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Example of tidal current periodicities from an upper cretaceous sandstone succession (Anambra Basin, S.E. Nigeria)
Ladipo, K.O. (1988). Example of tidal current periodicities from an upper cretaceous sandstone succession (Anambra Basin, S.E. Nigeria), in: de Boer, P.L. et al. (Ed.) Tide-influenced sedimentary environments and facies. Extended versions of papers presented at the Symposium on Classic Tidal Deposits, held August 1985 in Utrecht, Netherlands. pp. 333-340
In: de Boer, P.L. et al. (Ed.) (1988). Tide-influenced sedimentary environments and facies. Extended versions of papers presented at the Symposium on Classic Tidal Deposits, held August 1985 in Utrecht, Netherlands. D. Reidel Publishing: Dordrecht. ISBN 90-277-2622-1. ix, 530 pp.
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| Abstract |
The differentiation of fluvial and tide dominated mature sandstones, especially where palaeocurrent patterns are unidirectional, can be more conclusive where process interpretations of current reversals, unsteady flow conditions and, more importantly, periodicities in the currents can be demonstrated. The Ajali Sandstone of the Anambra Basin, S.E. Nigeria is a mature sandstone formation of Campanian - Maastrichtian age, previously interpreted as fluvial because of the unimodal palaeocurrent pattern. However, examples of bedform modification structures such as 'ebb-cap' ripple sets, reactivation surfaces, mud drapes and herringbone cross-bedding occur suggesting unsteady and reversing currents. The spacings between adjacent mud drapes show periodicities which suggest the influence of neap-spring cycles. The moving average method reveals more clearly the periodicities in the neapspring cycles which vary from as low as 13 up to 24, similar to those of the present day. The low numbers of neap-spring cycle may have resulted from such factors as the effects of mixed diurnal/semi-diurnal tidal systems, a halt in the migration of the bedform during neap tides or the erosion of bundles preceeding reactivation of the bedform. Major reactivation surfaces are followed by very thick bundles erosively overlying at least three or four preceeding erosion surfaces. Their occurrence may indicate reactivation of the bedform at spring tides, increased migration rates following storms on a tide-dominated shelf, or increased river discharge. |
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