Wyniki wyszukiwania - BazTech

1

Seismic and non-seismic soft-sediment deformation structures in the Proterozoic Bhander Limestone, central India

Sarkar S., Choudhuri A., Banerjee S., Van Loon A. J., Bose P. K.

Geologos

|

2014

|

Vol. 20, No. 2

89--103

EN

Numerous soft-sediment deformation structures occur within the Proterozoic Bhander Limestone of an intracratonic sag basin in a 750 m long section along the Thomas River, near Maihar, central India. Part of these deformation structures have most probably a non-seismic origin, but other structures are interpreted as resulting from earthquake-induced shocks. These seismic structures are concentrated in a 60 cm thick interval, which is interpreted as three stacked seismites. These three seismites are traceable over the entire length of the section. They divide the sedimentary succession in a lower part (including the seismites) deposited in a hypersaline lagoon, and an upper open-marine (shelf) part. Most of the soft-sediment deformations outside the seismite interval occur in a lagoonal intraclastic and muddy facies association. The SSDS within the seismite interval show a lateral continuity. They record simultaneous fluidisation and liquefaction. The bases of each of the three composing seismite bands are defined by small-scale shear folds, probably recording an earthquake and aftershocks. The presence of the three seismite bands at the boundary between the lagoonal and the overlying open-marine oolitic facies association suggests that the seismic event also triggered basin subsidence.

2

Jurassic evolution of the Pomeranian segment of the Mid-Polish Trough - basement vs. salt tectonics and subsidence patterns

Krzywiec P.

Volumina Jurassica

|

2006

|

Vol. 4, no. 1

54-56

EN

The Mid-Polish Trough (MPT) formed the axis of the Polish Basin that forms part of the Permian-Mesozoic system of West- and Central-European epicontinental basins. Prior to its Late Cretaceous-Paleocene inversion, the MPT was filled with several kilometres of Permian and Mesozoic sediments, including thick Zechstein salts that gave rise to the development of a complex system of salt structures in the central and northwest segments of the MPT. Thick Zechstein salts acted on a basin-wide scale as a mechanical decoupling layer during the Mesozoic evolution of the MPT. Due to this regional decoupling effect, Jurassic extensional faulting was mostly restricted to the sub-Zechstein salt basement whilst normal faulting played a subordinate role in the Jurassic syn-extensional sedimentary series that are characterized by gradual lateral thickness changes (Fig. 1A). Basement fault zones were reactivated as reverse fault zones during inversion of the Mid-Polish Trough that led to formation of the Mid-Polish Swell (Fig. 1A). Taking into account: the location of Mesozoic thickness gradients, the structural configuration of the sub-Zechstein basement, and the location of salt structures - a new tectonic map was constructed showing the inferred sub-salt fault zones that were active during the subsidence and inversion of the Pomeranian part of the MPT (Fig. 1B; cf. Krzywiec 2006). The NE boundary of the MPT was generally controlled by the SW margin of the East-European Craton, whilst its SW boundary coincides with a complex system of fault zones most probably inherited from earlier tectonic phases. Comparison of isopach maps of the Jurassic series (Dadlez 2003; Fig. 1C-E) with inferred sub-Zechstein fault zones shows the prominent role of these fault zones in development of the Jurassic sedimentary infill of the Pomeranian segment of the Mid-Polish Trough. The isopach map of Lower Jurassic series (Fig. 1C) shows a distinct thickness increase towards the axial parts of the MPT where they were partly eroded in response to inversion movements. Similarly, Middle Jurassic series have been deeply truncated and partly or even totally eroded due to the inversion-related uplift of the Mid-Polish Swell. Consequently, for these areas, the isopach map given in Fig. 1D shows tentative values only, with observed thickness values being restricted to the marginal and SE axial parts of the basin. Nevertheless, the gross thickness distribution is compatible with the concept of activity along inferred sub-salt basement fault zones controlling basin subsidence. The Upper Jurassic thickness map (Fig. 1E) is the least reliable map due to relatively widespread erosion of this complex caused by inversion and uplift of the axial part of the Mid-Polish Trough. Overall thickness changes within this complex are moderate, and they generally coincide with inferred basement fault zones. Regional thickness increase towards the SE suggests increased influence of the Tethyan domain on evolution of the Mid-Polish Trough.

3

Triassic-Jurassic evolution of the Pomeranian segment of the Mid-Polish Trough-basement tectonics and subsidence patterns

Krzywiec P.

Geological Quarterly

|

2006

|

Vol. 50, No. 1

139-150

EN

Based on reflection seismic data, a regional tectonicmodel was constructed for the sub-Zechstein basement of the Pomeranian (NW) segment of theMid-Polish Trough (MPT). This model is based on the concept that the thick Zechstein salts acted on a basin-wide scale as a mechanical decoupling layer during the Mesozoic evolution of the MPT. Due to this regional decoupling effect, Mesozoic extensional faulting was mostly restricted to the sub-Zechstein salt basement whilst normal faulting played a subordinate role in the Mesozoic syn-extensional sedimentary series characterized by gradual lateral thickness changes. Locally, normal faulting affecting Mesozoic series triggered the development of salt diapirs. Mechanical decoupling ofMesozoic series fromtheir pre-Zechstein substratum played also an important role during the Late Cretaceous-Paleogene inversion of the Mid-Polish Trough. Taking into account: 1— the location of Mesozoic thickness gradients, 2—the structural configuration of the sub-Zechstein basement, and 3—the location of salt structures, a tectonic map was constructed showing the inferred sub-salt fault zones that were active during the subsidence and inversion of the Pomeranian part of the MPT. A high degree of correlation was achieved between the seismically mapped regional sub-salt structural patterns and magnetic and gravity features, as well as the main inversion structures. Moreover, a very good correlation was established between the inferred basement fault zones and the gross thickness patterns of the Triassic-Jurassic successions. The NE boundary of theMPT was generally controlled by the SW margin of the East European Craton, whilst its SW boundary coincides with a system of fault zones most probably inherited from earlier tectonic phases. Contrary to previous hypotheses, there is no evidence for important strike-slip faulting transverse to the main axis of the Pomeranian segment of the MPT.