prerift and synrift sedimentation during early fault segmentation of a tertiary carbonate platform indonesia abstract eocene carbonate deposits of the barru area sulawesi indonesia provide a rare insight into sedimentation prior to and during propagation of normal faults to the surface three main successions late prerift latest prerift earliest synrift and synrift are characterised by distinctive facies associations and sequence development shallow water foraminiferal shoals and intervening lower energy depositional environments occurred during the late prerift in areas which latter formed footwall highs and hangingwall depocentres respectively during the latest prerift earliest synrift shallow water shelves deepened laterally into slope environments in developing hangingwall depocentres in both these sequences sections in developing hangingwall areas are thickest deepen up section and thin laterally towards growing footwall highs active faulting resulted in rapid drowning of hangingwall depocentres and massive reworking of material derived from collapse of the platform margin and adjacent shallow water emergent footwall highs differential subsidence controlling water depths and accommodation space types of carbonate producers and active faulting were the main factors affecting depositional environments and facies distributions carbonate producers are extremely sensitive indicators of depositional water depth and energy hence rapid lateral and vertical facies variations in the barru area provide quantifiable insight into environmental changes prior to and during active faulting

the apparent paradox of abundant foramol facies in low latitudes their environmental significance and effect on platform development recent studies of low latitude carbonates from se asia and australia have revealed deposits and platform types that do not fit easily into the perceived view of warm water tropical carbonates the sediments are classified as a foramol or foralgal facies and are dominated by non framework building light dependent biota such as perforate larger benthic foraminifera coralline algae and sometimes halimeda although ancient foramol deposits are often interpreted as an indication of non tropical conditions foramol facies have long been known from the tropics yet the environmental conditions in which they form are poorly known the aims of this paper are to evaluate how these deposits are best classified and more importantly whether there are any overriding controls that influence their common development in low latitude areas and if resultant platform development is affected the deposits are all best grouped within the photozoan association james n p 1997 the cool water depositional realm in james n p clarke j a d eds cool water carbonates sepm special publication 56 1 20 an assignment synonymous with warm water conditions the facies were also found to develop in conditions of limited light or oligophoty all the platforms described are characterised by having extensive areas of oligophotic facies generally in water depths extending down from 20 m but sometimes in shallower waters platforms types vary from land attached rimmed shelves homoclinal and distally steepened ramps to isolated banks and platforms but all have extensive moderate to deep photic zone development of oligophotic facies some workers might assign these platforms to the incipiently drowned platform type read j f 1985 carbonate platform facies models american association of petroleum geologists bulletin 69 1 21 however a morphological assignment is preferred here to signify that many of the deposits did not or may not form through drowning limited light in moderate to deeper depths of the photic zone often in regions with a reduced depth euphotic high light zone is seen as key to the extensive development of these deposits and the resultant platforms these conditions are often developed in humid low latitude areas of high terrestrial runoff and therefore regions of reduced water salinity or in areas of nutrient upwelling reduced water clarity due to nutrients plankton blooms suspended particulate matter upwelling and strong currents all promote the development of oligophotic conditions and facies on a regional scale time periods of relative rises in sealevel can also promote oligophotic facies development the findings of this study have broader implications for the development of low latitude platforms beyond australasia and during time periods when non framework building oligophotic biota are dominant sediment contributors the reconstruction of past climatic conditions based on study of foramol grain assemblages requires careful study to distinguish warm water deposits from those formed in cool waters

morphology faunas and genesis of ordovician hardgrounds from southern ontario canada abstract we have used associations of different microfacies to define facies or microfacies associations which form reasonably well defined sequences which we infer from analogies with recent and ancient carbonate environments to have been deposited in a shelf environment characterized by small scale topographic differentiation into shoal slope and basinal environments shoal environments are characterized by typically cross bedded well sorted bioclastic sands with intershoal areas consisting of interbedded bioclastic sands and heavily bioturbated finer grained carbonates slope and basinal environments are typically represented by proximal and distal cycles respectively these we compare with deposits of carbonate ramp bypass channels and with the more thoroughly studied deep water clastic submarine fans many of the strong variations in environmental energy in these proximal and distal cycles can be attributed to migration of channels on the fans and the effect of funnelling of storm surges down the channels although hardground morphology and faunas are mostly related to local effects such as intensity of scouring time of exposure topographic differentiation of the surface and other factors differing hardground types tend to be found in different environments smooth and rolling hardgrounds occur in the deeper distal environments where the beds were subject to only slight scour and often limited exposure before renewed sedimentation hummocky and undercut hardgrounds are characteristic of the middle parts of proximal cycles where they developed marginally to the main bypass channel and in intershoal areas both these areas are sites of intermittent sedimentation and moderate turbulence where cemented beds may be exposed for some time in environments optimal for attached benthos these hardgrounds usually contain the most diverse hardground biotas pebbly and reworked hardgrounds occur in coarse basal units of proximal cycles which are interpreted as the grain flow fillings of the central parts of bypass channels though isolated examples occur in intershoal areas and in the higher parts of proximal channels these hardgrounds contain low diversity faunas reflecting the stresses imposed by intermittent or constant abrasion though some contain more diverse faunal assemblages formed after redeposition

unravelling the depositional origins and diagenetic alteration of carbonate breccias carbonate breccias dissociated from their platform top counterparts are little studied despite their potential to reveal the nature of past shallow water carbonate systems and the sequential alteration of such systems a petrographic and stable isotopic study allowed evaluation of the sedimentological and diagenetic variability of the cenozoic batu gading limestone breccia of borneo sixteen lithofacies representing six facies groups have been identified mainly from the breccia clast on the basis of shared textural and compositional features clasts of the breccia are representative of shallow carbonate platform top and associated flank to basinal deposits dominant inputs are from rocky karstic shorelines or localised seagrass environments coral patch reef and larger foraminiferal rich deposits early pre brecciation alteration including micritisation rare dissolution of bioclasts minor syntaxial overgrowth cementation pervasive neomorphism and calcitisation of bioclasts and matrix was mainly associated with marine fluids in a near surface to shallow burial environment the final stages of pre brecciation diagenesis include mechanical compaction and cementation of open porosity in a shallow to moderate depth burial environment post brecciation diagenesis took place at increasingly moderate to deep burial depths under the influence of dominantly marine burial fluids extensive compaction circum clast dissolution seams and stylolites have resulted in a tightly fitted breccia fabric with some development of fractures and calcite cements a degree of facies specific controls are evident for the pre brecciation diagenesis pervasive mineralogical stabilisation and cementation have however led to a broad similarity of diagenetic features in the breccia clasts thereby effectively preserving depositional features of near original platform top and margin environments there is little intra clast alteration overprint associated with subsequent clast reworking and post brecciation diagenesis the diagenetic and to an extent depositional and clast characteristics of the batu gading deposits are diagnostic of breccia origins the predominance of early and pervasive stabilisation of calcitic components pervasive compaction resulting in a fitted texture and paucity of meteoric dissolution or cementation effects are collectively all indicators of slope deposition and lithification these features are comparable with other regional and global examples of submarine slope breccias and consistent with the prior interpretation that the carbonate platform at batu gading developed in a rotating wedge top basin wannier 2009 the results of this study along with regional analogues suggest the potential for reworked carbonates debris in slope settings to be a viable way of investigating carbonate platform variability and their subsequent alteration in the absence of preserved platform top or margin deposits

the continental margin of the mesozoic tethys in the western alps abstract most of the structural units of the western alps were derived from the european continental margin of the ligurian ocean a segment of the mesozoic tethys ocean their mesozoic palaeotectonic and stratigraphic evolution bears witness of the following main stages 1 deposition of the triassic platform carbonates essentially prerift but nevertheless bearing the imprint of some extensional movements 2 the liassic middle jurassic rifting corresponds to the creation of a horst and graben system with especially tilted blocks and hence a shoal and basin palaeogeography but without a preliminary doming event 3 the late jurassic early cretaceous opening and spreading of the ligurian ocean began with a general collapse of the continental margin thermal subsidence latest middle jurassic and earliest late jurassic in this paper emphasis is given to the refting derived structures more especially to the major tilted crustal blocks a few tens of kilometres wide which can be either reconstructed or directly observed the rifting stage lasted roughly 40 m y with the alternation of extensional tectonic phases and of relatively quiet periods during the extensional phases movements along fault planes and related episodes of tilting were followed by sudden and rapid episodes of subsidence the latter may be interpreted as resulting from the isostatic and thermal readjustment that follows a phase of stretching of the crust and of the lithosphere the tectonic evolution of the margin continued but decreased during the late jurassic early cretaceous oceanspreading stage tectonic activity resumed in the late cretaceous this probably resulting from the beginning of contraction of both the ocean and the continental margin leading progressively to the continental collision in the tertiary

formation processes of framboidal pyrite abstract pyrite framboid formation may be the result of four consecutive processes 1 nucleation and growth of initial iron monosulfide microcrystals 2 reaction of the microcrystals to greigite fe 3 s 4 3 aggregation of uniformly sized greigite microcrystals i e framboid growth and 4 replacement of greigite framboids by pyrite the uniform morphology uniform size range and ordering of the microcrystals in individual framboids as well as the range of observed framboid structures from irregular aggregates to densely packed spherical aggregates and polyframboids are consequences of these processes using dlvo theory derjaguin landau verwey and overbeek we have evaluated the stability of colloidal iron monosulfide suspensions with ionic strengths typical of marine and lacustrine waters in addition to van der waals attractive and double layer repulsive forces a term is included to account for the ferrimagnetic properties of greigite numerical models predict that magnetically saturated greigite particles 0 1 m in diameter will rapidly aggregate in either marine or fresh water the aggregation model is in agreement with the sequence of greigite formation followed by pyrite framboid formation established in a previous experimental study sweeney and kaplan 1973 and is consistent with the occurrence of framboids composed of other magnetic minerals e g greigite magnetite and magnesioferrite based on the temperature dependent magnetic properties of greigite and aging experiments in hydrothermal solutions this mechanism for framboid formation via precursor greigite could operate to temperatures of 200 c consistent with the occasional occurrence of pyrite framboids in the paragenesis of metalliferous ore deposits

controls on marine carbonate cement mineralogy review and reassessment abstract commonly cited models for controls on variations in carbonate mineralogy are only partly successful in accounting for natural mineralogical trends this limited success may result in part from a failure to recognize or address the ramifications of assumptions inherent to such models in general changes from calcite to aragonite or vice versa and variations in mgco3 incorporation in calcite are interpreted as resulting from 1 kinetic rather than thermodynamic effects 2 the effects of fluid chemistry rather than hydrologic biological or substrate effects 3 the effects of single parameters of fluid chemistry rather than the interactive or aggregate effects of several components and or 4 inorganic rather than organic parameters of fluid chemistry recent laboratory data suggest the necessity of a new approach to modeling controls on mineralogy these data indicate that no single fluid parameter is likely to be a sole or dominant control on carbonate mineralogy in natural environments in some cases thermodynamic stability differences may be as important as kinetic factors in determining mineralogy furthermore the effects of substrate hydrologic and biological factors and of organic compounds cannot be ruled out for most natural situations although at present reliable data are lacking to quantify the influence of these factors on mineralogy future models of controls on carbonate mineralogy need to consider the aggregate and interdependent effects of all of these factors

development patterns and controlling factors of tertiary carbonate buildups insights from high resolution 3d seismic and well data in the malampaya gas field offshore palawan philippines abstract the comprehensive subsurface database of the malampaya buildup late eocene to early miocene offshore nw palawan provides a rare insight into the development of south east asian cenozoic carbonate systems and their controlling factors the newly acquired high resolution three dimensional seismic survey combined with facies and well log analysis allowed a better understanding of the internal architecture of a carbonate platform whose development was largely controlled by tectonic deformation the malampaya carbonate system was initiated in the late eocene as an attached shelf influenced by significant clastic input the late eocene early oligocene shelf was subject to syn depositional extensional tectonics eastward tilting and block faulting that favoured the development of small size buildups on structural highs after a stage of eastward reef progradation an aggrading carbonate shelf frequently affected by subaerial exposure developed from the earliest late oligocene to the early miocene during this period recurrent reactivation of highs along the western and northeastern buildup margins determined the asymmetric morphology and internal architecture of the carbonate system the final demise of the carbonate buildup occurred in the late early miocene it resulted from an increase in subsidence rate and or a sharp increase in nutrient input additional parameters like eustacy oceanographic conditions and the type of carbonate producers played a subordinate role in the buildup development and ultimate demise

growth demise and dolomitization of miocene carbonate platforms on the marion plateau offshore ne australia abstract strontium isotope stratigraphy has been used to examine the timing of depositional events and dolomitization in two miocene carbonate platforms cored by ocean drilling program odp leg 194 just seaward of the great barrier reef the results provide firm constraints for correlating surfaces and depositional stages between the two platforms and thereby relating seismic sequences previously defined in the off platform sediments to the lithostratigraphic units described from cores in the seismically transparent platform top sites oyster bearing beds at the base of both platform successions yield early oligocene ages 29 31 ma thus dating initial transgression of the marion plateau s volcanic basement there followed a period of slow accumulation of shallow water grainstones rich in quartz and phosphate grains in late oligocene time 29 23 ma seismic megasequence a the main growth of the carbonate platforms took place in early to late miocene time 23 7 ma comprising five depositional sequences the first four of these seismic megasequence b are common to both platforms and terminated with a possible karst surface at 10 7 ma different sedimentologic expression of this megasequence in the two platforms reflects contrasting progradational versus aggradational geometries in the locations studied the final growth stage seismic megasequence c occurred only in the southern platform and terminated at 6 9 ma both platform demise events 10 7 and 6 9 ma approximately coincide with falls in global sea level combined with longer term trends of decreasing water temperature sr isotope ages of dolostones increase with depositional age and older dolostones in the southern platform have more coarsely crystalline and fabric destructive textures than overlying younger dolostones these relationships are consistent with dolomitization by normal seawater shortly after deposition and overprinting of multiple times of dolomite recrystallization and cementation in the deeper strata

matrix micrite δ13c and δ18o reveals synsedimentary marine lithification in upper jurassic ammonitico rosso limestones betic cordillera se spain abstract matrix micrites are a commonly used carbonate archive for the reconstruction of past environmental parameters but one that is submitted to known limitations main reasons for the often ambiguous value of many micrite based isotope data sets are the unknown origin of the micrite components and their poorly resolved diagenetic history here we present carbon and oxygen isotope data retrieved from oxfordian to tithonian ammonitico rosso nodular micrites sampled from three sections in the betic cordillera southern spain all three sections were correlated and sampled using a rigorous biostratigraphic framework a noteworthy feature is that analyzed matrix micrites are more conservative in terms of their isotopic composition than other carbonate materials commonly considered to resist diagenetic alteration under favourable circumstances remarkably this refers not only to 13 c ratios which reflect the typical late jurassic global trend but also to 18 o ratios that range around 0 3 the 18 o enriched oxygen isotope ratios are considered to represent diagenetic stabilization of carbonate ooze under the influence of marine porewaters within the sediment water interphase i e the immature sedimentary section usually submitted to biogenic activity this interpretation agrees with the very early lithification of micrite nodules with cements precipitated from marine porewaters enriched by the dissolution of aragonite skeletals i e ammonite shells according to the model proposed low sedimentation rates as well as rapid early marine differential cementation under the influence of currents and seawater pumping affected the sediment water interphase of epioceanic swells where deposition resulted in early lithified ammonitico rosso facies the data obtained show that special care must be taken to prevent oversimplified interpretations of carbonate archives particularly in the context of epioceanic settings

sequence stratigraphy in active extensional basins implications for the interpretation of ancient basin fills abstract systematic variations in sequences their component units and their stacking patterns exist within rift basins these variations can be related to displacement gradients associated with the large scale 12 50 km segmentation of normal fault zones which control accommodation sediment supply and basin physiography sediment supply is also strongly influenced by the nature of pre rift drainage networks and variations in bedrock lithology high rates of hangingwall subsidence close to the centre of normal fault segments may cancel out the effects of glacio eustatic sea level fall so that accommodation development is normally characterized by the continual addition of new space the resulting sequences lack type 1 sequence boundaries and lowstand systems tracts and stack into aggradational sequence sets the adjacent footwall is subject to uplift which may lead to subaerial exposure and incision generating a composite type 1 sequence boundary away from the fault zone and near segment boundaries slip rates are much lower and hence relative sea level change is dominated by eustasy here falls in relative sea level are important resulting in type 1 sequences sequence stacking patterns reflect not only eustasy and local fault controlled subsidence but also the interaction of these with adjacent uplifting footwalls and or regional uplift tectonic influence on sequence development will be more pronounced during greenhouse times than icehouse times

architecture and depositional sequences of tertiary fault block carbonate platforms an analysis from outcrop miocene gulf of suez and computer modelling abstract this study combines outcrop with seismic data and tectonostratigraphic modelling to characterise the stratigraphy of tertiary fault block carbonate platforms seismic sections from the middle east and southeast asia indicate that carbonate platforms commonly develop on fault blocks in the late syn rift to post rift stage of basin evolution they are characterised by retrogradational or drowning morphologies with deep water clastics evaporites sealing the platforms a new tectono stratigraphic modelling program simulates the development of carbonate platforms on domino style fault blocks and predicts a distinctive tectonic control on the evolving syn rift stratigraphy detailed field work from a three dimensionally exposed miocene syn rift platform from the gulf of suez gebel abu shaar egypt shows the existence of unconformity bound depositional sequences which are predicted by the program and are interpreted to have formed in response to fault block rotation the sequences are characterised by synchronous hangingwall subsidence and footwall uplift and erosion the seismic images the modelling and the outcrop study provide different levels of information on fault block platforms and their characteristic stratigraphy the scale of the modelling is of particular value as it provides a link between the seismic scale imaging and outcrop data

eustatic control of late quaternary sea level change in the arabian persian gulf accurate sea level reconstruction is critical in understanding the drivers of coastal evolution inliers of shallow marine limestone and aeolianite are exposed as zeugen carbonate capped erosional remnants on the southern coast of the arabian persian gulf these have generally been accepted as evidence of a eustatically driven last interglacial relative sea level highstand preceded by a penultimate glacial age lowstand instead recent optically stimulated luminescence osl dating suggests a last glacial age for these deposits requiring 100 m of uplift since the last glacial maximum in order to keep pace with eustatic sea level rise and implying the need for a wholesale revision of tectonic stratigraphic and sea level histories of the gulf these two hypotheses have radically different implications for regional neotectonics and land sea distribution histories here we test these hypotheses using osl dating of the zeugen formations these new ages are remarkably consistent with earlier interpretations of the formations being last interglacial or older in age showing that tectonic movements are negligible and eustatic sea level variations are responsible for local sea level changes in the gulf the cause of the large age differences between recent studies is unclear although it appears related to large differences in the measured accumulated dose in different osl samples

sedimentation during carbonate ramp to slope evolution in a tectonically active area bowland basin dinantian northern england the bowland basin northern england contains a series of carbonates and terrigenous mudstones deposited during the ivorian to early brigantian two regional depositional environments are indicated by facies and facies associations wackestone packstone and calcarenite facies indicate deposition in a carbonate ramp environment while lime mudstone wackestone calcarenite and limestone breccia conglomerate facies often extensively slumped represent a carbonate slope environment stratigraphic relations suggest that the depositional environment evolved from a ramp into a slope through the dinantian two main sediment sources are indicated by the sequence an extra basinal terrigenous mud source and a supply of carbonate from the margins of the basin deposition from suspension and from sediment gravity flows in situ production and remobilization of sediment during sedimentary sliding were important processes operating within the basin periods of enhanced tectonic activity in the late chadian to early arundian and late asbian to early brigantian are indicated by basin wide horizons of sedimentary slide and mass flow deposits both intervals were marked by a decline in carbonate production resulting from inundation and uplift emergence the first of these intervals separates deposition on a seafloor with gentle topography carbonate ramp from a situation where major lateral thickness and facies variations were present and deposition took place in a carbonate slope environment the second interval marks the end of major carbonate deposition within the bowland basin and the onset of regional terrigenous sedimentation

