Parasequence Sets Research Articles

Sequence stratigraphy of the Cambrian Terreneuvian Dalinzi Formation in southern Liaoning

As one of the only Cambrian Terreneuvian rock stratas in southern Liaoning, the Dalinzi Formation is of great significance for studying the evolution of the Early Cambrian sedimentary basin and the global sea level change in North China. Taking the Zhaokanzi section as an example, the sedimentary facies of the Dalinzi Formation in southern Liaoning were identified, and then the sequence stratigraphy was studied. The study suggests that the Dalinzi Formation is formed in the lagoon and tidal flat sedimentary environment, and a three-level sequence and several parasequences and parasequence sets can be divided. The relative sea level changes and sedimentary basin evolution are discussed.

Architecture of tectonic sequences, depositional systems, and tectonic controls of the sedimentary fills of the rift‐related Wenchang Formation in the Lufeng Depression, Pearl River Mouth Basin, China

Different sequence types were formed in various stages associated with tectonic variations and changes of the sediment supply in the rift‐related Wenchang Formation. Based on cores, wire logging, and seismic data, the sequence stratigraphy, depositional systems, and controls on the depositional systems of the Wenchang Formation in the Lufeng Depression were studied. The Wenchang Formation developed braided‐delta, lacustrine, fan‐delta, and nearshore subaqueous fan deposits and represents one first‐order sequence and three second‐order sequences, indicating three stages of tectonostratigraphic evolution. (a) The early syn‐rift sequence (SSQ1) developed fan‐delta and shallow lacustrine deposits. (b) The rift climax sequence (SSQ2) contains the early rift climax systems tract and the middle‐late rift climax systems tract. The early rift climax systems tract formed primarily braided‐delta and shallow lacustrine deposits, whereas the middle‐late rift climax systems tract developed mostly semi‐deep to deep lacustrine deposits. (c) The late syn‐rift sequence (SSQ3) developed braided‐delta and shallow lacustrine deposits. In the SSQ3 transgressive systems tract, retrogradational parasequence sets developed along the southern dip slope because of the weak sediment supply from the Huilu low uplift, whereas westward aggradational–progradational parasequence sets developed along the long axis because of the stronger sediment supply from the Lufeng eastern low uplift. Tectonic activity primarily controlled the early syn‐rift and rift climax deposition; syn‐depositional faults formed the transfer zones and slope break zones. Three types of transfer zones for sedimentary transport into the basin were distinguished, including synthetic approaching transfer zones, strike ramps, and collateral transfer zones. Three types of slope break zones were also recognised, including fault scarp zones controlling fan deltas and nearshore subaqueous fans, fault terrace zones controlling low‐stand fan deltas, and antithetic fault terrace dip‐slope zones controlling braided deltas.

Depositional Cycles in a Lower Cretaceous Limestone Reservoir, Onshore Abu Dhabi, U.A.E.

AbstractThe upper reservoir zone of the Lower Cretaceous Kharaib Formation (46–54 m thick in the studied wells) is regarded as the upper portion of a third-order depositional sequence comprising higher-order cycles. Whereas the third-order sequence interpretation is clearly supported by the upward-shoaling trend of the reservoir zone, relationships defining the component cycles have not previously been documented and are the focus of the present study. Core descriptions from four wells in a single oilfield reveal little evidence of facies changes or trends of facies patterns indicative of high-frequency depositional cycles. Cycle boundaries could possibly be represented by the repetitive pattern of coarse beds (rudstone and floatstone) 0.1–2 m thick, commonly having sharp basal contacts and gradational upper contacts with enclosing packstone to wackestone. Because the coarse beds do not appear correlative between wells, however, we prefer the alternative interpretation that they reflect episodic storm events which locally redistributed detritus, sourced from a patchwork of low-relief lithosomes, across the flat surface of the epeiric Kharaib platform–lagoon. Although the existence of high-order eustatic fluctuations during upper Kharaib deposition is well established, low-amplitude variations in water depth may not have touched down on the sea floor to significantly affect sediment textures in contrast with the dominant storm signal.Reservoir sub-zones used for production operations, but previously suggested to be fourth-order parasequence sets, are defined by dips in porosity-log profiles, reflecting thin (approximately 1 m) intervals of increased stylolite frequency. These boundaries are thus diagenetic in character, but their correlation over tens to hundreds of kilometers indicates an underlying depositional control. We suggest that the link between sea level and diagenesis is depositional-clay content, which facilitates stylolitic dissolution. Profiles of bulk-rock alumina analyses in the studied cores show subtle indications of higher clay content at the sub-zone tops. Much greater clay peaks mark the third-order sequence boundaries, resulting in the “dense” (very low porosity) zones above and below the studied reservoir zone and the increased stylolite frequency in the upper and lower several meters of the zone. Possible factors promoting clay influx across a carbonate shelf during falls in sea level include increased stream gradients and more humid climate.

