Climate-controlled mass extinctions, facies, and sea-level changes around the Devonian–Carboniferous boundary in the eastern Anti-Atlas (SE Morocco)

Abstract

Detailed sedimentological and biostratigraphical studies of successions in the eastern Anti-Atlas (SE Morocco) focused on changing depositional environments and reconstructions of sea-level changes during the late Famennian to middle Tournaisian. The investigations cover a transect from the central Maider to the easternmost and southern Tafilalt regions near the Moroccan/Algerian border. The Moroccan data are compared with the standard succession of the German Rhenish Massif and with the regional and global stratigraphic record. The results testify to high-frequency sea-level changes, including two global transgressive and anoxic events: the main Hangenberg Event (Hangenberg Black Shale level) at the top of the Wocklumeria Zone (Upper Devonian VI-E), and the Lower Alum Shale Event at the lower/middle Tournaisian (Lower Carboniferous I/II) boundary. Regionally, both anoxic intervals coincided with mass extinctions, followed by rapid radiation, especially of pelagic biota. A significant shallowing and regression occurred just below the Devonian–Carboniferous boundary at the northern margin of Gondwana and caused the sudden N/NW progradation of a large deltaic complex over 300–500 km. Thick siliciclastic successions filled fast subsiding synsedimentary troughs of the Maider and Amessoui Syncline (southern Tafilalt). Correlation with the glacial phases of southern Gondwana (South America, South Africa) indicates a glacial-eustatic origin of sea-level changes and a major sea-level fall in the scale of 100 m or more, coinciding with the main regressive phase of the extended Hangenberg Crisis interval. The new results are in accord with the hypothesis of an episode of cool-humid climate at the end of the Devonian that allowed contemporaneous glacial buildup in high latitudes and extensive clastic discharge in the middle latitudes of NW Africa.