The Lower Cretaceous tectonosequence constitutes a major chronostratigraphic interval in the Recôncavo Basin, Northeast Brazil. It encompasses a time span of ca. of 24 Ma and forms a continental sedimentary package that exceeds 5 km in thickness within its depocenters. The tectonosequence is bounded by two basinwide unconformities, the rift onset unconformity at its base and the breakup unconformity at its top. The basal deposits of the tectonosequence characterize transitional rift conditions. The bulk of the succession constitutes the record of the rift phase in the basin. Biostratigraphy in the Recôncavo Basin is based on nonmarine ostracods. The tectonosequence encompasses ostracod zones NRT 002 through NRT 009. Tectonic, sedimentologic, and paleoecologic characteristics permit the recognition of six tectono-depositional intervals within the tectonosequence. Tectono-depositional intervals cover a time span between 2 Ma and 7.5 Ma, and their boundaries are distinct marker beds. Lithologic, paleontologic, and geochemical characteristics of the marker beds suggest low sediment input at the time of their deposition. Tectonic and/or paleoclimatic changes may account for phases of marker bed creation. Within tectono-depositional inteivals II, IV, and V sedimentary cyclicity occurs. Sedimentary cycles spanning tens to hundreds of thousands years are termed tectono-depositional episodes. Such an episode is comparable in scale with a parasequence, and is also bounded by marker beds reflecting flooding events. Depositional systems within the tectonosequence show a change from lacustrine-dominated sedimentation at the base to fluvial-dominated deposition at the top. Reservoir potential increases toward the top of the tectonosequence, source rock and sealing conditions, however, follow the opposite path. The bulk of known hydrocarbon accumulations in the Recôncavo Basin occurs at the prerift/rift interface. Accumulation rate estimates show increasing values toward the top of the tectonosequence. This may be related to a better integration of the drainage system that fed into the basin and removal of possible structural barriers located along the basin's margins. Analysis of the sedimentary record of the tectonosequence suggests, besides tectonism, paleoclimate was an important mechanism controlling facies distribution and evolution. / text

A detailed study of modern washover fan (fan) morphologies will clarify common fan geometries, lead to a better model for a “typical” fan, identify the preservation potential and probable geometries of fan facies in subsurface datasets and outcrops, and ultimately improve hydrocarbon recovery in barrier island reservoir systems. This study uses satellite imagery to conduct a spatial analysis of 118 modern fans to quantify geomorphologic attributes of fans. A new classification scheme for fans is proposed that refines the current fan model, dividing fans into channelized and non-channelized fans. Channelized fans are subdivided according to the location of primary deposition: barrier depo-center or lagoonal depo-center. Non-channelized fans are subdivided based on morphology: dissipative, lobate, or apron-sourced. Quantitative cross-plots of morphologic relationships are analyzed to define trends in fan morphologies. The most common type of fan encountered in our study is a non-channelized, line-sourced, lobate washover fan with an area of less than 1 km2 that is fully contained on a barrier and exhibits no subaqueous deposition in back-barrier waters. The Lower Cretaceous McMurray Formation is the primary reservoir of the Athabasca Oil Sands in Alberta, Canada. The upper McMurray is commonly interpreted as deposits of embayed coastal systems. Our location is in an under-studied area located 80 km northwest of Fort McMurray. Lateral and vertical facies changes, sedimentary structures, key surfaces, trace fossils, and bitumen saturation were documented in eight cores located along a 20 km transect situated paleo-landward of a Devonian paleo-high acting as a bedrock-barrier. Our data indicate that a flood tidal delta complex prograded landward into a back-barrier embayment through the stable, bedrock-controlled inlet. This system overlies middle McMurray fluvial sands and Devonian basement and was transgressed by marine waters prior to deposition of the overlying Wabiskaw Formation. Flood tidal delta sandbodies are bitumen saturated and therefore make good reservoirs; however, heavily bioturbated tidal flats can act as a barrier to flow where they encase flood tidal deltas, as encased sands were devoid of bitumen. This complex coastal paleogeography produced back-barrier deposits that contain a slightly more diverse, marine trace fossil assemblage than might otherwise be expected. / text

