A REGIONAL INTERPRETATION OF THE BROWSE BASIN

1978 ◽  
Vol 18 (1) ◽  
pp. 23 ◽  
Author(s):  
G. A. Allen ◽  
L. G. G. Pearce ◽  
W. E. Gardner
Keyword(s):  
Ocean Circulation ◽  
Continental Margin ◽  
Middle Jurassic ◽  
Depositional Environment ◽  
Important Change ◽  
Structural Elements ◽  
Seaward Edge ◽  
Geological Event ◽  
Intracratonic Basin ◽  
Block Faulting

The Browse Basin, off the northwest coast of Australia, originated as an intracratonic basin. It resulted from tensional movements and developed into an Atlantic-type continental margin. Sedimentation, which commenced in the Late Carboniferous and extended through the Middle Jurassic, is confined mostly to a linear, northeast-trending depocentre located between the onshore Kimberley Block and the Scott Plateau to the west. This sedimentary series is characterised by rift valley type deposits laid down between successive episodes of tectonism. Tectonism near the end of the Middle Jurassic was associated with breakup of the continent along what developed as the seaward edge of the Scott Plateau. This geological event marks an important change in the depositional environment of the basin from pre-breakup, mainly paralic and fluviodeltaic to post-breakup, transgressive marine conditions. The post-breakup series was formed under relative tectonic quiescence, except for some local structural rejuvenation and regional subsidence of the outer continental margin which eventually resulted in the deposition of Cretaceous and Tertiary sediments across the Scott Plateau. A fully open marine environment, however, was not achieved basinwide until during the Late Cretaceous, when the Scott Plateau had subsided sufficiently to allow unrestricted ocean circulation. Evolution of the basin was completed by a seaward prograding, mainly carbonate Tertiary wedge.Geophysical data show several sub-parallel, structurally high Mesozoic trends, oriented towards the northeast. The Scott Reef gas/condensate discovery lies on one such trend. The structural elements were interpreted as being mostly initiated prior to breakup by episodes of block faulting which produced a horst and graben topography. The horst blocks were subsequently onlapped and draped by the post-breakup sediments. The hydrocarbon accumulation at Scott Reef is restricted to the horst block reservoirs, but hydrocarbon indications elsewhere within the basin in the post-breakup series suggest that accumulations could also exist in this section.

THE GEOLOGICAL EVOLUTION OF THE CONTINENTAL MARGIN OFF NORTHWEST AUSTRALIA

1976 ◽  
Vol 16 (1) ◽  
pp. 13 ◽  
Author(s):  
D.E. Powell
Keyword(s):  
Continental Margin ◽  
Middle Jurassic ◽  
Large Scale ◽  
Sedimentary Basins ◽  
Upper Jurassic ◽  
Hydrocarbon Generation ◽  
Carbonate Sediments ◽  
Intracratonic Basin ◽  
Uplift And Erosion ◽  
Depth Of Burial

The area comprising the Northwest Shelf of Australia is a good example of an 'Atlantic-type' continental margin. It is characterised by a series of major sedimentary basins of Mesozoic age, which generally parallel the present coastline. In each of these depocentres distinct lithotectonic units can be recognised which are related to phases of rifting and subsequent continental breakup. The pre-breakup rift valley and intracratonic basin stages are represented by a very thick Permian to Middle Jurassic series of mainly fluviodeltaic sediments. Breakup took place near the end of the Middle Jurassic and was accompanied by large-scale block faulting with associated uplift and erosion. As a result the ensuing Upper Jurassic to Lower Cretaceous marine transgression took place over a highly irregular palaeotopographic surface. With continuing post-breakup subsidence, open marine conditions became widespread by Upper Cretaceous time. Since the mid-Eocene the deposition of a thick prograding wedge of mainly carbonate sediments has given a general northwesterly regional tilt to the shelf. Such progradation is characteristic of a fully-evolved Atlantic-type continental margin.Hydrocarbon occurrences on the Northwest Shelf can be related to the tectonic evolution. Major gas/condensate discoveries have been encountered in fluviodeltaic reservoirs within the block-faulted pre-breakup sequence, sealed by post-breakup transgressive marine shales which also provide important source intervals. In addition, some sandstone units of the transgressive series are hydrocarbon-bearing. The prolonged post-breakup subsidence and accompanying thick sedimentation has ensured that source intervals have locally attained the necessary depth of burial for hydrocarbon generation.

scholarly journals New sea spiders from the Jurassic La Voulte-sur-Rhône Lagerstätte

