Braided River Deposits Research Articles

Genesis of an unusual clastic dike in an uncommon braided river deposit

A clastic dike containing unusually large clasts occurs in the Quaternary deposits that unconformably cover the Mesoproterozoic sediments in the Fangshan District, Beijing area, China. The material into which the dike intruded is also uncommon because it consists mainly of loess-type silts that were deposited by braided rivers. The intrusion of the dike is explained as the result of the expulsion of pore water into the coarse, gravel-containing layers of a braided river system. The large size of the clasts in the dike is explained by an exceptionally strong upwards-directed flow which owed its high energy to a high hydrostatic pressure that had been built up because pore water could not gradually seep through the impermeable silt-sized material during ongoing burial. This uncommon dike is compared with a second example, in similar Quaternary sediments covering the Mesozoic rocks in the Huairou District.

Cenozoic evolution of the Pamir and Tien Shan mountains reflected in syntectonic deposits of the Tajik Basin

Abstract The NE Tajik Basin in Central Asia, compressed between the ranges of the Tien Shan in the north and the Pamir in the south, is a key region for understanding the evolution of these mountain systems. Erosion and deposition history of the NE Tajik Basin and the adjoining orogens since the late Oligocene is reflected in the sedimentary record. The sedimentary rocks of the NE Tajik Basin are composed of thick units of proximal braided river deposits. They reflect large fluvial plains extending from the margins of the Northern Pamir and the Southern Tien Shan mountains, but are not related to the established lithostratigraphic scheme. Almost all Oligocene–Pliocene synorogenic deposits of the NE Tajik Basin were derived from the northern Pamir ranges, except upper Miocene–Recent proximal deposits close to the active margin of the Tien Shan. Initial uplift in some areas of the SW Tien Shan since the Oligocene was followed by a phase of low-energy sedimentation and a predominance of the southern source area. Since the middle Miocene, erosion of the ranges has occurred with the proximal sedimentation of coarse fluvial deposits along the northern margin of the Tajik Basin.

Morphological perspective on the sedimentary characteristics of a coarse, braided reach: Tagliamento River (NE Italy)

In order to understand heterogeneity distribution of hydraulic properties, many studies have proposed models of coarse, braided river deposits. However, they often focus either on the surface/near surface or on ancient deposit analysis. Furthermore, the link between morphological (surface) and sedimentological (outcrops) information has not been fully explored yet. This publication aims to characterize the morphodynamics of a braided, gravel-bed reach of the Tagliamento River (NE Italy) and to assess its relationship with the subsurface heterogeneity. The morphological analysis is based on a LiDAR-derived DEM, aerial and satellite photographs from 1998 to 2011, as well as field observations. A water-stage time series allows the morphological changes to be related to the discharge dynamics. The sedimentological knowledge on coarse, braided deposits was mainly gained from the observation of analog Pleistocene coarse deposits in Switzerland. The main geomorphological elements are identified in terms of their topographic signature and genesis, setting apart the trichotomy water–vegetation–bar. The braidplain is characterized by higher-lying zones with dentritic gully drainage networks and active zones where most of the morphology reworking occurs. Furthermore, two morphologies mark the active zones: a low-discharge morphology (low-discharge incisions and channels, slip-face lobes, etc.) superimposed on a high-discharge morphology (gravel sheets, scours, etc.). Each morphological element is related to a depositional (i.e., sedimentological) element whose preservation potential in the subsurface is assessed as a function of the river-bed aggradation dynamic. The settings that impact the subsurface flow in terms of fast pathway and connectivity are addressed.

