evidence of terrestrial organic matter deposition across the early toarcian recorded in the northern lusitanian basin portugal abstract the pliensbachian toarcian lower jurassic in the lusitanian basin portugal is particularly well exposed through marl limestone alternations very rich in nektonic and benthonic macrofauna in the general context of toarcian oceanic anoxic event t oae the lower toarcian polymorphum and levisoni ammonite zones marks important sedimentological changes in the marine paleoenvironment to better understand the paleoenvironmental changes that occurred during the latest pliensbachian early toarcian a high resolution study of organic matter was undertaken in the alcabideque section in the northern sector of the basin based on the analysis of 14 samples from a section 20 m thick this study involved organic geochemistry total organic carbon toc sulfur and biomarkers and palynofacies the results confirm that sediments are particularly poor in organic matter with the highest toc values reaching 0 41 wt around the top of polymorphum zone the palynofacies analysis provides evidence that the organic matter largely consists of particles belonging to phytoclasts and palynomorphs groups the phytoclasts present were generally degraded and oxidized with significant representation in the emaciatum and polymorphum zones the palynomorphs were mainly composed by sporomorphs with a sporadic increase in marine palynomorphs mainly dinocysts at the top of the emaciatum and polymorphum zones continental organic matter was predominant at the base of levisoni zone t oae through the deposition of brownish marls chocolate marls which was confirmed by the occurrence of tetrads and polyads pollen grain agglomerates and by biomarkers with the major presence of long chain n alkanes n alkane c17 c20 tricyclic terpane c24 tetracyclic terpane and c29 regular sterane the gammacerane index shows a peak at the top of polymorphum zone clearly associated with the increase of marine palynomorphs and the maximum marine influence in the series

calciturbidite dynamics and endobenthic colonisation example from a late barremian early cretaceous succession in southeastern france three lower cretaceous calciturbidite bundles well exposed in the southeastern france are studied with a combined sedimentological and ichnological approach they were deposited in a toe of slope setting in the western border of the vocontian trough during the late barremian the bundles appear to be the result of a cyclic sedimentation with recurrent ichnotaxa including common thalassinoides planolites zoophycos and less abundant taenidium chondrites and ophiomorpha these trace fossils constitute some ichnoassemblages that follow and superimpose each other analysis of the tiering produced may help to estimate the time interval between two turbiditic events indeed the presence of zoophycos indicates a low frequency of the turbiditic supplies which allowed the substrate to firm up a necessary condition for the construction and the persistence of this spreite trace fossil therefore a decreasing frequency of the turbiditic events is pointed out from the base to the top of each turbidite bundle the trace fossil distribution may also be influenced by the grain size in fact zoophycos producers seem to have thrived in a fine grained sediment 0 1 0 2 mm moreover the organic matter exported from the platform is better preserved in these fine grained substrates and may be more available to opportunistic burrowers in the studied succession two different morphologies of zoophycos have been observed one of them lobed form probably indicates an opportunistic behaviour of an organism quickly exploiting the organic matter between two turbiditic events by comparison the other unlobed form is produced later by a more specialised organism exploiting large amounts of organic matter during episodes of lower frequency of turbiditic supplies the ichnofauna studied is characterized by a low diversity and this may be related to an inner submarine fan setting

aalenian pulses of tectonic activity in the iberian basin spain in the northwest iberian range the aalenian to bajocian interval is represented by condensed as well as more expanded marine carbonate strata deposited in a shallow epicontinental sea setting precise biochronological data successive ammonites assemblages from 29 measured sections along with a bedby bed facies analysis allowed a detailed correlation between sections the definition of a number of successive transgressive regressive cycles and of two distinct sedimentation areas as well as the compilation of isopach maps for short time intervals duration of ammonites zone subzone and the assessment of sediment accumulation rates differences in facies and thickness in the studied interval and the sequential organization reveal significant changes in the depositional environment a tectonically controlled compartmentalization of the sedimentation area is suggested by a detailed reconstruction of the accumulation history an active extensional tectonic regime is supported by contemporaneous volcanic activity in the southeastern iberian basin a precise timing of the main tectonic pulses recorded in nw iberian basin for the upper toarcian lower bajocian interval is presented which may help to better resolve the stratigraphy in otherw european during this time interval

a longitudinal carbonate fan from the jurassic of the oman mountains the guweyza limestone formation of the hamrat ad duru abstract when sedimentological stratigraphical and structural data are considered the continental rise sediments of oman neo tethys the hamrat duru group can be restored to their original basin configuration prior to their southwest directed emplacement with the semail ophiolite onto the oman continental margin during the late cretaceous the hamrat duru group sediments are preserved in well exposed imbricate fans the largest of which forms the hamrat ad duru range in the south central oman mountains in the south central hamrat ad duru middle and upper jurassic ooid rich carbonate sediment was transported from the adjacent oman carbonate platform during periods of tectonic instability into the oman neo tethys hawasina basin by high and low density turbidity currents to form sediment sheets with a margin parallel axis of deposition palaeocurrents are northwest directed parallel to the oman margin along the southwest of the hamrat ad duru and northeast directed away from the margin in structurally higher more distal imbricates of the northeastern hamrat ad duru this implies sediment input at the southern end of the hamrat ad duru these trends are reflected in the distribution of sedimentary facies with most proximal facies developed in the southern hamrat ad duru passing into progressively more distal facies to the northwest and northeast sediment thinning and fining is more accentuated away from the margin towards the northeast and sedimentation was concentrated parallel to the oman margin the hamrat ad duru represents a longitudinal fan that was at least 120 km long and extended at least 60 km away from the margin

jurassic location of the yukon tanana terrane from palaeomagnetism of the folded mississippian tatlmain batholith and ragged stock

evidence for major environmental perturbation prior to and during the toarcian early jurassic oceanic anoxic event from the lusitanian basin portugal the timing and causal relationships between the pronounced negative c isotope excursion and paleoenvironmental perturbations associated with the toarcian oceanic anoxic event early jurassic remain unclear particularly because biotic crises and carbonate production decrease appear to have been initiated earlier than the main c isotope anomaly here we present a new quantification of late pliensbachian early toarcian calcareous nannofossils abundance and size from the peniche reference section portugal together with o and c isotope records of well preserved brachiopod shells from the same section the brachiopod shell 13c curve parallels that of bulk carbonate and records two pronounced negative isotopic excursions close to the pliensbachian toarcian boundary 2 and during the toarcian oceanic anoxic event 3 5 our results indicate that both c isotope negative excursions were characteristic of benthic and shallow water environments suggesting that these two carbon cycle perturbations affected all epioceanic reservoirs coeval shifts toward lower values of brachiopod oxygen isotope compositions and closely correlated northward migrations of mediterranean ammonite fauna suggest that both events coincided with major rises in seawater temperatures probably as a result of increased co2 levels and enhanced greenhouse conditions co2 induced changes in seawater chemistry likely affected the calcification potential of both neritic and pelagic systems as evidenced by synchronous drops of platform derived carbonate accumulation and drastic reductions in size 3 m of the main pelagic carbonate producer schizosphaerella we suggest that the early toarcian paleoenvironmental crisis occurred in two distinct episodes that were most likely related to two successive phases of intense volcanic degassing in the karoo ferrar province

benthic foraminiferal assemblages record major environmental perturbations during the late pliensbachian early toarcian interval in the peniche gssp portugal abstract this is the first ecostratigraphic and palaeoecological analysis of the benthic foraminiferal assemblages defined as morphogroups in the pliensbachian toarcian transition and the toarcian oceanic anoxic event t oae of the peniche section the toarcian global boundary stratotype section and point foraminiferal assemblages from the uppermost pliensbachian emaciatum zone reveal the presence of a stable benthic environment with good oxygen and availability of trophic resources as evidenced by the high diversity of specialists the pliensbachian toarcian transition reveals high foraminifera abundance mainly specialists although it is considered a slightly condensed interval the base of the levisoni zone shows dramatic changes in life style of foraminifera increase of epifauna and potentially deep infauna an increase in opportunistic forms and a decrease in diversity these changes suggest unfavourable conditions related to food availability diminution and depleted oxygenation corresponding to the beginning of the 13c negative excursion palaeoenvironmental conditions become severe in the lower to middle levisoni zone where there is a barren interval for foraminifera coincident with the highest values of total organic carbon after this interval foraminiferal assemblages experienced a recovery with increasing diversity and occurrence of specialists consistent with a well oxygenated environment and good food availability these changes observed in benthic foraminiferal fauna from the peniche section through the uppermost pliensbachian lower toarcian are comparable to what was reported previously on ostracods brachiopods and calcareous nannofossils foraminiferal assemblages from peniche section are comparable to other tethyan spain italy north africa and nw european sections england from the same stratigraphic interval with the suborder lagenina dominating the assemblages

a carbonate submarine fan sequence from the jurassic of portugal abstract a prograding carbonate submarine fan sequence is described from the toarcian aalenian of western portugal the sequence is predominantly composed of shallow water carbonate grains but can be interpreted using the current siliclastic submarine fan models basin plain to outer fan braided channel midfan and large channel fill sequences can be recognized the source of the carbonate grains was a platform developed on an uplifted hercynian horst to the west of present mainland portugal the fan sequence overlies restricted basin deposits with organic rich mudstones and shales this association of restricted basin facies and a thick over 300 m carbonate grainstone could be an attractive hydrocarbon play however such limestone sequences are easily misinterpreted as in situ shelf carb nates

the palynological response to the toarcian oceanic anoxic event early jurassic at peniche lusitanian basin western portugal abstract the uppermost pliensbachian and lower toarcian lower jurassic succession exposed at peniche in the central part of the lusitanian basin western portugal was examined for palynomorphs the 45 samples span the emaciaticeras emaciatum dactylioceras polymorphum and hildaites levisoni ammonite biozones abs and the succession includes the global boundary stratotype section and point gssp for the toarcian stage and the toarcian oceanic anoxic event t oae a low diversity dinoflagellate cyst flora typical of the sub boreal realm was recovered from the emaciaticeras emaciatum and dactylioceras polymorphum abs the dominant element is the cold water species luehndea spinosa which is an index for the pliensbachian to earliest toarcian and is thought to have migrated from the more northerly boreal realm prior to the t oae dinoflagellates thrived in the lusitanian basin except during a brief warm period in the earliest toarcian despite the latter the recovery from this event was relatively rapid and was characterised by a return to relatively cool temperatures the hildaites levisoni ab at peniche represents the t oae and the overlying strata and is characterised by a profound reduction in dinoflagellate cyst relative abundances this dinoflagellate cyst blackout and the associated rise of prasinophytes reflects significant environmental stress such as marine anoxia elevated temperatures and reduced salinity with the former two probably being most important the low proportions of dinoflagellate cysts following the t oae indicates a protracted recovery phase from the bottom and water column anoxia developed throughout the lusitanian basin

near surface circulation of the nordic seas as measured by lagrangian drifters in the period june 1991 to august 1993 107 argos tracked drifters drogued to 15 m depth were released in the nordic seas or greenland iceland and norwegian seas the drifter movements revealed the strong and spatially confined current systems along the surface salinity fronts of the iceland faroe frontal zone and of the norwegian coast and along the continental margins and their extensions to the barents sea and spitsbergen the norwegian atlantic current is composed of three distinct streams two continental margin and one coastal branches which join into one single swift mean current west of the lofoten and vesteralen islands where the strongest measured currents are in excess of 110 cm s 1 in addition to the general cyclonic gyre circulation in the nordic seas the drifters indicate smaller cyclonic circulation patterns in all the major subbasins i e the iceland plateau the norwegian the lofoten and the greenland basins no surface signature of the east icelandic current is disclosed by the drifters interpolated and low pass filtered position data were used to construct maps of 15 m depth ensemble mean velocity velocity variability and residence time vigorous eddy fields are dominant in the strong currents and in the lofoten basin eulerian correlations indicate that they tend to propagate to the west in contrast the iceland plateau appears quiescent both in the mean and eddy velocities single particle diffusivities are computed and are found to be in the range 1 7 107 cm2 s 1 the corresponding lagrangian timescale and space scale are 1 3 days and 10 40 km respectively these lagrangian drifter measurements compose the first basin scale accurate near surface velocity data set of the nordic seas