equatorial carbonates an earth systems approach the hypothesis here is that an earth systems processes to products approach can be used to better develop predictive models for the recognition and assessment of under evaluated equatorial carbonate systems warm temperatures together with common clastic fresh water and nutrient influx as well as basinal settings in the equatorial tropics all have a major impact on carbonate deposition and diagenesis specific features of equatorial carbonate systems resulting from the combination of processes acting in the region include common occurrence of photoautotrophs and heterotrophs aragonitic and or calcitic dominant mineralogies lack of coated grains or aggregates common associations with clastics lack of associations with evaporites and diversity of platform types including oligophotic ones additional diagenetic characteristics include common micritization and bioerosion paucity of marine cements extensive vadose dissolution and concomitant phreatic cementation there is also significant replacement of aragonite by calcite in regions of meteoric groundwater flow common burial compaction and leaching as well as localized massive dolomitization via sea water or continental derived groundwater flow although equatorial carbonates fall into the warm water photozoan association many of the features described above are at odds with models derived from their warm water arid zone counterparts instead a range of the equatorial carbonate features show some similarities with those formed in cool waters and there have been difficulties separating carbonates from these two very different climatic regimes recommendations for the recognition of phanerozoic regional equatorial carbonate development are i a diversity of calcitic and or aragonitic photoautotrophs plus ii common elements of the heterozoan association plus iii independent for example isotopic evidence for warm temperatures 22 c additional indicators towards a humid equatorial setting are iv situation in appropriate palaeolatitudes v lack of association with sedimentary evaporites coated grain or aggregates and vi geochemical evidence for reduced marine salinity and or nutrient upwelling the aim is that this work will lead to greater awareness and understanding of equatorial carbonate systems and contribute to the development of globally predictive models to better understand past and likely future environmental change

mesoscopic structures produced by plio pleistocene wrench faulting in south sulawesi indonesia abstract the bantimala complex and overlying cretaceous sediments of south sulawesi indonesia were intensely faulted in the plio pleistocene as a result of the northward movement of the banada sea microplate with respect to western indonesia the area is dominated by nnw striking sinistral wrench faults the structures in these faults formed at less than 250 c zones of intense rotation and faulting 200 m wide parallel the major faults they consist of lenses of a wide range of sedimentary and metamorphic rocks separated by narrow zones of foliated cataclasite within the lenses folding is non cylindrical and there is a weak stretching lineation parallel to the shear direction extension fractures and veins occur at 70 to the stretching lineation sinistral and dextral faults within the lenses are symmetrical to the major faults the fabric within these lenses suggests moderate horizontal extension rather than strong simple shear within the cataclasite the foliation is composed of anastomosing microfaults the sense of shear is demonstrated by offset on these microfaults and on smaller fractures within the microlithons elongate clasts are horizontally aligned within the cleavage and have symmetrical drag patterns many of the equidimensional clasts have asymmetrical drag patterns consistent with sinistral shear

synrift continental to marine depositional sequences tertiary gulf of aden yemen abstract tertiary synrift deposits along the northern margin of the gulf of aden republic of yemen provide new information on the controls on deposition and stratigraphic relationships during the transition from continental to marine rift sedimentation intracontinental rifting in the region commenced in the oligocene developing into a marine extensional margin in the miocene the outcropping part of a small subbasin at wadi hiru west of mukalla contains carbonate platform alluvial fan fan delta and raised beach deposits that record the development of the rift margin the spatial relationships between carbonate and clastic units their location adjacent to rift border faults and timing of sea level changes indicate that tectonics was the overriding control on relative sea level change accommodation space created by fault movement and the morphology of older sediment bodies dictated the three dimensional architecture of carbonate platforms and clastic fans fault movements are documented by changes in clast provenance in fanglomerates rift parallel and rift perpendicular faults formed a trap door configuration that controlled long lived pathways of terrigenous clastic supply throughout rifting five local depositional sequences bounded by erosion surfaces are recognized sequences have a distinct tectonic signature in the form of sequence boundaries overlain by thick fanglomerates followed by transgressive and highstand carbonates two of these sequences were dated using 87sr 86sr isotope dating the relative sea level curve derived from thi study bears little relationship to published eustatic curves

global and regional influences on equatorial shallow marine carbonates during the cenozoic abstract the se asian carbonate record allows insight into the poorly known response of equatorial marine systems to regional and global change during the cenozoic there is a marked change from larger benthic foraminifera to corals as dominant shallow marine carbonate producers in se asia around the oligo miocene boundary the early miocene acme of coral development in se asia lags oligocene coral development in the caribbean and mediterranean despite local tectonics providing apparently suitable habitable areas regional and global controls including changing co2 oceanography nutrient input and precipitation patterns are inferred to be the main cause of this lag in equatorial reefs it is inferred that moderate although falling level of co2 ca2 and ca mg when combined with the reduced salinities in humid equatorial waters all contributed to reduced aragonite saturation hindering reefal development compared with warm more arid regions during the oligocene by the early miocene atmospheric co2 levels had fallen to pre industrial levels although this was a relative arid phase globally in se asia palynological evidence indicates that the early miocene experienced everwet but more stable and less seasonal conditions than periods before or after tectonic convergence truncated deep throughflow of cool nutrient rich currents from the pacific to indian ocean around the beginning of the miocene thereby directly and perhaps indirectly though less seasonal conditions reducing nutrients it is inferred that aragonitic reefs were promoted where previously the waters had been more acidic more mesotrophic more turbid and less aragonite saturated extensive reefal development resulted in an order of magnitude expansion of shallow carbonate areas through buildup and pinnacle reef formation in the early miocene tectonics via increased habitat partitioning and reducing distances to other coral rich regions may also have contributed to enhanced reefal development declining reefal importance at the end of the early miocene resulted from uplift of land areas enhanced oceanic ventilation through thermohaline circulation and narrowing of oceanic gateways as well as increased seasonal runoff at least in se asia through initiation intensification of the monsoons implications of this study are that with current anthropogenically induced environmental changes it will be the diverse reefs of se asia that are likely to be amongst the first and hardest hit as oceanic aragonite saturation decreases and terrestrial nutrient runoff increases

a marine late jurassic syn rift succession in the lusitanian basin western portugal tectonic significance of stratigraphic signature abstract in the lusitanian basin which is located along the western iberian margin rapid subsidence in the oxfordian tithonian resulted from extension related to the opening of the north atlantic in the santa cruz area located in the western part of the lusitanian basin the kimmeridgian syn rift marine abadia formation and the overlying alluvial kimmeridgian tithonian praia da amoreira member of the lourinha formation were deposited in the middle part of the hangingwall dip slope of a larger half graben that constitutes the turcifal subbasin the marine part of the succession consists of base of slope and lower slope mudstones and sandy turbidites middle slope mudstones upper slope to shelfal shoreline mudstones and sandstones and fan deltaic deposits two intermediate scale fining to coarsening fucu units are present in the marine strata the lower fucu unit represents a normal base of slope lower slope to upper slope shoaling upward succession the unit reflects the progradation of a hangingwall shelfal ramp and infilling of an inherited rift bathymetry during a period of relative tectonic quiescence the upper fucu unit represents an intermediate scale deepening shoaling upward or backstepping forestepping sequence which is related to a single rift event the backstepping segment was deposited during a period of increasing basinal subsidence and basin floor tilt rates the early syn rotational stage it consists of submarine channel fill incised into slumped upper slope sediments and adjacent overbank deposits the backstepping segment terminates with a clay prone marine interval with abundant soft sediment deformation features which represent a period of maximum sea level stand during the rotational climax the overlying forestepping segment consists of a shoaling upward slope to fan deltaic succession which terminates with alluvial deposits it represents an interval with decreasing basinal subsidence and basin floor tilt rates and renewed overbalance of sediment supply which led to a regression during the late syn rotational stage in medial reaches of the hangingwall dip slope periods of increasing to decreasing rift activity are recorded by a backstepping forestepping package or a threefold sandstone mudstone sandstone lithosome motif the formation of smaller scale units superimposed on the intermediate scale fucu syn rotational motif were controlled predominantly by minor fault controlled subsidence events or higher frequency faulting events

cenozoic palaeogeographic evolution of sulawesi and borneo abstract sulawesi and borneo are located in the middle of the indonesian archipelago an area which has been extremely tectonically active throughout the cenozoic this paper compiles current knowledge on the geology and palaeogeography of this complex region and includes the first attempt to synthesise palaeogeographic data onto plate tectonic reconstructions construction of palaeogeographic maps helped to identify some of the strengths and weaknesses of current plate tectonic models for the region thereby highlighting areas where further geological research is required palaeogeographic maps presented using plate tectonic reconstructions as a base illustrate the evolution of borneo and sulawesi and highlight important changes in the environment during the cenozoic the tertiary geological history of eastern borneo and sulawesi is inextricably linked to the progressive accretion of continental and oceanic material from the east onto the eastern margin of sundaland and to the resultant development of volcanic arcs large tracts of western sulawesi eastern borneo the east java sea and the makassar straits formed an extensive basinal area throughout much of the tertiary implications for plate tectonics exploration for natural resources and biogeography are discussed from the palaeogeographic reconstructions of sulawesi and borneo

carbonate cement fabrics displayed a traverse across the margin of the bahamas platform near lee stocking island in the exuma cays abstract consolidated to friable carbonate rocks found in the lee stocking island area in the exuma cays include 1 reef rock 2 channel stromatolites 3 shallow water hardgrounds 4 beachrock rimming the islands and 5 pleistocene bedrock the most common cement fabrics observed are aragonitic fibers which include acicular fan druse and square tipped coarse fibers cementing beachrock and stromatolites and an isopachous needle fiber rim cementing hardgrounds and stromatolites less common are high mg calcite bladed textures of the reef rock and stromatolites two types of blades are present the more common stubby variety of either high mg or low mg calcite and an elongated variety of high mg calcite which was found in only three beachrock samples aragonitic micrite envelopes usually surround grains in beachrock hardgrounds and stromatolites but only in association with fibrous cement an aragonitic crust cements the surfaces of lime mud beds of the tidal channel while a high mg calcite cryptocrystalline cement occurs in all the rock types calcified algal filaments of high mg calcite from the abundant green and blue green algae in the area are a primary cement in stromatolites and a secondary cement in hardgrounds and beachrock a low mg calcite equant spar cements the pleistocene samples and is associated with meteoric diagenesis and cementation of the pleistocene surface cement precipitation coincides with the path of the cool oceanic water from exuma sound as it warms and loses co 2 and moves up onto the bank near lee stocking with the incoming tide cryptocrystalline cement is the first and commonest cement forming to the seaward while platformward fibrous cements become predominant as suggested by their crystal size and location on the shelf margin we think that the reef rock cryptocrystalline material are the fastest forming of the cements where the incoming oceanic water is more saturated with respect to calcium carbonate and undergoes the most significant warming the rate of the warming and degassing process is thought to increase in the tidal channel though the cementation rate is thought to fall slightly in response to a reduced availability of calcium carbonate on the platform interior further warming and degassing are believed to cause cement precipitation and the development of hardgrounds but these may form at a slower rate than that of the margin though this rate is still quite high cementation gradients occur from the tidal channel to the intertidal zones of 1 west norman s pond cay where cement fabric suggests a reduced calcium carbonate availability and 2 west lee stocking island where a change in mineralogy suggests a change in water chemistry thus a sequence of cement fabrics and mineralogies can be traced micritic textures occur in a more seaward position fine fibrous aragonite fibers in a more lagoonal and levee position and coarser aragonite fibers and mg calcite cements in the intertidal and supratidal position this sequence is thought to track the evolution of the water mass

linked sequence stratigraphic and structural evolution of propagating normal faults two distinct phases in the structural evolution of normal faults can be identified in the miocene gulf of suez rift 1 an initial growth fold stage when the fault is a buried structure and 2 a subsequent surface faulting stage during the growth fold stage strata thin and become truncated toward the fault zone and are rotated and diverge away from the buried fault into growth synclines in contrast once the fault breaks surface strata form a divergent wedge which is rotated and thickens into the fault the two tectono stratigraphic styles also occur contemporaneously along the length of a single fault segment growth folding characterizes deformation around the ends of fault segments where the fault is blind whereas the center of fault segments are characterized by surface faulting these observations suggest that marked along strike variation in stratal surfaces and facies stacking patterns will occur in depositional sequences in areas of normal faulting

carbonate platform growth influenced by contemporaneous basaltic intrusion albian of larrano spain carbonate platform growth in active tectonic settings may be strongly influenced by the structural evolution of the basin including volcanic activity in this paper the sedimentary tectonic evolution of the duranguesado carbonate platform larrano in northern spain is described and an evolutionary depositional model is presented the albian duranguesado carbonate platform deposits are dominated by rudist and coral limestones with small intervening argillaceous limestone filled troughs 10 30 m deep the platform succession is divided into two parts the lower platform deposits were intruded by volcanics and tilted before the deposition of the upper platform succession a volcanic vent plug filling an upward flaring pipe occurs in the lower carbonate platform succession the timing of intrusion is well constrained to the early albian tectonic extension and active deep seated strike slip faults induced magma ascent at a fault intersection sedimentological analysis of these areas indicates that before volcanic intrusion they acted as weakened zones of extension and were slightly more subsident basinal areas these sites contain anomalous accumulations of siliceous sponge spicule deposits linked to the release of hydrothermal fluids on the sea floor after the phase of intrusion tilting and erosion of the platform and its associated volcanic products occurred as the intrusion cooled the platform downwarped leading to the formation of an overlying perched capping basin bordered by carbonate platforms over the volcanic plug carbonate mounds grew on local palaeohighs the presence of strike slip and magma emplacement in the duranguesado platform is related to movements between the iberian and european lithospheric plates which were accommodated by rotation and lateral movement of the crust along wrench faults

distribution and growth styles of isolated carbonate platforms as a function of fault propagation abstract fault control on the position and distribution of isolated carbonate platforms is investigated in northwest australia using high quality 3d seismic and borehole data from the bonaparte basin specifically we address the relationship between carbonate productivity and fault growth so as to understand what are the primary controls on the growth of isolated carbonate platforms throw depth t z and throw distance t d profiles for normal faults suggest they formed fault segments that were linked at different times in the study area this caused differential vertical movements some of the normal faults propagated to the surface while others have upper tips that are 19 530 ms two way time below the sea floor with the largest throw values comprising faults underneath isolated carbonate platforms as a result four distinct zones correlate with variable geometries and sizes of carbonate platforms which are a function of the topographic relief generated by underlying propagating faults some relay ramps form the preferred location for the initiation and development of carbonate platforms together with adjacent structural highs due to the complex effect of fault propagation to the palaeo seafloor and soft linkage through relay ramps three distinct icp types are proposed 1 in the first type fault throw is larger than carbonate productivity 2 the second type considers fault throw to be equal or less than carbonate productivity and 3 in the third type fault throw post dates the growth of the carbonate platform s the analysis of fault propagation vs carbonate platform growth shown here is important as the three icp types proposed potentially correlate with variable fracture densities and distributions within the carbonate platforms based on our results types 2 and 3 above enhance fracture and fault dominated porosity and permeability to a greater degree making them favourable targets for hydrocarbon exploration

growth of syndepositional faults in carbonate strata upper permian capitan platform new mexico usa abstract the upper permian capitan platform new mexico is cut by syndepositional faults and fractures these are parallel to platform margin and cluster within strata that steepen and thicken abruptly into the basin faults are steep dip slip have measurable displacements of up to 24 m are typically associated with growth strata and mostly tip out blindly within the platform basinward throwing faults are typically reverse and are steeper than shelfward throwing faults which have normal geometry the sense of displacement across some initially basinward throwing faults changed as they developed these patterns indicate that faults were rotated as they grew synkinematic rotation of faults is interpreted to have occurred due to syndepositional compaction driven down to basin tilting of the capitan platform faults grew through interaction with inherited fractures and by segment linkage vertically separated fault segments had a tendency to grow downward to link with underlying segments thus promoting accumulation of displacement across faults without vertical propagation of fault tips four fault types are distinguished on the basis of structures associated with their upper terminations i faults breaking free surface ii faults tipping out within non folded growth strata iii faults tipping out below growth monoclines and iv buried faults with no expression on free surface fault tips evolved from one type into another in response to variations in the rates of fault growth and deposition fault tip structures also vary laterally over distance of 750 1400 m inferably as a result of variable distances from fault centres

earthquake premonitory processes evolution of stresses and electric current generation the principles and assumptions of the earthquake premonitory and rebound theory are reviewed the theory based on a continuum model of fracturing processes the stress evolution equations describe the dynamic processes governing a continuous distribution of dislocations special attention is paid to the problem of electric current generation in a seismic source zone electric current is considered as reflecting the rate of polarization which is influenced by motion of the charge bearing dislocations the relationship between the current density and stress accumulation rate is derived

late quaternary sea level changes of the persian gulf abstract late quaternary reflooding of the persian gulf climaxed with the mid holocene highstand previously variously dated between 6 and 3 4 ka examination of the stratigraphic and paleoenvironmental context of a mid holocene whale beaching allows us to accurately constrain the timing of the transgressive highstand and regressive phases of the mid to late holocene sea level highstand in the persian gulf mid holocene transgression of the gulf surpassed today s sea level by 7100 6890 cal yr bp attaining a highstand of 1 m above current sea level shortly after 5290 4570 cal yr bp before falling back to current levels by 1440 1170 cal yr bp the cetacean beached into an intertidal hardground pond during the transgressive phase 5300 4960 cal yr bp with continued transgression interring the skeleton in shallow subtidal sediments subsequent relative sea level fall produced a forced regression with consequent progradation of the coastal system these new ages refine previously reported timings for the mid to late holocene sea level highstand published for other regions by so doing they allow us to constrain the timing of this correlatable global eustatic event more accurately

tectonic and volcanic influences on the development and diachronous termination of a tertiary tropical carbonate platform abstract the demise of carbonate platforms has variously been related to factors such as tectonics influx of clastic material and environmental stress sometimes in combination with eustatic fluctuations however the precise controls on foundering of platforms are often poorly understood in sulawesi indonesia the extensive syntectonic tonasa carbonate platform of eocene to middle miocene age developed to the west of a volcanic arc and is overlain by middle to upper miocene volcanics these carbonates provide a unique opportunity to study the effects of tectonic and volcanic activity on the development and subsequent demise of a carbonate platform detailed field and laboratory analysis of the tonasa formation reveal that the shallow water deposits of the tonasa carbonate platform had their greatest areal extent in the late eocene although a variety of factors influenced platform development tectonics and volcanism were particularly important influencing platform evolution and diachronous termination in four main ways 1 during the paleogene calc alkaline volcanic activity limited the eastward lateral extent of the platform but had little effect on carbonate sedimentation in western south sulawesi 2 faulting in the latest late eocene resulted in segmentation of the platform and caused localized drowning in hangingwall areas and subaerial exposure on adjacent footwall highs 3 a further phase of faulting in the early to middle miocene just prior to and during the early stages of renewed volcanism in western south sulawesi resulted in reactivation of faults localized tilting of fault blocks formation of new graben and subaerial exposure of faulted footwall highs 4 in the middle miocene the influx of volcaniclastics close to volcanic centers rapidly buried most of the few remaining areas of shallow water carbonates and inhibited renewed carbonate production however carbonate production contemporaneous with volcanism occurred in more distal or localized areas shielded from volcaniclastic input

discontinuities in carbonate successions identification interpretation and classification of some italian examples abstract the growing use of unconformities as bounding surfaces for new types of stratigraphic units seems not to be matched by a corresponding effort on process oriented researches on unconformities themselves this paper aims at giving a contribution to classification and understanding of discontinuities in carbonate successions from the outcrop perspective based on some italian examples a number of integrated criteria geometry sedimentology diagenesis biostratigraphy is proposed to recognise stratigraphic breaks old terms are discussed and sometimes redefined while some new terms are introduced the term discontinuity surface ds is proposed as a general one to indicate any stratigraphic interface where an interruption of sedimentation can be proved a ds can be characterized as a firm ground or a rock ground depending on its coherence at the moment of the renewal of sedimentation polygenic and simple omission surfaces are separated within firm grounds if a recognizable gap is either present or not a third kind of firm ground revealed only by biostratigraphy has been called hidden discontinuity surface two categories of rock grounds are also distinguished hard grounds and inherited rock grounds if respectively generation of the ds and or deposition of the overlying sediments took place in the same environment of the underlying sediments or not a genetic interpretation for each type of discontinuity is proposed the largest variety of ds s occurs in pelagic sediments some discontinuities hard grounds and simple omission surfaces are attributed to increased bottom current activity during sea level falls others polygenic omission surfaces and hidden ds s are interpreted as submarine slide scars either with or without the overprint due to exposure on the seafloor the ds s separating different facies e g platform and pelagic ones are interpreted to be due to tectonics the relevance of the recognized ds s to sequence stratigraphy is briefly discussed

analysis of the electromagnetic field recorded in the friuli seismic zone northeast italy abstract some examples of unusual telluric activity were found during the italian polish magnetotelluric measurement campaign in the friuli seismic zone 1987 1988 the standard procedure for the elimination of the induction component from the telluric recordings and the calculation of the transfer functions were first applied however due to a high noise level in the observed telluric fields in the northern alpine region it appeared indispensable to develop new methods for the detection of any tectonically related component of the telluric field the common function defined as the average curve derived from two telluric stations and multiplied by the correlation coefficients moving window procedure allowed an increase in the telluric activity time changes of variances to be traced before and during seismic events in september 1987 and february 1988 another approach was based on the time frequency isoline calculations of the poynting vector of electromagnetic field positive isoline values opposite to the usual downward direction of this flux were discovered and correlated with a course of seismic activity some good results were found for the time intervals studied some considerations on a mechanism for the generation of an electric current in a zone of seismic preparation are discussed an accumulation of stress leads to an oriented motion of the charged charge bearing dislocations the mechanism consists of the formation of a kind of polarization current induced by the motion of these dislocations

