Distal Delta Research Articles

Organic geochemical, petrographic and palynological characterization of claystones of the Palaeogene Toraja Formation, and oil seeps in the Enrekang Sub-basin, south Sulawesi, Indonesia: Implications for hydrocarbon source rock potential

An organic geochemical, petrographical, and palynological evaluation was conducted on 30 claystone outcrop samples of the Toraja Formation, along with a geochemical analysis of an oil seep in the Enrekang Sub-basin. The aim of the study was to determine the correlation between oil and source rock in terms of age, depositional environment, organic material sources, and maturity level. The total organic carbon content of the claystone samples varies from 0.03 to 4.52 wt%, which are classified as poor to excellent. The claystones are immature to post-mature with a mixture of Type Ⅱ and Ⅲ kerogen. Their vitrinite reflectance values range from 0.47 to 4.52 %Ro. The samples of Toraja Formation rock and the oil seep source rock might have a similar depositional environment, a deltaic marine depositional setting with high oxidizing conditions. Organic material sources for rock and oil samples are dominated by terrestrial input. The oil is inferred to have originated from the Paleogene source rocks, which correlates in age with the Toraja Formation. The recovered palynomorphs from the studied rock samples suggest a late Eocene to Oligocene age with a strong terrestrial influence of shallow marine depositional setting. The biomarker analysis shows that the rock samples have a more substantial contribution from the terrigenous higher plants, while the oil sample indicates a higher degree of marine influence. The maturity levels are also different between the oil (peak mature) and the analyzed rock samples (immature). It is inferred that the oil seep source rock is equivalent to the analyzed rock sample but more mature, having been deposited under more marine conditions. The oil seep source rock is not exposed and is located in the deeper part of the basin. A deeper marine facies (i.e. distal delta front and prodelta facies) in front of the distributary mouth bar within a delta is interpreted as the source rock of the oil seep sample.

Cyclicity of the Lower Buntsandstein in the eastern part of the Central European Basin: implications for Early Triassic palaeogeography and for geochronological calibration

Lower Buntsandstein small–scale cycles recognized in the Central European Basin (CEB) are readily used for astrochronological calibration of the Early Triassic time scales, although they are not well studied sedimentologically. Three borehole sections from the eastern part of the CEB, forming a south-north transect perpendicular to the basin axis, were studied in terms to better understand the depositional history of the Lower Buntsandstein developed as the Baltic Formation in the studied Polish part of the basin. Eleven sedimentary facies were recognized, based on lithological and sedimentological investigations of 655.7 m of drill cores from the Otyń IG 1, Gorzów Wielkopolski IG 1 and Kamień Pomorski IG 1 boreholes. The facies can be grouped according to a lithological criterion into facies of predominantly siliciclastic lithology (including 9 facies types) and facies of predominantly carbonate lithology (including 2 facies types). Facies analysis allowed to distinguish 8 facies associations of: 1) alluvial fan, 2) playa, 3) sandy-muddy coastal plain, 4) embayment and distal delta, 5) lagoon, 6) sand bars or shoals, 7) ooidal shoals or bars, and 8) offshore. Deepening-upward (DC) and shallowing-upward (SC) sedimentary cycles were recognized in parts of the Baltic Formation, with DCs dominating in the southernmost located Otyń IG 1, and SCs dominating in Gorzów Wielkopolski IG 1, located in the axial part of the basin. Symmetrical cycles are very rare. The statistical significance of the sedimentary cycles is relatively low according to Markov-chain analysis conducted with the phpSedistat software of Stanova et al. (2009). Analysis of small–scale cycles performed on well logs of investigated boreholes and additional boreholes in the vicinity of Otyń IG 1, implementing the earlier study of Becker (2005), showed that the correlation of well-log cycles (GR cycles) and sedimentary cycles is not obvious. GR cycles can be roughly correlated with lithological carbonate–siliciclastic cycles (c-s cycles), reflecting alternations of facies groups of predominantly carbonate and siliciclastic lithology. Calibration of GR cycles to earlier magnetostratigraphic results of Nawrocki (1997) and Becker and Nawrocki (2014) showed that neither the boundaries of GR cycles serve as reference horizons, nor the cycles document equal time periods. All existing depositional models of the Lower Buntsandstein were discussed, stressing the possible simultaneous interaction of allochthonous and autochthonous processes. Moreover, the tectonic overprint of the Central European Basin system during the Early Triassic should be taken into account. The presented results suggest that the Lower Buntsandstein cyclicity of the CEB cannot serve as a basis for astrochronological analysis.

