Kring Noord KNGMG: lezing juni

NGMG kring Noord lezing heeft als onderwerp:
“Carbonates of Oman”. De lezing wordt gepresenteerd door Henk Droste (ex Shell)

De lezing wordt online worden gegeven van 17:00 tot 18:00 uur. U kunt vanaf 16:30 uur inloggen. U kunt deel nemen via deze Microsoft Teams link.

Korte samenvatting:

• The Sultanate of Oman is located on the eastern margin of the Arabian Plate. It has a unique plate tectonic setting with active plate boundaries of the Eurasian collision zone in the north, the Owen transform fault with the Indian Plate in the East, and the Gulf of Aden spreading center in the South. The mountain belts and uplifted areas linked to these plate boundaries expose an extremely varied sedimentary sequence that goes back more than 800 Ma in time. Due to the arid climate, the exposures are of very high quality and laterally continuous, and provide textbook examples for sedimentological, stratigraphic and structural studies. Furthermore, hydrocarbon exploration and production in the interior of Oman provided an extensive subsurface dataset that can be linked to the outcrops.  This allowed a much better understanding of the internal architecture and distribution of the different depositional systems in space and time.
• Oman was covered by shallow tropical seas during long periods of its geological history and carbonate rocks make up a major part of the sedimentary sequence. As the sedimentary record covers a long-time span, it nicely illustrates how carbonate systems changed through time in response to the evolution of carbonate producing organisms and chemical changes in the oceans.
• The oldest carbonate platforms in Oman were deposited during the Neoproterozoic when the reef producing organisms that we know today were absent. The only organic carbonate production was by microbial communities that trapped, bound and precipitated carbonate mud. Still, these communities built carbonate platforms of several 100’s m high, comparable to platforms we see today.
• A second period of major carbonate production was during the Permo Triassic when a carbonate platform of more that 1 km thick covered the northern part of Oman. Coral reefs covered the rifted margin along the NeoTethys ocean in the North.  The interior part of the platform was dominated by lagoonal carbonate mud and sands associated with evaporites reflecting the palaeogeographic position of Oman in the arid climate belt.
• Following an uplift along the eastern margin of Oman, carbonate deposition continued in the Jurassic. However, these carbonates were dominated by sands with carbonate ooids and reworked bioclasts and reef building organisms were absent. This complex of carbonate sand shoals prograded towards the west into the Rub Al Khali Basin and the platform had a low angle ramp morphology.
• During the Cretaceous there was again major carbonate platform development. It started with a strongly prograding carbonate shelf of several 100’s m high with spectacular clinoforms visible on seismic. During a middle Cretaceous relative rise in sea level this shelf developed into an aggradational epeiric carbonate platform with intra platforms basins. The main carbonate producers were rudist mollusks and calcareous plankton. The Cretaceous epeiric shelf persisted until the Turonian, when it was exposed by a regional uplift preceding the closure of the NeoTethys Ocean and collision with Eurasia.
• Following the Late Cretaceous deformation most of Oman was covered by a shallow interior sea with deposition of shallow marine carbonates and minor evaporite beds during most of the Cenozoic.  The main carbonate producers during this time were larger benthic foraminifera such as nummulites which were reworked in sand shoals, and, along the ocean margin coral and algal reefs.

Over de spreker:
Henk Droste studied Geology at the University of Amsterdam and worked 32 years for Shell in various positions in Research, Exploration and Production in The Netherlands, UK and Oman. Since his retirement in 2016, he is working as a geological consultant and trainer in Oman. He is a specialist on carbonates and the geology of the Arabian Plate with an extensive publication record. In 2020 he started a DPhil study at Oxford University on the sedimentary record of ophiolite obduction in North Oman.