Black Lake Reaction to Red River Course Changes

Julia H. Battle
University of Louisiana at Lafayette

The marginal lakes of the lower Red River in Texas, Arkansas and Louisiana are mentioned in geologists (Lyell 1830, Vetch 1906, Fisk 1944 and others), but the only studies that have been done on these lakes are on the recent deposits. This study of Black Lake, Natchitoches, Louisiana, compiled borings and test pit data from dams, and bridges and took original Vibra-core samples in the lake bottom and surrounding shores. Core analysis and Carbon- 14 dating of organic matter has revealed an unconformity in the depositional record. This unconformity coincides with base level change caused by a course change in the Red River. The Red River diverted its course to the Bayou Bourbeaux course just above Black Lake. And this course then captured Black Lake Bayou right below Black Lake. This capture caused a major base lowering for Black Lake Bayou that caused entrenchment and allowed Black Lake to drain. A non-depositional/erosional surface and soil formation can be see in the cores taken in Black Lake. The Red River again switched its course away from Black Lake Bayou allowing the base level to again rise causing aggradation in Black Lake Bayou and this in turn allowed the lake to refilled. The more recent sedimentation rates on top of this surface are similar to those seen at other lakes in this region. This study has allowed the dating of the Bayou Bourbeaux course at + 1400ybp, as well as a better understanding of the evolution of Black Lake.

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas