Terminal Distributary Channels Research Articles

Geomorphology of the NE Sicily continental shelf controlled by tidal currents, canyon head incision and river-derived sediments

The NE Sicily continental shelf, imaged by multibeam bathymetry data and CHIRP/sparker seismic profiles, is less than 5km-wide, and is located in a tectonically active margin characterized by strong regional uplift rates. In this paper, we show how variations of geomorphic elements in the study area are tied to spatial and temporal changes in the driving forces that control the seafloor processes. This study demonstrates that the geomorphology of continental shelves can vary over very short spatial scales depending on the uneven distribution of sediment supply from rivers and sediment transfer both across and along the shelf by oceanographic currents. In the northeastern part, three sandwave fields were mapped in the highstand sediment wedge that, due to the small size of rivers, is restricted to the inner shelf. The sandwave fields are found in proximity of the Messina Straits, a shallow water sill with strong tidal currents between the Tyrrhenian and the Ionian Seas. The bedform fields have sandwaves of variable shape, wavelength and orientation, reflecting along-shelf variations of tidal current strength and sediment grain size distribution. In the southwestern shelf, rivers are larger and form deltas that shape a considerable part of the shelf, often having their distal, still channelized delta front at the shelf edge. In some cases, deltas are built close to the heads of canyons and a large volume of the river-borne sediments is directly fed to the deep sea through delta front terminal distributary channels. Where rivers are small, the outer shelf lacks recent river borne sediment and presents a relict morphology consisting of submerged coastal systems formed during previous sea-level lowstands. The tectonics of the study area mainly consist of structures that have a NNE–SSW trend similar to the extensional faults responsible for the Siculo-Calabrian Rift Zone in the nearby emerged areas. Our study extends the area affected by the regional deformation belt into the NE Sicily offshore.

Facies architecture of asymmetrical branching distributary channels: Cretaceous Ferron Sandstone, Utah, USA

AbstractDistributary channel systems are an important component of deltaic systems, but details of their branching pattern, stream‐order, internal variability and relation with adjacent levée, bay and bayhead delta are rather poorly documented in ancient examples. Photomosaic and measured sections collected along a gooseneck‐shaped canyon in southern Utah allow direct mapping of the branching pattern of an ancient distributary system. The main channel belt is ca 250 m wide and narrows to ca 200 m downstream of the branching point. A subordinate channel belt, ca 80 m wide, branches off of the main channel, forming a distinctly asymmetrical branching pattern. Water discharge in the main channel is estimated to be 85 to 170 m3 sec−1. Comparison with palaeodischarge estimates of trunk rivers mapped in previous studies suggests that the branching documented in this study probably is a fourth‐order split. The distributary channels are characterized by a U‐shaped geometry filled with medium‐grained, cross‐bedded sandstone, and are dominated by lateral accretion, suggesting limited lateral migration and moderate sinuosity. Tidally influenced facies and limited trace fossils indicate direct marine influence. The distributary channels erode into adjacent levée and underlying heterolithic bay‐fill deposits, and the marine influence suggests that they were deposited on a lower delta plain, rather than on a non‐marine floodplain. The subordinate channel fed a bayhead delta, suggesting that it was formed by a partial avulsion, rather than bifurcation around a mouth bar, as is more characteristic of terminal distributary channels. Channel‐floor drapes, bar‐accretion drapes and abandoned channel fills within the sandstone channel belts represent the most important heterogeneity from the perspective of reservoir characterization.

Facies Architecture and Stratigraphic Evolution of A River-Dominated Delta Front, Turonian Ferron Sandstone, Utah, U.S.A

Abstract Facies architectural analysis of a river-dominated deltaic parasequence in the Turonian Ferron Sandstone Member, near Factory Butte, Utah, was conducted to determine the hierarchical spatial arrangement of mouth bars and their role in constructing the delta. Five architectural elements were identified using 21 measured sections, paleocurrent measurements, and bedding diagrams. They are: (1) prodelta (PF), (2) frontal splay (FS), (3) detached distal bars (DBs), (4) distributary mouth bars (DMBs), and (5) terminal distributary channels (TDCs). Lower in the parasequence, detached bars consist of proximally located cross-bedded and quasi-parallel laminated subaqueous bars that onlap the delta-front slope and grade distally into finer-grained distal delta front splays. These bars translate downstream in a progradational–aggradational–degradational trajectory and are overlapped by adjacent bars, forming a bar assemblage. These bars are interpreted to have been deposited by descending hyperpycnal flows as a decelerating axial jet. Deposition of these bars occurs at the delta-front to prodelta chokepoint, presumably due to flow deceleration. The distal bar assemblage is capped by an extensive but discontinuous shale drape, suggesting local abandonment. Upper facies assemblages show a distinct switch to predominantly cross-bedded distributary mouth bars, corresponding to a decrease in water depth, an increase in friction, and a likely transition into planar versus axial jets. This is indicated by aggrading cross-bedded distributary mouth bars that overlie the distal bars. Laterally, the mouth-bar deposits are interstratified with terminal distributary-channel deposits with prominent scour surfaces at the base. Separate distributary channels and their bars coalesce, ultimately to build the entire delta lobe. The detached distal bars prograde locally west to northwest and lack fair-weather wave-formed sedimentary structures, suggesting a local embayment along the regionally northeast prograding shoreline. Low levels of ichnofaunal diversity indicate a stressed, river-dominated setting. At the base of the section, frontal splays and detached bars, dominated by storm-driven river-flood deposits, are deposited over muddy prodelta facies. Detached bars are likely initiated about 500 meters distal of the distributary channel, in water depths of ∼ 10–30 meters, based on the thickness of the parasequence. Once this subaqueous platform is constructed by the distal bar assemblage, more proximal distributary mouth bars fill the remaining shallow-water accommodation. As the system continues to shallow, distributary channels override and scour the bars, reflecting reduced accommodation.

Channelized sandstone bodies (‘cordons’) in the Tassili N'Ajjer (Algeria & Libya): snapshots of a Late Ordovician proglacial outwash plain

Abstract The architecture, distribution and development of channelized sandstone bodies are described from Late Ordovician paraglacial successions of the Tassili N'Ajjer (SE Algeria and SW Libya) based on satellite images and field data (sedimentary logs, photomosaics). Sandstone bodies have a ribbon-like form at outcrop (often referred to as ‘cordons’ in the literature). They typify a fluvioglacial outwash plain deposited between a continental ice front and a marine delta-front zone. Channelized sandstone bodies are straight to sinuous, with widths ( W ) in the 60–600 m range, thicknesses ( T ) in the 5–30 m range and they have a mean W / T ratio of 16.5. They develop within an aggradational–progradational sand-dominated deltaic topset succession including at its distal end a terminal distributary channel and mouth-bar environments. The architecture of channel bodies and the related depositional facies, which includes climbing-dune cross-stratification, indicates that channelized sandstone bodies represent plugs of isolated channels related to high-magnitude flood events (glacier outbursts). These plugs form fossilized networks of both braided channels and interlaced anastomosed channels, offering snapshots of an outburst-related unconfined proglacial outwash braidplain constituted by the amalgamation of adjacent, elongated outwash fans.

Pleistocene shelf-margin delta: Intradeltaic deformation and sediment bypass, northern Gulf of Mexico

Recent studies of shelf-margin deltas in the Gulf of Mexico lack three-dimensional (3-D) seismic interpretation that allows prediction of lithology distribution, deformation features, and overall reservoir heterogeneity, and only a few 3-D studies of shelf-margin deltas in other parts of the world exist. This paper examines the 3-D geomorphology and internal facies architecture within a sequence-stratigraphic framework of a shelf-margin delta in a salt dome minibasin, within the Gulf of Mexico, offshore Louisiana, using 3-D seismic data. The 3-D data also allow an evaluation of the potential pathways for sediment bypass from delta front to slope and deep-water depositional environments. The delta consists of a series of offlapping sandy clinoforms, interpreted as being associated with a prolonged forced regression and ensuing lowstand of eustatic sea level, related to oxygen isotope stage 6, which lasted for about 45 k.y. The lowstand delta is onlapped by a transgressive mud wedge and is underlain and capped by regionally persistent highstand mudstones. The central part of the delta shows intradeltaic syndepositional growth faults, likely triggered by deposition of heavy delta-front sands over mobile prodeltaic muds, reflecting the river-dominated nature of the delta. A postdepositional shallow-water mass transport complex (MTC), which moved almost perpendicular to the direction of the regional delta progradation, remobilizes the deltaic deposits. The MTC was likely induced by uplift of the adjacent western salt dome. We hypothesize that the high degree of syndepositional and postdepositional deformation is related to the prolonged nature of the eustatic lowstand, as well as the salt tectonics. Tributive submarine slope channels form downdip of the delta front and may also reflect incision during the prolonged eustatic lowstand. The salt tectonics caused focusing of the dispersed delta-front sediments, mostly originating from terminal distributary channels, into the convergent tributive slope-channel system. Although this is an unstable supply-dominated shelf-margin delta, the salt tectonics likely prevented the delta from avulsing once it reached the shelf edge and also caused the focusing of dispersed sediment effectively into a point source for delivery to deep-water systems. This contrasts with less confined high-sediment supply delta systems farther along the coast, which lack linked submarine deposits because they reach the shelf margin before maximum eustatic lowstand and avulse before building significant deep-water systems.

