Monday July 6, 2026  Edition 118

I hope that those of you in the United States have enjoyed the July 4 holiday weekend, which marked the country’s 250th anniversary. For this historic occasion, I have designed a mineralogy puzzle on the U.S. flag (Check it out at the bottom of this week’s newsletter!). Let’s see if you can solve it.

Also, a note that beginning next week, Core Elements will shift to send every other Tuesday instead of every Monday. Thank you for your continued support and readership!

But first, let’s look at two interesting studies published in the AAPG Bulletin.

Rasoul Sorkhabi

Editor, Core Elements

New Insights on Offshore Myanmar

Offshore Western Myanmar and study area (AAPG Bulletin, 2026)

A paper in a recent issue of AAPG Bulletin caught my eye as it is about a region less discussed these days: Western offshore Myanmar.

Study area:

• The researchers focused on the thick Neogene sediments of the Ayeyarwady River offshore western Myanmar.
• This area lies between the subduction of the Indian Plate along the Andaman Trench beneath the Sunda Continental Plate.

Exploration background:

• In 2012, the first exploration well (Pyi Thar-1) in Block A-6 discovered biogenic gas in Upper Miocene sandstone reservoirs.
• Four additional wells were drilled from 2015 to 2018, two of which (Shwe Yee Htun-1 and Pyi Thit-1) also encountered biogenic gas in Neogene sediments.

What they did: Conducted by a group of geologists from Myanmar’s national oil company, MPRL, the study integrated the following methods:

• 2D and 3D seismic interpretation
• Well logs from five wells
• Petrography, heavy mineral analysis, and U-Pb geochronology of sediments
• Biostratigraphy

What they found:

• Existence of a Pliocene-Pleistocene fan system
• The fan sediments came from the proto-Ayeyarwady-Chindwin River and flowed east to west through a channel in the unstable continental slope of Late Miocene age (Exploration Block A-6).
• This Ayeyarwady fan includes gas-bearing sandstones.
• The sandstones are mainly lithic arkose and feldspathic arenites.
• The provenance (source area) of these deepwater sediments appears to be metamorphic and volcanic rocks.

Why it matters:

• Myanmar’s oil and gas industry dates to the 19th century, but it has historically been confined to onshore basins.
• Since 2012, western offshore Myanmar has drawn some attention for hydrocarbon exploration, but our knowledge base remains scarce.

Fluid Diapirs in the South China Sea

Yinggehia basin in South China Sea (AAPG Bulletin, June 2026)

Zonglin He and colleagues describe an interesting case of overpressure fluid diapir in the Yinggehai Basin in the June issue of AAPG Bulletin.

What are fluid diapirs?

Fluid diapirs form by upward intrusion of fluids along fracture zones as natural hydraulic fracturing and fluid charge occur simultaneously at the uplift point of the overpressure interface.

About the Yinggehai Basin:

• The basin is located in the South China Sea.
• It formed as a rift basin during the Paleocene and is filled with Eocene-Recent shallow water to bathyal sediments.

Case study:

• The DF1-1 diapir in the Yinggehai Basin is the most typical fluid diapir.
• It is host to multilayer gas accumulations discovered in different years:
  • 1992: Normal-pressure gas reservoirs found in the shallow upper submember of the second member of the Yinggehai Formation (Pliocene).
  • 1992: Slightly overpressured gas reservoirs found in the lower submember of the second member of the Yinggehai Formation (Pliocene).
  • 1999: Gas reservoirs exhibiting significant overpressure were encountered in the deep first member of the Huangliu Formation (Upper Miocene).

What they found: Results of the new study suggest that four episodes of natural gas charging with distinct compositions have occurred:

• First episode (3.4 to 2.9 Ma) hydrocarbon gas
• Second episode (1.8 to 0.4 Ma) hydrocarbon gas
• Third episode (0.4 Ma) dry gas and inorganic carbon dioxide
• Fourth episode (active) dry gas and inorganic carbon dioxide

Why it matters:

• This paper presents one of the best case studies of fluid diapirs in petroleum basins.
• The relatively young age of the fluid diapirs makes it easier to understand overpressure processes.

Can You Solve This Mineralogy Puzzle?

The U.S. Flag with nine minerals (Rasoul Sorkhabi)

I have created a U.S. flag with nine minerals in three colors: Blue, red, and white. Can you guess which minerals there are (numbered 1 through 9)?

Here are some hints: Apatite, Calcite, Garnet, Hematite, Kyanite, Lazurite, Muscovite, Plagioclase feldspar, Potassium feldspar, Quartz, Ruby, Sapphire, Selenite, Zircon.

Send your solution to editorial@aapg.org, and I will acknowledge your correct response in the next issue of Core Elements (first come, first served).

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