Monday, 27 October, 2025/Edition 82

In his 2002 bestseller Salt: A World History, Mark Kurlansky discusses how salt has historically been essential and valuable to human food, health, trade, and culture. Many places from Salt Lake City—where I live—to Salzburg, Austria have been centers of salt mining and trade.

A new book in two huge volumes published by the American Geophysical Union (AGU) discusses how salt is a core topic within geoscience. While going through these volumes I remembered the late Martin Jackson, one of the pioneer researchers in salt tectonics, whose course I took and who kindly accepted my visit to his salt tectonics lab at The University of Texas at Austin. Let’s look at salt in Earth Science.

Rasoul Sorkhabi

Editor, Core Elements

Evaporite Rocks and Salt Deposition

Anton Gvozdikov/Shutterstock.com

AGU Monograph 286 on Evaporite Rocks and Salt Deposition consists of 12 chapters totaling 550 pages. The volume is divided into two parts:

1. Chemical and physical properties of evaporite rocks

2. Salt deposition in different sedimentary environments

About the author: Webster Mohriak is a professor at Rio de Janeiro State University and has worked in the oil and gas industry for more than three decades. Mohriak has commented on his new publication in a YouTube video.

Stratigraphic distribution of major salt basins:

• Neoproterozoic: Salt basins in Australia, Africa, and the Middle East

• Cambrian: Middle East

• Silurian: North America

• Devonian: Eastern Europe

• Carboniferous: North and South America

• Permian: Europe, North, and South America

• Triassic: Central Atlantic rifts

• Jurassic: Gulf of Mexico and Central Europe

• Cretaceous: South Atlantic margin

• Paleogene: Rhine Graben and Iberia

• Neogene: North Africa, Red Sea, Dead Sea, Mediterranean, Anatolia

• Quaternary: Eastern and Northern Africa, Central Europe

Global distribution of lakes:

• Freshwater lakes (54 percent) such as Lake Baikal, Lake Tanganyika, Laker Superior, and Lake Malawi

• Salt lakes (46 percent) the largest being Caspian Sea (41 percent)

Salinity of select salt lakes: The average salinity of the oceans is 35 grams of salt per kilogram of water (or 35 parts per thousand).

• Highest saline lakes:

  • Don Juan Pond in Antarctica (403)

  • Lake Retba in Senegal (400)

  • Lake Vanda in Antarctica and Lake Karabogaz in Turkmenistan (350)

  • Lake Assal in Djibouti (348)

  • Dead Sea in Isreal and Jordan (337)

• Low salinity lakes:

  • Great Salt Lake in Utah (50–270)

  • Red Sea (36–41)

  • Mediterranean (38)

  • Caspian Sea (12)

Major evaporite minerals:

• The major evaporite minerals are: Halite, Sylvite, Anhydrite, Gypsum, Magnesite, Calcite

  • With chemical formulas: Halite (NaCl), Sylvite (KCl), Anhydrite (CaSO₄), Gypsum (CaSO₄.2H₂O), Magnesite (MgCO₃), Calcite (CaCO₃)

• Magnesite (3.0 gram per cubic centimeter) is the densest, and Sylvite (1.86) is the lightest evaporite mineral.

• Sylvite is highly radioactive with 500 gamma ray API units.

Modern evaporite environments:

• Coastal marine including tidal and sabkha environments 

  • Example: Persian Gulf

• Eolian or arid environments including salt flats, shallow brine lakes, and playa (seasonal) lakes between sand dunes

  • Example: North African Sahara

• Lacustrine

  • Example: Bristol Dry Lake in California

Major salt producers: In 2022, global production of salt was about 290 million tons. The six top producers are (in tons):

• China (64,000)

• India (45,000)

• The United States (42,000)

• Germany (15,000)

• Australia (13,000)

• Canada (11,000)  

Fun fact: Next time you receive your salary, remember that the Latin word salarium means “salt money” because in ancient Rome, wages were sometimes paid in salt.

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Salt Basin Analysis and Tectonics

Lubo Ivanko/Shutterstock.com

AGU Monograph 287 on Basin Analysis and Salt Tectonics has nine chapters totaling 530 pages and divided into two parts:

1. Analysis of giant salt basins

2. Salt tectonics and global implications

Giant Salt Basins

The oldest evaporite sediments on Earth are about two billion years old and drilled in the Baltic Shield.

Major salt basins explored by the petroleum industry include the:

• Red Sea: Miocene-age (Masiyah Salt) rift basin

• South Atlantic margin salt basins: Aptian-age rift basins, including the Kwanza Basin in offshore Angola and Santos Basin in offshore Brazil

• Gulf of Mexico: Middle Jurassic-age (Louann Salt) rift basin

• Mediterranean Sea: “Messinian Salinity Crisis”

• North-Central Europe: Permian-age Zechstein Basin in Germany, Poland, and the North Sea affected by extensional and compressional tectonics

• Zagros Basin: Compressional foreland basin superimposed on a passive margin with Infra-Cambrian, Upper Jurassic, Paleocene, and Miocene evaporites

• Permian Basin (Texas): Late Permian (Salado Salt) foreland basin

• Paradox Basin (Utah/Colorado): Pennsylvanian-age (Kungurian Salt) foreland basin

• Appalachian Basin: Silurian-age (Salina Group) foreland basin

• Dead Sea: Pliocene-age (Sedom Salt) transtensional (pull-apart) basin

Go deeper: Watch a computer simulation of salt tectonics on AGU YouTube channel related to this book.

 Chronology of salt basin studies:

• 1856: First description of a salt structure in the Atlas Mountains

• 1860: Discovery of salt domes in the Gulf Coast

• 1926: First AAPG symposium and publication on Geology of Salt Dome Oil Fields edited by Raymond Moore

• 1968: AAPG Memoir 8 on Salt Domes: Gulf Region, United States and Mexico edited by Michel Halbouty  

• 1995: AAPG Memoir 65 on Salt Tectonics: A Global Perspective edited by Martin Jackson and others based on the 1993 Hedberg Conference

• 2000: Sub-salt oil discovery in Gulf of Mexico

• 2006: Sub-salt oil discovery in Santos Basin, Brazil

• 2012: Geological Society of London Special Publication on Salt Tectonics, Sediments and Prospectivity edited by G.I. Alsop and others

• 2017: Salt Tectonics: Principles and Practice by Martin Jackson and Micheal Hudec

Bottom line: These two volumes offer the most comprehensive coverage of salt geology to researchers and professional geologists.

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