Evidence of fluvio-deltaic interaction in the Triassic Red Beds of the Iberian Meseta (Almedina, Ciudad Real, SE Spain)

Lagoonal deposits in the Upper Cretaceous Rock Springs Formation (Mesaverde Group), southwest Wyoming

Minor sedimentary structures were studied in cores and exposures from the deltaic and marginal deltaic plains of the Mississippi River. Selected active environments were sampled, and the occurrence of sedimentary structures from each was recorded. Individual structures were found to occur in more than one environment; however, suites of structures were characteristic. Within the study area the following twelve depositional environments have been investigated: shelf, prodelta, delta front (distal bar, distributary mouth bar, channel, and subaqueous levee), subaerial levee, marsh and swamp, interdistributary bay, mudflat, and fresh-water lake. Shelf deposits consisted of: (1) fine-grained clastics, burrowed and showing parallel laminations and (2) marine organic debris. Prodelta deposits are similar to clayey shelf deposits, but contain lenticular and parallel lamination with finely divided plant inclusions. The delta front is a complex of sub-environments constituting the advancing locus of active deposition of the prograding delta. The sloping seaward margin on this zone--the distal bar--exhibits current structures such as trough cross-laminations and current ripples as well as parallel and lenticular laminations, wave ripples, and burrows. The silty and sandy distributary mouth bar is characterized by a variety of small-scale, multi-directional cross-laminations and gas-heave structures. Channel deposits exhibit trough c oss-laminations, scour and fill, and distorted laminations, whereas subaqueous levees contain abundant ripple and unidirectional cross-laminations, parallel, wavy, and distorted laminations. In addition, subaerial levees are burrowed and oxidized. Marsh and swamp deposits are distinguished by abundant plant remains, burrows, and parallel laminations. Lenticular laminations, wave ripples, burrows, shell, and plant remains are characteristic of both interdistributary bay and fresh-water lakes. The mudflat assemblage of structures includes lenticular laminations, current and wave ripples, burrows, and shell remains. Not only are associations of sedimentary structures End_Page 521------------------------------ important in recognizing individual environments of deposition; equally important is the association of the environments to one another. This relationship must be understood for correct paleogeographic reconstruction of ancient deltaic deposits. The manner in which a sequence of marine and deltaic deposits might accumulate in a segment of a basin with resulting stratigraphic relationships of associated environmentally determined facies, is illustrated. End_of_Article - Last_Page 522------------

