Monday, 15 June, 2026/Edition 115

This week, we will focus on Southeast Asia, as the region is warming up for a renewed phase of exploration.

The SEAPEX Regional Convention was held in the Philippines in April; Indonesia announced a new bidding round in May; and the 55th IAGI-GEOSEA XIX conference will be held in Indonesia in November.

This edition is also dedicated to the memory of Chris Howells (1970–2026), who devoted his life to the geology of Southeast Asia.

Rasoul Sorkhabi

Editor, Core Elements

China’s Offshore Basins

Distribution map of petroleum basins in China (AAPG Bulletin, May 2026)

Weilin Zhu and Yuhong Xie provide an informative review of offshore Chinese basins in the AAPG Bulletin.

Basin data: The authors list 20 petroleum basins of China, of which seven are offshore.

• These offshore basins produced 1.4 million barrels of oil a day in 2024.
• They cover roughly 700,000 square kilometers.
• They contain recoverable reserves of more than 14 billion barrels of oil and 35 trillion cubic feet of gas.

Plate interactions: These basins were formed and evolved through interactions between the Eurasian, Pacific, Philippine Sea, and Indo-Australian tectonic plates.

Diverse tectonic styles: The basins evolved through multiple tectonic stages, including continental rift, subduction, back-arc rift, fore-arc fill, thermal sag, passive margin, and strike-slip pull-apart.

These basins contain two regional source rocks:

• Oil-prone Eocene lacustrine shales
• Oligocene-Miocene gas-prone paralic formations

Some basins are heavily dominated by oil or gas pools.

• Oil-dominated basins: The Bohai Bay and shallow-water northern South China Sea
• Gas-dominated basins: The East China Sea, Yinggehai, and the deepwater of the northern part of the South China Sea

Stratigraphy of sedimentary fill: Ranked based on oil and gas reserves, the seven offshore basins have the following stratigraphic fills:

1. Bohai Bay: Cambrian-Ordovician, Carboniferous-Permian, and Jurassic-Neogene periods
2. Pearl River Mouth: Paleocene-Neogene
3. East China Sea: Paleocene-Neogene
4. Yinggehai: Paleocene-Neogene
5. Qiongdongnan: Paleocene-Neogene
6. Beibu Gulf: Paleocene-Neogene
7. South Yellow Sea: Cambrian-Triassic, Cretaceous-Miocene

Tectonic Differentiation

Another paper in Petroleum Exploration and Development discusses tectonic differentiation of the Yinggehai, Qiongdongnan, Beibuwan, and Pearl River Mouth basins in the South China Sea.

Tectonic stages: Yuhong and colleagues discuss the evolution of these basins in three stages:

(1) Pre-rift stage

• Geological age: Late Cretaceous to Paleogene
• Tectonic type: Extension and activation of pre-existing faults
• Sedimentary response: Basement weathering and erosion

(2) Rift stage:

• Geological age: Eocene to Early Oligocene
• Tectonic type: Intense rifting and half grabens
• Sedimentary response: Lacustrine and fluvio-lacustrine deposits

(3) Post-rift stage:

• Geological age: Late Oligocene to Recent
• Tectonic type: Thermal subsidence and local structural inversion
• Sedimentary response: Marine deposits

Seismic Tomography and Tectonics of Northern Borneo

Aerial view of Borneo/ Yusnizam Yusof

Northern Borneo of Malaysia is both petroliferous and tectonically complex with multiple deformation histories.

Amy Gilligan and colleagues in JGR Solid Earth shed light on the tectonic evolution of the region using seismic tomography.

Data source:

• The researchers used distant earthquake data from 46 seismometers (Northern Borneo Orogeny Seismic Survey, 2018—2020) and 24 previous stations (Malaysian Meteorological Service) across the Sabah region.
• They used primary waves and surface waves for crustal imaging.
• The mapped crustal thickness variations to depths of 100 kilometers below the surface of Sabah.
• Crustal thickness changes reflect tectonic histories.

Crustal thickness:

• Crocker Range: 60 kilometers (thickened crust)
• Central Sabah: 24 kilometers (Miocene extension)
• Beneath Mt. Kinabalu: 30—35 kilometers (rather thin crust)

Tectonic evolution:

• Seduction of the proto-South China Sea beneath Sabah: Cretaceous to 21 Ma
• Postulated subduction of the Celebes Sea Plate terminating at 9 Ma
• Extension in central Sabah at 9 to 10 Ma
• Rapid emplacement and exhumation of granites at 7 Ma
• Fold-thrust belt development in the offshore 5 Ma to present

Why it matters: This research has implications for two sets of questions:

• How does one tectonic style change into another in the same region?
• How do tectonic styles impact sedimentary basins?

Geologist Dr. Christopher Gareth Howells died on 5 June—at age 56—after a period of serious illness.

• Howells was born and raised in Wales, and he was proud to be Welsh.
• He received his Bachelor’s of Science in Geology from the University of Bristol in 1991.
• He then completed his PhD in Geology from Royal Holloway, University of London in 1997. His dissertation was on the Ombilin Basin in West Sumatra.
• His career spanned more than 30 years of exploration, with a special focus on Southeast Asia. He worked for ARCO, Amerada Hess Corp., Anadarko, Petronas, Shell, Talisman Energy, TGS, and Mubadala Investment Company.
• In 2008, he launched his own consultancy, BEC Energy, from Kuala Lumpur, Malaysia.

Thanks to Gregory Solomon and Ian Cross for this information.

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