Abstract
Carbonate eolianites, less than 10,000 years old, are well exposed in sea cliffs and on rocky shore platforms along the northeast coast of San Salvador Island. These deposits formed when easterly trade winds blew carbonate sands landward from the beach zone as sea level rose over a previously exposed shelf during the Holocene transgression. Small, lobate, parabolic-like dunes coalesced laterally to form an elongate, transverse dune ridge oriented perpendicular to the prevailing wind direction. Detailed observations of small-scale sedimentary structures and laminations permit the distinction of sands deposited as climbing wind ripples, lee-side grainfalls, and lee-side sandflows. Micrite crusts and associated plant trace fossils characteristic of the dunal environment are common in the Rice Bay Formation, and these can be compared directly with identical features and plants found in modern carbonate dunes on San Salvador. Some eolian laminations dip into the present-day subtidal zone, confirming a post-depositional rise in sea level along this tectonically stable coast. The rocks are lithified sufficiently by freshwater, vadose, low Mg-calcite cement to form wave-resistant sea cliffs. A distinctive feature of these terrestrial carbonate rocks is the occurrence of a variety of animal trace fossils. Skolithos linearis burrows, up to 30 cm in length and 0.5 cm in diameter, are quite common. Comparison with traces found in modern carbonate dunes suggests that these trace fossils were made by burrowing insects or spiders. The most abundant and widespread trace fossil consists of closely spaced, irregular, small burrows up to 20 cm long in the horizontal plane and with uniform diameters of 0.3–0.4 cm. These burrows also extended downward as much as 3 cm into the sediments, and created a mottled texture in places. This trace fossil has been found only in lee-side sandflow and grainfall deposits. Such burrows probably were produced by insects or insect larvae, which favored the protected lee-side environment. The most unusual trace fossil in these Holocene eolianites is composed of a cluster of vertically oriented burrows. Each cluster consists of up to several hundred shafts, each with a diameter of 1–2 cm, that diverge upward from an approximately common point of origin. These structures can be 1.4 m or more high and greater than 1 m in transverse section across the circular shape produced by the upwardly radiating burrow cluster. These trace fossils probably represent the escape pathways of the hatchlings of an infaunal insect or similar invertebrate.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.