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STUDY TITLE: Investigation of an Ancient Bald Cypress Forest in the Northern Gulf of Mexico

REPORT TITLE: Investigation of an ancient bald cypress forest in the Northern Gulf of Mexico

CONTRACT NUMBER: M15AC00016

SPONSORING OCS REGION: Gulf of Mexico

APPLICABLE PLANNING AREA(S): Central Planning Area

FISCAL YEAR(S) OF PROJECT FUNDING: 2016–2018

COMPLETION DATE OF REPORT: December 2019

COSTS: $261,075

PROJECT MANAGER(S): Kristine L. DeLong1, Samuel J Bentley Sr.1, Kehui Xu1, Grant L. Harley2, Carl 

Andy Reese3, and Alicia Caporaso4 

AFFILIATION of Project manager: 1Louisiana State University, 2University of Idaho, 3University of 

Southern Mississippi, 4Bureau of Ocean Energy Management

ADDRESS: 1201 Elmwood Park Blvd, New Orleans, LA, 70123

PRINCIPAL INVESTIGATOR(S)*

: Kristine L. DeLong, Samuel J Bentley Sr., Kehui Xu, Grant L. Harley, 

and Carl Andy Reese

KEY WORDS: Quaternary Geology, Paleolandscapes, Paleoclimatology, Dendrochronology, Palynology, 

Macropaleontology, Regional Stratigraphy, Foraminifera, Site Preservation Modeling, Marine Geophysics, 

Sea Level, Bald Cypress, Paleobotany

BRIEF ABSTRACT: Preserved landscapes, such as buried wetland forests and marshlands, contain 

valuable information of past ecosystems, climate, and physical geology and geography. Identifying the

geological and geophysical characteristics of these formerly terrestrial habitats informs the Bureau of 

Ocean Energy Management’s (BOEM) Outer Continental Shelf (OCS) management needs and 

objectives. This project gathered and refined information on the geological, geophysical, ecological, and 

paleo-environmental characteristics of this glacial-age forest preserved on the OCS; the information will

help BOEM make responsible environmental decisions for proposed oil, gas, and other activities on the 

OCS. This project’s overarching goal was to document the well-preserved bald cypress forest buried in 

the sediments in the Northern Gulf of Mexico (GOM) continental shelf and to develop a model for other 

potential sites that could contain preserved wood on millennial and longer time scales. This study aimed 

to provide information on Northern GOM coastal geomorphology, sediment preservation of macro- and 

micro botanicals, and the glacial age environment.

BACKGROUND: In late 2004, a few months after Hurricane Ivan made landfall near Gulf Shores, 

Alabama, a local fisherman discovered an area with abundant fish. (Figure 1). Subsequent surveys found 

a 2.2 m depression in flat seafloor bottom characterize by sand and clay sediments. Scuba surveys in 

2013 found the depression contained layers of gray clay sediments with well-preserved woody remnants 

and several stumps exposed or partially exposed. Well-preserved wood has been found in anoxic peat 

bogs in freshwater environments, where anoxic sediments limit biological organisms and decomposition, 

but wood is rarely preserved in marine environments. This unique site and study have produced valuable 

information on Gulf Coast coastal geomorphology, sediments that preserve macrobotanicals, and glacial 

environmental and climate dynamics.
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Figure 1. Approximate location of the submerged cypress forest study site.

OBJECTIVES: The primary objective of this project was to document and characterize an area in the 

Northern GOM, off the coast of Alabama, that contains well-preserved ancient bald cypress stumps in 

order to generate information on the geological, geophysical, ecological, and paleoenvironmental 

characteristics of this geographical site type.

DESCRIPTION: The research was conducted by an interdisciplinary team consisting of two geological 

oceanographers with expertise in geoacoustics, coastal geological oceanography, and coastal sediment 

dynamics, three paleoclimatologists with expertise in the coastal GOM region, tree-rings, and pollen used 

to reconstruct past vegetation and climate, and one marine archaeologist, with additional researchers and 

graduate students participating in the field sample collection and laboratory analyses. 

Wood samples were collected in 2013. Sediment cores were collected in 2015 and 2016 at the site and at 

the area to the east and south of the exposed tree stumps. The cores were analyzed to characterize the 

sediments at the site, build stratigraphic relationships with the samples dating using radiometric and 

Optically Stimulated Luminescence methods, and to understand paleoenvironmental conditions.