Cyclostratigraphic and δ13C record of the Lower Cretaceous Adriatic Platform, Croatia: Assessment of Milankovitch-forcing

The 700-m-thick Hauterivian to Albian section from the interior of the large, Adriatic Platform is exposed on Mljet and Korčula islands, Croatia. The cyclic platform consists of meter-scale parasequences, bundled into parasequence sets, superbundles and then into breccia-bounded depositional sequences. Spectral analysis of time series (cycle number vs. cycle thickness) shows peaks in the short-term eccentricity (95 to 130 kyr) bands and 160 to 200 kyr bands.Isotope samples from micrite matrix of mudstone and wackestone have δ13C values generally from −1.5 to +2‰ VPDB, and δ18O from −1 to −3.5‰ VPDB. Adriatic Platform δ13C values are shifted ~2‰ VPDB more negative than marine pelagic values. A δ13C and δ18O meteoric signal is limited to just beneath sequence boundaries, suggesting that the isotopic shift is due mainly to marine phreatic‐ and synorogenic burial diagenesis. Major excursions on the 5-point smoothed δ13C profile of the Adriatic Platform, tied biostratigraphically to δ13C curves from pelagic sections, include the oceanic anoxic events OAE1a, 1b, and 1c.Time series constructed from δ13C values (unsmoothed data) vs. stratigraphic position show peaks in the Milankovitch band, especially short-term eccentricity. Most positive peaks are near parasequence set boundaries (50 to 60%) and regressive parts of parasequences (20%). Although diagenetically shifted, the δ13C record retains a highly clipped memory of astronomically-driven global δ13C fluctuations albeit modified by platform water restriction during cyclic deposition.

Fluvial sequences and basin development in the northern Galilee Basin

ABSTRACTIn the northern Galilee Basin, 10 third-order depositional sequences have been recognised in multi-suite geophysical logs of 16 wells and boreholes. Sequences can be subdivided into genetic systems tracts characterised by geometry, facies associations, types of bounding surface, parasequence set distribution and position within the sequence. Stacking trends of parasequence sets may be observed as a shift in the sand or shale base line. These sequences reflect basinal and hinterland tectonics with a subordinate climate and sea-level cycle signature. The initial development of the northern Galilee Basin in the upper Carboniferous reflects thermal subsidence that characterised the underlying Drummond Basin. This subsidence is overprinted by the commencement of foreland-basin tectonics associated with extension in the Bowen Basin. The foreland tectonics waned before a major regional uplift occurred in the northern Galilee Basin in the middle Permian. This uplift is associated with an early phase of the Hunter–Bowen Orogeny. A quiescent period where accommodation is controlled by sea-level changes is reflected in extensive development of mires. Renewed episodic contraction overprinted on thermal sag subsidence in the Lower Triassic reflects far-field tectonics associated with the Hunter–Bowen Orogeny. In the Upper Triassic, an end-phase event of the Hunter–Bowen Orogeny inverted the Galilee Basin.

Sequence Stratigraphy and Rudist Facies Development of the Upper Barremian‐Lower Cenomanian Platform, Northern Sinai, Egypt

AbstractThe Lower Cretaceous sections in northern Sinai are composed of the Risan Aneiza (upper Barremian‐middle Albian) and the Halal (middle Albian‐lower Cenomanian) formations. The facies reflect subtle paleobathymetry from inner to outer ramp facies. The inner ramp facies are peritidal, protected to open marine lagoons, shoals and rudist biostrome facies. The inner ramp facies grade northward into outer ramp deposits. The upper Barremian‐lower Cenomanian succession is subdivided into nine depositional sequences correlated with those recognized in the neighbouring Tethyan areas. These sequences are subdivided into 19 medium‐scale sequences based on the facies evolution, the recorded hardgrounds and flooding surfaces, interpreted as the result of eustatic sea level changes and local tectonic activities of the early Syrian Arc rifting stage. Each sequence contains a lower retrogradational parasequence set that constituted the transgressive systems tracts and an upper progradational parasequence set that formed the highstand systems tracts. Nine rudist levels are recorded in the upper Barremian through lower Cenomanian succession at Gabal Raghawi. At Gabal Yelleg two rudist levels are found in the Albian. The rudist levels are associated with the highstand systems tract deposits because of the suitability of the trophic conditions in the rudist‐dominated ramp.

