The Ordovician strata of the Ennedi Plateau, northeastern Chad (Erdi Basin)

Abstract

In the Ennedi Plateau, northeastern Chad, Cambrian(?)–Ordovician to Carboniferous strata represent one of the most proximal succession of the north-facing Gondwana platform. This study presents preliminary results related to the c. 200 m-thick Lower Sandstones and overlying Bedo Formation, which essentially record Early to Middle Ordovician flooding events and the end-Ordovician glaciation and subsequent deglaciation. In the Lower Sandstones, fluvial-dominated deposits (prevailing cross-stratification, NW to NNE paleocurrent trends) include intervening high-frequency marine incursions (tidal deposits, ichnofacies including Cruziana and Arthrophycus). Above an erosional unconformity, the end-Ordovician glacial record consists of fluvioglacial conglomeratic deposits atop the Lower Sandstones, which are in turn superimposed by the fine-grained Bedo Formation. The latter interval, onlapping an exhumed erosion surface showing north-trending km-scale glacial lineations, shows glaciomarine deposits only at its base and possibly include Lower Silurian deposits in its upper part.

Keywords

• Erdi Basin
• Palaeozoic
• Africa
• Glaciation
• Sandstone