Variations In Sediment Supply Research Articles

Hierarchical stratigraphic cycles in the non-marine Clair Group (Devonian) UKCS

Abstract The Devonian lower Clair Group ( c. 300–800 m thick) is dominantly composed of fluviatile sandstones and conglomerates, aeolian sandstones and minor floodplain and lacustrine shales. These facies are organized into stratigraphical cycles which have a three-fold hierarchy: an unconformity bounded cycle representing first order retreat and advance of the fluvial drainage system; three subsidiary second order cycles bounded by minor unconformities, and numerous third order cycles. These stratigraphical cycles exhibit common characteristics: they are bounded by sharp, commonly erosive surfaces; they are composed of a fining-upwards succession overlain by a variably developed coarsening-upward element; the fining-upward element records a progressive decrease in the fluvial component, and increasing proportion of aeolian, floodplain or lacustrine facies (this trend is reversed in the upper, coarsening-upward section). The grain size of the fluvial facies, and nature of the non-fluvial facies (aeolian vs floodplain/lacustrine) within any order of cycle is dependent on it’s position within a lower order (larger scale) cycle. The cycles are areally extensive, and are present in all wells within the Clair Basin, although spatial changes in internal facies make-up occur. The second order cycles show progressive onlap followed by offlap of the basin margin. These hierarchical cycles are interpreted to be the product of changes in the accommodation:supply ratio of the depositional system. An increasing accommodation:supply ratio provided space to preserve the record of waning fluvial influence, enhanced aeolian reworking, preserved floodplain fines or lacustrine mudrocks. In contrast, a reducing accommodation:supply ratio resulted in filling of accommodation space and sediment bypassing. Accommodation space variations were dictated by tectonic variations in strain rate, which caused incremental uplift of the basin margin and subsidence of the basin. Sediment supply changes were influenced by source area uplift, which changed sediment yield, and climate change which affected runoff. Climatic changes are detectable within the non-fluvial elements of the Clair Group by stratigraphic variations between aeolian, floodplain and lacustrine facies. These vary systematically within and between second order unconformity bounded units, suggesting a tectonic influence on climate. Within the second and third order cycles, those which were evolving towards, or were occurring within, semi-arid to arid climatic conditions are commonly (but not exclusively) biased towards fining-upward successions, whilst the more humid systems show a better developed coarsening-upward element. This may be the result of the changing impact of discharge versus sediment supply variations when one of these parameters became suppressed or enhanced under varying climatic conditions.

Variability of the modern sand cover on a tide and storm driven inner shelf, south Wellington, New Zealand

Abstract The embayed coast, south of Wellington, is notorious for the severity of its storms and tides. Time‐series side‐scan sonar and sediment surveys, made of the bays and inner shelf over an 11–16 year period, show that the general locations of four main seabed types—(1) a modern, fine‐medium sand cover, (2) a generally megarippled, coarse sand ‐ fine gravel substrate, (3) a basal cobble‐boulder deposit, and (4) greywacke basement—remain fairly stable despite considerable mobility at the edges of each deposit. The sand cover is best developed (1.5 m max. thickness) in the larger bays centred on Wellington Harbour entrance. Here it has undergone bouts of accretion (indicated by advances of cover edges) that have ended in erosion (with retreat of edges). Mobility of sand is induced on a daily to annual basis by tides reinforced by southerly swell and storm‐driven currents. These high‐frequency events are superimposed on annular to decadal variations that probably relate to the frequency of gales and storms, and to variations in sediment supply caused by local earthquakes, changes in land use, and climatic cycles. Outside the bays, on the open shelf, the combination of a more vigorous tidal flow and reduced sediment supply mean that the sand cover is much less extensive and more mobile. The seabed is predominantly coarse sand ‐ fine gravel with a megarippled surface formed by southerly swell. Tides become progressively stronger to the west, and, in the Narrows of Cook Strait, currents are sufficiently powerful to keep sand in near‐constant motion and erode the fine gravel down to underlying boulders and rock.

