Sprecher
Beschreibung
Exposed Devonian rocks are known only from northwest Saudi Arabia, adjacent to the Precambrian Arabian Shield. Most of the Devonian deposits, which comprises the upper Tawil, Jauf and most of the Jubah formations, occur in subsurface, both in the northwest but also in eastern Saudi Arabia. Some exploration wells have penetrated up to 2,300 ft of Devonian section throughout eastern Saudi Arabia and more than 5,000 ft in the centre of the Nafud Basin. Although the Devonian is seemingly conformable with the overlying Mississippian section, its upper boundary is often eroded by either the pre-Khuff (Mid Permian) or pre-Unavzah (Permo-Carboniferous) unconformities in eastern Saudi Arabia. The Saudi Arabian Devonian succession was generally deposited in a continental to shallow marine depositional system in which substantial siliciclastic-dominated deposits accumulated, in essentially broad transgressive-regressive cycles. A retrogradational cycle (fining-upward) encompassing the Early Devonian Tawil and Jauf formations, followed by a progradational cycle (coarsening-upward) through much of the Mid-Late Devonian Jubah Formation. The terrestrially dominated paleoenvironments of the upper Tawil, Jauf and Jubah formations provide a record of the rapid evolution of Devonian land plants in the form of their dispersed miospores. Thus, these palynomorphs are the chief biostratigraphic tool to age date and correlate these deposits. Acritarchs and chitinozoans are often absent or generally less abundant, although they occur in some specific levels. The current operational palynozonation is robust with nine palynozones combined with numerous palynological events.