Evolution of a Lake Margin Recorded in the Sutton Island Member of the Murray Formation, Gale Crater, Mars

AbstractThis study uses data from the Mars Science Laboratory Curiosity rover to document the facies of the Sutton Island member of the Murray formation, interpret paleoenvironments, and establish key stratigraphic transitions at Gale crater. Two facies associations were identified: Facies Association 1 (FA1) and Facies Association 2 (FA2). Individual facies in FA1 include planar‐laminated mudstone with minor intervals of planar sandstone, ripple cross‐laminated sandstone, cross‐stratified sandstone, and alternating laminated sandstone and mudstone. Meter‐thick packages of planar‐laminated mudstone in FA1 are interpreted to represent deposition in low‐energy ponded environments along the lake margin. Straight‐ and curve‐crested ripple cross‐laminated facies are interpreted to represent current‐influenced deposition. Cross‐stratified sandstone facies consist of dm‐thick sets that represent deposition in distal channels. Intercalated mm‐scale mudstone and sandstone laminae represent waning flow conditions and possible channel abandonment. Facies in FA1 collectively represent deposition in a distal delta plain. FA2 is comprised of planar‐laminated mudstone with minor sandstone and is interpreted to represent deposition in a lacustrine‐basin setting by suspension settling linked to density flows. FA1 transitions upward into FA2, defining a rapid transgression substantial enough to facilitate the deposition of distal lake facies above delta plain facies. The abrupt transition from FA2 back to FA1 deltaic deposits is suggestive of forced regression. Facies in FA1 and FA2 are consistent with the prevalence of aqueous environments recorded in other Murray formation members and extend our understanding of the dynamic sedimentary processes that characterized ancient lacustrine systems at Gale crater.

Facies association analysis of a Toarcian siliciclastic‑carbonate lacustrine system, Sichuan Basin, China

Globally, considerable coverage has been devoted to marine environment affected by the Jenkyns Event, but little attention has been given to lacustrine system. Here, siliciclastic‑carbonate samples of the Da'anzhai Member (J1dn) were examined for petrology and geochemistry in order to evaluate lithofacies characteristics, depositional processes and environmental changes of the palaeo-Sichuan lacustrine basin contemporaneous with the Jenkyns Event. Unique sedimentological and petrological features were used to identify five principal facies associations (FA) and depositional environments, including the distal delta front, accretionary bioclastic shoals, proximal bioclastic shoal ramp, distal bioclastic shoal ramp and (semi-)deep lacustrine environment. The vertical transitions of FA reveal that J1dn forms a complete lacustrine transgressive-regressive sedimentary system during the Toarcian, which can be further divided into 3 units in combination with standard gamma logging. The lower unit is characterised by frequent intermixing of multiple FA interpreted as frequent lake-level fluctuations. The middle unit is characterised by the deposition of clay-rich mudstone and the demise of bioclastic shoals interpreted as intensive lacustrine transgression that were at times affected by storm-induced waves or oscillatory currents coinciding with the initiation of the Jenkyns Event. The upper unit is characterised by the thicker and higher proportion of biogenic carbonate-rich lithofacies interpreted as the lake regression, contemporaneous with the end of the Jenkyns Event. Overall, clay-rich lithofacies from suspension settling, turbidity current or slumping triggered by storm events were deposited during a high relative lacustrine-level, accompanied by organic carbon-rich deposition and preservation. In contrast, carbonate-rich lithofacies were mainly controlled by biogenic carbonate sedimentation, associated with a low relative lacustrine-level unconducive to organic matter accumulation. Finally, the proposed depositional evolution model at the lake-level highstand stage and lowstand stage of the palaeo-Sichuan lacustrine basin provides new insights and understanding on the changing palaeolimnological history of the Toarcian lacustrine system.

The Mondot-1 Core, Aínsa Basin, Spanish Pyrenees: a deltaic reservoir teaching set with augmented reality

Abstract Well Mondot-1 was drilled, cored and logged behind an outcrop of the Eocene Sobrarbe deltaic complex in the Aínsa Basin, Spanish Pyrenees. The data acquired represent a fluvial-dominated delta system prograding over a carbonate slope in the presence of active tectonism, and form part of a basin-to-grain teaching set for subsurface professionals. This paper highlights the workflow step(s) to move from a 1D core description to 2D and 3D correlations, including some of the pitfalls caused by rapid lateral facies variability, which is a common challenge in subsurface reservoir description. The core allows direct log-to-lithology comparison across a full deltaic succession. In the proximal and distal delta fronts, there are clear differences from the closely adjacent outcrop that are ascribed to lateral facies changes and delta front slumping. Two approaches to core display are described, as means towards making such data available to a wider audience: an augmented reality display run over a slabbed core, and a virtual whiteboard display carrying easily scalable viewing possibilities. These approaches can be deployed for other cores, allowing visualization and analysis where people are otherwise unable to travel to the physical location, or in circumstances where the core is now inaccessible.