Interplay between river discharge and topography of the basin floor in a hyperpycnal lacustrine delta

AbstractBasin‐floor topography influences the flow path of hyperpycnal plumes and delta morphology during progradation of the Red River delta in Lake Texoma, USA. The Red River discharge is typically a hyperpycnal plume due to elevated total dissolved solids. Because the river plume is a bottom‐hugging hyperpycnal flow, lake bathymetry and topography strongly influence deposition and subsequent delta morphology. In addition to elevated total dissolved solid concentrations compared with Lake Texoma water, the density contrast of the Red River outflow is increased by high suspended‐sediment concentrations during high‐discharge events. Steep lateral slopes in the Lake Texoma basin deflect hyperpycnal river plumes and, subsequently, change the delta progradation direction before the delta reaches the opposite bank of the lake. Analysis of multi‐temporal aerial and satellite images indicates that the hyperpycnal delta follows the steepest lake‐bottom gradients, corresponding to the pre‐impoundment river thalweg (i.e. bypassing shallow parts of the lake). An analytical model for the hyperpycnal‐plume trajectory indicates plume deflection during low‐discharge or high‐discharge events, towards the deepest part of the basin. The magnitude of plume deflection is a function of river discharge and basin‐margin gradients. Plume deflection can vary between 10° and 80° from the channel axis towards the old river thalweg. The high deflection appears in the case of maximum basin side gradients of 12·8° and in conditions of low river discharge. During low‐discharge periods, the Red River delta builds a lobate shape with multiple terminal distributary channels whereas, during high‐discharge periods the Red River delta builds an elongate shape with a single large distributary channel. The elongate morphology of the delta is formed through the development of a single distributary channel and abandonment of the other distributaries. Therefore, the lobate shaped delta is expected to be preserved in the rock record.

Delta-front hyperpycnal bed geometry and implications for reservoir modeling: Cretaceous Panther Tongue delta, Book Cliffs, Utah

The Cretaceous Panther Tongue has an upward-coarsening and -thickening pattern and is well exposed in extensive large outcrops in the Book Cliffs area, west-central Utah. The deposits have been interpreted as having formed in a fluvial-dominated river delta environment that generated highly sediment-concentrated sustained (turbidity) flows during flooding, producing hyperpycnal-flow deposits on the delta front despite some resemblance to deep-water turbidites. The facies associations indicate terminal distributary channel, channel mouth, and proximal delta-front and distal delta-front depositional environments. The measured paleocurrents indicate a south-southwest transport of the sediments. The thickness of the hyperpycnal sandstone beds ranges from centimeters to meters. Sandstones are characteristically parallel laminated, sometimes structureless or rarely display inclined strata of cut-and-fill type. The sandstone hyperpycnal beds dominate the delta-front clinoforms and dip southward, consistent with the other paleocurrent indicators. Individual sandstone beds in the clinoforms have dips that range from 0.1 on the distal delta front (lower part of the outcrops) to 3 in the proximal parts (upper part of the outcrops). The hyperpycnal beds can be traced from a proximal mouth-bar environment to the distal delta front over a distance of hundreds of meters. As individual beds extend from mouth bar to distal delta-front environments, they become systematically finer grained and thinner. Over short distances (hundreds of meters), the beds thin with rates ranging between 0.0001 (i.e., dm/km) to 0.02 (i.e., tens of meters per kilometer). The sandstone beds thin to a greater degree in a dip direction than along strike, indicating a relatively strike-elongate (flow-normal) geometry of the hyperpycnal flows and of the delta lobes. The wider than longer geometry of the delta-front beds requires that reservoir development be more focused upon the downdip facies changes (heterogeneities) than the lateral (along strike) heterogeneities.

