seismic and geologic characteristics of drowning events on carbonate platforms carbonate platform drowning events are recorded in upper jurassic lower cretaceous carbonates of the baltimore canyon area offshore united states east coast and lower miocene carbonates of the pearl river mouth basin offshore people s republic of china cursory examination of seismic data from both areas would indicate that the platforms fit the classic definition of a drowning unconformity however detailed lithologic and paleontologic data indicate that the depositional erosional hiatuses vary widely in each area from 0 25 m y in the baltimore canyon area to a condensed section with no hiatus in the pearl river mouth basin the sedimentary sequence produced during drowning the drowning sequence in both areas is gradational with underlying shallow platform carbo ates and in some places overlying deeper marine limestones and shales the generalized facies models proposed for drowning events suggest that they may appear as instantaneous or gradual changes in geologic and seismic data however high resolution seismic data across the baltimore canyon and pearl river mouth basins show that some drowning sequences may be masked on conventionally processed seismic sections because of this resolution problem a distinction should be made between seismically and geologically defined unconformity surfaces the geologic characteristics of drowning events on carbonate platforms include a gradational lower and sometimes upper contact chemical sedimentation glauconite phosphate open marine shelf sediments and a variable hiatus at the upper boundary late growth shelf margin reefs also can be a diagnostic feature of drowned platforms seismic characteristics include horizontal to sub horizontal basinal marine onlap basin parallel reflector continuity above the carbonate sequence boundary and downlap of later highstand units evidence from platforms adjacent to continental margins baltimore canyon indicates that drowning occurs in a step wise fashion advancing more or less symmetrically across the platform from shelf to nearshore environments data from isolated open ocean atolls pearl river mouth basin indicate that they respond differently to drowning showing an asymmetric decrease in shallow platform environments as drowning occurs proper recognition by a geoscientist of the seismic and geologic characteristics of drowning events can lead to better reservoir and seal estimates and the correct reconstruction of the depositional tectonic and eustatic histories of an area

the early permian floras of prince edward island canada differentiating global from local effects of climate change new permian plant specimens are described from prince edward island canada they include attached specimens of leaf and stem genera walchia and tylodendron enabling reconstruction of this early permian conifer al though poorly preserved the study of these floras extends our knowledge of diversity and climate conditions in the re gion by placing these findings in a broader stratigraphic and geographic framework we can document the phytogeographic and climate trends through the carboniferous and permian in the maritimes basin combined data on temporal trends in climate sensitive sediments as well as macrofloral and microfloral diversities generally match the independently derived paleolatitudinal estimates these show the region migrating from the southern subtropics across the equator and into the northern subtropics between the early carboniferous and early permian evaporites and pedogenic carbonates together with low diversity floras match its subtropical position in the early carboniferous in contrast coals are present in the late carboniferous accompanied by high diversity macro and microfloral remains when the region was on or near the equator however the subsequent transition to pedogenic carbonates eolian sands and lower diversity floras is not matched by significant poleward latitudinal motion we ascribe these changes to a de crease in moisture availability as transgressions of epeiric seas became less frequent and finally stopped altogether causing an increase of continentality in euramerica resume cet article decrit de nouveaux specimens de plantes datant du permien provenant de l ile du prince edouard canada ils comprennent des specimens de feuilles et de tiges rattachees de genre walchia et tylodendron permettant la reconstruction de ce conifere du permien precoce bien que ces flores soient mal preservees leur etude etend nos connaissances de la diversite et des conditions climatiques de la region en placant ces decouvertes dans un cadre stratigraphique et geographique plus large nous pouvons documenter les tendances phytogeographiques et clima tiques du carbonifere et du permien dans le bassin des maritimes des donnees combinees sur les tendances temporel les dans des sediments sensibles au climat et des diversites relatives a la macro et a la microflore concordent generalement avec les estimations de paleoaltitude derivees de facon independante ces donnees montrent qu entre le carbonifere precoce et le permien precoce il y eut une migration des regions subtropicales meridionales par dela l equateur vers les regions subtropicales septentrionales des evaporites et des carbonates pedogenetiques avec des flo res faiblement diversifiees correspondent a sa position subtropicale au carbonifere precoce par contre on retrouve des charbons au carbonifere tardif accompagnes de restes de macro et de microflores grandement diversifiees lorsque la region etait a ou pres de l equateur toutefois la transition subsequente a des carbonates pedogenetiques a des sables eoliens et a une diversite florale moindre n est pas correlee par un mouvement meridien significatif vers le pole nous attribuons ces changements a une reduction de l humidite disponible alors que les transgressions des mers epicontinen tales devenaient de moins en moins frequentes et qu elles ont finalement cesse tout a fait causant une augmentation de la continentalite en euramerique

