geology of panamint valley saline valley pull apart system california palinspastic evidence for low angle geometry of a neogene range bounding fault geological studies support the interpretation that northern panamint valley and saline valley southeast california form paired pull apart basins on opposite sides of the right slip hunter mountain fault zone eight to ten km of late cenozoic net slip can be established on the hunter mountain fault zone palinspastic reconstruction of northern panamint valley indicates that the valley was formed by movement on a shallow crustal low angle normal fault of 0 15 degree west dip during the last 3 0 ma this interpretation appears to contradict the notions that little extension is accomodated in the uppermost crust by low angle faulting and that the most recent extension in the basin and range province is accomodated exclusively by high angle faulting saline valley however is interpreted to have formed by extension on closely spaced rotated planar normal faults thus within one geometric system of paired pull apart basins extension appears to have been accommodated in the shallow crust in two different ways

lithologic controls on morphology of pressure dissolution surfaces stylolites and dissolution seams in paleozoic carbonate rocks from the mideastern united states abstract examination of pressure dissolution surfaces stylolites and dissolution seams in carbonate rocks from the mideastern u s demonstrates that the morphology of these surfaces varies with rock fabric one can quantify the morphology of these pressure dissolution surfaces using four parameters thickness t of the insoluble residue defining the surface amplitude of irregularity i of the surface between vertical offsets amplitude of vertical offsets o of the surface and frequency f of vertical offsets along the surface i and o increase with t reflecting progressive development of stylolites whereas f is proportional to 1 t apparently because the physical strength of a stylolite inhibits the formation of offsets mean values of f o and t are greater in grainstones and packstones than in mudstones and wackestones and the abundance of dissolution seams relative to that of stylolites decreases through the lithologic spectrum from mudstones to grainstones these relationships suggest that development of pressure dissolution surfaces to form large stylolites depends on the heterogeneity of the limestone fabric maximum values of t and o in grainstones correlate with cement abundance t and o are low in grain rich cement poor grainstones even though grains are favored as leading or penetrating elements of stylolite columns dissolution seams surfaces with o and f near zero are found only in rocks containing fine grained dolomite t and i of those seams decrease with increasing dolomite abundance in dolomitic limestones and t and o are lower in dolostones than in limestones taken together these relationships suggest that extreme abundance of pressure resistant components such as carbonate grains and dolomite inhibit development of pressure dissolution surfaces in contrast stylolites are most extensively developed i e i t o and f are greatest in carbonate rocks in which these pressure resistant elements are mixed with less resistant components such as cement and carbonate mud the latter rocks which include packstones well cemented grainstones and slightly dolomitic limestones may undergo preferential removal from the stratigraphic record by pressure dissolution

diagenesis of a se asian cenozoic carbonate platform margin and its adjacent basinal deposits abstract this study provides insights into the diagenesis of a se asian tertiary carbonate platform and the variations in alteration that occur across platform top margin slope and adjacent basinal deposits a petrographic cathodoluminescent and stable isotopic study allowed evaluation of the diagenesis of the kedango limestone of borneo the kedango carbonate platform developed as a predominantly low to moderate energy system in the semi enclosed marine embayment of the kutai basin during the eocene to miocene early alteration through pervasive micritisation and minor isopachous fringing syntaxial overgrowth and bladed to radiaxial cements was due to marine diagenesis on the basis of limited relatively enriched stable isotope compositions and non luminescent cathodoluminescent cl characters minor early marine cementation formed just in the shallowest platform top and margin deposits and was likely promoted in high energy portions of the platform due to wave and or current activity dissolution cavities banded calcite cements with variable cl characteristics and depleted stable isotope compositions micritic sediment infiltration and alveolar textures are minor features but together are indicative of localised subaerial emergence and meteoric diagenesis the most prevalent and pervasive diagenetic feature of the deposits is the neomorphic alteration and replacement of metastable bioclasts and micritic matrix together with contiguous calcitisation of pore spaces burial fluids with a marine character are inferred as the parent diagenetic fluid since stable isotope compositions for the neomorphic spar is largely consistent with precipitation from se asian oligocene miocene seawater in a burial environment tectonic subsidence the protected semi enclosed marine embayment setting and probably terrestrial runoff together with component variability reflecting local environmental variations are inferred to have been major controlling influences on the diagenesis of the kedango platform variations in diagenesis across bathyal slope and shallow platform deposits of the kedango limestone are not as marked as in other platforms from the region

paleomagnetism of middle miocene volcanic rocks in the mojave sonora desert region of western arizona and southeastern california paleomagnetic directions have been obtained from 190 early to middle miocene 12 20 ma mafic volcanic flows in 16 mountain ranges in the mojave sonora desert region of western arizona and southeastern california these flows generally postdate early miocene tectonic deformation accommodated by low angle normal faults but predate high angle normal faulting in the region after detailed demagnetization experiments 179 flows yielded characteristic directions interpreted as original thermal remanent magnetizations trm because of the episodic nature of basaltic volcanism in this region the 179 flows yielded only 65 time distinct virtual geomagnetic poles vgps the angular dispersion of the 65 vgps is consistent with the angular dispersion expected for a data set that has adequately averaged geomagnetic secular variation the paleomagnetic pole calculated from the 65 cooling unit vgps is located at 85 5 n 108 9 within a 4 4 circle of 95 confidence this pole is statistically indistinguishable at 95 confidence from reference poles calculated from rocks of similar age in stable north america and from a paleomagnetic pole calculated from rocks of similar age in baja california the coincidence of paleomagnetic poles from the mojave sonora desert region with reference poles from the stable continental interior indicates that 1 significant vertical axis net tectonic rotations have not accompanied post middle miocene high angle normal faulting in this region 2 there has been no detectable post middle miocene latitudinal transport of the region and 3 long term nondipole components of the middle miocene geomagnetic field probably were no larger than those of the recent 0 5 ma geomagnetic field in contrast paleomagnetic data indicate vertical axis rotations of similar age rocks in the transverse ranges the eastern transverse ranges and the mojave block we speculate that a major structural discontinuity in the vicinity of the southeastward projection of the death valley fault zone separates western areas affected by vertical axis rotations from eastern areas that have not experienced such rotations

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

statistical evaluation of elemental concentrations in shallow marine deposits cretaceous lusitanian basin abstract the elemental geochemistry of ancient shallow marine carbonates represents an often underexplored archive of paleoenvironmental change and diagenetic pathways complex multi parameter datasets from a lithologically heterogeneous sedimentary succession in the southern part of the lusitanian basin ericeira portugal are presented and interpreted the section comprises marly carbonate and sandstone rich coastal marine deposits of early albian to early cenomanian age principal component analysis of bulk elemental abundance ca mg sr fe and mn lead to define four geochemical clusters based on common elemental attributes siliciclastics and dolomitized limestones facies yield evidence for significant diagenetic alteration but still preserve information on paleoshoreline position mixed carbonate siliciclastics and limestone facies bear evidence for relative sea level position and relevant paleoclimatic information in their elemental record accordingly mid albian mixed carbonate siliciclastic deposits present variable degrees of continental influx specifically a sharp increase of fe and mn concentrations in relation to continental input is in agreement with periods of enhanced hydrological cycling and increased weathering on adjacent emerged lands the progressive transition towards more marine conditions is accompanied by higher ca and sr content and represented by limestone facies corresponding to a higher sea level position during late albian to early cenomanian times moreover this facies records a trend towards warmer and more arid conditions early diagenetic stabilization and or dissolution of aragonite into low mg calcite can account for major elemental variations including higher sr content strongly coupled with ca content along with lower mg fe and mn concentrations data shown here provide solid evidence that the statistical analysis of the elemental record of ancient marine deposits when combined with conventional sedimentology and thin section petrography allow for elaborate conclusions on their depositional environment and diagenetic pathways cored wells and facies specific reservoir properties can be addressed by these methodologies able to detect and quantify changes in patterns both industry and academy can therefore benefit from approaching such a complex interplay

