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Determination of turbidity current erosional characteristics from reworked coccolith assemblages, Canary Basin, north‐east Atlantic
Author(s) -
WEAVER P. P. E.
Publication year - 1994
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/j.1365-3091.1994.tb01438.x
Subject(s) - turbidite , coccolith , geology , turbidity current , pelagic sediment , abyssal plain , pelagic zone , quaternary , oceanography , sediment , erosion , abyssal zone , paleontology , bathyal zone , range (aeronautics) , winnowing , structural basin , sedimentary depositional environment , carbonate , materials science , metallurgy , composite material , benthic zone , archaeology , history
Turbidites contain mixtures of sediments of various ages. These sediments can include both material that was eroded to form the initial turbidity current plus additions derived from erosion of the sea floor during transport. It has been possible to interpret the age range of sediments incorporated into individual turbidites from the Madeira Abyssal Plain by examining the proportions of microfossil (coccolith) species that they contain. The pelagic record of coccoliths is well known for the Quaternary period and shows a succession of dominant species or acmes each lasting a few tens of thousand years. Hence, erosion of sediment representing more than a few tens of thousand years will produce coccolith mixtures not seen in the pelagic record, but dependent upon the age range of the sediments that were eroded. This age range can be estimated by comparison with synthetic ratios of coccolith species created by combining ratios of species from successively older layers in the pelagic record. These can then be compared with the ratios found in individual turbidites until a match is found. The results show age ranges of 54–500 kyr for the sediment mixture in seven turbidites from the Madeira Abyssal Plain. Since the volumes of these turbidites are also known, and accumulation rates in their source areas can be estimated, it is possible to determine both the thickness and the area of the eroded sediment mass that generated the turbidity current. Minimum depths of erosion on the north‐west African continental margin vary from 8 to 50 m and minimum areas eroded from 1600 to 5800 km 2 . None of the turbidites examined contains a significant excess of surface sediment, suggesting that, once formed, the turbidity currents that transported them were virtually non‐erosional, and that they travelled several hundred kilometres in this state.