MP9: Chapter 6: Sinuous Rhizoliths Mimic Invertebrate Trace Fossils on Upper Pleistocene Caliche Surfaces, San Salvador Island, Bahamas
by H.A. Curran.
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This chapter is from GAC's Miscellaneous Publication 9: "Ichnology: Papers from Ichnia III" editted by Dr. Duncan McIlroy. To purchase the entire book on disc, please see the Miscellaneous Publications section of our bookstore at http://www.gac.ca/publications/view_pub.php?id=262.
The Pleistocene‒Holocene boundary on islands of the Bahama Archipelago is typically marked by a calichified paleosol horizon that formed on exposed limestone surfaces during lowered sea level of the Last Glacial. On the north coast of San Salvador, an extensive laminar caliche surface is present west of Singer Bar Point. Formed on Upper Pleistocene (Eemian) carbonate eolianite and overlain by Holocene eolianite, this surface bears numerous and distinctive large, sinuous structures typically preserved in half relief, and with sharp, parallel ridge-like edges that slope inward to form a smooth, medial trough having widths mostly between 1 and 3 cm. Individual structures can commonly be traced for lengths of several metres and exhibit complex patterns, with branching only occasionally present. Three hypotheses for the origin of these structures are presented and discussed: physical processes, invertebrate trails similar to the ichnogenus Archaeonassa, and formation by plant roots. The last hypothesis is favoured. Similar structures have been found on Upper Pleistocene laminar caliche surfaces at other coastal locations on San Salvador, and they likely are present on similar surfaces throughout the Bahamas and beyond. This suggests that structures of this origin may be far more common and widespread on the surfaces of Quaternary and older carbonate facies elsewhere than previously recognized.
Geological Association of Canada
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