DIFFICULTIES DETERMINING PALEOWIND DIRECTION FROM EOLIANITES ON AN ISLAND: AN EXAMPLE FROM PLEISTOCENE AND HOLOCENE EOLIANITES ON SAN SALVADOR, BAHAMAS

Islands are a complex setting for the deposition of eolianites with regional prevailing winds and local onshore winds both playing a role in the depositional process. It can be difficult to differentiate the extent of the role each of these wind types played in the deposition of eolianites on an island from evidence in the rock record. One way to overcome this difficulty is to collect paleowind data from as many locations as possible around the entire island. The island of San Salvador, Bahamas provides an outstanding location to study the direction of paleowinds that deposited Pleistocene and Holocene carbonate eolianites.

This research is an outgrowth of a class activity designed to provide students practice measuring strike and dip of bedding and cross-stratification in the field then calculating paleowind directions as vector means of the measured dip azimuths of cross-stratification in the lab. The results of the class activity differed from previously published interpretations of paleowind directions on San Salvador (White and Curran 1988; Caputo 1995) and beckoned for additional detailed study. During additional field seasons I collected measurements from eolian cross-stratification and calculated vector means of the cross-stratification dip azimuths for 11 locations on San Salvador that built on the initial results of the class activity. Vector means of the cross-stratification dip azimuths around San Salvador were directed onshore. The vector means directed onshore are indicative of deposition by onshore local winds. In contrast, deposition by regional winds would result in vector means all in the same general direction regardless of their location on the island. Lithified parabolic dunes with differing plan view orientations preserved on San Salvador are also indicative of deposition by paleowinds from multiple directions such as onshore winds.

These findings emphasize the need for practicing caution when assigning regional or local paleowinds as the driving force for eolianite deposition based on cross-strata measurements collected from only part of an island as previous studies have done on San Salvador. Not collecting cross-strata measurements from the largest possible geographic area of an island can lead to the misinterpretation of paleowind directions and paleo-atmospheric circulation.