Structure and stratigraphy of the Morar Group in Knoydart, NW Highlands: implications for the history of the Moine Nappe and stratigraphic links between the Moine and Torridonian successions

Synopsis The Caledonian Orogen in northern Scotland comprises two major thrust nappes: the Moine and the Sgurr Beag Nappe. The Moine Nappe contains early Neoproterozoic Morar Group rocks (Moine Supergroup) and basement inliers. This paper describes the structure and stratigraphy of the Knoydart peninsula, a key area within the southern Moine Nappe. The geology of Knoydart is dominated by a thick internally coherent sequence of Morar Group rocks. This sequence is shown to be deformed by large-scale, west-vergent and west-facing Caledonian (early Palaeozoic) folds that represent D 2 within the southern Moine Nappe. Subsequent D 3 deformation led to refolding or tightening of F 2 folds, so that the major Morar Antiform is, in essence, a composite F 2 /F 3 fold. F 2 and F 3 folds are broadly co-axial, but F 3 folds have steeper axial planes. The F 2 /F 3 folds refold a regional-scale, originally recumbent, isoclinal F 1 fold nappe of probable Knoydartian (mid-Neoproterozoic) age. The F 1 fold nappe is cored by a thin sliver of basement gneiss; the lower limb comprises migmatitic Morar Group rocks, exposed in the Morar Window. The upper limb of the F 1 fold nappe occupies most of Knoydart and is stratigraphically coherent and right-way-up. Within this sequence, the upper unit of the Lower Morar Psammite is barely deformed, preserving trough-cross-bedding and large-scale channels in thick beds. This suggests braided river deposition, similar to the Torridon Group west of the Moine Thrust and the Morar Group in the northern part of the Moine Nappe. On the basis of lithological similarity and stratigraphic disposition, it is suggested that the lowermost part of the Morar Group in Knoydart correlates with the Neoproterozoic Sleat Group on Skye.

Aspects of floodplain deposition in semi-arid ephemeral rivers, examples from the Kuiseb river valley, central Namibia

Topographic and sediment work in the Kuiseb river, currently an ephemeral stream in central Namibia, has shown that floodplain deposition took place mainly downstream from zones of significant external sediment input. Two floodplain types are identified as floodplain islands which developed as braided river deposits in the midstream section of the river, and infill deposits developed from anastomosing streams in the downstream section. The two types are dependent on the geometry of the river cross section and the amount of sediment available. The topography, sediment content (fine sand and silt units) and structure all imply the deposition of floodplain deposits under wetter conditions. Particle size analysis of floodplain silts in relation to river bed and sand dune silt, indicates a closer association between the floodplains and Quaternary Homeb deposits. These data suggest that the floodplains likely formed under locally wet conditions which eroded the Quaternary Homeb deposits during the early-mid Holocene.

Fluvial style in the Lower Old Red Sandstone: examples from southwest Wales, UK

Studies of the behaviour of different types of present-day river channels with regard to sediment transport and depositional processes enable interpretation of fluvial deposits throughout the stratigraphic record. Early studies concentrated on the deposits of meandering and braided rivers by examining the depositional style and architecture of the sandbodies. The Lower Old Red Sandstone of southwest Wales is however a mud-dominated succession and, while there is variety in the architecture of the sandstones, up to 80% of some formations is composed of mudrocks. Detailed analysis of the Late Silurian and Early Devonian successions in southwest Wales has enabled recognition of three different styles of sandbody architecture (decimetre- to metre-thick sheets, multi-storey amalgamations and ribbon geometries), two different types of conglomerate (extraformational and intraformational), three different mudrock facies (pedogenically modified, burrowed and massive) and two types of heterolithic deposits (inclined and non-inclined). Characteristics of these units throw more light on the fluvial styles, allowing inferences that ephemeral, mud-dominated river systems were also present. Detailed study of the alluvial deposits also indicates aspects of Siluro-Devonian climate and palaeogeography.

The Andean-type Gangdese Mountains: Paleoelevation record from the Paleocene–Eocene Linzhou Basin

