The Ordovician Strata of the Ennedi Plateau, Northeastern Chad (erdi Basin)

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.