syn depositional alteration of coral reef framework through bioerosion encrustation and cementation taphonomic signatures of reef accretion and reef depositional events the development of coral reef framework and the preservational character of both in situ and rubble coral is strongly influenced by a range of physical chemical and biologically mediated taphonomic processes these operate at or just below the reef framework water interface and can be defined as having either a constructive or destructive effect upon primary reef framework i e coral constituents constructional activities add additional calcium carbonate to the primary framework structure via secondary framework growth and early cementation destructive processes which remove or degrade primary and secondary framework carbonate are associated with the effects of either physical mainly storm disturbance or biological erosion termed bioerosion key bioeroding groups include the grazing fish and echinoid groups as well as the activities of an array of infaunal borers these include specific groups of sponges bivalves and worms termed macroborers as well as cyanobacteria chlorophytes rhodophytes and fungi termed microborers the relative importance of each process and the rates at which they operate vary spatially across individual reef systems in addition many of these processes leave distinctive signatures on or in the coral framework in some cases e g calcareous encrusters these are the skeletons of the organisms themselves whilst in other cases the organism may leave behind a trace of their activity e g macro and microborers these represent useful palaeoenvironmental tools firstly because they often have good preservation potential and secondly because the range and extent of many of the individual species groups and processes involved exhibit reasonably well constrained environment and or depth related distributions as a result these taphonomically important organisms or processes can be used to delineate between reef environments in core or outcrop and to aid the interpretation of reef depositional processes and events this review summarises current understanding regarding the distribution of these species processes within contemporary reef settings and considers the suites of taphonomic signatures that may aid in the recognition and interpretation of depositional environments and events

diagenesis of neogene delta front patch reefs alteration of coastal siliciclastic influenced carbonates from humid equatorial regions abstract this study offers insights into the diagenetic alteration of coastal carbonates that formed coevally with nearly continuous siliciclastic influx in a humid equatorial setting a multi disciplinary petrographic cathodoluminescent stable isotope trace element and major element investigation allowed characterization of diagenetic features paragenetic sequencing and an interpretation of diagenetic environments from neogene patch reefs of the samarinda region mahakam delta borneo se asia marine cements are absent from the patch reefs with grain micritization the only marine diagenetic feature recognized the predominant diagenetic feature within the patch reefs is pervasive neomorphic stabilization and cementation of aragonite reef components to calcite that pre dates all compaction features meteoric aquifer flow derived from the adjacent landmass is inferred as the main parent diagenetic fluid since 18o v pdb values of calcite cements of 3 6 to 11 7 are consistent with precipitation from se asian freshwater and inconsistent with a wholly marine origin late stage fracturing cementation and chemical compaction are relatively minor features and attest to a changing paleohydrologic and diagenetic environment evidence for a shallow to moderate burial diagenetic regime for these later features are maximum temperature of 53 c and burial depths 1000 m inferred from stable isotope values of calcite and late dolomite cements dolomite crystal fabrics the onset depth of stylolite or dissolution seam formation and regional geothermal gradients the humid tropical environment and ever wet conditions on the island of borneo together with rapid cenozoic uplift likely led to paleoaquifer flow with fluids focused through adjacent deltaic units into the reef carbonates in these coastal carbonates from the humid samarinda region continental groundwater flow has resulted in pervasive stabilization and calcitization features rare in arid or temperate counterparts

spatial geochemistry of upper jurassic marine carbonates iberian subplate abstract chemostratigraphy applied to ancient marine carbonates is commonly based on one dimensional stratigraphic sections or core data as demonstrated from modern oceans this approach underestimates the spatial complexity of physico chemical seawater properties here a several hundred kilometer long transect consisting of seven upper jurassic sections from settings ranging from proximal neritic middle shelf to the epioceanic distal fringe across the southern and eastern palaeomargins of the iberian sub plate reveals variability in sedimentologic stratigraphic and geochemical records the comparison of isotopic and elemental data from different carbonate materials matrix micrite carbonate cements in veinlets belemnite rostra and ammonite shells reveals differential diagenetic pathways microfacies cathodoluminescence and geochemical data retrieved from biostratigraphically well constrained sections reveal that epioceanic matrix micrite geochemical data provide valuable proxies for palaeo seawater properties our data are reviewed in the context of published late jurassic records the outcome shows a higher level of complexity including the potential admixture of marine continental and diagenetic geochemical signals in the epicontinental record the stratigraphic trend in carbon isotopes of epioceanic sections agrees upon that of upper jurassic reference sections from the northern tethyan margins while oxygen isotope ratios are relatively 18o enriched palaeo seawater temperatures across the transect investigated were estimated using 18o as tentative proxy for interpreting distance from shore differences in water masses relative depth variations and potential local forcing factors palaeoenvironmental conditions evaluated through the combined record of isotope 18o elemental mn and skeletal content contrast with relative fluctuations in sea level site specific changes in palaeoceanographic parameters such as water depth seawater temperature salinity and upwelling are considered in comparison to examples from ancient and modern oceans

questioning carbonate diagenetic paradigms evidence from the neogene of the bahamas carbonate diagenetic models have been heavily influenced by numerous studies of exposed quaternary limestones as a result meteoric diagenesis is often assumed to be the principle means of altering aragonite rich sediments into calcitic limestones however these models are limited by the scarcity of examples of aragonite rich sediments buried in seawater that have never been influenced by meteoric fluids the bahamas transect cores recovered originally aragonite rich sediments deposited in deep water beyond the easy reach of meteoric waters and provide an opportunity to test current diagenetic paradigms the bahamas transect consists of seven cores drilled in the prograding western margin of great bahama bank the two proximal cores clino and unda were drilled on the platform top and recovered shallow water platform to reef facies overlying deeper margin and proximal slope facies the five distal cores were drilled by odp leg 166 in up to 660 m of water and recovered carbonate slope facies all studied sections are neogene to pleistocene in age diagenetic environments were identified based on petrographic and scanning electron microscopy sem observations xrd mineralogy carbon and oxygen stable isotopic data and trace elements the upper 100 150 m of the two proximal cores were altered in meteoric to mixing zone diagenetic environments but all other intervals were altered exclusively in marine pore fluids during seafloor marineburial and deep burial diagenesis several of the findings of this study question current carbonate diagenetic paradigms these include 1 large scale sea level lowstands may not have chemically active meteoric lenses as we found no meteoric alteration at the 3120 m elevation of the latest pleistocene lowstand rather phreatic meteoric diagenesis appears restricted to within w10 m of the land surface 2 mixing zone diagenesis includes aragonite dissolution and minor lmc cementation but does not show the cavernous porosity or dolomitization predicted by mixing zone diagenetic models current models are based on coastal mixing zones which do not appear to be applicable to these more inland and perhaps more typical locations 3 marine burial diagenesis produces a mature limestone with fabrics formerly considered diagnostic for meteoric diagenesis such as moldic porosity aragonite neomorphism blocky calcite spar and calcite microspar however oxygen stable isotopic data average n 18 o 1x indicate alteration in marine pore fluids only the character of marine burial diagenesis is partially controlled by the nature of the sediment being altered we have identified two end member styles an open system style characterized by dissolution of aragonite without significant cementation and a more closed system style with aragonite dissolution

onshore to offshore trends in carbonate sequence development diagenesis and reservoir quality across a land attached shelf in se asia abstract although isolated miocene buildups in se asia commonly form prolific hydrocarbon reservoirs their equivalents on clastic dominated land attached shelves remain poorly known and underexplored here onshore to offshore trends in carbonate development and reservoir quality are assessed across the nw borneo shelf through study of surface outcrops and subsurface wells a multidisciplinary programme of fieldwork petrography and geochemical analyses allowed evaluation of spatio temporal variations in deposition diagenesis and pore system development together with an assessment of controlling influences in addition to field logging and sample collection 200 samples were studied via transmitted light cathodoluminescent and scanning electron microscopy together with stable isotopic characterisation o c and sr carbonates developed as localised low and higher relief buildups as well as more continuous sheet like deposits in near coast to shelf margin positions molluscs corals larger benthic foraminifera and coralline algae are common constituents most samples show evidence for marine micritisation and just in shelf margin positions isopachous cements however burial diagenesis predominates in the form of compaction neomorphism fracturing late leaching and dolomitisation near coastal carbonates commonly contain siliciclastics as do some shelf margin deposits that interdigitate with or are covered in siliciclastics some early probable meteoric leaching affected inner shelf deposits prior to pervasive neomorphic to blocky poikilotopic calcite cement formation on the basis of 18 o v pdb values of 4 5 to 7 9 equivalent to 18 o v smow values of 0 to 4 at 25 40 c and 13 c v pdb values of 0 6 to 1 6 cementation probably reflects alteration from terrestrial groundwaters in meteoric aquifers derived from the humid landmass of borneo despite this cementation moderate energy inner to mid shelf grainstones from the core of mounded carbonates still retain or have enhanced porosity 18 o v pdb values of 3 6 to 5 4 those for the late dolomites are suggestive of fluids of meteoric origin 18 o v pdb values of 5 2 to 7 4 equivalent to values of 0 3 to 6 3 v smow at 40 60 c critical factors for reservoir quality development in carbonates from siliciclastic dominated shelves in the equatorial tropics are 1 development and preservation of primary porosity 2 cementation associated with meteoric aquifers draining large humid equatorial landmasses and 3 burial leaching and fluid pathways

fault slip rates and earthquake histories for active faults in southern california abstract within the context of the historical record of seismicity we review the geological data bearing on the quaternary slip rates and paleoearthquake histories of active faults in southern california

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

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

diagenetic history and porosity evolution of an early miocene carbonate buildup upper burman limestone yadana gas field offshore myanmar abstract the miocene yadana carbonate platform is a major offshore gas reservoir located in the andaman sea offshore myanmar the integration of petrographic analysis of carbonate rocks stable isotope measurements and seismic interpretation provided new insights into the diagenetic history of the upper burman limestone reservoir the high 28 average porosity of the reservoir is dominantly related to strong development of microporosity moldic and vuggy porosity mud supported coral rich sediments record significant early marine dissolution of aragonite and early lithification of matrix that has led to the development of dense layers stable isotope and petrographic data from the top of the reservoir suggest that the long term depositional hiatus middle to late miocene was related to platform drowning and non deposition in a deep marine setting moderate dolomitization has affected the top and flanks of the platform during the depositional hiatus microporosity development and sparry calcite cementation mainly occurred in marine to marine shallow burial environments a major decrease in porosity averaging 10 below the gas water contact suggests a major phase of porosity evolution during and or after the hydrocarbon emplacement which is mainly related to 1 increased moldic and vuggy porosity development within the gas zone 2 microporosity preservation in loosely packed subrounded micrites within the gas zone and 3 microporosity reduction by calcite precipitation within the water zone leading to the development of densely packed euhedral micrites

crustal strain near the big bend of the san andreas fault analysis of the los padres tehachapi trilateration networks california in the region of the los padres tehachapi geodetic network the san andreas fault saf changes its orientation by over 30 degree from n 40 degree w close to that predicted by plate motion for a transform boundary to n 73 degree w the strain orientation near the saf is consistent with right lateral shear along the fault with maximum shear rate of 0 38 plus minus 0 01 mu rad yr at n 63 degree w in contrast away from the saf the strain orientations on both sides of the fault are consistent with the plate motion direction with maximum shear rate of 0 19 plus minus 0 01 mu rad yr at n 44 degree w the strain rate does not drop off rapidly away from the fault and thus the area is fit by either a broad shear zone below the saf or a single fault with a relatively deep locking depth the fit to the line length data is poor for locking depth d less than 25 km for d of 25 km a buried slip rate of 30 plus minus 6 mm yr is estimated the authors also estimated buried slip for models that include the garlock and big pine faults in addition to the saf slip rates on other faults are poorly constrained bymore the los padres tehachapi network the best fitting garlock fault model had computed left lateral slip rate of 11 plus minus 2 mm yr below 10 km buried left lateral slip of 15 plus minus 6 mm yr on the big pine fault within the western transverse ranges provides significant reduction in line length residuals however deformation there may be more complicated than a single vertical fault a subhorizontal detachment on the southern side of the saf cannot be well constrained by these data the authors investigated the location of the saf and found that a vertical fault below the surface trace fits the data much better than either a dipping fault zone located south of the surface trace less

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

source mechanisms of three moderate california earthquakes of july 1986 abstract we studied the source processes of three moderate size earthquakes in california the m s 6 0 event of july 8 1986 near palm springs the m s 5 8 shock of july 13 1986 offshore of oceanside and the m s 6 2 event of july 21 1986 in the chalfant valley on the east side of the sierra nevada the centroidal source parameters are estimated by inversion of long period p and sh waves recorded at teleseismic distances by seismographs of worldwide networks a more detailed description of the source is then obtained by analyzing broadband seismograms the north palm springs earthquake had a simple rupture process most of the seismic moment was released in the first 3 sec in a single step the strike of the source fault plane follows the average trend of the banning fault and its dip agrees with the dip of the fault plane delineated by the aftershocks the faulting mechanism of the main shock is right lateral strike slip with a sizable reverse component that is consistent with uplift north of the banning fault the earthquake offshore of oceanside had a slightly more complex rupture process the far field source time function consists of two pulses that represent the release of most of the moment in the first 3 sec the source mechanism indicates reverse faulting with the compressional axis trending northeast almost perpendicular to the trend of mapped faults offshore the event does not appear to be associated with major mapped faults in the area but the strike of one of the nodal planes agrees with the trend of the major mapped faults offshore and its mechanism is consistent with the missing component of plate convergence not taken up by the onshore strike slip fault systems and the idea of a weak san andreas fault system the rupture process of the chalfant valley earthquake was yet more complicated the source time function indicates that in a 4 sec time window three asperities were broken the source mechanism indicates right lateral strike slip faulting with a small normal faulting component on a fault that dips approximately 50 southwest earthquake activity suggests that presently the deformation in the northern part of the owens valley which includes the chalfant valley is dominated by conjugate strike slip faults which strike obliquely to the main range bounding normal faults the waveforms indicate the presence of a low velocity zone at a depth of about 20 km in the crust in the chalfant valley a synthesis of information from waveform modeling first motion fault plane solutions and aftershock distributions indicates that the nucleation and or termination of rupture for the north palm springs and the chalfant valley events were controlled by preexisting fault geometry

video cathodoluminescence microscopy of diagenetic cements and its applications abstract diagenetic studies of sedimentary rocks using cold cathodoluminescence cl microscopy have been severely limited because of the very low intensity of visible luminescent emissions which required long photographic exposure times and because of the difficulty in obtaining quantitative data from cl observations the solution to this problem is to fit the microscope with a high sensitivity digital colour video camera linked to a computer with image enhancement and image analysis software the new technique described in this paper produces digital cl images of consistent high quality both quickly and cheaply controls the capture and editing of cl images to reveal detailed textural information even from minerals exhibiting low level luminescence such as quartz acquires quantitative information on pore systems and the abundance of cement zones from cl images examples are presented to demonstrate the high quality of images produced in this way and the range of uses to which the new technique can be applied the ability to image exactly the same field of view in both plane polarised light and cl is a particular advantage image analysis techniques have been developed to give a statistical characterisation of both pore systems and cement phases that infill them the abundance of contrasting cement zones seen in cl can be measured and the abundance of cement phases can be mapped across a reservoir the history of porosity occlusion can be reconstructed quantitatively and integrated with burial history and hydrocarbon migration porosity can be measured accurately and since the technique obtains data on pore geometry as well as abundance the pore system can be characterised by pore size distributions and pseudo capillary pressure curves this also opens the possibility of estimating permeability from thin sections

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

coral reef diagenesis records pore fluid evolution and paleohydrology of a siliciclastic basin margin succession eocene south pyrenean foreland basin northeastern spain an integrated field petrographic and geochemical study has determined the fluid rock interaction history in part of an eocene reef complex on the margins of the siliciclastic dominated catalan sector of the south pyrenean foreland basin results show that at least four distinct fluid systems influenced the basin margin and demonstrate the sensitivity of reef rocks as paleohydrological archives in siliciclastic environments the earliest calcite cements precipitated from meteoric waters at shallow burial depths and mineralogical stabilization of reef carbonate was mostly completed during this episode textural and isotope trends typical of paleo exposure surfaces are lacking and trace element results suggest that meteoric waters were transmitted laterally and or upward into the reef via delta lobe sandstone paleoaquifers the distribution of late cements is highly variable and fracture fed demonstrating the importance of deformation in controlling fluid flow subsequent to reef lithification isotopic and elemental compositions of burial calcites plus their paragenetic association with barite and dolomite show that fluids of marine parentage were expelled from compacting basinal marls into the basin margin paleoaquifers the calders reef also records an episode of extrabasinal fluid circulation probably associated with faulting of the basin margin ferroan saddle dolomite contains fluid inclusions with elevated homogenization temperatures indicating thermal disequilibrium with the surrounding strata hydrothermal activity was possibly related to neogene extensional tectonics the final cement stage in the reef records the influence of telogenetic meteoric water possibly reflecting the present day basin margin hydrology