The Facies Analysis, Evolution, and Coal-Bearing Source Rock Features of the Middle–Late Triassic Shallow-Water Delta in the North Carnarvon Basin, Northwest Shelf of Australia

The sedimentary facies, architecture, and depositional mechanism of deltaic systems have been one of the global research hotspots in recent decades; however, the detailed distribution, sedimentary evolution, source rock potential, and major control factors of the coal-bearing shallow-water delta are still unclear. A typical shallow-water braided delta with coal-bearing source rocks developed in the Middle–Late Triassic Mungaroo Formation of the North Carnarvon Basin, which can be a good study area for an analysis of coal-bearing source rocks. In this study, the sedimentary facies, distribution and evolution, and coal-bearing source rock features of the Triassic strata were analyzed based on the integrated study of wireline logs, drilled cores, thin sections, seismic facies and attributes, and geochemical data. A range of shallow-water delta sedimentary facies was identified, including the proximal delta plain channel/interdistributary bay, distal delta plain channel/interdistributary bay, and the delta front. The coal-bearing shallow-water delta system of the Middle–Late Triassic Mungaroo Formation was characterized by the largest scale delta system with relatively broad proximal and distal delta plains and relatively narrow delta front subfacies. The scale of the delta system showed a trend of increasing from the Early Triassic Locker Shale to the Middle–Late Triassic Mungaroo Formation and then decreasing to the Late Triassic Brigadier Formation. The distal delta plain subfacies of the Mungaroo Formation should have the highest potential coal-bearing source rock, and the proximal delta plain also can be a favorable target for source rock evaluation. The major control factors of the coal-bearing source rocks of the Mungaroo shallow-water delta mainly included the Triassic megamonsoon climate, the topographic features, eustatic changes, and provenance supply. The proximal and distal delta plains of the shallow-water delta system with thin coal seams, carbonaceous mudstone, and dark mudstone lithologies’ association could be a favorable source rock exploration facies for the next stage of natural gas field exploration.

The influence of bioturbation on reservoir quality: Insights from the Columbus Basin, offshore Trinidad

Nine facies are recognised in two mid-Pliocene cores from the Columbus Basin, offshore east coast Trinidad. Facies successions are consistent with deposition within a deltaic-shoreface continuum. Lower shoreface deposits are heavily bioturbated by Scolicia, Asterosoma, Thalassinoides, Teichichnus, Palaeophycus and other elements of the Cruziana Ichnofacies whereas middle shoreface sandstone beds contain sand-filled burrows of the Skolithos Ichnofacies. Deltaic deposits record coarsening-upward successions with evidence of freshwater influx such as synaeresis cracks, fluid muds, and dispersed organic detritus. Prodelta and distal delta front deposits comprise heterolithic beds and contain sporadically distributed and diminutive structures belonging to the Phycosiphon Ichnofacies. Hummocky cross-stratification is prominent in storm-dominated proximal delta front sandstone deposits that are sparsely bioturbated by Ophiomorpha, Skolithos and other elements of the Rosselia Ichnofacies. Cryptic bioturbation is common at the top of these beds. Thin section examination, core plug analysis, and numerical modelling of the facies were undertaken to better understand fluid flow in bioturbated strata of the Columbus Basin. Whereas lithology and texture remain the primary control on reservoir quality, examples of biogenically enhanced permeability are present in the P3 and P7 cores. The highest permeability values are associated with highly bioturbated middle shoreface deposits that comprise clean, sand-filled burrows. Favourable permeability measurements are also attributed to cryptically bioturbated delta front sandstone beds. The latter display higher permeabilities when compared to unbioturbated and sparsely sandstone beds. Biogenic activity contributed to reduced permeabilities in lower shoreface and distal delta front deposits owing to extensive sediment packing and sediment mixing behaviours. Relationships between permeability and bioturbation intensity indicate that effective permeability in bioturbated intervals of the P3 and P7 cores are best characterised by the arithmetic mean of permeabilities and that simple statistical calculations can aid in the analysis of highly bioturbated facies (BI = 5–6).

From apex to shoreline: fluvio-deltaic architecture for the Holocene Rhine–Meuse delta, the Netherlands

