Wave-dominated Deltaic Deposits Research Articles

Ichnology of the Pliocene Casa Cruz Member (Moruga Formation), Trinidad, West Indies: Delineating depositional environments and environmental stresses

Integrated sedimentologic and ichnologic analysis of outcrops of the Casa Cruz Member (Moruga Formation, early to mid-Pliocene) yields distinct facies associations representing river- and wave-dominated deltaic deposits, and non-deltaic shoreface successions. This study demonstrates how river and wave processes interacted and their products were preserved across a small geographic area. It also shows evidence of the impact of these processes on infauna and epifauna. Wave-dominated delta front deposits comprise hummocky and swaley cross-stratified tempestites and wave-rippled sandstone beds. Event sedimentation and heightened water turbidity associated with frequent or intense storm events generated low intensity, sporadically distributed, reduced diversity trace fossil suites of the Rosselia ichnofacies. Wave-dominated prodelta deposits display diminutive structures ascribable to the Phycosiphon ichnofacies. Wave-dominated deposits transition into non-deltaic shoreface successions that contain densely bioturbated sediment with high diversity trace fossil suites belonging to the Cruziana ichnofacies. Common traces are Scolicia, Macaronichnus, Ophiomorpha, Thalassinoides, Planolites, Palaeophycus, and Skolithos. In contrast, river-dominated delta front and prodelta deposits are characterised by sandstone, siltstone and mudstone beds devoid of bioturbation. Syn-sedimentary deformational, current-generated structures, and organic particulates are abundant. Hyperpycnal discharge and concomitant increased sedimentation rates, freshets, and phytodetrital pulses linked to seasonal floods are possibly due to the presence of the Intertropical Convergence Zone at that time. This discharge generated extreme physical and chemical stress that inhibited benthic colonisation.

Sedimentological signatures and identification of Paleocene sedimentary facies in the Lishui Sag, East China Sea Shelf Basin

The Lishui Sag is on the southwest margin of the East China Sea Shelf Basin (ECSSB), which is located on the continental shelf of the East China Sea. The analysis of sedimentological signatures is based on 217 m (712 ft) of Paleocene cores showing a wide variety of lithofacies, sedimentary structures, ichnological data, seismic data, and log data. Eight lithofacies, nine typical ichnofabrics, and four ichnofacies combined with petrological, geophysical, and bioturbation information were identified as the key sedimentary facies characteristics for identifying three sedimentary systems in the study area. Eleven sedimentological facies are present in the three sedimentary systems: foreshore, upper shoreface, lower to middle shoreface, offshore transition, proximal fan delta front, distal fan delta front, wave-dominated delta front sand bar, wave-dominated delta front sand sheet, interbar, tide-influenced distributary channel, and tide-influenced interdistributary bay facies. The three sedimentary systems that were identified are fan delta, wave-influenced delta, and tide facies. Fan delta deposits are present in the southwest and northeast of the sag, with subaqueous fan delta front deposits dominating, whereas farther seaward successions are characterized by distal fan delta front deposits that are intensely bioturbated. Wave-dominated deltaic deposits occur mostly in the western and middle parts, where fluvial discharge in the delta front and prodelta have been repeatedly reworked by waves and formed some isolated bars distributed perpendicular to the source; these deposits are sparsely to intensely bioturbated. Tide facies develop locally and have been identified as distributary channels and interdistributary bay facies.

Discovery of late Tortonian incised valleys in the Saouaf Formation (northeastern Tunisia) - Evidence of high-frequency sea-level variations in the central Mediterranean

During the late Miocene, the connection between the Atlantic Ocean and the Mediterranean Sea was progressively restricted. Despite many discoveries of Messinian incised valleys and canyons in the peri-Mediterranean basins, the Tortonian incised valleys are poorly described. The Tortonian series exposed in the northeastern end of the Cap Bon peninsula (northeastern Tunisia, central Mediterranean) provide an excellent example of complex and extensive incised valleys system traceable for up to 5 km (entire length of the outcrop). Detailed facies and sedimentological analysis permitted the recognition of five distinct phases of incision. These valleys (approximately 300 m wide and 10 m to 30 m deep) were incised during sea-level fall and were filled during subsequent sea-level rise. These valleys are characterized by the lack of fluvial deposits at their bases. During sea-level rise, these valleys were filled mainly with cross-bedded estuarine sandstone forming multistorey channels and point-bar deposits. Tidal sand flat deposits are locally well developed at the margins of the valleys fills. These tide-dominated estuarine deposits, corresponding to the transgressive systems tracts, are arranged into fining-upward retrogradationnal parasequences. The highstand systems tracts correspond to wave-dominated deltaic deposits comprising offshore, offshore-transition and shoreface deposits. These successions are typically arranged in thickening and coarsening-upward parasequences. The upper surfaces of the highstand systems tracts are incised by later valleys. The formation and the filling of these valleys record the complex interplay of different allocyclic factors: (1) tectonic uplift due to the major compressive Atlassic phase, (2) high-frequency sea-level variations, (3) warm and humid climate, and (4) high river sediment input. The results of this study provide important data, such as incised valleys geometries, dimension, extension and connectivity. The results of this study emphasis the potential link between high-frequency sea-level variation and progressive restriction of the Mediterranean during the late Tortonian.

