Carbonate Eolianites from a Eustatically Influenced Ramp-Like Setting: The Quaternary of the Southern Arabian Gulf
Alun H. Williams, Gordon M. Walkden, 2001. "Carbonate Eolianites from a Eustatically Influenced Ramp-Like Setting: The Quaternary of the Southern Arabian Gulf", 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, accumulated through eolian reworking of marine sediments, occur extensively in the southern Arabian Gulf. In Abu Dhabi and Qatar these include widespread deposits belonging to the middle-late Pleistocene Ghayathi Formation, scattered coastal outcrops belonging to the Sangamonian Fuwayrit Formation, and semilithified deposits believed to be Wisconsin-Holocene in age. Deposition of these eolianites was intimately linked to fluctuations of sea level and climate. Sea level has controlled the amount and the nature of sediment available for eolian deposition, whereas paleoclimate has been the main factor influencing the size and location of the eolianites. The Ghayathi Formation provides an example of “regressive eolianites,” which were deposited through deflation of the shoreface during and following sea-level fall, accompanied by inland migration of eolian sediment. In contrast, the Fuwayrit Formation eolianites were deposited during highstand. The Wisconsin-Holocene semilithified eolian sands are best explained in terms of deposition during transgression. Negligible subsidence is believed to have occurred since the eolianites were deposited.
Modern carbonate dune accumulations are rare in the southern Arabian Gulf. In Abu Dhabi this seems to be largely a result of the present-day coastal geomorphology, with deposits limited by the size of barrier islands. In Qatar the buildup of eolianites is currently prevented by offshore deflation on the eastern coast.
In a ramp-like setting, such as the Arabian Gulf, eolian reworking of marine sediment can take place over a much longer period than in isolated platform settings, because sediment production is less dependent upon high sea levels. In addition, subaerial lithification of aragonitic sediments is retarded by the predominantly arid climate of the Arabian Gulf. In this respect, southern Gulf eolianites may be more analogous to ancient carbonate deposits than those from more humid Quaternary settings.
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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.