Review of Miocene Larger Foraminifera

E. Charlotte Glenn

Miocene larger foraminifera were generally restricted to shallow (< 100 m), warm, clear, normal marine environments and were primarily dependent on brief drifting of juveniles and rafting on vegetation for dispersal. These factors are reflected in both regional and local occurrences.

Regional occurrences of Miocene larger foraminifera vary with bio-province and time. The three main foraminiferal provinces (Central American, Mediterranean, and Indo-West Pacific) developed through a combination of tectonics, eustasy, climate, and faunal evolution and migration. Important effects of Miocene tectonics included widening of the Atlantic, early Miocene occlusion of the western neo-Tethys, and northern movement of the Australian plate into the tropics. Changes in climate primarily expanded or constricted latitudinal provincial boundaries. Eustatic sea level variations caused by the destruction of the late Miocene Mediterranean fauna. Globally, Miocene faunas underwent a progressive loss of taxa. This is particularly noticeable in post-early Miocene faunas of the Mediterra ean and Central American provinces. Although post-early Miocene taxa evolved in all three areas, faunal migration was prevented by environmental barriers.

For a given time and province, the occurrence of larger foraminifera in well-preserved Miocene reef facies is related to paleoenvironmental factors of water depth, turbidity, water energy, and substrate and to post-mortem processes of transport and selective test destruction. Environmentally related changes in test morphology, together with the relative abundances of planktonic species and small benthic taxa, allow an estimation of the magnitude of the various environmental factors, even without detailed foraminiferal taxonomy.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.