tectono stratigraphic signature of multiphased rifting on divergent margins deep offshore southwest iberia north atlantic 1 regional 2d multichannel seismic borehole dredge and outcrop data together with burial models for strata in southwest iberia are used to investigate the tectono stratigraphic signature of multiphased rifting on divergent margins our burial model reveals that mesozoic extension occurred during three main phases each comprising distinct subsidence pulses separated by short lived periods of crustal uplift the importance of the three phases varies across discrete sectors of the margin each one revealing similar depositional architectures and associated tectonic systems tracts 1 the rift initiation phase characterized by incipient subsidence and overall aggradation progradation over a basal unconformity 2 the rift climax phase which marks maxima of tectonic subsidence and is characterized by retrogradation progradation and 3 the late rift phase recording the progradational infill of the basin and the effects of eustasy the rift initiation systems tracts comprise sinemurian and late callovian early oxfordian strata marine units in the pliensbachian and late oxfordian kimmeridgian represent the rift climax phase a period marked by the development of maximum flooding surfaces late rift deposits were identified in the rhaetian hettangian toarcian bathonian and kimmeridgian berriasian the results of this work are important to the economic exploration of deep offshore rift basins as they reveal that sequence stratigraphy can be used to predict sedimentary facies distribution in more distal segments of such basins significantly this work recognizes that multiple tectonic stratigraphic rift cycles can occur on deep offshore rift basins from the onset of rift related extension until continental break up a character that contrast to what is known from deep sea drilling data from the distal margin of northwest iberia

architecture and evolution of calciclastic marginal slope fans of the ordovician carbonate platform in the yijianfang outcrop of the bachu area west tarim basin the ordovician carbonate platform at the yijianfang outcrop of the bachu uplift region in the western tarim basin contains four types of genetic facies associations developed in the calciclastic slope fan depositional system an olistostrome zone fan channels lobes and a marginal slope the olistostrome zone is characterized by olistoliths and slump fans whereas the fan channels and lobes are further divided into proximal and distal facies the marginal slope deposits constitute the background sedimentation in which the calciclastic slope fans are intercalated from proximal to distal parts of the fan channels and lobes their scale gradually becomes smaller and the size and sorting of grains become finer and better respectively analysis of the stratigraphic framework indicates that the fans formed in the lower strata of the upper ordovician lianglitage formation in four high frequency sequences i e pss1 pss4 field paleocurrent measurements indicate northeast southwest depositional strike for the early platform margin of the lianglitage formation sediments in the calciclastic slope fans were derived from the platform margin and evolution of the calciclastic slope fans was generally progradational from pss1 to pss2 and then continuously retrogradational from pss2 to pss4 the calciclastic slope fans in the outcrop area are not reservoir prone rocks but interpretation on these fans can provide useful information about potential hydrocarbon reservoirs along the platform margin the p wave velocity s wave velocity and density variations in each genetic facies may be used to identify the subsurface calciclastic slope fan depositional system

