72 research outputs found
Magnetic expression of the continent-ocean boundary between the western margin of Australia and the eastern Indian Ocean
Get PDFA comprehensive review of the Early Cretaceous seafloor-spreading magnetic anomalies (M0 to M10) in the eastern Indian Ocean leads to the isolation of a distinctive magnetic anomaly at the continent-ocean boundary (COB). This anomaly is traceable 2000 km southward from the rifted margin of the magnetically smooth central Exmouth Plateau, through the transform-faulted and rifted margins of the Cuvier Abyssal Plain and Carnarvon Terrace and the set of narrow spreading segments south of the Zenith-Wallaby Fracture Zone to the area west of Perth. The anomaly corresponds to the COB as indicated by: 1. the lower part of the continental slope in a mean water depth of 3.75 km for the rifted margin and 4.5 km for the transform-faulted margin and 2. a change in seismic-reflection character from the faulted breakup unconformity on the continent to the smooth but hyperbolic oceanic layer 2. The COB anomaly at the rifted margin is modelled by modifying the magnetization of the oldest oceanic block of the seafloor-spreading sequence adjacent to the continental crust; in places, the COB anomaly is flanked by smaller anomalies modelled as rift-related dykes in the adjacent continental crust. The amplitude of the COB anomaly, commonly twice or more that of the adjacent oceanic magnetic anomalies, is due either to a thicker or a more intensely magnetized source. The COB anomaly at the transform-faulted margin is modelled by a thick vertical body that extends 10 km seaward of the COB. The Wallaby Plateau is probably underlain by oceanic crust, as shown by the continuity of the abandoned spreading ridge of the Sonne Ridge southwestward from the Cuvier Abyssal Plain; the shape of the Wallaby Plateau and the volcanic composition of dredge-hauls indicate that it is probably a volcanic upgrowth of the oceanic crust as exemplified by Iceland today. Furthermore, like lceland, the Wallaby Plateau is crossed by magnetic anomalies that are possibly degraded seafloor-spreading anomalies. The Zenith Plateau lacks magnetic lineations and its crustal structure, like that of the Naturaliste Plateau to the south remains unknown.
ARK: https://n2t.net/ark:/88439/y098447
Permalink: https://geophysicsjournal.com/article/239
 
Early Jurassic palaeoenvironments in the Surat Basin, Australia - marine incursion into eastern Gondwana
Get PDFInterpretations of palaeodepositional environments are important for reconstructing Earth history. Only a few maps showing the Jurassic depositional environments in eastern Australia currently exist. Consequently, a detailed understanding of the setting of Australia in Gondwana is lacking. Core, wireline logs, two‐dimensional and three‐dimensional seismic from the Precipice Sandstone and Evergreen Formation in the Surat Basin have been used to construct maps showing the evolution of depositional environments through the Early Jurassic. The results indicate the succession consists of three third‐order sequences (Sequence 1 to Sequence 3) that were controlled by eustatic sea level. The lowstand systems tract in Sequence 1 comprises braidplain deposits, confined to a fairway that parallels the basin centre. The strata were initially deposited in two sub‐basins, with rivers flowing in different orientations in each sub‐basin. The transgressive systems tract of Sequence 1 to lowstand systems tract of Sequence 3 is dominated by fluvio–deltaic systems infilling a single merged basin centre. Finally, the transgressive and highstand systems tracts of Sequence 3 show nearshore environments depositing sediment into a shallow marine basin. In the youngest part of this interval, ironstone shoals are the most conspicuous facies, the thickness and number of which increase towards the north and east. This study interprets a corridor to the open ocean through the Clarence–Moreton Basin, or the Carpentaria and Papuan basins, evidence of which has been eroded. These results challenge a commonly held view that eastern Australia was not influenced by eustasy, and propose a more dynamic palaeogeographic setting comprising a mixture of fluvial, deltaic and shallow marine sedimentary environments. This work can be used to unravel the stratigraphic relationships between Mesozoic eastern Australian basins, or in other basins globally as an analogue for understanding the complex interplay of paralic depositional systems in data poor areas
Phanerozoic Australia in the Changing Configuration of Proto-Pangea Through Gondwanaland and Pangea to the Present Dispersed Continents
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Impact on Australia and Antarctica of the Collisional Merging of Gondwanaland and Laurussia in Pangea
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