Ripple-mark analysis of a fine-grained epeiric-sea deposit (Cambrian, South Australia).
Titel:
Ripple-mark analysis of a fine-grained epeiric-sea deposit (Cambrian, South Australia).
Auteur:
Moore, P. S.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 29 (1982) nr. 1-2 pagina's 71-81
Jaar:
1982-04
Inhoud:
The Cambrian Nildottie and Erudina Siltstone Members together comprise a thick (up to 460 m) and laterally extensive (over 5000 km2) sequence of predominantly silty redbeds in the Flinders Ranges of South Australia. The occurrence of desiccation cracks, halite imprints and arthropod markings throughout the sequence indicates extensive and persistent shallow-water marine conditions and, together with its epicontinental setting, classifies the sequence as an epeiric-sea deposit. The virtual absence of large-scale cross-stratification and lack of significant facies variation in the sequence pose a major problem for detailed palaeogeographic, sedimentologic and hydraulic study. This difficulty is largely overcome by detailed analysis of ripple marks. Oscillation-ripple data suggest that the strandline trended approximately NNE-SSW during deposition of the Nildottie and Erudina siltstone Members, with slightly deeper water occuring in the eastern outcrops, as interpreted from the orientation of near-symmetrical oscillation ripples. Throughout most of the area, water depth was probably only a few meters at most, with locally-generated, low amplitude, short-period waves being the main mechanism for sediment dispersal. A weak tidal influence is indicated by the minor presence of catenary ripples, which show a tendency to display the quadrimodal, bipolar-dominated palaeocurrent pattern that is a feature of many tidal deposits. Current lineations are rare, and reflect a minor longshore component of transport in the slightly deeper eastern areas. Sedimentological, palaeocurrent and hdydrological parameters derived from the ripple-mark study contribute to the understanding of the Nildottie and Erudina Siltstone Members in particular, and shallow epeiric sea deposits in general. The technique of ripple-mark analysis used herein may be a guide to other workers in this field.
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