Evidence of synsedimentary microbial activity and iron deposition in ferruginous crusts of the Late Cenomanian Utrillas Formation (Iberian Basin, central Spain)

Ferruginous sandstones and crusts are prominent sedimentary features throughout the continental (braided)-coastal siliciclastic (estuarine-tidal) wedges of the Late Cenomanian Utrillas Formation in the Iberian Basin. Crust types recognized are: Ferruginous sandy crusts (Fsc) with oxides-oxyhydroxides (hematite and goethite) concentrated on sandstone tops presenting a fibro-radial internal structure reminding organic structures that penetrate different mineral phases, suggesting the existence of bacterial activity in crust development; Ferruginous muddy crusts (Fmc) consisting of wavy, laminated, microbial mats, being composed mainly of hematite. On the other hand, a more dispersed and broader mineralization included as Ferruginous sandstones with iron oxides and oxyhydroxides (hematite and goethite) representing a limited cement phase on these sediments. The presence of microbial remains, ferruginous minerals, Microbially-induced sedimentary structures, microbial laminites and vertebrate tracks preserved due to the presence of biofilms suggest firstly a direct evidence of syn-depositional microbial activity in these sediments; and, secondly, that iron accumulation and ferruginous crusts development occurred immediately after deposition of the host, still soft sediments. Ferruginous crusts cap sedimentary cycles and they represent the gradual development of hard substrate conditions, and the development of a discontinuity surface at the top of the parasequence sets, related to very low sedimentary rates; the overlying sediments record subsequent flooding of underlying shallower environments; crusts are, consequently, interpreted as boundaries for these higher-order cycles in the Iberian Basin.

Lombardi reservoir, San Ardo field, California: Sequence stratigraphy in a deltaic environment associated with local tectoni

The Lombardi reservoir at San Ardo oil field in California is extremely sand rich (>90%) and appears to be a relatively simple reservoir several hundred feet thick. The purpose of this study is to characterize stratigraphic complexities in the Lombardi reservoir that may affect later production and interpret how changes in stratigraphic architecture are tied to local syndepositional tectonism. Two parasequence sets are present in the Lombardi: the reservoir exhibits clinoform geometries along the western edge of the field and stacking patterns within the reservoir change across the field. Based on stacking pattern, core, and correlation studies, two possible sequence boundaries are recognized in the Lombardi sand. A lower sequence boundary is proposed approximately in the middle of the Lombardi sand, and an upper sequence boundary is proposed at the top of the Lombardi sand. In the southern part of the field, the Lombardi sand consists of two progradational parasequence sets, separated by the mid-Lombardi sequence boundary. The upper sequence boundary clearly truncates underlying folded Lombardi sand. Just a few miles (∼5 km) away, in the northwest part of the field, the Lombardi sand consists of a lower progradational parasequence set and an upper retrogradational parasequence set, separated by the mid-Lombardi sequence boundary. The upper sequence boundary at the top of the Lombardi sand shows little evidence of truncation of underlying units and is recognized by onlapping of younger strata. The difference in reservoir architecture between the south and northwest part of the field, a distance of only a few miles (∼5 km), is interpreted to be related to syndepositional uplift accompanying tectonism in the south. In core, the Lombardi sand consists mostly of homogeneous sand and bioturbated sand, arranged in upward-coarsening successions. The Lombardi sand is interpreted to be the product of deltaic deposition based on (1) the presence of homogeneous and laminated sandstones interpreted to represent mass flow deposits and (2) its restricted geographic distribution within the Salinas basin. No evidence of deposition in a wave-dominated or tidal-dominated shoreline is indicated. The interpretation presented here is that the sediments were deposited on the front of a delta emptying into a wave-protected estuary or bay, with minimal tidal effects. Complexities in stratigraphic architecture along the western edge of the field do not currently affect production but will likely become important during later stages of field development. That is, in the developed part of the field, reservoir continuity is not an issue, because of high sand content and sheet-like geometries. However, at the margins of the field, which will be produced in the future, clinoform geometries and sandstone tongues clearly affect reservoir continuity and will create vertical compartments during draining.

Geologic-seismic models, prediction of shallow-water lacustrine delta sandbody and hydrocarbon potential in the Late Miocene, Huanghekou Sag, Bohai Bay Basin, northern China

The Huanghekou Sag is located at the southeast part of the Bohai Bay Basin, northern China. Large-scale shallow lake delta developed in the Neogene provided suitable geological conditions for the formation of a subtle oil-gas reservoir in this area. The key for analyzing sandstone reservoir and sedimentary facies is by using seismic attributes (amplitude) to establish the relationship between lithology combination and seismic attributes. The lower unit of Late Miocene Minghuazhen Formation at the BZ34 block in the Huanghekou Sag was subdivided into 10 parasequence sets (PSS). Thicker sandstones mainly occurred in PSS1 and PSS10, whereas thin sandstones are mostly observed within other parasequence sets. This study presents statistics and analyses of lithology, i.e., statistics of root-mean-square (RMS) amplitude and lithology of well locations in different parasequence sets of the study area, as well as 1-D forward seismic models of 7 types of lithology combinations, the establishment of a spatial distribution of 2-D sandbody, forward seismic models etc. Our study indicates that high amplitude peaks correspond to thicker sandbodies, while low amplitude indicates non-development of sandbodies (generally less than 2 m), and medium amplitude agrees well with large sets of mudstones interbedded with medium and thinner sandstones. Different sand–mudstone combinations genetically reflect a combination of multiple micro-facies, therefore, amplitude features can predict sandbodies as well as facies characteristics.

Tsunami killed and backwashed accumulated crinoids in Middle Triassic (Anisian) intracratonic Germanic Basin carbonates of central Europe

In Germany tens to hundreds of kilometres-laterally distributed sedimentological heterogene crinoid accumulation bed with partly articulated Encrinus liliiformis specimens is dated within a complete trans-regression cycle of higher order into the upper Illyrian, Anisian (Middle Triassic, pulcher biozone). The crinoid bearing layer differs much from under- and overlaying tempestite parasequence sets of the Meisner Formation. The tsunamite layer consists of different laterally grain size sorted facies types ranging from unsorted bioclastic floatstones of large-scaled antidune megaripples, which continue in oscillation-ripple-marked oolithic grainstone surfaces that end into crinoid filled scour troughs in wacke/mudstones (=horizontal grain sorting in backwash direction). The tsunamite bed of Lamerden that consists of mixed reworked oolithic bar to crinoid ramp facies areas (sediments/biota to the outer ramp facies) can be correlated to a crinoid bed of Bissendorf within northwestern Germany at minimum (about 50 km) and appears within the tectonical deepening period of the Central European intracratonic Germanic Basin. The heterotope crinoid taphocoenosis was built in the outer ramp Tonplatten facies, in the deepest part of the Germanic Basin (Hesse-Depression) due to backwash. The mixed macro fauna originate from the crinoid bioherms and terebratulid hardgrounds of the inner/middle ramp facies (such as the sediments). From 350 analysed crinoid individuals (of 1500), only 1 % are complete with 120–160 cm short-stemmed ecotypes of the inner ramp crinoid meadows which settled along the sand bars basinwards. The Lamerden crinoids are scattered or are concentrated differently condensed in scour trough-like structures on wackestones/mustone areas and more rare or scattered on osciallation-ripple marked grainstones and allow only local bottom current estimations. In interfingering floatstones, more rare crowns are found unsorted within dominat chaotic oriented terebratulids. Most crinoid specimens (83 %) were found with relic stems and the others (16 %), only as crowns. The echinoderms survived a tsunami event, for at least a few hours/days under 10–30 cm of mud coverage. Only 1 % of the crowns have opened arms (=postmortal embedding); all others (99 % are closed crowns) are “buried alive” specimens. The crinoids closed the nutrition canal immediately and started regeneration of the distal stem for new attachment purposes; therefore, those have all rounded distal stems. The northern German Lamerden crinoid layer is most similar to the southern German Neckarwestheim site, but is different in its origin to other German sites, where crinoids have been found around bioherms or with long-stemmed specimens not far from their patch-reef like habitats in channels of the upper middle ramp facies. The tsunamite demonstrate the problem of the “Triassic time scale” which is tempestite and Milankovitch cycle based on an intracratonic basin, because there seem to be several further tsunamite bioclastic layers, which were misidentified as “tempestites”.

