Origins, Timing, and Implications of Miocene to Pleistocene Turbidites, Debris Flows, and Slump Deposits of the Queensland Trough, Northeastern Australia (Site 823)

Abstract

More than 2000 turbidite, debris-flow, and slump deposits recovered at Site 823 record the history of the Queensland Trough since the middle Miocene and provide new insights about turbidites, debris flow, and slump deposits (herein termed gravity deposits). Changes in the composition and nature of gravity deposits through time can be related to tectonic movements, fluctuations in eustatic sea level, and sedimentological factors. The Queensland Trough is a long, relatively narrow, structural depression that formed as a result of Cretaceous to Tertiary rifting of the northeastern Australia continental margin. Thus, tectonics established the geometry of this marginal basin, and its steep slopes set the stage for repeated slope failures. Seismic data indicate that renewed faulting, subsidence, and associated tectonic tilting occurred during the early late Miocene (continuing into the early Pliocene), resulting in unstable slopes that were prone to slope failures and to generation of gravity deposits. Tectonic subsidence, together with a second-order eustatic highstand, resulted in platform drowning during the late Miocene.The composition of turbidites reflects their origin and provides insights about the nature of sedimentation on adjacent shelf areas. During relative highstands and times of platform drowning, planktonic foraminifers were reworked from slopes and/or drowned shelves and were redeposited in turbidites. During relative lowstands, quartz and other terrigenous sediment was shed into the basin. Quartzose turbidites and clay-rich hemipelagic muds also can record increased supply of terrigenous sediment from mainland Australia. Limestone fragments were eroded from carbonate platforms until the drowned platforms were buried under hemipelagic sediments following the late Miocene drowning event. Bioclastic grains and neritic foraminifers were reworked from neritic shelves during relative lowstands. During the late Pliocene (2.6 Ma), the increased abundance of bioclasts and quartz in turbidites signaled the shallowing and rejuvenation of the northeastern Australia continental shelf. However, a one-for-one relationship cannot be recognized between eustatic sea-level fluctuations and any single sedimentologic parameter. Perhaps, tectonism and sedimentological factors along the Queensland Trough played an equally important role in generating gravity deposits.Turbidites and other gravity deposits (such as those at Site 823) do not necessarily represent submarine fan deposits, particularly if they are composed of hemipelagic sediments reworked from drowned platforms and slopes. When shelves are drowned and terrigenous sediment is not directly supplied by nearby rivers/point sources, muddy terrigenous sediments blanket the entire slope and basin, rather than forming localized fans. Slope failures affect the entire slope, rather than localized submarine canyons. Slopes may become destabilized as a result of tectonic activity, inherent sediment weaknesses, and/or during relative sea-level lowstands. For this re...

3-D Seismic Characterization of Submarine Landslides on a Miocene Carbonate Platform (Luconia Province, Malaysia)

“…Numerous authors have classified slope-failure deposits and mechanisms (Kuenen and Migliorini 1975;Bouma 1962;Dott 1963;Stanley and Silverberg 1969;Schuster 1978;Lowe 1979;Eberli 1991;Einsele 1991;Watts et al 1993;Martinsen 1994;Hampton and Lee 1996;Reading 1996). These definitions, however, are difficult to apply to seismic data because they are based on attributes, such as flow rheology, transport mechanisms, internal geometry, and fabric and composition of the deposits, which are normally not detectable in seismic displays.…”

Origin of anhedral Sr‐rich calcite in deep‐water mixed sediment, north‐east Australia

“…Site 823 is located in 1600 m of water within the Queensland Trough that separates the epiconti- (Shipboard Scientific Party, 1991;Watts et al, 1993; this study) as well as sampling notation.…”

“…The stratigraphic succession records deep-water sedimentation at Site 823 since at least Middle Miocene time (Katz 81 Miller, 1993 other Leg 133 sites, Site 823 is unique for the abundance of turbidites, debrites and folded slump masses admixed and interbedded with periplatform carbonate and mixed sediment mud, hemipelagic mixed sediment and pelagic carbonate ( Fig. 2; Watts et al, 1993). An increased abundance of shelf-derived detritus at depths of >880m in Middle to Upper Miocene strata, and <250m in Upper Pliocene and Quaternary sediments (Gartner et a]., 1993), marks active shelf-margin reef development (McKenzie & Davies, 1993;Watts et al, 1993).…”

“…2; Watts et al, 1993). An increased abundance of shelf-derived detritus at depths of >880m in Middle to Upper Miocene strata, and <250m in Upper Pliocene and Quaternary sediments (Gartner et a]., 1993), marks active shelf-margin reef development (McKenzie & Davies, 1993;Watts et al, 1993). Hairline fractures and microfaults are common in strata below about 500m and are abundant below 700m, within lower Pliocene and Miocene strata, respectively.…”

“…Hairline fractures and microfaults are common in strata below about 500m and are abundant below 700m, within lower Pliocene and Miocene strata, respectively. Fracturing and mass wasting are believed to be coeval with episodic faulting along the margins of the Queensland Trough (Watts et al, 1993).…”