Fluvial-dominated Delta Research Articles

The Late Holocene evolution of the Adra Delta subaqueous system (Northern Alboran Sea): Seismic-stratigraphic and geomorphic evidence of millennial scale climatic and anthropic effects

The formation and development of a small Mediterranean deltaic system are investigated through a primary seismic stratigraphic interpretation of a high-resolution seismic profile network, combined with multiple bathymetric data (including multibeam bathymetric imagery) and collated with shallow sediment cores collected with a vibro-corer device.The submarine delta of the Adra River is divided into a basal patchy seismic unit and five wedge-shaped younger seismic units that are related to the Holocene highstand stabilization. Limited age control indicates that the two uppermost seismic units are very recent, most likely related to a dearth of fluvial fluxes led by channel deviations and by sediment retention. The formation of the three older seismic units is correlated to three humid periods during the Middle Holocene, Late Holocene and Little Ice Age, under a general context of progressive aridification of southeastern Iberia.The stacking patterns and spatial distribution of individual seismic units document a history of episodic progradation of successive prodeltaic lobes, with a long-term evolution mediated by climatically-induced changes in the river basin and more recent anthropogenic interventions. Overall, the subaqueous deltaic system registers the complete modification of a deltaic system that evolves from a fluvial-dominated delta to recent wave-dominated wedges. In between, the deltaic system exhibits a progressive asymmetric character, due to the instauration of Atlantic waters on the shelf and their subsequent eastward redistribution. The Adra deltaic system is proposed as an outstanding example of a small deltaic system that reacts almost immediately to the complex interaction between natural changes in the system and anthropogenic interventions in the drainage basin.

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.

Thalassinoides horizontalis Myrow, 1995 from the Middle-Upper Ordovician shallow marine siliciclastics of Iran (Lashkerak Formation)

Thalassinoides Ehrenberg, 1944 are relatively common bioturbational structures in carbonate shallow marine successions from the early Paleozoic. Much rarer is the reference to this ichnogenus in siliciclastic formations from the same age. In the Ordovician Lashkerak Formation cropping out at the Central Alborz mountains, Iran, Thalassinoides is a common trace fossil in wave-dominated shoreface complex and prodelta-mouth bar environments of a fluvial-dominated delta. We compare the Middle-to-Upper Ordovician branching networks of the Unit 2 of the Lashkerak Formation with the ichnospecies Thalassinoides horizontalis Myrow, 1995 emphasizing the almost entire bedding-parallel orientation, regular branching and lack of constrictions and swellings. The eodiagenetic halos developed from mucus-lining walls, or by change of the original sediment fabric, typical of this and other ichnospecies of Thalassinoides in carbonate settings are not found in sandstones. The almost polygonal mazes from the Lashkerak Formation are also compared with the recently erected Protopaleodictyon aitkeni Morgan, Henderson & Pratt (2019), considered as a giant graphoglyptid in an early evolutionary stage of these forms in shallow marine environments. Both trace fossils are similar in morphology, size, preservation, ichnofacies and interpreted function, thus being P. aitkeni a junior synonym of Thalassinoides horizontalis.

Sedimentology and reservoir characteristics of delta plain reservoirs: An example from Messinian Abu Madi Formation, Nile Delta

Delta plain sandstones represent one of the major deltaic hydrocarbon reservoir compartments. The present research provides integrated sedimentological, petrophysical, and petrographical analyses of delta plain reservoirs using an example from the gas-bearing Messinian Abu Madi in the central part of the Nile Delta. The Abu Madi reservoir is interpreted as a tidally-influenced, fluvial-dominated delta plain, and it is subdivided into four sedimentological architectural elements: distributary channel, crevasse channel (straight and meandering), crevasse splays, and interdistributary bay fill. Although the distributary channel has the best reservoir quality (HFU 4 and HFU 5), it is characterized by a high degree of heterogeneity due to the complex interaction between fluvial discharge and tidal currents; straight crevasse channels (HFU 3 and HFU 4) are similar to the distributary channel but have relatively fine grain size and small sand body volume. The meandering crevasse channels are of low reservoir quality (HFUs 1 and 2) due to the formation of point bar muddy inclined heterolithics. According to the results, the delta plain reservoirs are microscopically dominated by quartzose, and litho- and feldspathic quartzose microfacies. The common mud-matrix and poorly sorted fabric due to rapid deposition as well as reworking by tidal/wave currents, that represent the main depositional controls on reservoir quality. Meanwhile, dissolution, anhydrite, quartz, and calcite as well as authigenic kaolinite and chlorite clays are the main diagenetic control factors on reservoir quality.

Controls on composition and diagenesis of wave- and river-dominated deltas: impacts on reservoir properties. An example from the La Anita Formation (Argentina)

Wave-, tidal-, and fluvial-dominated deltas are important hydrocarbon reservoirs worldwide, and it is well known that depositional facies types, detrital composition and diagenetic products are key aspects when evaluating potential reservoir properties. Moreover, detrital composition and diagenetic products are controlled by external forces such as tectonism, climate, and depositional conditions.The Upper Cretaceous La Anita Formation (Austral-Magallanes Basin, Argentina) is a deltaic succession that shows a clear vertical variation in the relative role of wave, tidal and fluvial processes. The formation was accumulated during the foreland stage of the basin under relatively warm climate conditions. A detailed compositional and diagenetic analysis for these deposits is provided to evaluate the role of the controlling factors on the detrital and authigenic composition, and the impact on reservoir properties.Samples were analyzed by conventional petrography, X-ray diffraction and scanning electron microscopy to obtain a full spectrum of its detrital, authigenic and diagenetic composition. The analyzed sandstones were classified as lithic arenites which come from the fold-thrust belt region and from the magmatic arc located toward the westward. The clay mineral composition is characterized by variable proportions of illite, smectite, kaolinite and mixed-layer illite-smectite with the sporadic presence of chlorite. Stratigraphic variations in the abundance of authigenic kaolinite and smectite indicate a change in the climatic conditions during the depositions of the unit evolving from tropical to more temperate conditions. Diagenetic processes affecting the porosity are considered as controlled mainly by the lithological nature of the deposits and depositional facies type. Sandstone porosity is mainly primary in origin, moderate to good in abundance and show micropore to mesopore as the main pore-sizes.This work enhances that the diagenetic products are heavily controlled by the dominant depositional process. The presence of diagenetic products as quartz overgrowth and calcite and hematite cement reduces pore spaces and affects the reservoir properties. The development of these types of cement is conditioned by the relative dominance of wave and river processes. Under wave-dominated conditions, quartz tends to develop thick overgrowths. Conversely, under river-dominated conditions quartz overgrowths are thinner and calcite and hematite cementation patches are developed.

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.

Research about distal-basin shallow-river fluvial-dominated delta mode of Xiaoheba formation of Silurian of Southeastern Sichuan Basin and thinking about oil and gas exploration

Through precisely measured data of field outcrops, wells logging data and samples analytical data in the research area, it is considered that the topography of the sedimentary period of Xiaoheba formation is relatively flat, the water flow is shallow and wide and the fluctuation is frequent, the supply of source is abundant, and it has favorable sedimentary conditions to forming shallow-river fluvial-dominated delta. The delta in the research area is a distal-basin sedimentary, and due to multiple branches and long extension of the river channel, there are large area of delta front sand deposits with fine grained development, high maturity and underwater environment existed within the research area. The Xiaoheba formation in the Jiannan-Fuling three-dimensional seismic region has the obvious characteristics of strong peak progradation reflection. Based on the above analysis, the sedimentary mode of shallow-river fluvial-dominated delta of Xiaoheba formation of Southeastern Sichuan Basin is established and the reservoir forming conditions are discussed. It is considered that the Xiaoheba formation has excellent hydrocarbon source, high-quality reservoirs and effective migration channel. This research has certain guiding significance for the next stage of tight marine clastic rocks oil and gas exploration of Southeastern Sichuan Basin.

Numerical forward Modelling of River-dominated Deltas

A delta is a type of sedimentary system that is closely related to oil and gas. Shallow-lake delta deposits in the Mesozoic-Cenozoic strata of China are of particular interest. This delta has significant oil and gas reserves that are developed widely. Based on a numerical simulation of the sand body of the shallow-lake delta, this study analyzes the influence of various sediment conditions on the sand-body development. The formation and distribution rules of the sand body are concluded and verified, and the results can effectively guide the exploration and development of oil and gas resources. Unlike traditional flume experiments, this study adopts sediment numerical simulation technology. This approach is borrowed from the advanced achievements of computational fluid dynamics, and Delft3D is used to establish a three-dimensional numerical model of the delta. The calculation field was 20.5 km in length by 10 km in width. With the Mor-Factor set to 60, the simulation time was 45 days. The formation and the avulsion of the mouth bar, as well as the extension, migration and bifurcation of distributary channels, have been observed and studied through analysis of the simulation results. The vertical cross-section shows that the distributary channel was filled multiple times. According to distributary channel evolution characteristics combined with quantitative methods, the terminal distributary channels can be extremely developed under ideal conditions. Due to the cross-cutting and reform effort of distributary channels, sediments were spread widely and continuously. The results show that the numerical model works well in explaining the process of evolution in fluvial-dominated delta distributary channels. This study not only enables us to quantitatively understand the dynamic processes of terminal distributary channels in fluvial-dominated delta systems, but also provides a reference model for numerical simulation of hydrodynamics in sedimentology study.

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.

Seismic geomorphology and sedimentology of a fluvial-dominated delta: Implications for the Neogene reservoirs, offshore Bohai Bay Basin, China

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.

Magnetostratigraphy of a Middle Jurassic delta system (Lajas Formation), Portada Covunco section, southern Neuquén Basin, Argentina

A systematic paleomagnetic study was carried out in the Lajas Formation (Middle Jurassic), cropping out at the Covunco creek in the central part of the Neuquén basin. The Lajas Formation at the Portada Covunco section consists of a succession of conglomerates, sandstones and mudstones that reaches c. 290 m-thick. On the basis of lithological and textural features, sedimentary structures, strata geometries, and fossil content, 14 facies were defined that were grouped in two facies associations within a fluvial-dominated delta system. The age of the Lajas Formation is rather controversial, and has been assigned from sequence stratigraphy and palynological data. Thus from south to north, interpreted ages span the Upper Aalenian–Middle Bathonian through the Callovian. Therefore, magnetostratigraphy was used to better precise the age of the Formation at Portada Covunco. Paleomagnetic data obtained from 29 sampling sites present reliable behaviors. Rock magnetic studies (thermomagnetic curves, K vs H curves, IRM acquisition curves) suggest that the remanence is carried by Ti-poor magnetite. Anisotropy of magnetic susceptibility data show clustering of the Kmax axes produced by the action of paleocurrents. The characteristic remanent magnetization passed a tilt test and a reversal test that prove its primary origin. The resultant magnetostratigraphy is characterized by a reverse-dominant with minor normal polarity intervals. When compared with the Bajocian-Bathonian reference geomagnetic polarity time scale (GTS2016), the best fit is achieved in the Lower through Middle Bathonian (Chrons M41 to M39). A paleomagnetic pole was calculated for Portada Covunco located at 167.1°E, 59.4°S, N = 28, A95 = 3.6°, K = 57.2. When compared with the other available paleopole of the same age −170 Ma-derived from dykes exposed at Mamil Choique, Patagonia, Portada Covunco falls in the same paleomeridian although at a lower latitude. Thus, it is interpreted that the studied section was not subjected to rotations around vertical axis (R = 4° ± 10°), but was compacted, which produced inclination shallowing of the magnetic vector (F = 18° ± 11°). The calculated inclination shallowing and amount of compaction in the section are well within the expected values in medium to fine-grained sandstones. Using the paleomagnetic pole from Mamil Choique as reference, the locality of Portada Covunco would have been located at c. 33°S during the Bathonian, in agreement with paleoclimatic interpretations derived from palynological data.

Differentiation of delta and open marine deposits based on an integrated ichnological and sedimentological analysis of the Late Triassic Nayband Formation, Tabas Block, Central Iran

The palaeoenvironmental significance of trace fossil assemblages in the shallow marine deposits of the Late Triassic Nayband Formation of the Tabas Block, Central Iran has been assessed for the first time. The siliciclastic successions of the Nayband Formation, are highly bioturbated and allow relationships between changes in ichnoassemblages within a depositional system to be documented and placed in a palaeoenvironmental framework. The main purposes of this paper are: (1) to describe and illustrate the trace fossils assemblages of the Nayband Formation; (2) integration of ichnologic and sedimentologic data to evaluate different stress factors on the infaunal communities; and (3) to briefly discuss paleoenvironmental distribution of various trace fossil assemblages in order to differentiate between deltaic and non-deltaic shoreface successions. The Upper Triassic Nayband Formation has been studied and measured in one section, where the Nayband Formation is well accessible and continuously exposed. This section was logged and evaluated using physical sedimentology and ichnology in order to establish a basis for the interpretation of sedimentary processes (facies) and depositional systems. In this study, trace fossils (diversity, abundances, and ethologies) and the spatial arrangement of sedimentary structures are used to further refining the interpretation of environmental parameters such as hydrodynamic energy, water turbidity, substrate properties, food supply, temperature, oxygenation, salinity, and sedimentation rates. Based on facies characteristics and stratal geometries, the siliciclastic succession is divided into two facies associations, fluvial-dominated delta (FA), and open marine (FB). Twenty-eight ichnogenera have been identified in delta and open marine successions: The assemblage is dominated by Rhizocorallium, Thalassinoides, Ophiomorpha, Helminthopsis, Palaeophycus and Skolithos. Their distribution is clearly linked with lithofacies and depositional environments. High rates of fluvial discharge, high water turbidity, seasonally high rates of deposition and phytodetrital pulses in river-dominated deltas may cause marked variations in the temperature, oxygenation and salinity of the fluvial-dominated delta successions. All of these factors in combination lead to impoverishment in trace diversity and reduction in burrow size but to rapid colonization of the substrate by single-layer colonizers of opportunistic deposit feeders. Low ichnodiversity, low bioturbation intensities with highly bioturbated clusters shown by single colonization events by opportunistic, simple feeding strategies of trophic generalists and a paucity of suspension-feeding structures elements represent a “stressed”, non-archetypal Cruziana ichnofacies. The changes of behavioural complexity and the tiering profiles in the offshore-shoreface complex of the Nayband Formation when compared with the river-dominated delta successions represent the transition from epifaunal life habits with simple tiering structures to infaunal life habits with complex tiering pattern. The occurrence of diverse trace fossil suites attributable to the Zoophycos ichnofacies, the archetypal Cruziana ichnofacies and the Skolithos ichnofacies in wave-dominated shoreface-offshore complex point to stress-free environmental conditions in open waters due to persistent wave agitation, and hence, a wide colonization window.

Stratigraphy and depositional environments of the Mesaverde Group in the northern Bighorn Basin of Wyoming

Using single stratigraphic methods in the geological analysis of incompletely or poorly exposed sedimentary successions can lead to non-unique interpretations and increased potential for error. In this study of the Mesaverde outcrops (Eagle Formation, the Claggett Tongue of the Cody Shale, and the Judith River Formation) in the northern Bighorn Basin of Wyoming, which has limited and variable quality exposures, an integrated method utilizing sedimentological, ichnological, and palynological data was used in order to overcome these limitations. Ten facies are identified within the exposures examined. These facies are arranged so as to depict a broadly distal to proximal gradient recording the progradation of fluvial-dominated deltas into a shallow marine environment. The utilization of a Zobaa Ternary Plot and Calgary and Brown factor analysis (CABFAC) for palynofacies analysis in the study allows for corroboration of the lithological interpretation, which has not been possible in previous studies of correlative outcrops. It also enables the identification of environmental trends not seen in the lithological analysis, thus allowing for a more robust stratigraphic analysis. The methods used in this study not only decrease the inherent error in paleoenvironmental analysis of poorly exposed areas and thereby decrease variability in paleoenvironmental interpretations, but also allow identification of changes that are not evident from a single method approach. The result of utilizing this approach in areas of limited or poor quality exposure is a more comprehensive and well-informed regional stratigraphic framework.

Sedimentary facies and evolution of the lower Urho Formation in the 8th area of Karamay oilfield of Xinjiang, NW China

AbstractOn the basis of core descriptions, examinations of rock thin sections, and EMI logging, a fluvial-dominated fan delta depositional system consisting of the fan delta plain and front subfacies from the lower Urho Formation of the Upper Permian in the Karamay oilfield of Xinjiang, NW China, was recognized in this research. The typical characteristics of this kind of fan delta is the depositional processes that were dominated by the fluvial and tractive current structure that developed very well, while pro-fan delta and gravity deposition occurred very less. The key microfacies associations in the fan delta plain subfacies are braided channel, sheeted flow, mud flow, and sieve deposits, while the fan delta front subfacies commonly contains subaqueous channels, interdistributary channels, debris flow, grain flow, and subaqueous levee microfacies. A study of image logging, grain size, and compositions of rocks indicate that provenance directions are different from the early to the last depositional per...

Thin-bedded reservoir analogs in an ancient delta using terrestrial laser scanner and high-resolution ground-based hyperspectral cameras

Ground-based terrestrial laser scanning and hyperspectral sensors were used to image fine-scale heterogeneity in outcrops of prodeltaic heterolithic facies of Parasequence 6 of the Cretaceous Ferron Notom delta in Southern Utah. Previous work shows that Parasequence 6 is an upward coarsening fluvial-dominated, wave-influenced deltaic deposit containing heterolithic thin-bedded facies representing distal delta front and proximal prodelta environments. Primarily, the thin beds have been interpreted as turbidites, storm beds (tempestites), and hyperpycnites. These deposits represent analogs for thin-bedded unconventional pay zones that lie at the margins of conventional deltaic sandstone reservoirs.The terrestrial laser scanner was used to create a centimeter- to decimeter-scale, digital representation of the outcrops in three dimensions. Hyperspectral sensors record electromagnetic radiation reflected off the outcrops in 840 contiguous bands, which were then used to generate a spectral signature for each pixel sampled. The spectral signatures are a function of mineralogy, chemistry, surface alteration, grain-size, and cements, and were used to distinguish thin mudstones from sandstones within an interbedded succession at the base of a deltaic parasequence. Comparison between the spectral signatures recorded from the outcrop and those of reference materials, and with previous facies architecture studies, enables lithofacies to be identified and subsequently accurately mapped. Hyperspectral data are then draped over the terrestrial laser scanner model to generate a spatially-accurate detailed three-dimensional (3D) geologic map of the heterogeneity.Approximately 100m of outcrop was imaged laterally with the hyperspectral camera and terrestrial laser scanner on the previously mapped distal delta front and prodeltaic facies of Parasequence 6. Bed thickness data, based on measurements made along depositional dip versus strike, show that bed geometries are anisotropic. Reconstruction of the plan-view geometry shows that the thin-beds are lobate to elongate in plan-view profile and extend over distances of about 1km, indicative of the dispersive waning sediment transport processes found in storm-influenced fluvial-dominated deltas. The lobate geometry suggests that beds are laterally discontinuous, with a width to thickness ratio on the order of <10,000 (i.e. a 10cm bed extends for <1km). The combined terrestrial laser scanner and hyperspectral data provide continuous 3D maps of grain-size and lithology. The maps which emphasize the continuity and dimensions of thin beds are among important factors which impact reservoir behavior.

Palynotaphofacies analysis applied to Jurassic marine deposits, Neuquén Basin, Argentina

Fil: Martinez, Marcelo Adrian. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Instituto Geologico del Sur. Universidad Nacional del Sur. Departamento de Geologia. Instituto Geologico del Sur; Argentina

A seismic geomorphology study of the fluvial and lacustrine-delta facies of the Cretaceous Quantou-Nenjiang Formations in Songliao Basin, China

With the aid of seismic geomorphology method, depositional systems such as fluvial-delta and turbidity current of the Cretaceous Quantou-Nenjiang Formations in Sangliao Basin were studied in detail as well as the morphology, dimension, depositional structures and boundaries of these sedimentary bodies. A geological model of a point bar in a fluvial system and the method to identify paleocurrent direction were proposed. The delta of Yaojia Formation with a gentle slope less than 1.4‰ in trangressive system tract (TST) was controlled by lake waves. Subaqueous distributary channels were widely developed in large-scale delta front with a width more than 16 km. Fluvial-dominated deltas with leaf and bird's foot shapes were widespread in highstand system tract (HST) of Qinshankou and Nengjiang Formation with moderately high slope gradients of 4‰ and 6.7‰.The width of the leaf-like and bird's foot delta front ranges from 1 km to 4 km and 3 km–5 km respectively. The mouth bar were well preserved due to the poorly developed widely distributed subaqueous distributary channels and the delta plains having widths of 9 km–15 km, 16 km-25 km respectively. Many turbidity current systems were recognized in the TST of the first member of Nengjiang Formation and the distribution area is about 10,000 km2. Fourteen sublacustrine fans with different dimension were formed by ten fluvial-delta systems extending 30 km–70 km toward the lake from the west and south. With the application of seismic geomorphology, the analysis of fluvial system, delta system and turbidity current system could switch from approximation to quantitative analysis. Sedimentary model proposed for point bars and the quantitative analysis of delta system could provide new technical support for exploration and drilling plan. The research on turbidity current systems will also be beneficial for new exploration targets.

