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Ichnological Studies on Tempestites
Pages: 489-494
Year: Issue:  4
Journal: ACTA SEDIMENTOLOGICA SINICA

Keyword:  tempestites opportunistic trace fossils equilibrium trace fossils;
Abstract: Trace fossils are proving to be powerful tools for recognitionand interpretation of event beds. Tempestites contain a mixed trace fossil assemblage that reflects fluctuations in energy levels. The two different ichnocoenoses reflect varying behavioral responses of the organisms colonizing two successive, individually distinct habitats. The resident or fair-weather ichnocoenose can be considered representative of a stable benthic community, within which individual populations are at or near their carrying capacity. Periodic generation of the storm ichnocoenose, on the other hand, represents the flourishing of a community of opportunistic organisms in an unstable, high-stress, physically controlled environment. The general succession, typical terrigenous tempestites represented by the tempestites in the Upper Cretaceous Cardium Fm. of Alberta , Canada , consists of (1)a fair-weather resident trace fossil suite; (2) a sharp basal contact, with or without a basal lag; (3) parallel to subparallel laminations ( reflecting hummocky or swaley cross-stratification); (4) common escape structures; (5) the dwelling burrows of opportunistic organisms that colonize the unexploited storm unit; (6) gradational burrowed tops, representative of bioturbation resulting from subsequent burrowing by organisms from higher colonization levels; and (7) a fair-weather resident trace fossil suite indicative of a return to quiescent conditions following abatement. Up to now, the ichnology in the carbonate tempestites has not been well studied and reported. The succession found in the Upper Cambrian Gushan Fm. from eastern North China Platform can be regarded as the typical carbonate tempestites . The succession includes the following parts (from bottom to top): (1) the trace fossils on the sole of the thin-bedded limestone containing Phycodes, Thalassinoides, Palaeophycus and Planolites etc; (2) 12 cm thick muddy limestone or limestone with or without lamination; (3) the opportunistic trace fossils Diplocraterion, Arenicolites and Skolithos on the surface of the limestone; (4) the surface of the limestone covered by about 1 mm thick trilobite debris; (5)1 -2 mm thick mudstone or shale.
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