In:
Géologie Méditerranéenne, PERSEE Program, Vol. 10, No. 3 ( 1983), p. 345-359
Abstract:
The term megaturbidite has been defined for huge gravity deposits of about 200 meters thick and 150 km of outcropping. Megaturbidites are mainly constituted by resedimented carbo¬ nate elements and they occur as interferencial deposits on the nor¬ mal silico-clastic turbiditic sedimentation of the South-Pyrenean Eocene basin. They are related with major exceptional events as major earthquakes, tsunamis, and major tectonic activity. Autochtonous (in-situ) megaturbidite occurs on the Upper Cretaceous Northern basin of Pyrénées. Evolution of this basin is mainly controled by the Southern instable margin, under orogenic activity of the future Pyrenean belt (SOUQUET P. and DEBROAS E., 1980) and of the Northern Iberian margin (Bay of Biscay, BOILLOT G. 1980). Several types of transfert system (GORSLINE D.S. and EMERY K.O., 1959, GORSLINE D.S., 1978) act to supply sedi¬ ments into sedimentary marine basins. By mean of those transfert systems, sediments proceeding from the Continent, and from the Carbonate margin quickly fill by agravity the deeper part of the Cretaceous margin quickly flysch basin. Those gravity deposits show interferencial sedimentation and series of megaturbidites. One of those megaturbidites, also known as «Grande Barre Calcaire» here called G. B.C., is more probably related with a huge mass-flow. This G.B.C. has been observed on more than 90 km of outcrop, reaching a maximal thickness of 63 m, which decreases East (63 m) to West (20 m on the Basque Coast). Reworked palaeozoic to permo-triasic fragments constitue a good tool to follow the hydrodynamic behaviour and evolution of the initial mass flow and its derivated deposits of which megaturbidites are directly related. Thus, megaturbidites represent very sharp isochrons which can be used in petroleum geology for seismic sedimentology and seismic stratigraphy, and which allow good correlation in sub-surface studies. Senonian paleogeography and anatomy of sedimentary basin can be precised by use of megaturbidites as «key-beds», as well as tectonic deformation which then modified the basin, as for example the tectonic out coming of the Precambrian-Paleozoic Basque massif of Ursuya-Baygoura.
Type of Medium:
Online Resource
ISSN:
0397-2844
DOI:
10.3406/geolm.1983.1277
Language:
French
Publisher:
PERSEE Program
Publication Date:
1983
SSG:
13
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