A modelling simulation of the syn-rift and post-rift stratigraphies and subsidence history of the Western and Eastern Black Sea basins is described. The model uses the initial lithospheric conditions and rifting parameters (thinning factors, effective elastic thickness and depth of necking) derived by large-scale lithospheric deformation modelling. Using a stratigraphic modelling approach, supported by a large and high-quality data set, constraints on the palaeowater depth evolution of the basin and associated basement subsidence are provided. The model reproduces and provides explanations for several features of the stratigraphy of the Black Sea: the apparent near-absence of syn-rift strata (other than in the Western Pontides); thin to condensed early post-rift sequences in both basins; a thick Upper Eocene sequence in the Eastern Black Sea; a relatively thin Oligocene to Miocene sequence and a very thick Quaternary sequence. It also predicts the geometry and depth of the lake that developed in the centre of the Black Sea when the sea level fell by 1500 m during the Late Miocene.
The role of pre-rift rheology on the kinematics of extensional basin formation is examined. Constraints obtained on the effective elastic thickness and level of necking, inferred from forward modelling of a number of Alpine/Mediterranean basins (including the Gulf of Lion margin, the Valencia Trough, the Tyrrhenian Sea and the Pannonian Basin), are interpreted in terms of the pre-rift rheology of the lithosphere underlying these basins. The Gulf of Lion/Tyrrhenian Sea basins and the Pannonian Basin appear to be end-members in terms of the inferred depth levels of necking. The models support the existence of spatial variations in crustal and lithospheric strength, as inferred from previous rheological modelling for other segments of the European lithosphere, and provide constraints on the ratio of crustal and subcrustal strength during extension. The results of these studies are compared with predictions on the kinematics of extension for a number of intracratonic basins, including the Black Sea basins, the Transantar, ctic Mountains/Ross Sea and Saudi Arabian Red Sea margins, and the Baikal and East African rifts. The kinematics of extension appears to be largely controlled by the (transient) thermal regime of the pre-rift lithosphere and the crustal thickness distribution. These usually result from orogenic processes operating on the lithosphere before extensional basin formation. Predictions are made for the level of external forces required to initiate rifting in intracratonic and Alpine/ Mediterranean settings. The models also shed light on the relative parts played by far-field versus near-field stresses and inferred variations in strain rate during the evolution of these basins.
We demonstrate the key role of pre-rifl rheology on the kinematics of basin formation in the Western and Eastern Black Sea basins. Constraints on modelling results are provided by a large data-set based on more than 50,000 km of multichannel seismics, offshore and onshore wells, regional gravity and magnetic surveys, refraction seismics and field studies. The model supports the presence of important differences in the thickness and in the thermal state of the lithosphere which rifted to form the Western (middle Barremian) and the Eastern (middle Paleocene) Black Sea subbasins. A 200 km and a 80 km thick pre-rift lithosphere appear to have driven the deformation in the Western and in the Eastern Black Sea, respectively. Differences in the geometry and in the mechanical properties of the pre-rift lithosphere have a strong control on the depth of necking and, thus, on the basin morphology. The model sheds light on palaeotectonic and palaeogeographic reconstructions, duration of rifting events, location of subsiding areas and erosional surfaces. The western and the eastern parts of the Black Sea appear to be two distinct basins, characterised by different evolutionary paths determined by different pre-rift conditions.
We present the results of quantitative forward modeling of the Sardinian rifted margin of the Tyrrhenian Sea. The purpose of this study is to investigate the thermomechanical structure that affects the thinning of the lithosphere across the margin. The role of lithospheric necking during basin formation, constrained by basement topography, Moho depth, and gravity anomalies, is modeled for different compensation models. Independent constraints are obtained from the analysis of the predicted thermal structure. A deep level of necking (25 km) is required to explain the observed crustal geometries and gravity anomaly signature. The model predicts spatial and temporal variations in rheology during extension with important implications for kinematics of lithospheric thinning. Prerift lithospheric conditions, strain rate, and temperature during extension appear to be the key controls on the style of lithospheric rifting and necking in the Tyrrhenian Sea. A forward model for basin stratigraphy is presented for the polyphase history of the Tyrrhenian rifting. This model provides quantitative estimates of time-space dependent crustal thinning and rates of extension. Research School of Sedimentary Geology. References Banda, E., and S. Cloetingh, Physical properties of the lithosphere, in The European Geotraverse, a Continent Revealed, edited Volcanism of the southern Tyrrhenian Sea and its geodynamics implication, J. Geophys. Res., 78, 5221-5232, 1973. Barrole, R., Seismic evidence of an earlier SPADINI ET AL.: MODELING OF THE TYRRHENLAN RWFING 643 Pliocene erosional surface in the deep part of the Tyrrhenian Sea, in Sedimentary Basins of Mediterranean Margin, edited by F.C. Wezel, pp. 127-14.5, Tecnoprint, Bologna, 1981. Bassi, G., Relative importance of strain rate and rheology for the mode of continental extension. Geophys. J. Int., in press, 1995. Bassi, G., C.E. Keen, and P. Potter, Contrasting styles of rifting: models and examples from the eastern Canadian margin, Tectonics, 12, 639-655, 1993. Bertotti, G., and M. ter Voorde, Thermal effects of normal faulting during rifted basin formation. 2: the Lugano-Val Grande normal t•ult and the role of the pre-existing thermal anomalies, Tectonophysics, 240, 145-157, 1994. Braun, J., and C. Beaumont, A physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins, Geology, 17, 760-764, 1989. Cassinis, R., R. Franciosi, and S. Scarascia, The structures of the Earth's crust in Italy: A preliminary typology based on seismic data.
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