Sediment-organism zonation and the evolution of Holocene tidal sequences in southern Australia
Belperio, A.P.; Gostin, V.A.; Cann, J.H.; Murray-Wallace, C.V. (1988). Sediment-organism zonation and the evolution of Holocene tidal sequences in southern Australia, 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. 475-497 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., more |
| Authors | | Top | - Belperio, A.P.
- Gostin, V.A.
- Cann, J.H.
- Murray-Wallace, C.V.
| | |
| Abstract | Regressive intertidal sequences have developed around the margins of major gulfs and within protected embayments and lagoons of southern Australia over the past 7000 years of relative sea level stability. Bioclastic (foram, mollusc, algae) and mixed terrigenous-carbonate clastic sediments dominate in largely mesotidal environments. Evaporites and autochthonous carbonates characterise environments that have become isolated from normal tidal inundation or circulation. Subtidal seagrass meadows are major areas of skeletal carbonate production with accumulation rates in excess of 2 mm per year. The coastal banks created by the seagrass rapidly accrete to low tide level. Intertidal environments with well defined plant-sediment associations prograde across the shallow banks. Zonation of vegetation largely reflects frequency of tidal inundation, but is also affected by exposure to waves. Along relatively sheltered coasts, the zonation of vegetation and sedimentary environments commences with muddy, low intertidal sand flats colonised with patchy Zostera and Heterozostera seagrasses. Mangroves (Avicennia marina) and associated sediments occur between mean sea level and spring high tide level. Vegetated, high intertidal mud flats (samphire salt marsh) merge with the mangrove woodland and extensive cyanobacterial mats colonise the floor of the tidal swamps and extend into supratidal areas. Poorly developed sabkhas occur at supratidal levels that are only occasionally inundated by storm surges or are influenced by groundwater seepage. Distinctive foraminiferal assemblages occur within each environment. Shorelines exposed to greater wave activity have a broad intertidal sand flat seaward of a low, but well defined strandline. A narrow series of stranded foredunes separate the exposed flat from protected salt marsh and supratidal flats to leeward. Here, cyanobacterial mats colonise both the upper portion of the exposed sand flat as well as the protected vegetated flats. Along ocean coastlines, intertidal facies develop within small embayments and lagoons protected by Holocene or Pleistocene barrier complexes. The lithostratigraphy generated within these protected environments is similar, but on a smaller scale, to that constructed along sheltered gulf coasts, but the sediment includes a substantial proportion of reworked clastic detritus. Catastrophic closure of tidal inlets by migrating aeolian dunes or flood tide deltas can drastically alter sedimentation processes, leading to the formation of coastal saline lakes that are non-tidal and dominated• by processes of evaporation and groundwater seepage. In this situation, crystalline gypsum and marginal carbonates sharply overlie partially developed, regressive, peritidal sequences. |
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