Paleoelevation reconstruction using oxygen isotopes is making a significant contribution to understanding the Cenozoic uplift of the Himalayas and the Tibetan Plateau. This paper presents new oxygen and carbon isotopic compositions from well dated Tertiary paleosols, lacustrine calcareous carbonates, and marls from the Nianbo (60–54 Ma) and upper Pana Formations (51–48 Ma) of the Linzizong Group in the Linzhou (Penbo) Basin. The sediments of the Nianbo Formation, which are >180 m-thick, were deposited in alluvial fans, braided rivers, fan deltas, and on nearshore to offshore lacustrine settings, whereas those of the upper Pana Formation are >100 m-thick and are comprised predominantly of proximal alluvial fan and braided river deposits. Correlations between the lithofacies and stable isotopic compositions suggest that the basin was mainly a hydrologically open environment. It is confirmed that the δ18Oc and δ13Cc values from Nianbo and Pana Formations have not yet been reset by late-stage diagenesis based on petrographic examination, oxygen isotope of the fossil ostracodes, and tectonic deformation of strata. The paleoelevations are reconstructed using the corrected most negative paleosurface water δ18Opsw values. These imply that the Linzhou area had attained an elevation of 4500±400 m during the period of the Indo-Asian collision, i.e., achieved a near-present elevation, and may form an Andean-type mountain range stretching the Gangdese arc before collision. The Gangdese Mountains probably maintained high elevations since at least the Paleocene and could play a crucial role in the climate change in the interior of the Tibetan Plateau during the Early Cenozoic. The paleogeomorphic scenario of the Eocene Tibet is proposed to exist at two high mountains in excess of 4500 m that sandwiched a low elevation basin.

Characterization of a Massive Sandstone Interval: Example from Doko Member of Bida Formation, Northern Bida Basin, Nigeria

A field mapping and laboratory study was undertaken to characterize the lower portion of Bida Formation around Jima and Doko areas near Bida, central Nigeria. Field mapping revealed four lithofacies for the sandy braided river deposits. They are: (1) lithofacies Fa consists of gravely, very coarse sandstones; (2) lithofacies Fb is characterized by gravely, medium to very coarse grained sandstones; (3) lithofacies Fc is identified by coarse silt to fine grained sandstones; (4) lithofacies Fd is recognized by sheet-like beds of fine to medium grained sandstones. They record channel flow (Fa), subaqueous dune (Fb), overbank (Fc) and crevasse splay deposits (Fd) respectively. The four lithofacies allowed the definition of two architectural elements: (1) channel architectural element (CH) and (2) overbank architectural element (OF). A CH element overlain by an OF element defines a unit bar; while stacked, multiple CH overlain by an OF delineate a compound bar. Computation of grain size data for Fa and Fb facies yielded permeability values of 19.4 to 352.3 millidarcies using empirically generated equation. Because permeability values do not vary much, it is suggested that Fa and Fb be treated as one homogeneous entity if object based reservoir modelling of the sandstones is to be done. This work shows that detailed field mapping integrated with grain size data can offer valuable information useful for aquifer and reservoir studies of the sandstones.

Classification and characterization of barrier-intercalation in sandy braided river reservoirs: Taking Hegli Oilfield of Muglad Basin in Sudan as an example

Abstract Based on comprehensive analysis of core data, well logs and outcrops, the barrier-intercalations in the sandy braided river of Hegli Oilfield, Muglad Basin, Sudan were classified and analyzed. The barrier-intercalations in single wells were identified using grey theory, which, in combination of the modern braided river deposit measurements, was used to establish the quantitative calculation formulas for different barrier-intercalations in different scale. Three hierarchies of the barrier-intercalations are developed in the sandy braided river reservoirs in the study area, including barriers between the two single layers, intercalations between the two single sandbodies and intercalations in a single braided river bar. The barriers are 700–1 500 m wide and 1 000–2 000 m long, in continuous sheet shape. The intercalations of abandoned channel are 170–350 m wide; the intercalations of chute are 60–100 m wide and 900–1 500 m long; and the intercalations of braided river bars are 100–400 m wide and 300–800 m long. Based on the constraint of barrier- intercalation scale, 3-D geological models which accurately delineate different types of barrier-intercalations were built by facies-control and stochastic modeling.

