ABSTRACT

A paraconformity representing at most several thousand years separates vadose-cemented eolianites from modern uncemented dune sands on the southern part of Isla Cancun, Yucatan Peninsula. Both eolian sands are carbonate grainstones composed of thinly coated skeletal fragments. Structures and textures which could be preserved in the rock record to indicate this paraconformity include: 1) stairstep erosional surfaces where weakly cemented older eolianite has been differentially eroded along bedding planes, 2) sand-filled polygonal cracks apparently formed by compaction, 3) local encrustation of the older eolianite's surface by algae and/or incipient calichification, 4) small solution pits, 5) wind-scour marks, and 6) a variety of pseudoburrow structures formed by vegetation, ants, and d ssolution.

Comparable (in terms of time) paraconformities are probably common in the rock record but would be difficult to recognize because 1) rocks above and below are of similar composition, 2) large exposures are needed to recognize the diagnostic structures, 3) pseudoburrows may be abundant, and 4) distinctive diagenetic textures may be obscured by subsequent diagenesis. Furthermore, eolianites such as these have low preservation potential. However. the diagnostic textures for recognizing this paraconformity could form in subtidal carbonates during subaerial exposure. Some could even form along a subtidal paraconformity surface by processes of submarine erosion of semilithified marine-cemented bottom sediments.