Seasonal sediment storage on mudflats adjacent to the Amazon River

210Pb and 234Th activity profiles in sediment cores from underconsolidated mudflats 300 km downdrift of the Amazon river mouth record an ephemeral surface layer of fine-grained sediment up to 1.5 m thick. This layer contains about l.5 × 10 8 tons of Amazon sediment deposited rapidly (~1 cm/d) from a fluid-mud suspension (10–400 g/l) during the months between January and June. Virtually the entire layer is remobilized in July–December and the sediment is advected alongshore to the northwest. Seasonal variations in trade-wind strength and in supply of Amazon shelf sediment are thought to control emplacement, and removal of this ephemeral deposit. Solitary surface gravity waves characteristic of this setting generate a net landward sediment flux, which, with shore-normal tidal currents, controls spatial geometry of the surface layer. The resultant lens-shaped deposit dissipates incident wave energy and provides a substrate above mean high water for mangrove colonization and irregular shoreline progradation of meters per year. Macroscale (sand/silt laminations) and microscale (plasmic fabric) sedimentary structures in the ephemeral layer record diverse temporal variations (e.g., tidal and wave-induced) in bottom shear stress and sediment supply. Ephemeral deposition of 10 8 tons is inferred to be common in coastal areas associated with large and energetic river dispersal systems.

Sampling the oxygen minimum zone off Pakistan: glacial-interglacial variations of anoxia and productivity (preliminary results, sonne 90 cruise)

During cruise sonne 90 the well developed oxygen minimum zone (OMZ) in the northeastern Arabian Sea was sampled in great detail to study surface ocean productivity and organic carbon accumulation/preservation during the last hundred to hundred thousands of years. Nearly anoxic conditions on and below the seafloor are indicated by the lack of macrobenthos and nekton, absence of bioturbation, high marine organic carbon accumulation and preservation of laminated sediments between about 300 and 1000 m water depth on the steep continental slope. This pattern approximately coincides with the zone of extremely low O 2 concentrations presently observed in the water column. Accumulation of organic material on the deeper slope near the lower boundary of the OMZ is enhanced by downslope transport. Downcore we observe a complex alternation of dark-colored, laminated, and light-colored, homogeneous facies. In general, laminated, organic carbon-rich intervals were deposited under suboxic bottom water and enhanced productivity conditions, mainly during warm stages (e.g., Bölling/Alleröd and Holocene from 8000 yrs B.P. to Recent). The homogeneous, bioturbated intervals indicate normal bottom water oxygen levels and reduced productivity during or just after cold stages (e.g. Terminations IA and B, and Younger Dryas). The striking facies similarities of the sedimentary record in cores collected from different areas and water depths suggest a unique pattern of late Pleistocene C org accumulation in the northeastern Arabian Sea which depends mainly on regional surface ocean productivity and intermediate water oxygenation. However, the sedimentary record is also influenced by variations in sediment supply from the Makran and Karachi shelf and from Indus River discharge during rapid sea-level changes.

Geophysical Techniques for Evaluating the Internal Structure of Cheniers, Southwestern Louisiana: ABSTRACT

ABSTRACT Historically, Louisiana chenier plain studies have consisted of surficial mapping, sediment analyses, cores, and direct observation of limited exposures from borrow pits. Ground penetrating radar (GPR), a shallow geophysical technique, provides high resolution profiles of contrasts in electrical permittivity that can be correlated with sedimentary layers in sand and gravel depositional environments not effected by salt water. Reconnaissance vertical electrical soundings (VES) were performed at several sites to determine the applicability of GPR on the chenier plain. Based on resistivity data, three field sites were targeted for GPR profiling. GPR profiles were collected using a Geophysical Survey Systems, Inc. Subsurface Interface Radar 10A unit with a 500MHz antenna on a grid designed to assess three-dimensional variability in subsurface characteristics of each chenier. Topographic corrections were applied for each processed profile to adjust for surface elevation differences that effect reflection orientation. At selected chenier locations, subsurface reflections reveal a complex internal structure within these clastic deposits. However, at the interface with adjacent or subsurface fine-grained deposits, clay and/or conductive pore water limit penetration. Electrical resistivity proved to be a valuable reconnaissance tool for determining applicability of GPR, and VES models correlated directly with vibracore data. Preliminary interpretations of radar profiles suggest cheniers evolve through multiple processes in different environments. Radar facies observed in dip-oriented profiles at two sites are described as landward stepping foresets and may be interpreted as transgressive washover deposits. Bedset orientation of strike-oriented profiles indicates a westward component of migration. At a third site landward and seaward dipping reflections, interpreted as upper shoreface and washover deposits, indicate shifting shoreline position related to transgression and regression associated with variations in sediment supply.

