A seismic stratigraphic investigation of the late Wisconsin Mississippi fanlobes

Author(s): Wagner, John B.
Source: 85p. Institution: Louisiana State University, Baton Rouge, LA, United States
Note: In English. 40 refs. Master's thesis
Summary: The two Late Wisconsin Mississippi Fanlobes are depositional units, which were identified on the basis of reflection terminations (including erosional truncation, toplap, downlap, and onlap) and define seismic sequences. The sequence boundaries defined are Horizon "20" (40-55,000 years B. P.), and Horizon "30" (approximately 84,000 years B. P.), and are interpreted to represent condensed sections representing quiet periods or periods of low sediment accumulation rates associated with high stands of sea-level. Seismically, the sequence boundaries are observed as high amplitude, sometimes seen as a doublet reflector, continuous reflectors that can be correlated nearly throughout the entire fan. The two fanlobe sequences defined were: Sequence VII, which has as its base Horizon "30" and as its top Horizon "20", and reaches a maximum thickness of 350 meters; Sequence VIII, has Horizon "20" as its base and the modern fan surface (Horizon "0") as its top, with maximum thickness of 500 meters in the middle fan region. The mapping of sequence boundaries (Horizons "20" and "30"), in two and three dimensions, illustrate the similarity of these paleo-isobath surfaces with the modern bathymetric map (Horizon "0"), indicating the cyclic nature of fanlobe development in response to changing sea-level. Three-dimensional modeling of the fanlobe sequences (Sequence VII and Sequence VIII), dramatically illustrates the influence of pre-existing topography on fanlobe geometry. Distribution of facies on the modern fan surface as well as within the fanlobe sequences, convey that mass movement and channel/overbank processes are primary processes responsible for fanlobe construction and are the main components of individual fanlobe sequences. Reflection configuration patterns (both internal and external geometries) within the depositional sequences, or fanlobes, were determined in order to perform a reflection character analysis on each of the four subdivisions (upslope erosional canyon, upper fan, middle fan, and lower fan) of a fanlobe sequence.
Year of Publication: 1988
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
Key Words: 20 Geophysics, Applied; 24 Surficial Geology, Quaternary Geology; Acoustical methods; Atlantic Ocean; Cenozoic; DSDP Site 615; DSDP Site 617; DSDP Site 620; DSDP Site 621; Deep Sea Drilling Project; Geophysical methods; Geophysical profiles; Geophysical surveys; Gulf of Mexico; IPOD; Leg 96; Lithostratigraphy; Marine environment; Marine sediments; Mississippi Canyon; Mississippi Fan; North Atlantic; Ocean floors; Paleoenvironment; Pleistocene; Quaternary; Sea-level changes; Sediments; Seismic methods; Seismic profiles; Seismic stratigraphy; Side-scanning methods; Sonar methods; Submarine fans; Surveys; Upper Pleistocene; Upper Wisconsinan; Wisconsinan
Coordinates: N240000 N290000 W0850000 W0900000
Record ID: 2012088307
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute.