Fine-grained Turbidite Systems Research Articles

A diverse deep-sea trace fossil assemblage from the Adriatic Flysch Formation (middle Eocene – middle Miocene), Montenegro (central Mediterranean)

Our study of ichnofossils in the Adriatic Flysch suggests that mid-fan environments, with 30 ichnospecies and 13 architectural designs, provided most productive and best preservation conditions in the fine-grained turbidite system of the Dinarides-Albanides-Helenides deep foreland basin. The Adriatic Flysch Formation at its type section in Crnjak Cove (Montenegro) represents a 300-m-thick turbidite succession deposited from the middle Eocene to the middle Miocene. The flysch is exposed in an asymmetrical syncline in a 750-m-long outcrop. The conglomerates, sandstones, and mudstones are arranged in seven distinct turbidite facies, which represent three superimposed submarine fans. The inner-, mid-, and outer-fan facies of the submarine fans contain sixteen ichnogenera and thirty three ichnospecies, which exhibit thirteen architectural designs. The inner fan conglomerates and coarse-grained sandstones contain a low diversity (Ophiomorpha rudis, Ophiomorpha annulata, and Halopoa imbricata), a low disparity (two architectural designs), and a low-density post-depositional trace fossil assemblages of the Ophiomorpha rudis ichnosubfacies of the Nereites ichnofacies. The mid-fan greywackes contain very diverse pre-depositional trace fossils (Belorhaphe zickzack, ?Cosmorhaphe isp., Desmograpton dertonensis, Gordia isp., Helminthopsis isp., Helminthorhaphe flexuosa, ?Megagrapton isp., Paleodictyon arvense, Paleodictyon hexagonum, Paleodictyon itallicum, Paleodictyon latum, Paleodictyon majus, Paleodictyon maximum, Paleodictyon strozzii, Paleodictyon isp., Scolicia strozzii, Squamodictyon isp.) having six architectural designs and abundant post-depositional trace fossils (Halopoa imbricata, Ophiomorpha annulata, Ophiomorpha nodosa, Ophiomorpha rudis, Planolites beverleyensis, Planolites montanus, Palaeophycus alternatus, Palaeophycus striatus, Palaeophycus tubularis, Rhizocorallium commune, Scolicia prisca, Scolicia strozzii, Zoophycos isp.) exhibiting seven architectural designs, which constitute the Paleodictyon-Ophiomorpha rudis ichnosubfacies of the Nereites icnhnofacies in the Adriatic Flysch. The waning turbidity currents with slower rates of sediment deposition and deficiency of nutrients favored grapholyptid colonization of the outer fans. Relatively low abundance, and great diversity of graphoglyptids (Helminthorhaphe flexuosa, Desmograpton dertonensis, ?Megagrapton isp., Paleodictyon arvense, Paleodictyon hexagonum, Paleodictyon majus, Paleodictyon minimum, Paleodictyon strozzii, Paleodictyon isp., Squamodictyon isp.), but low disparity (three architectural designs), represents the Paleodictyon ichnosubfacies of the Nereites ichnofacies in the outer fan facies of the Adriatic Flysch. The diversity of pre-depositional ichnofossils in the Adriatic Flysch exceeds post-depositional forms, reflecting a dominance of K-selected over r-selected population strategies in a stable oligotrophic environment.

Morphology of turbidite systems within an active continental margin (the Palomares Margin, western Mediterranean)

The Palomares Margin, an NNE–SSW segment of the South Iberian Margin located between the Alboran and the Algerian–Balearic basins, is dissected by two major submarine canyon systems: the Gata (in the South) and the Alías–Almanzora (in the North). New swath bathymetry, side-scan sonar images, accompanied by 5kHz and TOPAS subbottom profiles, allow us to recognize these canyons as Mediterranean examples of medium-sized turbidite systems developed in a tectonically active margin.The Gata Turbidite System is confined between residual basement seamounts and exhibits incised braided channels that feed a discrete deep-sea fan, which points to a dominantly coarse-grained turbiditic system. The Alías–Almanzora Turbidite System, larger and less confined, is a good example of nested turbiditic system within the canyon. Concentric sediment waves characterize the Alías–Almanzora deep-sea fan, and the size and acoustic character of these bedforms suggest a fine-grained turbidite system. Both canyons are deeply entrenched on a narrow continental shelf and terminate at the base of the continental slope as channels that feed deep sea fans. While the Alías–Almanzora Turbidite System is the offshore continuation of seasonal rivers, the Gata Turbidite System is exclusively formed by headward erosion along the continental slope. In both cases, left-lateral transpressive deformation influences their location, longitudinal profiles, incision at the upper sections, and canyon bending associated with specific fault segments.

Seismic Architecture and Lithofacies of Turbidites in Lake Mead (Arizona and Nevada, U.S.A.), an Analogue for Topographically Complex Basins

Abstract Turbidites, which have accumulated in Lake Mead since completion of the Hoover Dam in 1935, have been mapped using high-resolution seismic and coring techniques. This lake is an exceptional natural laboratory for studying fine-grained turbidite systems in complex topographic settings. The lake comprises four relatively broad basins separated by narrow canyons, and turbidity currents run the full length of the lake. The mean grain size of turbidites is mostly coarse silt, and the sand content decreases from 11–30% in beds in the easternmost basin nearest the source to 3–14% in the central basins to 1–2% in the most distal basin. Regionally, the seismic amplitude mimics the core results and decreases away from the source. The facies and morphology of the sediment surface varies between basins and suggests a regional progression from higher-energy and possibly channelized flows in the easternmost basin to unchannelized flows in the central two basins to unchannelized flows that are ponded by the Hoover Dam in the westernmost basin. At the local scale, turbidites are nearly flat-lying in the central two basins, but here the morphology of the basin walls strongly affects the distribution of facies. One of the two basins is relatively narrow, and in sinuous sections reflection amplitude increases toward the outsides of meanders. Where a narrow canyon debouches into a broad basin, reflection amplitude decreases radially away from the canyon mouth and forms a fan-like deposit. The fine-grained nature of the turbidites in the most distal basin and the fact that reflections drape the underlying pre-impoundment surface suggest ponding here. The progression from ponding in the most distal basin to possibly channelized flows in the most proximal basin shows in plan view a progression similar to the stratigraphic progression documented in several minibasins in the Gulf of Mexico.

ABSTRACT: Reservoir Architecture of a Fine-Grained Turbidite System >From Outcrop Exposures of the Triassic Montney Formation, Western Canada Sedimentary Basin

ABSTRACT: Reservoir Architecture of a Fine-Grained Turbidite System >From Outcrop Exposures of the Triassic Montney Formation, Western Canada Sedimentary Basin

Coarse-grained and fine-grained turbidite systems as end member models: applicability and dangers

Submarine fan/turbidite systems can have any net-to-gross percentage. Prior to developing a model that best represents the deposits under investigation, the earth scientist should have an adequate understanding of the major external parameters that influence the transport and deposition of sediment. Tectonics influence the sediment source area and its overall distance to the shoreline, shelf width and basin morphology. The sand/clay ratio and size range dictate how far sediment can be transported. Climate influences erosion, transport and diagenesis. Relative sea-level fluctuations impact the transport from coast to basin. Using those parameters and two end-members—coarse-grained and fine-grained—an applicable model can be developed that best characterizes the fan under consideration.