2007 ◽  
Vol 274 (1625) ◽  
pp. 2555-2561 ◽  
Author(s):  
S Charbonnier ◽  
J Vannier ◽  
B Riou
Keyword(s):  
Deep Sea ◽  
Middle Jurassic ◽  
Evolutionary History ◽  
Depositional Environment ◽  
Ecological Stability ◽  
Sea Spiders ◽  
History Of

The diverse and exceptionally well-preserved pycnogonids described herein from the Middle Jurassic La Voulte Lagerstätte fill a 400 Myr gap of knowledge in the evolutionary history of this enigmatic group of marine arthropods. They reveal very close morphological and functional (locomotion, feeding) similarities with present-day pycnogonids and, by contrast, marked differences with all Palaeozoic representatives of the group. This suggests a relatively recent, possibly Mesozoic origin for at least three major extant lineages of pycnogonids (Ammotheidae, Colossendeidae, Endeidae). Combined evidence from depositional environment, faunal associates and recent analogues indicate that the La Voulte pycnogonids probably lived in the upper bathyal zone ( ca 200 m). Our results point to a remarkable morphological and ecological stability of this arthropod group over at least 160 Myr and suggest that the colonization of the deep sea by pycnogonids occurred before the Jurassic.

Late Mesozoic Paleo-Pacific Plate “scissors-like” subduction: Insight from the magmatism in the Gan-Hang Belt, Southeast China

2020 ◽  
Author(s):  
Liu Boran ◽  
Zhao Xilin ◽  
Yu Shengyao ◽  
Jiang Yang ◽  
Mao Jianren ◽  
...  
Keyword(s):  
Continental Margin ◽  
Middle Jurassic ◽  
Tectonic Setting ◽  
Pacific Plate ◽  
Geochemical Data ◽  
Asian Continent ◽  
Southeast China ◽  
Late Mesozoic ◽  
Extensional Tectonic ◽  
Roll Back

Though it is widely accepted that the Paleo-Pacific Plate has a subducted beneath the eastern Asian continent, controversy still exists regarding the initial timing and geodynamic model of the subduction. In this contribution, we report new geochronology and geochemical data of granitic plutons within the Gan-Hang Belt in Southeast China. The Damaoshan pluton yields zircon U-Pb ages of 139.60 ± 0.69 Ma and 133.90 ± 1.70 Ma, and the Qianshan and Fenglonggu plutons are dated at 135.70 ± 1.30 Ma and 135.33 ± 0.93 Ma, respectively. The Hecun and Huangtuling plutons yield ages of 157.85 ± 0.77 Ma and 167.10 ± 7.50 Ma, respectively. The Damaoshan pluton has an obvious A-type geochemical signature in terms of major and trace element compositions, such as high K2O+Na2O contents (average 8.46 wt%) and FeOT/MgO ratios (average 10.29). The low CaO/Na2O ratios but high Al2O3/TiO2 (average is 110.05), Rb/Ba (average is 9.14), and Rb/Sr (average is 22.53) ratios indicate a derivation from pelite-derived melt. Meanwhile, we also studied the Mesozoic adakites related to magmatic ore formed during a compressive tectonic setting as well as the later bimodal dikes and A-type granitic plutons formed during the extensional tectonic setting in the Gan-Hang Belt. The multiphase qualitative plutons with geochemical characteristics of the adakitic and island arc types (175−150 Ma) related to the northwestward subduction of the Paleo-Pacific Plate, several bimodal dikes, and A-type granitic plutons (135−123 Ma) related to the subducted slab roll-back are found within the Gan-Hang Belt. All of these plutons show a decreasing trend of isotopic ages from the inland area to the coast, from SW to NE. We propose that the distribution pattern of these plutons in Southeast China was controlled by a scissors-like subduction and slab roll-back of the Paleo-Pacific Plate, which occurred roughly from SW to NE along the continental margin approximately during the Middle Jurassic to the Early Cretaceous.

