PRIMARY SEDIMENTARY STRUCTURES FORMED BY TURBIDITY CURRENTS AND RELATED RESEDIMENTATION MECHANISMS

1965 ◽  
pp. 192-219 ◽  
Author(s):  
JOHN E. SANDERS
Keyword(s):  
Turbidity Currents ◽  
Sedimentary Structures

The Sedimentary Structures and Depositional Mechanics of Certain Ordovician Turbidites, Cloridorme Formation, Gaspé Peninsula, Quebec

1975 ◽  
Vol 12 (11) ◽  
pp. 1934-1952 ◽  
Author(s):  
Keith Skipper ◽  
Gerard V. Middleton
Keyword(s):  
Large Scale ◽  
Fine Sand ◽  
Coarse Sand ◽  
Turbidity Currents ◽  
Upstream Migration ◽  
High Concentration ◽  
Sedimentary Structures ◽  
The North ◽  
Gaspe Peninsula ◽  
Gaspé Peninsula

Turbidites, belonging to the β1, member, Cloridorme Formation, are exposed on the north shore of the Gaspé Peninsula, Quebec. Their structural attitude is such that vertical sections through turbidite beds are exposed on the wave-cut platform and their strike is approximately parallel to the paleocurrent direction, as shown by sole marks on the bases of beds.Certain thick turbidite beds, in a distal position, display a sequence of sedimentary structures which differs from the sequence defined by Bouma. Three broad divisions are recognized: a basal division consists of either limestone or quartz granule to pebble conglomerate (0–4 cm thick) or coarse sand graywacke or calcareous wacke (0–15 cm thick). Basal divisions of calcareous wacke frequently display ripple-lamination, parallel lamination, or upstream-inclined laminae. Where the upstream inclined laminae form a single set, they occur below a sinuous profile (wavelength 40–80 cm, and amplitude 2–5 cm).A second division (0–330 cm thick) consists in most places of spindle- or globular-shaped calcareous nodules scattered in an argillaceous host. In some beds, streaking and lobing of light colored, carbonate bearing material is associated with these nodules. Internal hemi-ellipsoid structures, arranged en echelon and convex towards the base of the bed, are displayed from the second division. The upper division consists of fine grained siltstone and shale.The upstream-inclined laminae in the basal division of calcareous wacke beds are interpreted as being the result of the upstream migration of antidunes. The nodules within the second division developed as 'pseudo-nodules'. The hemi-ellipsoid structures resemble damped, large scale (macroturbulent) eddies associated with the flow of dense grain dispersions.Correlation of these beds has been achieved over a distance of 12 km. Basal divisions of granule and pebble conglomerate persist over this distance and show that coarse particles may be transported by turbidity currents over long distances. The sedimentary structures of the basal divisions of several calcareous wacke beds might be interpreted as the result of either an increase in flow regime downcurrent, or of nonpreservation of structures at up-current localities.The beds were probably deposited from turbidity currents composed largely of mud and fine sand, but containing a zone of coarse grains concentrated near the bed. The basal division was deposited from this lower zone and a period of traction formed rippled, flat, or antidune bed forms. Stratification in the basal division was preserved by the rapid deposition on top of sediment that settled en masse from the subsequent high concentration body of the current. The formation of a succession of 'quick' beds led to the sedimentation of the second division. The flows responsible for the sequence of structures observed and the downcurrent persistence of the beds probably approached closely a state of 'autosuspension'.

The Denbigh Grits; Wenlock Greywackes in Wales

1957 ◽  
Vol 94 (6) ◽  
pp. 433-451 ◽  
Author(s):  
W. A. Cummins
Keyword(s):  
Turbidity Currents ◽  
Sedimentary Structures ◽  
South West

AbstractThe petrography of the greywackes is described, with special emphasis on rock and mineral grains indicative of provenance. Sedimentary structures are discussed, and current directions based on flute cast measurements are recorded. The stratigraphy and palaeontology of the Denbigh Grits, and the facies of other parts of the Wenlock in the Welsh area are also considered. It is concluded that the greywackes were derived from an area of Pre-Cambrian rocks near south-west Wales and that they were transported along the axes of subsiding troughs by turbidity currents.

Characteristics of a Campanian delta deposit controlled by alternating river floods and tides: the Loyd Sandstone, Rangely Anticline, Colorado, U.S.A.

2019 ◽  
Vol 89 (12) ◽  
pp. 1181-1206 ◽  
Author(s):  
Peter P. Flaig ◽  
Stephen T. Hasiotis ◽  
Timothy J. Prather ◽  
Darrin Burton
Keyword(s):  
Trace Fossil ◽  
High Abundance ◽  
Turbidity Currents ◽  
Piceance Basin ◽  
Delta Front ◽  
River Flooding ◽  
Mancos Shale ◽  
Sedimentary Structures ◽  
Normal Regression ◽  
High Diversity

ABSTRACT The Campanian Loyd Sandstone Member of the Mancos Shale (Loyd) along the Rangely Anticline, Piceance Basin, Colorado, contains a series of multi-meter-thick, heterolithic, coarsening-upward successions (CUSs) with internal clinoforms comprising low-angle-dipping (< 5°), parallel-laminated sandstone beds interbedded with bioturbated flaser-wavy-lenticular bedded sandstone and siltstone. Loyd clinoforms are delta foresets composed of prodelta and delta-front deposits, including mouthbars. Many CUSs exhibit scours filled with bioturbated sandstone, or interbedded bioturbated sandstone and siltstone or mudstone representing aggradational fill of subaqueous terminal distributary channels or the migration of mouthbars into channel scours. Mud drapes on sedimentary structures and mud rip-up clasts are extremely common. A high-abundance, high-diversity, trace-fossil assemblage includes vertical, 1–4-m-deep Ophiomorpha that may penetrate multiple bedsets of parallel-laminated sandstones and highly bioturbated finer-grained interbeds. Bioturbation increases sandstone content in finer-grained interbeds, and provides sandy conduits that increase connectivity between beds. Although parallel-laminated sandstones volumetrically dominate Loyd delta clinoforms, they likely represent relatively short-term freshwater and sediment input during river flooding that produced delta-front turbidity currents. Interbedded finer-grained beds, mud-draped sedimentary structures, and the high-abundance, high-diversity trace-fossil assemblages record longer amounts of time during reduced fluvial discharge, tidal reworking of sediments, and intense bioturbation under marine salinities. Controls on the internal characteristics of the Loyd delta deposits include: 1) a high sediment influx into a relatively shallow marine basin protected from wave action during normal regression; 2) relatively short-duration, episodic freshwater and sediment discharge from distributaries that reduced salinities, deposited sand as turbidity currents, and promoted delta-front channelization; and 3) longer-duration periods of reduced discharge with deposition of finer-grained sediment, tidal reworking, and bioturbation of sediments under higher salinities. These controls combined to produce the heterolithic, highly bioturbated, river-flood delivered, and tidally modified clinoforms of the Loyd that differ from deposits typically considered to be classic examples of fluvial-flood-dominated or extensively tidally modified deltas.

XXII.—Silurian Greywackes in Peeblesshire

1955 ◽  
Vol 65 (3) ◽  
pp. 327-357 ◽  
Author(s):  
Ewart Kendall Walton
Keyword(s):  
Volcanic Rocks ◽  
Source Rocks ◽  
Turbidity Currents ◽  
Chemical Analyses ◽  
Rock Fragments ◽  
Intermediate Group ◽  
The Third ◽  
Sedimentary Structures ◽  
Land Mass

SynopsisSedimentary structures in the greywackes of Peeblesshire, including graded bedding, cross-lamination and load-cast structures, are described and their origin discussed.Petrographically the greywackes are poorly sorted sediments composed of a variety of minerals and rock fragments. The minerals include quartz, felspar, augite and horn-blende, mica and chlorite, while the dominant rock fragments are andesites, spilites, quartz-keratophyres and granites.Three groups of greywackes are recognized according to their mineralogy. The first, the Pyroxenous group, contains augite and hornblende. Rocks of the second group, the Intermediate group, are without these minerals, while the third group consists of rocks rich in garnet—the Garnetiferous group. These mineralogical differences are reflected in differences in the chemical analyses of the three groups. From consideration of the chemical and modal analyses it is suggested that differences in source rocks have influenced the composition of the greywackes more than variations in the intensity of alteration due to weathering and transport.It is concluded that the greywackes have been formed from the rapid erosion of a land mass largely covered by Ordovician volcanic rocks, but also with developments of lowgrade regionally metamorphosed rocks and others resembling Torridonian arkoses. Sedimentation features are due to accumulation controlled largely by the action of turbidity currents.

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