First evidence of the Upper Jurassic deposits in the Middle Atlas (Marmoucha syncline, Morocco) and connections to the Tethyan Domain

Abstract

The Marmoucha syncline is located in the eastern part of the Middle Atlas. In this syncline, the “Gypsum marls” (Bathonian-?Callovian) are covered by red detrital deposits which outcrop in Aït Bazza locality. The upper limit of these detrital deposits is below the transgressional unconformity of the Albian?-Cenomanian marine series. The present work introduces a synthesis of stratigraphical, sedimentological and micropalaeontological studies, which has led to new dating and to the identification of different depositional environments. These results have allowed us to define a new chrono-lithostratigraphic unit, the "Aït Bazza Formation", which comprises three superimposed members AB1-3 separated by two sedimentary discontinuities. This formation, exceeding 300 m in thickness, is formed by conglomerate, sandstone, sand and varicoloured marls. Micropalaeontological bulk sampling in marly horizons revealed associations of charophytes and ostracods, particularly in Member AB2. The charophytes are represented by oogonia of small Porocharaceae, Clavatoraceae such as Hemiglobator rectispirale, Dictyoclavator ramalhoi, and Nodosoclavator bradleyi that characterise the Tithonian. The ostracod microfauna is diverse, consisting of non-marine and lagoonal- shallow marine species at several horizons, associated with sea urchin spines and rare foraminifera, which indicate fluvio-deltaic sedimentary environments subjected to marine influences. This new age constraints of AB2 Mb to the Late Jurassic, and the discovery of marine influences in this eastern part of the folded Middle Atlas, consequently indicates the existence of palaeogeographical connections with the Tethyan domain located to the NE in the Rif foreland.