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

tertiary syntectonic carbonate platform development in indonesia cenozoic tropical carbonate sedimentation was strongly influenced by local and regional tectonics in se asia this paper outlines the evolution of the syntectonic eocene to middle miocene tonasa formation of south sulawesi evaluating controls on sedimentation facies distribution and sequence development development of a facies model for this cenozoic tropical carbonate platform provides a meaningful analogue for similar less well studied se asian carbonates which commonly comprise targets for hydrocarbon exploration this study also has considerable implications for the study of syntectonic carbonates controls on carbonate sedimentation carbonate platform development in backarc areas and se asian tectonics detailed facies mapping logging petrographic and biostratigraphic analyses indicate that the tonasa formation was deposited initially as part of a transgressive sequence in a backarc setting by late eocene times shallow water carbonates were being deposited over much of south sulawesi forming a widespread 100 km long platform area shallow water sedimentation continued unabated in some areas of the platform until the middle miocene elsewhere active normal faulting resulted in fault block platforms with local subaerial exposure of footwall blocks and the formation of basinal graben in adjacent hangingwall areas platform top facies were aggradational and dominated by larger benthic foraminifera low angle slopes particularly hangingwall dip slopes were characterized by the development of ramps faults controlled in part by pre existing structures were periodically active and formed steep escarpment margins variable regional subsidence strongly influenced the development of the tonasa carbonate platform whereas platform wide effects caused by regional eustacy have not been identified computer modelling of the tonasa platform confirms that the accommodation space and sedimentary geometries observed can be produced by block faulting and regional subsidence alone modelling also reveals that regional subsidence and extension oblique to the main stretching direction were low on the margins of the backarc basin shallow water accumulation rates for this foraminifera dominated tropical carbonate platform were an order of magnitude lower than those for modern warm water platforms dominated by corals or ooids

cenozoic carbonates in southeast asia implications for equatorial carbonate development cenozoic equatorial carbonate production was at its most extensive and diverse in the seas of southeast asia yet the carbonates of this region remain poorly documented this paper presents the first published review of carbonate deposition during the cenozoic collating sedimentological data for carbonate successions throughout the region current models of warm water carbonate platform evolution sedimentation and facies distribution inspired by studies of the classic sub tropical areas provide inadequate analogues for the evaluation of modern or cenozoic equatorial carbonates in southeast asia the equatorial carbonates differ in being dominated by bioclasts coated grains and associations with evaporites or dolomites are rare the carbonate systems occur in a range of depositional settings which were often affected by coeval tectonism siliciclastic input or volcanism an understanding of the carbonate depositional environments spatial facies distributions and controls on deposition and diagenesis is essential in order to characterize equatorial carbonate development and to evaluate their considerable economic potential

interpretation of long period magnetotelluric soundings in friuli north east italy and the electrical characteristic of the lithosphere summary one year long records of two magnetotelluric mt stations located in the seismic friuli region north east italy were analysed in the 60 28 800s period range the aim was the investigation of the deep lithospheric electric structure the computation of the impedances was made by an iterative signal to noise enhancing method impedances were analysed with complex singular value decomposition svd some tests were made trying to consider the distortion due to the shallow in homogeneities 1 d inversion of the apparent resistivity curves was carried out the models obtained indicate that the lithosphere thickens from 90 to 120 km westward in agreement with surface wave inversion the westernmost sounding located in an area of thickened crust indicates the presence of a 10 km thick intracrustal conductor which may be associated with incipient melting of lower crustal rocks

dolomite formation within microbial mats in the coastal sabkha of abu dhabi united arab emirates microbial mediation is the only demonstrated mechanism to precipitate dolomite under earth surface conditions a link between microbial activity and dolomite formation in the sabkha of abu dhabi has until now not been evaluated even though this environment is cited frequently as the type analogue for many ancient evaporitic sequences such an evaluation is the purpose of this study which is based on a geochemical and petrographic investigation of three sites located on the coastal sabkha of abu dhabi along a transect from the intertidal to the supratidal zone this investigation revealed a close association between microbial mats and dolomite suggesting that microbes are involved in the mineralization process observations using scanning electron microscopy equipped with a cryotransfer system indicate that authigenic dolomite precipitates within the exopolymeric substances constituting the microbial mats in current models microbial dolomite precipitation is linked to an active microbial activity that sustains high ph and alkalinity and decreased sulphate concentrations in pore waters such models can be applied to the sabkha environment to explain dolomite formation within microbial mats present at the surface of the intertidal zone by contrast these models cannot be applied to the supratidal zone where abundant dolomite is present within buried mats that no longer show signs of intensive microbial activity as no abiotic mechanism is known to form dolomite at earth surface conditions two different hypotheses can reconcile this result in a first scenario all of the dolomite present in the supratidal zone formed in the past when the mats were active at the surface in a second scenario dolomite formation continues within the buried and inactive mats in order to explain dolomite formation in the absence of active microbial metabolisms a revised microbial model is proposed in which the mineral template properties of exopolymeric substances play a crucial role

magneto telluric recordings from the friuli seismic zone northeast italy abstract magneto telluric measurements were undertaken in the friuli seismic area of north east italy the purpose was to find possible correlations between magneto telluric signals and seismic activity two stations were operational between july 1987 and june 1988 apparent resistivity curves were found for september 1987 and january 1988 data and a magneto telluric inversion problem was solved artificial noise and natural disturbances of the electromagnetic field especially those related to tectonic processes are discussed

late holocene to recent aragonite cemented transgressive lag deposits in the abu dhabi lagoon and intertidal sabkha modern cemented intervals beachrock firmgrounds to hardgrounds and concretionary layers form in the lagoon and intertidal sabkha of abu dhabi seafloor lithification actively occurs in open current swept channels in lowlying areas between ooid shoals in the intertidal zone of the middle lagoon some centimetres beneath the inner lagoonal seafloor i e within the sediment column and at the sediment surface the intertidal sabkha the concept of concretionary sub hardgrounds i e laminar cementation of sediments formed within the sediment column beneath the shallow redox boundary is introduced and discussed based on calibrated radiocarbon ages seafloor lithification commenced during the middle to late holocene ca 9000 cal yr bp and proceeds to the present day lithification occurs in the context of the actualistic relative sea level rise shifting the coastline landward across the extremely low angle carbonate ramp the cemented intervals are interpreted as parasequence boundaries in the sense of marine flooding surfaces but in most cases the sedimentary cover overlying the transgressive surface has not yet been deposited aragonite micritic calcite and less commonly gypsum cements lithify the firmground hardground intervals cements are described and placed into context with their depositional and marine diagenetic environments and characterized by means of scanning electron microscope petrography cathodoluminescence microscopy and raman spectroscopy the morphology of aragonitic cements changes from needleshaped forms in lithified decapod burrows of the outer lagoon ooidal shoals to complex columnar lath and platy crystals in the inner lagoon precipitation experiments provide first tentative evidence for the parameters that induce changes in aragonite cement morphology data shown here shed light on ancient formerly aragonite cemented seafloors now altered to diagenetic calcites but also document the complexity of highly dynamic near coastal depositional environments