Abstract. Despite extensive research on alluvial architecture, there is still a pressing need for data from modern fluvio-deltaic environments. Previous research in the fluvial-dominated proximal and central Rhine–Meuse delta (the Netherlands) has yielded clear spatial trends in alluvial architecture. In this paper, we include the backwater length to establish architectural trends from apex to shoreline. Channel-belt sand body width / thickness ratios and interconnectedness were determined, and the proportions of fluvial channel-belt deposits, fluvial overbank deposits, organics and intertidal deposits were calculated for the complete fluvio-deltaic wedge based on high-resolution geological cross sections. It was found that the average width / thickness ratio of channel-belt sand bodies in the proximal delta is 5 times higher than in the distal delta. Other down-valley trends include an 80 % decrease in the channel deposit proportion (CDP) and a near-constant proportion of overbank deposits. Additionally, interconnectedness in the proximal delta is 3 times higher than in the distal delta. Based on the Rhine–Meuse dataset, we propose a linear empirical function to model the spatial variability of CDP. It is argued that this relationship is driven by four key factors: channel lateral-migration rate, channel-belt longevity, creation of accommodation space and inherited floodplain width. Additionally, it is established that the sensitivity of CDP to changes in the ratio between channel-belt sand body width and floodplain width (normalized channel-belt sand body width) varies spatially and is greatest in the central and distal delta. Furthermore, the proportion of fluvial channel-belt sands is generally an appropriate proxy for the total sand content of fluvio-deltaic successions, although its suitability as a total sand indicator rapidly fades in the distal delta. Characteristics of the backwater zone of the Rhine–Meuse delta are (1) sand body width / thickness ratios that are lower as a consequence of channel narrowing (not deepening), (2) a rapid increase and then a drop in the organic proportion, (3) an increase in the total sand proportion towards the shoreline, and (4) a drop in the connectedness ratio. For this paper, unique high-resolution quantitative data and spatial trends of the alluvial architecture are presented for an entire delta, providing data that can be used to further improve existing fluvial stratigraphy models.

Paleodepositional Environment and Sequence Stratigraphy of Miocene Sediments in Well TN-1, Coastal Swamp Depobelt, Niger Delta Basin, Nigeria

This research focused on the interpretation of paleodepositional environment and development of a sequence stratigraphic framework for the well TN-1 section, located in the coastal swamp depositional belt of the Niger Delta Basin. Integration of interpreted litho- and biofacies data sets that facilitated the interpretation of the paleodepositional environment enabled the erection of a sequence-stratigraphic framework. Three lithotypes (sand, clay, and shale) distributed within fourteen facies variants were integrated with palynomorph components to delineate five paleodepositional cycles ranging from distal delta plain to bathyal. Eight systems tracts (closely related to depositional cycles, but transcended depositional boundaries in some intervals) that hosted three maximum flooding surfaces (MFS), three sequence boundaries (SBs), distributed within four third-order and three second-order sequences, were defined. Age-significant palynomorphs recovered indicated an Aquitanian to Messinian age range (with non-deposition or erosion of Burdigalian, Langhian, Serravallian Stages sediments), distributed within five pollen zones (P628–P840) that correlated with published global cycles. This study demonstrates the significance of integrated studies to erect a sequence-stratigraphic framework applicable for field and basin-scale exploration and exploitation purposes.
 Keywords: Sequence stratigraphy, paleodepositional cycles, systems tract, cyclic sedimentation,lithofacies analysis, integrated studies.

Evolution of a fluvial-dominated delta during the Oligocene of the Colombian Caribbean: Sedimentological and ichnological signatures in well-cores

Basin analysis from Colombian Caribbean is particularly important given the interest in finding hydrocarbon reservoirs, but their complex geological evolution, and the frequent lateral and vertical variation of facies difficult a conclusive characterization, highlights the need for detailed sedimentological and ichnological studies. The study succession corresponds to an interval of a well core drilled in the south of the Sinú-San Jacinto Basin (Colombian Caribbean), with 1069 ft (~326 m) thick of an Oligocene siliciclastic succession, interpreted in general terms, as deposited in a deltaic system. The integrated sedimentological/ichnological analysis allows the differentiation of dominant facies, with predominant lithologies such as conglomerates, sandstones, mudrocks, bioclastic sediments, as well as coal beds. The ichnological assemblage is low in abundance and moderately diverse, composed by Conichnus, Cylindrichnus, Dactyloidites, Macaronichnus, Ophiomorpha, Phycosiphon, Skolithos, Taenidium, Teichichnus, and Thalassinoides, as well as rhizoliths.The complexity of the sedimentary system is reflected in its evolution throughout the Oligocene. A type succession with coarsening-upward trend was identified and it is repeated through the succession studied. It presents a general trend from bioclastic sediments (bioclastic conglomerates, sandstones and mudrocks) that pass into horizontal lamination and massive mudrocks occasionally bioturbated by Phycosiphon, and interbedded by mudrocks and sandstones with lenticular bedding, and the occurrence of Teichichnus. Above, bioturbated muddy sandstones with Ophiomorpha, Taenidium, Thalassinoides, and rarely Teichichnus, muddy sandstones with planar cross-lamination, and horizontal lamination sandstones with Dactyloidites, Ophiomorpha, Skolithos, and Thalassinoides are registered. Transition to carbonaceous mudrocks with Teichichnus, coal medium beds, and fine-to coarse-grained sandstones sometimes with Macaronichnus and/or Ophiomorpha is observed. Towards the top, are observed mudrocks with rhizoliths. This succession is interrupted by massive and horizontal lamination sandstones with low bioturbation index generated by the ichnological assemblage and/or by the exclusive occurrence of Ophiomorpha and/or Taenidium. Massive sandstones with erosive bases, asymmetrical ripples, and high content of organic debris are occasionally recorded. This succession reflects a progradational trend similar to those of fluvial-dominated deltaic sequences.Detailed analysis revealed that even the fluvial processes were dominant in the deltaic system; however, local tidal and wave influence is recorded. Moreover, integration of sedimentological and ichnological information allows characterizing the evolution of the different sub-environments of the deltaic system, as prodelta bay, distal delta front, proximal delta front, distributary channels, mouth bars, and lower delta plain, and this is essential for areas of economic interest.

