Latest Paleozoic-Early Mesozoic Paleography, Northwestern Africa

Abstract

Late Paleozoic: Variscan orogeny in northwestern Africa was followed by regional stability and emergence. Marine deposition continued only in the southeastern corner along the southwestern margin of the Pelagian cratonic block. Early Triassic: Thick detrital deposits prograded eastward across the edge of the Pelagian block while nonmarine detrital sediments accumulated in the Northern Sahara Salt Basin to the west. Middle Triassic: Tethys spread across the eastern half of northwestern Africa. Its open marine facies was confined to the Pelagian block; a marginal facies reached the Northern Sahara Salt Basin and encroached on the eastern and northeastern flanks of the Variscan domain. Late Triassic to early Liassic: Grabens developed along northeasterly trends in the western half of northwestern Africa as well as along the more easterly-trending Gibraltar and South Atlas fracture zones. A vast saline province encompassed the northeasterly grabens in Morocco and adjacent Algeria, the Moroccan continental margin, the Saharan Atlas segment of the South Atlas fracture zone, and the Northern Sahara Salt Basin. Thick detrital deposits accumulated only in southwestern Morocco along and adjacent to the South Atlas fracture zone. During deposition of the upper part of these sequences multiple basaltic flows were extruded throughout the western half of the region. Along the northern margin of the Variscan domain and in the Saharan Atlas trend altered basaltic lava occurs in extruded evaporite-rich melange. Middle to late Liassic: Tethyan carbonate facies spread across most of northwestern Africa and reached the central Atlantic rift belt. Subsidence along fracture trends established in Late Triassic time induced a deeper-water (pelagic) facies at about the time that significant seafloor spreading began in the North Atlantic Basin.