Geophysical data collected used an Edgetech 512i CHIRP (subbottom sonar, side-scan sonarsub-bottom 

profiler), Edgetech 4600 (multibeam and side scan sonar), Edgetech DS2000 (combined CHIRP subbottom and side-scan unit), Valeport sound velocity profiler, Hemisphere Differential GPS/SMC motion 

compensation system, and a marine magnetometer. Survey lines of 75 m and 100 m in strike and dip 

orientation, respectively, provided ~50 to 100% swath overlap of the bathymetric data. This survey 

methodology yielded continuously generated bathymetric digital elevation models and backscatter maps, 

and a dense grid of two-dimensional seismic reflection profiles imaging the top 10–20 m of the seafloor 

subsurface. 
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Laboratory methods included core logging and descriptions, organic content determinations (loss on 

ignition), pollen, and microfossil analyses. Wood samples collected from the site were shared among

Louisiana State University, the University of Southern Mississippi, and the University of Idaho for analysis. 

Geophysical data collected during field operations were processed and analyzed. Sediment cores were 

logged and analyzed for sediment, pollen, seeds, and microfossils.

SIGNIFICANT CONCLUSIONS: Buried tree stumps were not confidently resolvable within the subsurface 

using CHIRP sub-bottom profiling. 

Pollen assemblages have been determined for one recovered core (15DF1). The peat and mud deposits 

in this core have been dated to MIS 3–4 during a period of rapid global sea-level variations, providing a 

glimpse into the response of late Pleistocene plants to climate change and sea-level rise. Based on the 

radiocarbon dates obtained in the upper section of the peat, the marine transgression that probably 

caused the final burial of the peat occurred around 40 ka BP near the end of MIS 3. Pollen results within 

the peat suggest a transition from a cypress-tupelo gum backwater to a more open community dominated 

by grasses and sedges. During this transition, there may be evidence of a no-modern analog cypress–

alder community.

A confident causal mechanism for the synchronous mortality and rapid growth variability at the end of the 

Submerged Forest tree-ring chronology (SFC) record could not be identified in the tree-ring analysis. The 

most likely causes were either singular or combined events of drought and saltwater intrusion from sealevel rise or storm surge. The 489-year SFC record presented provides a baseline on which to build future 

research at the site.

A working hypothesis could explain forest preservation based on radiocarbon dates in the range of ~42–

45 ka cal BP (see Table 2 in the report), regional stratigraphy and geomorphology and the published 

range of sea sea-level estimates for MIS 1–4. If organic-rich sediments (identified in core 15DF1) were 

deposited ~42–74 ka cal BP, then elevation and sea level estimates combined with and OSL dates (see 

Table 3 in the report) suggest that the forest location was well inland from the coast at the time of forest 

growth, ~30 to 50 m above the paleoshoreline, which is consistent with bald cypress biogeographical 

distribution. A short pulse of sea-level rise (~65 ka) could potentially have caused floodplain aggradation 

at the forest site, burying and preserving the forest through subsequent sea-level fall, transgression, and 

ravinement. An alternative hypothesis is that forest burial was not associated with allogenic forcing, but 

was instead caused by an autogenic process, such as a crevasse splay of the river channel proximal to 

the forest.

STUDY RESULTS: The swamp sediments found in cores that were identified in topographic lows are 

hypothesized to have been preserved and buried by fluvial and/or floodplain sediment accumulation. 

Accommodation for this sediment accumulation and preservation is indicated in the local divergence of 

the two lower seismic surfaces in Figure 2. As sea level rose and transgression occurred during the Late 

Pleistocene, sediments within the incised valleys were first eroded by transgression of the coastline and 

associated wave energy and later covered by Holocene shelf sands as sea level rose, causing the 

coastline position to retreat. Coastal wave erosion during transgression likely eroded high ground, but 

enough sediment layers remained to keep the cypress forest blanketed and favoring preservation.

If other locations on Northern GOM had similar geomorphology and environmental conditions, then other 

sites located within GOM incised valleys at similar elevations may also contain preserved glacial age 

forests. It is likely that a “bathtub ring” of other sites located within GOM incised valleys at similar 

elevations were also preserved. Such locations may contain other well-preserved sediments, wood, and 

other artifacts that may provide further insights into paleo-oceanographic and paleoenvironmental studies 

of continental margins around the world.
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Figure 2. Three-dimensional subsurface model of the study area

A) White dashed circle represents where stumps are exposed on the surface. B) Core data (15DF1) were

imported to aid interpretations with grain size (red) and LOI (green) shown. The transgressive surface is 

relatively flat-lying while the basal surface geometry exhibits topographical highs. No cores penetrated the 

basal surface. Vertical exaggeration (V.E.) is 50x.

STUDY PRODUCT(S):

DeLong KL, Bentley Sr SJ, Xu K, Harley GL, Reese CA, Obelcz J, Gonzalez S, Truong JT. 2020. 

Investigation of an ancient bald cypress forest in the Northern Gulf of Mexico. New Orleans (LA): 

US Department of the Interior, Bureau of Ocean Energy Management. 108 p. Contract No.: 

M15AC00016. Report No.: OCS Study BOEM 2020-034. 

*

P.I.’s affiliation may be different than that listed for Project Manager(s).