Sedimentary facies and depositional model of shallow water delta dominated by fluvial for Chang 8 oil-bearing group of Yanchang Formation in southwestern Ordos Basin, China

A systematic analysis of southwestern Ordos Basin’s sedimentary characteristics, internal architectural element association styles and depositional model was illustrated through core statistics, well logging data and outcrop observations in Chang 8 oil-bearing group. This analysis indicates that shallow water delta sediments dominated by a fluvial system is the primary sedimentary system of the Chang 8 oil-bearing group of the Yanchang Formation in southwestern Ordos Basin. Four microfacies with fine grain sizes are identified: distributary channels, sheet sandstone, mouth bar and interdistributary fines. According to the sandbody’s spatial distribution and internal architecture, two types of sandbody architectural element associations are identified: amalgamated distributary channels and thin-layer lobate sandstone. In this sedimentary system, net-like distributary channels at the delta with a narrow ribbon shape compose the skeleton of the sandbody that extends further into the delta front and shades into contiguous lobate distribution sheet sandstone in the distal delta front. The mouth bar is largely absent in this system. By analyzing the palaeogeomorphology, the palaeostructure background, sedimentary characteristics, sedimentary facies types and spatial distribution of sedimentary facies during the Chang 8 period, a distinctive depositional model of the Chang 8 shallow water fluvial-dominated delta was established, which primarily consists of straight multi-phase amalgamated distributary channels in the delta plain, net-like distributary channels frequently diverting and converging in the proximal delta front, sheet sandstones with dispersing contiguous lobate shapes in the distal delta front, and prodelta or shallow lake mudstones.

Climate changes and solar cycles recorded at the Holocene Paraná Delta, and their impact on human population.

The Paraná delta, growing at a rate of c. 2 km2 yr−1 since 6,000 yrs, is one of the most complete records of the Late Holocene in southern South America. The evolution of this 17,400 km2 delta enclosed in Plata estuary, can be tracked by a series of 343 successive coastal-ridges showing a c.11 years period, in coincidence with sunspot cycle, also found in some North Hemisphere coastal-ridge successions. The Paraná delta shifted from fluvial, to wave-dominated, and back to the present fluvial-dominated delta, in response to climate changes associated with wind activity correlating with South American glacial cycles. The wave-dominated windy period coincides with the activation of the Pampean Sand Sea, suggesting desert conditions prevailed on the Pampas between 5,300 and 1,700 yrs, in coincidence with scarce or absent pre-historic aborigine remains (“archeological silence”). Further warmer and less windy conditions allowed human repopulation. Results suggest that aside the solar forcing, both short and medium term climate changes controlled delta evolution. An important learning is that a slight cooling would turn the highly productive pampas, into that unproductive desert and, given the lack of artificial irrigation systems, changing present-day warmhouse into a cooling cycle might be economically catastrophic for the region.

Paleoenvironmental evolution of the late Pliocene–early Pleistocene fluvio-deltaic sequence of the Denizli Basin (SW Turkey)

Abstract The late Pliocene–early Pleistocene Tosunlar succession (Denizli Basin, southwestern Turkey) represents fluvial-dominated delta environments at the margins of a brackish long-lived lake. Two main facies associations are documented: (i) a delta front facies association, with a distal (DF1) and proximal (DF2) deposits; and (ii) a delta plain facies association that contains distributary channel (DP1) and interdistributary swamp (DP2) deposits. The stable isotopic analysis of the mollusc faunas exhibit a narrow range of values (–4.68