Punctuated environmental change along the Holocene (< 6 ka) bank margin ofsouth-west Exuma Sound, Bahamas

Characteristics of environmental change along the Holocene (<6 ka BP) bank margin of south-west Exuma Sound, Bahamas, are defined by comparing mineral , isotope and lithologic stratigraphic patterns in deep-water (1081 m) slop e strata in ODP Hole 631A (Exuma Sound) with proximal (approximate to 6 km) shoal-water and insular geology of the Lee Stocking Island (LSI) region. A fter platform submergence, a bank-top transition from non-skeletal- to skel etal-dominated deposition occurred in the LSI region by approximate to 3.8 ka, and is recorded in the adjacent slope sediments by a contemporaneous ch ange in the abundance of transported allochems. The transition at Site 631 is punctuated by an anomalous shift in foraminiferal delta(13)C (-1 parts p er thousand) and delta(18)O (-3 parts per thousand), which may represent a period of climate change that established a brackish coastal zone at least 6 km wide, coincident (approximate to 3.8-4 ka) with bank-top erosion and p edogenesis. Non-skeletal allochems reappeared in Hole 631A sediments as the dominant transported allochem type by approximate to 2.4 ka, then again ov er the last several hundred years, and are contemporaneous with periods of increased platform-margin circulation in the LSI region. Such rejuvenation of platform circulation may have resulted from rapid relative rises in sea level, superimposed on the net gradual post-glacial rise. At Site 631, a pr ominent (25%) decline in aragonite abundance occurred during the period fro m 2.4 ka to the last few hundred years, and coincided with an increase in m agnesian calcite and skeletal debris, and a positive shift in foraminiferal delta(18)O values. These patterns lend support to the hypothesis that, dur ing this period, the LSI margin was barred by skeletal shoals, allowing ban k-top trapping of aragonite and hypersaline water, with increased coastal s alinity (resulting from reflux of hypersaline waters through the shoals) an d/or cooled coastal waters (caused by reduced exchange of warmed bank-deriv ed water relative to wind-generated upwelling). Along the Exuma slope, a di agenetic overprint may further enhance the recent decline in aragonite accu mulation. Integration of Holocene deepwater slope and bank-top stratigraphi es along the bank margin of south-west Exuma Sound reveals a pattern of pun ctuated environmental change superimposed on longer term development of int erglacial conditions.