diagenesis and fracturing of a large scale syntectonic carbonate platform abstract the influence of coeval tectonics on carbonate platform development is widely documented yet the diagenesis of such syntectonic platforms is barely evaluated an outcrop petrographic and geochemical study details here for the first time the diagenesis of the tonasa limestone formation developed in an extensional regime in central indonesia this equatorial carbonate system was affected by block faulting tilt block rotation differential uplift and subsidence throughout its eocene to early miocene history wilson 1999 wilson et al 2000 the tonasa carbonate platform is dominated by alteration in shallow to deeper burial depths by fluids with predominantly marine precursor origins mechanical and chemical compaction features are common as are a range of mainly burial related granular mosaic blocky and equant calcite cements earlier marine cements and meteoric influences are rare being highly localised to block faulted highs and or bathymetrically upstanding platform margin areas early marine micritisation of allochems was common on the platform top tectonic uplift together with a major oceanic throughflow current are thought to be key influences on localised karstification meteoric diagenesis and marine cementation the distribution and orientation of faults fractures and calcite veins together with evidence for their relative timing are the strongest manifestation of tectonism coeval with diagenesis there is concordance in the orientation and timing of structures affecting the tonasa platform with those basin wide with the potential for reactivation of pre existing basement fabrics tectonic subsidence including fault associated differential subsidence controlled the degree of burial diagenesis impacting different areas of the platform a predominance of burial diagenetic features and dearth of earlier marine or meteoric cementation is seen in other tertiary equatorial platforms and is partly attributed to 1 predominance of non framework building larger benthic foraminifera and or algae that are prone to remobilisation have low production rates and limited potential to build to sea level and 2 high runoff due to the equatorial humid climate contributing to lowered marine salinities in se asia underlying tectonic reasons for the preponderance of a regional diagenetic signature over a syntectonic one fracturing excepted are 1 development on the flanks of a backarc basin not on typical continental crust 2 key platform influencing structures are oblique to the main extensional direction in the basin and 3 development in an overall subsiding tectonic regime post dating basin initiation the aim here is that this study will contribute to understanding diagenetic alteration of syntectonic carbonate platforms and those from equatorial regions

differential early diagenetic low mg calcite cementation and rhythmic hardground development in campanian maastrichtian chalk abstract the campanian maastrichtian limestones in the south of the netherlands are well sorted fine grained mudstones and silt to fine sand sized bioclastic grainstones these limestones show a distinct lithological cyclicity manifested by fining upward grain size cycles with calcite cemented layers or hardgrounds capping each cycle in the lower part of the succession the cyclicity is further enhanced by nodular chert layers these fining upward cycles are caused by fair weather or storm wave related energy fluctuations and consequently changing rates of deposition differences in composition and texture and differences in the degree of early diagenesis cemented layers and hardgrounds are the result of differential early marine calcite cementation in these limestones early calcite cementation cannot be explained by the supply of cementing materials from saturated seawater an alternative model for early marine calcite cementation is proposed in which early calcite cementation occurred within the sediment at some distance below the seafloor as a result of organic matter degradation and internal redistribution of bioclastic carbonate bacterial organic matter degradation caused dissolution of relatively unstable high mg calcite and or aragonite in the oxic zone followed by precipitation of calcite cement as a consequence of bacterial iron reduction duringperiods with a lower sedimentation rate any significant early cementation and replacement of high mg calcite occurred when younger oxic burrows dissected older burrowed sediment with a more advanced stage of organic matter degradation in particular iron reduction cementation also occurred when redox boundaries repeatedly moved through the same layers during periods with low nett sedimentation and increased storm activity and erosion the differences in the degree of early diagenetic calcite cementation were further enhanced during paleocene karstification and development of secondary porosity by dissolution of remaining unstable carbonate grains and by associated meteoric water calcite cementation

early depositional history of a rift basin miocene in western sinai abstract the cenozoic stratigraphic record in the gulf of suez provides a model of six events for the early sedimentologic history of a rifted basin classic exposures on the east coast of the suez in the western sinai yield a composite section of the miocene succession 1 1 oligocene early miocene nukul formation terrigenous clastics in fluvial fandelta and littoral environments filled local valleys 2 2 during early miocene transgression lower rudies member nearshore and shelf sediments accumulated at a rate no less than 4 cm 1000 yrs rates of accumulation increased dramatically at the beginning of the middle miocene 3 3 during the early part of the middle miocene basinal muds and evaporites upper rudeis member kareem formation and part of belayim formation accumulated at a rate of 106 146 cm 1000 yrs 4 4 rates slowed during short term shoaling periods when shelf carbonates hammam faraun member were deposited 5 5 a fifth event is represented by more than 2 km of late miocene evaporites zeit south gharib formations which accumulated at a minimum rate of 32 cm 1000 yrs 6 6 the post evaporite event of alluvial and shallow deep marine sedimentation began in the pliocene and is continuing today local carbonate buildups developed upon fault blocks during the second and fourth stages evaporite deposition can be a very rapid process in the filling of rifted basins

tectonic control on carbonate platform facies distribution and sequence development miocene gulf of suez abstract mid miocene deposition in the southwestern gulf of suez was governed by an extensional fault block topography shallow marine carbonates and clastics were deposited around the exposed block crests and in marginal half grabens of the rift while central troughs were filled by slope aprons and turbiditic and pelagic mudstones fan deltas developed at points along the fault block escarpments syn rift platform carbonates from one block crest esh el mellaha are described here the platform evolved in three stages generating three sedimentary sequences sequences 1 and 2 were separated by boundary fault reactivation sequences 2 and 3 by sea level drawdown exposure and karstification the sediments comprise six lithofacies associations la 1 6 reef la 1 fore reef la 2 and back reef embayment la 3 sediments form a small reef rimmed platform in sequence 1 at the southern end of the block fringing reefs and reef lagoon systems also developed along the footwall escarpment and on fan deltas which bridged the block bounding fault fringing reefs in sequence 2 generated a carbonate talus veneer la 4 along the whole 80 km length of the esh el mellaha fault scarp carbonate slope and reefal sediments preserved on the footwall exhibit abundant evidence of syndepositional fault movements with truncation of escarpment fringing sequences and repeated generation of reefal wedges minor drowning at the sequence 1 2 boundary caused deepening of lagoons progradation of leeward reefal margins with lagoonal patch reef development and back stepping and vertical accretion of the reefal rim platform development was followed by algal laminated dolomitic sediments la 5 in the area of the old platform interior sequence 3 much of the esh el mellaha ridge remained exposed during platform growth and shed coarse alluvial clastic sediments la 6 into the peripheral marine environments the relationships demonstrated between miocene sedimentation and structural setting have parallels in the modern environments of the zeit bay area