do seismic reflections necessarily have chronostratigraphic significance many seismic reflections from within sedimentary successions are thought to be generated along stratal surfaces because those surfaces are laterally continuous and have marked acoustic impedance contrasts as stratal surfaces are isochronous those reflections are then also taken as being chronostratigraphically significant in contrast seismic reflections are thought not to be generated along the boundaries of lithostratigraphic units because those boundaries are discontinuous and gradational nevertheless synthetic seismic analysis shows that seismic reflections should in many circumstances be expected to follow lithostratigraphic unit boundaries not stratal surfaces as these lithostratigraphic unit boundaries will generally be diachronous seismic reflections from within sedimentary successions should evidently not be treated as necessarily having chronostratigraphic significance

seismic models of a prograding carbonate platform vercors south east france abstract the southern vercors area south east france displays superb exposures of a lower cretaceous prograding carbonate platform these exposures allow a geometrical sequence analysis to be combined with detailed outcrop observations two dimensional seismic modelling techniques were used to determine the seismic response of three of these exposures the montagnette the archiane valley and the rocher de combau the outcrops display prograding and retreating series of clinoforms interfingering with fine grained basinal sediments photographs from different angles of view combined with detailed field observations were used to construct lithological profiles with a resolution of f few metres p wave velocities and bulk densities were measured from cored hand specimens and selected values were assigned to lithostratigraphic units in each profile the vertical incidence modelling technique was then used to compute migrated time sections of reflectivity these were convolved with source wavelets of different frequencies to produce the final synthetic seismic profiles none of the modelled outcrop geometries is correctly portrayed seismically at 25 50 hz frequencies not only do the synthetic seismic profiles show less detail they also show misleading geometries in most seismic models for instance pseudo unconformities are present that correspond to rapid changes in dip and in facies in outcrop furthermore the seismic tool is not able to resolve between stratal patterns punctuated by unconformities and those with gradual shifts in facies belts accompanied by complex interfingering relationships this implies that an unconformity recognized on a real seismic line should not automatically be assumed to represent a true stratal unconformity large outcrops are often used to show the validity of sequence stratigraphy a concept mainly based on the analysis of seismic lines this study however shows that there is no one to one relationship between geometries observed in outcrop and in seismic lines seismic modelling of outcrops therefore provides a means for evaluating outcrop geometries in terms of seismic stratigraphy

3d seismic interpretation of dissolution pipes in the south china sea genesis by subsurface fluid induced collapse a large suite of remarkable pipe structures has been identified from high resolution 3d seismic data in the dongsha massif northern south china sea the diameters and heights of the collapse structures range from c 100 m to 710 m and c 134 m to 1010 m respectively these pipes vary from cylindrical to a steep conical geometry narrowing upwards they are rooted in a major carbonate succession that was originally deposited as a large carbonate platform system these pipe structures are interpreted as resulting from carbonate diagenesis and dissolution at a deep burial stage i e they are not classical karst collapse structures as suggested in previous studies instead they are analogous to pipe like collapse structures described from the ordovician ellenburger group of west texas the dissolution pipes formed at different times during the neogene with the earliest pipes developing during the early middle miocene 15 0 ma and with at least one peak of pipe formation during the dongsha event began at 5 5 ma this regional event was associated with magma intrusion uplifting and faulting in the study area stable isotope data of reservoir rocks in the area of pipe development suggest that cementation was linked to magmatically driven hydrothermal circulation during the dongsha event small scale pipes are densely clustered above the main oil reservoir and given that petroleum is known to have been generated during the time interval of pipe formation we suggest that corrosive carbonic acid derived from flushing of petroleum reservoirs may have been a contributory factor to the dissolution and collapse process c 2013 elsevier b v all rights reserved

sequence stratigraphy of the aux vases sandstone a major oil producer in the illinois basin the aux vases sandstone mississippian has contributed between 10 and 25 of all the oil produced in illinois the aux vases is not only an important oil reservoir but is also an important source of groundwater quarrying stone and fluorspar using sequence stratigraphy a more accurate stratigraphic interpretation of this economically important formation can be discerned and thereby enable more effective exploration for the resources contained therein

