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Heine C.,University of Sydney | Muller R.D.,University of Sydney | Steinberger B.,Norges Geologiske Undersokelse | DiCaprio L.,University of Sydney
Tectonophysics | Year: 2010

It is well documented that the Cenozoic progressive flooding of Australia, contemporaneous with a eustatic sea level fall, requires a downward tilting of the Australian Plate towards the SE Asian subduction system. Previously, this large-scale, mantle-convection driven dynamic topography effect has been approximated by computing the time-dependent vertical shifts and tilts of a plane, but the observed subsidence and uplift anomalies indicate a more complex interplay between time-dependent mantle convection and plate motion. We combine plate kinematics with a global mantle backward-advection model based on shear-wave mantle tomography, paleogeographic data, eustatic sea level estimates and basin stratigraphy to reconstruct the Australian flooding history for the last 70 Myrs on a continental scale. We compute time-dependent dynamic surface topography and continental inundation of a digital elevation model adjusted for sediment accumulation. Our model reveals two evolving dynamic topography lows, over which the Australian plate has progressively moved. We interpret the southern low to be caused by sinking slab material with an origin along the eastern Gondwana subduction zone in the Cretaceous, whereas the northern low, which first straddles northern Australia in the Oligocene, is mainly attributable to material subducted north and northeast of Australia. Our model accounts for the Paleogene exposure of the Gulf of Carpentaria region at a time when sea level was much higher than today, and explains anomalous Late Tertiary subsidence on Australia's northern, western and southern margins. The resolution of our model, which excludes short-wavelength mantle density anomalies and is restricted to depths larger than 220 km, is not sufficient to model the two well recorded episodes of major transgressions in South Australia in the Eocene and Miocene. However, the overall, long-wavelength spatio-temporal pattern of Australia's inundation record is well captured by combining our modelled dynamic topography with a recent eustatic sea level curve. We suggest that the apparent Late Cenozoic northward tilting of Australia was a stepwise function of South Australia first moving away northwards from the Gondwana subduction-related dynamic topography low in the Oligocene, now found under the Australian-Antarctic Discordance, followed by a drawing down of northern Australia as it overrode a slab burial ground now underlying much of the northern half of Australia, starting in the Miocene. Our model suggests that today's geography of Australia is strongly dependent on mantle forces. Without mantle convection, which draws Australia down by up to 300 m, nearly all of Australia's continental shelves would be exposed. We conclude that dissecting the interplay between eustasy and mantle-driven dynamic topography is critical for understanding hinterland uplift, basin subsidence, the formation and destruction of shallow epeiric seas and their facies distribution, but also for the evolution of petroleum systems. © 2009 Elsevier B.V. All rights reserved.

Peron-Pinvidic G.,Norges Geologiske Undersokelse | Manatschal G.,French National Center for Scientific Research
Petroleum Geoscience | Year: 2010

The conjunction of high-quality seismic surveys, deep sea drilling, and progress in numerical modelling has changed the way of thinking about how continents rift and oceans form. In particular the discovery of exhumed continental mantle and hyper-extended crust in deep-water rifted margins has led to a paradigm shift in research into the evolution of rifted margins. Although rifted margins now appear to be more complex and their architecture more diverse than previously thought, their study worldwide shows that there are in fact a limited number of structures observed in seismic images that characterize their architecture. These 'building stones' include crustal blocks of various sizes, often referred to as microcontinents, continental ribbons, H-blocks, extensional allochthons and outer highs. The aim of this paper is to define the characteristics of these continental blocks and to describe their relationship and position within the rifted margins, and to understand the underlying processes that govern their formation. We propose, using the example of the North Atlantic, that these crustal blocks are the result of specific rift processes that correspond to the sequential evolution from stretching, to thinning and exhumation of the continental lithosphere. We show that the relationship between the various rift structures provides fundamental insights into the controlling processes that thin and finally rupture continental lithosphere. © 2010 EAGE/Geological Society of London.

