Density Flow Deposits Research Articles

Seismic architecture of a Lower Cretaceous platform-to-slope system, Santa Agueda and Poza Rica fields, Mexico

Two three-dimensional seismic data sets over the Albian western Golden Lane margin and time-equivalent basinal deposits of Poza Rica field allowed us to investigate the linked architecture of a steep-sided carbonate platform (El Abra Formation) and a thick accumulation of redeposited carbonate sediment at the toe of the slope and in the basinal area (Tamabra Formation). Regional seismic cross sections show that the most aggrading Albian platform has an eroded platform top, a scalloped margin, and a channelized slope that are equivalent to a 20-km (12.4-mi)-wide, westward-thinning, thick toe-of-slope apron made of chaotic, contorted, mounded, moderate- to high-amplitude reflections. Detailed reflection geometries in the Albian toe-of-slope and basinal deposits consist of chaotic to short, discontinuous, low-amplitude reflection at the toe of the slope of the Golden Lane platform, laterally changing to a discontinuous mounded, shingling reflection, which ultimately turns into high-amplitude parallel reflections. We interpret this lateral change to reflect the seismic signature of the change from the block- and debris-flow–dominated toe-of-slope area, to debris-flow and concentrated density flow deposits in the basin that ultimately grade laterally into pelagic deposits. On a flattened seismic slice, mounded reflections correspond to lobate to fan-shaped seismic events several kilometers wide that are interpreted as a carbonate basin-floor fan. Comparison between core and seismic data shows a dominance of debris flows in the lower two Albian sequences (Albian 1 and Albian 2) that grade vertically into more lobate concentrated density flows and turbidites in the upper two Albian sequences (Albian 3 and Albian 4). Seismic data used in this study, combined with core observations, do not support the interpretation of the Albian Tamabra Formation being of shallow-water origin. Seismic features identified as basin-floor fan, channel, and debris-flow deposits have a shape and size that are similar to those of other redeposited basinal carbonate deposits elsewhere. The seismic architecture shows that the Poza Rica field is a typical example of thick accumulation of grainy porous carbonate deposits in a basinal setting. This example shows the potential of a large hydrocarbon accumulation in a tectonically modified stratigraphic trap around shallow-water carbonate platforms.

Relationships between high‐magnitude relative sea‐level changes and filling of a coarse‐grained submarine canyon (Pleistocene, Ionian Calabria, Southern Italy)

AbstractA middle Pleistocene coarse‐grained canyon fill succession (the Serra Mulara Formation) crops out in the northern sector of the Crotone Basin, a forearc basin located on the Ionian side of the Calabrian Arc and active from the Serravallian to middle Pleistocene. This succession is an example of coarse‐grained submarine canyon fill, which consists of a north‐west to south‐east elongated body (4·25 km long and up to 1·5 km wide) laterally confined by a deep‐water clayey and silty succession and located behind the modern Neto delta (north of Crotone). The thickness of the unit reaches 178 m. The lower part of the canyon fill is dominated by gravelly to sandy density‐flow deposits containing abundant bivalve and gastropod fragments, passing upward into a succession composed of metre‐scale to decimetre‐scale density‐flow deposits forming sandstone–mudstone couplets. Sandstone deposits are mostly structureless and planar‐laminated, whereas the clayey layers record hemipelagic deposition during quieter phases. This succession is overlain by another composed of thicker structureless sandstones alternating with layers of interlaminated mudstones and sandstones, which contain leaf remnants and fresh water ostracods, and are linked directly to river floods. The canyon fill is overlain by gravelly to sandy continental deposits recording a later stage of emergence. Facies analysis, together with micropalaeontological data from the hemipelagic units, suggests that the studied canyon fill records, firstly, a progressive gravel material cut‐off during deposition due to an overall relative sea‐level rise, leading to a progressive increase in the entrapment of sediment in fluvial to shallow‐marine systems, and secondly, a generalized relative sea‐level lowering. This trend probably reflects high‐magnitude glacio‐eustatic changes combined with the regional uplift of the region, ultimately leading to emergence.

Onset of submarine debris flow deposition far from original giant landslide

Submarine landslides can generate sediment-laden flows whose scale is impressive. Individual flow deposits have been mapped that extend for 1,500 km offshore from northwest Africa. These are the longest run-out sediment density flow deposits yet documented on Earth. This contribution analyses one of these deposits, which contains ten times the mass of sediment transported annually by all of the world's rivers. Understanding how this type of submarine flow evolves is a significant problem, because they are extremely difficult to monitor directly. Previous work has shown how progressive disintegration of landslide blocks can generate debris flow, the deposit of which extends downslope from the original landslide. We provide evidence that submarine flows can produce giant debris flow deposits that start several hundred kilometres from the original landslide, encased within deposits of a more dilute flow type called turbidity current. Very little sediment was deposited across the intervening large expanse of sea floor, where the flow was locally very erosive. Sediment deposition was finally triggered by a remarkably small but abrupt decrease in sea-floor gradient from 0.05 degrees to 0.01 degrees. This debris flow was probably generated by flow transformation from the decelerating turbidity current. The alternative is that non-channelized debris flow left almost no trace of its passage across one hundred kilometres of flat (0.2 degrees to 0.05 degrees) sea floor. Our work shows that initially well-mixed and highly erosive submarine flows can produce extensive debris flow deposits beyond subtle slope breaks located far out in the deep ocean.

Three-dimensional geological and synthetic seismic model of Early Permian redeposited basinal carbonate deposits, Victorio Canyon, west Texas

The Lower Permian outcrops of Victorio Canyon, in the Sierra Diablo Mountains in west Texas, show undisturbed stratigraphy of carbonate toe-of-slope and basinal deposits. These rocks consist of a vertical stack of carbonate debris-flow deposits and hyperconcentrated density-flow deposits, thick skeletal-ooid grainstone deposited as basin-floor fans, various reworked muddy carbonate deposits, and fine siliciclastic siltstones. This succession was deposited within five sequences that include the upper Hueco Formation (late Wolfcampian) through the Bone Spring Formation (middle Leonardian). Using a ground-based light detecting and ranging-generated high-resolution digital outcrop model (DOM) aged as a template, we mapped and digitized the stratigraphy of the toe-of-slope and basinal deposits on the 5-cm (2-in.) precision DOM. On the basis of the digitized stratigraphic contacts, several regional surfaces were constructed, and a 3-D geocellular model was built. Facies information within this model is extrapolated from measured section data using both a kriging algorithm and stochastic simulations. Using impedance values extracted from a subsurface analog, a 3-D impedance model was created for both the kriged and the stochastic models. Both models incorporate fine-scale stratigraphic architecture. In addition, the stochastic impedance model incorporates spatially correlated noise, resulting in more realistic synthetic seismograms. Three-dimensional synthetic seismograms were calculated at 20, 40, and 80 Hz. The reservoir-prone facies is skeletal-ooid grainstone deposited as a 1.5-km 750-m (0.93-mi 2460-ft) basin-floor fan up to 15 m (49 ft) thick. This basin-floor fan is subtly imaged in vertical seismic section at a frequency below 80 Hz. It is, however, better recognized on time slices with peak frequency as low as 20 Hz and even better delineated on horizon slices that parallel the stratigraphy.

Late Archaean synorogenic basins of the Eastern Goldfields Superterrane, Yilgarn Craton, Western Australia: Part II. Kurnalpi Terrane

