Fan Deposits Research Articles

Cenozoic growth of the Eastern Kunlun Range (northern Tibetan Plateau): evidence from sedimentary records in the southwest Qaidam Basin

ABSTRACT The Cenozoic sedimentary infill of the Qaidam Basin in the northern Tibetan Plateau provide significant insights into the uplift history and the tectonic evolution of the basin-bounding mountain ranges. Along the SW basin margin, a continuous record is preserved in the ~3000-m-thick Cenozoic succession at the Changweitai area. An up-section switch from marginal and deep lacustrine sedimentation to lacustrine delta-alluvial fan deposition indicates progradation and increasingly basinward advance of sediment transportation systems. Provenance data from sandstone petrology, palaeocurrent analysis and zircon U-Pb geochronology suggest that the Eastern Kunlun Range has been consistently providing material to the SW Qaidam basin since the deposition of the upper Xiaganchaigou Formation, indicating its latest uplift episode prior to the Late Eocene (before 35.5 Ma). However, variation in depositional systems indicates a clear shift in sediment provenance between the deposition of the Xiayoushashan Formation and the Shangyoushashan Formation. We propose that the Cenozoic Eastern Kunlun Range experienced a northward encroachment of shortening into the Qaidam Basin. During the Early Miocene, extensive topographic growth of the Altyn Tagh Range caused by reactivation of the Altyn Tagh strike-slip fault, provided the main source of sediment for the western Qaidam basin. Subsequently, a new source for the basin was provided by the uplifting Qimen Tagh subrange since ~15 Ma.

Luminescence dating of Quaternary alluvial successions, Sellicks Creek, South Mount Lofty Ranges, southern Australia

Quaternary alluvial and colluvial sediments infill major river valleys and form alluvial fans and colluvium-filled bedrock depressions on the range fronts and within the Mount Lofty Ranges of southern Australia. A complex association of alluvial successions occurs in the Sellicks Creek drainage basin, as revealed from lithostratigraphy, physical landscape setting and optically stimulated luminescence (OSL) ages. Correlation of OSL ages with the Marine Oxygen Isotope record reveals that the alluvial successions represent multiple episodes of alluvial sedimentation since the penultimate glaciation (Marine Isotope Stage 6; MIS 6). The successions include a penultimate glacial maximum alluvium (Taringa Formation; 160 ± 15 ka; MIS 6), an unnamed alluvial succession (42 ± 3.2 ka; MIS 3), a late last glacial colluvial succession within bedrock depressions (ca 15 ka; MIS 2) and a late last glacial alluvium (ca 15 ka; MIS 2) in the lowest, distal portion of Sellicks Creek. In addition, the Waldeila Formation, a Holocene alluvium (3.5 ± 0.3 ka; MIS 1), and sediments deposited during a phase of Post-European Settlement Aggradation (PESA) are also identified. The age and spatial distribution of the red/brown successions, mapped as the Upper Pleistocene Pooraka Formation, directly relate to different topographic and tectonic settings. Neotectonic uplift locally enhanced erosion and sedimentation, while differences in drainage basin sizes along the margin of the ranges have influenced the timing and delivery of sediment in downstream locations. Close to the Willunga Fault Scarp at Sellicks Creek, sediments resembling the Pooraka Formation have yielded a pooled mean OSL age of 83.9 ± 7 ka (MIS 5a) corroborating the previously identified extended time range for deposition of the formation. Elsewhere, within major river valleys, the Pooraka Formation was deposited during the last interglacial maximum (128–118 ka; MIS 5e). In general, alluviation occurred during interglacial and interstadial pluvial events, while erosion predominated during drier glacial episodes. In both cases, contemporaneous erosion and sedimentation continued to affect the landscape. For example, in the Sellicks Creek drainage basin, which lies across an actively uplifting fault zone, late glacial age sediments (MIS 2) occur within the ranges and near the distal margin of the alluvial fan complex. OSL dating of the alluvial successions reported in this paper highlights linkages between the terrestrial and marine environments in association with sea-level (base-level) and climatic perturbations. While the alluvial successions relate largely to climatically driven changes, especially in major river valleys, tectonics, eustasy, geomorphic setting and topography have influenced erosion and sedimentation, especially on steep-sloped alluvial fan environments.KEY POINTSLuminescence dating of the Sellicks Creek alluvial fan complex reveals that sedimentation occurred predominantly during the later stages of glacial cycles accompanying lower sea-levels than present.Luminescence dating confirms that the stratigraphically lower portions of the Pooraka Formation are beyond the range of radiocarbon dating.Upper Pleistocene alluvial fan sedimentation at Sellicks Creek correlates with pluvial events in southeastern Australia.

Tectono‐sedimentary evolution of transverse extensional faults in a foreland basin: Response to changes in tectonic plate processes

AbstractLate Paleocene to Middle Eocene strata in the easternmost part of the Southern Pyrenees, up to 4 km thick, provide information on tectono‐sedimentary evolution of faults transversal to the Pyrenean chain. To know how changes in tectonic plate processes control the structural evolution of transverse faults and the synchronous thickness and lithological distribution of sedimentary strata in a foreland basin, field observations, interpretation of 2D seismic lines tied to lithostratigraphic data of exploration wells and gravity modelling constrains were carried out. This resulted in the following two tectono‐sedimentary phases in a foreland basin: first phase, dominated by transverse extensional faulting, synchronous with deposition of marine carbonates (ca. 57 to 51 Ma); and second phase, characterized by transverse contractional faulting, coeval to accumulation of marine and transitional siliciclastics (51 to 44 Ma). During the first phase, Iberia and Adria were moving to the east and west respectively. Therefore, lithospheric flexure in the easternmost part of the Iberian plate was developed due to that Sardinia was over‐thrusting Iberia. Consequently, activation of E‐dipping normal faults was generated giving rise to thick‐deep and thin‐shallow carbonate platform deposits across the hanging walls and footwalls of the transverse structures. During the second phase, a shearing interaction between Iberia and Sardinia prevailed re‐activating the transverse faults as contractional structures generating thin‐shelf and thick‐submarine fan deposits across the hanging walls and footwalls of the transverse structures. In the transition between the first and second phases, evaporitic conditions dominated in the basin suggesting a tectonic control on basin marine restriction. The results of our study demonstrate how thickness and lithology distribution, controlled by transverse faulting in a compressional regimen, are influenced by phases related to processes affecting motions and interactions between tectonic plates and continental blocks.

Coexisting seismic behavior of transform faults revealed by high-resolution bathymetry

AbstractTransform faults have anomalously low rates of seismicity, but it’s not clear whether this reflects persistent earthquake-generating fault patches surrounded by creep, or the presence of creep and earthquakes at different times along the same patch. We use new, autonomous underwater vehicle high-resolution seafloor mapping to image the morphology of and offsets along transform fault segments in the Gulf of California, offshore Mexico. Fault zone structure imaged in this study shows evidence for the initiation and cessation of activity along individual fault splays over geologic time. A series of six identically offset depositional fans evidence 21–23 m of slip along the main transform fault, which could not have been produced by a single earthquake given the length of the transform. Rather, the lack of smaller-magnitude offsets indicates synchronous deposition and an absence of multiple slope failure–inducing earthquakes, which is consistent with the idea that creep and/or small-magnitude events occur asynchronously with large earthquakes in the slip history of a given transform fault segment.

Tributary-junction alluvial fan response to an ENSO rainfall event in the El Huasco watershed, northern Chile