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.

Prevention of infectious complications in predicted severe acute pancreatitis (SAP) – a single center randomized controlled trial

Venezuela has the largest hydrocarbon reserves in the world and most of these are within the Orinoco Oil Belt. The Oficina Formation of the Orinoco Oil Belt and the Oritupano Field comprises a wide range of environments formed under variable salinity conditions. These include freshwater fluvial and fluvio-tidal transition zones, brackish-water estuarine and delta-plain segments, alternating brackish-water and near-normal marine delta-front and prodelta settings, and normal-marine wave-dominated shoreface and offshore-shelf environments. The Oficina Formation thus provides an ideal opportunity to evaluate trace-fossil distribution and ichnofacies gradients along a depositional profile and to calibrate salinity-related trace-fossil models. The Oficina Formation contains four softground ichnofacies (Scoyenia, depauperate Cruziana, Skolithos, and archetypal Cruziana) and two substrate-controlled ichnofacies (Teredolites and Glossifungites). Fluvial deposits in freshwater portions of tide-influenced, estuarine channels and distributary channels of tide-dominated deltas are locally intensely bioturbated, displaying low-diversity occurrences of the Scoyenia Ichnofacies. Brackish-water delta-plain and estuarine deposits display lower degrees of bioturbation and low ichnodiversity, as revealed by depauperate Cruziana Ichnofacies and the Skolithos Ichnofacies. Wave-dominated deltaic deposits display the Skolithos and the depauperate Cruziana Ichnofacies, but the presence of some ichnotaxa (e.g., Chondrites) suggests periods of lower salinity stress, probably during times of reduced freshwater discharge. Open-marine deposits are characterized by intense bioturbation and very high diversity, as shown by the archetypal Cruziana Ichnofacies in low-energy distal settings, whereas high-energy proximal settings are characterized by the Skolithos Ichnofacies. Faunal distribution is strongly controlled by salinity, which makes trace-fossil evidence particularly useful for paleoenvironmental characterization of marginal-marine systems. In addition, the Glossifungites and Teredolites Ichnofacies indicate erosional exhumation of marginal-marine deposits, outlining transgressive surfaces of erosion. The Oficina Formation shows remarkable similarities in sedimentary facies and both trace-fossil and micropaleontological content with the Cretaceous McMurray Formation of western Canada.

From freshwater to fully marine: Exploring animal-substrate interactions along a salinity gradient (Miocene Oficina Formation of Venezuela)

Venezuela has the largest hydrocarbon reserves in the world and most of these are within the Orinoco Oil Belt. The Oficina Formation of the Orinoco Oil Belt and the Oritupano Field comprises a wide range of environments formed under variable salinity conditions. These include freshwater fluvial and fluvio-tidal transition zones, brackish-water estuarine and delta-plain segments, alternating brackish-water and near-normal marine delta-front and prodelta settings, and normal-marine wave-dominated shoreface and offshore-shelf environments. The Oficina Formation thus provides an ideal opportunity to evaluate trace-fossil distribution and ichnofacies gradients along a depositional profile and to calibrate salinity-related trace-fossil models. The Oficina Formation contains four softground ichnofacies (Scoyenia, depauperate Cruziana, Skolithos, and archetypal Cruziana) and two substrate-controlled ichnofacies (Teredolites and Glossifungites). Fluvial deposits in freshwater portions of tide-influenced, estuarine channels and distributary channels of tide-dominated deltas are locally intensely bioturbated, displaying low-diversity occurrences of the Scoyenia Ichnofacies. Brackish-water delta-plain and estuarine deposits display lower degrees of bioturbation and low ichnodiversity, as revealed by depauperate Cruziana Ichnofacies and the Skolithos Ichnofacies. Wave-dominated deltaic deposits display the Skolithos and the depauperate Cruziana Ichnofacies, but the presence of some ichnotaxa (e.g., Chondrites) suggests periods of lower salinity stress, probably during times of reduced freshwater discharge. Open-marine deposits are characterized by intense bioturbation and very high diversity, as shown by the archetypal Cruziana Ichnofacies in low-energy distal settings, whereas high-energy proximal settings are characterized by the Skolithos Ichnofacies. Faunal distribution is strongly controlled by salinity, which makes trace-fossil evidence particularly useful for paleoenvironmental characterization of marginal-marine systems. In addition, the Glossifungites and Teredolites Ichnofacies indicate erosional exhumation of marginal-marine deposits, outlining transgressive surfaces of erosion. The Oficina Formation shows remarkable similarities in sedimentary facies and both trace-fossil and micropaleontological content with the Cretaceous McMurray Formation of western Canada.

