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Recognition of massive Upper Cretaceous carbonate bodies as olistoliths using rudist bivalves as internal bedding indicators (Campanian Merfeg Formation, Central Tunisia)

Negra, M. Hédi; Skelton, Peter W.; Gili, Eulàlia; Valldeperas, F. Xavier and Argles, Tom (2016). Recognition of massive Upper Cretaceous carbonate bodies as olistoliths using rudist bivalves as internal bedding indicators (Campanian Merfeg Formation, Central Tunisia). Cretaceous Research, 66 pp. 177–193.

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The Merfeg Formation (upper Campanian) of Central Tunisia crops out around the southwestern periclinal termination of Jebel el Kébar, near Sidi Bouzid. At its base is a massively bedded unit of locally dolomitized, sparsely fossiliferous micritic to microbioclastic limestone that contains several discrete, plurimetric mound-like bodies (lithosomes) of micritic limestone containing locally abundant rudists and corals. The lithosomes are separated laterally from one another by megabreccias and conglomerates containing clasts of similar lithology and are overlain, with sharp contact, by onlapping argillaceous pelagic limestones, within which are intercalated at least two more, somewhat thinner rudist/coral limestone units. This complex of facies is laterally equivalent to thicker, deep platform limestones of the Abiod Formation to the north and east, and to restricted carbonate platform facies of the Berda Formation to the south and west. The lithosomes have previously been interpreted as in situ downslope mudmounds that became capped by rudist and coral formations, cemented, and then surrounded by erosively emplaced debris flows. However, our detailed studies of rudist orientations imply variable and in some cases relatively high angles of bedding within the lithosomes with respect to the regional dip of the host strata. Such steep inclinations of internal bedding are unlikely to have been primary. Accordingly, we propose an alternative interpretation that the lithosomes were platform-derived olistoliths, emplaced along with the associated debris flow deposits. Micritic beds, neighbouring the olistoliths are of variable thickness and contain rare large inoceramids and randomly oriented rudists, as well as locally developed microbioclastic beds with planar and small-scale swaley cross stratification. These micritic and microbioclastic beds are, by contrast, interpreted as primary (i.e., non-olistostromal) slope deposits. Whether the proposed catastrophic collapses of the original platform margin were induced by sea-level fall or seismically triggered (or a combination of the two) remains uncertain.

Item Type: Journal Item
Copyright Holders: 2016 Elsevier Ltd
ISSN: 0195-6671
Keywords: Olistoliths; Rudist limestones; Late Cretaceous; Tunisia
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Environment, Earth and Ecosystem Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Item ID: 48849
Depositing User: Thomas Argles
Date Deposited: 07 Mar 2017 15:08
Last Modified: 15 Sep 2019 07:53
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