Semester of Graduation

Summer

Degree

Master of Science (MS)

Department

Geology & Geophysics

Document Type

Thesis

Abstract

A cluster of previously buried Taxodium distichum stumps are exposed and preserved in growth position at the bottom of a trough on the inner Gulf of Mexico (GOM) continental shelf in 18 m water depth and 13 km offshore Orange Beach, AL. Radiocarbon ages from wood and optically stimulated luminescence (OSL) dating of sediments suggest a Marine Isotope Stage (MIS) 3 age, or older. This study builds on the previous work of Gonzalez (2018) and Obeclz (2017). Five biofacies were identified in vibracore collected in 2015 and 2016: 1) the Holocene Mississippi-Alabama-Florida (MAFLA) sand sheet, 2) a Holocene interbedded sand and mud facies, 3) a Pleistocene interbedded sand and mud facies, 4) a paleosol, and 5) a Pleistocene interbedded mud and peat facies associated with the in situ stump horizon. The seafloor, a transgressive ravinement surface, and a basal contact between undifferentiated Pleistocene terrestrial facies and an older, steeply dipping clinoform package are resolved from geophysical data. Foraminiferal assemblage analysis revealed the transitional layer of interbedded sand and mud above the floodplain facies was late Holocene in origin and was part of a lower shoreface or marine-dominated estuarine environment. Stratigraphy of the area suggests paleotopographic relief was established prior to 56 ±5 ka and persisted until Holocene transgression. Two major factors allowed for unusual preservation of the in situ stump horizon: (1) paleotopographic relief created enough accommodation for sediment infill to bury and preserve the forest, and (2) significant pulses of sea level rise during MIS 3–4 produced widespread, rapid floodplain aggradation within the incised complex.

Date

5-25-2018

Committee Chair

Bentley, Samuel

DOI

10.31390/gradschool_theses.4727

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