Water discharge variations control fluvial stratigraphic architecture in the Middle Eocene Escanilla formation, Spain
Nikhil SharmaAlexander C. WhittakerStephen WatkinsLuís ValeroJean VéritéCai PuigdefàbregasThierry AdatteMiguel GarcésFrançois GuillocheauSébastien Castelltort
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Ancient fluvial deposits typically display repetitive changes in their depositional architecture such as alternating intervals of coarse-grained highly amalgamated (HA), laterally-stacked, channel bodies, and finer-grained less amalgamated (LA), vertically-stacked, channels encased in floodplain deposits. Such patterns are usually ascribed to slower, respectively higher, rates of base level rise (accommodation). However, “upstream” factors such as water discharge and sediment flux also play a potential role in determining stratigraphic architecture, yet this possibility has never been tested despite the recent advances in the field of palaeohydraulic reconstructions from fluvial accumulations. Here, we chronicle riverbed gradient evolution within three Middle Eocene (~ 40 Ma) fluvial HA-LA sequences in the Escanilla Formation in the south-Pyrenean foreland basin. This work documents, for the first time in a fossil fluvial system, how the ancient riverbed systematically evolved from lower slopes in coarser-grained HA intervals, and higher slopes in finer-grained LA intervals, suggesting that bed slope changes were determined primarily by climate-controlled water discharge variations rather than base level changes as often hypothesized. This highlights the important connection betweenclimate and landscape evolution and has fundamental implications for our ability to reconstruct ancient hydroclimates from the interpretation of fluvial sedimentary sequences.The stratigraphic distributions of Early Jurassic,Middle Jurassic and Late Jurassic in Qaidam Basin are greatly different.The deposit center had two times of great transpositions.The first transposition was from northwest to north,and the second one was from north to east.In the Early Jurassic,the paleoclimate was warm and damp,while the marshes,ravels and lakes in fault basin were distributed in the northwest.In the Middle Jurassic,the paleoclimate was warm and damp,while marshes,ravels and lakes in broad basin were distributed in the northern edge of the basin.In the Late Jurassic,the paleoclimate was dry,and mountain aprons were distributed in the east.The analyses on ages of granites in the northwestern basin and on the ancient latitudes of Qaidam plate,Tarim plate and Qiangtang plate based on paleomagnetic stratigraphy show that the origin of greatly sedimentary transpositions in Jurassic relied on the different interaction plates.
Paleoclimatology
Molasse
Mountain formation
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Evolution of the Xichang basin may be divided into 3 stages such as basement formation stage,passive continental Mar.gin stage and inland basin stage which may be subdivided into 7 sub-stages such as basement formation,passive continental Mar.gin,relic Mar.ine,foreland basin,inland basin,basin shrinkage and basin reformation.Every stage or sub-stage is characterized by its special sedimentary environment and depositional fabric controlled by tectonism and faulting.
Basement
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Summary In the scope of our project, we made an approach to link 3D seismic image and geological information from wells to reconstruct, as detailed as possible, the paleoenvironment of the studied segment of the Upper Cretaceous basin in the central part of the Carpathian Foredeep (Poland), based on the chronostratigraphic method. For depositional systems recognition, seismic attributes were incorporated. The interpretation was performed simultaneously with Wheeler diagrams analysis and interpretation of geological data from the wells. The analysis shows various paleomorphological elements within the studied segment of the Upper Cretaceous basin that affect the type and diversity of sedimentation. The significant influence of tectonic processes on the depositional history of the sedimentary basin was also evidenced. The proposed approach based on chronostratigraphic image and Wheeler diagram analysis in combination with tectonostratigraphic interpretation allowed for detailed recognition of the sedimentary paleoenvironment and reconstruction of the depositional and tectonic history of the analysed segment of the Carpathian Foreland basin. The depositional and tectonic history of the Upper Cretaceous series analysed is related both to regional processes, occurring throughout the Late Cretaceous sedimentary basin, and to local manifestations of small-scale tectonics.