Geodynamic evolution of the Canadian Cordillera — progress and problems

1979 ◽  
Vol 16 (3) ◽  
pp. 770-791 ◽  
Author(s):  
J. W. H. Monger ◽  
R. A. Price
Keyword(s):  
Continental Margin ◽  
Middle Jurassic ◽  
Rocky Mountain ◽  
Ocean Basin ◽  
Strike Slip ◽  
Granitic Rocks ◽  
Canadian Cordillera ◽  
Thrust Faulting ◽  
Western Cordillera ◽  
Geophysical Surveys

The present geodynamic pattern of the Canadian Cordillera, the main features of which were probably established in Miocene time, involves a combination of right-hand strike-slip movements on transform faults along the continental margin, and, in the south and extreme north, convergence in subduction zones in which oceanic lithosphere moves beneath the continent, with consequent magmatism along the continental margin. In the southern Canadian Cordillera, geophysical surveys have outlined the subducting slab and the asthenospheric bulge that occurs beneath and behind the magmatic arc. They also show that there is now no root of thickened Precambrian continental crust beneath the tectonically shortened supracrustal strata in the southern parts of the Omineca Crystalline Belt and Rocky Mountain Belt.The Rocky Mountain, Omineca Crystalline, Intermontane, Coast Plutonic, and Insular Belts, the structural and physiographic provinces that dominate the present configuration of the Canadian Cordillera, were established with the initial uplift and the intrusion of granitic rocks in the Omineca Crystalline Belt in Middle and Late Jurassic time and in the Coast Plutonic Complex in Early Cretaceous time, and they dominated patterns of uplift, erosion and deposition through Cretaceous and Paleogene time. Their development may be due to compression with thrust faulting in the eastern Cordillera, and to magmatism that accompanied subduction and to accretion of an exotic terrane, Wrangellia, in the western Cordillera. Major right-lateral strike-slip faulting, which occurred well east of but sub-parallel with the continental margin during Late Cretaceous and Paleogene time, accompanied major tectonic shortening due to thrusting and folding in the Rocky Mountain Belt as well as the main subduction-related (?) magmatism in the Coast Plutonic Complex.The configuration of the western Cordillera prior to late Middle Jurassic time is enigmatic. Late Paleozoic and early Mesozoic volcanogenic strata form a complex collage of volcanic arcs and subduction complexes that was assembled mainly in the Mesozoic. The change in locus of deposition between Upper Triassic and Lower to Middle Jurassic volcanogenic assemblages, and the thrust faulting in the northern Cordillera may record emplacement of another exotic terrane, the Stikine block, in latest Triassic to Middle Jurassic time.The earliest stage in the evolution of the Cordilleran fold belt involved the protracted (1500 to 380 Ma) development of a northeasterly tapering sedimentary wedge that discordantly overlaps Precambrian structures of the cratonic basement. This miogeoclinal wedge may be a continental margin terrace wedge that was prograded into an ocean basin, but it has features that may be more indicative of progradation into a marginal basin in which there was intermittent volcanic activity, than into a stable expanding ocean basin of the Atlantic type.

scholarly journals Middle Jurassic (Bajocian) planktonic foraminifera from the northwest Australian margin

2020 ◽  
Vol 39 (2) ◽  
pp. 93-115
Author(s):  
Marjorie Apthorpe
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Southern Hemisphere ◽  
Continental Margin ◽  
Middle Jurassic ◽  
Planktonic Foraminifera ◽  
Microscope Images ◽  
Northwestern Australia ◽  
Tethys Ocean ◽  
Scanning Electron

Abstract. The aim of this paper is to document three well-preserved morphotypes of Middle Jurassic (Bajocian) planktonic foraminifera from the continental margin of northwestern Australia. This location is on the southern shelf of the Middle Jurassic Tethys Ocean, and these occurrences of planktonic or meroplanktonic species are the first to be reported from the Jurassic of the Southern Hemisphere. The morphotypes include a new subspecies of Globuligerina bathoniana (Pazdrowa): Globuligerina bathoniana australiana n. ssp. Two other taxa are also described: Globuligerina altissapertura n. sp. and Mermaidogerina loopae n. gen. n. sp. The microstructure of the wall is shown in scanning electron microscope images. The change from chamber to chamber in the formation of the surface ornament by secondary lamination, and its subsequent burial within the wall, is demonstrated in detail.

scholarly journals The depositional environment of the Laptev Sea continental margin: preliminary results from the R/V Polarstern ARK IX-4 cruise

1995 ◽  
Vol 14 (1) ◽  
pp. 43-54
Author(s):  
D. Nürnberg ◽  
D. K. Fütterer ◽  
F. Niessen ◽  
N. Nørgaard-Pedersen ◽  
C. J. Schubert ◽  
...  
Keyword(s):  
Continental Margin ◽  
Depositional Environment ◽  
Laptev Sea ◽  
Preliminary Results ◽  
The Laptev Sea
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