Selective colonization after storm events in a delta environment: applied ichnology from the early Miocene of Taiwan

The sedimentological and palaeoecological interpretation of early Miocene age shallow marine deposits from one of the most emblematic geological areas of Taiwan – Yehliu peninsula – is not easy to approach in detail, and several contrasting proposals can be found in the literature. The present ichnological study helps to corroborate a delta environment as the most likely palaeoenvironmental setting, and to recognize the different sub-environments and hydrodynamic processes involved. The distal delta front displays the greatest trace fossil diversity, assigned to the Cruziana ichnofacies, including Ophiomorpha, Phycosiphon, Planolites, Rosselia, Schaubcylindrichnus, Scolicia, Thalassinoides and vertical equilibrium adjustment structures. The delta front records predominantly vertical traces attributable to the Skolithos ichnofacies. Amalgamated shell beds (most likely related to storm events) show concentrations of broken bivalve shells. After storm a selective colonization is interpreted, firstly by bioerosive tracemakers during times of decreasing sedimentation rate, followed by a dominance of trophic generalists such as those producing Ophiomorpha during post-storm sedimentation.

Facies characteristics and stratigraphy of an Upper Cretaceous mud‐dominated subaqueous delta: Medicine Hat Member (Niobrara Formation), Alberta, Canada

AbstractThe Medicine Hat Member in Alberta, Canada, is a muddy interval with thin sandstones. However, the sedimentology and stratigraphy are poorly understood – a reflection of the limited knowledge of mud‐dominated successions. Here facies analysis and stratigraphy from core and wireline logs were used to construct a depositional framework for the interval in a stratigraphical context. Sedimentological and ichnological results show that the Medicine Hat Member was deposited in shallow water within a mud‐dominated subaqueous delta system under the combined influence of river flow, waves, storms and longshore currents. Four facies are recognized, which are interpreted as distal delta front, proximal prodelta, distal prodelta and interdistributary bay deposits. The distal delta front is dominated by sandy storm deposits and thin storm‐flood hyperpycnites. The prodelta, on the other hand, is characterized by muddy storm deposits and wave‐enhanced sediment gravity flow deposits, with only subordinate hyperpycnites. Ichnological assemblages in both the delta front and prodelta are impoverished, indicating persistent physico‐chemical environmental stresses. Interdistributary bay deposits are uncommon and are differentiated based on more robust ichnological assemblages and higher bioturbation intensities. Subsurface correlations reveal shallowing‐upward parasequences that have aggradational and progradational stacking patterns and a very low depositional gradient (ca 0.03° to 0.1°). The stratigraphy reflects rapid progradation with fixed accommodation in a low‐gradient setting; coeval flexural subsidence in the foredeep was dampened by underlying basement structures. Furthermore, previous suggestions that the Bow Island Arch impacted sediment distributions are not substantiated by the low angle geometry of clinoforms. Data from this study supports the interpretation that Medicine Hat deltas were fed by rivers flowing north through Montana because parasequences are sandier towards the south. This study fills a crucial gap in the literature by providing a rock record example of a mud‐dominated subaqueous delta system and serves as a basis for comparison in core studies of similar units globally.

Sedimentary environment and provenance of sandstones from the Qadir member in the Nayband Formation, Tabas block, east-central Iran

Qadir Member of Nayband Formation, located in East of Central Iran, has developed to a great extent. Investigation of the lithofacies and sedimentary environment, resulted in identification of the deltaic and marine deposits. Based on field evidence and facies features, Qadir Member consists of two lithofacies, including carbonate and siliciclastic facies. The siliciclastic facies were identified as having four sandstone facies including Sr, Sh, Sp, St, three fine-grained lithofacies, including FI, Fm, Fl (Sr) / Sr (FI) and one coal facies. Also, regarding the field, laboratory studies, and identification of lithofacies, the coastal plain, deltaic (including deltaic plain, proximal delta front, distal delta front, and prodelta) and open marine environments were identified for Qadir Member which is is under the impact of tidal currents. The chemical weathering index (71%) indicated semi-arid to semi-humid conditions and plotting the geochemical data showed the provenance of re-cycling and active continental margin and because of Chemical Index of Alteration, the weathering rate was found to be rather medium to high. The geochemical diagrams also showed a probable source of the intermediate igneous and sedimentary rocks. The active continental margin conditions for this deposit could suggest the Neotethys subduction under Iran’s plate and volcanic activity at the end of Triassic, which coincided with the early Cimmerian orogeny in Alborz and Central East Iranian Microcontinent.

High-Resolution Seismic Stratigraphy Offshore Haeundae Beach in Busan, South Korea

Choi, D.-L.; Shin, D.-H.; Jin, J.-Y.; Lee. Y.-K., and Kum, B.-C., 2020. High-resolution seismic stratigraphy offshore Haeundae beach in Busan, South Korea. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Geospatial Research of Coastal Environments. Journal of Coastal Research, Special Issue No. 102, pp. 187-193. Coconut Creek (Florida), ISSN 0749-0208.The stratigraphic architecture of the Haeundae shallow sea was evaluated using numerous high-resolution single-channel seismic profiles and drilled cores. Two major seismic units over the basement, the lower Unit II and upper Unit I, as well as two subunits (Units Ia and Ib) in the upper Unit I were identified in the study area. Unit II shows numerous chaotic diffraction hyperbolic seismic reflection patterns overlying high amplitude, and irregular reflection of the bedrock surface, corresponding well with the gravel-dominated deposits. Unit II is interpreted as nonmarine alluvial deposits in the Quaternary glaciations. Unit I is present over Unit II with two distinct subunits at different locations: Unit Ia, distributed inshore within ∼10 m depth, and Unit Ib, offshore beyond ∼13 m depth. Unit Ia, which is accumulated more in the western inshore section, exhibits an acoustically semi-transparent and sigmoidal clinoform wedge and is well correlated with sand-dominated deposits from core data. Unit Ib, which pinches out landward but gradually thickens seaward, is generally characterized by transparent seismic facies, likely made up of very fine sandy to muddy sediments from surface sediments. The depositional environments of Units Ia and Ib are categorized as shoreface settings and the landward innermost part of the Nakdong distal delta system during late Holocene sea-level highstand, respectively. Due to severe weather conditions associated with winter storms and summer typhoons as well as human interventions, the sediment morphology and its distribution are thought to have constantly been reactivated and modified.

Integrated outcrop and subsurface geomodeling of the Turonian Wall Creek Member of the Frontier Formation, Powder River Basin, Wyoming, USA

Inter-well heterogeneities influencing fluid migration in deltaic reservoirs are controlled by lateral lithofacies changes and vertical complexities such as low permeability thin-beds (i.e. mudstones). Subsurface tools cannot adequately predict the spatial and stratigraphic organization of these architectural elements, nor their influence on effective reservoir properties and connectivity. Our outcrop-based geomodeling study of the Turonian Wall Creek Member of the Frontier Formation in the Powder River Basin, Wyoming, USA, integrates subsurface production and flow simulation data to quantify the impact of multi-scale stratigraphic heterogeneity on analogous reservoir behavior and horizontal well design. The upscaled representation of thin-bed complexity in our 500 m × 715 m x 15 m geomodel is derived through flow simulation of internally nested, facies specific, centimeter-scale models (basic depositional element models or BDEMs). These BDEMs are populated with quantitative data of mudstone thin-bed geometries directly derived from digital outcrop measurements and measurements in the field, and aided by subsurface (core) petrophysical properties. Reservoir simulations are performed using various landing zone and completion configurations, and under both single-phase and multi-phase flow conditions history matched to subsurface production data.Results from our workflow demonstrate that, in heterolithic settings, the permeability of mudstone thin-beds impart the most significant impacts toward upscaled reservoir behavior, and deliver unique Kv/Kh flow anisotropies dependent on the governing depositional environment. Thin, laterally continuous and planar mudstone beds in the wave-and river-dominated distal delta front setting have the greatest negative effect on Kv and a minimal impact on Kh, promoting laterally continuous and vertically baffled flow units. Conversely, the more curvilinear and intersecting architectures of mudstone beds in the tidal dune facies maintain better vertical connectivity but decreased Kh compared to the wave-influenced facies. Reservoir flow is only sensitive to changes in engineering design (landing zone, well orientation, completion size) where thin-beds act as complete barriers rather than baffles to flow. Layer cake subsurface models failing to account for high-resolution stratigraphic architectures are likely to overestimate reservoir production where thin-beds act as barriers capable of appreciable reservoir compartmentalization, which in our models is more characteristic of the distal delta front setting. Synthesized results of this study are immediately applicable toward development planning in similar tight sandstone reservoirs.