Morphological and Stratigraphical Signature of Floods In A Braided Gravel-Bed River Revealed From Flume Experiments

The alluvial deposits of braided rivers consist of channel-form bounding surfaces due to channel cutting and migration. It is unknown, however, to what extent these bounding surfaces result either from more gradual channel processes or from large but infrequent flood events. Field measurements of morphodynamically formed bounding surfaces associated with floods are not currently available. Flume experiments are useful here since concurrent observations of channel migration and the formation of bounding surfaces can be made whilst conditions are controlled. We report on two flume experiments with the objective to determine the effects of floods on i) channel cutting and migration and ii) alluvial architecture of braided gravel-bed rivers. One of the experiments has a constant bankfull discharge, and the other is run with a schematized long-duration low flow and short-duration high flow but otherwise similar conditions. High-resolution digital elevation models (DEMs) are used to monitor channel migration and to create the three-dimensional braid-belt architecture. The data demonstrate that the flood events result in longer bars and more frequent chute cutoffs. The DEMs show neither deeper channels nor bar aggradation during multiple flood events compared to a steady bankfull discharge. Consequently, the braid-belt architecture that forms during these large floods does not significantly differ from the stratigraphic architecture that forms during more frequent bankfull flows. This implies that these events cannot be differentiated based on stratigraphy. Furthermore, we find that between 10% and 40% of the mean channel depth is preserved. This can be used to characterize braid-belt architecture for purposes of reservoir engineering and provides error bounds to reconstruct paleochannel dimensions from stratigraphy.

Characteristics of the Braided River Deposits in the Tenth Member of Jurassic Yan'an Formation From Jiyuan Area in the Western Ordos Basin, China

The sandstone in Jurassic Yan'an formation of the Jiyuan area is an important oil exploration target in the Ordos Basin, medium China. The sedimentary facies of Yan'an Formation in Jiyuan Oilfield was interpreted jointly with sedimentary structure, characters of sedimentary sequence, and logging data in this study. It was considered that the sedimentary facies of the tenth member of Yan'an Formation was braided river, which mainly contained three sedimentary microfacies including braided channel, channel bar, and floodplain deposits. The distribution and model of the braided river deposits of the tenth member of Yan'an Formation was concluded.

Sedimentology and Reservoir Characteristics of He8 Member, in a Gas Field of Ordos Basin, Northern China

The rapid lateral variation of fluvial sand-bodies seriously affect the development of oil and gas field. One long-term base-level cycle (LSC), four middle-term base-level cycles (MSC) and nine short-term base level cycles (SSC) are recognized by researching the stacking patterns and volumetric partitioning according to the core, well log and seismic data in He8 member of A gas field, Ordos basin. The base level cycles which are mainly base level rise half cycles are mainly composed of braided and meandering river deposits. The evolution of depositional system has experienced three stages: braided river deposition in the earlier stage, braided and meandering river transition coexistence in the middle stage and only meandering river deposition in later period. The braided channel sand, mid-channel bar and point bar are mainly reservoirs which show belt and ribbon along the SEE trending. These sand-bodies are vertically and laterally stacked with good continuity in the early MSC1, MSC2 and MSC3, while isolated and with poor continutiy in the early MSC4. The sedimentary microfacies and diagenesis affect the fluvial reservoir quality including lateral continuity, porosity and permeability and the buried depth of the good reservoirs with development of secondary solution pores is less than 3500m in this area.

Sequence stratigraphy and sedimentary facies in the lower member of the Permian Shanxi formation, northeastern Ordos Basin, China

The Lower Permian Shanxi (山西) Formation is one of the main gas-bearing stratigraphic units in northeastern Ordos (鄂尔多斯) Basin, China. Based on an integrated investigation of well logs, cores, and outcrop, we delineated the sedimentary facies of the lower member of the Shanxi Formation and divided the succession into three third-order sequences from base to top as SQ1, SQ2, and SQ3. The lower region of Shanxi Formation was deposited in the following sedimentary facies or subfacies: subaqueous braided channel, subaqueous interdistributary, mouth bar, swamp and shelf in the Daniudi (大牛地) Gas Field and braided channel, and shelf and lake at Heidaigou (黑岱沟) outcrop. Braided-river deposits form the lowstand systems tract (LST) in each sequence. Braided channels mark the sequence boundaries at Heidaigou outcrop. A shelf and lake depositional environment with dark gray mudstone forms the transgressive systems tract (TST). The location where dark gray mudstone first appears above the braided channel marks the first flooding surface (FFS), and the end of that marks the maximum flooding surface (MFS). The highstand systems tract (HST) deposits are fine-grained sediments with an aggradational parasequence at Heidaigou outcrop and swamp coalbed in the Daniudi Gas Field. Mouth-bar sand bodies in braided delta front, which form the LST in each sequence, form excellent reservoirs in the Daniudi Gas Field.

