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Coastal and Marine Geology Program
Stratigraphy and Geologic History of Anna Maria Island, Manatee County, Florida

West-Central Florida Coastal Studies Home
Open File Report: Second West-Central Florida Coastal Studies Workshop
Chief Scientist
John M. Pekala, Department of Geology, University of South Florida, Tampa, FL
Richard A. Davis, Jr., Department of Geology, University of South Florida, Tampa, FL


Figure 1: Map of Anna Maria Island showing locations of data collection.

A detailed study of various elements of the low- and mixed-energy, west Florida coast has been conducted over the past few decades, however, detailed stratigraphic analysis of drumstick barrier islands along the coast has been limited. A study has been designed, incorporating stratigraphic and seismic data, surface sediment analysis, process-response models, radiocarbon dating, and historical records to construct a complete geologic history of a Holocene drumstick barrier island. Anna Maria Island, located in Manatee County, Florida (Figure 1), is well suited for this type of study because of its classic drumstick morphology. Data obtained in this study will be useful in predicting future development, migration, and stability of Anna Maria Island as well as helping to understand the late Holocene history of the mouth of Tampa Bay. Information presented in this study adds to the database of knowledge of the west-central Florida barrier island chain, especially the stratigraphy and geologic development of barrier islands.

Thirty-five vibracores were taken in order to examine the stratigraphy along one shore-parallel and eight shore-normal transects through the island. A few cores penetrated pre-Holocene deposits ranging in age from 9730-18,010 YBP (Figure 2). Pre-Holocene deposits have been reported to exist at shallow depths (2-10 m below sea-level) at the north end of the barrier island chain (Davis and Kuhn, 1985; Evans et al., 1985) and south of Anna Maria Island in Sarasota Bay (Davis et al., 1989), and under back-barrier areas of Longboat Key (FitzGerald, 1995). Bases on these reports and an investigation of the seismic stratigraphy of the area (Duncan, 1993), it is likely that additional cores in the vicinity of Anna Maria Island would penetrate pre-Holocene deposits as well. Seismic data (Duncan, 1993) indicate that up to 20 m of valley fill in the mouth of Tampa Bay rests under the north end of Anna Maria Island.

Eight lithofacies have been designated. Shelly, fine to medium, clean sand containing shell beds is commonly found at shallow depths (<2m) and likely represents beach and washover sands (Figure 3). Below this unit lies highly bioturbated, fine sand, containing some mud and shell material, possibly deposited in a shallow back-barrier lagoon. In a few cores, an organic-stained, well-sorted, fine, quartz sand, lacking shell material has been found at depths greater than 2.5 meters, possibly representing pre-Holocene deposition (Figure 3). Additional stratigraphic and sedimentologic analysis will allow for the changes in morphology of a large drumstick barrier island to be traced through time and for the construction of a Holocene geologic history of Anna Maria Island (Figure 4).
stratigraphic log

Figure 2: Stratigraphic log of core AM-26 taken from the northern backbarrier area of Anna Maria Island and showing the hiatus between preserved marine and non-marine accumulations based on radiocarbon dating. Location of core is shown on Figure 1.

paleogeographic map sequence

Figure 4: Sequence of paleogeographic maps of Anna Maria Island showing various stages of development from about 3,000 YBP to the present.


  • Davis, Richard A., Jr. and Kuhn, Bernard J., 1985, Origin and development of AncloteKey, west-peninsular Florida, Mar. Geol., v. 63, p. 153-172.
  • Davis, Richard A., Jr., Knowles, Stephen C., and Bland, Michael J., 1989, Role of hurricanes in the Holocene stratigraphy of estuaries: Examples from the gulf coast of Florida, Journal of Sedimentary Petrology, vol. 59, no. 6, p. 1052-1061.
  • Duncan, David S., 1993, Neogene to Recent seismic stratigraphy of the lower Tampa Bay estuary: West-central Florida, Unpublished Master's Thesis, University of South Florida, Tampa, Florida, 101 p.
  • Evans, Mark W., Hine, Albert C., Belknap, Daniel F., and Davis, Richard A., Jr., 1985, Bedrock controls on barrier island development: West-central Florida coast, Marine Geology, v. 63, p. 263-283.

Coastal & Marine Geology Program > St. Petersburg Coastal and Marine Science Center > West-Central Florida Coastal Studies Project > Second West-Central Florida Coastal Studies Workshop > Morphodynamics > Stratigraphy and Geologic History of Anna Maria Island, Manatee County, Florida U. S. Department of the Interior | U.S. Geological Survey
Center for Coastal & Regional Marine Studies

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Updated May 06, 2013 @ 09:24 AM  (JSS)