The Diatomaceous and Fish-Bearing Beida Stage of Algeria

Abstract

The Beida stage is an Upper Miocene marine deposit of alternating diatomite, foraminiferal marl, clay shale, opaline marlstone, limestone, volcanic ash, and other sediments. It extends for over 200 kilometers east-west through the coastal ranges of Western Algeria. In addition to diatoms and foraminifera, it contains radiolaria, sponge spicules, and a variety of larger invertebrate fossils, together with well-preserved fossil fish. It commonly shows traces of petroleum and is undoubtedly the mother-rock of such oil, the origin of which is referable to the diatoms and other micro-organisms, and probably in part to the fish. The association of diatomite, ash, fish skeletons, and petroleum mark it as a special type of deposit, which likewise occurs in numerous other countries-notably in the Miocene of Sicily, Italy, the Caucasus, and California. The lithologic and faunal evidence indicates that the Beida was formed in a comparatively shallow and quiet arm of the sea. The abundance of diatoms is believed to be related to the silica supplied to the sea by volcanic eruptions. The fish comprise a mingling of littoral and pelagic forms, with some that represent brackish and even fresh-water forms. Their abundance in several horizons represents recurrent disasters to the fish life, probably connected with vulcanism, followed by rapid burial of the bodies of the fish along and near the shores.