the relationship between shellbed type and sequence architecture examples from japan and new zealand abstract examples of lithology fossil content and taphonomic features of shellbeds and intervening less fossiliferous intervals are presented from four plio pleistocene successions shimosa group boso peninsula omma formation hokuriku area japan and okehu kai iwi and shakespeare groups in wanganui and the rangitikei group along the rangitikei river in new zealand as for pre pliocene 3rd and 4th order depositional sequences plio pleistocene 5th to 7th order depositional sequences contain a variety of shellbeds which are often associated with surfaces or intervals that are characterized by sedimentary condensation omission or erosion e g sequence boundaries ravinement surfaces downlap surfaces and condensed sections stratigraphic patterns of shellbed type tend to be similar and repetitive within a basin and a locality this demonstrates that a specific palaeogeography played an important role in determining the nature of shellbeds for example shellbeds formed in the context of toplap are common only in the shimosa group which was deposited in a moderately sheltered sea the palaeo tokyo bay toplap shellbeds are rare in other sequences formed in more open conditions despite the variability resulting from such basin characteristics common styles of shellbeds can be recognized that formed under conditions of marine onlap backlap downlap and toplap each type of shellbed has a characteristic fossil composition and taphonomy onlap and toplap shellbeds contain low diversity macrobenthic associations including glycymeris mercenaria paphies or other bivalves having robust shells which are often abraded or fragmented backlap shellbeds which are equivalent to the condensed section formed at the maximum transgression are characterized by dominance of epifaunal macrobenthos such as bryozoa brachiopoda pectinid and ostreid bivalves preserved in a slightly cemented glauconitic muddy matrix in contrast to fossils in such condensed sections the shell density and species diversity of downlap shellbed associations are rather low and in a few examples the macrobenthic association was buried rapidly in a lower unit of the highstand systems tract hst stratigraphically located above the condensed sections variations in the stratigraphic distribution of shellbed types are reflected in symmetrical and asymmetrical sequence architectures symmetrical sequences have roughly the same thickness of transgressive systems tracts tst and highstand systems tracts hst and have well segregated shellbeds that were formed during marine onlap and backlap asymmetrical cycles have very thin tsts and much thicker hsts and are characterized by the amalgamation of condensed onlap and backlap shellbeds such contrasting cycle architectures are interpreted to reflect inner symmetrical and outer asymmetrical shelf palaeodepositional settings the amalgamated onlap backlap shellbeds appear to be common in plio pleistocene sequences owing to the short duration of glacio eustatic sea level changes with dominant frequencies of 20 000 40 000 or 100 000 years shellbeds in the plio pleistocene are relatively simple and thin compared to those formed in ordinary third order depositional sequences infauna dominated benthic associations are generally more common than in third order cycles and epifaunal associations facilitated by taphonomic feedback on sediment starved shell gravel substrates occur only in the condensed section corresponding to maximum transgression in most plio pleistocene sequences

evolution of large normal faults evidence from seismic reflection data recent advances have been made in understanding how extensional faults and basins develop as faults propagate and link evidence for these linkage patterns in seismic reflection data can be seen in data from east africa early fault linkage patterns for boundary faults can follow three possible paths fault linkage and propagation occur either 1 prior to significant basin formation 2 after minor faulting has created an extensive area of subsidence or 3 during basin development the data from east africa show examples mainly of paths 1 and 2 transverse anticlines anticlines developed parallel to and in the hanging wall of the strike of faults associated with boundary faults are common features they represent either the sites of old synthetic transfer zones or a region of low fault displacement along the strike of a fault where two or more depocenters of different ages overlap as fault activity decreases over time displacement tends to be concentrated on progressively narrower parts of the fault this pattern is developed particularly well in continental rifts and may help discriminate late synrift sedimentation from postrift sedimentation where strike lines across the hanging wall of the fault are observable

discontinuity surfaces clinoforms and facies architecture in a wave dominated shoreface shelf parasequence abstract detailed outcrop analysis of a wave dominated shoreface shelf parasequence exposed in the book cliffs utah reveals minor stratigraphic discontinuities which define clinoforms two types of discontinuity are recognized each with a distinctive lithologic character and geometry nondepositional discontinuities are marked by an abrupt decrease in the thickness and amalgamation of storm generated event beds and are interpreted to record hiatuses in sedimentation these discontinuities define clinoforms with a concave upward geometry that dip gently 0 02 0 58 over distances of 800 6000 m down depositional dip erosional discontinuities are marked by an abrupt increase in event bed amalgamation grain size and sand content and are interpreted as enhanced storm wave scours these discontinuities define more steeply dipping 0 22 0 95 concave upward clinoforms that extend over 100 1600 m down depositional dip and 500 1500 m along depositional strike the distribution and amalgamation of minor stratigraphic discontinuities defines linear zones of distinctive facies architecture that are oriented parallel to the paleoshoreline trend using the simple assumption that the shoreface shelf equilibrium profile remained approximately constant for each type of discontinuity throughout shoreface migration the bruun rule intra parasequence facies architecture can be speculatively interpreted in terms of shoreline trajectory which reflects the balance between sediment supply and accommodation the resulting interpretations support the notion that shoreline trajectory exerts a strong control on intra parasequence facies architecture and preservation of the shoreface shelf profile

geologic framework of upper miocene and pliocene gas plays of the macuspana basin southeastern mexico this integrated study provides a geological and geochemical framework for upper miocene and pliocene siliciclastic gas plays in the macuspana basin structural controls for the plays are deep seated faults that tap mesozoic thermogenic gas sources areas of intense shale diapirism and folding and areas with structural inversion that could enhance trapping and reservoir productivity early neogene thrusting south of the basin triggered evacuation of oligocene shale along northwest dipping listric faults in the eastern and southeastern basin margin these faults are associated with large scale rollover structures and thick 500 m upper miocene shoreface and wave dominated deltaic complexes a second phase of extension in the early pliocene formed a set of broad southeast dipping listric faults in the western basin controlling thick accumulations of stacked pliocene shoreface deposits trap formation and enhancement in the southern basin margin are linked to late miocene to pliocene inversion the primary stratigraphic controls on play occurrence in the upper miocene in the onshore part of the basin are the regional facies distribution of northwest prograding shoreface and wave dominated deltaic systems there was a shift in pliocene sedimentation from the southeast to the west and northwest parts of the basin where thick successions of aggradational shoreface and wave dominated deltaic deposits accumulated in depocenters defined by shale evacuation along growth faults valley fill deposits in both the upper miocene and pliocene resulted from shortlived periods of base level change induced by either uplift on the southern basin margin or eustasy the offshore part of the basin is inferred to consist of deep water turbidite deposits that formed downdip westward of a hypothesized mixed clastic carbonate prograding complex from the yucatan platform three petroleum systems mesozoic paleogene lower neogene and upper miocene pliocene contributed to the hydrocarbon accumulations and hydrocarbon generation and migration in the basin principal upper jurassic lower cretaceous source rocks generated wet thermogenic gases and oil secondary lower tertiary source rocks generated dominantly dry biogenic gases mixtures of the two gas types are common numerous deep seated growth faults and faults serve as pathways for mesozoic sourced hydrocarbons surface seeps and abundant gas shows suggest that hydrocarbons are being generated today