Alluvial fans and fan deltas are constructed by similar processes; both require a highland and adjacent lowland for development. Alluvial fans are associated with interior basins, whereas fan deltas develop along coastlines. A fan delta is an alluvial fan which progrades into a marine body of water. Modern alluvial fans are present in both arid and humid regions throughout the world, ranging from Arctic to lower latitudes. Geometry and facies are controlled by rate of basin subsidence, source material, and frequency and magnitude of floods. In arid regions, where fans are most common, principal processes include debris-flows, sieve deposition, and fluvial deposition. Processes are intermittent and commonly one is dominant. Debris-flows and sieve deposits are major contributors to the upper 1/3 to ½ of a fan. Sieve deposits are generally confined to the fan apex. Debris-flows, characterized by a heterogeneous mixture of clay- to boulder-size material, extend for considerable distances downfan where they grade to mudflows containing few large clasts. Debris-flows reflect a fin -grained source area. Fluvial processes are dominant on the distal fan. Humid-region fans, e.g., Kosi River fan of India, are constructed entirely by fluvial processes during large annual floods. Compared to arid-region fans, humid-region fans have a low slope from apex to toe, are large in areal extent, and thin in cross section. Humid-region fans also contain smaller clasts, less fine material in the upper fan, and sediment is better sorted. Source-area vegetation aids in breakdown of rock material into smaller particles than under arid conditions. Erosion is great in humid areas because of intense flooding. Alluvial fans in closed drainage basins commonly are associated with lakes. Where alluvial fans build into basins with through-flowing streams, braided-stream deposits of the distal fan are interbedded with floodplain deposits. Fan deltas may be distinguished from alluvial fans only by the nature of related facies. Modern fan deltas develop in areas of high or low rainfall, from deserts to tropical rain forests, and are associated with a wide range of marine depositional environments, e.g., reef-lagoonal to submarine fan association. Types of depositional environments associated with fan deltas are determined by such factors as tidal range, shelf width, and climate. Fan deltas differ considerably from modern oceanic (high-constructive) deltas which are constructed by continuously flowing, large rivers characterized by a large suspension-load/bed-load ratio. Deltaic plains of oceanic deltas generally are covered by dense vegetation, whereas subaerial parts of fan deltas are virtually barren. Oceanic deltas have ragged lobate or digitate margins indented by interdistributary bays; fan deltas commonly have a smoothly arcuate distal end with no interdistributary bays. Prodelta deposits associated with oceanic deltas are commonly the thickest delta facies; equivalent facies of fan deltas are comparatively thin. Fan-delta deposits are continually reworked by marine processes. Deposition is sporadic, therefore marine processes are effective in redistributing prodelta sediment. Marine currents redeposit sediment along the distal fan as beaches and associated berms, and within adjacent shallow marine areas as thin sand sheets and local fan-margin islands or spits. Many ancient clastic-wedge deposits from Precambrian to Pleistocene ages are alluvial-fan systems. Deposits composing these systems become finer in the direction of transport. Lacustrine or fluvial deposits commonly are associated with the finer grained alluvial-fan deposits. Ancient alluvial fans are known from the (1) Precambrian of Texas, (2) Devonian of Norway, (3) Carboniferous of Canada, (4) Permian-Triassic of England, (5) Triassic of the Connecticut Valley, and (6) Pleistocene of California. Ancient fan deltas have been described as fanglomerates, continental deposits, and tectonic deltas. Subaerial facies have the same character as ancient alluvial fans but are associated with marine facies ranging from turbidites to tidal-flat deposits. Ancient fan deltas occur in the (1) Devonian of New York and Northwest Territories, (2) Pennsylvanian-Permian terrigenous clastics shed off the Ancestral Rockies, Amarillo Mountains, Wichita Mountains, and Arbuckle Mountains, (3) Miocene of Texas and California, and (4) the Pleistocene of Baja California. Fan deltas and possibly high-destructive deltas prograded shorelines and filled basins during early geologic periods, prior to evolution of terrestrial vegetation. High-destructive deltas are produced by marine reworking of river-borne sediment. Streams associated with high-destructive deltas are characterized by short duration peak discharge which allows sediment deposited at the mouths to be immediately reworked into spits and beach ridges. Lag time between precipitation and runoff was short and the fluvial systems which developed these 2 delta types were either braided streams or coarse-grained meander belts. End_of_Article - Last_Page 155------------

Facies analysis of the Quaternary fluvial system of Khor Eit, Red Sea coast, Sudan

The Oligocene-Miocene Ciénaga de Oro Formation, located in the San Jacinto Fold Belt Basin (SJFB) of northwestern Colombia, records a complex interplay of fluvial, wave, and tidal (Fwt) processes. This study integrates sedimentologic and ichnologic data to reconstruct depositional environments and corresponding paleoecologic conditions. Two facies associations were identified: FA1 (deltaic), including distributary channels, interdistributary bays, lagoons, marshes, and delta front deposits; and FA2 (strandplain), comprising backshore, foreshore, and shoreface deposits. The succession reflects a deltaic system, varying laterally to a strandplain. Ichnologic analysis reveals archetypal ichnofacies, such as the Skolithos Ichnofacies in the high-energy shoreface, the Rosselia Ichnofacies in the delta front, and the Teichichnus Ichnofacies in the interdistributary bays and lagoons. These trace fossils indicate varying stress factors, including high sedimentation rates, alternating hydrodynamic energy conditions, elevated water turbidity, and salinity fluctuations, which influenced benthic communities. The stratal stacking pattern is progradational and aggradational, indicating that deposition occurred in a highstand systems tract (HST). This study provides a depositional model for mixed influence deltaic (Fwt) and strandplain systems in a tropical area, enhancing our understanding of the Oligocene-Miocene evolution of the SJFB and offering insights applicable to similar systems in low-latitude settings.

