Tropical view of Quaternary sequence stratigraphy: Siliciclastic accumulation on slopes east of the Great Barrier Reef since the Last Glacial Maximum

Abstract

Generic models of continental-margin evolution predict that siliciclastic fluxes to slopes should be maximal and minimal during major sea-level lowstands and transgressions, respectively. Here we document the opposite for the northeast Australian margin, the largest extant mixed siliciclastic-carbonate depositional system. Cores from slopes of this margin consistently contain siliciclastic-rich intervals, ϳ0.3-1 m thick, in the upper few meters. Radiocarbon dates of planktonic foraminifera show that this interval was deposited between 12 and 7 ka and represents greatly increased siliciclastic fluxes during late transgression. This massive terrigenous discharge to slopes occurred along at least 450 km of the margin, irrespective of modern variations in bathymetry or climate. Although we cannot dismiss a significantly different early Holocene climate with greatly enhanced sediment discharge, available data instead suggest that rivers aggraded on the shelf during lowstand because of an extensive subaerially exposed reef system. This phenomenon may occur on other margins rimmed by reefs, requiring a major revision of concepts used to interpret mixed siliciclastic-carbonate systems. Figure 1. Sediment accumulation on slopes of tropical mixed system as (A) conventionally modeled and (B) observed on northeast Australian margin, with (C) respect to relative sea level. MAR-mass-accumulation rate.

Will reducing agricultural runoff drive recovery of coral biodiversity and macroalgae cover on the Great Barrier Reef?

“…Here, geological evidence suggests that these reef systems have coexisted with very high water turbidity for millennia. Throughout the Quaternary life cycles of the GBR with glacio-eustatic changes in sea level, carbonate production and early reef initiation occurred during periods of high coastal water turbidity, maintained by sediment supply and oceanographic processes (e.g., Dunbar andDickens 2003, Page et al 2003). Over geological timescales, reef development and water quality are inextricably linked, and on that fact we are in complete agreement with DF10.…”

Late Quaternary siliciclastic/carbonate sedimentation model for the Capricorn Channel, southern Great Barrier Reef province, Australia

“…Both regions experience summer monsoonal rains and the present sediment yield from the Burdekin River is estimated to be similar to that of the Fitzroy River (Neil et al, 2002;Furnas, 2003). Paleoclimate evidence from vegetation changes in northern Queensland suggests that precipitation was reduced during the glacials (Kershaw et al, 2007), but then increased during the transgression, especially between 11 and 7 ka BP (Kershaw, 1985;Page et al, 2003). This would have resulted in increased water and sediment discharge during the late transgression.…”

“…1), suggest that lowstand shedding of terrigenous mud is responsible for a dilution of the carbonate content in glacial-aged sediments from slope cores (Kudrass, 1982;Troedson and Davies, 2001). However, recent detailed studies of the tropical carbonate/ siliciclastic system of the central Great Barrier Reef (GBR) province (15-18°S) have challenged the conventional reciprocal model (Dunbar et al, 2000;Page et al, 2003;Dunbar and Dickens, 2003a,b;Francis et al, 2007). Their results, from a series of well dated marine cores from the north Queensland margin (Fig.…”

Orbital-scale variation in the magnetic content as a result of sea level changes in Papua New Guinea over the past 400 ka

“…Past study in the Pandora Trough (nearby the GoP) has shown this similar property: Numerous siliciclastic turbidites were recorded in the LGM and Younger Dryas in the Pandora Trough, and extremely high accumulation rate was observed during 15,800-17,700 years . However, also nearby the GoP, some studies showed different flux features: Records of the siliciclastic fluxes from the Great Barrier Reef (GBR), Queensland Trough, and Ashmore Troughs were lower in lowstand periods and were higher during late transgression (Dunbar et al 2000;Page et al 2003;Carson et al 2008). Therefore, sedimentary responses to sea level change would vary from one margin to another due to Fig.…”