exploration history of liuhua 11 1 field pearl river mouth basin china 1 stratigraphic analysis of sparse seismic data in 1981 indicated the presence of a lower miocene carbonate platform complex over the western part of the dongsha massif 220 km 137 mi southeast of hong kong two bank edge trends were recognized and a large structural closure within the carbonate platform was mapped along the axis of the uplift the study also predicted the presence of a widespread thick basal sandstone below the carbonate complex that could serve as a conduit for long distance migration of hydrocarbons into the closure although the prospect was a high risk play in deep water 38 km 24 mi south of the edge of a paleogene basin with possible oil source rocks it was intriguing because of its size and similarity to the giant bombay high oil field offshor india after drilling by other companies demonstrated that oil had migrated well out of the source basin huizhou sag amoco negotiated for contract area 29 04 and was awarded the area in november 1985 the first amoco well lh 11 1 1a tested 2240 bbl day of 21 degree api oil from a 75 m 246 ft pay section in a carbonate platform sequence topped at 1197 m 3927 ft a 401 m 1316 ft lower carbonate section and a 149 m 489 ft sandstone unit resting on basement were water bearing additional drilling has confirmed a giant in place oil accumulation but commerciality is yet to be determined the carbonate complex includes a leached limestone platform facies with a reefal southwestern margin and has excellent porosity and permeability the oil is less waxy and heavier than other huizhou ag sourced oils because of biodegradation after migration

sequence stratigraphy of a carbonate clastic ramp the cincinnatian series upper ordovician in its type area the cincinnatian series consists of five depositional sequences each is composed of a thin transgressive systems tract and a much thicker shallowing upward highstand systems tract whereas the highstand systems tracts are relatively poor in micrite but rich in terrigenous shale the transgressive systems tracts are composed of cleaner carbonate facies ranging from coarse grained calcarenites to micrite rich wackestones and micstones this alternation of carbonate and terrigenousfacies types resulted from the trapping of clastic sediment near its presumed source in the appalachians during a relative sea level rise and it may be a feature common to sequences in other mixed carbonate clastic settings these depositional sequences were produced by eustatic fluctuations as shown by the limited extent to which the sequences can be traced into more proximal portions of the appalachian basin the recognition of depositional sequences clarifies the regional paleogeography and simplifies regional lithostratigraphic nomenclature within current biostratigraphic resolution sequences in the cincinnatian series appear to have chronostratigraphic significance and thereby offer an additional means of intrabasinal correlation in the upper ordovician

large scale facies sequences in alluvial overbank environments abstract gradational coarsening upwards or fining upwards sequences order of meters thick in overbank environments can be produced by progressive crevasse splay levee progradation or abandonment while the channel belt remains unchanged in position in contrast meter scale facies sequences related to periodic channel bell avulsion may show relatively abrupt changes in facies and paleocurrent direction simulation models suggest that the number of such avulsion related facies changes in any overbank sequence bounded above and below by channel belt deposits is on the order of 1 to 10 this is confirmed using an ancient example in this example the average thickness of each avulsion bounded overbank facies sequence was 3 m assuming an average recurrence interval for avulsions of about 1 000 ye rs the mean overbank deposition rate was about 3 mm per year

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

seismic characterization of switching platform geometries and dominant carbonate producers miocene las negras spain the primary goals of seismic interpretation and quantification are to understand and define reservoir architecture and the distribution of petrophysical properties since seismic interpretation is associated with major uncertainties outcrop analogues are used to support and improve the resulting conceptual models in this study the miocene carbonates of cerro de la molata las negras south east spain have been selected as an outcrop analogue the heterogeneous carbonate rocks of the cerro de la molata platform formed by a variety of carbonate producing factories resulting in various platform morphologies and a wide range of physical properties based on textural thin sections and petrophysical porosity density carbonate content and acoustic properties analyses of the sediment s eleven individual facies types were determined the data were used to produce synthetic seismic profiles of the outcrop the profiles demonstrate that the spatial distribution of the facies and the linked petrophysical properties are of key importance in the appearance of the synthetic seismic sections they reveal that carbonate factory and facies specific reflection patterns are determined by porosity contrasts diagenetic modifications and the input of non carbonate sediment the reflectors of the seismograms created with high frequency wavelets are coherent with the spatial distribution of the predefined facies within the depositional sequences the synthetic seismograms resulting from convolution with lower frequency wavelets do not show these details the major reflectors coincide with i the boundary between the volcanic basement and the overlying carbonates ii the platform geometries related to changes in carbonate factories thus sequence boundaries and iii diagenetic zones changes in seismic response related to diagenesis switching carbonate producers and linked platform geometries are an important finding that needs to be considered when interpreting seismic datasets this article is protected by copyright all rights reserved

