Driftwood dropstones in Middle Miocene Climate Optimum shallow marine strata (Calvert Cliffs, Maryland Coastal Plain): Erratic pebbles no certain proxy for cold climate

Published Date
Palaeogeography, Palaeoclimatology, Palaeoecology
15 March 2012, Vol.323:100–109, doi:10.1016/j.palaeo.2012.01.035

Author 

• Peter R. Vogt ^a,b,,
• Mary Parrish ^b

• aMarine Science Institute, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
• bNational Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA

Received 1 August 2011. Revised 21 January 2012. Accepted 27 January 2012. Available online 3 February 2012. 

Abstract

Sparse lithic erratics (pebbles to cobbles) sampled from three shallow marine strata deposited during the Middle Miocene Climate Optimum (MMCO, ca. 16–14 Ma) along the western Atlantic margin (exposed in the Calvert Cliffs, Maryland) suggest transport and deposition not from ice but from the roots of trees uprooted during floods and carried out to sea. Evidence for driftwood transport includes carbonized wood in the same strata. More than half the ca. 225 erratics were quarried in the largely metamorphic Piedmont province (including a few from the Port Deposit Gneiss, still outcropping on the lower Susquehanna River).

The lowest sampled bed (Parker Creek Bone Bed) is assigned to the ca. 15.7–15.5 Ma peak warmth of the MMCO, which we attribute in part to CO₂ from the coevally erupted Grande Ronde flood basalts (GRFB), the peak effusiveness episode of the Columbia River Flood Basalts (CRFB) The three sampled beds predate the ca. 13.9 Ma Antarctic cryosphere expansion, which may be recorded in the Calvert Cliffs by a unique buried channel.

Highlights

► Erratics in Mid-Miocene marine strata (Maryland, USA) rafted in tree roots, not ice. ► Erratic provenance mostly Piedmont, a few traced to modern gneiss formation. ► Sea-level fall during 13.9 Ma Antarctic ice expansion recorded as buried channel. ► Strata record Middle Miocene Climate Optimum (MMCO), greatest shelf water depths. ► MMCO warmth coincides with peak eruption rates (and CO₂?) of Columbia River basalts.

Keywords

Middle Miocene Climate Optimum

Ice-rafted detritus

Driftwood dropstones

Calvert Formation

Columbia River Flood Basalts

East Antarctic ice sheet expansion

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  Corresponding author at: Marine Science Institute, University of California at Santa Barbara, Santa Barbara, CA 93106, USA.

Copyright © 2012 Elsevier B.V. Published by Elsevier B.V. All rights reserved.

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