Lower-middle ordovician sedimentary environment and provenance of the suri formation in the northern region of the Famatina belt, Catamarca, Argentina

The Suri Formation is a sedimentary-volcanic succession in the Famatina belt formed during Lower - Middle Ordovician arc magmatism along the western margin of Gondwana. This study reports new lithostratigrafic data relating to the Suri Formation in the Chaschuil valley (Catamarca). The survey defines the main characteristics of volcanism and sedimentation through facies analysis. Epiclastic, volcaniclastic, pyroclastic and peperitic facies were recognized and interpreted in five facies association. The features and relationships of the facies associations indicate environments such as apron volcaniclastic, inner to an outer shelf, and fan distal delta, interbedded with effusive and explosive volcanism. Volcanic activity and relative sea-level changes were controls on sedimentation style in basins adjacent to the volcanic edifice. The study reports U–Pb geochronological analysis of zircon from a sandstone sample of the Suri Formation to infer detrital provenance. The detrital zircon pattern with peaks at 486 Ma points to active Famatinian magmatism as recorded on the nearby Narváez batholith. Eruptive masses experienced rapid reworking, short sedimentary transport and intra-arc deposition. The maximum deposition age of detrital zircon corresponds to a subordinate age cluster at 464.4 ± 4.4 Ma and reflects synchronism between volcano-sedimentary deposition in the Suri Formation and plutonic-volcanic construction of the Las Planchadas Formation.

The role of shelf morphology on storm‐bed variability and stratigraphic architecture, Lower Cretaceous, Svalbard

AbstractThe dominance of isotropic hummocky cross‐stratification, recording deposition solely by oscillatory flows, in many ancient storm‐dominated shoreface–shelf successions is enigmatic. Based on conventional sedimentological investigations, this study shows that storm deposits in three different and stratigraphically separated siliciclastic sediment wedges within the Lower Cretaceous succession in Svalbard record various depositional processes and principally contrasting sequence stratigraphic architectures. The lower wedge is characterized by low, but comparatively steeper, depositional dips than the middle and upper wedges, and records a change from storm‐dominated offshore transition – lower shoreface to storm‐dominated prodelta – distal delta front deposits. The occurrence of anisotropic hummocky cross‐stratification sandstone beds, scour‐and‐fill features of possible hyperpycnal‐flow origin, and wave‐modified turbidites within this part of the wedge suggests that the proximity to a fluvio‐deltaic system influenced the observed storm‐bed variability. The mudstone‐dominated part of the lower wedge records offshore shelf deposition below storm‐wave base. In the middle wedge, scours, gutter casts and anisotropic hummocky cross‐stratified storm beds occur in inferred distal settings in association with bathymetric steps situated across the platform break of retrogradationally stacked parasequences. These steps gave rise to localized, steeper‐gradient depositional dips which promoted the generation of basinward‐directed flows that occasionally scoured into the underlying seafloor. Storm‐wave and tidal current interaction promoted the development and migration of large‐scale, compound bedforms and smaller‐scale hummocky bedforms preserved as anisotropic hummocky cross‐stratification. The upper wedge consists of thick, seaward‐stepping successions of isotropic hummocky cross‐stratification‐bearing sandstone beds attributed to progradation across a shallow, gently dipping ramp‐type shelf. The associated distal facies are characterized by abundant lenticular, wave ripple cross‐laminated sandstone, suggesting that the basin floor was predominantly positioned above, but near, storm‐wave base. Consequently, shelf morphology and physiography, and the nature of the feeder system (for example, proximity to deltaic systems) are inferred to exert some control on storm‐bed variability and the resulting stratigraphic architecture.

Ichnological analysis of the Lower Morne L'Enfer Formation, Cedros Bay, Trinidad, West Indies: evidence of delta asymmetry

The Pliocene Silt and Sandstone Members of the Lower Morne L'Enfer Formation at Cedros Bay, SW Trinidad, reflect mixed wave, fluvial and tidal influence. Integrated ichnological analyses of these deposits reveal that the prodelta and delta front successions vary notably along-strike. These along-strike variations fit well into an asymmetric delta model. Trace fossil assemblages on the downdrift side of the delta lobe are characterised by diminutive, morphologically simple and facies-crossing forms due to heightened riverine influence. Ichnofossil assemblages on the updrift side of the lobe are robust and diverse, as a result of persistent wave reworking, generally unstressed. Mud- and silt-dominated prodelta and delta front deposits in the downdrift region are characterised by a low abundance and low diversity trace fossil assemblage reflecting a stressed expression of the Cruziana ichnofacies. Slumping and scouring structures are common within the distal prodelta deposits. Prodelta to distal delta front intervals on the updrift side are densely bioturbated. These trace fossil assemblages are abundant and diverse, representing a proximal to archetypal expression of the Cruziana ichnofacies. These deposits coarsen upward into fine grained sandstone beds of the proximal delta front. Strong storm influence in the proximal delta front produced amalgamated tempestite beds void of bioturbation. Lower to middle shoreface deposits comprise fine grained sandstone dominated by robust burrows of suspension feeders attributable to a proximal expression of the Skolithos ichnofacies.

