REGIONAL AND CLIMATIC CONTRIBUTIONS TO THE FORMATION OF HOLOCENE SERPULID TUBE/TUFA MOUNDS OF THE ENRIQUILLO VALLEY, DOMINICAN REPUBLIC

Unusual, meter-scale Holocene serpulid tube/tufa mounds of the Enriquillo Valley, Dominican Republic resemble buildups in only two other localities described in the literature: the Miocene Paratethys Basin of the Ukraine/Poland and the Upper Triassic Western Tethys of Italy. The rarity of such buildups and the similarity of these three localities indicate that the buildups form as a result of a very specific convergence of conditions. In each area, restricted waters of less-than-normal marine salinities reduced ecological competition and favored opportunistic serpulid aggregation, as well as concentrated calcium carbonate for tufa precipitation. In the Enriquillo Valley, limited hard substrate, calcium carbonate-rich springs entering the surface of ancient Lago Enriquillo, and periods of lake-level stability also contributed to mound formation.

Factors leading to mound formation in the Enriquillo Valley were in turn a result of the larger-scale paleoenvironment characteristic of the mid-Holocene Caribbean. Around 5 ka, slowed sea level rise, possible regional tectonic uplift, and a northward migration of the Intertropical Convergence Zone (ITCZ) restricted the ancient Enriquillo seaway. This restriction caused the demise of the seaway's fringing coral reef, whose fossil colonies often form the substrate of the younger serpulid tube/tufa mounds. Later ITCZ migration resulted in repeated changes in Lago Enriquillo water level and salinity, creating conditions that supported not only mound formation, but also a diverse array of molluscs and ostracodes. The combined Enriquillo fossil record between 5.5 ka and 3.5 ka reflects dramatic and frequent small-scale environmental changes that were triggered by global climate variations.