Tributary-junction alluvial fans situated at the intersection of confined valleys with <100 km2 tributary catchments are of special interest to evaluate the heterogeneous consequences of extreme rainfall events in arid zones. These fans record the episodic sedimentological behaviour of the hillslope response to rainstorm events within tributary catchments, together with the influence on the main fluvial systems. In this paper, we benefit from the March 2015 event (23–26 March 2015), which produced 75–46 mm of precipitation over four days in the southern portion of the Atacama Desert. This storm event triggered several debris flows in El Huasco River watershed tributaries and, therefore, tributary-junction alluvial fans received a total of ∼106 m3 of sediments across 49 activated catchments. We find that the characteristic storm signature across the catchments can be synthetised in a conceptual fan formation model based on field mapping of facies (F1 to F6) present in the fans. The characteristic signature is a record of initially high sediment-to-water flows restricted to the fan environments (mainly debris flows) followed by later, more dilute (mainly hyper-concentrated to fluvial) flows that incise the tributary-junction alluvial fan deposits and link tributary catchments with the main river. These later-stage flood event deposits, locally, are capable of ponding and compartmentalising the main river where the longitudinal connectivity of the tributary-junction catchment is effective. This situation improves tributary-junction fan slope and main-trunk-channel linkages. This approach provides a reference framework for understanding the distribution and routing of effective runoff from similar rainfall events that control the aggradation and incision of the fluvial system, which is of great value when studying past stratigraphic arrangements in these arid alleys.

Investigation of the Norcia basin (Central Italy) through ambient vibration measurements and geological surveys

During the 2016–2017, a seismic sequence struck the Central Italy, involving four regions (Umbria, Marche, Abruzzo and Lazio) and causing important damages and victims in inhabited areas such as Norcia and Amatrice towns. The strongest event of the seismic sequence was a Mw 6.5 event with epicenter at about 5 km far from the Norcia area, which is an intermontane basin prone to ground motion amplification. The historical town of Norcia and the surrounding hamlets were recently investigated by the microzonation activity, but information on the geometry and velocity are still partial considering the entire basin. Indeed, past studies aimed at reconstructing the elastic and geometrical properties focusing mainly on the northern part of the basin. Specifically in this paper, we integrated seismic and geological data to get a better knowledge of the properties of the Quaternary Norcia basin. A geological survey was carried out to provide a geological map and three geological cross-sections. We analyzed new seismic ambient vibrations data, collected by single-seismic stations, to infer the distribution of resonant frequency (f0) for the entire basin. We used passive arrays of seismic stations to better define the velocity profiles of the area. In the northern part of the basin, two 2D arrays with elliptical-like shapes were deployed showing strong discrepancies of the elastic soil properties in proximity of Norcia town. We found shear-wave velocities of the near-surface profile of about 300–400 and 500–800 m/s in presence of palustrine and alluvial fan deposits, respectively. Further, the values of f0 are abruptly varying from 0.5 Hz in the SW sector of Norcia village up to 2 Hz in its NE sector. Ambient vibration data reveal less pronounced variation of f0 in the southern part of the basin, with resonant values that are almost in the range 1–1.3 Hz. In the southern sector, a 1D array was arranged along a 5-km line and was analyzed by means of seismic noise cross-correlation analysis suggesting the presence of a deeper seismic contrast. The integration of geophysical and geological results has allowed to infer insights on the subsurface geometry of the basin.

Rapid exhumation since at least 13 Ma in the Himalaya recorded by detrital apatite fission-track dating of Bengal fan (IODP Expedition 354) and modern Himalayan river sediments

Apatite fission-track analysis of middle Bengal fan sediments (IODP expedition 354) and modern Himalayan river sediments shows that most of the detrital apatites are very young compared to their depositional ages, independent of their uranium content. Bengal fan apatites display an average central age lag time as short as 2.26±1.6 Myr since at least ∼13 Ma. Such lag times reflect a mean exhumation rate on the order of at least 1-3 km/Myr. The occurrence of detrital apatites with relatively short AFT lag times since at least 13 Ma indicates that there have always been areas of rapid erosional exhumation, supplying detrital apatites to the fluvial system and delivering them to the paleo-Ganges and/or –Brahmaputra plains and finally to the Bengal fan. It also supports that temporary storage of detrital apatites in the floodplains or delta has always been negligible since at least 13 Ma. Comparison of the AFT data of the Bengal fan with those of the Central and Eastern proximal Neogene Himalayan foreland basin shows that both paleo-Ganga and –Brahmaputra catchments provided apatites with similar short lag time to the distal Bengal Fan basin.In the modern drainage system of the Bengal fan, the apatites with young fission-track cooling ages are principally derived from areas where the topography has a sharp relief controlled by threshold hillslope processes and stream power resulting in landslide erosion as a coupled response to tectonic and fluvial forcing. By analogy with the modern erosion processes in the Himalayan range, we suggest that over the past 13 Ma, apatites were mainly derived from areas of sharp relief, where river stream power was high and hill slopes close to the threshold angle. As the exhumation signal is rather consistent since the late Miocene the detrital apatite fission-track data are either not sensitive enough to detect rapid climatically controlled changes in exhumation rates, or overall long-term erosion rates on the orogen scale are not strongly affected by climatic variations such as the variability of the Indian Summer Monsoon. Given the already rapid exhumation rates controlled by tectonics, the impact of climate variability on surface erosion rates cannot be detected with our data, especially in the case of erosion processes dominated by threshold hillslope model.

Quantitative assessment of uncertainties in modeled crater retention ages on Mars

With increasing high-resolution coverage of Mars' surface, crater count analysis is being used to estimate the formative ages of small depositional features (<1000 km2) to constrain timing of climate-driven events. We introduce a probabilistic cratering model that quantifies how modeled age estimates vary strongly with crater obliteration rates (β, defined as the combined rate of erosion and infilling), minimum crater diameter counted, and surface area size. Model results show that crater obliteration introduces significant uncertainty on small surfaces, where moderate obliteration rates (β ~ 25 nm a−1) require surface areas of about 10,000 km2 to date 2 to 3 Ga surfaces accurately, and strongly obliterated surfaces (β = 200 nm a−1) require surface areas up to 100,000 km2. In practice, smaller areas can nonetheless be analyzed probabilistically by estimating a range of likely obliteration rate and modeled age combinations and optimizing these values relative to observed crater count data, resulting in a distribution of possible modeled surface ages and associated β. We demonstrate this method using data from the Coprates Chasma landslide (~200 km2) and numerous fan and delta deposits in the Gale crater region. Although the deposits in and around Gale are <1000 km2, a probabilistic analysis enables us to suggest that deltaic deposits in and near Gale have a higher probability of being older (~>3 Ga) than nearby fans (~1–3 Ga). This analysis provides a simple quantitative framework for assigning probable surface age ranges for small features on Mars.

Sediment transport mechanisms revealed by quantitative analyses of seafloor morphology: New evidence from multibeam bathymetry of the Israel exclusive economic zone

Abstract This study synthesizes 15 years (2001–2016) of detailed multibeam hydrographic mapping covering the entire 26,500 km2 of the Israeli Exclusive Economic Zone (EEZ). Multibeam data were collected on-board three research vessels across the continental shelf, slope, and the deep Levant basin; between water depths of about 15 m to 2100 m. Single-channel 3.5 kHz seismic reflection chirp profiles were collected simultaneously with the multibeam surveys in selected parts of the area. The new data enabled the first comprehensive quantitative seafloor morphological analysis of the slope and deep basin. Using GIS techniques on the high-resolution multibeam data, we analyze the spatial distribution and quantitatively describe the seafloor morphologies in detail. High-resolution chirp seismic profiles demonstrate the underlying shallow structure. Results indicate that the seabed comprises five main morphologies: folds, faults, sediment waves, deepwater channels, and sediment fan lobes. Quantitative morphological analysis and seismic data interpretation were used to derive field relations between these morphologies, which along with previously collected multi-channel seismic reflection data, suggest that a concentric fold geometry formed around the Nile outlet during the late Pliocene to early Pleistocene, as part of a general thin-skin radial salt-tectonic deformation above the Messinian mobile unit. This radial motion was accompanied by displacement along NNE-trending strike-slip faults in the basin, and an extensional component across E-W trending strike-slip faults along the Levant margin. While some of these displacements continue to deform the modern seabed (across Area A), others are covered by a wedge of Quaternary deposits, mainly in the northeastern part of the basin (Area B). Areas A and B also differ in grain size distribution, as indicated by backscatter analysis of the multibeam data. These observations divide the Israeli EEZ into two distinct areas: (Area A) Nile derived siliciclastic sediments transported directly into the deep basin via confined (forming meandering channels and overbank deposits) and unconfined flows (forming fans and lobes). The wedge consisting of Area B was fed by erosion products of the Nile outlet that were transported northwards along the continental shelf by seafloor currents of the Levant Jet System, and glided down the northern Levant continental slope as turbidity currents. This supply built at least seven sequences of Quaternary sediment waves that form upslope migrating cyclic steps. The complete data coverage and quantitative morphological analysis presented here introduce new spatial and temporal constraints that call for a reexamination of previous seabed sampling locations not accounting for detailed bathymetry, and to augment future seabed sampling efforts, understanding the sediment supply paths across the basin, and the geomorphological footprint of salt tectonics processes.

Martian fan deposits: Insights on depositional processes and origin from mass balance survey

Fan deposits located at the mouths of Martian valleys have been interpreted as indicators of wet conditions during Mars history. However, the processes, time and amount of water needed to carve the valleys and form the fans are still debated. Here we present a detailed morphometric and mass balance analysis of valleys and fan-shaped deposits using high resolution topography, which provides new insights into past depositional environments.Based on morphometric and volumetric measurements, we found that several Martian fans previously interpreted as deltas can be categorized into two main types. Type I fans are more numerous, relatively well preserved, are associated with smaller and less mature drainage networks and were deposited on steeper gradients. The balance between eroded and deposited materials indicates that this set of fans might have been formed mainly in subaerial settings by depositional processes other than typical deltaic sedimentation (e.g. alluvial, glacial, mass-wasting in general), since a significant loss of sediment during deposition did not occur (we obtained a volume ratio of eroded vs. deposited materials of approximately 1). Therefore, we propose that the identified Type I fans were not deposited in prevailing subaqueous deltaic settings, but mainly in subaerial conditions with perhaps sporadic presence of ephemeral bodies of standing water within the basins.In contrast, Type II fans are less abundant, highly eroded, were deposited on flatter areas and formed downstream of more mature drainage networks with longer, deeper and wider valleys. The mass balance for this set of fans clearly shows that considerable amounts of sediment were not retained in the fans, implying large offshore transport of sediment during their formation (eroded vs. deposited volume ratios between 3 and 10 are probable). This evidence supports a fluvio-deltaic origin for this class of fans, indicating the existence of paleolakes over substantial periods of time.Based on the collected morphometric measurements and mass balance modeling we conclude that only a small percentage of the fans (Type II fans correspond to ∼1/3 of the sampled areas) are consistent with the occurrence of favorable and durable conditions for life, i.e. long-lived integrated fluvial, deltaic and lacustrine environments. Whereas, the majority of fans might have been formed in subaerial settings with significant contributions of alternative processes besides fluvial transport and deposition thus not necessarily requiring the occurrence of extended epochs of clement climatic conditions.

Dyke failures in the Province of Groningen (Netherlands) associated with the 1717 Christmas flood: a reconstruction based on geoscientific field data and numerical simulations

AbstractThe 1717 Christmas flood is one of the most catastrophic storm surges the Frisian coast (Netherlands and Germany) has ever experienced. With more than 13,700 casualties it is the last severe storm surge with a death toll of this order. At the same time, little is known about the hydrodynamic conditions and the morphological effects associated with this storm surge.In this study, 41 potential dyke failures in the Province of Groningen (Netherlands) associated with the 1717 Christmas flood were systematically reconstructed and mapped by using historical maps and literature and by analysing the recent topography in search of typical pothole structures and sediment fans. The dimensions of the sediment fans as derived from the topography show a good accordance with the dimensions documented by vibracore profiles, direct push tests and electrical resistivity tomography data taken at three fieldwork sites. Moreover, the fan dimensions closely agree with the dimensions as simulated using a process-based morphodynamic numerical model for one of the three sites, the village of Wierhuizen. Consequently, the recent topography is still indicative for the locations and dimensions of dyke failures and sediment fans associated with the 1717 Christmas flood. Considering the large number of detected dyke failures (41) and the large dimensions of the potholes and particularly of the sediment fans up to a few hundred metres wide and up to 0.7 m thick, this study proves significant morphological effects of the 1717 Christmas flood on the mainland of the Province of Groningen.Based on the numerical simulation approach and the comparison with field data and field observations, a maximum seaward water level of 5 m NAP for the dyke failure at Wierhuizen during the Christmas flood can be derived. A similar maximum water level is indicated for the two other fieldwork sites Vierhuizen and Kohol, which is in good agreement with the maximum storm surge level of 4.62 m NAP historically documented for the city of Emden located almost 50 km to the east of Wierhuizen.The results of the current study demonstrate that the reconstruction of historical dyke failures based on (i) historical sources, (ii) recent lidar/high-resolution topographical data, (iii) multi-proxy sedimentary field data and (iv) hydro- and morphodynamic numerical simulations is a highly promising approach to derive hydrodynamic conditions and the morphological onshore response of the 1717 Christmas flood in the Province of Groningen. This knowledge is essential to improve our understanding of extreme storm surge dynamics, their influence on the coastal landscape and the associated hazards for the coastal population.

LARGE-SCALE CARTOGRAPHIC REPRESENTATION OF RELIEF FEATURES FROM SANDYZATION PROCESS

Abstract: In topographic maps, contour lines and elevation points usually represent the variation of height and slope. Contour lines interval defines the level of detail for relief representation. Geomorphological features we can identify on maps are related to contour lines generalization. In this study, we aim to define the necessary level of detail for the cartographic representation of relief features from the sandyzation process. The methodology comprises: defining the relief features associated with sandyzation at the study area by literature review; describing the aspects of data survey using Remotely Piloted Aircraft (RPA) to generate the orthophoto mosaic and the Digital Surface Model (DSM); and using the DSM to extract contour lines at different scales. We defined eight relief features (denudational landform, rill, ravine, micro-residual hill, dune, depositional fan, concentrated flow, and gully) for contour cartographic representation at 1:5,000, 1:1,000, 1:500, 1:200, and 1:100 scales. The results show the scales in which the relief features have their geomorphological characteristics better represented by contours lines. Since there is no reference for suitable scales for the cartographic representation of landforms related to the sandyzation process, this study can contribute to geomorphological researches in areas where this process occurs.

The age of deposition of accumulative fan sediments in Serteyka River Valley (Western Russia)

In the region of the Serteyka River, an extensive accumulative fan was studied. The main goal of the research is an attempt to reconstruct the palaeogeographic development of erosive cuts in Western Russia. The geological structure of the fan and its surroundings was recognized. The fan is built by deluvium sediments, which can be divided into: lower diluvium unit, middle diluvium unit and upper diluvium unit. The top of the fan is built by tillage diamicton. The fan was formed at the earliest from the 2nd half of the 17th century (during the Little Ice Age pessimum). Samples were taken for AMS, OSL, Pb210 dating to determine the phases of fans development. The AMS dating produced mixed results. This was due to the redeposition of the material. Using the OSL method, two samples were dated from the bottom of the clastic fan deposits. Dates from the Neolithic period were obtained, additionally in inversion. It was caused by inaccurate bleaching of the quartz grains. The top part of the fan was dated using the Pb210 method. Slope sediments can be extremely difficult to dating. This may be due to the redeposition of the material, the presence of hiatuses and inaccurate bleaching of samples. The individual units of deluvium sediments differ in colour, structural and textural features.

Identification and Interpretation of fan deposits in Block H12 of Beixi subsag, Beier depression, Hailar basin

Fan deposits in the Nantun formation in Beier depression have been drilled in the past two decades. It’s difficult to identify and describe subtle traps formed by fans by seismic interpretation. By using a combination of seismic interpretation techniques on the workstation, most of these traps can be identified. By high resolution seismic synthesis records, it is clear to know that the location of the fan body on the seismic profile, and its property. Because of multi-layered and uneven thickness, it is impossible to delineate fan delta features in Nantun formation by one single seismic attribute, Multi-attribute analysis can extend resolution of the seismic data, improve visualization of layer internal composition, see your sand bodies delineation more clearly. Seismic inversion using high resolution log curves and borehole data as a guide can get reservoir thickness. 3d visualization of automatic tracking results makes the reservoir more intuitive. Based on the stratum seismic interpretation, using seismic attribute analysis can depict the shape of the fan, using wave impedance inversion can predict the thickness of the fan, and using automatic tracking technology can display the whole fan.

