Abstract The shoreface translation model (STM) incorporates advances in the theory for coastal responses to changes in relative sea level, exposing some well-entrenched misconceptions about the formation of transgressive and regressive strata at chronosomal scales. The STM is a mass-conserving, morphological-behavior model that provides added generality to the updated theory by allowing for open sediment budgets (on the shoreface and in the lagoon) and time-dependent changes in shoreface and barrier geometries. Both the theoretical basis and application of the STM give neutral transgression for balanced sediment budgets on gently sloping surfaces undergoing a marine transgression. Under these conditions, no transgressive strata are formed, and the land surface being transgressed is not disturbed en masse. Consequently, shoreface-ravinement surfaces are not necessarily inherent by-products of transgression as assumed previously. Simulated transgressive strata are laid down (aggradational transgressions) only if there is a positive net littoral sediment supply (from deltaic sources or erosion of shoreline promontories), significant deposition in the lagoon (due to trapping of fine marine sediments or direct fluvial inputs), or both. Shoreface-ravinement surfaces are produced only under conditions of negative littoral sediment budgets or if the land surface being transgressed is steeper than the shoreface (degradational transgressions). For negative sediment budgets, simulated shoreface ravinements form on low-gradient surfaces without seaward sediment displacement or genetically related aggradation of the seabed farther offshore. Ravinements also can develop during progressive deepening of the shoreface during transgression and highstands. Simulated highstand ravinements are consistent with, and provide an alternative explanation for, coarse-sand lags found on the lower shoreface of many accommodation-dominated shelves today. Simulated forced regression results in massive in-situ reworking of the highstand shelf surface, inevitably producing a strandplain stratum characterized by (1) an unconformity at its base and (2) shoreface isochrons, as opposed to the landward-dipping, backbarrier isochrons that characterize transgressive barriers (which consist of washover and tidal-delta sand deposits). The revised approach to simulating each of these intrachronosomal-forming processes has significance for sequence models and the interpretation of stratigraphic data at basin-fill scales.

Abstract: Vibracores collected from the middle and outer continental shelf of New South Wales, Australia (32.5° to 34.8°S) contain a well- preserved record of cool-water carbonate sedimentation during the last three glacial lowstands. The cores show an increase in the proportion of carbonate with increasing water depth and distance offshore and mimic a pattern previously identified for surficial shelf sediments. Degraded biogenic sand and shell gravel on the winnowed surface of the outer shelf (water depths of 135 to 150 m) is underlain by thick sequences of well-preserved, shallow-marine bivalves (dominantly Pecten fumatus) in a carbonate sand matrix. These cool-water bivalves occur cyclically in at least 10 cores from the outer shelf, separated by intervening deposits of deeper water species in finer grained carbonate sand. Numerous radiocarbon dates confirm that the uppermost Peclen unit is of last glacial age (13,000 to 27,000 yr BP), while amino acid racemisation analyses of the lithologically analogous underlying Peclen units indicate that previous late Pleistocene lowstand events (isotopic stages 6 and 8) are also preserved. These lowstand, carbonate-rich sediments contrast sharply with the predominantly quartzose sand characteristic of the highstand inner shelf and indicate that little terrigenous sand was supplied to the shelf during lowstands. The sedimentary sequence identified in the outer shelf cores also indicates a marked change in environmental conditions from productive, shallow-marine carbonate sedimentation during the last glacial lowstand to non-deposition and bioerosion during the highstand, with intervening periods of intermediate water depth (isotope stages 3 and 4?) also characterized by carbonate sedimentation. This cycle was repeated during previous late Quaternary sea-level fluctuations, and the data indicate on-going accretion of the outer shelf sediment wedge at a rate of 1 to 4 m/100,000 years.

Abstract Stratigraphies and radiocarbon age structures of four estuaries in SE Australia are described. Two different estuary types, wave-dominated barrier estuaries and more tidally-influenced drowned valley estuaries, are represented, each with examples showing contrasting river catchments and sediment discharges that control the rate the estuaries infill with sediment. Primary differences that arise from geological inheritance and mainly affect estuary-mouth conditions were established on this coast at the end of the postglacial marine transgression once sea levels stabilised about 6.5 ka ago. Since then, up to 50 m of Holocene sediments have been deposited in some estuaries. Central basin muds are most extensive in barrier estuaries behind bay barriers with constricted tidal inlets and have accumulated at rates ranging from 0.1 to 15.0 mm yr −1 , an upper limit imposed by rising sea level. Barrier estuaries experience most rapid environmental changes at mature stages of development as terrestrial flood plains spread seawards over shallow estuarine basins. Surprisingly, their flood-tide delta deposits seem to have grown little under stillstand conditions. In contrast, drowned-valley estuaries with open mouths and full tidal ranges contain large tidal-delta sand bodies that have grown landwards at rates of 1–4 m yr −1 during both rising sea-level and highstand conditions. As these estuaries approach maturity they discharge fine sediment to the sea thus retarding subsequent infilling. Estuaries with good flushing characteristics at their mouths, therefore, experience less radical environmental fluctuations due to both natural and man-induced changes than do estuaries with impeded tidal exchange.