Facies models for regressive, tide‐influenced deltaic systems are under‐represented in the literature compared with their fluvial‐dominated and wave‐dominated counterparts. Here, a facies model is presented of the mixed, tide‐influenced and wave‐influenced deltaic strata of the Sego Sandstone, which was deposited in the Western Interior Seaway of North America during the Late Cretaceous. Previous work on the Sego Sandstone has focused on the medial to distal parts of the outcrop belt where tides and waves interact. This study focuses on the proximal outcrop belt, in which fluvial and tidal processes interact. Five facies associations are recognized. Bioturbated mudstones (Facies Association 1) were deposited in an offshore environment and are gradationally overlain by hummocky cross‐stratified sandstones (Facies Association 2) deposited in a wave‐dominated lower shoreface environment. These facies associations are erosionally overlain by tide‐dominated cross‐bedded sandstones (Facies Association 4) interbedded with ripple cross‐laminated heterolithic sandstones (Facies Association 3) and channelized mudstones (Facies Association 5). Palaeocurrent directions derived from cross‐bedding indicate bidirectional currents which are flood‐dominated in the lower part of the studied interval and become increasingly ebb‐directed/fluvial‐directed upward. At the top of the succession, ebb‐dominated/fluvial‐dominated, high relief, narrow channel forms are present, which are interpreted as distributary channels. When distributary channels are abandoned they effectively become estuaries with landward sediment transport and fining trends. These estuaries have sandstones of Facies Association 4 at their mouth and fine landward through heterolithic sandstones of Facies Association 3 to channelized mudstones of Facies Association 5. Therefore, the complex distribution of relatively mud‐rich and sand‐rich deposits in the tide‐dominated part of the lower Sego Sandstone is attributed to the avulsion history of active fluvial distributaries, in response to a subtly expressed allogenic change in sediment supply and relative sea‐level controls and autocyclic delta lobe abandonment.

Fluvial strata deposited before the advent of land plants are commonly sheet‐like in geometry, lacking in channel forms. Although some pre‐vegetation strata contrast strongly with fluvial strata from later eras, the characterization of pre‐Devonian fluvial drainage systems remains incomplete. Field studies of the fluvial facies and architecture of the Series Rouge are presented to identify the products and processes of fluvial deposition occurring at high latitudes in the early Cambrian. Three different depositional styles or facies associations are recognized. Facies Association 1 is the most abundant (67%) comprising repetitively stacked sheets of trough cross‐stratified sandstone interpreted to represent the preferential preservation of the deepest parts of low sinuosity, braided river channels, 4 to 6 m deep. Facies Association 2 is also common (30%) and displays more complex facies sequences that include stacked sheets of trough cross‐strata, sets of large‐scale tabular cross‐strata, planar strata and subordinate mudstone. These facies are interpreted to reflect deposition in braided rivers with deeper channels, 6 to 8 m deep. These channels were more sinuous and subject to steady lateral migration which resulted in preservation of both deep and shallow parts of the river. Facies Association 3 is uncommon (3%) comprising interbedded sequences of cross‐stratified sandstone and mudstone interpreted to reflect deposition on a muddy coastal plain in a mixture of braided and meandering channels, 1 to 3 m deep. The fluvial strata of the Series Rouge indicate that these pre‐vegetation drainage systems were predominantly braided fluvial in origin. However, the style of braided fluvial deposition varied according to discharge and valley slope, the braided rivers becoming more migratory with decreasing slope. Meandering channel deposition was locally evident but was restricted to channels of low discharge crossing low gradient muddy coastal plains.