Lower Cretaceous lacustrine successions, North Yellow Sea Basin, eastern China: Rift basin sequence stratigraphy and stacking patterns in response to magmatic activity

A series of Mesozoic rift basins formed in eastern China were associated with magmatic activity and subduction along the Eurasia, Izanagi and Pacific plate margins. The impact of magmatic activity on lacustrine sequence development was documented with well-log and 3-D seismic data from the Jupiter Depression in the North Yellow Sea Basin. We identified key surfaces, retrogradational and progradational parasequence sets, and defined the characteristics of systems tracts and the internal sequence components for the Lower Cretaceous (K1SQ1). A 2-D SEDPAK numerical stratigraphic forward modeling was used to further constrain sequence development in the Jupiter Depression by considering different modeling parameters and the spatial-temporal characteristics of magmatic activity. Modeling results were compared and matched with the sequence architecture observed from seismic and well interpretations. Magmatic activity impacts on the development of the K1SQ1 sequence in the North Yellow Sea Basin include topographic variation, lake level fluctuation, and sediment supply ratios. Results suggest that magmatic upwelling uplifted the northwestern area of the Jupiter Depression and formed its slope break during the late Jurassic or early Cretaceous. Along with uplifting, relative lake level dropped sharply and lake accommodation was reduced, but with increased sediment supply. Therefore, sediment accumulated along the slope break as a lowstand systems tract. Later on, as lake level continuously rose, transgressive and highstand systems tracts were developed. The proposed stacking pattern provides an analog, and a useful model, for lacustrine sequence development in response to magmatic activities in eastern China and other rift basins of similar tectonic setting.

500 m of rapid base level rise along an inner passive margin – Seismic observations from the Pliocene Molo Formation, mid Norway

The positions of late Cenozoic coasts, related base level changes and tectonic events are still an enigma along large parts of the North Atlantic passive margin due to severe glacial erosion and inconclusive biostratigraphic ages. Periglacial paleo-coastlines are best preserved along the mid Norwegian margin from where we show the first 3D seismic images of a transgressive coastal delta (lower Molo Formation) that constrains the late Cenozoic geological history.Well data, 2D seismic sections and a 990 km2 3D survey, located above the Froan Basin and the Draugen oil field, are used to investigate the 60 km-wide and 600 km long coast-parallel Molo Formation. We interpret the Molo Formation to be younger (mainly Pliocene) than the Kai Formation (Mid and late Miocene) and propose a further subdivision of the Molo Formation into a lower, largely transgressive and an upper highstand regressive unit.A relative base level fall of several hundred meters is recorded at the onset of the Miocene compression phase (mid Miocene). Simultaneously, the Mid Miocene Unconformity (MMU) developed and the syntectonic and lowstand Kai Formation was deposited to the west of the study area. Upon termination of the Miocene compression phase a cumulative base level rise in the order of 500 m is interpreted. The lower Molo Formation is interpreted as a coastal delta sequence and characterized by a sand-rich parasequence set that exhibits a largely progradational motif. The deposits record a stepped landward migration of the paleo coastline during the initial transgression. Locally, the relative position of topset-foreset rollovers and trajectory analysis document 90 m of the base level rise. The upper Molo Formation is interpreted as a fluvial-dominated, wave-influenced progradational shelf-edge delta. Fluctuations in base level are interpreted to be largely tectonically driven.

A depositional model for offshore deposits of the lower Blue Gate Member, Mancos Shale, Uinta Basin, Utah, USA

AbstractDepositional models that use heterogeneity in mud‐dominated successions to distinguish and diagnose environments within the offshore realm are still in their infancy, despite significant recent advances in understanding the complex and dynamic processes of mud deposition. Six cored intervals of the main body of the Mancos Shale, the lower Blue Gate Member, Uinta Basin, were examined sedimentologically, stratigraphically and geochemically in order to evaluate facies heterogeneity and depositional mechanisms. Unique sedimentological and geochemical features are used to identify three offshore environments of deposition: the prodelta, the mudbelt and the sediment‐starved shelf. Prodelta deposits consist of interlaminated siltstone and sandstone and exhibit variable and stressed trace fossil assemblages, and indicators of high sedimentation rates. The prodelta was dominated by river‐fed hyperpycnal flow. Mudbelt deposits consist of interlaminated siltstone and sandstone and are characterized by higher bioturbation indices and more diverse trace fossil assemblages. Ripples, scours, truncations and normally graded laminations are abundant in prodelta and mudbelt deposits indicating dynamic current conditions. Mudbelt sediment dispersal was achieved by both combined flow above storm wave base and current‐enhanced and wave‐enhanced sediment gravity flows below storm wave base. Sediment‐starved shelf deposits are dominantly siltstone to claystone with the highest calcite and organic content. Bioturbation is limited to absent. Sediment‐starved shelf deposits were the result of a combination of shelfal currents and hypopycnal settling of sediment. Despite representing the smallest volume, sediment‐starved shelf deposits are the most prospective for shale hydrocarbon resource development, due to elevated organic and carbonate content. Sediment‐starved shelf deposits are found in either retrogradational to aggradational parasequence sets or early distal aggradational to progradational parasequence sets, bounding the maximum flooding surface. An improved framework classification of offshore mudstone depositional processes based on diagnostic sedimentary criteria advances our predictive ability in complex and dynamic mud‐dominated environments and informs resource prospectivity.