anatomy of extremely thin marine sequences landward of a passive margin hinge zone neogene calvert cliffs succession maryland u s a abstract detailed examination of neogene strata in cliffs 25 35 m high along the western shore of chesapeake bay maryland reveals the complexity of the surviving record of siliciclastic sequences 150 km inland of the structural hinge zone of the atlantic passive margin previous study of the lower to middle miocene calvert plum point member and choptank formations documented a series of third order sequences 7 10 m thick in which lowstand deposits are entirely lacking transgressive tracts comprise a mosaic of condensed bioclastic facies and regressive highstand tracts are present but partially truncated by the next sequence boundary smaller scale fourth order cyclic units could not be resolved together these sequences constitute t e transgressive and early highstand tracts of a larger second order miocene composite sequence the present paper documents stratigraphic relations higher in the calvert cliffs succession including the upper miocene st marys formation which represents late highstand marine deposits of the miocene second order sequence and younger neogene fluvial and tidal inlet deposits representing incised valley deposits of the succeeding second order cycle the st marys formation consists of a series of tabular units 2 5 m thick each with an exclusively transgressive array of facies and bounded by stranding surfaces of abrupt shallowing these units which are opposite to the flooding surface bounded regressive facies arrays of model parasequences are best characterized as shaved sequences in which only the transgressive tract survives and are stacked into larger transgressive highstand and forced regression sets biostratigraphic analyses by others indicate that this onshore record contains the same number of third order 1 my duration units as present offshore and so thinning landward of the hinge zone was accomplished not by omission or erosion of entire cycles of deposition but instead by omission of some subsidiary elements e g lowstand tracts by erosional shaving of sequence tops removing the entire regressive tract in some sequences by a reduced number of component high order cycles surviving per larger set and by qualitative changes in the anatomy or composition of elements e g condensed transgressive tracts shaved sequences rather than parasequences all of these differences can be attributed to limited accommodation ut preservation of an onshore record of each baselevel cycle was probably also favored by the large amplitude and rapidity of eustatic fluctuations during the miocene

predictive distribution of shallow marine low porosity pseudomatrix rich sandstones in a sequence stratigraphic framework example from the ferron sandstone upper cretaceous usa reservoir quality prediction can be considerably improved with an integrated approach between sequence stratigraphy and diagenesis here we demonstrate that the occurrence of low porosity sandstones pseudomatrix rich i e matrix formed by mechanical compaction and squeezing of soft clasts in intergranular pores deposited in shallow marine settings can be predicted in a sequence stratigraphic framework these sandstones occur as lags bounding parasequences and thus may form baffles and barriers for vertical fluid flow and reservoir compartments between two sandstone bodies of adjacent parasequences the prediction of their occurrence and precise spatial distribution is therefore very useful for production of shallow marine reservoirs

progradational gravel beach sequences in a moderate to high energy microtidal marine environment the anatomy of progradational gravel beaches was analysed in two different tectonic settings the strongly subsiding messinian foreland basin of the eastern southern alps and the rising pleistocene marine terraces of the outer margin of the apenninic chain progradation took place near the mouths of fan delta or braid delta distributaries debouching in microtidal landlocked basins palaeo adriatic and palaeo ionian seas a wind wave climate comparable to that of the present day was characterized by periodic intense storm activity most of the beachface progradation is thought to have taken place during the post storm recovery and fair weather stages whereas the impact of storms is mostly recorded by the cutting of erosional surfaces on the beachface and by emplacement of poorly sorted and coarse grained gravels on the shoreface by storm intensified seaward trending flows and behind the highest berms by washover processes analysis of the sequences led to the identification of a number of typical divisions which are differently developed in the two settings compared here the characteristics of the apenninic sequences suggest a strongly variable wind wave climate with periodic changes from a relatively dissipative barred morphology during storms accompanied by strong longshore currents and rip development to a more reflective state typical of recovery and fair weather stages the southern alpine sequences on the other hand are characterized by poor evidence of barred morphology and of longshore currents and widespread effects of shear and gravity sorting in the lower beachface gravels these features indicate a comparatively more reflective average state due to location of beaches along the deeply embayed head of the palaeo adriatic and the very narrow directional width of the incoming wave spectrum which was almost shore normal most of the time in addition to well developed shape zonation of gravels the common presence of wave generated gravel megaripples in the southern alpine sequences indicates the greater influence of long period waves due to the greater available fetch distances in both settings the cyclicity is thought to be genetically related to minor changes of sea level

the architectural variability of small scale cycles in shelf and ramp clastic systems the controlling factors many sedimentary successions are composed of metre to decametre scale cycles exhibiting various stratal architectures that depend on the complex interplay among several syndepositional controlling factors these controlling factors may produce extremely different stratal and facies architectures along relatively brief distances in the same basin but in contrast they also may form similar architectures in basins that experience a radically different tectonic setting the recognition of factors that controlled the architecture of small scale cycles therefore is very important to reconstruct the depositional history of sedimentary successions these factors include 1 the interplay between the rate of accommodation development and the rate of sediment supply a s 2 the amplitude and shape of the relative sea level curve 3 the position in the shoreface shelf system 4 the basin physiography 5 the shoreline trajectory 6 the climate driven environmental energy 7 the siliciclastic input vs carbonate production shoreface to shelf small scale cycles can be grouped into three main categories r cycles showing a dominant regressive interval t r cycles with transgressive and regressive intervals of similar thickness t cycles showing a dominant transgressive interval although some depositional settings may favour the deposition of a particular type of cycle these cycle motifs appear to be mainly controlled by the interaction of local and wider scale controlling factors for example t cycles may be present in both subsiding and uplifting settings depending on the interplay between the a s and the other factors cited above as a result r t r and t cycles may be recognized within the same depositional system these evidences suggest that care must be taken to apply general models that predict the stratal architecture of cycles mainly in function of the long term a s the correct prediction of the cycle architecture is important also for hydrocarbon researches as the thickness of potential reservoir deposits is the result of the interplay among factors discussed here

sedimentology of rift climax deep water systems lower rudeis formation hammam faraun fault block suez rift egypt abstract in most marine rift basins subsidence outpaces sedimentation during rift climax times typically this results in sediment starved hangingwall depocentres dominated by deep marine mudstones with subordinate local development of coarser clastics in the immediate hangingwall derived from restricted catchments on the immediate footwall scarp to highlight the spatial variability of rift climax facies and the controls upon them we have investigated the detailed three dimensional geometry and facies relationships of the extremely well exposed miocene rift climax lower rudeis formation in the immediate hangingwall to the thal fault zone suez rift egypt detailed sedimentological analyses allows the lower rudeis formation to be divided into two contemporaneous depositional systems 1 a laterally continuous slope system comprising hangingwall restricted interpretation of individual facies facies relationships and their spatial variability indicate that deposition in the immediate hangingwall to the thal fault occurred via a range of submarine concentrated density flows surge like turbidity flows mass wasting and hemipelagic processes major controls on the spatial variability and stratigraphic architecture of the depositional systems identified reflect the influence of the steep footwall physiography accommodation and drainage evolution associated with the growth of the thal fault the under filled nature of the hangingwall depocentre combined with the steep footwall gradient result in a steep fault controlled basin margin characterised by either slope bypass or erosion with limited coastal plain or shelf area sediment supply to the slope apron deposits is controlled in part by the evolution and size of small footwall drainage catchments in contrast the localized submarine fan is interpreted to have been fed by a larger antecedent drainage network the structural style of the immediate footwall is also believed to exert a control on facies development and stratigraphic evolution in particular fault scarp degradation is enhanced by fault propagation folding which creates basinward dipping bedding planes in the pre rift footwall strata that large pre rift blocks slide on

