Monday, 23 March, 2026/Edition 103

Spring is here! Recently, I was watching a BBC documentary on the four seasons. Our Earth is indeed a wonderful planet, which deserves our gratitude and care. American poet Gary Snyder has a beautiful poem on Gratitude that I enjoy.

This edition of Core Elements celebrates spring and history. This week, we will look at two new books for spring reading, but first, I would like to introduce some of the most-cited papers published in the AAPG Bulletin, which is in its 110th year of publication (it's as old as the AAPG itself).

And, if you want to dive even deeper into petroleum history, the 2026 Petroleum History Institute symposium and field trip will be held in Bakersfield, California, in April. I hope to see you there!

Rasoul Sorkhabi

Editor, Core Elements

AAPG Bulletin: Top 10 Most-Cited Papers

AAPG/YouTube.com

Citation by other researchers is an index for the importance of research papers. I did a survey of select papers published in the AAPG Bulletin from its first volume in 1917 to volume 109 published in 2025, and I recorded their citations from Google Scholar (as of 19 March).

This survey is not comprehensive. If you know of any AAPG Bulletin paper with more than 3,000 citations, please let me know (write to editorial@aapg.org).

Go deeper:

• Watch the video above for an overview of the AAPG Bulletin. You can also learn more about the Bulletin here. 

• AAPG members receive a free subscription to the Bulletin. If you are not a member, you can apply to become one here.

Top 10 Most-Cited Papers

#1. Unconventional shale-gas systems: The Mississippian Barnett Shale of north-central Texas as one model for thermogenic shale-gas assessment

• Citations: 4,583

• Authors and year published: Danile M. Jarvie, R. J. Hill, T. E. Ruble, and R. M. Pollastro (2007)

• Volume: 91(4): 475-499

• Significance: The U.S. shale revolution began with the Barnett Shale, and this paper was a pioneering study of this formation.

#2. Fractured shale-gas systems

• Citations: 4,016

• Author and year published: John B. Curtis (2002)

•  Volume: 86 (1): 1921-1938

• Significance: This is another pioneering paper on shale gas focused on fractures.

#3. Guidelines for evaluating petroleum source rock using programmed pyrolysis

• Citations: 3,760

• Author and year published: Kenneth E. Peters (1986)

• Volume: 70(3): 318-329

• Significance: The paper provides a workflow on how to use pyrolysis data for source rock evaluation.

#4. Plate tectonics and sandstone compositions

• Citations: 3,503

• Authors and year published: William R. Dickinson and C. A. Suczek (1979)

• Volume: 63(12): 2164-2182

• Significance: This is an early paper linking basin infills to plate tectonic settings.

#5. Structural history and tectonics of Iran: a review

• Citations: 3,437

• Author and year published: Jovan Stöcklin (1968)

• Volume: 52(7): 1229-1258

• Significance: This paper was the first to synthesize the tectonic framework of Iran’s geology. Its author, Jovan Stöcklin (1921–2008), was a renowned Swiss geologist and played a leading role in the formation of the Geological Survey of Iran in 1962. 

#6. Practical petrographic classification of limestones

• Citations: 3,229

• Author and year published: Robert L. Folk (1959)

• Volume: 43 (1): 1-38

• Significance: Robert Folk (1925–2018), author of Petrology of Sedimentary Rocks, proposed Folk’s classification of carbonate rocks based on the nature of visible grains embedded in matrix. This classification was largely supplanted by the Dunham classification.

#7. Geologic nomenclature and classification of porosity in sedimentary carbonates

• Citations: 3,204

• Authors and year published: P. W. Choquette and L. C. Pray, L. C. (1970)

• Volume: 54(2): 207-250

• Significance: This is another early and influential paper on carbonate reservoirs focused on porosity.

#8. Evaluation of a simple model of vitrinite reflectance based on chemical kinetics

• Citations: 3,024

• Authors and year published: J. J. Sweeney and A. K. Burnham (1990)

• Volume: 74(10), 1559-1570

• Significance: This paper is one of the benchmark papers that established the basis for Easy Ro estimation in basin modeling.

#9. Outline of the geology of the Niger Delta

• Citations: 2,337

• Authors and year published: K. C. Short and A. J. Stäuble (1967)

• Volume: 51 (5): 761-779

• Significance: This research is a classic paper from the late 60s, when the Niger Delta was becoming a hotspot for oil exploration.

#10. Stratigraphic nomenclature of the Iranian oil consortium agreement area

• Citations: 2,155

• Authors and year published: G. A. James and J. G. Wynd (1965)

• Volume: 49(12): 2182-2245

• Significance: After the 1950s, oil and gas fields in Iran were extensively explored by international oil companies. This classic paper sums up the stratigraphic knowledge of the Zagros Superbasin in the 1960s (but it is still useful today).

What’s next: Which paper is the most cited among all AAPG publications (more than 10,000 citations)? I will share the results of my research next week.

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Spring Reading Recommendations

Image courtesy of Rasoul Sorkhabi

Books nourish our minds and enrich our lives. Here are two science books for spring reading. And yes, I have read them, so these are my personal recommendations.

#1. Becoming Earth: How Our Planet Came to Life

Author: Ferris Jabr is an Oregon-based journalist who has published his work in various magazines. This is his first book, published in 2024.

What’s inside:

• The book is divided into three parts: Rock (the lithosphere), Water (the atmosphere), and Air (the atmosphere).

• Each part describes how the biosphere interacts with Earth.

Significance: The book is based on James Lovelock’s Gaia theory, which suggests that Earth is a living system on a planetary scale.

#2. The Whispers of Rocks: The Stories That Stone Tells About Our World and Our Lives

Author: Anjana Khatwa holds a PhD in geoscience and is a freelance writer. She lives on the Jurassic Coast in Dorset, United Kingdom. This is her first book, published in November 2025.

What’s inside: Across its 10 chapters, the book takes the reader on a journey through deep time through selected rock samples from around the world.

Significance: Through engaging stories, the book also juxtaposes geology against native peoples’ reverence and cultural importance for specific rocks.

Happy reading!

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