Subaerial crusts, caliche profiles, and breccia horizons: Comparison of some Holocene and Mississippian exposure surfaces, Barbados and Kentucky

摘要

Roadcuts along Interstate Highway 64 in northeastern Kentucky expose a succession of Mississippian carbonates that contain a number of ancient exposure surfaces. These subaerial surfaces vary from thin surficial crusts to thick caliche profiles and complex brecciated horizons, and to a large extent they are similar, in both fabric and inferred origin, to subaerial surfaces developed on Pleistocene reef sediments exposed on Barbados. The most characteristic fabrics include laminations, micritic pellets, multiple episodes of fracturing, root voids, and a diversity of carbonate cement morphologies. In fact, variations in the form and distribution of the cements provide some of the most positive criteria for recognizing near-surface subaerial diagenesis. Evidence of vadose diagenesis 2 to 3 m below some of the ancient exposure surfaces indicates that relative fluctuations in sea level of at least this magnitude occurred during Mississippian time.