Sediments and Fauna of the Rhone Delta, France: ABSTRACT

Abstract

The Rhone delta is an example of a rapidly growing delta, prograding over a relatively steep slope into the essentially tideless, highly saline Mediterranean. Detailed studies of the sediments and microfaunas by the author and his colleagues have shown that rate of deposition, even more than depth, is the primary factor controlling the nature of the sediments and faunas offshore. Our classification of deltaic-marine environments is accordingly based on rates and depth of deposition. These studies, supplemented by earlier work in the land part of the delta (Kruit, 1955), have provided the basis for the interpretation of 26 core holes drilled to the top of the Pleistocene basement. A clearcut distinction can be made between the onlap complex of coastal-plain sediments formed under conditions of rising sea level during the late Pleistocene--middle Holocene and the offlap delta consisting of marine sediments laid down under conditions of stable sea level since 5,500 B.P. All core holes through the offlap delta reveal a transgressive-regressive sequence. Those sequences with a typical fluviomarine regressive development consist of (in upward direction): 1) a thin slow-deposition basal bryozoa bed; 2) moderate-deposition distal-fluviomarine clays; 3) rapid-deposition proximal-fluviomarine clays and silts; and 4) rapid-deposition fluviomarine-barrier sands. End_of_Article - Last_Page 347------------