Holocene erosion and deposition within a small catchment of the northeastern Borisoglebsk Upland (Central European Russia)

During the Holocene, interfluvial landscapes of European plains have experienced alternating periods of relative stability and significant shifts in climate, soil and geomorphological development. Assumed to be an arena of major transformation their evolutionary model is not entirely resolved yet. Based on lithostratigraphic, geomorphologic and soil survey, new results on the Holocene dynamics of fluvial and related processes including landscape stabilization phases for one of the gully catchments draining the Borisoglebsk Upland northeastern slope towards the Nero Lake are presented. Common absence of the early Holocene deposits can be explained by generally negative sediment budget of the catchment. Nevertheless, continuous erosion was not likely whether rare climatic extremes probably were the case. A series of middle Holocene dates obtained by analyzing total organic carbon from organic-accumulative layers of buried soils, lake gyttja and peats highlights strong evidence of the synchronous phase of landscape stabilization in both upper and lower parts of the Puzhbol catchment accompanied by active infilling of small erosion cuts in its middle part. The upper part of the Puzhbol Gully fan sediment shows clear evidence of synchronous accumulation of agrogenic colluvium and gully alluvium since XIIth Century on top of the lake terrace deposits.

COMPUTER MODELING OF TERRIGENOUS SEDIMENTATION AS A NEW TOOL FOR PREDICTION OF HYDROCARBON RESERVOIR ARCHITECTURE

The subject of the article is a new approach based on the integration of seismic facies analysis with modeling of sedimentation system – submarine fan, which is a potential lithological trap. The new approach allows introducing sedimentation systems modeling into the traditional process of seismic data interpretation. The approach was tested on data of the target interval in Cherkashin formation (West Siberia, Priobskoye-Salym region, Neocomian progradation complex). The presence of submarine fans selected as test-subjects for modeling is confirmed by lithofacial analysis, distribution of effective thicknesses over the area according to drilling results, seismic facies analysis. Two criteria were used to evaluate the simulation results: compare the shape of the model with the results of seismic facies analysis and comparison of the parameters describing the geological process and selected in the modeling process with modern data on turbidite systems. Modeling of submarine fan sedimentation was carried out in the Geological Process Modeling (GPM) module of the Petrel software (Schlumberger), Seismic Facies Analysis – in tratimagic software (Emerson). The approach can be recommended for studying of deep-water Achimov deposits; predicting the development of the distal parts of the submarine fan, not evident in the seismic data and predicting the internal architecture of the potential lithological traps.

Middle to Late Pleistocene Architecture and Stratigraphy of the Lower Bengal Fan—Integrating Multichannel Seismic Data and IODP Expedition 354 Results

AbstractUtilizing a novel data set of integrated high‐resolution multichannel seismic data with IODP Expedition 354 drilling results, a Middle to Late Pleistocene stratigraphy for the lower Bengal Fan is developed. The study reveals a high lateral and temporal variability of deposition expressed by lateral shifts (often exceeding 100 km) between successive channel‐levee systems (CLSs), which occurred on average every ~15 kyr independent from sea‐level changes. The CLSs are embedded in sheeted sediments deposited out of unchannelized turbidity currents, which represent almost two thirds of the lower Bengal Fan sediments. On 100‐kyr timescales, CLSs and sheeted/unchannelized sediments build up subfans, which alternately occupied the western and the eastern Bengal Fan, while the remaining area was draped by ~10 to 20 m‐thick layers of background/hemipelagic sediments. Three subfans have been reconstructed: Subfan B (1.24–0.68 Ma) formed concurrently with the Middle Pleistocene Hemipelagic Layer, Subfan C (0.68–0.25 Ma) covered the entire study area, and Subfan D (0.25 Ma to recent) deposited concomitant with the Late Pleistocene Hemipelagic Layer. The continuous succession of subfans indicates an uninterrupted fan activity independent from sea‐level cycles at least since the Middle Pleistocene. This remarkable independent behavior in terms of sediment supply has not been observed at the Amazon Fan but is in agreement with observations from the Congo Fan. Finally, the analysis of a complete cross section through the lower Bengal Fan reveals that almost half of the sediment represents sands, indicating that the lower Bengal Fan may not generally be classified as “mud rich” (≤30% sand).