depositional environment diagenetic evolution and their impact on the reservoir quality of the carboniferous kt ii carbonate in the zhanazhol reservoir pre caspian basin kazakhstan abstract the carboniferous kt carbonate unit late serpukhovain to early moscovian of the zhanazhol reservoir in the pre caspian basin is a giant condensate reservoir with great heterogeneity although the depositional characteristics and their impact on reservoir quality have been well documented by previous studies few studies have focused on diagenesis the interplay between depositional environment and their controls on reservoir heterogeneity in this study combining sedimentological petrographic and geochemical analyses we reconstructed the depositional settings and diagenetic history of the kt carbonate and assess their impacts on reservoir quality according to the vertical and lateral distribution of 12 observed microfacies types we proposed a depositional model of a northward deepening ramp consisting of tidal flat inner ramp and middle ramp which has played a critical role in controlling the reservoir quality mainly through grain types and matrix content fusulinidal grainstones packstones have the best reservoir quality because of its porous fusulinidal fragments and low micritic matrix content the major diagenetic events including cementation eight cement types dissolution fabric and non fabric selective dissolution compaction pressure dissolution and microfracturing early and late were grouped into six diagenetic environments marine meteoric shallow burial epigenic karstification intermediate burial and deep burial marine cementation and compaction are the main reason for porosity decreasing in upper inner ramp and middle ramp respectively the minor moldic pores created by fabric selective dissolution during meteoric stage were enlarged by freshwater leaching during epigenic karstification and its associated cementation occluded pores in the underlying bioclastic grainstones packstones late non fabric selective dissolution and cementation likely resulted in local porosity rearrangements without net porosity gain or loss but certainly reduced reservoir heterogeneity the interaction between depositional environment and diagenetic evolution played a vital role in the formation of two types of vertical distribution patterns of porosity types and understanding this interaction and its impacts on reservoir quality within a sequence stratigraphic framework can more reliably predict the distribution of reservoir properties and provides insights for adjacent fields with similar settings

impacts of light penetration on the bathymetry of reef microboring communities implications for the development of microendolithic trace assemblages abstract sediment samples recovered from three proximate reef environments in north jamaica characterised by different light penetration regimes reveal marked variations in the bathymetric range of sediment microboring communities in contrast to clear water environments assemblages developed in turbid water conditions undergo both bathymetric restriction and compression in their range in clear water sites the upper photic lower photic zone transition occurs between depths of 20 30 m this is marked by a shift from a predominance of cyanobacterial e g eurygonum nodosum scolecia filosa fasciculus frutex and fasciculus dactylus and chlorophyte e g rhopalia catenata fasciculus grandis reticulina elegans and scolecia botulifera traces to assemblages dominated by the traces e nodosum and s filosa cyanobacteria f grandis chlorophyte palaeoconchocelis starmarchii rhodophyte and orthogonum fusiferum and saccomorpha sphaerula fungi at sites characterised by intermediate levels of turbidity this same assemblage transition occurs at around 15 20 m depth and at the most turbid site at depths of only 5 10 m integration of assemblage data and light readings indicates that this transition occurs where percentages of surface light illumination are reduced to around 10 15 compression of the lower photic zone is so extreme at the most turbid site that microboring assemblages at only 30 m depth show evidence of a transition to an assemblage associated with dysphotic

diagenetic evolution of the eocene ramp carbonates a paradigm from the nile valley egypt petrographical and geochemical attributes abstract carbonate rocks of east nile valley in egypt have been investigated as a paradigm for revealing the diagenetic evolution of the eocene ramp carbonates the integration of petrographical elemental geochemical and stable isotopic data revealed that the studied carbonates have been influenced by a sequence of diagenetic processes which are included in three diagenetic episodes i e eogenesis mesogenesis and telogenesis and are related to four diagenetic environments i e marine phreatic meteoric phreatic burial and uplifting environments the paragenetic sequence of the studied carbonates commences with the eodiagenetic episode which includes the marine and meteoric phreatic diagenetic environments the marine phreatic diagenetic environment comprises micritization glauconitization pyritization marine cementation fibrous calcite and syntaxial overgrowth rim cements early dolomitization formation of fine crystalline matrix replacive dolomites and early stages of mechanical compaction before significant burial the meteoric phreatic diagenetic environment includes the neomorphism dissolution meteoric cementation earlier phases of sparry calcite cements and precipitation of megaquartz in the void spaces of the peritidal carbonates during the mesogenesis episode the studied carbonates were exposed to burial diagenesis the shallow burial diagenesis resulted in the creation of point tangenetial contacts between the allochemical constituents and the precipitation of a medium coarse crystalline dolomite cement filling the dissolved fossils and dissolution pores the deep burial diagenetic processes embody the chemical compaction condensed fitted interpeneteration and pressure dissolution fabrics fracturing and burial cementation the telodiagenesis represents the last episode in the diagenetic history of the studied carbonates it witnessed the fracturing meteoric vadose cementation and hematitization processes

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

spatio temporal evolution of a tertiary carbonate platform margin and adjacent basinal deposits abstract the variability in low to moderate energy carbonate platform margins is poorly known from the geological record here the spatial and temporal evolution of platform margin and adjacent basinal deposits is evaluated from the little known tertiary kedango limestone that developed in a semi enclosed marine embayment in se asia the hypothesis here is that platform margin development will reflect regional and perhaps global influences such as tectonics eustasy or biotic change rather than windward leeward effects and storms that typically impact strongly upon open oceanic platforms the development of the carbonate platform was determined through logging petrography facies evaluation provenance and high resolution dating studies eleven carbonate facies were identified from the 30 km long western margin of the 600 m thick platform and its adjacent slope and basinal deposits larger benthic foraminifera and coralline algal packstones and wackestones dominated in shallow waters during the oligo miocene coral patch reef related floatstones rudstones and less commonly boundstones were also present on the platform top perhaps surprisingly for a low energy platform there was considerable variation along the platform margin and much reworking of material into slope and basinal deposits during the oligo miocene reworked material includes shallow water bioclasts clasts from older siliciclastics fresh feldspars lithified slope and platform top carbonate clasts some of the latter showing evidence for karstification the western platform margin varied laterally over a few kilometres from a gently sloping unrimmed platform to a probable bank top with in places coral fringed bypass and erosional faulted escarpment margins eustasy may have influenced shallowing and deepening trends on the platform top but apparently had little impact on mass wasting instead platform margin development was strongly impacted by tectonics including active faulting terrestrial runoff together with changes in carbonate producers and local variability on the platform top

space geodetic measurement of crustal deformation in central and southern california 1984 1992 we estimate the velocity field in central and southern california using global positioning system gps observations from 1986 to 1992 and very long baseline interferometry vlbi observations from 1984 to 1991 our core network includes 12 gps sites spaced approximately 50 km apart mostly in the western transverse ranges and the coastal borderlands the precision and accuracy of the relative horizontal velocities estimated for these core stations are adequately described by a 95 confidence ellipse with a semiminor axis of approximately 2 mm yr oriented roughly north south and a semimajor axis of approximately 3 mm yr oriented east west

neogene clockwise tectonic rotation of the eastern transverse ranges california suggested by paleomagnetic vectors results from a paleomagnetic study of neogene volcanic rocks situated within and around the pinto basin region of the eastern transverse ranges suggest that the ranges have undergone a clockwise tectonic rotation of 41 4 7 7 since late miocene time both normal and reversed polarities are observed and inclination data indicate no significant flattening the rotation was accompanied by progressive sinistral slip on the several east west trending faults which bound and transect the eastern transverse ranges a computation using the observed amount of cumulative left slip on the east west trending faults of the eastern transverse ranges 50 km and the spacing between the pinto mountain and salton creek faults which bound the region 70 km indicates that 35 of clockwise rotation is required which roughly agrees with the paleomagnetic data removal of the eastern transverse ranges rotation in a reconstruction shows that the distributed dextral shear across the mojave desert region to the north must have been on the order of 100 km since late miocene time from the results of this study we infer that crustal rotation of the eastern transverse ranges began later and is of less magnitude than that of the western transverse ranges

