Lower Pearl River Valley:  Pleistocene Coastal Plain and

Terrace Development.  Alluvial Allostratigraphy in Louisiana.

Ervin G. Otvos

Department of Coastal Sciences, University of Southern Mississippi,

703 E. Beach Dr., Ocean Springs, Mississippi  39564

ABSTRACT

Luminescence dates reveal that the youngest Pleistocene coastal plain that frames the entrenched lower Pearl Valley in Louisiana and Mississippi consists of Last Interglacial and Eowisconsin units; at one site, of mid-Wisconsin alluvium.  Sangamon–early Wisconsin (OIS 5d-4) coastal plain aggradation followed an earlier (OIS 7-6) coastal plain aggradation/incision cycle.  A complex history of recurring valley terrace construction and incision stages is apparent from valley terrace dates that range between 74.1- 31.9 ka B.P.  Latest Wisconsin and Holocene sediment veneer blanketed early and mid-Wisconsin deposits in the valley floor after deep entrenchment and intensive terrace erosion associated with Late Glacial Maximum (LGM) record low sea level at ~22-18 ka B.P.  Rejecting my luminescence dates, Heinrich (2006) continued to use only “conceptually” described theoretical allounits.  These coastal Louisiana Pleistocene entities are not bound by unconformities established in the subsurface are defined only by overlying and laterally adjacent terrace, valley, upland, and other landform surfaces.  The ages assigned to these “operational allounits” were only “inferred” and occasionally contradictory.  This “virtual” approach also “created” a large entrenched and subsequently filled, although entirely fictitious Pearl distributary valley.  While designated as “coastal” or “estuarine” in map legends, many, often shore-parallel ridge, in reality are not wave-built remnant barriers or beach ridges.  Often representing relict local drainage divides, occasionally carved along shore-parallel tectonic lineaments, they were excavated by surface erosion from the underlying Prairie alluvium.  The Prairie also buries the westernmost link of the northeastern Gulf interglacial Gulfport barrier chain at the Pearl delta.

Otvos, E. G., 2009, Lower Pearl River Valley:  Pleistocene coastal plain and terrace development.  Alluvial allostratigraphy in Louisiana.:  Gulf Coast Association of Geological Societies Transactions, v. 59, p. 573-583.

AAPG Search and Discover Article #90093 © 2009 GCAGS 59th Annual Meeting, Shreveport, Louisiana