Quantification of Slip Rate and Sediment Supply Variations Along Normal Fault Segments: Impact on Sequence Stratigraphy in Marine Rifts: ABSTRACT

Quantification of Slip Rate and Sediment Supply Variations Along Normal Fault Segments: Impact on Sequence Stratigraphy in Marine Rifts: ABSTRACT

Computer modelling of the influence of tectonics on sequence architecture of coarse-grained fan deltas

Fan delta deposition and extensional faulting are combined in a computer model using a general tectonosedimentary forward modelling equation. Fan delta forms and architectures resulting from tectonic activity are investigated using this model. Fan deltas formed during periods of tectonic quiescence are shown to have a sheet-like form and grow mainly as a result of progradation. Topset development is limited, resulting in the development of oblique to sigmoidal clinoforms. Fan deltas formed during periods of tectonic activity have a more wedge-shaped form and are restricted to a region adjacent to the controlling fault. These fan deltas grow as a result of both progradation and aggradation, resulting in the development of sigmoidal clinoforms. Under conditions of constant tectonic subsidence and sediment supply, fan deltas are shown to undergo a brief period of progradation followed by aggradation and a long period of retrogradation. This is a consequence of an increasing amount of sediment being deposited as topset material as the delta progrades and the position of the offlap break being displaced basinward during hangingwall subsidence. Other controls on fan delta architecture, such as variations in sediment supply and sea/lake level, are also considered. Pleistocene-Recent, Gilbert-type fan deltas from the southern margin of the Gulf of Corinth rift, Greece contain many of the features described above and modelling is used to investigate whether it is possible to identify the controls on their sequence architectures.

Post-Calabrian sequence stratigraphy of the northwestern Alboran Sea (southwestern Mediterranean)

The post-Calabrian sedimentary column of the northwestern Alboran Sea comprises three depositional sequences. The two older depositional sequences are defined by lowstand systems tracts (shelf-margin deltas, slope, base-of-slope, and basin deposits, and the Guadiaro channel-levee complex). In contrast, the most recent depositional sequence also includes transgressive (relict shelf facies) and high-stand (the Guadalmedina-Guadalhorce prodelta and hemipelagic facies) systems tracts. The stratigraphic architecture of these depositional sequences is controlled by the synchronism between high frequency sea-level changes, variations in sediment supply, and sedimentary processes. The configuration of the depositional sequences is variable and their distribution is complex, as a result of the relative importance played by sea-level changes and tectonism through the area. The sequence boundaries are represented by polygenetic surfaces in the proximal margin, and by monogenetic surfaces in the distal margin and basin. Each polygenetic surface results from the interaction between the sequence boundary with the lowstand erosional truncation surface and the transgressive surface, both developed during the previous sea-level cycle. The monogenetic surfaces correspond to unconformities and their correlative conformities, formed during sea-level lowstands. This pattern of depositional sequences developed in the margin and basin of the northwestern Alboran Sea shows differences with the Exxon Sequence Stratigraphy Model as traditionally applied: sea-level change control is essentially recognized through lowstand systems tracts, and sequence boundary coincides with lowstand erosional truncation surface and transgressive surface, both developed during the previous sea-level cycle.

Processes of late Quaternary turbidity current flow and deposition on the Var deep‐sea fan, north‐west Mediterranean Sea

