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The Oligocene-Miocene transition on coral reefs in the Falcón basin (NW Venezuela)


Johnson, K G; Sánchez-Villagra, M R; Aguilera, O A (2009). The Oligocene-Miocene transition on coral reefs in the Falcón basin (NW Venezuela). Palaios, 24(1):59-69.

Abstract

The Oligocene–Miocene Transition (OMT) was an interval of regional environmental and biotic change on Caribbean reefs. During the late Oligocene, a diverse Tethyan biota contributed to extensive reef building across the region, but by the early Miocene, reef building had declined, and a regional extinction had removed up to 50% of the late Oligocene diversity. The general decline in reef building in the Caribbean has been attributed to changes in regional water quality. New collections of scleractinian reef corals from four different units in the northwestern Falcón Basin of Venezuela include distinct late Oligocene and early Miocene assemblages. The distribution of fossil coral species and reef limestones suggests that the thick carbonates of the San Luis Formation were deposited during the late Oligocene and that changing water quality during the OMT resulted in the demise of San Luis coral-reef ecosystems. Previous studies have noted an increase in surface-water productivity after the OMT in the region and have suggested oceanographic reorganization as the primary cause; this interval, however, also coincides with a switch in the outlet position of an ancestral Orinoco River. A change in the terrestrial geography of South America might have caused the regional decline in reef building by altering surface-water characteristics, just as modern Orinoco and Amazon outflows exert strong control on shallow-water habitats off the coast of northeastern South America.

Abstract

The Oligocene–Miocene Transition (OMT) was an interval of regional environmental and biotic change on Caribbean reefs. During the late Oligocene, a diverse Tethyan biota contributed to extensive reef building across the region, but by the early Miocene, reef building had declined, and a regional extinction had removed up to 50% of the late Oligocene diversity. The general decline in reef building in the Caribbean has been attributed to changes in regional water quality. New collections of scleractinian reef corals from four different units in the northwestern Falcón Basin of Venezuela include distinct late Oligocene and early Miocene assemblages. The distribution of fossil coral species and reef limestones suggests that the thick carbonates of the San Luis Formation were deposited during the late Oligocene and that changing water quality during the OMT resulted in the demise of San Luis coral-reef ecosystems. Previous studies have noted an increase in surface-water productivity after the OMT in the region and have suggested oceanographic reorganization as the primary cause; this interval, however, also coincides with a switch in the outlet position of an ancestral Orinoco River. A change in the terrestrial geography of South America might have caused the regional decline in reef building by altering surface-water characteristics, just as modern Orinoco and Amazon outflows exert strong control on shallow-water habitats off the coast of northeastern South America.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Paleontological Institute and Museum
Dewey Decimal Classification:560 Fossils & prehistoric life
Language:English
Date:2009
Deposited On:25 Mar 2009 13:27
Last Modified:06 Dec 2017 19:21
Publisher:SEPM Society for Sedimentary Geology
ISSN:0883-1351
Publisher DOI:https://doi.org/10.2110/palo.2008.p08-004r

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