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The Early Cretaceous Heishidu Formation (HsdF), distributed between the southern Xiaotian Mozitang fault (XMF) and northern Jinzhai Xianghongdian Xitanchi fault in the north margin of the Dabie Mountains, elongates in east westward, and thickness is more than 1 km. The lithofacies are mainly composed of Bcm, Gcg, Gcm, Gm, Sg, Ss, Fc, Fm, Fr, C and so on, and depositional systems include alluvial fan, fluvial, fan delta and lacustrine deposits, and fluvial deposits are mainly composed of sediments of floodplain and crevasse splays. HsdF developed the fining upward sequences, and alluvial fan in the early stage, floodplain and crevasse splay and fan delta in the middle stage, and lacustrine turbidites in the late stage. Alluvial fan and lacustrine turbidites mainly developed in Xiaotian area on the eastern part of the basin, floodplain and crevasse splay in Huoshan area on the western, and fan delta on both parts. The basin might be attributed to an asymmetric down faulted lake, and its evolution might be controlled by XMF.
Alluvial fan
Crevasse
Conglomerate
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The modern structural, drainage, and depositional systems of the Lake Hazar Basin in southeastern Turkey exhibit an "instantaneous" picture of faulting and sedimentation within an actively evolving pull-apart basin. A general sedimentation model is proposed which consists of two types of drainage and depositional systems. Streams entering the basin laterally cross numerous oblique-slip faults and are short, steep, associated with small drainage basins, and characterized by profiles with many knickpoints. They build alluvial fan deltas which are small, steep, and composed of coarse-grained debris flow and fluvial deposits. Fluvial deposits consist of braided channel and bar, sheetflood, and overbank facies. Streams entering the basin longitudinally flow along the surface trace of single faults and are long, gently-sloping, associated with large drainage basins, and characterized by smooth profiles. They build large, gently-sloping, alluvial fan deltas composed of fluvial and lacustrine deposits. Lacustrine deposits include shoreline, nearshore, and offshore facies. The relative relief of both systems is similar. The primary difference is gradient, which is controlled by position relative to the faults. This model is comparable with those proposed to account for sedimentation in ancient strike-slip basin deposits.
Overbank
Alluvial fan
Debris flow
Sinuosity
Sedimentation
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Abstract Sedimentological outcrop analysis and sub‐surface ground‐penetrating radar (GPR) surveys are combined to characterize the three‐dimensional sedimentary architecture of Quaternary coarse‐grained fluvial deposits in the Neckar Valley (SW Germany). Two units characterized by different architectural styles are distinguished within the upper part of the gravel body, separated by an erosional unconformity: (i) a lower unit dominated by trough‐shaped depositional elements with erosional, concave‐up bounding surfaces that are filled by cross‐bedded sets of mainly openwork and filled framework gravel; and (ii) an upper unit characterized by gently inclined sheets of massive and openwork gravels with thin, sandy interlayers that show lateral accretion on a lower erosional unconformity. The former is interpreted as confluence scour pool elements formed in a multi‐channel, possibly braided river system, the latter as extensive point bar deposits formed by the lateral migration of a meandering river channel. The lateral accretion elements are locally cut by chute channels mainly filled by gravels rich in fines, and by fine‐grained abandoned channel fills. The lateral accretion elements are associated with gravel dune deposits characterized by steeply inclined cross‐beds of alternating open and filled framework gravel. Floodplain fines with a cutbank and point bar morphology cover the gravel deposits. The GPR images, revealing the three‐dimensional geometries of the depositional elements and their stacking patterns, confirm a change in sedimentary style between the two stratigraphic units. The change occurred at the onset of the Holocene, as indicated by 14 C‐dating of wood fragments, and is related to a re‐organization of the fluvial system that probably was driven by climatic changes. The integration of sedimentological and GPR results highlights the heterogeneity of the fluvial deposits, a factor that is important for modelling groundwater flow in valley‐fill aquifers.
