We are pleased to start 2024 with a talk from Prof. Michael Stephenson on “Palynology of the Hercynian unconformity across the Arabian plate, from the Levant to southern Arabia”. As usual, the meeting will be upstairs at the RCA Conwy, LL32 8AN, with doors opening for refreshments at 18:00 and the talk scheduled to start at 18:30. All are welcome but please let us know (e-mail admin@geoscience.wales) if you plan to attend, so we may cater accordingly.
Abstract
The areal extent of the Hercynian unconformity and the hiatus it represents are important economically because typical Arabian source and reservoir rocks are often not present because of erosion (or non-deposition) related to the unconformity. Rocks affected by this include the Berwath, Jubah, and Jauf formations in Saudi Arabia and other Gulf states; and the Misfar Group and Haima Supergroup in Oman. The unconformity therefore affects access to geological formations that could hold oil and gas, or could be suitable for CCS targets, for geothermal, or for heat and cool storage.
This survey of the palynostratigraphy of the HU indicates that the range of its associated hiatus, due to either non-deposition or erosion (or both), varies considerably across the Arabian Plate depending on the position of the sequence in relation to the three main highs or arches, and any Hercynian faulting or other uplift in basinal region, for example in the Ghawar region. As expected, the succession spanning the HU is most complete in basinal areas, for example in the Nafud-Ma’aniya Basin where a very short temporal hiatus of maximum duration of approximately Serpukhovian to Bashkirian, occurs in well KH-5/1 close to the axis of the Basin. The variability of the effects of Hercynian movements may be a consequence simply of distance from Hercynian activity, or of depths within the basin that meant that uplift was not large enough to lead to either erosion or non-deposition.
Palynological assemblages in rocks above above the HU indicate the diachronous onset of the basal Khuff clastics northwest through the Arabian Plate over a period of around 15 my, from the early Wordian (base ~269 My) in Oman in the south of the Arabian Plate to the Changhsingian (base ~254 My) in Jordan in the north of the Arabian Plate. The oldest strata above the HU across the Arabian Plate also indicate systematic variation, probably due to palaeoclimate with assemblages of probably similar age in Iraq and northern Saudi Arabia showing some similarities to those of Oman, the differences probably being due to a strong climatic gradient at the time. Those below the unconformity are shown to vary considerably across the Arabian Plate depending on the position of the sequence in relation to the three main highs or arches, and any Hercynian faulting or other uplift in basinal regions, for example in the Ghawar region.
This talk contains only information in the public domain.