reservoir potential of carbonate rocks in the kutai basin region east kalimantan indonesia abstract fifteen percent of the exploration wells drilled in the kutai basin region were targeted for stratigraphic play types carbonate reservoirs comprise almost 70 of the objectives in these stratigraphic plays there was need for a better understanding of the carbonate reservoir potential in the region accordingly this study was carried out the distribution depositional environment as well as factors controlling the quality of carbonate reservoirs are reviewed and analyzed carbonate reservoirs in the study area can be found sparsely throughout the kutai basin carbonates range in age from oligocene bebulu limestone to late miocene dian limestone the main constituents of these carbonate build ups are platy corals encrusting red algae and larger benthonic foraminifera most of the carbonates were deposited in a shallow marine environment inner to middle shelf during rises in relative sea level highstand system tracts are characterized by well developed carbonate facies belts the carbonate build ups generally occur as isolated bedded mounds from a few feet up to 1000 ft in thickness the preservation of primary porosity is generally poor due to diagenetic processes during burial history particularly the infilling of pores by non ferroan calcite cement the development of secondary porosity is limited due to the retardation of subsurface fluid flow by non permeable layers and the absence of solution effects due to sub aerial exposure and karstification preserved porosities are mainly present as vugs best developed in coarse grained shelf margin facies which may not have subsequently been completely filled by calcite cement early hydrocarbon migration may retard the diagenetic processes and preserve the primary carbonate porosity

modern fringing reef carbonates from equatorial se asia an integrated environmental sediment and satellite characterisation study abstract fringing reefs of se asia may conservatively comprise 30 of the world s coral reef area but remain almost unstudied white 1987 tomascik et al 1997 this study provides insights into the primary sedimentological and early alteration characteristics of an isolated fringing reef system kaledupa hoga from the tukang besi archipelago se asia a combined multispectral satellite imagery field and petrographic study allowed for the generation of an environmental facies map which acts as a model for the distribution of primary sedimentological characteristics in relation to the primary environmental facies the islands of the tukang besi archipelago are mesotidal 71 accuracy when compared with field and sedimentary data with the exception of the reef crest and reef slope that commonly have widths on a sub imaging resolution although field and satellite imagery observations reveal ten environmental facies sedimentological characterisation results in a lower number of distinctive categories due to the similarity of many deposits foreshore backshore and bare intertidal deposits are distinctive and are composed of reef derived material that has been reworked shorewards seagrass associated facies all show some fine silt clay sized material

seismicity of the garlock fault california the garlock fault is a 265 km long left slip fault striking northeastward from the san andreas fault in southern california relocations of earthquakes that occurred from 1932 to 1981 on and near this major fault were made using the master event technique the spatial distribution of seismicity along the fault is different west and east of its midpoint near rand where the largest en echelon offset and a marked change in strike occur these two segments also display distinct geologic features and different seismic and aseismic behavior the 150 km long segment west of rand has shown continuous low seismic activity during the past 50 yr well documented aseismic creep and has a relatively complex fault trace in contrast the 155 km long segment east of rand has very few small earthquakes no demonstrable creep and a simpler fault trace p wave first motion studies substantiate predominantly left slip motion along the garlock fault overall energy release during this 50 yr period gives a seismic moment rate of 2 75 10 21 dyne cm yr much lower than that inferred from holocene geologic offsets thus indicating that the garlock fault currently represents a temporal seismic gap and that the potential exists for large earthquakes if behavior of the garlock fault is similar to that of the san andreas the western segment of the fault can be compared with the central creeping segment of the san andreas and the eastern segment with those segments broken by the 1857 and 1906 earthquakes thus larger events might be expected on the eastern segment than on the western segment or if the entire fault breaks during a single event larger displacements toward the east

the july 1986 oceanside ml 5 3 earthquake sequence in the continental borderland southern california an earthquake of m l 5 3 occurred at 32 58 7 n 117 51 5 w southwest of oceanside in san diego county at 13 47 13 july 1986 ut this main shock was followed by an extensive aftershock sequence with 55 events of m l 3 0 during july 1986 the epicenters of the main shock and aftershocks are located at the northern end of the san diego trough bahia soledad fault zone sdt bs where it changes strike from northwest to a more westerly direction through a left offset or a bend in the fault the northwest striking sdt bs is one of three strike slip fault systems that constitute the offshore agua blanca fault system the spatial distribution of the aftershocks indicates a unilateral 7 to 9 km long rupture to the east southeast away from the epicenter of the main shock the focal mechanism of the main shock also has an east southeast striking and south dipping plane with mostly reverse movement on it focal mechanisms of the m l 3 0 aftershocks show both reverse and strike slip movement the reverse focal mechanisms indicate that this sequence may have occurred on a thrust fault that provides for a left stepping offset or a bend in the san diego trough fault as movement is transferred to the west along the santa cruz catalina island escarpment some of the aftershocks that are located to the southeast of the main shock and have strike slip focal mechanisms suggest activation of the northwest trending san diego trough fault a stress inversion of the focal mechanism data shows that the maximum principal stress determined from the focal mechanisms of the main shock and 22 aftershocks that occurred within 36 hours of the main shock has an azimuth of s30 w plunging 18 the maximum principal stress determined from 30 aftershocks that occurred from 15 july to 2 october 1986 has an azimuth of s20 w plunging 18 the values the measure of the relative sizes of the principal stresses are approximately 0 07 and 0 1 respectively indicating that the intermediate and minimum principal stress are of similar magnitude the results of the stress inversion and the focal mechanisms that showed reverse faulting suggest that the inner continental borderland offshore from oceanside is not currently a pure strike slip tectonic regime but rather a strike slip mixed with reverse faulting regime when the 52 aftershock focal mechanisms are divided into four groups and the stress inversion is repeated the change in stress can be described as a progressive counter clockwise rotation of 14 of the orientation of the maximum principal stress to a more southerly direction with the greatest change in stress orientation observed shortly after the main shock the abundance of aftershocks may be related to the large temporal variation in stress orientation that in turn may have resulted from the small stress drop of the main shock

paleo oceanographic and tectonic settings of early miocene reefs and associated carbonates of offshore southeast asia the late oligocene to early middle miocene was a period of widespread reef and associated carbonate deposition over a wide latitudinal range in the offshore region of southeast asia a generally rising eustatic sea level during this period allowed the accumulation of thick reefal units an expansion of the coral algal regional facies belt north to japan and south to new zealand occurred during the early miocene as the result of a reduced oceanic latitudinal temperature gradient an episode of enhanced organic carbon burial is reflected in a positive dgr13c excursion from 17 5 to 13 5 ma increasing paleo oceanographic equability may have resulted in reduced ocean circulation with the resultant development of an expanded oxygen minimum zone marine oil prone or anic carbon was deposited in silled anoxic basins both bounded by and within island arc systems a combination of tectonic and paleo oceanographic factors therefore created conditions that favored contemporaneous deposition of organic carbon rich source beds and reef reservoirs during the latest early to early middle miocene paleogeographic and facies reconstructions for an 18 m y interval indicate that deposition occurred in three tectonic settings 1 passive continental margins 2 convergent plate boundaries and 3 obliquely convergent plate boundaries in all these settings the vertical motion histories of fault bounded blocks and of larger tectonic elements within which they are contained directly controlled the geographical distribution of carbonate buildups their scal and morphology duration diagenesis and relationship to siliciclastics

controls on platform scale patterns of surface sediments shallow holocene platforms bahamas isolated carbonate platforms occur throughout geological history and commonly exhibit considerable spatial variability to evaluate the controls on the nature of sediment accumulation across the expansive shallow platform tops this study systematically compares and contrasts patterns in surface sediments from several shallow 10 m holocene bahamian examples remote sensing data field observations petrographic characterization and quantitative grain size analyses reveal the spatial patterns of sediment accumulation on crooked acklins platform and the berry islands bank integration of these data with synoptic observations of waves tides and currents along with regional geochemical data provides a means to explore the factors that influence platform scale sedimentary patterns these data illustrate that the platform interiors of both crooked acklins platform and berry islands bank are blanketed with medium to coarse sand size sediment peloids are most common in the interior of crooked acklins platform whereas the berry islands bank includes more abundant composite grains in both areas very little mud is present with surface sediments averaging 2 mud comparison of these results with published data from little bahama bank great bahama bank and caicos platform suggest that contrary to previous interpretations the presence of open margins and or brisk winds are not necessary for the occurrence of a platform top with little mud although the muddy sediment fraction of the interior can be suspended by elevated wave energy wind generated current speeds in protected platform interiors are relatively low instead in parts of the platform interiors transport and winnowing of fines is enhanced greatly by tidal currents which carry suspended sediments off the shallow platforms even if shielded by islands beyond physical influences however regional geochemical compilations suggest that the bahamian tides supply highly supersaturated waters rich in dissolved oxygen to these platform interiors this exchange is interpreted to facilitate favourable conditions for calcium carbonate precipitation in the form of ooids marine cements and hardened peloids across vast expanses of the platform interiors such fundamental controls on holocene platform scale sediment dynamics are likely to have influenced carbonate systems through the geological record

