Paper No. 13
Presentation Time: 12:00 PM


CAPUTO, Mario V., Department of Geological Sciences, San Diego State University, San Diego, CA 92182 and GLUMAC, Bosiljka, Department of Geosciences, Smith College, Clark Science Center, 44 College Lane, Northampton, MA 01063,

Previously studied physical and petrologic features indicate an eolian origin for Holocene calcarenites at the peninsular ridge of North Point on San Salvador Island, Bahamas. Further study revealed clues to internal architecture, dune morphology, and weather conditions preserved in the Holocene North Point Member of the Rice Bay Formation. Wind-ripple strata are primary architectural elements. Sets of these strata are bounded by discordant erosional surfaces, and comprise >90% of stratification, forming topset, brinkset, and especially foreset beds as wind-ripple crossbeds. Secondary elements are bedsets of sandflows with wind-ripple and grainfall strata. Such bedsets are scarce, are no more than 1 m thick, and are termed slipface crossbeds. Dip azimuths of bedset bounding and reactivation surfaces, slipface crossbeds, and dune flanks span nearly 360o. Dome dunes are suggested by the wide span of dip azimuths, scarcity of slipface crossbeds, and overall mound-swale landscape of the present North Point peninsula that mimics Holocene dune landscape. Deeply eroded exposures show cores of smaller juvenile dome and lobate dunes buried by overlapping larger mature domes and interdome swales.

Wind-ripple strata are disturbed locally by insect burrows. Plant traces and caliche crusts increase in abundance upward and are prevalent in the upper 1-2 m of dome summits. Structures created by climbing adhesion ripples indicate wind-transported sand during rainfall. Crest orientation and northeast climb of adhesion ripples, crest orientation and southwest climb of some wind ripples, and strata of juvenile lobate dunes convex to the southwest show a prevailing southwest flow direction of Holocene Northeast Trade Winds. Coastal moisture rendered the dune sand cohesive so that avalanches or grainflows happened rarely when sand was dry and wind speed and sediment transport fostered the migration of small transverse dunes. Because basal parts of the North Point Member are heavily weathered or lie below present sea level, dune growth on the emergent North Point peninsula during Holocene time is conjectural. In the path of unobstructed trade winds, low mounds of rippled sand enabled growth of small dome, lobate, or perhaps transverse dunes. On this foundation, mature dome dunes merged laterally to build a peninsular ridge.