late leaching under deep burial conditions a case study from the miocene zhujiang carbonate reservoir south china sea abstract the zhujiang carbonates are the hydrocarbon reservoir rock of the liuhua 11 1 field they comprise three porous zones of around 20 m intercalated with tight zones parallel to bedding thin section cathodoluminescence and stable isotope data were combined with well log information in order to investigate the origin and spatial distribution of the abundant porosity the vast majority of pores in the porous zones was generated or overprinted in deep burial settings by late leaching two tight zones however lack this porosity because of meteoric cementation and increased compaction and related calcite precipitation prior to late leaching we propose that migrating corrosive fluids were diverted along bedding parallel flow barriers of the tight zones and leached the intervals in between the porous zones thereby emphasizing the depositional pattern

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

redefinition of the meramecian chesterian boundary mississippian the meramecian chesterian mississippi boundary in the type area is currently defined as the highest occurrence of the crinoid platycrinites penicillus and the lowest occurrence of the crinoid genera agassizocrinus and talarocrinus because these taxa have not been reported outside eastern north america attempts have been made to use conodonts and foraminifera to extend the meramecian chesterian boundary outside the type area unfortunately changes in conodont and foraminiferal assemblages do not coincide with the currently defined meramecian chesterian boundary and use of these fossil groups does not allow exact placement of the boundary outside of eastern north america the authors suggest that the meramecian chesterian boundary be redefined as the boundary between foraminiferal zones 15 and 16i of the mamet scheme irrespective of the occurrence of platycrinites penicillus this change in definition places the ste genevieve limestone genevievian stage in the lowermost part of the chesterian series with which it is biotically and sedimentologically more allied than with the underlying st louis limestone this change provides a sound biostratigraphic base for correlating the meramecian chesterian boundary outside of the type area foraminifera conodonts brachiopods and corals all show significant changes at or slightly below the st louis ste genevieve contact rather than at the genevievian chesterian contact more 52 references less

origin of seismic reflections in a carbonate gas field lower miocene offshore myanmar abstract the geological origin of seismic reflections within a carbonate gas reservoir has been determined on the basis of an integrative analysis of cores well logs pre production and 4d time lapse seismic data the gas reservoir is subdivided into meter to decameter thick diagenetic units which are characterized by distinct acoustic properties low impedance units are dominant and consist of highly microporous and vuggy foraminiferal coralline algal floatstones intervals whose porosity has been significantly enhanced in burial diagenetic environments high to moderate acoustic impedance units thickness 1 20 m are related to various depositional and diagenetic fabrics 1 early lithified coral floatstones 2 foraminiferal rudstone whose intergranular space is occluded by shallow burial sparry calcite and 3 carbonate breccia with neomorphosed corals occurring below an intra formational subaerial exposure surface within the gas zone seismic reflection horizons may form at the boundary between two diagenetic units with contrasted acoustic impedance or may result from the interference between reflection at base and top of such intervals a stratigraphy cross cutting reflection horizon has been shown to form at a major and laterally continuous shift in porosity which is related to a differential diagenetic evolution between the gas and the water zone during or after hydrocarbon emplacement finally the analysis of the geological origin of seismic reflections has been proved to help predicting and mapping the major heterogeneities with significant impact on flow during production

liuhua 11 1 field south china sea a shallow carbonate reservoir developed using ultrahigh resolution 3 d seismic inversion and attribute based reservoir modeling liuhua 11 1 field is 130 miles southeast of hong kong in 1000 ft of water figure 1 the field discovered in 1987 is being developed by the consortium of bp amoco china national offshore oil and kerr mcgee the reservoir zone at 3850 ft subsea is producing 16 22 api oil through 25 long radius horizontal wells success depends on limiting bottom water production which in turn makes accurate reservoir description critically important figure 1 pearl river mouth basin index map and geologic setting to better define reservoir heterogeneity an ultrahigh resolution 3 d seismic survey was acquired in july 1997 acquisition was conducted during calm seas with short 1500 m streamers and shallow 3 5 m tow depths the 180 hz field data enhanced during processing produced peak frequencies of 240 hz approximately four million traces were processed at a bin spacing of 5 5 m over 100 km2 the seismic data were first converted to acoustic impedance by using geologically constrained inversion techniques and then to porosity based on a linear impedance versus porosity relationship drilling data were integrated to create detailed maps of reservoir structure and stratigraphy petrophysical data and modeling were combined with the seismic inversion to create a spatial distribution of porosity permeability and saturation faults fractures and solution collapse phenomena were analyzed using coherence technology complex attribute analyses added additional understanding of rock matrix continuity this information has been used to build reservoir characterization and simulation models that have been tuned and validated using history matching to predict future reservoir performance the geoscience interpretation and characterization of the reservoir for simulation are the focus of this paper liuhua reef carbonates are composed largely of shallow water foram algal packstones and boundstones belonging to the miocene zhujiang formation in place reserves are projected at 1 2 billion barrels over the entire closure only the western part of

development and controlling factors of miocene carbonate platform in the nam con son basin southwestern south china sea miocene carbonate platforms are located on intrabasinal structural highs and along the southern margin of the nam con son basin also referred to as the wanan basin by chinese southwestern south china sea these isolated platforms together cover a gross area of over 25 000 km 2 we map the platforms reconstruct their evolution and evaluate the controls on platform growth and demise within the regional geological setting using available seismic and well data the platforms initiated in the late early miocene and reached their widest extent during the middle miocene the platform margins were controlled by synsedimentary faults associated with carbonate slope failure deposits and or reef talus the platforms formed as isolated platform platform growth history involves six phases start up second start up keep up exposure renewal and drowning phases quantitative analysis of the basin evolution indicates that tectonism eustasy the supply of both terrigenous sediment and nutrients were the dominant controls on platform development and demise c 2013 elsevier ltd all rights reserved

first documentation of seismic stratigraphy and depositional signatures of zhongsha atoll macclesfield bank south china sea abstract carbonate platforms form informative archives for paleoclimates and their internal structures can also hold crucial information about the tectonic history and carbonate evolution of the ocean basins the zhongsha atoll macclesfield bank forms the largest atoll system in the south china sea with a surface area of 23500 km2 however the internal structure and evolution of this atoll system is completely unknown 2d multichannel seismic reflection data were acquired in 2017 over the zhongsha atoll in the south china sea to unravel the stratigraphy geomorphology depositional processes and seismic facies of one of the world s largest atoll for the first time this neogene carbonate platform comprises more than 1 km thick carbonate sequence and overlies a metamorphic basement the southeastern part of the atoll comprises a fault controlled graben system which was formed during the cenozoic rifting stage of the south china sea most of the faults trend ne sw and e w and terminate at or slightly above the top of middle miocene strata atolls and abundant organic reefs initiated on the positive relief and closely mimicked the underlying topography during the early miocene shallow water carbonates continued growing through middle miocene to present times regional uplift led to subaerial exposure termination of platform growth and karstification during the miocene we also reveal a number of fluid flow features such as vertical sub bottom venting features chimneys and pipes chaotic reflection zones which provide the first evidence of active fluid venting in the area of zhongsha atoll the neogene sedimentation history of zhongsha atoll further provide an important paleoenvironmental context for future scientific drilling to better constrain the evolution of asia monsoon

late carboniferous and early permian drainage patterns in atlantic canada paleoflow data have been compiled for late carboniferous late westphalian a to early permian alluvial deposits over a large area of atlantic canada the data which include more than 36 000 measurements of large scale trough cross strata indicate a predominantly northeasterly paleoflow and suggest that a major source area lay to the southwest of the region throughout the 30 ma period represented uplands within the basin deflected paleoflow and probably formed important local drainage and sediment sources tectonostratigraphic analysis suggests that the drainage originated in the fold and thrust belt of the central appalachians and parts of the northern appalachians rivers probably followed northeast oriented structural lineaments through the older acadian mountains of the northern appalachians a considerable proportion of the rising orogen s drainage and probably detritus may have traversed basins along the strike of the mountain belt a situation analogous to that of the modern himalayas

stratigraphic well correlations for 3 d static modeling of carbonate reservoirs the principles and purposes of stratigraphic well correlation in carbonate sedimentary systems are defined and discussed within the context of static reservoir modeling the challenge of well correlations is to relate the heterogeneities measured at core and well scales to the spatial heterogeneities at reservoir and flow unit scales the introduction of a priori knowledge in the process of stratigraphic well correlation is critical to support the stratigraphic rules and to establish a coherent geological and petrophysical concept the links between well correlation and geostatistics are discussed with regard to the stationarity hypothesis and property trend analysis we stress that wells are incomplete and biased samples of the geological reality which is not dependent unlike the dynamic reservoir behavior on the well numbers location and spacing stratigraphic rules are applied as a function of the well spacing relative to the geological reality a simple trigonometric method combining angle of base profile paleobathymetry and well spacing is introduced to check the validity of the well correlation in carbonate ramp like systems two models based respectively on outcrop and subsurface with seismic data are discussed in detail to show the combined influence of the data set sedimentary systems and diagenetic transformations on stratigraphic well correlations