paleocene carbonate turbidites of the şarkisla region turkey their significance in an orogenic basin abstract a paleocene carbonate sequence occurs in the southwestern part of the sivas refahiye basin arkisla province sivas turkey and is located in the northeast of central anatolia conclusions concerning the late mesozoic to early cenozoic sedimentary evolution have been derived mainly from the carbonate turbidites the vertical and lateral relationships of these rocks suggest deposition in a submarine fan complex three major megacycles characterized by a thickening and coarsening upward trend are seen in the upper cretaceous lower paleocene succession they are considered to represent basin facies in the lower levels passing upward into sediment attributed to distal fan facies on the basis of bed thickness distributions and bioclastic hemipelagic ratios agglomerates occur as laterally discontinuous mass flow deposits which formed on the slopes of local volcanoes located in the deeper part of the basin thin lava sheets are the products of stratovolcanoes which result from regional tectonic subsidence olistoliths occurring at several stratigraphic levels probably are the result of seismic events related to contemporaneous volcano tectonic activity two major turbiditic megacycles occur also in the middle and upper parts of the succession middle and upper paleocene the lower megacycle of this sequence conforms to the distal division of a suprafan lobe while the upper part is marked by a conspicuous thickening and coarsening upward character indicating a suprafan lobe environment this evidence is consistent with an overall progradation of the fan complex during the paleocene paleocurrent features and slump structures indicate that the marginal slopes of the basin extended in a northeast southwest direction and were inclined to the north sedimentologic stratigraphic tectonic and volcanic data from this sequence suggest that during the paleocene this area formed as an arc related basin

carbonate shedding and sedimentary cyclicities of a distally steepened carbonate ramp miocene great bahama bank depositional geometries as imaged in seis mic lines logging data and quantitative petrographic data were used to analyse the slope and toe of slope deposits of the miocene distally steepened carbonate ramp of great bahama bank the shedding pattern along the slope of this ramp is more complex than it is along the slope of the pliocene pleistocene flat topped carbonate platform compositional changes and compositional trends of periplatform sediments correlate with the positions of geophysically defined sequence boundaries two types of depositional sequences occur the first sequence is characterised by laterally traceable sequence internal reflections whereas the second type contains major intrasequen tial incisions erosional incisions and sedimentary infills of these canyons by turbidites formed during sea level lowstands as is indicated by the composition of the turbidites having a mixture of shallow water and pelagic particles highstand turbidites are charac terised by more extensive laterally traceable geome tries and by the occurrence of abundant shallow water particles in contrast to highstand turbidites shed from the pliocene pleistocene flat topped platform shal low water components in highstand turbidites of the miocene ramp are of skeletal origin the stacking pat tern of the periplatform deposits is controlled by sea level fluctuations four orders of sea level changes are distinguished third order cycles are delimited by sequence boundaries and fourth 100 000 a order cycles govern the bundling of turbidites into packages fifth 40 000 a and sixth 23 000 a order cycles are recorded in the background sediments and resolvable with spectral analysis

aspects of the structural evolution of the lusitanian basin in portugal and the shelf and slope area offshore portugal abstract the study provides a regional seismic interpretation and mapping of the mesozoic and cenozoic succession of the lusitanian basin and the shelf and slope area off portugal the seismic study is compared with previous studies of the lusitanian basin from the late triassic to the cretaceous the study area experienced four rift phases and intermittent periods of tectonic quiescence the triassic rifting was concentrated in the central part of the lusitanian basin and in the southernmost part of the study area both as symmetrical grabens and half grabens the evolution of half grabens was particularly prominent in the south the triassic fault controlled subsidence ceased during the latest late triassic and was succeeded by regional subsidence during the early early jurassic hettangian when deposition of evaporites took place a second rift phase was initiated in the early jurassic most likely during the sinemurian pliensbachian this resulted in minor salt movements along the most prominent faults the second phase was concentrated to the area south of the nazare fault zone and resulted here in the accumulation of a thick sinemurian callovian succession following a major hiatus probably as a result of the opening of the central atlantic resumed deposition occurred during the late jurassic evidence for late jurassic fault controlled subsidence is widespread over the whole basin the pattern of late jurassic subsidence appears to change across the nazare fault zone north of the nazare fault fault controlled subsidence occurred mainly along nnw sse trending faults and to the south of this fault zone a nne ssw fault pattern seems to dominate the oxfordian rift phase is testified in onlapping of the oxfordian succession on salt pillows which formed in association with fault activity the fourth and final rift phase was in the latest late jurassic or earliest early cretaceous the jurassic extensional tectonism resulted in triggering of salt movement and the development of salt structures along fault zones however only salt pillow development can be demonstrated the extensional tectonics ceased during the early cretaceous during most of the cretaceous regional subsidence occurred resulting in the deposition of a uniform lower and upper cretaceous succession marked inversion of former normal faults particularly along ne sw trending faults and development of salt diapirs occurred during the middle miocene probably followed by tectonic pulses during the late miocene to present the inversion was most prominent in the central and southern parts of the study area in between these two areas affected by structural inversion fault controlled subsidence resulted in the formation of the cenozoic lower tagus basin northwest of the nazare fault zone the effect of the compressional tectonic regime quickly dies out and extensional tectonic environment seems to have prevailed the miocene compressional stress was mainly oriented nw se shifting to more n s in the southern part