Application of sequence stratigraphy to Triassic terrestrial strata in Tahe area of Tarim Basin

Based on a synthetic geological study of drilling, well logging and seismic data, core observations and geochemical analysis, it is recognized that Triassic sedimentary facies in the Tahe area of Tarim Basin include braided river deposits filling erosional valleys, and sublacustrine fan, canyon and delta facies. Braided river deposits filling erosional valleys are dominated by coarse-grained lithic quartz sandstone with oblique bedding, and represent the most important sedimentation type of sandstone in the study area. Sublacustrine fan and canyon facies are mainly distributed in the Middle Oil Member. Most delta sediments are deposited in highstand system tract (HST). Because of frequent changes in base level, delta sediments are commonly eroded and rarely preserved. Sedimentary cycles are clearly reflected by lithology, sedimentary structures and well logging data, and are closely related to the changes in lacustrine level. In accordance with the basic principle of sequence subdivision, seven type-I boundaries can be recognized in Triassic strata and six type-I sequences are subdivided correspondingly. In general, lowstand system tract (LST) is well developed within stratigraphic sequences and forms the main body of reservoir sandstone in this area; highstand system tract (HST) and transgressive system tract (TST) are often eroded by upper sequences or missed. Although various factors have different influences on terrestrial sequence stratigraphy, the classical sequence stratigraphy theory proposed by VAIL can be applied to terrestrial strata.

Sandstones, glaciers, burrows and transgressions: The Lower Palaeozoic of Jabel az-Zalmah, Al Kufrah Basin, Libya

Field studies in the Jabel az-Zalmah region, at the northern flank of Al Kufrah Basin provide new insights into the stratigraphy and evolving depositional environments of Cambro–Ordovician through Devonian sediments. At the base of the succession, the Hawaz Formation is about 300m thick and is characterised by frequently Skolithos-burrowed, fine to medium grained sandstones with occasional silty intervals and rare conglomerates deposited in a generally high-energy tidal shelf setting. Bioturbation is pervasive, and includes spectacular Cruziana traces produced by Early to Mid Ordovician trilobites at the bottom and the top of the Hawaz Formation respectively. These strata were incised during the late Ordovician (Hirnantian) glaciation. Ice sheets flowing over Jabel az-Zalmah cut a palaeo-topography of up to 100m relief. This relief is overlain by a coarsening upward succession of clastic sedimentary rocks, recording re-advance of an ice sheet, which overrode the uppermost sandstones. Ice sheet retreat was accompanied by marine transgression and erosion, which left a thin transgressive lag-conglomerate, capped sharply by siltstones of the Tannezuft Formation. Progradation resumed after post-glacial maximum flooding, depositing tide, storm, and river-influenced parasequences of a major delta complex (200m thick Acacus Formation). Fluvial incision, and the development of a disconformity, preceded the deposition of the Tadrart Formation (50m thick), a succession of trough-cross bedded braided river deposits. Transgression, and the re-establishment of shallow or marginal marine systems, is represented by the extensively bioturbated Binem Formation in which Zoophycos burrows offer a tentative Middle Devonian stratigraphic fix. An understanding of the lithological character of the Lower Palaeozoic strata in Jabel az-Zalmah, together with the character of unconformities that punctuate the succession, will be vital for successful hydrocarbon exploration in this frontier basin which has, until now, been unsuccessful.