Three Gita Member reservoirs 34-1, 33-6, and 33-4 produce from solution gas drive with rapid pressure decline and low recovery factor. After successful oil production enhancements through waterflooding injections prompt the need for a reservoir model in further field development. Before such models were built reservoir characterization was carried out to determine facies and depositional environment for facies modeling. The study integrated core, wireline log, petrophysical logs, seismic attribute, petrography, etc. Next, well correlation was carried out to distribute stratigraphic markers. Finally, seismic attribute and well correlation were integrated to construct pie chart and depositional environment map. External geometry from seismic attribute revealed distributary channel with point bars which act as reservoir and consist of medium-fine grained planar tabular cross bedding sandstone, mud drapes sandstone, and ripple-wavy lamination sandstone. The wireline log showed fining-upward pattern and core displayed abundant channel rip up clasts, sharp or erosional contact with underlying lithology. Frequent mud drapes found within channel sandstone indicate tidal influence in proximity to marine environment probably in lower delta plain. Channels are trending west-east (34-1) and north-south (33-6 and 33-4). Other facies associations are shallow marine, swamp, interdistributary bay, and tidally influenced interdistributary bay. Shallow marine FA consists of skeletal limestone (Lm), calcareous mudstone, and calcareous sandstone (Sc). Rootlet mudstone (Fb) and interlamination of carbonaceous mudstone with very fine-grain sandstone (Fl) formed interdistributary bay FA. Swamp FA consists of coal and coaly mudstone. Tidally influenced interdistributary bay FA consists of carbonaceous laminated mudstone high in carbon (Flb), intensely bioturbated carbonaceous mudstone (Flb), very finely laminated mudstone-very fine grain sandstone (Fl) and black fissile shale (Fm).

Discovery of the Breagh gas field in the Southern North Sea (SNS) has demonstrated the potential that the Lower Carboniferous (Visean, 346.7–330.9 Ma) Farne Group reservoirs have to contribute to the UK's future energy mix. New biostratigraphic correlations provide a basis to compare Asbian and Brigantian sedimentary cores from the Breagh Field and age-equivalent sediments exposed on the Northumberland Coast, which has proved critical in gaining an understanding of exploration and development opportunities. Thirteen facies associations characterize the mixed carbonate–siliciclastic system, grouped into: marine, delta front, delta shoreface, lower delta plain and upper delta plain gross depositional environments. The facies associations are interpreted as depositing in a mixed carbonate and siliciclastic fluvio-deltaic environment, and are arranged into coarsening- and cleaning-upward cycles (parasequences) bounded by flooding surfaces. Most cycles are characterized by mouth bars, distributary channels, interdistributary bays and common braided rivers, interpreted as river-dominated deltaic deposits. Some cycles include rare shoreface and tidally-influenced deposits, interpreted as river-dominated and wave- or tide-influenced deltaic deposits. The depositional processes that formed each cycle have important implications for the reservoir net/gross ratio (where this ratio indicates the proportion of sandstone beds in a cycle), thickness and lateral extent. The deltaic deposits were controlled by a combination of tectonic and eustatic (allocyclic) events and delta avulsion (autocyclic) processes, and are likely to reflect a changing tectonic regime, from extension within elongate fault-bounded basins (synrift) to passive regional thermal subsidence (post-rift). Deep incision by the Base Permian Unconformity across the Breagh Field has removed the Westphalian, Namurian and upper Visean, to leave the more prospective thicker clastic reservoirs within closure. Thematic collection: This article is part of the Under-explored plays and frontier basins of the UK continental shelf collection available at: https://www.lyellcollection.org/cc/under-explored-plays-and-frontier-basins-of-the-uk-continental-shelf

Fluvial-dominated deltas are common along modern and ancient coasts and act as important hydrocarbon reservoirs. In this paper, an integration of high-resolution three-dimensional seismic, well log, and core data are employed to investigate the seismic geomorphology, depositional facies, reservoir types, and controlling factors of fluvial-dominated delta deposition in the lower segment of the Minghuazheng Formation (N1mL), Bohai Bay Basin, China. Three typical seismic facies and seismic geomorphologic units are identified. Seismic facies 1 displays discrete high-amplitude reflection and a distinct U-shape incision. In plan form, this seismic facies shows a linear, dendritic, and sinuous morphology with high root-mean-square amplitudes. Seismic facies 2 occurs interspersed with seismic facies 1 and shows low-frequency and low-amplitude reflection. Seismic facies 3 shows a continuous high-amplitude reflection and uniform sheet-like morphology covering more than 10 km2 (>3.86 mi2). The N1mL was primarily deposited in the upper delta plain, lower delta plain, and delta front environments and is dominated by three major facies types: (1) distributary channel (seismic facies 1), (2) interdistributary bay (seismic facies 2), and (3) sheet sand (seismic facies 3). Among them, the distributary channel sandstones and sheet sandstones are the major reservoirs in the N1mL. Fluvial processes and lake level cycles were important factors in the development and distribution of reservoirs and traps in fluvial-dominated delta systems. Integration of the seismic geomorphology and a modern geomorphology investigation provide an effective way to predict the sandstone reservoirs and traps in fluvial-dominated delta systems.

