Triassic-jurassic Boundary on the Southern Margin of Tethys: Implications of Facies, Tectonics and Volcanism

The facies changes, tectonics and magmatism across the Triassic–Jurassic boundary in the southern Tethyan margin have been studied in Egypt, Sudan, Jordan and Saudi Arabia. In Saudi Arabia and Jordan an unconformable contact is recognized between the Upper Triassic and Lower Jurassic rocks. This unconformity surface is marked by the truncation of the fluvial clastics of the uppermost Triassic before and during the deposition of the lowermost Jurassic carbonate, recording a regression-transgression pulse. In Egypt and Sudan, there is substantial ambiguity in the position of the Triassic-Jurassic contact, because Middle and Upper Triassic rocks are not present and the Lower Triassic rocks are overlain directly by Lower and Middle Jurassic rocks. This unconformity may have resulted from the east-west tectonics and possibly volcanic activity that took place during this period (Late Triassic-Early Jurassic). Numerous tectonic processes were active during the time represented by this unconformity, most of which were east-west uplifts that dominated in Egypt, following which the Upper Triassic rocks were eroded or not deposited. In the Arabian Basin, east-west tectonics (in the south) and northeastdirected tectonics (in the north) caused intermittent erosion of the Upper Triassic facies. Magmatism that was active at the end of the Triassic generated hydrothermal iron deposits within the fluvial sandstones and triggered volcanic eruptions in the south and some northern parts of Egypt.