Maximum extent of ice sheets in Morocco during the Late Ordovician glaciation

Le Heron, D. P. and Ghienne, J. F. and El Houicha, M. and Khoukhi, Y. and Rubino, J. L. (2007) Maximum extent of ice sheets in Morocco during the Late Ordovician glaciation. Palaeogeography, Palaeoclimatology, Palaeoecology, 245 (1-2). pp. 200-226. DOI

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New field data demonstrate that during the Late Ordovician (Hirnantian) glaciation, an ice sheet expanding northwestwards over the Anti-Atlas range reached into the southern Meseta of northern Morocco. Its growth to a glacial maximum position resulted in extensive subglacial erosion and deformation including the development of soft-sediment striated surfaces and streamlined subglacial bedforms preserved between the High Atlas of Marrakech and Rehamna. These features imply that this ice mass extended > 200 km further than previously thought, and increase its size by at least ca. 190, 000 km2 (comparable in area to the UK). Correlation between a measured section in the High Atlas of Marrakech and that of the southern Meseta identifies sedimentary evolution within an ice-contact system common to both. These findings imply that the West African Craton and northern Morocco were in full glaciological communication during the latest Ordovician. Palaeogeographic reconstruction shows that beyond the ice sheet, south and southeastward palaeoslopes persisted on the shelf. A palaeohigh beyond the main ice sheet was a major source for sand, feeding delta systems that grew along the shelf as far as the shelf break. This palaeohigh probably formed as a result of rift shoulder uplift and supported a satellite ice mass. In the eastern Meseta, a thick (350 m) underflow-dominated deep-marine fan was fed both from this shelf delta system and from glaciogenic debris derived from the main ice sheet. The occurrence of this unexpected deep-marine area in northern Morocco implies that continued northward advance of the ice sheet was hampered by a dramatic break in bathymetry. Two depositional units are recognised across the Meseta, containing four distinct sedimentary cycles, each recognised as a glacioeustatic response to the waxing and waning of ice masses elsewhere in West Gondwana.

Item Type: Article
Uncontrolled Keywords: IA49 IA54 2007 P
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title: Palaeogeography, Palaeoclimatology, Palaeoecology
Volume: 245
Page Range: pp. 200-226
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 16 Feb 2009 13:02
Last Modified: 23 Jul 2013 10:07

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