Recognition and significance of sharp-based mouth-bar deposits in the Eocene Green River Formation, Uinta Basin, Utah

Sandstone bodies in the Sunnyside Delta Interval of the Eocene Green River Formation, Uinta Basin, previously considered as point bars formed in meandering rivers and other types of fluvial bars, are herein interpreted as delta mouth-bar deposits. The sandstone bodies have been examined in a 2300 m long cliff section along the Argyle and Nine Mile Canyons at the southern margin of the Uinta lake basin. The sandstone bodies occur in three stratigraphic intervals, separated by lacustrine mudstone and limestone. Together these stratigraphic intervals form a regressive-transgressive sequence. Individual sandstone bodies are texturally sharp-based towards mudstone substratum. In proximal parts, the mouth-bar deposits only contain sandstone, whereas in frontal and lateral positions mudstone drapes separate mouth-bar clinothems. The clinothems pass gradually into greenish-grey lacustrine mudstone at their toes. Horizontally bedded or laminated lacustrine mudstone onlaps the convex-upward sandstone bars. The mouth-bar deposits are connected to terminal distributary channel deposits. Together, these mouth-bar/channel sandstone bodies accumulated from unidirectional jet flow during three stages of delta advance, separated by lacustrine flooding intervals. Key criteria to distinguish the mouth-bar deposits from fluvial point bar deposits are: (i) geometry; (ii) bounding contacts; (iii) internal structure; (iv) palaeocurrent orientations; and (v) the genetic association of the deposits with lacustrine mudstone and limestone.

Tide- and wave-generated fluid mud deposits in the Tilje Formation (Jurassic), offshore Norway

Research Article| June 01, 2009 Tide- and wave-generated fluid mud deposits in the Tilje Formation (Jurassic), offshore Norway Aitor A. Ichaso; Aitor A. Ichaso 1Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, Ontario K7L 3N6, Canada Search for other works by this author on: GSW Google Scholar Robert W. Dalrymple Robert W. Dalrymple 1Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, Ontario K7L 3N6, Canada Search for other works by this author on: GSW Google Scholar Geology (2009) 37 (6): 539–542. https://doi.org/10.1130/G25481A.1 Article history received: 28 Aug 2008 rev-recd: 16 Jan 2009 accepted: 22 Jan 2009 first online: 02 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 Aitor A. Ichaso, Robert W. Dalrymple; Tide- and wave-generated fluid mud deposits in the Tilje Formation (Jurassic), offshore Norway. Geology 2009;; 37 (6): 539–542. doi: https://doi.org/10.1130/G25481A.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 The Tilje Formation (Early Jurassic; 120–300 m thick) consists predominantly of heterolithic deposits and is thought to have accumulated in tide-dominated estuarine and deltaic environments in an active rift setting. Anomalously thick (>0.5 cm) and internally structureless mudstone layers, which are interpreted to represent fluid-mud deposits, are widespread and occur in three different environmental settings: (1) in the basal part of upward-fining tidalfluvial channels where they generate upward-sanding successions: (2) in the deposits of mouth bars and terminal distributary channels where they are associated with the coarsest sands and the least-bioturbated sediments, suggesting deposition during tidally modulated river floods; and (3) in delta-front successions where they immediately overlie thick, wave-generated storm beds, suggesting that these fluid-mud deposits result from wave resuspension of previously deposited mud. These observations provide criteria for the recognition of ancient fluid-muds and for interpreting their origin. The tectonic setting may be responsible for their abundance. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Terminal Distributary Channels and Delta Front Architecture of River-Dominated Delta Systems

Abstract Using modern and ancient examples we show that river-dominated deltas formed in shallow basins have multiple coeval terminal distributary channels at different scales. Sediment dispersion through multiple terminal distributary channels results in an overall lobate shape of the river-dominated delta that is opposite to the digitate Mississippi type, but similar with deltas described as wave-dominated. The examples of deltas that we present show typical coarsening-upward delta-front facies successions but do not contain deep distributary channels, as have been routinely interpreted in many ancient deltas. We show that shallow-water river-dominated delta-front deposits are typically capped by small terminal distributary channels, the cross-sectional area of which represents a small fraction of the main fluvial trunk channel. Recognizing terminal distributary channels is critical in interpretation of river-dominated deltas. Terminal distributary channels are the most distal channelized features and can be both subaerial and subaqueous. Their dimensions vary between tens of meters to kilometers in width, with common values of 100–400 m and depths of 1–3 m, and are rarely incised. The orientation of the terminal distributary channels for the same system has a large variation, with values between 123° (Volga Delta) and 248° (Lena Delta). Terminal distributary channels are intimately associated with mouth-bar deposits and are infilled by aggradation and lateral or upstream migration of the mouth bars. Deposits of terminal distributary channels have characteristic sedimentary structures of unidirectional effluent flow but also show evidence of reworking by waves and tides.

ABSTRACT: Terminal Distributary Channels, Cretaceous Panther Tongue Sandstone, Utah

ABSTRACT: Terminal Distributary Channels, Cretaceous Panther Tongue Sandstone, Utah