acoustic properties of carbonates effects of rock texture and implications for fluid substitution more than 250 plugs from outcrops and three nearby boreholes in an undisturbed reef of miocene tortonian age were quantitatively analyzed for texture mineralogy and acoustic properties we measured the p and s waves of carbonate rocks under dry humidified and brine saturated conditions at 10 mpa effective pressure with an ultrasonic pulse transmission technique 1 mhz the data set was compared with an extensive database of petrophysical measurements of a variety of rock types encountered in carbonate sedimentary sequences two major textural groups were distinguished on the basis of trends in plots of compressional wave velocity versus poisson s ratio a specific ratio of p wave over s wave velocity in granular rocks the framework of depositional grains is the main medium for acoustic wave propagation in crystalline rocks this medium is provided by a framework of interlocking crystals formed during diagenesis rock textures are connected to primary depositionalparameters and a diagenetic ov

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

igneous activity in the bornu basin onshore ne nigeria implications for opening of the south atlantic the structure of igneous plumbing systems in circum south atlantic intra continental rift basins e g the west and central african rift systems remains enigmatic owing to poor subsurface data coverage and quality how magmatism in these basins related to the opening of the south atlantic is thus poorly understood we integrate 2d and 3d seismic reflection data c 27 600 km 2 data from 23 boreholes and field observations from the bornu basin and upper benue trough onshore ne nigeria to examine the timing and development of igneous bodies possibly related to opening of the south atlantic we identify numerous sills which typically have saucer shaped and en echelon morphologies and extrusive volcanic cones the igneous rocks are alkali basalts and dolerites seismic stratigraphic relationships indicate that emplacement occurred in the early cretaceous albian to cenomanian c 120 ma late cretaceous santonian to early campanian c 83 ma and cenozoic miocene c 22 ma magmatism was broadly coeval with major plate boundary interactions characterized by major azimuthal changes in fracture zones in the developing south atlantic ocean the broad temporal correlation between intra continental rift basin magmatism and plate boundary interactions suggests that periods of magma emplacement may have in some way been instigated by stress dissipation into intra continental rift basins

well log and seismic character of liuhua 11 1 field south china sea relationship between diagenesis and seismic reflections abstract an integrated analysis of log petrographic and seismic data shows that the seismic reflections of liuhua 11 1 field image variations in porosity crossplots of velocity versus porosity density versus porosity velocity versus density and velocity versus gamma ray demonstrate that the acoustic impedance contrasts and consequently seismic reflections represent the alternation of tight and porous zones a detailed examination of a continuous core suggests that the majority of porosity is related to a phase of leaching in the deep burial realm that postdates pressure solution this implies that seismic reflections do not necessarily image depositional surfaces on the other hand seismic interpretation of areally more extensive 2 d lines and lithofacies analysis indicate that these diagenetically induced porosity units correspond to depositional events we conclude that the late diagenetic overprint follows primary depositional bedding and therefore seismic reflections still image the depositional architecture of the carbonate platform

early permian fossil vertebrate footprints and their stratigraphic setting in megacyclic sequence ii red beds prim point prince edward island vertebrate trace fossils are reported for the first time from red beds near the top of megacyclic sequence ii at prim point in southwestern prince edward island they occur as casts of tetrapod trackways the ichnocoenose also includes a rich invertebrate ichnofauna the trackmakers thrived in an area of sparse vegetation and occupied out of channel river sediments most likely crevasse splay deposits amphisauropus latus represented by three trackways has been previously reported from germany poland and czechoslovakia it is here interpreted as the track of a cotylosaur it occurs together with the track of gilmoreichnus kablikae which is either a captorhinomorph or possibly a juvenile pelycosaur these facilitate the assignment of a late early permian late autunian age to the strata the third set of footprints those of a small herbivorous pelycosaur compare most closely with ichniotherium willsi known hitherto from the keele beds latest stephanian of the english midlands this ichnocoenose oc