Geomorphological knowledge is critical in understanding watershed scale surface processes, including steep mountainous areas and flat lowlands, particularly if the mid- and downstream areas are densely populated and hazard assessments are highly required. However, our knowledge about such surface processes has relatively been limited in some areas in South Asia due likely to the lack of comprehensive studies of geomorphology and related fields. This article undertakes an overview of the geomorphological processes of the disaster-prone deltaic landscape of the Ganges–Brahmaputra–Meghna (GBM), particularly focusing on fluvial processes. The area locates in the downstream of the watershed system including Himalayan Mountains and highly connected with the upper basin morphodynamics, hydrology, and sediment flux. The previous studies are summarized at different geomorphic settings concerning hillslopes, fluvial plains, and coastal areas to provide clarity about the geomorphic processes linking erosion-prone upstream source areas to deposition-dominated downstream areas. The review found that most of the geomorphic researches in Bangladesh are exploring landslide inventory and susceptibility mapping in hilly areas; river channel or riverbank shifting, riverbank erosion and accretion in fluvial environments; watershed morphometric analysis and geomorphic unit identification in plain land; and coastline shifting or coastal erosion and accretion in coastal environments at a small scale. Then, we discuss the fluvial dynamics and sediment transport of the GBM river system to address the knowledge gap in the context of deltaic plain land in Bangladesh, where upstream fluvial sedimentation processes impact the geomorphic connectivity from Himalayan to the Bay of Bengal. Although some studies on the fluvial dynamics and sediment dispersal in the upstream GBM river basin are present, the fluvial processes in the downstream domain of Bangladesh are not fully understood with a limited number of research with field-based approaches. Some future perspectives of geomorphic research in Bangladesh are then mentioned to understand better the complex geomorphological settings in the entire GBM watershed and to strengthen the existing research capacity. This review will also develop a holistic understanding of fluvial geomorphic processes of the GBM River to the policymakers and may be helpful to improve the transboundary river basin management policies or strategies.

ABSTRACTThe Eocene Pinghu Formation in the Xihu Depression of the East China Sea Shelf preserves mixed‐process deltaic deposits and contains a large number of thin coal seams. This study improves the prediction of coal seam occurrences based on facies distribution and stratigraphic architecture models of deltaic deposits, using core and wireline log datasets. Sedimentological analysis reveals four facies associations, which represent delta plain (including distributary channels and interdistributary bays), delta front, prodelta and tidal flat. These facies associations reflect and preserve the interaction of fluvial and marine processes. Delta‐plain and delta‐front deposits record progressively greater tidal influences when traced southward. Well‐log correlations show that coal‐forming mires on the tide‐influenced lower delta plain were relatively favourable for peat accumulation because the stability of the tidal channels led to a stable platform for peat accumulation on the lower delta plain. The temporal and spatial distribution of coal seams is a function of both autogenic and allogenic responses to forcing. Increased probability of frequent changes in subsidence rates and sea‐level in an active tectonic setting and erosion by channels resulted in thin single‐layer coal seams (mostly 0.5 to 1.0 m). Autogenic processes (for example, delta growth and delta lobe switching) played a significant role in the areal distribution, lateral variation in thickness (ranging from 3 to 71 m) and large cumulative thicknesses (up to 71 m) of coal seams. A general vertical decrease in coal seam thickness likely records a cooling palaeoclimate during deposition of the Pinghu Formation. By comparing delta plain processes to favourable environments of peat accumulation in modern systems with favourable mineralogical, chemical and physical conditions, it can be concluded that: (i) relatively few and discontinuous coal seams developed on the tide‐dominated delta plain generated; (ii) laterally discontinuous and ribbon‐shaped coal seams developed in tide‐influenced deltas; whereas (iii) coal seams formed in river‐dominated deltaic environments have better lateral continuity.