Unternehr P.,Total S.A. | Peron-Pinvidic G.,Norges Geologiske Undersokelse | Manatschal G.,French National Center for Scientific Research | Sutra E.,French National Center for Scientific Research
Petroleum Geoscience | Year: 2010

The discovery of giant hydrocarbon reservoirs in the pre-salt sequence of the deep-water Brazilian rifted margin together with the new acquisition of high-quality reflection and refraction seismic surveys across many rifted margins worldwide has attracted the interest of industry and researchers to deep-water rifted margins. For the first time, the new data sets enable the imaging and description of the pre-salt structures, which indicate that deep-water rifted margins are very different from what classical models had predicted thus far. Instead of the expected fault-bounded basins and a sharp ocean-continent boundary, the new data suggest the existence of a sag basin lying on hyper-extended crust with little indication for brittle high-angle faulting, a transitional domain between continental and oceanic crust showing neither characteristics of oceanic nor continental material, and very asymmetrical distal conjugate rifted margins. These observations raise significant doubts on the validity of the classical concepts used in rheology, mechanics and isostasy to explain extensional systems leading to seafloor spreading. They also require new concepts and more data in order to understand how these rifted margins evolved in time and space. This has important implications for the exploration and evaluation of petroleum systems in the frontier areas of hydrocarbon exploration. In this study we publish two multi-channel seismic sections across the Angola and conjugate Brazilian rifted margins that we consider as 'type' sections for hyperextended magma-poor rifted margins in the South Atlantic. The aim of this study is to discuss various possible interpretations and models to explain the high-resolution seismic images presented in this paper. © 2010 EAGE/Geological Society of London.

Thorsnes T.,Norges Geologiske Undersokelse
Hydro International | Year: 2013

The annual Seabed Mapping and Inspection conference took place from February 6-8, 2013 in Geilo, Norway. The conference was held in Geilo, a beautiful winter paradise with 39 downhill slopes and 550km cross country tracks, more or less as far away from the ocean as one can get in Norway. The multi-beam echo sounder technology has revolutionized the world of marine mapping, and the Norwegian company Kongsberg with its EM series has been at the forefront of this development. Eddy Lund from Kongsberg, soon to retire, gave a lively description of the early development of this industry. He emphasized the importance of the cooperation with and economic support from the oil company Statoil, which needed the technology for its field developments. Acoustic and chemical sensors to detect natural gas leakages or leakages from man-made subsea constructions were presented by Terje Thorsnes from the Geological Survey of Norway, and Per Sparrevik from the Norwegian Geotechnical Institute.

Hermanns R.L.,Norges Geologiske Undersokelse | Niedermann S.,Helmholtz Center Potsdam
Special Paper of the Geological Society of America | Year: 2011

Two earthquakes are recorded in lake sediments of a former rock-avalanche-dammed lake at the outlet of the Calchaquíes valleys, Argentina. The lake existed between 13,830 ± 790 and 4810 ± 500 a, as indicated by 10Be exposure ages of the landslide deposits that impounded that lake and caused the dam erosion. Two reverse faults, with buckle folds in the footwall and slump folds in the hanging wall, indicate that two earthquakes took place while the lake sediments were water saturated, i.e., during the lake phase. Two folds only a few meters apart occur within the same lake sediment sequence over a distance of 1.3 km on two layers. Within the same two layers, there are mixed zones of convolute bedding extending several hundred meters toward the center of the former lake, which are interpreted to be seismites. These disturbed zones occur also in other subbasins of the former lake that were not affected by faulting and folding. One seismite horizon was AMS (accelerator mass spectrometry) 14C dated to 7500 ± 70 cal yr B.P. by organic material. This age agrees with the 10Be surface exposure age of 7820 ± 830 a for a cluster of four landslides 40 km NNW of the outlet of this lake, suggesting that a strong earthquake occurred at this time. © 2011 The Geological Society of America.

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