carbonate cement stratigraphy and timing of diagenesis in a miocene mixed carbonate clastic sequence offshore sabah malaysia constraints from cathodoluminescence geochemistry and isotope studies a mixed carbonate clastic sequence is one of several miocene hydrocarbon bearing reservoirs in the northwestern sabah basin this sequence consists of bioclast rich sandstones interpreted as prograding storm shoal deposits the sequence contains a complex variety of carbonate nodules the sequence has undergone nine stages of cementation that completely occluded pores each stage represents a distinctive cement texture precipitating at specific temperatures and burial conditions the diagenetic evolution began with a syndepositional iron free marine calcite ca1 followed by an early methane derived dolomite do1 bladed calcite ca2 blocky vein filling fe calcites ca3ca4 clay mineral associated dolomite do2 fe dolomite and ankerite do3do4 and late iron rich calcite ca5 each stage of cement has distinctive sr2 mn2 mg2 fe2 ca2 and na contents reflecting changes in the palaeo porefluid systems with time the cements are correlatable over the whole study area precipitation occurred from very early to late stages of diagenesis at near surface to 2 0 km depths with progressive burial and temperature increase oxygen isotope values become strongly negative stage ca4 13c 0 5 pdb 18o 5 7 pdb the cements were precipitated at 20 75 c the source of carbon varies from marine dissolved carbonates to fermentation of organic matter methane meteoric waters and possibly hydrothermal fluids strontium isotope dating of do1 with 13c 32 5 pdb 18o 2 60 pdb and do2 13c 3 0 pdb 18o 2 5 pdb dolomites indicates that these dolomitization events took place at 10 5 ma and 8 9 ma respectively assuming precipitation within a completely open seawater system the do1 dolomite was precipitated from a methane derived brine at the boundary between the serravallian and tortonian stages after major uplift and induced faulting at a sea level lowstand the do2 dolomite was precipitated during intermediate to deep burial diagenesis during smectite illite transformation before hydrocarbon emplacement

sedimentology and diagenesis of tertiary carbonates on the mangkalihat peninsula borneo implications for subsurface reservoir quality abstract combined field and laboratory studies of surface exposures on the mangkalihat peninsula borneo provide new constraints on the chronostratigraphy sedimentology and diagenesis of tertiary carbonate deposits the reservoir characteristics of carbonate facies are described providing an analogue model for carbonate reservoirs in the subsurface of this region a mixed carbonate siliciclastic shelf with intervening probably fault bounded deeper water areas developed on the eastern part of the mangkalihat peninsula in the late eocene to oligocene during the oligo miocene shallow water platform carbonates accumulated over much of the area of the mangkalihat peninsula this platform had a steep reef rimmed or possibly locally faulted northern margin where high energy conditions prevailed and marine cements were pervasive in contrast the platform interior was a low energy area affected by leaching of aragonitic bioclasts the best reservoir quality on the platform occurs in moderate energy grainstones and packstones tens to hundreds of metres towards the platform interior from the platform margin where a combination of primary intergranular and secondary mouldic porosity results in good porosity and permeability

radiaxial fibrous calcite as early burial open system cement isotopic evidence from permian of china abstract the nanpanjiang basin of south china occupies about 100 000 km2 in southern guizhou and eastern yunnan provinces and northwestern guangxi autonomous region the basin contains a thick paleozoic carbonate sequence overlain by about 3 000 m of triassic basinal deposits permian carbonate rocks comprise a large portion of the paleozoic strata and form several platforms separated by basins containing dark thin bedded limestones siliceous shales and cherts the platform margins are rimmed by sponge or algal reefs radiaxial fibrous calcite rfc is the most abundant cement in very coarse sponge or algal debris of upper permian reef and fore reef sediments exposed along the western margin of the nanpanjiang basin small volumes of syndepositional cements interpreted to have been fibrous magnesian calcites and botryoidal aragonite predate rfc coarse blocky burial calcite postdates rfc evidence that rfc was precipitated during sediment deposition was not found rfc occurs as isopach layers up to 15 mm thick and exhibits white gray and black bands about 1 mm wide the presence of microdolomite inclusions in these cements indicates that they were originally magnesian calcites dgr18o of rfc cements are more positive than any of the earlier or later components of the reef and fore eef facies analyses of successive bands reveals the most positive dgr18o near the center of the isopach layers dgr13c of successive bands reveals generally more negative values toward the centers of layers rfc layers are interpreted to have precipitated during early burial of the platform margin while reef and fore reef sediments were in communication with seawater cement layers recorded isotopic characteristics of seawater as platform edge sediments subsided through the water column at the basin margin dgr18o of successive bands records cooler water at depth in the basin followed by geothermal warming dgr13c records increased incorporation of light carbon as the platform subsided through the oxygen minimum zone followed by a return to normal values at depth these data and interpretations suggest rfc layers precipitated very slowly during time spans commensurate with those of subsiding platforms millions of years isotopic characteristics of rfc may not reflect shallow seawater rather they may reflect burial environments where dgr18o is affected by cooler water and dgr13c is affected by biologic activity end of article last page 261

fluid rock interactions during continuous diagenesis of sandstone reservoirs and their effects on reservoir porosity the cretaceous sandstone reservoir in the kuche depression tarim basin western china was investigated with reference to its reservoir property evolution during diagenesis six general diagenetic stages were recognised through petrographic mineralogical and geochemical analyses fluid rock interaction experiments were conducted under these six continuous diagenetic conditions that is with a simulation sequence of compaction early diagenesis organic acid incursion i elevated temperature pressure organic acid incursion ii late diagenesis corresponding to these six experimental stages a total of six models were constructed finally an extended model of fluid rock interaction during diagenesis at a geological timescale from 30 ma to present was constructed after various parameters had been validated results demonstrate the diagenetic stages from both the experimental and numerical simulations generally matched findings obtained from the petrographic and geochemical analyses i with compaction becoming weakened cementation by various minerals was gradually increased ii quartz overgrowth occurred because the contemporaneous sedimentary water was alkaline iii most minerals for example calcite and feldspar minerals displayed dissolution owing to the first organic acid incursion resulting in the visual porosity to increase to 29 26 iv increases of temperature and pressure caused a minor fluctuation of the porosity change v the cement that formed during earlier stages largely dissolved with the second organic acid incursion vi during the last stage the reservoir fluid was diluted by sedimentary alkaline water and most minerals precipitated under an alkalic environment the present porosity simulated is about 11 4 comparable with the actually measured data this study demonstrates that the combination of petrographic observations laboratory experiments and numerical simulations can not only reconstruct the diagenetic process but also provide a quantitative evaluation and prediction of reservoir petrophysical properties this article is protected by copyright all rights reserved

biofilm related calcification sediment trapping and constructive micrite envelopes a criterion for the recognition of ancient grass bed environments micrite envelopes are a common feature in carbonate sediments and are typically associated with the micrite filling of borings produced by microendolithic organisms these are referred to as destructive micrite envelopes and have long been recognized as reflecting an important early diagenetic process recent analysis of sediments collected from back reef environments at discovery bay north jamaica however has demonstrated envelope formation on the surfaces of carbonate grains clearly distinct from the micrite filling of microborings such constructive envelopes occur almost exclusively in sediments from grass bed environments and are always intimately associated with biofilms comprising abundant mucilage cyanobacteria bacteria and diatoms it is suggested that these envelopes represent a product of both biologically mediated micrite precipitation occurring within the biofilm mucilage and around the biofilm components i e cyanobacteria and diatoms and associated trapping of carbonate mud and fine grained sediment their recognition only within grass bed sediments may enable their use as a diagnostic feature of grass bed environments or vegetation stabilized substrates in the rock record