Stratigraphic architecture and sedimentology of a Late Pleistocene subaqueous moraine complex, southwest Ireland

AbstractGlacigenic sediments exposed in coastal cliffs cut through undulatory terrain fronting the Last Glacial Maximum laterofrontal moraine at Waterville on the Iveragh Peninsula, southwest Ireland, comprise three lithofacies. Lithofacies 1 and 2 consist of interdigitated, offlapping and superimposed ice‐proximal subaqueous outwash and stacked sequences of cohesionless and cohesive subaqueous debris flows, winnowed lag gravels and coarse‐grained suspension deposits. These are indicative of sedimentation in and around small grounding line fans that prograded from an oscillating glacier margin into a proglacial, interlobate lake. Lithofacies 3 comprises braided river deposits that have undergone significant syn‐sedimentary soft‐sediment deformation. Deposition was likely related to proglacial outwash activity and records the reduction of accommodation space for subaqueous sedimentation, either through the lowering of proglacial water levels or due to basin infilling. The stratigraphic architecture and sedimentology of the moraine at Waterville highlight the role of ice‐marginal depositional processes in the construction of morphostratigraphically significant ‘end moraine’ complexes in Great Britain and Ireland. Traditional ‘tills’ in these moraines are often crudely stratified diamictons and gravelly clinoforms deposited in ice‐proximal subaqueous and subaerial fans. Copyright © 2011 John Wiley & Sons, Ltd.

Three-dimensional high resolution fluvio-glacial aquifer analog: Part 1: Field study

Summary Describing the complex structures that exist in many sedimentary aquifers is crucial for reliable groundwater flow and transport simulation. However, hardly any aquifer can be inspected in such detail that all decimeter to meter heterogeneity is resolved. Aquifer analogs serve as surrogates to construct models of equivalent heterogeneity, and thus imitate those features relevant for flow or transport processes. Gravel pits found in excavation show excellent sections of the sedimentary sequence and thus offer direct insight into the structural and textural composition of the subsoil. This paper describes an approach to also inspect the third dimension: by mapping during the ongoing excavation it is possible to obtain a three-dimensional representation of the subsurface within a short period of time. A detailed description of a case study is presented and the findings from sedimentological, hydrogeological and geophysical analyses are compared. The gravel pit is located near the town of Herten in southwest Germany, where relatively young unconsolidated fluvio-glacial and fluvial sediments in the Rhine basin are mined. The excavated gravel body is built up by architectural elements typical for braided river deposits. The study generated a high-resolution data set of lithofacies, hydrofacies and ground penetrating radar (GPR) profiles. It represents the basis for a full three-dimensional geostatistical reconstruction presented in the second part ( Comunian et al., 2011 ).

Geometry and grain-size characteristics of the basal surface of a braided river deposit

Research Article| March 01, 2011 Geometry and grain-size characteristics of the basal surface of a braided river deposit J. Tobias Gardner; J. Tobias Gardner Department of Geography, University of Western Ontario, London, Ontario N6A 5C2, Canada Search for other works by this author on: GSW Google Scholar Peter E. Ashmore Peter E. Ashmore Department of Geography, University of Western Ontario, London, Ontario N6A 5C2, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information J. Tobias Gardner Department of Geography, University of Western Ontario, London, Ontario N6A 5C2, Canada Peter E. Ashmore Department of Geography, University of Western Ontario, London, Ontario N6A 5C2, Canada Publisher: Geological Society of America Received: 03 Aug 2010 Revision Received: 05 Oct 2010 Accepted: 08 Oct 2010 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2011 Geological Society of America Geology (2011) 39 (3): 247–250. https://doi.org/10.1130/G31639.1 Article history Received: 03 Aug 2010 Revision Received: 05 Oct 2010 Accepted: 08 Oct 2010 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation J. Tobias Gardner, Peter E. Ashmore; Geometry and grain-size characteristics of the basal surface of a braided river deposit. Geology 2011;; 39 (3): 247–250. doi: https://doi.org/10.1130/G31639.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Description of the three-dimensional geometry and grain-size patterns of fluvial deposits and their relationship to the morphodynamics of the river has been an elusive objective in sedimentology, hindered by limited exposure and the time scale of fluvial dynamics. In small-scale physical models the time scales are short enough to map river morphology and sedimentology during significant (and continuous) morphological development of the river and its deposits, especially for braided rivers. Using close-range digital photogrammetry, the dynamics of the river morphology, and resulting deposit geometry and sedimentology, were captured using digital elevation model differencing techniques, combined with automated grain-size mapping from image texture analysis. Using these novel methods we show the temporal development and characteristics of braided river deposit geometry, and, for the first time, map the characteristics and development of the basal surface of braided river deposits in relation to river morphodynamics and formative processes. The basal surface has considerable relief, wide variation in grain size similar to that of the river as a whole, develops progressively over time by switching of channels producing adjacent patches and ribbons of basal incision of different ages, and is only partially related to bed scour associated with laterally migrating channel confluences You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Soft-sediment deformation structures in the late Miocene Şelmo Formation around Adıyaman area, Southeastern Turkey

