HOW (AND WHY) THE CARBONATE SEDIMENTS AND SEASCAPES OF THE BAHAMIAN ARCHIPELAGO ARE ANOMALOUS: A GLOBAL PERSPECTIVE

Holocene and Pleistocene sediment accumulations of the Bahamian archipelago have been studied for over a century, and have provided many valuable insights that have been applied to interpret ancient analogs. Yet, in many regards, the sediments and the geomorphology of the region are quite distinct from other Holocene shallow-water carbonate systems globally. The purpose of this presentation is to highlight some of the contrasts and to speculate on possible controls.

Sedimentologically and geomorphically, the Bahamas are unique in that they include: 1) Ubiquitous peloids. Peloids are the dominant and volumetrically most abundant grain type across broad expanses of Bahamian platform interiors. Yet, peloids have only been recognized in sediment on three Pacific atolls, where they represent minor components. 2) Abundant ooids. Ooids occur across the archipelago, although their abundance generally increases southward. These ooids collectively form expansive shoal complexes, which can be larger and broader than most Pacific atolls. Recent ooids have been described on only two Pacific atolls. 3) Hardgrounds of marine cement, both near the margins and in the interiors of some Bahamian platforms. Hardgrounds can be expansive, and form a foundation for patch reefs in some platform interiors. Pacific platforms include broad marine cementation of note only near the margins; 4) Coral-green algal dominated marginal reefs, best developed on waveward margins. These systems contrast with the well-developed red algal ridges that occur at comparable geomorphic positions and surround many Pacific atolls.

These distinct aspects of Bahamian platforms are interpreted to reflect a unique convergence of physical and chemical oceanographic influences. Although microtidal, vigorous tides in the Bahamas exchange copious volumes of seawater that is markedly supersaturated with respect to carbonates, while simultaneously agitating the seafloor with every changing tide. Nowhere in the Pacific do these fundamental controls occur together as in the Bahamas. Thus, the distinct sedimentological and geomorphical character of the Bahamas provides unique constraints on fundamental controls on the character of carbonate sediments, today and perhaps in the geologic record.