The Upper Jurassic and Lower Cretaceous series of southern Tunisia and northwestern Libya revisited

Abstract

The Upper Jurassic–Lower Cretaceous series in southern Tunisia and northwestern Libya are revisited in the light of fieldwork, facies patterns, biostratigraphy and wellbore data. Five megacycles delineated by major unconformities are described. The megacycles I & II (Callovian–Tithonian) capped by the Neo-Cimmerian unconformity contain marine, neritic and lagoonal facies that extend from the northwestern Libya (Shakshuk and Ar Rajban Fms) to southern Tunisia (Calcaires et Marnes de Foum Tataouine Fm). These equate with the neritic, Callovian–Upper Tithonian, Upper Nara Formation in the central Tunisia. The megacycle III contains marine dolostones, sands and lagoonal clays at the base, overlain by marine Green Clays that alternate dolostones and sands, capped by the Early Barremian unconformity. The megacycle IV that terminates in the Austrian unconformity is Barremian–Early Aptian coarse-grained sands enriched in vertebrate remains and quartz pebbles, and conglomerates with quartzite cobbles deposited in a broad area from northwestern Libya to central Tunisia. The megacycle V starts in the Middle–Upper Aptian dolostones and continues by coarse-grained Albian sand sequences with quartz pebbles and dolostone and clay stringers that pass upwards into the Upper Albian and Cenomanian carbonate, marl and gypsum sequences. The megacycle III correlates the Kabaw Formation in the northwestern Libya with the Sidi Khalif and Meloussi Formations in the central Tunisia (Berriasian–Hauterivian), and the megacycle IV correlates the lower Member of Kiklah Formation of northwestern Libya with the Barremian Boudinar, Bouhema and Sidi Aich Formations in the central Tunisia. Well to well correlations indicate that the Middle–Upper Aptian dolostones that are coeval with the Orbata Formation in the Salt Marshes rift-basin and central Tunisia, pinch-out toward the Dahar cuestas in Tunisia and the Nalut and Nafusa cliffs in northwestern Libya where Albian sands disconformably overlie their Barremian–Early Aptian counterparts or even the Berriasian Hauterivian megacycle III with Green Clays in exposed areas (Tataouine, Nalut) through the Austrian unconformity. The Stage ages and lithostratigraphic subdivisions suggested by previous authors are discussed and the new biostratigraphical results explain the geology of the region and correlations help establish a new lithostratigraphical chart for the study area.