Abstract: Geologic Setting and Preservation of a Late Pleistocene Bald Cypress Forest Discovered on the Northern Gulf of Mexico Continental Shelf (2016 Ocean Sciences Meeting)

Geologic Setting and Preservation of a Late Pleistocene Bald Cypress Forest Discovered on the Northern Gulf of Mexico Continental Shelf

Suyapa Michell Gonzalez Rodriguez¹, Samuel J Bentley², Kristine L DeLong³, Kehui Xu⁴, Grant L. Harley⁵, Andy Reese⁵ and Jeffrey Obelcz⁶, (1)Louisiana State University (LSU), Department of Geology and Geophysics, Baton Rouge, LA, United States, (2)Louisiana State University, Baton Rouge, LA, United States, (3)Louisiana State University, Department of Geography and Anthropology, Baton Rouge, LA, United States, (4)Louisiana State University, Department of Oceanography and Coastal Sciences, Baton Rouge, LA, United States, (5)University of Southern Mississippi, Geography and Geology, Stennis Space Center, MS, United States, (6)Coastal Studies Institute, Baton Rouge, LA, United States

Abstract:

Following landfall of Hurricane Ivan in 2004, a previously buried bald cypress forest (Taxodium distichum) was discovered on the continental shelf seafloor, offshore of Orange Beach, Alabama, USA, in ~20 m of water. The forest is preserved as stumps in life position with little evidence of decay and large pieces of trunks, roots, and branches. Analysis shows the forest is older than can be dated with conventional C-14 methods. Comparison of Pleistocene sea level curves with the study area depth suggests that the forest developed and was likely buried during marine isotope stage 3 or 4, or perhaps older stages. Condition of sampled wood suggests that the forest was buried and preserved in anoxic sediments for millennia, prior to recent exhumation. To better understand the puzzling geological conditions that could allow forest preservation during sea level fall and shelf exposure spanning >30,000 years, submersible vibracores (to 6 m length) and geophysical data (swath bathymetry, sidescan, and chirp subbottom) were collected in August 2015. Cores are being analyzed using a Geotek Multi Sensor Core Logger, granulometric and sediment composition analyses, and a wide range of paleoenvironmental observations. This presentation focuses on the geological setting and mode of forest preservation.

Preliminary analysis of sediment types and stratigraphy in cores shows that the local stratigraphy is broadly consistent with previous regional shelf-stratigraphic studies, consisting of (top to bottom) a surface layer of Holocene transgressive sands (to ~3 m thick) unconformably overlying Pleistocene terrestrial and coastal deposits. However, the Pleistocene lithofacies (fluvial, backswamp, or possibly delta plain muds) differ considerably in both depositional environment and degree of environmental preservation compared to previous studies. Ongoing analysis will focus on elucidating the succession of events that allows preservation of this unique Pleistocene sedimentary archive.

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