Tight oil accumulation of the redeposited carbonates in the continental rift basin: A case study from Member 3 of Shahejie Formation in Shulu sag of Jizhong depression, North China

Tight oil in the redeposited carbonates was mainly distributed in the Lower Submember of Member 3 of Shahejie Formation in Shulu sag of Jizhong depression, North China. Through high-resolution 3D seismic data, well logging data and drilling data, the Lower Submember of Member 3 of Shahejie Formation was divided into 5 third-order sequences and 15 parasequence sets. The redeposited marl and rudstone were major reserving horizons of tight oil, and ten reserving space types were developed and could be classified into two main categories, i.e., pores and fractures. Two types of tight oil reservoirs were established, i.e., the marl hydrocarbon reservoir of the source-reservoir integration and the rudstone hydrocarbon reservoirs of the source-reservoir paragenesis. The assemblage relationship among the high-quality source rocks, system tracts with the source-reservoir configuration was the major control factor for tight oil accumulation in the redeposited carbonates. The lacustrine transgressive system tracts and highstand systems tracts in SQ1 to SQ5 were the favorable horizons for development of the marl hydrocarbon reservoir, the lowstand system tracts in SQ1 to SQ3 were the favorable horizons for development of the rudstone hydrocarbon reservoir.

Facies Characterization of the Surma Group (Miocene) Sediments from Jalalabad Gas Field, Sylhet Trough, Bangladesh: Study from Cores and Wireline Log

ABSTRACT The Sylhet trough located on the north-eastern margin of present Bengal basin, contains ~22 km of Tertiary sediments and well known as a hydrocarbon producing province. A detailed facies characterization of the subsurface Miocene Surma Group sediments (especial emphasis on reservoirs sandstones) from Jalalabad gas field within the Sylhet trough has been done using core log analysis and wireline log (gamma ray) interpretation. Texture and sedimentary structures of the cores suggests that the nine individual lithofacies types which can be grouped together into three facies associations, namely, fine-grained facies associations (FFA), medium-grained facies association (MFA) and coarse-grained facies associations (CFA). Major changes in gamma ray log motifs and various bounding discontinuities indicate six para-sequence sets (basin wide) and twenty eight para-sequences (local environmental changes) within the depth range from 2200-2800 m. Detailed facies analysis of the cores and wireline log reveals that the interbedding facies within the associations in the Surma Group commonly develop small-scale fining-upward (FU) cycles, coarsening-upward (CU) and random intercalations (RD). The sediments of the Surma Group of the Jalalabad field have been interpreted as deposits of the shallow marine to tide-dominated deltaic depositional setting. The cyclic nature of sedimentation pattern of the Surma Group probably records an almost continuous existence of this prograding deltaic regime and a tectonic setting characterized by a mixture of prolonged basin subsidence and regional transgression coupled with sporadic regressive phases.

Paleoenvironment of deposition of Miocene succession in well BK-10 of Bengal Basin using electrofacies and lithofacies modeling approaches

Integrating well log and core samples data were applied to interpret paleoenvironment of deposition of Miocene succession for understanding of reservoir facies model from a well Bakhrabad (BK)-10 of Bengal Basin. Miocene succession was subdivided into two depositional sequences/models which contain 9 para sequence sets and 35 para sequences. Detailed examination of well log data, based on considering GR (gamma ray) log shapes, size, lithologic variations permit a subdivision into five electrofacies models, e.g., bell, funnel, cylindrical, egg/bow and linear shape models. The succession consists of alternating shales, shaly sand, silts and sandstones, with minor mudstones. The study revealed eight distinct lithofacies models namely, shale dominated facies, heterolithic sandstone facies, cross bedding facies, parallel laminated shale with alternate sand/silt facies, ripple-lamination facies, bioturbation facies, wavy bedded facies and laminated shale facies. The depositional models for the Miocene sediments encountered in the studied well BK-10 inferred to be that of delta-front setting and fluvio-deltaic to shallow marine environments. Based on lithofacies and electrofacies models associations, Miocene succession interpreted as a coarsening upward deltaic progradation; although more repetitive marine transgression and regression sedimentary processes might have an impact on the architecture of reservoir facies model.

Half-year results of Johnson Matthey for the six months ended 30 Sep 2016

Most shallow marine sections described from the Lower Triassic formed in mixed carbonate-siliciclastic systems. Shallow marine limestones from an isolated carbonate platform, the Great Bank of Guizhou, in the Nanpanjiang Basin, South China, provide a unique opportunity to examine a pure peritidal carbonate depositional system. The platform had a low-relief bank profile in the Early Triassic with oolite shoals at the margin, shallow-subtidal and peritidal deposits in the interior, and pelagics, debris-flow deposits and turbidites on gentle basin-margin slopes. Interior strata are 265 m thick beginning in the lowermost Triassic with Renalcis biostromes, followed by lime mudstone, oolite, and cyclic peritidal limestone.The cyclic limestone is Olenekian in age, 164 m thick, and contains up to 83 cycles (parasequences). Parasequences are 0.2–7.4 m thick and typically shallow upward from subtidal oolite grainstone and skeletal packstone facies followed by Renalcis reef mounds or biostromes and capped by intertidal flaser-bedded ribbon rock. The skeletal packstone and reef mounds contain a low-diversity biota of cyanobacteria, echinoderms, bivalves, gastropods, lingulid brachiopods, spirorbids, and ostracodes. Ribbon rock contains alternating lime mud and fine peloidal packstone and grainstone laminae, scour surfaces, ripple cross lamination, lime-mud drapes, and minor prism cracks. Parasequence stacking patterns exhibit gradual increase and decrease of parasequence thickness, defining a third-order sequence boundary and several 4th-order parasequence sets that correlate between interior sections. Parasequence stacking patterns similar to those of Lower Palaeozoic green-house sequences and different from ice-house sequences.The Lower Triassic platform-interior parasequences represent an anachronistic facies in that they are strikingly similar to the common Renalcis-mound, ribbon rock parasequences of the Lower Palaeozoic and different from other Permo–Triassic parasequences (e.g. Capitan shelf parasequences or Loferites). Facies similarities such as Renalcis mounds and flaser-bedded intertidal ribbon rock reflect anomalous oceanic conditions resulting in low biodiversity and low intensity of bioturbation after the end-Permian extinction. Similarities in parasequence stacking patterns reflect low-amplitude, high-frequency sea-level fluctuations resulting from green-house conditions common to the Early Palaeozoic and Early Triassic.

Preserved Stratigraphic Architecture and Evolution of A Net-Transgressive Mixed Wave- and Tide-Influenced Coastal System: The Cliff House Sandstone, Northwestern New Mexico, U.S.A.

Abstract: The Cretaceous Cliff House Sandstone comprises a thick (400 m) net-transgressive succession representing a mixed wave- and tide-influenced shallow-marine system that migrated episodically landwards. This study examines the youngest part (middle Campanian) of the Cliff House Sandstone, exposed in Chaco Cultural Natural Historical Park, northwest New Mexico, U.S.A. Detailed mapping of facies architecture between a three-dimensional network of measured sections has allowed the character, geometry, and distribution of key stratigraphic surfaces and stratal units to be reconstructed. Upward-shallowing facies successions (parasequences) are separated by laterally extensive transgressive erosion (ravinement) surfaces cut by both wave and tide processes. Preservation of facies tracts in each parasequence is controlled by the depth of erosion and migration trajectory of the overlying ravinement surfaces. In most parasequences, there is no preservation of the proximal wave-dominated facies tracts (foreshore, upper-shoreface), resulting in thin (4–7 m) top-truncated packages. Four distinct shallow marine tongues (parasequence sets) have been identified, consisting of ten parasequences with a total stratigraphic thickness of ∼ 100 m. Each tongue records an episode of complex shoreline migration history (multiple regressive–transgressive phases) in an overall net-transgressive system. The ravinement surfaces provide a stratigraphic framework in which to understand partitioning of tide- and wave-dominated deposits in a net-transgressive system, and a model is presented to account for the sediment distribution and stratigraphic architecture observed in each parasequence. Despite a complex internal architecture, parasequences exhibit a predictable pattern which can be related to the regressive and transgressive phases of deposition. Preservation of wave-dominated facies tracts is associated with shoreline regression, while tide-dominated facies tracts are interpreted to record sediment accumulation during shoreline transgression that also resulted in significant erosion of the underlying regressive deposits. The interplay between erosion, sediment bypass, and deposition during regression and transgression is shown to ultimately control the preservation and stratigraphic architecture of the larger-scale net-transgressive coastal system. While the Cliff House Sandstone exhibits a facies composition and quantitative stacking patterns (shoreline trajectory) similar to other studied examples, differences in the dip-extent of the wave-dominated sandstone tongue has resulted in a more disconnected architecture between the high-frequency cycles. Understanding the variety of stratal geometries that ravinement surfaces can generate is therefore crucial to predicting the spatial distribution and facies architecture in transgressive systems.

Sequence stratigraphy, sedimentary facies and reservoir quality of Es4s, southern slope of Dongying Depression, Bohai Bay Basin, East China

Thin-bedded beach-bar sandstone reservoirs are common in the Eocene Shahejie Formation (Es4s) of Niuzhuang Sag, along the southern gentle slope of the Dongying Depression. Here we report on the link between sequence stratigraphy, sedimentary facies and diagenetic effects on reservoir quality. Seismic data, wireline logs, core observations and analyses are used to interpret depositional settings and sequence stratigraphic framework. Petrographic study based on microscopic observation of optical, cathodoluminescence (CL), confocal laser scanning (LSCM) and scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses were used to describe the fabric, texture, allogenic and authigenic mineralogy of these highly heterogeneous sandstone reservoirs. The Es4s interval is interpreted as third-order sequence, composed of a lowstand systems tract (LST), a transgressive systems tract (TST) and a highstand systems tract (HST). On the fourth order, twenty-nine parasequences and seven parasequence sets have been identified. Sand bodies were deposited mainly in the shoreface shallow lake beach-bar (clastic beach-bar), semi-deep lake (carbonate beach-bar) and the fluvial channels. The depositional and diagenetic heterogeneities were mainly due to the following factors: (1) fine grain size, poor sorting, and continuous thin inter-bedded mud layers with siltstone/fine-sandstone having argillaceous layers in regular intervals, (2) immature sediment composition, and (3) even with the dissolution of grains and several fractures, destruction of porosity by cementation and compaction. Secondary pores from feldspar dissolution are better developed in sandstones with increased cementation. Grain coating smectite clays preserved the primary porosity at places while dominating pore filling authigenic illite and illite/smectite clays reduced permeability with little impact on porosity. Due to the high degree of heterogeneity in the Es4s beach-bar interval, it is recognized as middle to low permeable reservoir. The aforementioned study reflects significant insight into the understanding of the properties of the beach-bar sands and valuable for the comprehensive reservoir characterization and overall reservoir bed quality.

Characterization, architecture and controls of Cold Lake marginal-marine oil sands: the Grand Rapids Formation (Upper Mannville) of east-central Alberta, Canada

Abstract Hydrocarbons have been produced from the Grand Rapids oil sands for decades; however, large volumes still remain in place, mostly due to the extreme complexity of the reservoirs. Detailed examination of wireline logs and cores from 1127 wells within the 400 km2 Manatokan Field (Twp 62–63; Rge 4–5 W4M) are used to characterize the deposits, define the stratigraphic framework, establish the depositional architecture, and infer the mechanisms and parameters controlling the deposition of the formation. Twenty-one facies are identified based on detailed core analysis (sedimentology, ichnology, geochemistry), and are organized into five recurring facies associations: 1) wave-dominated shoreface deposits; 2) delta-influenced shoreface deposits; 3) interdistributary bay deposits; 4) marine-influenced fluvial deposits; and 5) coastal plain deposits. Shoreface deposits, which form correlatable 3–30 m-thick coarsening-up cycles, are classified as wave-dominated fluvial-influenced to fluvial-dominated wave-influenced, potentially tide-affected (Wft to Fwt). Marine-influenced fluvial deposits are mostly emplaced as point bars within 100–2000 m wide and 3–30 m deep fluvial bodies distributed within the strata. The established stratigraphic framework subdivides the formation into 11 parasequences, 7 parasequence sets, 7 stratigraphic levels containing fluvial bodies and 2 depositional sequences capped by sequence boundaries. Those observations contrast with previous interpretations that recognized seven sequences boundaries capping each of the parasequence sets. However, stratigraphy of the Grand Rapids Formation is primarily controlled by eustacy: sequences and parasequence sets are primarily influenced by long-period moderate-amplitude (1.2–2.4 m.y.; 15–30 m) and short-period low-amplitude (0.4 m.y.; <10 m) glacio-eustatic sea-level cyclicity, respectively. Individual parasequences are likely controlled by short-period allocyclic (100 to 20 kyr climatic variations) and/or autocyclic parameters (delta lobe switching every 5 to 2 kyr) that affect regional and local sediment flux. These parameters and different timescales explain the peculiar distribution of reservoirs in the field with small and isolated geobodies.