Transition from alluvial plain to tide-dominated coastal deposits associated with the Tournaisian marine transgression in southwest Ireland
Diemer, J.A.; Bridge, J.S. (1988). Transition from alluvial plain to tide-dominated coastal deposits associated with the Tournaisian marine transgression in southwest Ireland, 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. 359-388
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., meer
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| Auteurs | | Top |
- Diemer, J.A.
- Bridge, J.S.
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| Abstract |
The 'Old Red Sandstone' and 'Lower Limestone Shale' of Kerry Head, southwest Ireland record the marine transgression of a continental margin associated with rising sea level. The Upper Devonian 'Old Red Sandstone', comprising sandstone bodies and sandstone-mudstone interbeds, changes stratigraphically upwards as follows: (1) mean grain size of sandstone bodies decreases; (2) colours change from mainly red and gray to yellow and green; (3) plant remains become better preserved. The sandstone bodies are interpreted as deposits of laterally migrating, aggrading, southerly-flowing rivers. The river channels were undivided, had sinuosities less than 1.2 and decreased in slope as the coastline approached from the south. The sandstone-mudstone interbeds are interpreted as deposits of vegetated floodplains (containing levees, crevasse splays and floodbasins) beneath which the water table was progressively rising. The Tournaisian 'Lower Limestone Shale' comprises lateral-accretion deposits which fine upwards from large scale cross-stratified sandstone to current-dominated heterolithic beds, interbedded with current- and wave-dominated heterolithic beds and desiccated crypt algal laminites. The large-scale cross-strata occur with additional structures in bundles which together indicate unsteady and reversing currents. Wave-dominated heterolithic beds and hummocky crossstratified sandstone become more abundant stratigraphically upwards. A transported brachiopod-crinoid-bryozoan assemblage which is locally abundant above erosion surfaces becomes more diverse upwards. Trace fossils belong to the Skolithos and Cruziana ichnofacies. The 'Lower Limestone Shale' is interpreted as deposits of laterally-migrating and aggrading estuarine channels associated with tidal flats which gradually gave way to estuarine embayments dominated by waves. Tectonic subsidence, which allowed the Kerry Head sequence to accumulate, was possibly due to flexure of the crust associated with isostatic sediment loading in the rifted (stretched) Munster Basin to the south. The Tournaisian transgression probably resulted from a combination of eustatic sea-level rise and tectonic subsidence exceeding deposition. Evidence for coeval climatic change is lacking. |
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