About This Item
Share This Item
Mesozoic Tethyan sedimentation may be explained tentatively by assuming a paleogeographic east-west-trending, narrow furrow dividing Europe from Africa. Along its northern margin are aligned the Carpathians, Northern Alps, Corsica-Sardinia, and Beticum; along the southern side are the Dinarides, Southern Alps, Apennines, Sicily, and the Atlas Mountains.
A slow transgression from Late Permian to early Lias is recognized from the Dolomites through Lombardy and Tuscany, and as far south as Sicily and the Atlas Mountains. The transgressive sequence overlying the continental facies is composed of clastic, shallow-marine deposits, evaporites, clayey or carbonate lagoon/tidal-flat deposits, shelf limestones, and cherty, pelagic limestones, or uninterrupted shelf sequences. The same facies sequence is recognized in the horizontal plane in two main directions along the main transgressive trend, and perpendicular to the isopach lines symmetrically disposed on both sides of the furrow. This situation is detected from Late Permian to Late Triassic, and is related to a slow downwarping. During early to middle Hettangian, a carbonate-shelf facies pread over the area, testifying to general marine conditions.
In late Hettangian time, a pelagic realm covered the region, and the facies distribution was controlled by faults parallel with or perpendicular to the main furrow. Thus, pelagic basins between small carbonate platforms were formed abruptly, attesting to the disintegration of the previous larger platform. However, tectonic control maintained the previous trend. In fact, the first pelagic facies are late Hettangian in Tuscany and Pliensbachian in Umbria. During Malm time, in the Ligurian region, continental crust broke up with extrusion of ophiolites which promoted jasper sedimentation, diminishing from Tuscany toward Umbria.
We conclude that the embryonic tectonic movements are detectable over great distances, through a slow shifting of facies in time and space. The rapid tectonic movements, instead,
account for the sudden appearance of pelagic facies which follow platform disintegration.
End_of_Article - Last_Page 774------------