The Penny Dam, Belches, Yilgangi, White Hills, Granny, Royal, Lucky, Brock and Wallaby Supersequences of the Kurnalpi Terrane crop out in synclines that are the erosional remnants of basins that developed as linear zones of subsidence between approximately north-trending compartment-bounding faults. Dominant sedimentary facies range from gravel-rich and sand-rich concentrated density-flow deposits to thickly and thinly bedded Bouma-type turbidites. Background deposits are black shales or laminated green mudstones, and banded iron formation is preserved in some condensed sections. Periods of non-deposition are recorded by bedded chert, which is the product of early diagenetic sea-floor silicification. The basins were separate deep-marine canyon to linear-fan systems that were linked laterally and distally by mud-rich deposits. There is only minor evidence for fault-anchored, canyon-margin slope aprons. Basin development occurred during two stages separated by a period of deformation, uplift and erosion. Sparse palaeocurrents establish sediment dispersal was to the south or southeast, indicating that uplift to the north or northwest controlled palaeoslopes. Stacking of lithofacies is aggradational, and consistent with deposition in fault-bound basins. Tectonostratigraphic equivalence with siliciclastic supersequences of the Kalgoorlie and Gindalbie Terranes is established by common depositional systems, stratigraphic styles and stratigraphic responses to tectonic forcing. Consequently, the siliciclastic supersequences represent overlap (or late-stage) basins that tied together arc-related terranes following terrane amalgamation. Similar depositional facies, aggradational styles of facies stacking and two-stage development characterise the syncollisional Plio-Pleistocene Coastal Range Basin of Taiwan. Modern analogues are the deep-marine Southern Longitudinal and Taitung Troughs off southeastern Taiwan that are being filled by synorogenic sediments derived from the Taiwan Orogen.

Discrimination of density flow deposits using elemental geochemistry—Implications for subtle provenance differentiation in a narrow submarine canyon, Palaeogene, Danish North Sea

Elemental geochemistry of 1131 sandstone samples has been used to characterise five Palaeogene sandstone members in a system of density flow deposits within an incised submarine canyon, Danish North Sea. Diagenetic overprinting has complicated the use of most main and trace elements, but a group of “heavy mineral bound” elements with low mobility (Ti, Y, Zr, Nb and Th) has proved highly potential for correlation. The individual sandstone members exhibit very consistent relations between the “heavy mineral elements” along the canyon and, based on Zr/Ti plots, two families of sandstone members can be distinguished. The families are recognised on variations in inclination and intersection of linear regression lines which are related to subtle variations in provenance/source area. The inclination is believed to be controlled by the detrital heavy mineral (HM) suite and composition, whereas the intersections are controlled by the background contribution, such as HM inclusions in detrital rock forming minerals, e.g. quartz and/or feldspar, as well as substituted and/or adhered elements in glauconite. The correlation pattern has been used to suggest a re-interpretation of the stratigraphic relation of some of the sands.

Marine volcaniclastics of the Hidden Lake Formation (Coniacian) of James Ross Island, Antarctica: an enigmatic element in the history of a back-arc basin

Abstract The Coniacian Hidden Lake Formation of James Ross Island, Antarctica is a 300–400 m-thick succession of marine volcaniclastic conglomerates, sandstones and mudstones. It occurs at a point of transition in the evolution of the James Ross Basin, as it is underlain by deep-marine strata and overlain by shallow-marine strata. The succession reflects the two main factors controlling the deposition of the formation: (1) the influx of large quantities of volcaniclastic sediment; and (2) a pronounced inversion event in the early Coniacian heralding the cessation of transpressive tectonic activity in the James Ross Basin. The succession is dominated by a range of sediment density-flow deposits, which, combined with the limited faunas and the lack of wave-induced structures, suggest deposition in a relatively deep-marine environment below storm-wave base. Three main facies associations are recorded representing base-of-slope, fan-delta and basin-floor depositional environments. The volcaniclastic fan-delta association is dominated by fresh pyroclastic detritus and was deposited in response to volcanic eruptions on the adjacent arc. Thick beds of parallel-stratified sandstone record deposition from sustained, concentrated sediment density flows. The conditions immediately following pyroclastic eruptions lend themselves to the deposition of such deposits, as vegetation cover is destroyed and large amounts of poorly consolidated sediment are available for reworking. An enigmatic feature of the succession is the presence of units of cross-bedded sandstones thought to be of tidal origin that are locally abundant and are intimately interbedded with sediment density-flow deposits. The occurrence of tidal sediments in a substorm-wave base setting is explained by appealing to partial basin inversion during the final phases of strike-slip tectonic activity in the basin creating an irregular basin floor that focused and amplified tidal currents. The infilling of this basin topography by sediment and waning intrabasinal tectonism during the Coniacian resulted in the progressive elimination of this basin-floor topography and the onset of shallow-marine shelf sedimentation.