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

shallow burial diagenesis of skeletal carbonates selective loss of aragonite shell material miocene to recent queensland plateau and queensland trough ne australia implications for shallow cool water carbonates in burial environments carbonate sediments undergo mineralogical stabilization and increasing lithification with depth as yet however little knowledge exists with respect to the corresponding effects on fossil preservation and taphonomic modification of the original sediment composition countings of particles 63 m in miocene to recent periplatform sediments odp leg 133 ne australia exhibit a clear trend of reduction of skeletal aragonite downcore low and high mg calcite grains occur in a continuous order of magnitude over the studied interval 600 m sub bottom depth original microtextures are retained in high mg calcite biota although converted to low mg calcite thus the conversion to low mg calcite appears to occur without introducing a significant quantitative bias aragonite skeletons pelagic gastropods however exhibit a successive exposure of deeper crystal layers and a chalky preservation with burial depth which we interpret to result from dissolution hints for the originally more numerous existence of aragonite biota exist in soft sediments and chalks by the presence of internal moulds shells replaced by microspar and mouldic porosity in early cemented hardgrounds in deep sections barren of aragonite the number of casts and replaced shells remains unchanged and is insignificant as compared to aragonitic biota probably originally present within the sediment 2 in ooze chalk vs 30 50 of grains in modern periplatform sediments therefore palaeontological information must be significantly biased through selective removal of aragonite rates of preservation and destruction depend on external factors during sediment accretion sedimentation rates clay content total organic carbon content and rates of fluid flow within the sediment these observations are relevant with respect to the diagenetic potential and patterns of fossil preservation in little cemented calcitic cool water carbonates because they may originally have contained more aragonite biota as important constituents of an ecosystem than is commonly suspected and calcite aragonite ratios in ancient carbonate sediments may not necessarily reflect original input signals climate or sea level

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

geophysical correlation of the aptian and albian formations in the wessex basin of southern england using geophysical borehole log signatures and basic lithological information from sidewall cores and well cuttings division and correlation of the mid cretaceous sediments of the wessex basin can be achieved a sub gault early albian unconformity surface is mapped with some accuracy across the hampshire dorset area and the deposits of a previous aptian transgression are observed the distinctive log signatures aid in facies reconstructions and sequence stratigraphical analysis especially the onlap of basal gault horizons onto and across basement highs the highly variable thickness and lithological distributions characteristic of the wealden pass upward into laterally extensive facies distributions in the lower greensand and gault sequence boundaries are identified at the base of the wealden lower greensand gault within the gault cristatum subzone and base chalk

late cenozoic tectonics of the northwestern san bernardino mountains southern california the late cenozoic structural and stratigraphic history of the northwestern san bernardino mountains supports two distinct episodes of uplift in late miocene to earliest pliocene and quaternary time that we hypothesize are related to movements on low angle structures beneath the range in this paper we document the nature distribution and timing of late cenozoic deformation and deposition in the northwestern san bernardino mountains and we illustrate the neotectonic evolution of the area in a series of interpretive paleotectonic block diagrams in the first episode of deformation late miocene to earliest pliocene motion on the south southwest directed squaw peak thrust system disrupted drainage in pre existing miocene nonmarine basins and uplifted the western third of the present range to form the ancestral san bernardino mountains crystalline rocks of the san bernardino mountains were thrust southward across the present site of the san andreas fault between 9 5 and 4 1 ma at a time when the san gabriel fault was the active strand of the san andreas transform system we speculate that the liebre mountain crystalline block at the northern margin of the ridge basin may be the missing upper plate of the squaw peak thrust now offset along the san andreas fault the second episode of deformation began with uplift of the northern plateau of the modern san bernardino mountains on north directed range front thrusts in early pleistocene time between 2 0 and 1 5 ma synchronous uplift of the northern plateau recorded in early pleistocene fanglomerates on the northwestern margin of the range is interpreted to be the result of movement of a relatively coherent crustal block northward up a south dipping detachment ramp beneath the central range in middle pleistocene time activity on the northern range front began to wane and the locus of uplift shifted to a narrow zone of arching and northward tilting adjacent to the san andreas fault which subsequently migrated rapidly northwestward along the san andreas fault from the western san bernardino mountains into the northeastern san gabriel mountains we attribute this pattern of deformation to the passage of a bulge or strike slip ramp attached to the southwest side of the san andreas fault at depth

deformation across the western united states a local estimate of pacific north america transform deformation we obtain a locally based estimate of pacific north america relative motion and an uncertainty in this estimate by integrating deformation rate along three different paths leading west across southwestern north america from east of the rio grande rift to near the continental escarpment data are primarily quaternary geologic slip rate estimates and resulting deformation determinations therefore are instantaneous in a geologic sense but long term with respect to earthquake cycles we deduce a rate of motion of the pacific plate relative to north america that is 48 2 mm yr a rate indistinguishable from that predicted by the global kinematic models rm2 and nuvel 1 however we obtain an orientation that is 5 9 counterclockwise of these models a more westerly motion of the pacific plate with respect to north america is calculated from all three paths the relatively westerly motion of the pacific plate is accommodated by deformation in the north american continent that includes slip on relatively counterclockwise oriented strike slip faults including the san andreas fault which is especially relevant in and south of the transverse ranges and a margin normal component of net extension across the continent which is especially relevant north of the transverse ranges deformation of the sw united states occurs in regionally coherent domains within which the style of deformation is approximately uniform in the vicinity of the transverse ranges two important shear systems splay from the san andreas fault the eastern california shear zone trending nnw from the eastern transverse ranges and the trans peninsular faults trending sse from the western and central transverse ranges within the transverse ranges the right lateral san andreas fault steps left seemingly requiring large amounts of convergence there however most of this convergence is avoided through a funneling flow of the crust toward the western transverse ranges and into the relatively narrow central california coast ranges and the northern motion of the mojave the former process involves an alternation of rotation direction from counterclockwise in and south of the central transverse ranges to clockwise in the western transverse ranges

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

development patterns of an isolated oligo mesophotic carbonate buildup early miocene yadana field offshore myanmar abstract the development history of an oligo mesophotic early miocene isolated carbonate system 160 m in thickness forming the uppermost part of the oligo miocene yadana buildup northern andaman sea has been evidenced from the integration of sedimentological core studies from 4 wells cumulated core length 343 m well correlations seismic interpretation and analysis of the ecological requirements of the main skeletal components three types of carbonate factory operated on the top of the platform depending on water depth turbidity and nutrient level 1 a scleractinian factory developing under mesophotic conditions during periods of high particulate organic matter supplies 2 an echinodermal factory occupying dysphotic to aphotic area of the platform coevally with the scleractinian factory 3 a large benthic foraminiferal coralline algal factories prevailing under oligo mesophotic and oligo mesotrophic conditions the limited lateral changes in facies between wells together with the seismic expression of the yadana buildup suggest deposition on a flat topped shelf carbonate production and accumulation on the yadana platform was mainly controlled by light penetration nutrient content and hydrodynamic conditions scleractinian rich facies resulted from transport of coral pieces derived from mesophotic environments mounds and deposited in deeper low light mud rich environments in which lived abundant communities of suspension feeders such as ophiuroids changes in monsoonal intensity terrestrial runoff from the irrawaddy river upwelling currents and internal waves activity during the early miocene are likely responsible for significant variations in water turbidity and nutrient concentration in the andaman sea thus promoting the development of an oligo mesophotic incipiently drowned platform

recognition and documentation of depositional sequences from outcrop an example from the aptian and albian on the eastern margin of the wessex basin stratigraphic data relating to the aptian and albian sediments around folkestone in southeast england on the eastern margin of the wessex basin are plotted graphically to illustrate biostratigraphic gaps and condensed intervals these are then used to suggest candidate sequence boundaries notated lg1 4 and gl 3 which are named after the lower greensand and gault the biostratigraphic subzones apparently unrepresented in the area are lg1 obsoletus and bodei lg2 gracite and debile lg3 schrammeni gl bulliensis candidate sequence boundaries g2 cristatum subzone and g3 auritus subzone are erosion surfaces correlating with probable biostratigraphic gaps elsewhere in the basin the age of lg4 is uncertain but must lie within the mammillatum superzone all candidate sequence boundaries correspond closely to those predicted by recent global sea level cycle charts and additionally there is a close match between predicted maximum flooding surfaces and the occurrence of condensed intervals most of the candidate sequence boundaries could have been formed as a result of rapid and at least regionally extensive relative sea level falls but the sedimentological contexts of lg3 and gl suggest that these may have been generated by transgression related sediment condensation the minor sequence boundary in the loricatus zone intermedius subzone illustrated in the cycle charts cannot be unambiguously recognized at outcrop in the folkestone area additional sequence boundaries not shown in the cycle charts may also be present in the wessex basin