Deltaic process and architectural evolution during cross-shelf transits, Maastrichtian Fox Hills Formation, Washakie Basin, Wyoming

The topset compartments of two Maastrichtian basin-scale clinothems are characterized, with focus on the function they played in constructing the Lance–Fox Hills–Lewis shelf-margin sedimentary prism in the Laramide Washakie Basin, south Wyoming. Approximately 1000 well logs were used to map the delta lobes and complexes on the Fox Hills shelf and to detail their depositional character, dimensions, and orientation as they autogenically shifted during transit from an inner-shelf to shelf-edge position. The regressive transits of the deltas initiated up to 40 km (25 mi) landward from the preexisting shelf-edge and preserved river and wave-dominated deltaic deposits that thicken and concentrate sand on the outer shelf. Tidally influenced deltas (now outcropping) also occur in localized areas along the paleoshelf edge, probably where wave influence was reduced along invaginated coastal segments. Net sandstone maps of the individual clinothem topsets show that (1) coeval delta lobes exist within each clinothem, suggesting multiple rivers; (2) delta lobes have a likely autogenic compensational stacking pattern; and (3) deltas thicken and storm-wave influence become dominant closer to the shelf edge. Our results support the ideas of (1) predictable increased wave influence and (2) change to strike-elongate architecture as deltas transit the shelf. In addition, along-strike changes in process dominance cause deltaic reservoirs to be highly variable in their orientation, external shape, and internal character. Some process changes are interpreted to be autogenic responses during overall shoreline progradation. The study also provides new data on delta-lobe and delta-complex thicknesses as well as on deltaic coastline versus shelf-edge progradation rates.

Geologic framework of upper Miocene and Pliocene gas plays of the Macuspana Basin, southeastern Mexico

This integrated study provides a geological and geochemical framework for upper Miocene and Pliocene siliciclastic gas plays in the Macuspana Basin. Structural controls for the plays are deep-seated faults that tap Mesozoic thermogenic gas sources, areas of intense shale diapirism and folding, and areas with structural inversion that could enhance trapping and reservoir productivity. Early Neogene thrusting south of the basin triggered evacuation of Oligocene shale along northwest-dipping listric faults in the eastern and southeastern basin margin. These faults are associated with large-scale rollover structures and thick (500 m) upper Miocene shoreface and wave-dominated deltaic complexes. A second phase of extension in the early Pliocene formed a set of broad, southeast-dipping listric faults in the western basin, controlling thick accumulations of stacked Pliocene shoreface deposits. Trap formation and enhancement in the southern basin margin are linked to late Miocene to Pliocene inversion.The primary stratigraphic controls on play occurrence in the upper Miocene in the onshore part of the basin are the regional facies distribution of northwest-prograding shoreface and wave-dominated deltaic systems. There was a shift in Pliocene sedimentation from the southeast to the west and northwest parts of the basin, where thick successions of aggradational shoreface and wave-dominated deltaic deposits accumulated in depocenters defined by shale evacuation along growth faults. Valley-fill deposits in both the upper Miocene and Pliocene resulted from shortlived periods of base-level change induced by either uplift on the southern basin margin or eustasy. The offshore part of the basin is inferred to consist of deep-water turbidite deposits that formed downdip (westward) of a hypothesized mixed clastic-carbonate prograding complex from the Yucatan platform.Three petroleum systems (Mesozoic, Paleogene–lower Neogene, and upper Miocene–Pliocene) contributed to the hydrocarbon accumulations and hydrocarbon generation and migration in the basin. Principal Upper Jurassic/Lower Cretaceous source rocks generated wet thermogenic gases and oil. Secondary lower Tertiary source rocks generated dominantly dry biogenic gases. Mixtures of the two gas types are common. Numerous deep-seated growth faults and faults serve as pathways for Mesozoic-sourced hydrocarbons. Surface seeps and abundant gas shows suggest that hydrocarbons are being generated today.