ABSTRACTHigh‐resolution seismic boomer profiles, with a vertical resolution of less than 1 m, together with piston cores and previous side‐scan sonar data, are used to describe late Quaternary sedimentation on the Var deep‐sea fan. Chronological control is provided by foram biostratigraphy and radiocarbon dating in cores, and is extended over the fan by seismic correlation. Regional erosional events correspond to the oxygen isotopic stage 2 and 6 glacial maxima.Cores and seismic data define a widespread surface sand layer that is correlated with prodelta failure in 1979 and subsequent submarine cable breaks. Numerical modelling constrains the character of this 1979 turbidity current. It originated from a relatively small slide on the upper prodelta that put sufficient material in suspension to form an accelerating turbidity current which eroded sand from the Var Canyon. The turbidity current was only 30 m thick on the Upper Valley, but experienced significant flow expansion in the Middle Valley to thicknesses of more than 120 m, where it spilled over the eastern Var Sedimentary Ridge at a velocity of about 2·5 m s−1. Other Holocene turbidity currents (with a recurrence interval of 1000 years) were somewhat muddier and thicker, but also deposited sand on the levees of the Middle Valley, and are inferred to have had a similar slide‐related origin.Late Pleistocene turbidity currents deposited thick mud beds on the Var Sedimentary Ridge. The presence of sediment waves and the mean cross‐flow slope inferred from levee asymmetry indicates that some of these flows were many hundreds of metres thick and flowed at velocities of about 0·35 m s−1. This contrast with Holocene turbidites suggests that a slide origin is unlikely. Estimated times for deposition of thick mud beds on the levees are many days to weeks. The Late Pleistocene flows may therefore result from hyperpycnal flow of glacial outwash in the Var River. The variation in the Late Pleistocene to Holocene turbidite sedimentation is controlled more by variations in sediment supply than by sea‐level change.

Fluvial response to foreland basin overfilling; the Late Permian Rangal Coal Measures in the Bowen Basin, Queensland, Australia

The latest Permian Rangal Coal Measures and equivalents accumulated during a phase of declining volcanism and active thrust loading in the complex retroarc foreland Bowen Basin in eastern Queensland, Australia. The unit was formed in predominantly alluvial environments which covered the entire Bowen Basin and it represents the final phase of coal formation in the basin.Large opencut mine exposures, mainly in the Blackwater area, have allowed the establishment of a facies scheme for the Rangal Coal Measures. Seven facies have been recognised on the basis of lithology, geometrical criteria and palaeocurrent relationships. (1) Sheet-like Sandstone Channel Bodies; (2) Laterally Accreted, Heterolithic Channel Bodies; (3) Levee (Proximal Overbank) Deposits; (4) Minor Crevasse Channel Fill; (5) Floodbasin; (6) Stagnant Lake Floor; and (7) Mire. Together, these constitute an array typical of alluvial, coal-bearing systems.The depositional style of the Rangal Coal Measure channels is unusual, and considered to be related to the periodic oversupply of coarse sediment to the system. Heterolithic channel fills (Facies 2), which comprise alternations of thinly interbedded sandstone/siltstone and sharp-bounded sandstone, formed under conditions of dramatically variable sediment supply. Such channel deposits, while formed dominantly by lateral accretion, were the product of only slightly sinuous streams (less than 1.5). Facies 1 sheet sandstones, however, are interpreted to have formed during times of sand oversupply to the basin, and were the product of low-sinuosity, probably braided streams. The overall character of the Rangals is considered a response to overfilling of the basin by immature, volcanic sediment released by the uplift of thrust sheets in the adjacent orogen.

Downstream variation in bed material characteristics: a turbulence-controlled form-process feedback mechanism

Abstract Downstream changes in bed material characteristics represent an element of the sediment transport process which is of immediate geomorphological and economic significance. Particle size trends represent the joint effect of abrasion and sorting, often complicated by in situ weathering and variable sediment supply. In principle, the combined effects of abrasion and shorting can be explained if attention is paid to the role and characteristics of near-bed turbulence, via the mechanisms of ‘abrasion in place’ and the size-dependent particle acceptance or rejection involved in Bluck’s ‘turbulence template’. Field data describing spatially- and stage-dependent differences in turbulence characteristics by which the significance of such processes can be quantified are, however, lacking. In this paper, high-frequency three-dimensional velocity data obtained with an ultrasonic current meter in a braided section of Langden Brook, Lancashire, are used to demonstrate significant variations in turbulence parameters at the bar-pool scale. These are related to grain abrasion, sorting and the arrangement of grains in surface microtopographic bedforms using a force-balance model which incorporates turbulent velocity components in two dimensions. Following Bluck, it is suggested that bar forms act as, and result from, sediment trapping phenomena, whose fundamental controls lie in the characteristics of turbulence at the bar surface. Variations in turbulence provide a physical rationale for differing values of sorting/abrasion coefficients used in descriptive models of longitudinal size contrasts. In contrast to single-thread channels, however, spatially- and stage-dependent variation in turbulence characteristics is more marked in braided environments. Consequently, greater research effort is required to fully incorporate this into a spatially-realized form-process feedback mechanism applicable at the reach-scale and beyond.