In the Sergipe-Alagoas Basin, along the northeast coast of Brazil, the lacustrine, middle rift sequence is composed of the Lower Cretaceous Morro do Chaves and Coqueiro Seco Formations. Subsurface analysis permitted recognition and mapping of four principal types of depositional systems that infilled the basin with more than 3,000 meters of clastic-carbonate sediments: Morro do Chaves carbonate platform, Coqueiro Seco fluvial-deltaic, Coqueiro Seco fan delta, and Coqueiro Seco slope systems. The generally poor quality of seismic profiles in this rift sequence precludes conventional seismic stratigraphic approaches. Morro do Chaves lacustrine carbonate platform sediments were deposited on shallow positive areas flanking the principal point sources (rivers), and are composed of massively bedded, high energy limestones. Contemporaneous with shallow-water sedimentation, deepwater euxinic and bituminous lacustrine shales were deposited under starved basin conditions. Sublacustrine canyon excavation attested to the presence of a destructional slope episode. Coqueiro Seco fluvial-deltaic, fan delta, and slope sediments are principally terrigenous. Fluvialdeltaic and fan delta facies display high sand/shale ratios and blocky to massive E-log patterns; slope facies display serrate to digitate E-log patterns and are less sandy. Delta plain channel-fill facies and coarse-grained meanderbelt fluvial facies are dominant in fluvial-deltaic systems, and proximal to medial conglomerates and coarse conglomeratic sandstones are dominant facies in fan delta systems. Slope facies are composed of sublacustrine fans composed of fine-to medium-grained sandstones enveloped by thick, subbituminous shales, and thin, marly, lacustrine limestones. Coqueiro Seco clastic systems prograded across the basin and buried Morro do Chaves carbonate platforms in response to tectonic pulses related to rift development. Cyclic sedimentation occurred in the highly unstable Alagoas Sub-basin where fluvial-deltaic and slope systems are dominant, but fan delta and slope systems in the less complex Rio São Francisco Sub-basin do not exhibit cyclicity. Coqueiro Seco fluvial-deltaic, fan delta and slope sedimentation terminated because of continued basin subsidence and diminishing sediment supply as source areas were leveled. Consequently, the basin became the site of lacustrine shale deposition represented by the Ponta Verde Formation in the Alagoas Sub-basin. The rift sequence is truncated by a pre-Aptian unconformity in the Rio São Francisco Sub-basin. Evaluation of petroleum occurrences in relationship to defined depositional systems permitted recognition of several types of plays characterized by unique structural and stratigraphic relationships exhibited by reservoirs, source beds and structure. The Coqueiro Seco slope play, formed by updip pinchout of turbidite fans, is judged the most promising in the sequence. / text

This study has looked at an assemblage of fossilised teeth from Mesozoic marine amniotes from the Kristianstad basin in southern Sweden in order to make an estimate of the ecomorph diversity within said assemblage through looking at the morphology of the teeth. This was done as a pilot study to see if further studies would be able to produce worthwhile results. The assemblage consists largely of isolated tooth crowns, mostly from small- to medium sized mosasaurs such as Clidastes and Eonatator, but also contains larger mosasaurs, as well as a couple of plesiosaurs and one species of a marine crocodile. The analysis was performed on images of teeth using software developed for use in morphometrics. The resulting graphs imply a division into three guilds; the first represented by the short and blunt teeth of the crocodilian, the second by the elongated teeth of the plesiosaurs, and the third by the knife-like teeth of the mosasaurs. Since the mosasaurs overlap to a high degree in tooth shape, but also show quite diversity in size, it is possible the main dividing factor would have been size rather than type of prey. Further studies would be able to get a more accurate image of the ecology of this fauna by increasing the number of specimen in the analysis as well as taking into consideration more factors from other studies of similar taxa, such as jaw sizes, bite marks and gut contents. / Det här arbetet har studerat fossila tänder tillhörande Mesozoiska marina amnioter från Kristianstadsbassängen i södra Sverige, med avsikt att göra en uppskattning av den ekomorfa spridningen inom gruppen genom att studera tändernas form. Detta är enbart en pilotstudie för att se om fortsatta studier kan ge givande resultat. Det studerade materialet är en del av en samling till stor del bestående av enbart lösa tandkronor, mest från små till medelstora mosasaurier, såsom Clidastes och Eonatator, men även från större mosasaurier, så väl som ett par plesiosaurier och en marin krokodil-art. För analysen användes en programvara specifikt utvecklad för morfometri. De resulterande graferna antyder en indelning i tre “gillen”; det första representeras av de korta och trubbiga tänderna tillhörande krokodilen, det andra av de långsmala tänderna hos plesiosaurierna, och det tredje av de knivlika mosasaurietänderna. Eftersom mosasaurierna överlappar till stor grad gällande formen på tänderna, men skiljer sig mycket åt i storlek, så är det troligt att det snarare var storleken på bytesdjuren, och inte vilken typ, som skiljde dem åt. Framtida studier skulle kunna ge en bättre bild av den här faunans ekosystem dels genom att inkludera fler exemplar i analysen, och dels genom att inkludera andra faktorer från studier av liknande taxa, såsom käkstorlek, bitmärken och maginnehåll.

