Post‐glacial seismic stratigraphy, central Great Barrier Reef, Australia

Abstract

A regional programme of continuous seismic (boomer) profiling in the central Great Barrier Reef Province has identified a widespread shallow seismic discontinuity (reflector A) which is interpreted as the pre‐Holocene surface. Nine seismic facies units are distinguished primarily on the basis of the seismic records, but also with the aid of additional criteria such as location and surface sediment types. Two units underlie reflector A and are pre‐Holocene. These units are interpreted as: (a) Permo‐Carboniferous bedrock, and (b) Pleistocene/? Tertiary sediments, consisting of both shelf‐wide terrigenous units, and carbonate mounds and platforms under present reefs. Seven units are post‐glacial and overlie reflector A. These units are interpreted as: (c) fluvial/estuarine channel fill, (d) relict delta‐front deposits, (e) relict transgressive veneer, (f) coastal coarse and (g) fine deposits, (h) modern reef and (i) reef talus. In general post‐glacial sediment cover is very thin and in many places on the mid‐shelf the pre‐Holocene units crop out. Substantial post‐glacial accumulations are limited to protected coastal embayments and to offshore reef masses.

Phosphorus speciation in the sediment and mass balance for the central region of the Great Barrier Reef continental shelf (Australia)

“…But, without other means to estimate the time span over the integrated depth, we made the assumption that sediment deposition has remained constant over this long time frame. Radiocarbon, seismic profiling and stratigraphic studies show good evidence that there is very little variation of the sedimentation rate on the GBR shelf over the last millennium (Johnson and Searle, 1984;Harris et al, 1990;Heap et al, 2001 andDunbar andDickens, 2003). The chemical composition of the cores (available in Electronic annex, EA-1) also shows little variation with depth, suggesting that our assumption may be justified.…”

“…The related MAR is likely <0.01 g cm À2 year À1 as in this part of the shelf, seismic stratigraphic studies show good evidence of very thin Holocene sediment deposits (usually <1 m) (Johnson and Searle, 1984;Scoffin and Tudhope, 1985;Harris et al, 1990). The shelf coral reef platforms have at least two different depositional environments: the windward hard coral-algal pavements, and the protected leeward interior lagoon and flanks of reefs.…”

“…In each compartment, the following processes were considered: Table 2 Depth integrated changes in sediment P forms (negative values represent P loss, and positive values represent an increase in P fraction, compared to P concentration at the core surface), time span on depth interval ( 210 Pb estimate) and the related P flux released by diffusion (estimated from depth profiles of solid forms of P and 210 Pb data); in comparison with P benthic fluxes, measured by incubation at nearby stations (Johnson and Searle, 1984;Dunbar and Dickens, 2003). Within each box, ND represents the P nutrient demand.…”

Development of depositional systems in the southeastern Yellow Sea during the postglacial transgression

“…The shore-normal progradation over the estuarine channel fills suggests that the wedge comprises relict delta-front sediments deposited over the backfilled channels during the transgression (Johnson and Searle, 1984). The intercalated sand layers are indicative of fluctuation in sediment supply, leading to the sediment progradation (e.g., short-period regressive wedge in Lobo et al, 2001).…”

Contradicting Barrier Reef relationships for Darwin’s Evolution of reef types

“…13). Here, seismic profiling has been successful in delineating the filled Pleistocene channels of the Herbert and Burdkin Rivers (Johnson and Searle 1984;Fielding et al 2003). The Burdekin River channel has been traced farthest seaward, becoming progressively smaller as it traverses the outer reef shelf until disappearing over the outermost 10 km of the shelf (Fielding et al 2003).…”