DEEP-WATER INCISED VALLEY DEPOSITS AT THE EDIACARAN-CAMBRIAN B

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• journal_title：PALAIOS
• Contributor：JONATHAN P. WILSON ; JOHN P. GROTZINGER ; WOODWARD W. FISCHER ; KEVIN P. HAND ; SÖREN JENSEN ; ANDREW H. KNOLL ; JOHN ABELSON ; JOANNAH M. METZ ; NICOLA MCLOUGHLIN ; PHOEBE A. COHEN ; MICHAEL M. TICE
• Publisher：SEPM Society for Sedimentary Geology
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.2110/palo.2011.p11-036r
• journal_abbrev：PALAIOS
• issn：0883-1351
• volume：27
• issue：4
• firstpage：252
• section：RESEARCH ARTICLES

摘要

<p id="p-1">Valley-filling deposits of the Nama Group, southern Namibia, record two episodes of erosional downcutting and backfill, developed close together in time near the Ediacaran-Cambrian boundary. Geochronological constraints indicate that the older valley fill began 539.4 ± 1 Ma or later; the younger of these deposits contains unusually well-preserved populations of the basal Cambrian trace fossil pan class="named-content genus-species" id="named-content-3">Treptichnus pedumpan>. Facies analysis shows that pan class="named-content genus-species" id="named-content-4">T. pedumpan> is closely linked to a nearshore sandstone deposit, indicating a close environmental or taphonomic connection to very shallow, mud-draped sandy seafloor swept by tidal currents. Facies restriction may limit the biostratigraphic potential of pan class="named-content genus-species" id="named-content-5">T. pedumpan> in Namibia and elsewhere, but it also illuminates functional and ecological interpretation. The pan class="named-content genus-species" id="named-content-6">T. pedumpan> tracemaker was a motile bilaterian animal that lived below the sediment-water interface—propelling itself forward in upward-curving projections that breached the sediment surface. The pan class="named-content genus-species" id="named-content-7">T. pedumpan> animal, therefore, lived infaunally, perhaps to avoid predation, surfacing regularly to feed and take in oxygen. Alternatively, the pan class="named-content genus-species" id="named-content-8">T. pedumpan> animal may have been a deposit feeder that surfaced largely for purposes of gas exchange, an interpretation that has some support in the observed association of pan class="named-content genus-species" id="named-content-9">T. pedumpan> with mud drapes. pan class="named-content genus-species" id="named-content-10">Treptichnus pedumpan> provides our oldest record of animals that combined anatomical and behavioral complexity. Insights from comparative biology suggest that basal Cambrian pan class="named-content genus-species" id="named-content-11">T. pedumpan> animals already possessed the anatomical, neurological, and genetic complexity needed to enable the body plan and behavioral diversification recorded by younger Cambrian fossils. p>