Sedimentology and sequence stratigraphy of the Early Cretaceous Centenario Formation (upper member) in the north-eastern border of the Neuquén Basin, Argentina

A regional study of the Burgan formation has been carried out over the North Kuwait Fields to understand the variation in depositional environment, oil occurrence and control of trapping mechanism on the quality of oil. The Burgan Formation in North Kuwait comprises fluvial, deltaic and marine sediments deposited during the Lower Albian period in response to global changes in sea level. There is a systematic gradation of depositional environments in Burgan during this period. Oil entrapment in this formation shows regional variation. Both stratigraphic and structural controls on oil accumulation are dominant in the region. The oil quality becomes heavier towards North and has a strong structural control. Significant volume of inplace oil has been estimated during this study which would be pursued for commercial exploitation of this deep heavy oil reservoir. Burgan clastic sedimentation over Shuaiba carbonates was initiated by a regional fall in sealevel and establishment of a deltaic setting. Reservoir facies include mouth bars and distributary channels along with non-reservoir facies of interdistributary bay and shallow marine environments. After a significant hiatus, the braided channel systems with massive amalgamated sand bodies were established in response to significant fall in seal level. Subsequently a significant marker in form of a marine and shoreface sand with associated marine shale was deposited with a rise in sea level. Estuarine channels and bay shales were deposited above this surface. The upper part of Lower Burgan has transgressive sand bodies. The Middle Burgan is dominated by marine shale and shoreface sand deposits in response to further rise in sea level. The Upper part of Burgan is mainly comprising estuarine channel sands and interdistributary bay deposits. In a regional context, the sedimentation pattern shows increasing marine influence to East-Northeast directions. The oil quality in Burgan is intricately related to the structure and trapping mechanisms. A post Mishrif time tilt in structure has resulted in a deeper relict oil water contact in Lower Burgan towards West of Sabiriyah. In the area towards North of Raudhatain structure, the fluid contact shows significant tilt towards North with a rising structure. The doubly plunging anticlines of Raudhatain and Sabiriyah structures have lighter oil in Burgan formation in a structural trap. Further north of Raudhatain, the oil is heavy although there is lateral reservoir continuity. Significant faults have been mapped in this area. The structure is shallower towards North with progressively deeper fluid contact in Lower Burgan. Origin of heavy oil appears be due to significant spilling of lighter oil along faults and upstructure migration due to structural tilting and transtensional deformation. Significant accumulation of heavy oil has been established in Basal Burgan, Lower Burgan and Upper Burgan Formations. Heavy oil inflow in form of testing and sampling is seen in 12 wells. Aggressive plans are in place to map the oil quality and to formulate a long term exploitation strategy.

Five oriented cores from the Cities Service Co. enhanced oil-recovery project, Madison Block (Unit B) of the Seeley-Wickfield, were analyzed. Primary production, air, and water drives in the Middle Pennsylvanian Bartlesville Sandstone (Cherokee Group) have produced 12.5 million bbl of oil with 18.6 million bbl remaining. Six depositional facies are recognized in the cores. The End_Page 942------------------------------ facies are, in ascending order, a prodelta shale and siltstone facies, a distributary channel sandstone facies, an overbank shale and siltstone facies, an interdistributary bay and splay channel facies, an estuarine sandstone, shale, and siltstone facies, and a lagoonal sandstone and siltstone facies. This genetic vertical sequence package, typical of fluvial-deltaic sediments, is typified by an upward change in the scale of sedimentary structures, an increase in radioactivity of the gamma ray log, a decrease in grain size, a decrease in permeability, and a subsequent increase in the amount of interstitial clay matrix. Permeability is primarily controlled by packing, sorting, the presence of ductile rock fragments, and the amount of clay matrix. Permeability of the distributary channel sandstone facies, the primary reservoir, decreases from 60 to 100 md in trough cross-bedded sandstones to 20 to 60 md in rippled sandstones and siltstones. Low permeability values (0 to 20 md) are characteristic of facies containing siltstone and shale. The distributary channel sandstone facies (28 to 62 ft or 8 to 19 m thick) is continuous across the pilot project area and varies in thickness in a predictable manner. Dip directions of trough cross-beds observed in four oriented cores suggest that the distributary channel flowed to the west-southwest across the project area. The overbank shale and siltstone facies and the interdistributary bay and splay channel facies are not continuous across the project area and are interpreted to have been deposited in the topographically low area adjacent to the distributary channel. End_of_Article - Last_Page 943------------