Abstract: Submerged Relict Forests off Northwest Florida Coast--Paleoenvironmental Significance

Marc A. Lawrence, H. K. Brooks

Pine taproots (Pinus ellioti) in growth position and associated deposits including freshwater peats are exposed below sea level in an artificial channel cut across the barrier spit at the mouth of St. Andrew Bay, near Panama City, Florida. This unique exposure from a tectonically stable area offers a view of a barrier in cross section with implications on middle Wisconsin and Holocene sea-level curves.

Two major sequences were identified. The lower sequence from 21 to 50 ft (6.4 to 15.2 m) below mean sea level is interpreted as a swamp or barrier-flat deposit and lies conformably on a lagoonal deposit. The remains of at least 200 pine trees are present along the side of the present ship channel. The forest remnants are mostly taproots in growth position apparently preserved by their high pitch content and rapid burial during storm conditions. Representative tree remains and peat samples from the same strata produced a stratigraphic sequence of radiocarbon ages ranging from 28,120 + 2,080/ - 1,650 to 21,980 ± 790 years BP dating this deposit as middle Wisconsin. These deposits are capped by a resistant humate-cemented sand layer probably formed under ground-water conditions duri g the subsequent lower sea-level stand. Paleoclimatic indicators in the sediments are characteristic of a more arid environment.

Lying unconformably on the middle Wisconsin deposits is a barrier sequence from 21 ft (6.4 m) below MSL up to the present dunes. Within this sequence from 7 to 10 ft (2.1 to 3.0 m) below MSL another exposure of pine taproots in growth position and peat yields radiocarbon ages of 4,890 ± 100 to 4,720 ± 110 years BP, dating this sequence as Holocene.

These data, coupled with previous studies of similar deposits containing tree remains in growth position 2 mi offshore, give a more accurate picture of the environmental evolution of this area and provide additional information as to middle Wisconsin and Holocene sea-level fluctuations and barrier formation and migration.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA