摘要:

The base of the Late Devonian–Early Carboniferous Drummond Basin, a major backarc extensional feature in eastern Australia which formed in response to detachment faulting, is extensively exposed in central Queensland. Here a crystalline basin floor is overlain by the Silver Hills Volcanics, a synrift sequence of predominantly silicic ash flow tuffs and lavas ranging to over 2 km in thickness. Detailed mapping of faults and stratigraphic logging of thickness changes within the Silver Hills Volcanics have allowed the rift‐phase structural architecture that accompanied initial subsidence near the basin margin to be resolved. A complex mosaic of block faults with throws of up to 1 km is indicated. Locally developed mosaics may conform to, or depart from, the configuration predicted by the detachment faulting model. Structural fabric of the basement was a critical determinant of the extensional geometry. Distributed shear along pre‐existing penetrative planar fabrics is considered to have accommodated hangingwall extension at lower strain rates whereas the propagation of tension fractures and the development of block faults by failure on pre‐existing, brittle, basement dislocations facilitated extension at higher strain rates. The detachment fault inferred to lie beneath the extended hangingwall carapace has not been mapped at the surface and is thought to dissipate into a broad zone of distributed shear within basement to the east of the basin. Volcanism coincided with the initiation of extensional movements at which time deep crustal repositories for evolved magma were tapped by extensional fractures. The main extensional faults cutting the basinal succession were not used as conduits for magmatic products which were sourced from the basin margin and from extended hinterland to t

ISSN:0950-091X    

DOI:10.1046/j.1365-2117.1996.00161.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

Integrated analysis and modelling of apatite fission track with vitrinite reflectance (VR) data allows the timing, magnitude and pattern of Palaeogene subsidence and Neogene inversion to be established for an uplifted and largely denuded basin: the Buller Coalfield, New Zealand. At the time of maximum subsidence in the late Oligocene, the basin consisted of an extensional half graben, bounded to the west by the Kongahu Fault Zone (KFZ), with up to 6 km of upper Eocene to Oligocene section adjacent to it; currently, only a few tens of metres of basal coal measures on basement are preserved on top of a range 800–1000 m above sea level. Integrated modelling of the VR and fission track data show that the deepest parts of the basin were inverted during two Miocene compressional phases (24–19 Ma and 13–8 Ma), and are consistent with a further phase of inversion during the Quaternary that formed the present topography. Palinspastic restoration of the three phases of inversion shows that the basin was not inverted in a simple way: most of the rock uplift/denudation adjacent to the KFZ occurred during the early Miocene phase, and at the same time burial occurred in the south‐eastern part of the basin (maximum temperatures were experienced at different times at different places in the basin); during the middle to late Miocene there was broad uplift in the central and eastern parts of the coalfield. Because the timing and magnitude of uplift have been derived from the zone of inversion, they can be compared independently with the timing of unconformity development and rapid subsidence in the adjacent foredeeps, particularly the Westport Trough. For the middle to late Miocene phase of inversion, we show that during the first 1–2 million years of compression, the uplift within the coalfield also involved the margins of the Westport Trough, contributing to unconformity development; subsequently, uplift continued on the inversion structure but the margins of the Westport Trough subsided rapidly. This is explained by a model of stick slip behaviour on the boundary faults, especially for the KFZ. When compression started the fault zone has locked and uplift extends into the basin, whereas subsequently the fault zone unlocks, and the inversion structure overrides the basin margin, thereby loading it and causing s

ISSN:0950-091X    

DOI:10.1046/j.1365-2117.1996.00152.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

The Neoproterozoic basins of central Australia share many features of architecture and sedimentary fill, suggesting common large‐scale extrinsic causal mechanisms. In an attempt to improve understanding of these mechanisms we have gathered and analysed new deep seismic reflection data and re‐evaluated existing seismic and well‐log data from the eastern Officer Basin, the largest and most poorly known of Australia's intracratonic basins.The Officer Basin is asymmetric and has a steep thrust‐controlled northern margin paralleled by sub‐basins as much as 10 km in depth. Further south the basin shallows gradually onto a broad platform. The basin rests on a thick crust (≈42 km) that is pervaded by a complex of northward‐dipping surfaces most of which terminate erosionally against the sediments of the Officer Basin and are interpreted as prebasinal features, possibly faults. Some appear to have been zones of crustal weakness which were reactivated as thrust complexes and played a major role in basin evolution.The sedimentary succession can be subdivided into six megasequences separated by major tectonically and erosionally enhanced sequence boundaries. The megasequences have distinctive sequence stacking patterns suggesting that they were deposited in response to episodic subsidence induced by a major extrinsic tectonic event. The basin initially formed as part of a giant sag basin which incorporated all the present‐day intracratonic basins (Amadeus, Georgina, Ngalia, Officer and Savory Basins) in a single large ‘superbasin’ perhaps as a response to mantle processes. Subsidence then ceased for ≈100 Myr producing a regional erosion surface. Beginning in the Torrensian or Sturtian five more major events of varying regional significance influenced the basin's evolution. Four were compressional events, the first of which activated major thrust complexes along the present basin margins, forming deep foreland sub‐basins with elevated intervening basement blocks. Once activated, the thrust complexes and sub‐basins persisted throughout the life of the intracratonic basins. From this epoch the intracratonic basins of central Australia were decoupled from the giant sag basin and became interrelated but independent features.Available information suggests that the Officer, Amadeus, Georgina, Ngalia and Savory Basins are related and are perhaps products of major tectonic events associated with the assembly and ultimate dispersal of the Proterozoic supercontinent. The closing phases of these basins were strongly influenced by events occurring along the newly created active eastern margin of the Australian

ISSN:0950-091X    

DOI:10.1046/j.1365-2117.1996.00223.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY

摘要:

The earliest evolution of the North Alpine Foreland Basin in Switzerland was characterized by deposition in small, structurally partitioned sub‐basins during the Late Cretaceous and Early Tertiary, rather than in a single, large foredeep. These sub‐basins, which were probably located between old rift margin fault‐blocks reactivated during Alpine compression, were incorporated into the thrust wedge during thin‐skinned deformation. In eastern Switzerland, the most external sub‐basins with respect to the orogenic wedge (North Helvetic Flysch and Blattengrat units) have at their base an unconformity attributed to flexural forebulge erosion. More internal sub‐basins (Sardona and Prättigau units) contain a conformable succession from the underlying passive margin stage and are dominated by deep‐water sedimentation. In western Switzerland, both external sub‐basins, now found in the Helvetic Diablerets and Wildhorn nappes, and deep‐water internal sub‐basins (Höchst‐Meilleret Flysch, Neisen Flysch, Tarentaise Flysch) preserve a well‐developed basal unconformity. Comparison of the eastern and western Swiss transects shows important intrabasinal lateral variations to be present.The western Swiss area was a topographic high for much of the Late Cretaceous and Early Tertiary; this is demonstrated by the increased chronostratigraphic gap at the karstified basal unconformity surface in western Switzerland. The strata onlapping this unconformity young to the west, suggesting that drowning of the emergent area was delayed compared with the east. In addition, reactivation and uplift of the rift margin structures occurred earlier in western Switzerland compared with eastern Switzerland. There is therefore strong evidence for lateral topographic gradients in the early foreland basin caused by differential amounts of tectonic reactivation of rift margin structures. In the early foreland basin‐fill, these lateral variations are as important in determining depositional patterns as strike‐no

ISSN:0950-091X    

DOI:10.1046/j.1365-2117.1996.00244.x

出版商:Blackwell Science Ltd.    

年代:1996

数据来源: WILEY