geological significance of seismic reflections and imaging of the reservoir architecture in the malampaya gas field philippines the integration of petrographic analyses of cores and thin sections petrophysical measurements and well logs demonstrates that variations in acoustic impedance in the malampaya buildup upper eocene to lower miocene offshore northwest palawan are related to vertical changes in porosity and pore type which are dominantly controlled by diagenetic processes the nido limestone was subdivided into 10 50 m 30 150 ft thick units characterized by specific diagenetic patterns and petrophysical properties diagenetic units the alternation between tight and porous diagenetic units is mainly controlled by meteoric diagenesis leaching and pedogenesis and by late burial cementation and leaching well to seismic ties show that the main seismic reflectors within the buildup interior reflect the boundaries between diagenetic units most of the negative amplitude reflectors are related to unconformities whereas positive amplitude reflectors have a more questionable chronostratigraphic value and may represent the bases of cemented lenses that can crosscut time lines comparison with other southeast asian tertiary buildups indicates different origins of seismic reflections related to distinct patterns of diagenetic evolution the identification of such seismodiagenetic units and of their controlling factors is of paramount importance for the architecture and the petrophysical characterization of carbonate reservoirs

the chronostratigraphic significance of seismic reflections along the bahamas transect abstract continuous cores drilled during the bahamas drilling project bdp and the ocean drilling program odp leg 166 along a transect from the top of great bahama bank to the basin in the straits of florida provide a unique data set to test the assumption in seismic stratigraphy that seismic reflections are time lines and thus have a chronostratigraphic significance seismic reflections that are identified as seismic sequence boundaries ssbs were dated by means of biostratigraphy in the five odp sites and by a combination of biostratigraphy magnetostratigraphy and sr isotope stratigraphy in the two bdp sites the seismic reflection horizons are carried across a variety of facies belts from shallow water carbonates over slope carbonates to drift deposits in the straits of florida within this system 17 ssbs were identified and dated despite the fact that the seismic reflections cross several facies belts their ages remain remarkably constant the average offset in all sites is 0 38 myr in no cases do the seismic reflections cut across time lines the age differences are the combined result of the biostratigraphic sampling frequency the spacing of marker species that required extrapolation of ages and the resolution of the seismic data in addition uncertainties of age determination in the proximal sites where age diagnostic fauna are rare add to the age differences between sites therefore it can be concluded that the seismic reflections which mark the ssbs along the bahamas transect are time lines and can be used as stratigraphic markers this finding implies that depositional surfaces are preferentially imaged by reflected seismic waves and that an impedance contrast exists across these surfaces facies successions across the sequence boundaries indicate that the sequence boundaries coincide with the change of deposition from times of high to low sea level in the carbonate setting of great bahama bank sea level changes produce changes in sediment composition sedimentation rate and diagenesis from the platform top to the basin the combination of these factors generates differences in sonic velocity and thus in impedance that cause the seismic reflection the impedance contrasts decrease from the proximal to the distal sites which is reflected in the seismic data by a decrease of the seismic amplitude in the basinal area

seismic model of a progradational carbonate platform picco di vallandro the dolomites northern italy we present a seismic model of a well exposed carbonate platform to basin transition from the triassic succession at picco di vallandro the dolomites northern italy the core of this model is a detailed lithologic cross section that represents 1500 m of stratigraphic section over a distance of 3 5 km the cross section is based on detailed measured sections photo interpretation and careful projection of surface mapping into the plane of section samples from the measured sections provide control on velocity and density distribution and these data were used to generate an impedance model from the cross section the impedance model was convolved with a zero phase 25 hz peak frequency wavelet to produce the seismic model the results illustrate how the platform to basin transition might be imaged by conventional seismic reflection data how the reflections relate to the distribution of lithology and through going geological surfaces and how constructive and destructive interference and seismic resolution combine to produce individual reflections the picco di vallandro section displays several scales of progradation and retrogradation ranging from stacked buildups that are several hundreds of meters thick to the interfingering of individual beds the seismic model displays this complexity with varying degrees of success the individual buildups are well imaged but as expected smaller features are not as clearly reproduced by the model intermediate scale sections that represent platform retrogradation are shown as surfaces of onlap in the seismic model but field work shows that the platform was still shedding sediment while retreating and that no simple onlap surface exists in the outcropping section a similar lack of stratigraphic resolution is shown by the model at the downlapping clinoforms which do not correspond to iscrete stratal surfaces but to the toe of slope position where major bedding units thin below seismic resolution smaller features such as the position of downslope terminations of carbonate breccia wedges are not resolved by the model toe of slope packages of limestone turbidites are represented only by reflection segments of higher amplitude the decreasing seismic resolution is caused by limited seismic bandwidths and by the effects of constructive and destructive interference interference has the largest effects at the complexly interfingering buildup to basin transition or at the most detailed part of our model an understanding of these types of seismic limitations and their controls is important as we try to extract more and more stratigraphic information from seismic data p

