During the early Holocene, rising waters of the Caribbean Sea flooded the Enriquillo Valley of southwestern Dominican Republic. A fringing coral reef developed and flourished along the margins of the Enriquillo Seaway for several millennia, until the seaway became restricted due to a combination of slowed sea-level rise, tectonic uplift, and increased sedimentation. Following changes in salinity and death of the coral reef by about 5 ka, meter-scale bioherms composed of the tubes of opportunistic, aggregating serpulid worms and associated with carbonate tufa that precipitated from the ancient lake or declining seaway waters formed along the steep walls of the valley over a period of 1,000 years or more. Paleoenvironmental conditions likely conducive to formation of these unusual bioherms include: non-normal marine salinity, warm and restricted waters, periods of stable water level, high Ca2+ and CO32− influx, and moderate wave action. Although apparently rare elsewhere in the rock record, occurrences of serpulid-tufa bioherms provide useful constraints on paleoenvironmental settings. In previous literature, variations in terminology used to describe both tufa and serpulid-tufa bioherms have hindered intersite comparisons. Herein, serpulid-tufa bioherm structures are described at macro-, meso-, and microscales, and the varied bioherm macromorphologies are classified as individual, clustered, terraced, and patch types. These form descriptions are compared with previously published classifications of similar structures; the goal is to facilitate development of a comprehensive and universal classification of serpulid-tufa bioherms to further understand their formation and paleoenvironmental significance.

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