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ABSTRACT

The absolute abundance and flux of the Ext. Gp were generally greater at bathyal than at deeper abyssal depths and in more eutrophic rather than oligotrophic regions. Peak Ext. Gp fluxes, relative abundance and species richness occurred between the middle Eocene and early Miocene but some short abundance peaks in the Pliocene–MPT were associated with brief periods of locally high productivity.

The oldest Ext. Gp species originated in the Jurassic and eight more appeared in the Early Cretaceous. The peak of Ext. Gp species originations (2.7% myr-1) was Late Cretaceous, except in the Glandulonodosariidae (Paleocene) and Plectofrondiculariidae (middle to late Eocene). A secondary peak of originations (2% myr-1) occurred in the late Eocene across all Ext. Gp families. More than 80% of Ext. Gp species originated during the Cretaceous–Eocene (Greenhouse World) compared with c. 30% of modern deep-sea benthic foraminifera. The Cretaceous–Cenozoic Ext. Gp species had an even spread of species durations between five and 85 myrs (except plectofrondiculariids), with mean species durations of 50 myrs (Pleurostomellidae), 47 myrs (Glandulonodosariidae), 46 myrs (Stilostomellidae), 44 myrs (Ellipsoidinidae), 41 myrs (Chrysalogoniidae) and 20 myrs (Plectofrondiculariidae). Cenozoic Ext. Gp faunas are dominated by mostly long-lived species of just three genera – Strictocostella, Siphonodosaria and Pleurostomella.

The Ext. Gp was largely unaffected by the K/Pg or PETM extinction events. The late Eocene–Oligocene cooling was the first interval where the Ext. Gp showed an above background level of faunal change or instability and species turnover (1% myr-1, esp. Ellipsoidinidae, Plectofrondiculariidae, Glandulonodosariidae). After an early Miocene decline, extinctions began accelerating in the middle to late Miocene (1% myr-1) concurrent with progressive cooling of mid and high latitude climate and surface waters. During the Middle Miocene Climate Transition, Ext. Gp relative abundance declined and some local changes in assemblage composition occurred, but there was no pulse in global species turnover. The rate of extinctions accelerated further in the Pliocene (3% myr -1, dominantly stilostomellids), accompanied by significant changes in the composition of the dominant and overall Ext. Gp fauna as they became less diverse. With one exception, the remaining 40% of the total Cretaceous–Cenozoic diversity of the Ext. Gp disappeared during the Pleistocene, mainly during the MPT.

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