THE QUATERNARY FLUVIO-LACUSTRINE FORMATIONS OF TIDDAS (SEPTENTRIONAL BORDER OF CENTRAL MOROCCO) SEDIMENTOLOGY, PALEOENVIRONEMNT AND CHRONOSTRATIGRAPHIC PRECISION

Quaternary continental formations identified at about twenty km southwest of Tiddas (Province of Khemisset, central Morocco) on the left bank of Bou Regreg River, consist of the Hançala, the Zwirga, the Bir Dallah and the Bir Oughioul Formations. The present work consists of a sedimentological study of this later Formation which is found to have been deposited in fluvio-lacustrine environments and of being of and age posterior to 0.62 Ma, e.g. Middle Pleistocene (Moroccan Amirian) based on basaltic tuffs fond at the base of this Formation. These tuffs were petrographically correlated with Quaternary basalt which was radiometrically dated in Central Morocco. Both this age and the sedimentologically inferred depositional environments of this Formation are corroborated by the discovery of skeletal remains of the genus Hippopotamus in its deposits. In fact, a comparative study of the discovered bones of this specimen with two known fossil species of Western Europe (Hippopotamus major and Hippopotamus incognitus) and with the current form Hippopotamus amphibious indicates that the Tiddas Hippopotamus is of an intermediate age between these fossil species and can thus be attributed at late Middle Pleistocene-early Upper Pleistocene age. In fact, the comparative study of the discovered remains of Hippopotamus of Tiddas both with the present-day form (Hippopotamus amphibus) and with two European specimens (Hippopotamus incognitus and Hippopotamus major) places Hippopotamus of Tiddas in the interval of late Middle Pleistocene-Early upper Pleistocene. During this period, the northern margin of Central Morocco was, most likely, characterized by a wetter climate than the current one, a distensile tectonics and an intense volcanism upstream of the Bou Regreg River. These conditions would have favored the installation of fluvio-lacustrine environments where aquatic forms, such as Hippopotamus, proliferated.