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Sequence and style in scleractinian coral preservation in reefs and associated facies
Studies of reefs and proximal facies in the Pleistocene of East Africa, and in the Tertiary and Miocene of Bahrain yield predictable sequences of coral sediment distribution patterns. These can be sub-divided into micro-facies ranging from the supratidal to at least â33 m. Many of these suites are comparable with facies found today around Heron Island, on the Australian Great Barrier Reef, upon which a series of facies and fabric models are reconstructed. In depths of less than â15 m five main types of facies-linked preservational styles of corals are recognised and their chemical properties are analysed experimentally: (1) essentially unaltered; (2) red-algal encrusted; (3) moldic rhodoliths after sponge borings; (4) intensely endolithically bored intertidal debris; and (5) sterile, internally zoned, leached and abraded skeletons from the strand-line. These represent a linear sequence from off-shore to the storm ridge, which are modelled into transgressive and regressive cycles. The probability of their preservation and the relative proportion of their products, from any one time interval, increase in a landward direction.
Scleractinian standards are established by tracing six taxonomically distinguishable groups represented amongst Astrocoeniina, Fungiina and Faviina in the quasi-fossil strandline shingle to their origins. Each coral or coral-fragment acquires a distinct suite of epibionts on the host's death, and undergoes characteristic chemical alteration related to its micro-environment. Consequently, the same genus develops various modifications reflecting its history of postmortem transport prior to ultimate burial. Thus, the chemical integrity of the skeleton never remains completely intact, as those specimens that are not subject to encrustation and the influences of endo- and epilithic biota are the more susceptible to diagenetic exchange with percolating pore waters. Preferred pathways for interstitial trace-element enrichment are detected by means of dosing the sea-water with uranium: these are best developed at skeletal margins and along trabecular axes in sterilised specimens.
The applicability of these data to bore-hole records is tested by reference to the Heron Island core log. While the implications for the analysis of diagenetically advanced material is demonstrated by Jurassic and Carboniferous examples, these data have profound implications for assessing the reliability of isotope geochemistry and radiometric dating
Short-term progressive early diagenesis in density bands of recent corals:Porites Colonies, Mauritius Island, Indian Ocean
Die Bedeutung der Mikroarchitektur und Mikrostruktur in der FossilĂŒberlieferung taxonomisch eng verwandter Steinkorallen
RÀumliche Unterschiede in der PorositÀtsentwicklung von Karbonatsedimenten und-gesteinen
Autochthonous facies and allochthonous debris flows compared: Early oligocene carbonate facies patterns of the Lower Inn Valley (Tyrol, Austria)
Heliolitid corals and their competitors: a case study from the Wellin patch reefs, Middle Devonian, Belgium
peer reviewedWellin patch reefs are small Upper Eifelian build?ups within the fine?grained argillaceous limestone of the Hanonet Formation. Whereas the reefs themselves are not well exposed, their fossil assemblage is accessible in the hills near the town of Wellin, approximately 40xA0km SE of Dinant in Belgium. It is especially rich in massive stromatoporoids, heliolitids and other tabulate corals. They exhibit predominantly domical and bulbous morphologies. This paper focuses primarily on the palaeoautoecology of the heliolitid corals and their relationships with other organisms. Cases of mutual overgrowth between heliolitids, other corals and stromatoporids suggest a high degree of competition for space on the reefs, possibly related to the scarcity of hard substrates. Coral and stromatoporoid growth forms, as well as the prevalence of micritic matrix, point to a relatively low energy environment. However, abundant growth interruption surfaces, sediment intercalations and rejuvenations of corals suggest episodically increased hydrodynamic regime and sediment supply. It is inferred that the patch reefs developed in a relatively shallow environment, where the reefal assemblage was regularly affected by storms. Heliolitids exhibited high sediment tolerance and relied on passive sediment removal for survival. They also could regenerate effectively and commonly overgrew their epibionts, after the colonyâs growth was hampered by the sediment. This is recorded in extremely abundant growth interruption surfaces, which allow the analysis of the impact of sediment influxes on the heliolitid corals. ? 2021 Lethaia Foundation. Published by John Wiley & Sons Lt