Toe-of-slope deposits of a Givetian reef-rimmed platform: provenance of calcareous density-flow deposits (Rabat-Tiflet-Zone, Morocco)

Givetian subaqueous density-flow deposits reveal the existence of a peritidal carbonate platform in sedimentary basins preserved within the Rabat-Tiflet-Zone of Morocco. The calcareous component assemblage displays a photozoan carbonate production mode of the neritic source environments. Characteristic elements of the allochthonous faunal association are colonial tabulate corals, stromatoporoids, crinoids, bryozoans and thick-shelled brachiopods. Active growing reefs and cortoid sand shoals at the platform margin as well as periplatform carbonates at the uppermost slope settings contributed bioclastic and lithoclastic lime debris to the toe-of-slope of the carbonate apron. Bipartite cobble rudstone beds are interpreted as deposits of hyperconcentrated density flows, which cannot be maintained on very low-angle slopes for as long as more dilute flows and represent short run-out distances. Beds consisting of mostly well-organized pebbly grainstones, packstones and grainstone-wackestone couplets are deposits of surge-like concentrated flows and turbidity flows.

TUNNEL VALLEYS AND DENSITY FLOW PROCESSES IN THE UPPER ORDOVICIAN GLACIAL SUCCESSION, ILLIZI BASIN, ALGERIA: INFLUENCE ON RESERVOIR QUALITY

Upper Ordovician syn‐glacial deposits form a gas reservoir at the Tiguentourine field, Illizi Basin, Algeria. The reservoir geology of these glacial deposits has been investigated with the objective of understanding the widely varying thickness of the sequence and the controls on reservoir quality.A general depositional model was developed following a review of outcrops in the Tassili N'Ajjer region, some 200km south of Tiguentourine. In these outcrops, elongate tunnel valleys were observed to be incised into the subglacial surface, and these were interpreted to have been formed by subglacial meltwater flows. The isopach map of the Tiguentourine field syn‐glacial sequence, derived from well penetrations and a 3D seismic survey, indicates there were two elongate depressions analogous to, but broader than, the tunnel valleys observed at outcrop.The sedimentary rocks encountered at outcrop and in the subsurface were broadly similar. Initial sedimentation in the tunnel valleys typically comprised medium‐ to coarsegrained, structured sandstones. These were interpreted as the deposits of glaciofluvial currents flowing along the tunnel valleys. They were succeeded by a range of density flow deposits (muddy and sandy debrites, high‐ and low‐density turbidites). In the outcrops, the turbidites are seen to evolve upwards from an amalgamated sheet complex to sinuous channel forms. Long wavelength (>2m), low amplitude, symmetrical dunes were noted in these high‐density turbidites; they were interpreted to be the products of sustained, possibly hyperpycnal, turbidity currents. In the subsurface, pelagic deposits with graptolites were recorded towards the top of the succession indicating a glacial‐marine environment. At its maximum extent, the ice is believed to have been grounded on the continental shelf. The synglacial succession in the south Illizi Basin was interpreted as a product of glacial retreat, with the hardground at the top of the sequence probably the result of isostatic uplift.

Turbidite to storm transition in a migrating foreland basin: the Kendal Group (Upper Silurian), northwest England

AbstractThe uppermost Windermere Supergroup (Kendal Group) of northwest England records the passage from Wenlock and lower Ludlow deep water ‘flysch’ deposits to upper Ludlow and Přídolí shallower water ‘molasse’ deposits within an evolving foreland basin. An upwards progression is preserved from oxygen-poor basin-slope turbidite deposits through more oxygenated, bioturbated dilute density flow deposits, to storm and wave-influenced sediments. The storm-influenced sediments display hummocky cross-stratification, a Skolithos ichnofacies, shelly lags, and symmetrical wave ripple cross-lamination. Convolute lamination increases in magnitude and frequency in the upper part of the sequence, apparently nucleated above ripple crests. Tropical hurricanes probably controlled storm deposition, as suggested by late Silurian palaeogeographic reconstructions. Structures in the heterolithic muddy siltstones suggest deposition in a lower energy, wave-influenced setting. Mud-drapes, short wavelength symmetrical ripples and multi-directional ripple cross-lamination are common. The Kendal Group shows a regional palaeocurrent distribution consistent with an arcuate basin geometry, bounded to the northwest and northeast by topographic slopes. As well as a temporal trend, facies and faunal diachroneity imply a southwards migration of the foreland basin depocentre through Ludlow and Přídolí time, probably ahead of a rising mountain front to the north. The increase in pre-lithification sediment disturbance may reflect greater earthquake activity as this mountain front advanced and the basin began to invert.