Characterization and Architecture of Fluvial Sand Bodies in an Intracratonic Alluvial Fan

The fluvial deposits of the Tortola alluvial fan of late Oligocene to early Miocene were deposited in the intracratonic Loranca Basin (Spain). the fluvial facies comprise individual and amalgamated sand bodies embedded in flood-plain fines. The succession is a labyrinth-type reservoir analog. A distal and proximal fan locality have been compared. The sand bodies were characterized and quantified by means of three-dimensional (3-D) morphology and facies analysis, sandbody size statistics, permeability and gamma-ray log profiles, and geometry of permeability baffles. A classification of the sand bodies in six genetic types was established: meander-loop, low-sinuosity channel-fill, braided channel-fill, deltaic, interchannel bar, and crevasse-splay deposits. This classification is conditioned by a set og geological rules. The external geometry, internal organization, and spatial arrangement of the genetic types is determined by variation in hydrodynamic conditions, sediment supply, fan morphology, and basin subsidence. Significant differences in reservoir quality exist between the genetic types, and between the two fan localities. Analysis of the sequential development of the two localities shows that the 3-D architecture is the result of coalescing fan depositional systems: a minor fluvial fan systems from the eastern basin margin, and local minor fluvial systems. Shifting of the channels on the fan surfacemore » due to avulsion processes, differential basin subsidence, and tectonic movements influenced fan formation and hence reservoir quality.« less

Mechanism of Suspended Sediment Supply to Headwater Rivers and Its Seasonal Variation in West Central Hokkaido, Japan.

Source of suspended sediment was identified from grain size distribution in two headwater basins in West Central Hokkaido, Japan. The fine grains in river bed sediment were supplied to the river water as suspended sediment in the early snowmelt season, whereas those in hillslope sediment were washed out into the rivers in the summer rainy season. The fine grains probably accumulated in the bed sediment during winter, and were stirred up into river water as the river discharge increased. Since the fine grains in the river bed sediment were gradually exhausted, further stirring up could occur only when the river discharge exceeded that season's previous maximum. The fine grains in the hillslope sediment were most likely to be stored during the dry period from May to July, only to be washed away during the summer rainy season. Thus the suspended sediment supply from the hillslope is sparse in the snowmelt season. This type of seasonal variation in suspended sediment supply is probably common to headwater basins in the cold and humid climate of West Central Hokkaido, Japan.

Astronomically induced paleoclimatic oscillations reflected in Pliocene turbidite deposits on Corfu (Greece): Implications for the interpretation of higher order cyclicity in ancient turbidite systems

Research Article| April 01, 1993 Astronomically induced paleoclimatic oscillations reflected in Pliocene turbidite deposits on Corfu (Greece): Implications for the interpretation of higher order cyclicity in ancient turbidite systems GertJan Weltje; GertJan Weltje 1Comparative Sedimentology Division, Institute of Earth Sciences, P.O. Box 80.021, NL 3508 TA Utrecht, Netherlands Search for other works by this author on: GSW Google Scholar Poppe L. de Boer Poppe L. de Boer 1Comparative Sedimentology Division, Institute of Earth Sciences, P.O. Box 80.021, NL 3508 TA Utrecht, Netherlands Search for other works by this author on: GSW Google Scholar Geology (1993) 21 (4): 307–310. https://doi.org/10.1130/0091-7613(1993)021<0307:AIPORI>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation GertJan Weltje, Poppe L. de Boer; Astronomically induced paleoclimatic oscillations reflected in Pliocene turbidite deposits on Corfu (Greece): Implications for the interpretation of higher order cyclicity in ancient turbidite systems. Geology 1993;; 21 (4): 307–310. doi: https://doi.org/10.1130/0091-7613(1993)021<0307:AIPORI>2.3.CO;2 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 growth pattern of fan lobes in the early Pliocene Corfu turbidite system (Greece) demonstrates that regional climatic fluctuations in the land-locked Mediterranean completely concealed global glacioeustatic effects. The temporal evolution of the fan lobes studied closely matches the astronomical precession cycle in this time interval (∼23 ka), strongly suggesting that regular waxing and waning of the sediment supply to the delta-fed turbidite system were directly driven by changes of precipitation and continental runoff. The common lack of high-resolution time control in ancient turbidite systems may lead to mistaken interpretations of higher order cyclicity in ancient turbidite sequences produced by precession-induced variations of sediment supply at low paleolatitudes. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Fluvial, coastal, nearshore, and shelf deposition in the Upper Proterozoic (?) to Lower Cambrian Addy Quartzite, northeastern Washington