The Eagle Ford is a well-known source rock for both sandstone (Woodbine) and carbonate (Austin and Buda) hydrocarbon reservoirs in East and South Texas. Recent discoveries have demonstrated that source rocks, such as the Eagle Ford, are capable of producing significant volumes of gas and oil. At the same time, variations in well producibility indicate that these rocks, like conventional reservoirs, display considerable geological heterogeneity. Yet, only limited research has been published on the subsurface stratigraphy and character of Eagle Ford facies. Understanding the types, controls, and distribution of these heterogeneities requires in-depth rock-based studies. In order to characterize Eagle Ford facies, 27 cores from 13 counties were investigated for rock textures, fabrics, sedimentary structures, and fossil assemblages. These studies were supported by light and electron microscopy as well as analysis of elemental chemistry and mineralogy. Regional subsurface stratigraphic correlations and facies distributions were defined using wireline logs calibrated from core studies. In South Texas, the Eagle Ford Formation was deposited during a second-order transgressive/regressive cycle on the flooded, oxygen-restricted Comanche Shelf. Nine depositional facies consisting predominately of organic-rich, fine-grained (5.0 % TOC) to coarser-grained (3.05 % TOC) fabrics were identified. Facies developed in low-energy environments episodically interrupted by higher-energy, event sedimentation (current winnowing, cohesive and non-cohesive density flows, and turbidity flows). Locally, these rocks show evidence of early diagenetic recrystallization of calcite. Concurrent water anoxia and organic matter preservation persisted locally into later Austin deposition, resulting in formation of a three-fold division of the Cenomanian-Coniacian Eagle Ford Formation. Common facies of lower and upper Eagle Ford members include (1) unlaminated, fissile, clay- and silica-rich, organic-rich mudrocks, (2) laminated, calcareous, organic-rich mudrocks, and (3) laminated, foraminifera- and peloid-rich, organic-rich packstones. The transitional Eagle Ford member consists of highly-cyclic (1) ripple-laminated, organic-rich wackestone (cycle base) and (2) burrowed, organic-lean lime wackestones (cycle top). Transitional Eagle Ford facies developed in oxygen-restricted, basinal depositional environments as distal equivalents to burrowed, foraminiferal lime wackestones of the Austin Formation. Facies complexities in the Eagle Ford stem from complicated and interrelated processes of sediment production and distribution, diagenesis, and water column chemistry. Integrated core studies shed light on both controls of facies formation and their spatial distribution. These findings provide a framework for upscaling the fine-scale, heterogeneous character of shelfal Eagle Ford mudrocks; thus allowing development of predictive models into the distribution of key reservoir properties in the subsurface. / text

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Determining the distribution of porosity and permeability is one of the main challenges in carbonate petroleum reservoir characterization and requires a thorough understanding of pore type and origin, as well as their spatial distributions. Conventional studies of carbonate reservoirs require interpretation and analysis of cores to understand porosity. This study investigates the use of NMR logs in the determination of pore type and origin. This study is based on the analysis of both thin section petrographic and NMR data from a single well that cored the Lower Cretaceous (Aptian) shelf carbonates belonging to the Shuaiba Formation of the Middle East. Photographs of thin sections were used to determine pore type and origin according to Ahr's genetic classification of carbonate porosity. Descriptive statistics and modeling were used to analyze the NMR T2relaxation time distributions. Descriptive statistical analyses included estimating arithmetic average, standard deviation, skewness, median, mode and 90th percentile. T2modeling was performed by fitting multiple log-normal distributions to the measured T2distribution. Data from thin section petrography and from NMR measurements were then compared using conditional probabilities. As expected, thin section analysis revealed the predominance of mud-supported fabrics and micropores between matrix grains Vugs and dissolved rudistid fragments account for most of the macro porosity. Descriptive statistics showed that the mode and th percentile of the T2distribution had the greatest power to discriminate pores by origin. The first principal component (PC1) of the mode-90th percentile system was then used to compute the probabilities of having each pore origin, knowing that PC1 belongs to a given interval. Results were good, with each origin being predictable within a certain range of PC1. Decomposition of the T2distributions was performed using up to 3 log-normal component distributions. Samples of different pore origin behaved distinctively. Depositional porosity showed no increase in fit quality with increasing number of distributions whereas facies selective and diagenetic porosity did, with diagenetic porosity showing the greatest increase.

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