Fine description of sedimentary system in Wuerxun Sag of Hailaer Basin

Wuerxun depression is one of the depressions with great exploration potential in Hailaer Basin and has submitted large-scale reserves. At present, it has entered the stage of fine exploration, and the exploration object has changed from structural reservoir to lithologic reservoir exploration. The remaining targets are mainly concentrated in the trough and surrounding areas, with strong concealment and difficult to identify. Fine identification of sand bodies, genesis, types and distribution of sedimentary fans are one of the key factors restricting oil and gas exploration. Based on core observation and genetic mechanism, three sedimentary facies models of Braided River Delta, fan delta and sublacustrine fan are established. In this paper, the method of “sequence control, cycle correlation and hierarchical closure” is used to fine characterize the fan delta sedimentary system in this area, which lays a foundation for the study of sedimentary microfacies of subdivision layers, optimization of lithologic reservoir targets and guidance of oil and gas exploration deployment.

Evolution of landscape in a piedmont section of Eastern Himalayan foothills along India-Bhutan border: A tectono-geomorphic perspective

The present study area involves part of a deformed coalesced fan located along the Himalayan Frontal Thrust (HFT) on the east of river Tista near the India-Bhutan border. The area is marked by two spectacular E-W trending south-sloping scarps namely the Matiali (ca. 60 m) and Chalsa (ca. 90 m) Scarps and a north-sloping E-W trending Thaljhora (ca. 80 m) Scarp. Our work comprises of a comparative study of geomorphology and geologic history in the adjacent interfluves of Jaldhaka-Gathia and Neora-Murti rivers to understand the tectonic history of the area. We mapped the Jaldhaka-Gathia river interfluve at a 1:25,000 scale and report a hitherto unidentified northerly sloping small scarp of ca. 5m height named the Nagrakata Scarp. This scarp was identified using satellite images, DEMs, and total station survey. We interpret that the two north-sloping, E-W trending scarps (Thaljhora and Nagrakata Scarps) are manifestations of steep limbs of anticlines over blind south-dipping back thrusts. Together they form a wrinkle-ridge pair behind the north-dipping HFT, which is manifested by south-sloping Chalsa Scarp. We propose a plausible geomorphic model interpreting that deformation along the small fan in the Jaldhaka-Gathia interfluves is younger compared to fan deposition and deformation in the adjacent Mal-Murti interfluve. The most recent geomorphology of the Jaldhaka-Gathia interfluve is controlled by tectonism associated with the thrust below the Nagrakata Scarp where the youngest deformation episode is recorded to at around ∼6 ka and is likely related to motion on a splay off of the thrust beneath the Thaljhora Scarp.

Deep-sea fans: tapping into Earth's changing landscapes

ABSTRACTDeep-sea fan sediments carry physical and chemical signatures that reflect the conditions under which their native landscapes evolved. Fans are long-lived, strongly net-depositional heaps of terrigenous debris, in some cases directly connected to a major river catchment. Here we use recent findings from deep-sea fans around the world to reason that modern fans might be our most continuous record of Cenozoic landscape change over large geographic scales. We opt for the use of multiple signatures that indicate major shifts in composition, because this approach avoids the problems inherent to measuring sediment flux alone. We emphasize the importance of looking across grain size, in particular at the clay fraction, the fastest carrier of sedimentary signals. Highlighted cases show the range of environmental signals preserved in deep-sea fans, observed over millennial and longer time scales, and how these signals help us understand the climate–surface interactions important to the carbon cycle. Revisiting legacy core with new techniques, in addition to future drilling campaigns, can provide the observational constraints needed to fill recognized gaps in climate models and landscape–erosion projections.