Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Harry Roberts

Abstract

Wetland loss in Terrebonne and Lafourche Parishes, Louisiana, largely results from two subsurface processes: (1) consolidation of recently deposited deltaic materials; and (2) active faulting. The impact of each is addressed. Cryogenic sampling techniques were utilized to obtain in-situ sediment samples from seven (7) modern deltaic environments in the greater Mississippi River delta plain. Consolidometer testing identifies peaty facies as most-subject to consolidation settlement, followed by prodelta and bay mud facies. Sandy facies from the other tested environments are not subject to significant consolidation settlement. Compression index values generated here are used to calculate settlement in a vertical stack at the P-1-90 and P-6S-93 borings. Results indicate most settlement occurs in the uppermost two (2) meters of section, although the uppermost ten (10) meters is identified in density studies. Data indicate a direct relationship between the thickness of peaty facies capping the recently abandoned Lafourche Delta and present patterns of coastal tract land loss. Locally, consolidation settlement is high where the thickness of consolidation-prone peaty sediments is great and vice versa. Interdistributary areas contain thick deposits of peaty sediments, and these areas are preferentially being lost to the expansion of greater Terrebonne Bay. A model for the development of Terrebonne Bay, which includes initiating erosion and subsequent compactional deformation is proposed. Active faults produce thicker Topstratum and Lafourche Delta sections and preferentially accumulate consolidation-prone sediments on their downthrown sides. The mapped distribution of faults is coincident with new areas of marsh development in the western and central parts of the study area.

Pages

375

Share

COinS