siliciclastic sequence stratigraphy and petroleum geology where to from here modern sequence stratigraphy has its roots in the development of seismic stratigraphy in the late 1960s to middle 1970s peter r vail and his colleagues at exxon production research company developed stratigraphic techniques and principles based on time stratigraphic rather than rock stratigraphic lithostratigraphic relationships using multi fold seismic reflection data seismic stratigraphic units called depositional sequences were recognized within which the strata seemed conformable and free of any internal stratal discontinuities based on global seismic stratigraphic observations these workers inferred a eustatic signal and developed global sea level curves despite shortcomings the sequence stratigraphic approach represents a powerful geological tool at the field development scale improved reservoir source and seal prediction can enhance petroleum recovery at the exploration scale this approach can be instrumental in developing new play concepts in both mature and frontier basins to realize the full potential of this method earlier conceptual models must be substantiated and modified 80 refs 2 tabs

seismic models of a carbonate foreslope to basin transition picco di vallandro dolomite alps northern italy detailed geologic cross sections augmented by laboratory calibration of lithology and acoustic impedance have been used to produce synthetic reflection seismic sections of a carbonate foreslope to basin transition two areas from the picco di vallandro region of the dolomite alps were modeled a progradational section and a retrogradational backstepping section the resulting models show how these complex areas of strata interfingering might be displayed on conventional reflection seismic lines in the area of progradation rapid stratigraphic thinning below seismic detectibility coupled with abrupt impedance changes produces a reflection discontinuity between steeply dipping reflections of the foreslope and gently dipping parallel reflections of the basin section this apparent downlap surface marks the toe of slope for successive clinoforms but does not correspond to a discrete stratigraphic surface in the backstepping example similar stratigraphic thinning and impedance changes create an apparent onlap surface wavelet interference causes complications in both examples these models indicate how stratigraphic complexity can be simplified by the seismic reflection process and suggest that caution should be exercised when using seismic data to construct general models in areas of complex depositional geometries and rapidly changing facies

aspects of seismic character and extent of upper carboniferous coal measures gulf of st lawrence and sydney basins abstract a seismic facies related to upper carboniferous coal measures has been mapped in the gulf of st lawrence sydney basin region of atlantic canada the inferred original extent of this area of coal deposition is over 100 000 km 2 which is two to three orders of magnitude larger than the fault bounded terrestrial coal basins on the surrounding landmass the depositional continuity of this seismic sequence is on the scale of cyclothem deposition in the illinois basin and mid continent basin region of the united states and suggests an analogous stable cratonic shelf setting for the gulf of st lawrence sydney basin region in paleogeographic reconstructions for the late carboniferous cyclothems in a paleoequatorial setting in the mid continent basin of euramerica have been correlated with cyclothems in a similar setting on the russian platform the gulf of st lawrence and sydney basins lie midway between these two regions it will be an interesting test of these correlations to determine the exact age and environment of the coal measures seismic facies

drowning history of a miocene carbonate platform zhujiang formation south china sea abstract the identification and interpretation of drowning events in the geologic record can aid significantly to the reconstruction of the depositional tectonic and eustatic history of a study area and often improve reservoir and seal prediction in carbonate rocks the differentiation between drowned platforms showing a record of continuous deepening and those with a record of exposure followed by rapid deepening remains however problematic the zhujiang carbonate platform liuhua 11 1 field south china sea study shown here provides an example of an integrated approach combining high resolution geochemistry microfacies analyses and foraminiferal biostratigraphy in order to improve the reconstruction of environmental conditions prior during and after platform demise and drowning the zhujiang carbonate platform displays the following vertical succession of four facies types i skeletal grain facies with a miogypsinid lepidocyclinid dominated fauna deposited in a moderately deep heterostegina sp and spiroclypeids possibly capped by a subaerial exposure surface well rounded rhodoids representing a mesotrophic lagoon dominate the upper portions of the rhodoid facies iv pelagic marine shales of the hanjiang formation burying the carbonate platform after drowning this facies succession in combination with geochemical evidence suggests a deepening upward trend this trend might have been interrupted by transient subaerial exposure but no evidence for meteoric diagenesis was found at the drowning unconformity topping the carbonate platform instead microfacies analyses suggest that platform demise may be related to progressive changes in environmental conditions including increasing nutrient levels and or decreasing temperature up core towards the drowning unconformity these findings are of significance for those concerned with miocene carbonate factories and more specifically the demise of carbonate platforms in general