Palaeoclimate in earliest post Hercynian Arabian basins
How did palaeoclimate vary across the Arabian region in basins following Hercynian tectonism – and how did this affect sedimentary facies and therefore petroleum potential? Recent palaeotemperature and palaeoprecipitation modelling (Li et al., 2022) as part of the Earth Explorer Deep-time Digital Earth tool, allows some of these questions to be answered. Modelling indicates the palaeogeographic limits of glacially-influenced sedimentation in the earliest post Hercynian (the oldest Unayzah, Al Khlata and Akbarah units), and shows a very steep palaeotemperature gradient north to south in the region, which no doubt had a strong influence on facies.
Earth Explorer from DDE
The palaeoclimate part of Earth Explorer uses the data and visualisations of Li et al. (2022). Li et al. (2022) produced an open access climate dataset of 55 snapshot simulations for the past 540 million years, with a 10-million-year interval, using the Community Earth System Model version 1.2.2 (CESM1.2.2). The climate simulation dataset includes global distributions of monthly surface temperatures and precipitation, with a 1° horizontal resolution of 0.9° × 1.25° in latitude and longitude. The PaleoDEM and points/polyline/polygon (rotation and geometry files) of Scotese and Wright (2018) were used. Temperatures shown are annual mean surface temperatures, and precipitation is annual mean precipitation or mean precipitation per day (see Li et al. 2022).
The post Hercynian landscape
Interpreting the sub-crop pattern beneath the Hercynian unconformity, Faqira et al. (2009) defined three major Hercynian arches in the Arabian Plate: the Levant, the Al Batin and Oman-Hadhramaut arches, separated by two large basins in which the pre-Hercynian section (Cambrian – Devonian) is generally preserved, and further overlain by Carboniferous to Lower Permian clastic sedimentary rocks, which include the Unayzah Formation in Saudi Arabia, the Al-Khlata and Gharif formations in Oman, the Kuhlan and Akbhara formations in Yemen, and the Ga’ara Formation in Iraq.
Palaeoclimate modelling
Fig. 1 shows the Serpukhovian/Bashkirian palaeogeography in DDE Earth Explorer and the structural makeup of the region from Scotese and Wright (2018).
Explorer allows a Serpukhovian/Bashkirian palaeoclimate profile through the Gondwana to Tethys margin at the approximate age of the acme of Hercynian activity in the Arabia region (see Stephenson 2024; Stephenson et al. 2017). Fig. 1 illustrates the palaeogeography of the time. The highland areas in the SE presumably relate to the triple-junction highland area in Oman proposed by Belushi et al. (1996).
Fig. 2. Serpukhovian/Bashkirian mean annual surface temperature (MAT) in °C; 0°C palaeoisotherm and trend of MAT with paleolatitude, along palaeolongitude 40°E
Palaeoclimate modelling based on first principles physico-climatic and topographic data from Li et al. (2022) visualised in Earth Explorer shows the 0°C palaeoisotherm which theoretically confines the glacially-influenced sedimentation to the south. This seems to correspond with the present day distribution of the glacially influenced Al Khlata Formation in Oman, the Kuhlan and Akbarah formations in Yemen (Stephenson et al. 2012), as well as the more southerly occurrences of the glacially-influenced Unayzah B and C units in southern Saudi Arabia. The 0°C palaeoisotherm tends not to support glacially influenced sedimentation further north in Saudi Arabia around Ghawar, for example as advocated by (Melvyn and Sprague 2006), at least in the Serpukhovian/Bashkirian.
Fig. 3 shows the variation in precipitation from north to south through the region from around 700mm in the north (palaeolatitude 30°C) to higher amounts in the south (>1000mm). Inset shows palaeoprecipitation profile along palaeolongitude 40°E.
Impact on facies and petroleum prospectivity
Glacially influenced sedimentary rocks are well known to provide the reservoirs (diamictite, glaciofluvial and glaciodeltaic sandstones) for petroleum, often sourced in the Arabian Palaeozoic by Lower Palaeozoic hot shales. Thus palaeotemperature variation places a useful theoretical boundary for the development of glacially influenced sediments. The variation in palaeoprecipitation perhaps also provides some input to facies types within clastic palaeoenvironments, which in the Arabia area in the Serpukhovian/Bashkirian would have ranged from relatively wet environments in the south, to potentially semi-arid environments in the north. This obviously had a strong influence on the palaeovegetation (see Stephenson 2024 and in Stephenson 2025, in press).
References
Al-Belushi, Juma D., Kenneth W. Glennie, Brian P.J. Williams; Permo-Carboniferous Glaciogenic Al Khlata Formation, Oman: A New Hypothesis for Origin of its Glaciation. GeoArabia 1996;; 1 (3): 389–404. doi: https://doi.org/10.2113/geoarabia0103389
Faqira, Mohammad, Rademakers, Martin, AbdulKader M. Afifi 2009. New insights into the Hercynian Orogeny, and their implications for the Paleozoic Hydrocarbon System in the Arabian Plate. GeoArabia, v. 14, no. 3, 2009, p. 199-228
Li, X., Hu, Y., Guo, J. et al., 2022. A high-resolution climate simulation dataset for the past 540 million years. Sci Data 9, 371, https://doi.org/10.1038/s41597-022-01490-4
Melvin, J., Sprague, R. A., 2006. Advances in Arabian stratigraphy: Origin and stratigraphic architecture of glaciogenic sediments in Permian-Carboniferous lower Unayzah sandstones, eastern central Saudi Arabia. GeoArabia 11, 105–152. doi: https://doi.org/10.2113/geoarabia1104105
Scotese, C.. Wright, N., 2018. Earthbyte https://www.earthbyte.org/paleodem-resource-scotese-and-wright-2018/
Stephenson, M H 2024. Palynology of strata associated with the Hercynian Unconformity across the Arabian Plate, from the Levant to southern Arabia, Geological Society, London, Special Publications Volume 550 https://doi.org/10.1144/SP550-2023-182
Stephenson, M H, Jan, I U, and Al-Mashaikie, S Z A K. 2012. Palynology and correlation of Carboniferous – Permian glacigene rocks in Oman, Yemen and Pakistan. Gondwana Research, 24, 203-211.
Stephenson, M H, Kader Al-Mashaikie, S Z A, and Kurukchi, W M. 2017. Palynological assemblages across the Hercynian unconformity in Western Iraq. Revue de Micropaleontologie, 60, 417-432.
Stephenson, MH, Shen, S., Fan, J. Hu, L., Qi, J. in press. Effect of steep climate gradient on palynological assemblages on the Arabian part of the Tethys shore in two Carboniferous-Permian ice age time slices. Review of Palaeobotany and Palynology
About Michael H. Stephenson
Prof Mike Stephenson is a palynologist and stratigrapher at Stephenson Geoscience Consulting. He is an acknowledged expert in Middle-Eastern Palaeozoic palynology and stratigraphy with around 200 commercial reports and 120 peer-reviewed papers on palynology and stratigraphy. His particular expertise is pre-Khuff palynology including regional correlation projects in the Al Khlata, Gharif, Misfar, Jauf, Unayzah and Khuff formations.
Mike is available for consulting.