sedimentary organic matter and early toarcian environmental changes in the lusitanian basin portugal abstract the objective of this study is to investigate the relationship between early toarcian climatic events and the composition of kerogen assemblages in the lusitanian basin portugal in particular we aim to understand how the pliensbachian toarcian event pl toa event and toarcian oceanic anoxic event toae affected the continental areas of the western iberian margin and how possible variations in continental sources of organic matter om were expressed in marginal marine and hemipelagic depositional environments during the early toarcian we present here a characterisation total organic carbon toc total sulphur ts 13c in kerogen concentrate 13ckerogen and palynofacies of kerogen assemblages from several uppermost pliensbachian emaciatum ammonite zone lower toarcian sections in the lusitanian basin western iberian margin including the peniche section which contains the toarcian gssp in all sections toc concentration is low average 0 4 wt with the highest values reaching up to 2 1 wt in a discrete level located approximately 10 5 m above the base of the levisoni zone at peniche the toae negative carbon isotope excursion is observed in kerogen concentrate at the base of the levisoni zone throughout the basin palynofacies analysis demonstrates that the kerogen assemblages are mostly of terrestrial affinity with the dominance of the phytoclast group and terrestrial palynomorphs and with punctual increases in amorphous organic matter freshwater e g botryococcus sp and marine microplankton dinoflagellate cysts acritarchs and prasinophyte algae in specific stratigraphic intervals a change in palynofacies assemblages associated with the toae is observed around the base of levisoni zone although with slight differences between sections the toae interval records an increase in non opaque translucent phytoclasts nop and cuticle fragments and is also associated with an increased contribution of terrestrial palynomorphs increase in sporomorphs and classopollis in tetrads and agglomerates and decrease in marine palynomorphs the increases in nop and terrestrial palynomorphs support the postulated enhancement of the hydrological cycle and increased export of terrestrial om into marine environments during the early toarcian especially during the toae in the western iberian margin understanding the impact of the early toarcian climatic events on land based ecosystems may provide important insights into current climate change

distal alluvial fan sediments from the upper jurassic of portugal controls on their cyclicity and channel formation the lusitanian basin of west central portugai is an iberian atlantic margin basin during a late jurassic rifting event a series of alluvial fans distributed coarse basement derived clastics southeastward from the western margin of the basin the distal part of this sequence which is about 140 m thick consists of heterolithic massive sandstone and massive mudrock facies arranged in crude fining upwards cycles 1 15 m thick these form discrete packets of sediment in a strongly aggrada tional sequence and are interpreted as the products of sheetflooding as the active area of sedimenta tion on the fan surface switched channelized flow was not necessarily an early feature of cycle development considerable fluctuations in discharge occurred and were probably related to climatic factors large quantities of tractional and suspended sediment were transported at high stages and were rapidly deposited as flows waned caliche soil profiles indicate a seasonal semi and climate however other features such as widespread soft sediment deformation the lack of desiccation structures and the absence of evaporites suggests that areas of active sedimentation often remained wet three fining upward megacycles are distinguished these indicate rapid advance of fan toes triggered by tectonic activity followed by gradual retreat