Point bar
Outcrop
Bedrock
Lithology
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Mineral resource classification
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The Chepaizi-Mosuowan paleo-uplift is a large-scale uplift stretching across the Junggar Basin formed during the Yanshanian. It has experienced four evolutionary stages: the initial forming stage (J1), the intense development stage (J2+3), the waning and burial stage (K-E), and the tilting and extinction stage (N-Q). The most intense period of activities is the Middle Jurassic. Dur-ing the Early Jurassic, the Chepaizi-Mosuowan paleo-structure was a low amplitude uplift. Because of the subsequent strong uplifting during Middle-Late Jurassic, the Middle and Upper Jurassic were eroded. With the evolution of the Chepaizi-Mosuowan paleo-uplift, the sedimentary pattern of the basin changed, and the paleo-uplift separated the northern depositional systems from those in the south side. As a result, the basin tectonics controlled the distribution and evolution of the depositional systems. During Early Jurassic, while the paleo-uplift was low, its controlling effect on depositional systems was limited and sediments coming from the northwest could reach the central and southern parts of the basin. With the strong uplifting of the Chepaizi-Mosuowan paleo-structure during Middle-Late Jurassic, sediments from the northwest provenance could only deposit in the northern graben of the paleo-uplift. The intense erosion of the Middle-Upper Jurassic also changed the former sedimentary center of the basin into a source area, supplying sediments for grabens on both sides of the paleo-uplift. In the Cretaceous, regional subsidence caused the paleo-uplift to be buried again and subsequently sediments accumulated on top of it. The depositional facies are dominated by fluvial in the Early Cretaceous and shallow lacustrine to deltaic in the Late Cretaceous. In the history of the long-lasting development of this paleo-uplift, large-scale erosions of the paleohigh not only provided sufficient sediments to the center of the Junggar Basin, but also created favorable conditions for the formation of various subtle traps such as lithologic and stratigraphic traps.
Tectonic uplift
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The influence of palaeodrainage characteristics, palaeogeography and tectonic setting are rarely considered as controls on stratigraphic organization in palaeovalley or incised valley systems. This study is an examination of the influence of source region vs. downstream base level controls on the sedimentary architecture of a set of bedrock‐confined palaeovalleys developed along the distal margin of the Alpine foreland basin in south‐eastern France. Three distinct facies associations are observed within the palaeovalley fills. Fluvial facies association A is mainly dominated by poorly sorted, highly disorganized, clast‐to‐matrix‐supported cobble‐to‐boulder conglomerates that are interpreted as streamflood deposits. Facies association B comprises mainly yellow siltstones and is interpreted as recording deposition in an estuarine basin environment. Estuarine marine facies association C comprises interstratified estuarine siltstones and clean, well‐sorted washover sandstones. The sedimentary characteristics of the valley fill successions are related to the proximity of depositional sites to sediment source areas. Palaeovalleys located proximal to structurally controlled basement palaeohighs are entirely dominated by coarse fluvial streamflood deposits. In contrast, distal palaeovalley segments, which are located several kilometres downstream, contain successions showing upward transition from coarse fluvial facies into estuarine central basin fines, and finally into estuarine‐marginal marine facies. Facies distributions suggest that the fluvial deposits form wedge‐shaped, downstream‐thinning sediment bodies, whereas the estuarine deposits form an upstream‐thinning wedge. The vertical stacking of fluvial to estuarine to marginal marine depositional environments records the fluvial aggradation and subsequent transgression of relatively small bedrock‐confined river valleys, which drained a rugged, upland terrain. Facies geometries suggest that a fluvial sediment wedge initially prograded downvalley, in response to high bed load sediment yields. Subsequently, palaeovalleys became drowned during the passage of a marine transgression, with the establishment of estuarine conditions. Initial fluvial aggradation and subsequent marine flooding of the palaeovalleys is a consequence of the interaction of high local rates of sediment supply and relative sea‐level rise driven by flexural subsidence of the basin.
Bedrock
Aggradation
Marine transgression
Alluvial fan
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