Taphonomic signatures of turbid-zone reef development: Examples from Paluma Shoals and Lugger Shoal, inshore central Great Barrier Reef, Australia

Numerous coral reefs and coral communities occur along the nearshore regions of the central Great Barrier Reef (Australia) coastline. These develop under conditions of episodically high, wave-induced sediment resuspension and turbidity, and terrigenoclastic sediment accumulation. Cores recovered from two such reefs at Paluma Shoals and Lugger Bay are used to assess the taphonomic features and processes associated with framework development in such settings. Reef framework development is dominated by the accumulation of mainly rabble coral and isolated in situ coral colonies. The reef fabric varies from clast- to matrix-supported in character and the matrix comprises poorly sorted mixed terrigenoclastic/carbonate sediments. Taphonomic signatures from the different reef sites and facies show little variability and thus a distinct suite of taphonomic criteria, indicative of nearshore, turbid-zone reef development, are delineated. The degree of both calcareous encrustation and internal bioerosion exhibits a high degree of between-clast variability and many clasts are preserved in near pristine condition; where present calcareous encrustation is restricted to thin, isolated crusts comprising mainly of the coralline algae Lithoporella or Lithothamnion, and isolated serpulid worms and cemented bivalves. No biological binding of framework constituents occurs. Bioerosion is dominated by traces of Entobia sp. (sponge borings) and, locally, Gastrochaenolites sp. (bivalve traces), although only a limited suite of bioerosion trace morphologies is present. There is little or no cementation of the reef framework and only isolated acicular aragonite or peloidal micrite cements occur within intra-skeletal cavities. Significant occlusion of primary and secondary skeletal porosity by uncemented, fine-grained, mainly terrigenous sediment is, however, common throughout the reef sequence. The taphonomic criteria identified all have good preservation potential and should be readily identifiable within core sections. Such criteria thus have potential for aiding the recognition of reefs that either developed under similar environmental conditions of high turbidity and terrigenous-sediment accumulation, or which were subject to similar conditions during more short-lived phases of reef accretion. (c) 2006 Elsevier B.V. All rights reserved.