Facies and sequence stratigraphy of a Late Barremian wave-dominated deltaic deposit, Agadir Basin, Morocco

Abstract The late Barremian succession in the Agadir Basin of the Moroccan Western High Atlas represents wave-dominated deltaic deposits. The succession is represented by stacked thickening and coarsening upwards parasequences 5–15 m thick formed during fifth- or fourth-order regression and building a third-order highstand systems tract. Vertical facies transitions in parasequences reflect flooding followed by shoaling of diverse shelf environments ranging from offshore transition interbedded mudstones, siltstones and thin sandstones, lower shoreface/lower delta front hummocky bedforms to upper shoreface/upper delta front cross-bedded sandstones. The regional configuration reflects the progradation of wave-dominated deltas over an offshore setting. The maximum sea-level fall led to the development of a sequence boundary that is an unconformity. The subsequent early Aptian relative sea-level rise contributes to the development of an extensive conglomerate lagged transgressive surface of erosion. The latter and the sequence boundary are amalgamated forming a composite surface.

Depositional Model for Understanding Geometry of Cretaceous Coals: Major Coal Seams, Rock Springs Formation, Green River Basin, Wyoming

The Upper Cretaceous Rock Springs Formation of the Green River basin ranges from marine strata of prodelta origin to marginal marine and nonmarine equivalents of delta-front and delta-plain-fluvial strata. Coal exploration drill holes, measured sections, and underground mine data have been analyzed to reconstruct the depositional setting of the Rock Springs Formation. Extensive sheet sandstones are inferred to be delta-front deposits reflecting the cuspate to arcuate geometry of wave-dominated deltaic deposits. Extensive coal deposits up to 22 ft (6.7 m) thick that developed on top of delta-front sandstones extend for 15 mi (24.1 km) along depositional dip, and 36 mi (58 km) along depositional strike. These coal deposits are referred to as type A coal seams. Coal deposits 1-17 ft (0.3-5.2 m) thick that developed in upper delta-plain-fluvial environments are less than 20 mi (32.2 km) in length. These deposits are referred to as type B coal seams. Type C seams are persistent, thin coal deposits 1-8 ft (0.3-2.4 m) thick, developed on top of delta-plain-fluvial deposits less than 25 mi (40.2 km) in length, and they mark the delta-lobe abandonment phase. Approximately 15 major coal zones exist in the Rock Springs Formation. The geometry of types A, B, and C reflects a genetic relationship to both deltaic and fluvial units in the marginal marine and nonmarine components of the Rock Springs Formation. A model for predicting coal-seam thickness and continuity is believed to be applicable to additional exploration in the Green River basin and in other Cretaceous coal-bearing basins in the Western Interior.

Comparison of Wave-Dominated Deltaic Deposits and Associated Sand-Rich Strand Plains, Mesaverde Group, Northwest Colorado: ABSTRACT

The Mesaverde Group (Campanian) in northwestern Colorado is a thick (> 700 m) clastic wedge that prograded eastward into the Western Interior seaway. Models of the main depositional systems in this group were constructed through the study of rock textures and physical and biogenic structures. The geometry of lithofacies was determined from outcrops and End_Page 551------------------------------ analysis of 250 electric logs in the Sand Wash basin. Lithofacies geometry and relations combined with the interpretation of inferred processes from sedimentary structures were used to develop depositional models. The Mesaverde Group can be subdivided into wave-dominated deltaic deposits and their flanking sand-rich strand-plain, interdeltaic deposits. Deltaic headlands were approximately 20 km wide, while the strand plains extended downdrift for at least 60 km. Near deltaic depositional axes, multiple straight and meandering distributaries replace the upper part of the shoreface sequence. Fluvial plain deposits cap this sequence with point-bar sandstones, splays, overbank mudstones, and coals. In interdeltaic areas, progradational shoreface sandstones were deposited and are overlain by coastal plain brackish and freshwater deposits and coals. Marine flooding of the coastal plain was probably due to a combination of subsidence and formation of flanking lows adjacent to depositional axes due to oading. The progradational shoreface is a coarsening-upward sequence 30 to 120 m thick. The sequence includes a basal bioturbated mudstone which becomes interbedded vertically with hummocky cross-stratified sandstones that are capped by an 18 to 60 m thick sandstone. The base of the thick sandstone contains hummocky cross-bedding that grades vertically into troughs that are capped with very low angle cross-bed sets. End_of_Article - Last_Page 552------------