integrated 3 d reservoir modeling based on 3 d seismic the tertiary malampaya and camago buildups offshore palawan philippines three dimensional 3 d seismic interpretation and drilling results indicate complex sedimentary geometries of the malampaya and camago build ups offshore palawan philippines with localized progradation due to unidirectional offbank transport alternating with vertical aggradation successive reduction of size during buildup growth and backstepping of the protected landward margin in response to transgression ultimately appear to have triggered the demise of carbonate production and platform drowning the shallow water platform top sediments repeatedly show signs of subaerial exposure before reflooding a modeling functionality was developed to allow development of multiple scenario 3 d reservoir models in an exploration or appraisal stage the model enables merging of seismic scale observations based on 3 d volume and horizon analyses with subseismic scale information from well data however inherent noise within the seismic data introduced by the complex buildup morphology has resulted in inconsistent attribute distribution and fault dimming these difficulties are compounded by erratic velocity distribution within the limestone nonhyperbolic move out and a narrow relatively low frequency spectrum all of which prevent the use of the 3 d seismic volume as hard data but rather allow its use as a soft constraint for guiding the geological interpretation and ultimately the modeling process seismic data quality in such complex morphologic settings and scarcity of well data hamper greatly the use of geostatistically driven modeling approaches therefore a new functionality was developed within shell s proprietary integrated 3 d modeling suite geocap which allows deterministic model reservoirs using seismic horizon and volume interpretation sequence and cyclo stratigraphic architecture and the concept of reservoir rock type seismic velocity in clean carbonate formations is predominantly a function of porosity distribution to assess time to depth conversion uncertainty the reservoir rock type based models were first produced in the time domain only after differential 3 d depth conversion of these models could the scenarios be reconstructed in the depth domain the depth models subsequently were used to derive permeability and saturation 3 d distortions and thus hydrocarbon volumes for each deterministic scenario the models were then used for simulation purposes

grain susceptibility to the effects of microboring implications for the preservation of skeletal carbonates the boring activity of microendolithic organisms such as cyanobacteria chlorophytes rhodophytes and fungi represents a major destructive process affecting sediment preservation within reef environments this study demonstrates the presence of two distinct assemblages of microborers within sediments collected from the fringing reefs of north jamaica correlating to the upper 18 m depth photic zones the upper photic zone assemblage is dominated by cyanobacteria and chlorophytes whilst rhodophytes and fungi become more abundant with increasing water depth most significant from a grain preservation perspective is the variable nature of grain infestation observed between different reef sites and different carbonate grain types the highest degree of grain infestation occurs within shallow low energy back reef environments and the most susceptible grains at all sites are corals molluscs and foraminifera coralline algae halimeda and echinoid fragments are rarely heavily infested high rates of infestation at back reef sites result in rapid diminution of the most susceptible grains especially coral which are either underrepresented or contribute only to the finer sediment fractions in the subsurface fore reef grain assemblages undergo relatively little alteration microboring therefore has potential to bias the fossil record by removing the most susceptible skeletal grains the impact of microboring upon back reef grain assemblages must be considered when attempting to model depositional processes within both modern and ancient reef environments

geochemistry of meteoric calcite cements in some pleistocene limestones in this study the stable isotope and trace element geochemistries of meteoric cements in pleistocene limestones from enewetak atoll western pacific ocean cat island bahamas and yucatan were characterized to help interpret similar cements in ancient rocks meteoric calcite cements have a narrow range of 18o values and a broad range of 13c values in each geographical province these pleistocene cements were precipitated from water with stable oxygen isotopic compositions similar to modern rainwater in each location enewetak calcite cements have a mean 18o composition of 6 5 0 pdb and 13c values ranging from 9 6 to 0 4 0 pdb sparry calcite cements from cat island have a mean 18o composition of 4 1 0 and 13c values ranging from 6 3 to 1 1 0 sparry cements from yucatan have a mean 18o composition of 5 7 0 and 13c values of 8 0 to 2 7 0 the mean 18o values of these pleistocene meteoric calcite cements vary by 2 4 0 due to climatic variations not related directly to latitude the 13c compositions of meteoric cements are distinctly lower than those of the depositional sediments variations in 13c are not simply a function of distance below an exposure surface meteoric phreatic cements often have 13c compositions of less than 4 0 0 which suggests that soil derived co2 and organic material were washed into the water table penecontemporaneous with precipitation of phreatic cements concentrations of strontium and magnesium are quite variable within and between the three geographical provinces mean strontium concentrations for sparry calcite cements are for enewetak atoll 620 ppm 510 ppm for cat island 1200 ppm 980 ppm and for yucatan 700 ppm 390 ppm equant cements intraskeletal cements and bahamian cements have higher mean strontium concentrations than other cements equant and intraskeletal cements probably precipitated in more closed or stagnant aqueous environments bahamian depositional sediments had higher strontium concentrations which probably caused high strontium concentrations in their cements magnesium concentrations in pleistocene meteoric cements are similar in samples from enewetak atoll mean 1 00 mol mgco3 0 60 mol mgco3 and cat island mean 0 84 mol mgco3 0 52mol mgco3 but yucatan samples have higher magnesium concentrations mean 2 20 mol mgco3 0 84mol mgco3 higher magnesium concentrations in some yucatan cements probably reflect precipitation in environments where sea water mixed with fresh water

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

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

crustal structure of the offshore southern santa maria basin and transverse ranges southern california from deep seismic reflection data seismic reflection data from the 1986 edge pacific gas and electric experiment together with refraction and gravity data are used to construct an integrated north south geophysical cross section along the offshore santa maria basin and across the offshore extension of the transverse ranges thrust faults offsetting acoustic basement and folding miocene sediments root in a midcrustal detachment at 12 13 km depth the detachment coincides with an increase in reflectivity seen on the seismic reflection section and the maximum depth of earthquakes a high velocity oceanic crustal layer at the base of the crust 17 22 km and moho 25 km is offset by a low angle thrust fault with an apparent dip 10 to the north offshore point arguello gravity models indicate crustal thickening and a change in the depth to moho from 25 to 30 km in this region however the contribution of elastic flexure from loading of the transverse ranges is considered to be minor in this part of the borderland the cross section constrains neogene shortening to less than 3 based on faulting and folding of the sedimentary section shortening of the upper crust is balanced by a combination of ductile flow and subduction of the oceanic crust beneath the midcrustal detachment

structural controls on the evolution of the kutai basin east kalimantan abstract the kutai basin formed in the middle eocene as a result of extension linked to the opening of the makassar straits and philippine sea seismic profiles across the northern margin of the kutai basin show inverted middle eocene half graben oriented nne ssw and n s field observations geophysical data and computer modelling elucidate the evolution of one such inversion fold nw se and ne sw trending fractures and vein sets in the cretaceous basement have been reactivated during the tertiary offset of middle eocene carbonate horizons and rapid syn tectonic thickening of upper oligocene sediments on seismic sections indicate late oligocene extension on nw se trending en echelon extensional faults early middle miocene n7 n8 inversion was concentrated on east facing half graben and asymmetric inversion anticlines are found on both northern and southern margins of the basin slicken fibre measurements indicate a shortening direction oriented 290 310 ne sw faults were reactivated with a dominantly dextral transpressional sense of displacement faults oriented nw se were reactivated with both sinistral and dextral senses of movement leading to the offset of fold axes above basement faults the presence of dominantly wnw vergent thrusts indicates likely compression from the ese initial extension during the middle eocene was accommodated on nne ssw n s and ne sw trending faults renewed extension on nw se trending faults during the late oligocene occurred under a different kinematic regime indicating a rotation of the extension direction by between 45 and 90 miocene collisions with the margins of northern and eastern sundaland triggered the punctuated inversion of the basin inversion was concentrated in the weak continental crust underlying both the kutai basin and various tertiary basins in sulawesi whereas the stronger oceanic crust or attenuated continental crust underlying the makassar straits acted as a passive conduit for compressional stresses