Quaternary Carbonate Eolianites of the Bahamas: Useful Analogues for the Interpretation of Ancient Rocks?
James L. Carew, John E. Mylroie, 2001. "Quaternary Carbonate Eolianites of the Bahamas: Useful Analogues for the Interpretation of Ancient Rocks?", Modern and Ancient Carbonate Eolianites: Sedimentology, Sequence Stratigraphy, and Diagenesis, F. E. (Rick) Abegg, David B. Loope, Paul M. (Mitch) Harris
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Quaternary carbonate eolianites on Babaroian islands form a complex constructional topography composed of deposits formed during different glacioeustatic sea-level highstands. These eolianites constitute spatially and temporally discontinuous sediment packages. Within deposits formed during individual sea-level highstand events, eolianites from transgressive, stillstand, and regressive phases can be differentiated, but only if exposure is good and detailed study is undertaken. The eolianites may be stacked atop one another, or they may be in contact with marine deposits. Eolianites may overlie older marine deposits, interfinger with coeval marine rocks, or be overlain by younger marine facies. Depositional packages including eolianites that are deposited during a single sea-level highstand are commonly bounded above and below by erosion surfaces characterized by terra rossa paleosols. However, the patchiness of eolian deposition, the occurrence of calcarenite protosols, possible erosion of a paleosol during an ensuing transgression, and the possibility of soil movement downward into karst features can create confusion about actual unit boundaries. Interpretation of carbonate eolianite sequences in the ancient rock record may be enhanced if the complexities of the Quaternary eolianite record are appreciated. The depth of study required to successfully interpret well-exposed Quaternary eolianites implies that ancient eolianites, with less exposure and greater diagenesis, are unlikely to be resolved to a similar degree.
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Carbonate eolianites had long been considered to be limited to the Quaternary, but a number of Mesozoic and Paleozoic examples have been documented in the past 15 years. Thus, an increased awareness of carbonate eolianites is required to properly interpret the rock record and to assess their spatial and temporal distribution. The papers of this volume will help geologists to: (1) recognize carbonate eolianites and understand their preservation potential—recognitional criteria for most carbonate environments are common knowledge, but this is less true for carbonate eolianites; (2) understand their sedimentologic and diagenetic variability—diagenesis of carbonate eolianites has important economic considerations. Whereas Quaternary eolian limestones are commonly porous, Paleozoic and Mesozoic examples are typically tight owing to compaction; (3) understand the Psilionichnus (marginal marine) and Scoyenia (nonmarine) Ichnofacies—carbonate eolianites are not devoid of trace fossils; (4) interpret them in a sequence stratigraphic framework—interpretations of relative sea level during eolian deposition can be difficult, as differences between transgressive, regressive, and deflationsourced eolianites are subtle. Thus, the placement of sequence boundaries within interbedded eolian and subtidal carbonate successions is not entirely straightforward.