geometry and petrophysical parameters of a calcarenitic turbidite lobe barremian aptian pas de la cluse france abstract several bioclastic resedimentation systems late barremian to early aptian in age outcrop in southeastern france the upslope portion of a calcarenitic turbidite lobe outcrops as a cliff 2 3 km wide and up to 45 m high oriented roughly perpendicular to the direction of palaeoflow it has been studied through 31 sections the studied body is point sourced and corresponds to a channel lobe transition located at the toe of slope of a urgonian carbonate platform on the western edge of the vocontian trough french subalpine chains the internal geometry of the lobe is the result of repeated erosion and filling of channels creating well defined stacked units filling phases result in lobe shaped morphology units evolve from base to top in an ordered way first the sediments exported from the platform and deposited in the basin are represented by decimetre thick sheet like and fine grained bouma a e and ab e sequences in this first unit erosion is limited and represented by shallow and symmetrical channels this initial phase of deposition corresponds to the formation of a lobe with a positive morphology the next phase of system development is more erosional and this is dominated by migrating sinuous channels several metres deep filled with coarse grained poorly graded turbidites these channels are first filled through lateral accretion and then sediment spills over to create a sub lobe the mixture of channel and lobe features could be considered as a carbonate equivalent of the channel levee system of siliciclastic deposits finally the system ends with the deposition of a flat based unit this unit extends for more than 2 km and is composed of the southwards lateral accretion of hundreds of metres wide sequences each composed of a debris flow deposit capped by a coarse grained calcarenite bed these sigmoidal bodies could be the ultimate forms of a spreading out phenomenon of the lobe overall the pas de la cluse system is a coarsening upward body as the grain size is related to the nature of the material this coarsening upward implies either an evolution in the nature of the carbonate material produced on the platform from grainy to bioconstructed a displacement of the source sediment from inner platform to margin or a displacement of the channel head through time from distal to proximal the upward evolution from classic turbidites to debris flow deposits can be explained either by the way the platform facies evolved with time in a depositional sequence or through retrogressive erosion by successive slope failures that cut deeper and deeper into the platform slope although its present day porosity is low the size of the system and the fact that it is encased in marls make it an interesting outcrop analogue for hydrocarbon exploration

carbonate reservoir outcrop analogues with a glance at pore scale middle jurassic lusitanian basin portugal abstract the middle jurassic carbonate successions from the lusitanian basin portugal show a range of facies deposited across a ramp depositional system well exposed over large areas these facies are valuable for understanding reservoirs and related seal and trap configurations namely in carbonate ramps this paper documents primarily shallow water units corresponding to the dominant reservoir type facies highlighting their potential as analogues particularly at outcrop but integrating main macro and micro scale characteristics the mid and inner ramp sediments which include the key studied units consist of peloidal intraclastic bioturbated fossiliferous limestones oolitic skeletal and coral algal limestones assigned to shoals and barrier island complex fossiliferous oncoidal fenestral deposits from lagoonal peritidal and locally pedogenic settings dolostones and dolomitic limestones facies with higher potential reservoir features are addressed in more detail in three broad groups sandbodies biostromes dolostones dolomitic limestones the remaining facies are more briefly described the most widespread reservoir lithofacies are cross stratified or massive oolitic and bioclastic grainstones to rudstones and coral dominated biostromes the larger scale sandbody units show a dominant sheet like geometry but wedges and smaller scale lensoid units occur grading into and interfingering with other facies types the reservoir facies are closely associated with hence often encased by flow baffle or barrier seal facies either landwards lagoonal peritidal or seawards mid outer ramp this architecture coupled with varied diagenetic paragenesis created a range of stratigraphic and diagenetic traps that may be perceived as play similarities in potential exploration situations the present reservoir quality is mostly low to moderate but examples of high excellent porosities and locally enhanced permeabilities occur overall these units are highly suitable field analogues to clarify processes leading to depositional diagenetic fractured and hybrid reservoir types moreover they clearly indicate how shoreface dynamics shallow water carbonate factory productivity and diagenesis lead to more complex reservoirs than usually appreciated in mostly homoclinal depositional systems