The Şelmo Formation was deposited in the basins associated with the Southeastern Anatolian Thrust Belt and East Anatolian Fault Zone in SE Turkey. These structures developed as a result of compressional stresses created by the movement of the Arabian plate to the north and the Eurasian plate to the west from early Miocene to late Pliocene. The outcrops of the Şelmo Formation in the Adýyaman area (SE Turkey) comprise braided river deposits (lower alluvial unit) at the base, lacustrine and deltaic deposits in the middle (lacustrine unit) and low sinuousity river and alluvial deposits at the top (upper alluvial unit). Soft-sediment deformation structures were developed in sandstone, siltstone and marl of the deltaic and lacustrine unit of the Şelmo Formation. These are slumps, recumbent folds, load casts, ball-and-pillow structures, flame structures, neptunian dykes, chaotically associated structures and synsedimentary faults. The tectonic setting of the basin, the lateral extent of the soft-sediment deformation structures over tens of kilometers, their similarities to deformation structures interpreted as being induced seismically in other regions worldwide or in a laboratory setting, and being confined by undeformed layers suggest that the main trigger system was related to seismic activity in the area.

Deposition in the Kuznetsk Basin, Siberia: Insights into the Permian–Triassic transition and the Mesozoic evolution of Central Asia

This paper describes the Permian–Mesozoic stratigraphy of the Kuznetsk Basin, southern Siberia, which is adjacent to the vast and hydrocarbon-rich West Siberian Basin and on the edge of the Siberian flood basalts. The basin fill is Permian to Cretaceous in age, and is dominated by non-marine siliciclastics up to ∼ 7 km thick. Palaeocurrent indicators show dominant flow to the north/northeast during the Permian to Jurassic. Fourteen lithofacies are grouped in three facies associations: fluvial channel belt, overbank and floodplain/floodplain pond. Coal-bearing Permian siliciclastics are interpreted as meandering river deposits in a foreland basin, with subsidence generated by thrust-sheet loading from at least three basin margins. These sediments pass abruptly but conformably upwards into coal-barren sandstones and conglomerates and siltstones, interpreted as braided river deposits. Two basalt flows occur within the coal-barren succession. A recently-published, precise Ar-Ar age of 250.3 ± 0.7 Ma for the lower of these basalts, < 50 m above the sedimentary transition, suggests that the Permian–Triassic boundary occurs just above this flow. We relate the loss of coal-producing flora and the increase in mean sediment grain size to vegetation loss, in turn triggered by the eruption of the Siberian flood basalts to the north. End-Permian and Lower Triassic(?) strata are overlain by Lower Jurassic fluvial siliciclastics via a gentle angular unconformity. Conglomerates punctuate a sandstone-dominated succession that continues in to the Middle Jurassic. Both the basal unconformity and the rejuvenation in sedimentation may result from intracontinental thrusting at the basin margins and beyond; this thrusting was triggered by orogenies at the Eurasian margin. Lower and mid Cretaceous siliciclastics are poorly exposed and crop out only locally: field relations indicate an angular unconformity at their base. The end-Permian stratigraphy in the Kuznetsk Basin documents the environmental crisis at the time of the Siberian flood basalts, and reinforces the link between these eruptions and climatic and environmental deterioration. The Mesozoic sedimentary record highlights how episodic deformation influenced sediment supply to the West Siberian Basin, and is an example of the record of Eurasian assembly and deformation preserved within the continental interior.