Quartzose and lesser argillaceous strata of the approximately 1300 m thick Upper Proterozoic (?) to Lower Cambrian Addy Quartzite of northeastern Washington record shelf, coastal, and continental sedimentation on an actively subsiding, relatively young passive margin. The lower 400 to 500 m of the Addy Quartzite was deposited immediately following the initiation of subsidence in a wave-dominated coastal and eventually storm-dominated shelf environment. This sequence records relative sea level rise that culminated in high-stand conditions. These sediments grade upwards into approximately 150 m of fluvial strata that record progradation of terrestrial environments during a period of relative sea level fall and a regional low-stand. The upper 700 m of the Addy Quartzite fines upwards from nearshore- to shallow-marine-dominated sediments into shelf-dominated deposits. This sequence marks the reestablishment of net sea level rise. The overall fining-upwards trend displayed by the Addy Quartzite indicates that regional subsidence of the newly formed passive margin was one of the most important factors controlling Addy sedimentation. However, variation seen in this trend throughout the Addy Quartzite indicates that rates of sea level rise associated with subsidence fluctuated and occasionally even reversed. Causes for the variation are inferred to be related to variations in subsidence rates and sediment supply. Textural and compositional data suggest Addy detritus was derived from relatively proximal recycled sedimentary source terranes and more distal continental crystalline terranes.

Holocene coastal evolution under the influence of episodic tectonic uplift: Examples from New Zealand and Japan

Coastal geomorphology in many parts of New Zealand and Japan has been strongly influenced by tectonic uplift since the culmination of the Holocene transgression at 5.5–7 ka ago. Examples of historic coastal uplift in Japan and New Zealand, accompanied by major earthquakes provide analogues for interpreting coasts where Holocene marine terraces are arranged in staircase fashion. Despite complexities in their origin, there is commonly only one shore platform for each relative stillstand of sea level. Shore platforms are subhorizontal, and are usually graded to low tide level. The width of platforms depends primarily on the erodibility of bedrock and the length of time available for formation. The simplest setting for assessing the influence of uplift on coastal evolution requires readily erodible, homogeneous bedrock, and a microtidal environment so that wide shore platforms of limited surface relief can be cut within ± 1.0 m of mean sea level. Earthquake-related uplift (where uplift is greater than the tidal range) is an instantaneous and catastrophic event that overwhelms on-going processes of shore platform formation. Determining the degree of tectonic control on coastal evolution is more difficult where hard or layered, dipping, bedrock exists or where the coast is subject to spatial variation in wave energy. Temporal and spatial variation in wave energy and variation in sediment supply make beach ridges more difficult to relate to former sea-level positions than either hard or soft bedrock platforms. More precise measurement of past uplift events are possible in coral reef environments than at higher latitude sites because coral reef colonies grow within ± 0.10 m of the mean low water spring tide and are sensitive to sea-level changes.

Evidence of Holocene sea-level change from the Northumberland coast, eastern England

Palaeoenvironmental investigations in the coastal lowlands of Northumberland provide chronological and altitudinal information regarding Holocene sea-level trends. Intercalated sequences of marine and terrestrial sediments at Elwick, Alnmouth and Warkworth contain a series of index points which are used to construct the trend of relative sea-level for the last 8000 years, during which relative sea-level has changed by only approximately 2.6 m. Both regional (eustatic and glacioisostatic) and local (sediment supply and coastal morphology) factors can be identified in the Holocene evolution of the Northumberland coast. It is evident that the regional sea-level signal in the lower part of the sedimentary record becomes progressively suppressed towards the present day by the more site-specific factors. Although a regional transgressive phase has been identified up to 5630–5970 cal. bc, the coastal systems of Northumberland are characterized by a range of responses to the low rates of relative sea-level change (generally less than 1 mm a −1 ) coupled with local variations in sediment supply.