the vertical compartmentalization of reservoirs an example from an outcrop analog crotone basin southern italy the lower pliocene shallow marine successions deposited within half graben subbasins exposed in the northern crotone basin southern italy are good examples illustrating the variable development of small scale cycles 2 15 m 6 6 49 ft thick within the hanging wall blocks of normal growth faults shallow marine small scale cycles forming the successions deposited near the immediate hanging wall of half graben subbasins show a clear alternation between well cemented shell rich intervals and weakly cemented siliciclastic sandstones in contrast the shallow marine successions deposited in hanging wall dip slope locations and in the footwalls show a poorly preserved cyclicity related to lower subsidence rates and a higher degree of cycle amalgamation the vertical alternation between well cemented carbonate rich intervals and less cemented sandstones creates a marked heterogeneity in the permeability of these shallow marine half graben fills which are sealed by impermeable offshore and lagoonal mudstones and may be considered as an outcrop analog of potential reservoirs as a consequence of the well developed cyclicity therefore the potential reservoir is vertically compartmentalized this feature tends to vanish toward the hanging wall dip slopes where the cyclicity is remarkably less appreciable the correct prediction of geometry and effective volume of reservoirs and in particular the recognition of their vertical compartmentalization have an important impact on hydrocarbon exploration and production the developed conceptual model of compartmentalized half graben fill may be useful in several contexts to study fault bounded basins from a reservoir point of view

high resolution sequence stratigraphy of clastic shelves iii applications to reservoir geology abstract high frequency clastic shelf sequences contain porous deposits consisting of coastal to shallow water sandstones and conglomerates which may represent very good reservoirs and therefore critical targets for exploration and production as well as for fluid hydrocarbon water or co2 storage the study of these reservoirs following a sequence stratigraphic approach is essential to predict their features and distribution within systems tracts forming high frequency sequences which in turn compose higher rank systems tracts and sequences a critical aspect to improve the exploitability of the reservoirs is their heterogeneity which directly affects the volume of the reservoirs and determine internal compartmentalization the heterogeneity can be primary related to depositional processes influencing grain size and facies distribution and secondary related to diagenesis in particular the primary heterogeneity is referred to the facies variability from distal to proximal settings to the accumulation of condensed shell beds and to facies characteristics of bedsets whereas the secondary heterogeneity derives from diagenetic processes at sequence stratigraphic surfaces and facies contacts and within sandbodies both the distribution of reservoirs and their heterogeneity can be predicted following a high resolution sequence stratigraphic approach ultimately the integration of subsurface data with the analysis of outcrop analogs is essential to better understand the features of clastic shelf reservoirs and to develop 3d models of fluid migration

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

sedimentology and high resolution sequence stratigraphy of the late middle to late miocene angostura formation western borbon basin northwestern ecuador an integrated analysis of facies and palaeontological content of the middle to late miocene c 12 4 9 1 ma angostura formation led to the identification of facies associations indicative of shoreface and inner shelf settings the angostura formation comprises eight high frequency sequences that are stacked to form a tectonically driven lowstand sequence set the most complete examples of sequences are bounded by transgressively modified unconformities and exhibit a threefold subdivision 1 a basal suite of deepening upward shoreface sediments transgressive systems tract including a base of cycle shell concentration 2 a mid cycle shell bed consisting of molluscan shells dispersed in a matrix of inner shelf muddy fine grained sandstones 3 a shallowing upward unit of inner shelf to lower shoreface sediments almost barren of mollusc fossils highstand systems tract biostratigraphic constraints allowed a reasonable correlation between sequence bounding unconformities and the late middle to late miocene high frequency glacio eustatic changes derived from recent 18 o studies this correlation has far reaching implications and leads to the following conclusions 1 glacio eustasy in tune with oxygen isotope changes at fourth order frequency 200 ka 1 ma duration may have been the principal factor regulating stratigraphic packaging in the angostura formation 2 these sequences provide an excellent shallow marine outcrop record of late middle to late miocene antarctic glaciations

helium transfer from water into quartz crystals a new approach for porewater dating several important fundamental and applied problems require a quantification of slow rates of groundwater flow to resolve these problems helium appears to be a promising tracer in this contribution we discuss a new approach which gives the helium inventory in a rock pore water system by using the relevant mineral record i e without extraction and investigation of the porewater samples some u and th poor minerals such as quartz quartz separates from permo carboniferous formation sandstone shale interlayering molasses basin northern switzerland hereafter pcf are used in this study contain excessive helium having migrated into their internal helium accessible volume hav from the surrounding porewater i n tolstikhin b e lehmann h h loosli a gautschi helium and argon isotopes in rocks minerals and related groundwaters a case study in northern switzerland geochim cosmochim acta 60 1996 1497 1514 these volumes are estimated by using helium as a nano size penetrating tool i e by saturation of the minerals with helium under controlled pressure temperature conditions and subsequent measurements of the helium saturated concentrations in the quartz separates hav total volume ratios vary from 0 017 to 0 16 along with the measured initial unsaturated he concentration the hav gives the internal helium pressure the mean value obtained for 7 samples 25 sample aliquots is p 0 45f0 15 atm 1 r the product of helium pressure and solubility 7 35 10 3 cc stp he cc h2o for the temperature and salinity of pcf aquifers reported in f j pearson w balderer h h loosli b e lehmann a matter t peters h schmassmann a gautschi applied isotope hydrogeology a case study in northern switzerland elsevier amsterdam 1991 439 pp is the mineral derived he concentration in the respective porewater cpw 0 0035f0 0017 cc he cc h2o this value is in full accord with measured he concentrations in pcf aquifers cpcf varying from 0 0045 to 0 0016 cc he cc h2o this agreement validates the proposed approach and also shows that the mineral porewater helium concentration equilibrium has been established indeed estimates of the he migration rates through our quartz samples show that in 6000 years the internal pressure should equilibrate with he concentration in related porewater of pcf and this time interval is short compared to independent estimates i n tolstikhin b e lehmann h h loosli a gautschi helium and argon isotopes in rocks minerals and related groundwaters a case study in northern switzerland geochim cosmochim acta 60 1996 1497 1514 the helium inventory in the rock porewater assemblage shows that helium abundance in pore waters is indeed important in shale samples with 15 porosity porewaters contain more helium than the host minerals altogether porewater heliumconcentration profiles available from the mineral record along with helium production rates are input parameters allowing model s of helium migration through a hydrological structure to be developed quite high helium concentrations in pcf porewaters imply slow removal mechanisms which will be discussed elsewhere

stratigraphy and sedimentology of fault controlled backstepping shorefaces middle pliocene of crotone basin southern italy abstract the middle pliocene sedimentary succession of the crotone basin in the calabria peloritani terrane southern italy was deposited during extensional tectonism dominated by a system of horst and half grabens the studied succession spartizzo lagoonal clays and scandale shallow marine deposits is up to 250 m thick and represents a barrier lagoon system that spans a tectonically controlled transgressive phase the succession is internally organised into six higher frequency cycles 20 80 m thick most of these cycles are formed by transgressive lagoonal deposits separated from the overlying regressive shoreface units by a wave ravinement surface lowstand fluvial deposits were recognized locally at the base of the last cycle the shoreface units are up to 50 m thick and typically consist of a coarsening upward succession of isolated to amalgamated hummocky cross strata that merge upwards into swaley and trough cross strata ne trending synsedimentary normal faults strongly controlled the deposition and enhanced subsidence and thickness expansion within the half graben basins

