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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 57 (1973)

Issue: 4. (April)

First Page: 776

Last Page: 777

Title: Paleontologic Evidence for Mid-Miocene Refrigeration, from Subsurface Marine Shale, Louisiana Gulf Coast: ABSTRACT

Author(s): Dorothy Jung Echols, Doris Malkin Curtis

Article Type: Meeting abstract


The Harang facies, a regional, diachronic middle Miocene shale in Louisiana, has characteristics that can be interpreted as indications of deep-water or cold-water deposition. It consists of a seaward-thickening subsurface wedge of dark-gray to brown or black marine shale and clay with interbedded sandstones, containing a distinctive foraminiferal biofacies. The biofacies is characterized by an abundant and diversified benthonic foraminiferal fauna, including huge arenaceous forms

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and a small percentage of planktonic Foraminifera. Globorotalia fohsi, G. mayeri, G. menardii, and other planktonic species are sinistrally coiled. The change from random to predominantly sinistral coiling coincides approximately with the inception of Harang deposition (±12-14 m.y. B.P.). The faunal assemblages indicate a muddy-water, outer neritic to bathyal environment, and suggest a cool water mass. The apparent anomaly of a cold-water fauna in this stratigraphic position in this area might be explained by upwelling, paleogeographic changes, and/or significant Miocene refrigeration.

During the time span that includes Harang deposition, continental glaciation in Antarctica, cold-water invertebrate faunas, cool-climate floras, and other evidences of cool climate in many parts of the world indicate mid-Miocene refrigeration. Although some conflicting evidence also exists, we conclude that the distinctive characteristics of the Harang biofacies are related to a cool water mass which was part of a worldwide cooling phenomenon.

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Copyright 1997 American Association of Petroleum Geologists