SEDIMENTOLOGICAL AND STRATIGRAPHIC CHARACTERIZATION OF HOLOCENE ESTUARINE FILL IN WEEKS BAY, ALABAMA

Using a shallow piston coring device, we have collected 12 sediment cores up to 4 m in length from Weeks Bay, a small sub-estuary (c. 7 km²) of Mobile Bay in southwest Alabama. The cores were collected along North-South (5 cores) and East-West (7 cores) transects. Each core was examined for variations in stratigraphy, mineralogy, grain size and when possible, faunal content. Three of the cores along the north-south transect were sub-sampled for grain size and mineralogical variation on a 1-cm scale. The rest were sampled on a 3-cm scale. Age ranges were variable with depth of penetration, but one core yielded a C¹⁴ radiometric age of approximately 6000 years B.P. These data in conjunction with additional radiocarbon dates derived from deeper boreholes are being used to establish the Holocene stratigraphy of the Weeks Bay area.

Cores collected proximal to shorelines were dominated by sandy-silt and quartz sand and preserved a record of high energy, shoreface deposition. Cores collected from central portions of the bay consisted primarily of bioturbated, blue-grey, silty-clay, the most common sediment that is presently being deposited in sheltered and other low energy areas of Weeks Bay. However, the majority of the central Weeks Bay cores also contained sporadic, thin layers (<1 cm) of fine to medium sand. These layers were probably derived through episodic storms or flood events.

Sandy intervals rarely contain any organic detritus, but finer grain sizes contain diatoms, shell fragments, pollen and abundant comminuted plant detritus. Foraminifera have not been observed in any of the cores collected in this study.