basin physiography and tectonic influence on sequence architecture and stacking pattern pleistocene succession of the canoa basin central ecuador facies shell bed features and sequence stratigraphic framework for the shallow marine pleistocene upper canoa and tablazo formations are presented based on outcrop data from the southern coast of cabo san lorenzo ecuador sediments of this succession exhibit a distinct cyclic pattern consisting of a stack of eight depositional sequences cyclothems likely developed under the main control of orbitally induced sea level changes as a rule within the studied interval an idealized cyclothem is composed of a transgressive systems tract tst and a highstand systems tract hst whereas deposits attributable to the lowstand and falling stage systems tracts are not present transgressive lithosomes may be defined by estuarine deposits interposed between the sequence boundary and the ravinement surface back barrier wedge and by upward fining shoreface to inner shelf facies successions above the ravinement backstepping shelf wedge separated by an expanded siliciclastic core hiatal shell concentrations occur at the base onlap shell beds and the top backlap shell beds of the transgressive shelf wedges and some occur at the base of highstand systems tracts downlap shell beds on the basis of sedimentary facies geometry taphonomy and paleoecology of shell beds and the nature of the transition between siliciclastic and mollusk bearing sediments cyclothems were classified into two main types that show dependence upon paleoshoreline morphological configuration sheltered in the upper canoa formation and exposed in the tablazo formation notwithstanding the different synsedimentary tectonic and climatic regimes the ecuadorian cyclothems share basic patterns of condensation and facies assemblages with other roughly coeval cyclothemic successions around the world this suggests that 1 hiatal shell bed development is not just a temperate latitude phenomenon 2 a global process such as glacio eustatic sea level change is the primary mechanism of control for the general architecture of sequences and 3 specific paleogeographic settings play an important role by determining the taphonomic and paleoecologic characteristics of key shell beds the nature of their contacts with the encasing sediments and the type of the component set of facies at a multicycle time scale tectonics influenced the long term trend of the relative sea level changes and consequently the large scale stratigraphic organization owing to the continued tectonic uplift of the area successive high frequency depositional sequences are nested to form a longer order falling stage sequence set

a sequence stratigraphic model for an intensely bioturbated shallow marine sandstone the bridport sand formation wessex basin uk the bridport sand formation is an intensely bioturbated sandstone that represents part of a mixed siliciclastic carbonate shallow marine depositional system at outcrop and in subsurface cores conventional facies analysis was combined with ichnofabric analysis to identify facies successions bounded by a hierarchy of key stratigraphic surfaces the geometry of these surfaces and the lateral relationships between the facies successions that they bound have been constrained locally using 3d seismic data facies analysis suggests that the bridport sand formation represents progradation of a low energy siliciclastic shoreface dominated by storm event beds reworked by bioturbation the shoreface sandstones form the upper part of a thick up to 200 m steep 2 3 mud dominated slope that extends into the underlying down cliff clay clinoform surfaces representing the shoreface slope system are grouped into progradational sets each set contains clinoform surfaces arranged in a downstepping offlapping manner that indicates forced regressive progradation which was punctuated by flooding surfaces that are expressed in core and well log data in proximal locations progradational shoreface sandstones corresponding to a clinoform set are truncated by conglomerate lags containing clasts of bored reworked shoreface sandstones which are interpreted as marking sequence boundaries in medial locations progradational clinoform sets are overlain across an erosion surface by thin 10 m and overlie conglomerate lags at sequence boundaries sequence boundaries are thus interpreted as being amalgamated with overlying transgressive surfaces to form composite erosion surfaces in distal locations oolitic ironstones that formed under conditions of extended physical reworking overlie composite sequence boundaries and transgressive surfaces over most of the wessex basin clinoform sets corresponding to high frequency sequences are laterally offset thus defining a low frequency sequence architecture characterized by high net siliciclastic sediment input and low net accommodation aggradational stacking of high frequency sequences occurs in fault bounded depocentres which had higher rates of localized tectonic subsidence

brittle deformations in the upper pleistocene deposits of the crotone peninsula calabria southern italy abstract the structural setting of the crotone peninsula calabria southern italy is discussed in this paper structural analyses were carried out both on a regional and an outcrop scale to detect the main structural systems and the stress field which affected the area during the late pleistocene the tectonic features observed in the area are represented by normal faults and extensional joints the regional scale faults are arranged in five main systems striking ene wsw nne ssw e w nw se and nnw sse they are responsible for the dislocation of four marine depositional units cutro terrace correlatable with the isotopic stage 7 s leonardo campolongo isola di capo rizzuto terrace correlatable with the isotopic substage 5e le castella capo rizzuto terrace correlatable with the isotopic substage 5c and capo colonne terrace correlatable with the isotopic substage 5a in several distinct terraces from the studies carried out on a mesostructural scale it is possible to conclude that for the last 200 000 yrs the crotone peninsula was affected by an extensional stress field the comparison between the average uplift rates calculated for the crotone peninsula terraces and those computed for several upper pleistocene deposits located in sicily calabria and campania suggests that the intense tectonics which affected the crotone peninsula can be related to the geodynamic activity of the calabrian arc

structural evolution of the tyrrhenian back arc basin abstract the tyrrhenian basin has developed as a marginal basin through drifting of the calabrian sicilian arc system towards the east southeast the main structural features of the basin result from this movement the tensional structures normal faults of the margins are mainly aligned n10 to n30 e the transform faults are oriented n110 n120 e except for a previous structuralization linked to the western mediterranean rifting and drifting the first extensional movements affected the tyrrhenian area as early as lower miocene time during the post burdigalian nevertheless the main rifting phase which led to oceanic accretion was initiated during the late tortonian the narrow central oceanic area generated mainly around the early pliocene is restricted to the rift s axis the marginal basin type of evolution of the tyrrhenian sea is most probably directly linked to subduction of the ionian lithosphere nevertheless interferences between collision in the surrounding apennines calabria or sicilides and subduction processes have dominated this special back arc basin evolution since late tortonian time the tyrrhenian arc shows a regional n120 e oriented tensional pattern short compressional events occur briefly in middle pliocene and middle pleistocene times correlated with brief paroxysmal phases of extension and subsidence the deformation depends on the presence of a subduction zone parallel to the calabrian arc swell which allows the migration of the unblocked segments of the arc in a n120 e direction