The oldest record of Ediacaran macrofossils in Gondwana (~563 Ma, Itajaí Basin, Brazil)

The Avalon biota (Ediacaran Period, 570–559 Ma) marks the first appearance of macroscopic and complex benthic communities in the fossil record. This assemblage is known from a few localities worldwide, mainly in Canada and England. Here, we report for the first time the presence of Ediacaran macrofossils in deposits of similar age from Gondwana (Itajaí Basin, southern Brazil). Our new radiometric date (~563 Ma) indicates that the Itajaí Basin can be chronocorrelated with the classic Avalonian deposits and thus represents one of the oldest records of the Ediacaran biota in Gondwana. We describe the presence of the Ediacaran genus Palaeopascichnus, as well as discs (Aspidella and Nimbia), and other problematic forms. Contrary to the deep-marine macroorganisms of the Avalon Assemblage, the Itajaí fossils are associated with abundant and exceptionally preserved three-dimensional microbial mats and microbially induced sedimentary structures (MISS) in relatively shallow settings (upper slope and distal delta front deposits). In this sense, the Itajaí biota could represent early adaptations of benthic macrobiota to the shallower and more photic environments that characterize the later White Sea Assemblage.

Ichnological signatures from wave- and fluvial-dominated deltas: The La Anita Formation, Upper Cretaceous, Austral-Magallanes Basin, Patagonia

Depositional processes operating in deltaic shorelines create a variety of physico-chemical stressful conditions that impact directly on benthic fauna. The ichnological signatures of deltaic successions reflect these physico-chemical stresses, such as rapid sediment influx, elevated water turbidity, periodically reduced oxygenation, salinity fluctuations, and wave- and tidal-energy. In the Campanian La Anita Formation of the Austral-Magallanes Basin, two examples of deltaic successions, each showing different relative dominance of wave and fluvial processes, are described in detail, allowing the recognition of contrasting stresses that acted differentially in a wave-dominated, fluvial-influenced delta and a fluvial-dominated delta. Variations in the burrowing intensity and ichnodiversity allowed us to discriminate the different physico-chemical stresses. In the wave-dominated, fluvial-influenced deltaic deposits, the alternation between fair-weather waves and storm events acted as the main controlling factor on benthic fauna in the facies of the prodelta and distal delta front, displaying facies-crossing and horizontal elements attributable to the Skolithos and Cruziana Ichnofacies, such as Arenicolites isp., Chondrites isp., Cylindrichnus isp., Diplocraterion isp., Gyrochorte isp., Ophiomorpha isp., Palaeophycus isp., Planolites isp., Rhizocorallium isp., Rossellia isp., Schaubcylindrichnus isp. and Skolithos isp. Water turbidity and periodically reduced bottom water oxygenation conditions also played an important but subordinate role. The proximal delta front, and distributary and terminal distributary channel deposits show low burrowing intensities and ichnodiversities with structures attributable to the depauperate Skolithos Ichnofacies with few Diplocraterion isp., Gordia isp., Lockeia isp., Macaronichnus isp., Ophiomorpha isp., Schaubcylindrichnus coronus and Siphonichnus isp., showing stress conditions associated with rapid sediment influx, high energy and reduced salinity conditions related to fluvial discharges as the most important controlling factors. Periodically, fluctuations in salinity conditions due to river discharges and channel avulsion may have also played important roles. The fluvial-dominated deltaic deposits show that the controlling factors were associated with fluvial discharge and river-sediment influx with no clear influence of wave or tidal action. The facies of the distal delta front were controlled by episodic sedimentation, elevated water turbidity, periodically reduced oxygenation and salinity fluctuations, the associated trace fossil suite consists of a monospecific assemblage of Ophiomorpha isp. and sparse Palaeophycus isp. The proximal delta front and the distributary channel deposits are mostly unburrowed, locally displaying a few Arenicolites isp., Lockeia isp., Ophiomorpha isp., Psilonichnus isp. and Teredolites isp. The development of these suites was controlled mainly by heightened sedimentation rates influx triggered by high fluvial discharges, elevated water turbidity due to heightened suspended load and buoyant plumes, periodic fluctuations in salinity conditions caused by river discharges and channel avulsion. Interdistributary areas are characterized by facies preserving evidence that reduced oxygenation was the most important controlling factor in this subenvironment. Fluvial processes generate the most extreme stressful conditions for benthic colonization by tracemakers. Wave processes tend to buffer the stresses produced by river discharge. The effect of waves on fluvial stress is reflected in the higher bioturbation intensities and ichnodiversities that the wave-dominated deltaic deposits of the La Anita Formation delta show in relation to the fluvial-dominated ones.