Facies descriptions and associations in ancient reworked (?transgressive) shelf sandstones: Cambrian and Cretaceous examples

ABSTRACTPreferred facies trends in ancient shallow‐marine sediments have been determined by Markov‐chain and substitutability analyses of detailed sections measured in Lower Cambrian outcrops in the Southern Canadian Rocky Mountains (St Piran Formation, 600 m of vertical section; Fort Mountain Formation, 500 m of vertical section), and in a Cretaceous subsurface reservoir in south‐central Alberta (Viking Formation in the Garrington Field: 69 cores).Those sections with more defined cycles are interpreted to result from progradation of shelf‐ridge sands and gravels; examples with less defined order originated as inter‐ridge deposits, in zones with complex palaeoflows and in areas of subdued palaeotopographic relief. The highest degree of facies organization (&gt; 80% significant facies transitions) occurs in the Cretaceous Viking Formation sandstone and conglomerate ridges, interpreted to have had abundant sediment supply, water depths between fair‐ and storm‐weather wave‐base, and a strong littoral current system. A moderate degree of facies organization (70% significant facies transitions) occurs in the inter‐ridge deposits of the Cambrian Fort Mountain Formation, interpreted to have had a variable sediment supply, water depths above storm‐weather wavebase, and a variable, oscillating tidal current system. A poor degree of facies organization (&lt; 45% significant facies transitions) occur in the ridge deposits of the Cambrian Fort Mountain and St Piran formations and in the inter‐ridge deposits of the Cambrian St Piran and Cretaceous Viking formations. This facies disorganization occurs in sites where there was continuous and rapid subsidence (Cambrian) or in areas of subdued seafloor relief with complex current systems (Cretaceous). The pattern of facies relationships also varies. Relatively short linear patterns occur in all of the shelf‐ridge deposits. This contrasts with the inter‐ridge deposits in which there are long linear patterns or complex ring structures, interpreted to result from complex palaeoflow patterns in areas of subdued seafloor topography. Various statistical techniques (including Markov‐chain and substitutability analyses) can aid the interpretation of very complex lithological successions, as shown by the shelf sandstones and conglomerates examined in this study.

Stratigraphy and Petroleum Potential of the Mississippian Chainman Shale and Diamond Peak Formation, East-Central Nevada

An eastward-thinning and shallowing-upward Middle and Late Mississippian group of sedimentary rocks accumulated east of the Antler orogenic highland. The Chainman Shale consists of fine-grained siliciclastic and carbonate rocks deposited in deep-water and slope environments; it ranges from 400 ft thick in the east to 2,400 ft thick in the west, where it interfingers with the Diamond Peak Formation. Fine- to coarse-grained siliciclastic and carbonate rocks up to 5,100 ft thick comprise the Diamond Peak Formation and were deposited in submarine fan, fluvial, shoreline, and deltaic settings. Antler basin, up to 600 ft of medium-grained siliciclastic strata, the Scotty Wash Quartzite, represent deposition in shelf and deltaic environments. The Chainman, Diamond Peak, Scotty Wash, and Pennsylvanian Ely Limestone comprise two unconformity-bounded stratigraphic sequences. Sequence 1 strata were deposited in an asymmetric basin formed by subsidence due to thrust loading, which controlled sedimentation. Sequence 2 strata were deposited in a symmetric, shallow to emergent setting where variation in subsidence and sediment supply controlled sedimentation. Mississippian sandstone reservoir quality is a function of depositional environment, with maximum porosity occurring in Diamond Peak shoreline strata (sequence 2) in the central Antler basin. Organic carbon and maturation data suggest the Chainman Shale is presentlymore » generating hydrocarbons capable of sourcing structural-, stratigraphic-, and unconformity-controlled traps in east-central Nevada.« less

The Ebro margin study, northwestern Mediterranean Sea — an introduction

The Ebro continental margin from the coast to the deep sea off northeastern Spain was selected for a multidisciplinary project because of the abundant Ebro River sediment supply, Pliocene and Quaternary progradation, and margin development in a restricted basin where a variety of controlling factors could be evaluated. The nature of this young passive margin for the last 5 m.y. was investigated with particular emphasis on marine circulation, sediment dynamics, sediment geochemistry, depositional facies, seismic stratigraphy, geotechnical properties, geological hazards and human influences. These studies show the importance of marine circulation, variation in sediment supply, sea-level oscillation and tectonic setting for the understanding of modern and ancient margin depositional processes and growth patterns.