Geologic Reservoir Model for the Triassic Doig Formation, Northeast British Columbia, Canada

A subsurface investigation of the mid-Triassic Doig formation in northeastern British Columbia documented two main reservoir facies. Both are a product of mass movement and sediment gravity flow processes on a progradational, tectonically active continental shelf margin. Substrate instability was likely a product of sediment loading, perhaps in concert with seismic activity. Sedimentary facies and reservoir parameters were determined from analysis of approximately 150 cores and 900 well logs. Laterally discontinuous Doig sandstones are up to 60 m thick and trend northeasterly within the study area. The main reservoir facies are incised density flow deposits and laterally extensive slump deposits. Reservoir quality within these sands is extremely variable with porosity ranging from less than 5% to 15%. In core, these deposits consist of moderately well sorted, very fine grained sandstones with no vertical grain size variation. The best production to date is in the Buick Creek field with initial flows of 346 BOPD. The slump deposits are thinner and tend to be more elongate parallel to paleoshoreline. These sands were subject to some wave or current reworking. Modern analogs where similar processes and products of deposition are known to occur include the Gulf of Alaska continental shelf and the Frasermore » River Delta slope. Doig sandstones usually are enclosed in fine-grained shelf deposits that provide a good stratigraphic trapping mechanism. Successful development of Doig reservoirs must incorporate geologic modes that assist in understanding the complex and highly variable reservoir quality of sandstones units.« less

Oil Shale Sedimentology and Geochemistry in Cenozoic Mae Sot Basin, Thailand

The intermontane Mae Sot basin, Thailand, contains carbonate-rich oil shales in which oil yield, mineralogy, and major and trace element geochemistry are related to the rock type. Higher grade oil shale is significantly enriched in silicate minerals (quartz, feldspars, clays, and analcite) relative to carbonates, and in dolomite relative to calcite. Couplets of organic-rich and mineral-rich laminae increase in mean thickness from 0.080 mm to 0.670 mm from high to low-grade oil shale. The organic material consists mainly of lamalginite, and yields up to 341 L of oil/MT (81.8 gal/ton) on retorting. Fish and vascular-plant fragments are the main megafossils. Mappable oil shale sequences 10 m (33 ft) thick are interstratified with marlstone-sandstone sequences 70 m (230 ft) thick. Markov chain analysis applied to stratigraphic sequences indicates that low-grade oil shale passes gradually into high-grade oil shale, and vice versa. The strata are interpreted as the deposits of extensive fresh to brackish lakes, with oil shale sequences formed in perennial, stratified lakes and marlstone-sandstone sequences formed in shallow perennial lakes and subaerially exposed flats. Dolomite in the oil shales was authigenic. The systematic changes in mineralogy and geochemistry between rock types probably reflect a gradient in redox potential from the center to the margins of the lake. Sandstone and siltstone beds and some carbonate laminae are interpret d as density flow deposits and form a significant proportion of the sequences. The episodic deposition of oil shales reflects changes in lake level within the enclosed basin, probably due to climatic fluctuations on a 24,000 to 46,000-year scale.

Quartz Microtextures as Indicators of Subaqueous Density Flow: ABSTRACT

Quartz samples from density flow deposits from the Colombia basin (Caribbean Sea) were analyzed for surficial microtextural associations using the scanning electron microscope. Microtextural abrasion patterns were found to vary in the A division of turbidites, grain-flow deposits, debris-flow deposits, and in material resulting from washover on the Magdalena deep-sea fan. The observed microtextural patterns are useful criteria for the identification of the transport mechanisms of other deposits assumed to have resulted from density flows. Relative distances of travel of contemporaneous turbidites could be ascertained from impact densities on A division sand grains. The limiting conditions on such analyses are a minimum of postdepositional alteration of the mechanical textures of the grains and a lack of intense abrasion features received during episodes of predensity-flow transport. End_of_Article - Last_Page 2206------------