storm and tide dominated shorelines in cretaceous moosebar lower gates interval outcrop equivalents of deep basin gas trap in western canada the moosebar and gates formations crop out in the deformed foothills belt south of fort st john british columbia they permit examination of the depositional environments of sandstones and conglomerates that are gas bearing in the equivalent wilrich falher interval of the deep basin of alberta and british columbia the moosebar gates interval consists of several upward coarsening and marine to nonmarine sequences moosebar bioturbated shales pass upward into turbidites and offshore storm deposits flow directions indicate a north dipping paleoslope a second coarsening upward sequence at the top of the moosebar and base of the gates terminates in a lenticular fluvial conglomerate up to 30 m thick which is overlain by coals carbonaceous mudstones and sandstones above the carbonaceous zone a major lateral facies change is observed fluvial conglomerates in the south grade into beach conglomerates northward the upper part of the beach conglomerate consists of exposed three dimensional storm berms at least 500 m long up to 1 5 m high with wavelengths of 12 to 24 m the berms trend east west seaward of the conglomerate beach are herringbone cross bedded tidal sandstones with a marine trace fauna graded sharp based conglomerates also are present probably washed out to sea by storms farther north at the same stratigraphic level is a series of partly overlapping conglomerate bars up to 5 m thick and 40 to 50 m across the tops of these bars are covered with storm formed symmetric conglomeratic dunes details of the orientation and geometry of these conglomerate bodies along with their internal structure and pebble fabrics suggest that four major environments fluvial beach offshore conglomerate bars and offshore graded storm conglomerates should be identifiable and predictable in the subsurface

sequence stratigraphy and architectural variability in growth fault bounded basin fills a review of plio pleistocene stratal units of the crotone basin southern italy field examples from the pliocene to pleistocene succession of the crotone basin document the variability of stratal architecture in syntectonic units deposited in normal fault bounded basins relatively thick trangressive intervals are common within these successions as shown in the zinga 2 zinga 3 and strongoli stratal units transgressive packages are formed by lagoonal mudstones that are abruptly overlain by shoreface sandstones aggradational highstand shallow marine packages are typical of the lower pliocene succession in half graben basins these deposits resulted from balanced conditions between the rate of sediment supply and the rate of creation of accommodation relatively thick forced regressive deposits are common within basins during phases where the accommodation supply ratio is low e g the middle pleistocene san mauro sandstone these deposits influenced by growth faulting and folding recorded base level lowering linked to glacio eustasy a complex stratal architecture may be the consequence of the alternation between tectonic subsidence and uplift e g the serra piani stratal unit such variations are thought to be related to the onset of an earliest mid pliocene transpressional tectonic phase the studied deposits therefore show a marked tectonic control that strongly influenced their stratal architecture these examples represent interesting cases of sequence stratigraphic analysis in growth faulted contexts

carbonate cementation in a sequence stratigraphic framework upper cretaceous sandstones book cliffs utah colorado abstract three macroscopic diagenetic features can be recognized in the sandstones of the upper cretaceous desert member of the blackhawk formation and castlegate sandstone of the mesaverde group exposed in the book cliffs utah each of which have distinctive form geometry and stratigraphic distribution diagenetic alterations are 1 leached zones whitecaps up to 10 m thick beneath coal beds 2 large up to 8 m concretionary carbonate cemented bodies in amalgamated shoreface and thin fluvial sandstones and 3 thin up to 2 m laterally extensive carbonate cemented horizons beneath major marine flooding surfaces each feature has distinct petrographic and geochemical signatures and formed through discrete diagenetic processes large isolated carbonate cemented bodies are composed of ferroan dolomite most of which precipitated during early diagenesis field and petrographic data coupled with stable isotope data early cements 13c 2 5 to 3 4o oo vpdb 18o 7 8 to 12 0o oo vpdb 87sr 86sr 0 7078 later cements 13c 3 1 to 5 7o oo vpdb 18o 12 0 to 15 1o oo vpdb 87sr 86sr 0 7093 suggest precipitation from meteoric fluids input into sediments during times of relative sea level fall the source of carbonate for the dolomite cement was dissolution of detrital dolomite from beneath coals by organic acids and subsequent mobilization by meteoric fluids carbonate precipitation in laterally extensive cement horizons appears to have started as a result of hiatus in sediment accumulation during marine flooding events relative sea level rise cement precipitation in these horizons continued through sediment burial as a result of organic matter oxidation reactions in overlying organic rich mudstones the results of this study show a link between sedimentation related to changes in relative sea level and diagenesis leading to the potential for the development of process based predictive models of early diagenesis in depositional successions

distribution of diagenetic alterations in fluvial deltaic and shallow marine sandstones within a sequence stratigraphic framework evidence from the mullaghmore formation carboniferous nw ireland abstract the distribution of diagenetic alterations in the fluvial deltaic and shallow marine arkosic to subarkosic sandstones average q72f26l02 of the mullaghmore formation carboniferous nw ireland can be predicted within a sequence stratigraphic framework eogenetic calcite 18opdb 13 3 to 6 5 13cpdb 3 0 to 3 4 and 87sr 86sr 0 706721 to 0 709227 and ferron dolomite feco3 8 12 mol 18opdb 14 2 to 7 8 13cpdb 1 4 to 1 0 and 87sr 86sr 0 709051 to 0 709167 occur in bioclast rich transgressive lag deposits at parasequence boundaries and transgressive surfaces and in wave influenced deltaic highstand systems tract hst deposits mesogenetic illite chlorite baroque dolomite feco3 16 mol 18opdb 14 2 to 12 7 13cpdb 3 8 to 1 0 quartz and calcite 18opdb 15 7 to 12 5 13cpdb 5 8 to 3 7 and 87sr 86sr 0 709016 to 0 709122 were formed mainly in the bioclast poor deposits which were not pervasively cemented by carbonates during near surface eodiagenesis these deposits include fluvial incised valley sandstones of lowstand systems tract lst and fluvial dominated deltaic sandstones of transgressive systems tract tst and hst illite is the dominant diagenetic clay mineral in the fluvial incised valley sandstones of lst possibly because of simultaneous albitization of k feldspars conversely chlorite dominates in the fluvial dominated deltaic sandstones of tst and hst because of the presence of suitable precursor clays the integration of diagenesis into sequence stratigraphic framework of clastic sequences should improve the ability to predict the spatial and temporal distribution of diagenetic alterations and related reservoir quality modifications of sandstone deposits

sedimentology and high frequency sequence stratigraphy of a forearc extensional basin the miocene caleta herradura formation mejillones peninsula northern chile abstract facies and sequence stratigraphic interpretation for the 380 m thick caleta herradura formation miocene are presented based on detailed and comprehensive outcrop data from the caleta herradura half graben mejillones peninsula northern chile the caleta herradura formation contains an array of lithofacies comprising sandstones sandy mudstones diatomites and breccio conglomerates that are interpreted as the products of inner shelf to non marine depositional settings complete exposure allows for recognition of a number of distinct and laterally persistent key stratal surfaces that permitted the identification of twenty five high frequency meter to tens of meters scale sequences based on their internal organization two main motifs of such unconformity bounded depositional packages can be distinguished deepening and deepening to shallowing upwards transgressive and highstand systems tracts were resolved based on such facies stacking patterns the origin of sequences is difficult to decipher and remains somewhat uncertain however several lines of direct and indirect evidence constrain interpretations for both the sequence architecture and bounding unconformities and help to discriminate between the various mechanisms that may have driven their development in essence these demonstrate that neither tectonically driven sea level oscillations nor climatically induced changes in sediment supply can adequately explain the distinctive features of unconformities and the facies architecture of sediments they delimit instead these high frequency changes in relative sea level are best explained as a consequence of glacio eustatic oscillations the contemporaneous deep ocean proxy records appear to support a causal link between the observed stratigraphic cyclicity and glacio eustatic changes in sea level due to modulation of short term milankovitch scale events by longer period astronomical variations however the type of astronomical forcing remains elusive hindered by lack of adequate age controls and a poor understanding of pacing mechanisms of high frequency climate changes during the middle to late miocene

regressive and transgressive cycles in a rift basin depositional model and sedimentary partitioning of the middle jurassic hugin formation southern viking graben north sea abstract the jurassic hugin formation consists of shallow marine sandstones that belong to a significant hydrocarbon reservoir in the sleipner area in the norwegian north sea the formation encompasses coarsening upward units of mouth bar and shoreface facies interpreted to record delta outbuilding during regression and fining upward units with tidal channel dune and tidal flat facies interpreted as part of an estuary environment during transgression the correlations reveal that the studied part of the hugin formation consists of 8 sequences each with a transgressive and a regressive unit representing the transgressive systems tract and the highstand systems tract respectively the sequences are stacked retrogradationally landward as a result of rapid tectonic subsidence and rifting of the viking graben rifting led to the development of an elongate graben where tidal currents were amplified wave action damped and longshore drift as sediments supply reduced or absent lowstand and forced regressive systems tracts are not identified and their absence is interpreted to reflect suppression of relative sea level falls in a rapidly subsiding basin where the basin subsidence rate outpaced any potential fall in eustatic sea level through facies interpretation and sequence stratigraphic correlations between wells these regressive and transgressive units are shown to exhibit characteristic thickness trends in the form of sigmoidal shaped wedges stacked in an offset manner in a landward to basinward orientation these thickness trends illustrate sediment partitioning within the sequences and are explained by the relationship between accommodation versus sediment supply in terms of mass balance during regression the focus of sedimentation was pushed basinward and during transgression it was pushed landward as sediments were trapped there the mapping of these sequence stratigraphic units serves as input to reservoir models and to help increase recovery and identify new exploration targets

relationships between fault controlled subsidence and preservation of shallow marine small scale cycles example from the lower pliocene of the crotone basin southern italy abstract the northern part of the crotone basin southern italy was characterized by the activity of pliocene growth faults bounding half graben sub basins the thickest unit deposited during growth fault activity is the lower pliocene belvedere formation up to 450 m thick which shows a small scale highly regular rhythmic cyclicity this sandstone unit was deposited in a shallow marine environment and its accumulation was mostly influenced by storm processes and locally by flows in tectonically confined areas the meter scale cycles are represented by rhythmic alternations between shell rich intervals characterized by storm structures or large scale cross sets and shell poor sandy intervals that are commonly burrowed and poorly stratified the better preserved cycles commonly show a fining upward trend with minor progradation in their upper part and may be bounded at the base by a shell lag the deposition of large scale cross sets is thought to be the consequence of the creation of fault scarps which led to tectonic confinement in the half graben basins in the tectonically confined areas tidal currents were enhanced and large subaqueous dunes migrated the evidence suggests that the observed cyclicity was generated by sea level and climatic variations that controlled the sediment input into the basin the relationship between large scale cross sets and tectonic confinement demonstrates that local extensional tectonics significantly influenced the sedimentation the excellent preservation of the observed small scale cycles is thought to be the consequence of deposition in the highly subsiding half graben sub basins on the structural highs this cyclicity is amalgamate and less appreciable the data presented may be significant for a better understanding of the role of subsidence in preserving sedimentary successions in these growth faulted settings

raised pleistocene marine terraces of the crotone peninsula calabria southern italy facies analysis and organization of their deposits abstract wide marine terraces well known in the italian literature are present in the crotone peninsula ionian calabria they are related to the interplay between pleistocene sea level changes and the progressive uplift of the calabrian arc from the middle pleistocene onwards we present a description of facies organization and stratigraphical characteristics of the terrace deposits along with a new geological map of the area all the marine terraces unconformably overlie a plio pleistocene slope succession known as cutro clay the oldest and highest terrace named cutro terrace is placed between 90 and 200 m of elevation and is gently inclined south eastwards four younger terraces placed at progressively lower elevations and dipping seawards at low angles have been recognized the sedimentary deposits of the terraces are represented by mixed carbonate and siliciclastic bodies up to 10 m thick algal reefs and grainstone to rudstone deposits are common in the south eastern part of the study area whereas mostly siliciclastic sandstone units of shoreface environments are more abundant northwards and westwards the deposits of some terraces are made up of minor cycles bounded by subaerial transgressive and flooding surfaces referred to minor sea level fluctuations nne ene e and wnw trending normal fault systems are present within the study area and dissect the marine terraces specifically the activation of ene trending faults took place after the formation of the oldest terrace but prior to the formation of the younger terraces

sequence stratigraphy of sixth order 41 k y pliocene pleistocene cyclothems wanganui basin new zealand a case for the regressive systems tract this study is based on a late pliocene and early pleistocene approximately 2 6 1 7 ma succession about 1 km thick of 20 sixth order 41 k y duration cyclothems of shelf origin exposed in the rangitikei river valley in the eastern part of wanganui basin the cyclothems correlate with 18 o isotope stages 100 58 and each 41 k y glacialinterglacial stage couplet is represented by an individual depositional sequence comprising transgressive highstand and regressive systems tracts unlike most examples inferred from the stratigraphic record these systems tracts were deposited during phases of known sea level cycles indicated by the contemporary oxygen isotope ice volume curve because of the high rate of subsidence of wanganui basin glacioeustatic sea level falls during most cycles were not of sufficient magnitude to expose the outer shelf thus the rangitikei section provides an exceptional example of regressive strata deposited landward of the contemporary shelf break simple one dimensional modeling shows that moderate to high rates of basin subsidence 1 2 mm yr and low rates of sedimentation 0 2 mm yr during transgressions combined to produce an accommodation surplus at the relative highstand this surplus accommodation was infilled during the late highstand and ensuing fall partly by aggradational highstand systems tract shelf siltstone and chiefly by strongly progradational shoreface sediments of the regressive systems tract rangitikei regressive systems tracts are distinguished from forced regressive systems tracts sensu hunt and tucker 1992 by their different stratal geometry by definition forced regressive systems tracts display an erosional contact with the underlying highstand systems tracts and typically occur as a series of downstepped disjunct shoreline wedges stranded on the shelf and or slope in contrast regressive systems tracts exhibit a gradational lower contact above which parasequences are stacked in a strongly progradational pattern terminated by the superjacent sequence boundary cyclothems display two types of motif termed rangitikei dt depositional transgression and rangitikei nt nondepositional transgression which include the following architectural elements in ascending stratigraphic order 1 a basal sequence boundary that is coincident with either the transgressive surface of erosion which displays small scale up to 50 cm erosional relief and may be penetrated by the ichnofossil ophiomorpha or its deeper water correlative conformity 2 either a thick 5 30 m transgressive systems tract comprising a deepening upward nearshore to inner shelf mixed carbonate siliciclastic lithofacies succession depositional transgression or a thin 2 m transgressive systems tract comprising condensed fossiliferous facies deposited on the sediment starved offshore shelf nondepositional transgression 3 a sharp downlap surface separating condensed fossiliferous facies of the transgressive systems tract from terrigenous siltstone of the superjacent highstand systems tract 4 a highstand systems tract comprising a 10 20 m thick interval of aggradational shelf siltstone and 5 a thick up to 45 m progradational inner shelf to shoreface lithofacies assemblage ascribed to the regressive systems tract condensed shell beds are associated with intrasequence and sequence bounding discontinuities and together with the sedimentological and stratal characteristics of the sequences are important indicators of stratigraphic architecture four types of shell bed are associated with surfaces formed by four different types of stratal termination onlap backlap downlap and flooding surface shell beds cf kidwell 1991 are associated respectively with the transgressive surface of erosion apparent truncation at the top of the transgressive systems tract the downlap surface and local marine flooding surfaces a fifth shell bed type termed a compound shell bed forms in offshore environments where the downlap surface converges with the sequence boundary and elements of both the downlap and the backlap shell beds become mixed or superposed the shell beds mark zones of stratal attenuation and can be used as surrogates for seismic discontinuities when applying sequence stratigraphic concepts at outcrop scale

gravity constraints on the crustal structure and slab evolution along a transcarpathian transect abstract a new unified bouguer anomaly map of the carpathian arc and the pannonian basin has been compiled from previously prepared and recently published gravity maps in order to constrain the crustal structure and the tectonic evolution of the area a two dimensional gravity model is presented along a western carpathians pannonian basin southern carpathians transect the model is based on deep seismic lines where available and on detailed geological sections the results confirm that the extensional crustal structure of the pannonian basin revealed by deep seismic surveys agrees with the gravity data furthermore they suggest that the western and southern carpathians area at different stages of their evolution the subducted oceanic slab under the western carpathians has already been assimilated to the asthenosphere while a crustal slab is still present under the southern carpathians these findings are compatible with the observation that the last major phase of crustal shortening terminated at the early middle miocene in the western carpathians but continued throughout the pliocene in the southern carpathians

numerical modelling of depositional sequences in half graben rift basins a three dimensional numerical model of sediment transport and deposition in coarse grained deltas is used to investigate the controls on depositional sequence variability in marine half graben extensional basins subject to eustatic sea level change using rates of sea level change sediment supply and fault slip reported from active rift basins the evolution of deltas located in three contrasting structural settings is documented 1 footwall sourced deltas in high subsidence locations near the centre of a lault segment 2 deltas fed by large drainage catchments at fault tips and 3 deltas sourced from drainage catchments on the hangingwall dip slope different es in the three dimensional form and internal stratigraphy of the deltas result from variations in tilting of the hangingwall and the impact of border fault slip rates on accommodation development because subsidence rates near the centre of fault segments are greater than all but the fastest eustatic falls footwall sourced deltas lack sequence boundaries and are characterized by stacked highstand systems tracts high subsidence and steep bathymetry adjacent to the fault result in limited progradation in contrast the lower subsidence rate settings of the fault tip and hangingwall dip slope deltas mean that they are subject to relative sea level fall and associated fluvial incision and forced regression low gradients and tectonic tilting of the hangingwall influence the geometry of these deltas with fault tip deltas preferentially prograding axially along the fault creating elongate delta lobes in contrast broad sheet like delta lobes characterize the hangingwall dip slope deltas the model results suggest that different systems tracts may be coeval over length scales of several kilometres and that key stratal surfaces defining and subdividing depositional sequences may only be of local extent i urthermore the results highlight pitfalls in sequence stratigraphic interpretation and problems in interpreting controlling processes from the preserved stiatigraphic product

calcarenite and sapropel deposition in the mediterranean pliocene shallow and deep water record of astronomically driven climatic events introductionsapropelformationinthemediterra nean basin during the pliocene andquaternary has been widely debated the time and phase relationship ofsapropels to astronomic cycles hasbeen established and a high reso lution sapropel based astronomictime scale has been reconstructedfor mediterranean neogene deposits e g hilgen 1991 lourens etal 1996 hilgenetal 1999 sapropels provide a deep water basin wide record of astronomicallydriven climatic events they occur asindividualcyclesthatcanbecorrelatedtoprecessionalminima 19 23kyr orassmall andlarge scaleclusters 100 400kyr withmoredevelopedindivid ualsapropels correspondingtoeccen tricity maxima obliquity 41kyr controls the thin thick pattern ofcyclicity e g lourens etal 1996 pliocene large scale sapropel clustersfollowmajorcoolingeventsreferredtoas the forerunners of the quaternarynorthern hemisphere glaciation keigwin 1987 raymo etal 1989 tiedemann etal 1994 rio et al 1997 these events dated at 3 1 2 7and 2 1ma are recorded in themediterranean basins by importantmicro and macrofaunal turnovers monegattiandra 2001 palaeoceanographic events relatedto sapropel formation have usuallybeen studied from a deep water per spective theirshallow waterrecordisless well known the stratigraphicarchitectureofplioceneshallow waterdepositsoftheapennine maghrebianbasins is frequently characterized bythe rhythmic alternation of coarse grained calcarenites and siliciclasticmudstones our observations suggestthat calcarenites are not randomlydistributed in the stratigraphic col umn but they occur in well de nedtimeslicesstartingfrom3 1ma theycanbetracedthroughdi erentgeody namicsettings suggestinganin uenceof climatic and or eustatic forcing individual calcarenites occur in clus tershavingthesameageaslong termsapropelclusters thiscorrelationsug gests that tightly linked factors con trolledtheformationofbothdeposits this paper documents the large scale 10

sequence stratigraphic responses to shoreline perpendicular growth faulting in shallow marine reservoirs of the champion field offshore brunei darussalam south china sea the champion field offshore brunei darussalam comprises a thick middle upper miocene succession of shallow marine sediments associated with major growth fault systems and deposited as part of the paleo baram delta the structural evolution of the champion field has resulted in an unusual situation where growth faults strike perpendicular to the paleoshoreline orientation shoreface parasequences and tidal estuarine complexes are mapped directly from three dimensional 3 d seismic data calibrated from wells the seismic interpretations provide chronostratigraphic correlations that are more robust than some well based markers because the seismic interpretations have better spatial coverage depositional responses to growth faulting are defined by two end member models 1 layer thickening and 2 addition of layers in the hanging wall layer addition makes correlation across faults problematical growth may be accommodated by either or a combination of these processes and areas of layer addition are related to transgressive events in the hanging wall topographic changes thought to be associated with fault movements may fundamentally change shoreline type sand body orientations and petrophysical properties for discrete periods of time these stratigraphic complexities are linked spatiotemporally to accommodation history but cannot be adequately predicted from well data alone

high resolution sequence stratigraphy of clastic shelves v criteria to discriminate between stratigraphic sequences and sedimentological cycles abstract in contrast to high frequency sequences driven by high magnitude relative sea level changes those controlled by short term minor relative sea level and or sediment supply changes may be difficult to discriminate from sedimentological cycles i e bedsets unrelated to shoreline shifts especially in case of limited outcrop exposures in fact meter scale fully shallow marine high frequency sequences and typical meter scale bedsets may share a similar simple facies succession documenting either an upward increase or decrease of event beds it is therefore necessary to define a set of criteria that allows to discriminate between thin high frequency sequences and bedsets based on sedimentological stratigraphic micropaleontological mineralogical and diagenetic data in particular the sedimentological and stratigraphic criteria that aid discriminating between high frequency sequences and bedsets include 1 occurrence of environmental changes across bounding surfaces 2 occurrence of water depth changes across bounding surfaces 3 physical appearance of bounding surfaces and associated substrate controlled ichnofacies 4 lateral extent of bounding surfaces 5 presence of condensed deposits 6 cycle thickness 7 recognition of a set of clinoforms in a regressive shoreface shelf succession moreover the formation of wave ravinement surfaces in the shoreface is usually associated with an increase in the percentage of benthic micro foraminifera specimens documenting energetic conditions and in the abundance of heavy minerals extensive cementation may also be found just below and or above transgressive surfaces however the integration of more than one of the above criteria is necessary to reliably discriminate between sequence stratigraphic surfaces and therefore high frequency sequences and bedset boundaries the latter being only related to changes of energy level and or local sediment supply without shoreline shifts this work is essential to correctly reconstruct the sequence stratigraphic framework of a given succession and to interpret the factors that controlled the cyclicity

composite sedimentary record of falling stages of pleistocene glacio eustatic cycles in a shelf setting crotone basin south italy abstract a thick pleistocene shelf and nearshore cyclical succession was deposited in the s mauro sub basin of the crotone basin southern italy the regressive units of the cycles are mostly represented by coastal siliciclastic and bioclastic prograding wedges showing a clinoform geometry these are separated by blanket like deposits of high lateral persistence recording major transgressive episodes the aim of this paper is 1 to describe facies patterns and depositional setting of two prograding wedges particularly focussing on their polycyclic internal architecture 2 to analyze these units within a sequence stratigraphic framework and 3 to speculate on the possible origin of the small scale cyclicity the two wedges analyzed in this paper consist of a number of shingles individual shingles consist of two physically connected units 1 a relatively thin package of sigmoid clinoforms grading into 2 a volumetrically dominant package of oblique tangential clinoforms with toplap terminations the shingles are bounded by seaward dipping surfaces with sigmoid clinoform geometry which are ravinement surfaces updip passing into conformable flooding surfaces downdip the wedges are thus organized into high frequency small scale sequences each comprising transgressive highstand and falling stage systems tracts as a whole individual prograding wedges are interpreted as forced regressive units as the shoreline was subject to an overall shift basinwards and downwards along a low angle trajectory in spite of the repeated minor relative sea level rises tectonic subsidence and particularly the syndepositional growth of gentle synclines are thought to have been the key factors allowing the preservation of these forced regressive units progradation of the wedges took place in a high energy wave climate characterized by high frequency of storms and very efficient alongshore redistribution of sediments recurrent storm driven offshore currents led to intense reworking of sediments on the topset platform and gravity spreading on the foreset slope of the prograding wedges well oxygenated conditions over the shelf due to intensified storm activity during glacial periods may have enhanced the rate of production of skeletal foramol type carbonates it can reasonably be assumed that progradation took place from a line source and that the sand bodies are to be regarded as coastal prograding bodies in spite of active syndepositional tectonics the cycles can be correlated to pleistocene high amplitude sea level oscillations the older of the two wedges can be correlated through bio magnetostratigraphy to the major climatic transition which occurred from the marine oxygen isotope stage 25 to 24 22 rio et al 1996 the younger probably developed during the sea level fall that ended with substage 18 2 as suggested by sequence and bio stratigraphic data the prograding wedges are thus interpreted to record long lived sea level falls of fourth order cycles due to the particular depositional setting we are inclined to exclude authigenic mechanisms in the origin of small scale cyclicity although the concomitance and interaction of different controlling factors may be taken into account it is tempting to ascribe this cyclicity to minor eustatic changes punctuating long lived erratic falling stages possibly accompanied by climate driven fluctuations of sediment supply shelf perched and shelf edge prograding units consisting of foramol type carbonates are apparently a common falling stage to lowstand depositional feature in the mediterranean area during the late pliocene and pleistocene

normal fault growth and its function on the control of sedimentation during basin formation a case study from field exposures of the upper cambrian owen conglomerate west coast range western tasmania australia the evolution of a complex ancient segmented basin margin fault system was examined using integrated structural relationships lithostratigraphic architecture facies architecture and paleoflow trends to define the control on synrift development during the deposition of the upper cambrian owen conglomerate west coast range western tasmania australia four distinct stages are recognized during the evolution of the normal fault array the rift initiation stage defined early fault nucleation and isolated growth before fault interaction led to strain localization and the abandonment of antithetic faults renewed fault initiation led to further fault growth prior to the transition to rift climax stage with the development of a throughgoing linked array boundary faults propagated to near maximum length prior to significant basin formation whereas segment interaction clearly exerted a primary control on synrift distribution and paleogeography temporal fault evolution is marked by highly varied displacement patterns and pronounced lateral shifts in maximum synrift thickness accumulations the case study presented here is compared with existing models of fault growth and provides a field example for the assessment of basin formation particularly in polydeformed terranes which can offer crucial high resolution temporal data on fault system evolution associated stratal architectures and sediment dispersal patterns

sedimentological aspects of the humber group upper jurassic of the south central graben uk north sea complex structure poorly understood sedimentology and poor biostratigraphic control make the upper jurassic humber group of the south central graben one of the least understood and most complex hydrocarbon reservoirs of the north sea detailed logging of available core from 19 exploration wells has been combined with an improved understanding of the relevance of trace fossils and a recognition of important base level variations to provide a greatly enhanced understanding of the depositional system active within the area at that time a new sedimentological model based upon the distribution of facies and facies associations illustrates that upper jurassic structure and consequent basin geometry were the principal controls upon the distribution of depositional environments rifting and second order transgression controlled the back stepping onlap patterns observed and higher frequency base level fluctuations controlled the internal architecture of individual sandbodies the model presented accounts for features of these deposits that were previously considered anomalous such as the thickness of bioturbated sandstones paucity of foreshore deposits and complex age relationships of sands

shell beds as tools in basin analysis the jurassic of kachchh western india skeletal concentrations are ubiquitous in bathonian oxfordian shallow water sediments of the pericratonic basins of kachchh and rajasthan western india by analysing the biofabric of the concentrations and the taphonomic signatures of individual components it is possible to distinguish between the final concentration process recorded by the biofabric and events taking place prior to final deposition recorded by taphonomic signatures the skeletal concentrations are grouped in nine genetic types ranging from fair weather wave concentrations to storm concentrations and condensed concentrations they mainly reflect biological and hydraulic processes and in some instances permit estimates of their duration and show a rough zonation along a bathymetric gradient plotted against the stratigraphic sections the skeletal concentrations show in accordance with other sedimentological data three orders of bathymetric trends the first two orders are shallowing deepening cycles which possibly correspond to eustatic changes in sea level the third order represents parasequences with a strongly asymmetric sedimentary record skeletal concentrations are a useful additional tool in basin analysis but are best used in combination with other data

stratigraphic control on laterally persistent cementation book cliffs utah field data from the upper cretaceous blackhawk formation in the book clitfs utah colorado demonstrate the presence of laterally extensive carbonate cements beneath major marine flooding surfaces the occurrence of firmgrounds compaction around concretions and high minus cement porosities indicate that cementation occurred during early diagenesis it is proposed that the early cementation associated with these marine flooding surfaces occurred as a result of reduced sediment accumulation rates or non depositional hiatuses linked to abrupt deepening during marine flooding these reduced sediment accumulation rates extended sediment residence time within early diagenetic zones leading to enhanced early cementation in shallow marine sandstones and mudstones