aggregates of hematite the filamentous structures consist of strand forming buds hypha like extensions and thin strands that compose mat like arrangements they resemble microbial filaments that were replaced by opaline silica and fossilized the occurrence of spherical hematite as protuberances on hematite free opaline hyphae is interpreted as accretion of dissolved iron onto extracellular polymers phosphate sites in polymeric substances expelled from the microbial filaments might have adsorbed yttrium and heavy rare earth elements from groundwater to the iron accreting polymers these would have resulted in botryoidal aggregates of hematite with xenotime inclusions the presence of authigenic xenotime in the weathering zone opens a new possibility to constrain the evolution of lateritic profiles by xenotime geochronology

neritic carbonate crisis during the early bajocian divergent responses to a global environmental perturbation abstract the early bajocian witnessed a global environmental perturbation characterized by faunal and floral turnovers and a positive carbon isotope excursion in italy this environmental perturbation coincided with an eutrophication event and a carbonate crisis but this has so far not been adequately reported from other settings leaving doubt about the extent and nature of these phenomena in this paper we are reporting on an extensive neritic carbonate factory demise that occurs in the upper lower bajocian of morocco more precisely in the upper propinquans lower humphriesianum zones this demise coincided with the acme of the global carbon isotope perturbation recorded by a 3 positive carbon isotope excursion in the bulk organic matter of morocco but not in the micritic phase due to the fact that the moroccan carbonate 13c record is more sensitive to local rather than global influences furthermore we observe that the lower bajocian of morocco is relatively enriched in arenitic siliciclastic deposits suggesting increased weathering and nutrient levels along the northwestern margin of africa during the early bajocian however comparison with neighboring european basins highlights the non uniqueness and different timing of the response of shallow water carbonates to the early bajocian environmental perturbations as some regions present no sign of carbonate factory crisis hence we postulate that local factors were important in mediating the response of neritic carbonate factories to this global environmental perturbation we notably highlight the role of large early bajocian sea level fluctuation as a trigger for carbonate factory change and demise in morocco

carbonate platform depositional sequences upper cretaceous south central pyrenees spain abstract the upper cretaceous cenomanian maastrichtian of the south central pyrenees shows five carbonate platform sequences where the major parameters are tectonism relative sea level fluctuations and inherited depositional profile depositional geometries and basin analysis permit an understanding of the depositional history five depositional sequences have been recognized 1 the santa fe sequence middle upper cenomanian a ramp to a skeletal rimmed shelf with an escarpment bypass margin the lower boundary is an angular unconformity and the upper one records a sea level drop the platform location of the margin was determined by a listric normal fault 2 an abrupt sea level rise drowned the former platform the congost sequence turonian lower coniacian a distally steepened ramp with erosional distal deep slope the depositional model was largely controlled by pre existing basin morphology cessation of platform development was due to a relative sea level drop 3 the sant corneli sequence upper coniacian lower santonian a mixed terrigenous skeletal homoclinal ramp with upright margin deep slope and dysaerobic basin the slope results from the backstepping by 24 km of the previous margin and gentle basin tilting the platform margin remained more or less at the same position and relief between platform and slope increased indicating continuous relative sea level rise the upper boundary is an angular unconformity at the platform margin produced by an abrupt sea level rise and platform drowning and by listric normal faulting 4 the vallcarga sequence upper santonian campanian a distal steepened skeletal homoclinal ramp erosional escarpment and turbidite basin which corresponds to the mesozoic maximum marine expansion a listric normal fault created two depositional areas a more or less flat footwall block with a north northwest prograding carbonate ramp

stratigraphical evidence for the depression of the northern margin of the menderes tauride block turkey during the late cretaceous abstract upper cretaceous units on the menderes tauride block show a transition from a passive continental margin to a pelagic basin this transition is related to the emplacement of ophiolitic nappes the pelagic sediments were studied in the aydincik and arslankoy mersin areas in the central tauride region and in the munzur mountains in eastern tauride region in the aydincik area upper cretaceous units consist of upper campanian carbonate breccias with rudist fragments upper campanian lower maastrichtian slope to basinal sediments overlie these carbonate breccias disconformably in the arslankoy area the upper campanian maastrichtian yavca formation consists of globotruncana bearing biomicrites siliciclastic turbidites calciturbidites and debris flows and overlies jurassic cretaceous platform carbonates disconformably the uppermost levels of the liassic cenomanian platform carbonates in the munzur mountains are composed of cenomanian hippurites orbitolina bearing reefal limestones and then turonian campanian globotruncanidae bearing biomicrites the stratigraphic sequence in the menderes tauride block shows that rifting to form a northern neotethyan basin took place in the triassic and gave rise to the inner tauride ocean from jurassic to cenomanian times the northern part of the menderes tauride platform formed a passive continental margin in the late cretaceous the inner tauride ocean is believed to have commenced intra oceanic northward subduction inner tauride oceanic crust derived nappes were emplaced southward onto the menderes tauride block flexural foreland basins in which pelagic sediments were deposited were formed in the taurus mountains related to southward thrusting and the emplacement of the ophiolite nappes