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Holocene delta progradation into an epeiric sea in northeastern Australia
journal contributionposted on 2020-04-01, 00:00 authored by E L Porritt, B G Jones, D M Price, Rafael Cabral Carvalho
Progradation of the Quaternary Gilbert River megafan and Holocene delta, located in the low gradient intracratonic basin and epeiric sea of the Gulf of Carpentaria, Australia, has been enhanced by the slight fall in sea level during the late Holocene. The monsoonal floods and channel avulsions on the megafan have controlled the rate of progradation and supply of sediment to the delta front. The mixed-influence delta can be classified as a tide dominated, fluvially influenced and wave affected (Tfw) delta. Palaeogeographic reconstruction of the Gilbert River megafan, delta and palaeoshorelines was created through GIS analysis of beach and chenier ridges combined with field observations, previous cross-section data, and radiocarbon and thermoluminescence dating. Progradation rates on the Gilbert River delta are about 0.85 to 0.9 m/yr in the northern and central parts of the delta and increase to 1.8 m/yr in the southern part of the delta. Sedimentation rates vary from 0.2 to 1.0 mm/yr with a total Holocene delta volume of about 9.4 × 109 m3 and a sediment supply rate of ~1 Mm3/yr. The low sediment supply rate is characteristic of most Australian river systems but is about two orders of magnitude less than on many of the larger Southeast Asian deltas. The low onshore and offshore accommodation space on the Gilbert and Mitchell River deltas is a function of the epeiric sea setting of these deltas, and hence the thin succession of Holocene sediments on these deltas also represent a significant difference from most Southeast Asian deltas.