An ocean's birth certificate
On the remote shores of Disko Island and the Nuussuaq Peninsula in western Greenland, dramatic coastal cliffs expose a unique geological archive: The Vaigat Formation. This sequence of volcanic and sedimentary rocks documents the final separation of Greenland from Europe, a process that created the nascent North Atlantic Ocean. The formation itself is a thick sequence, reaching up to 1,600 meters in some areas, composed primarily of picrites—a type of basalt rich in olivine—and dark, organic-rich shales.
These layers were deposited between 62 and 54 million years ago, during the Paleocene and Eocene epochs. The process was driven by one of Earth's largest known volcanic events, the formation of the North Atlantic Igneous Province (NAIP). This province eventually poured out an estimated 6.6 million cubic kilometers of lava, building a massive plateau that was later rifted apart by continental drift. The Vaigat Formation's layers of shale are sandwiched between these enormous flood basalts, preserving a high-resolution record of the environmental conditions during the birth of an ocean. The black shales get their color from high concentrations of organic carbon, preserved in the low-oxygen (anoxic) bottom waters of the newly forming, restricted seaway.
A hothouse world's diary
The Vaigat Formation is a record of continental rifting; it is a record of a planet experiencing extreme climate change. Its layers correspond with the Paleocene-Eocene Thermal Maximum (PETM), a brief period around 56 million years ago when global temperatures soared by 5–8°C. This "hyperthermal" event was triggered by a massive release of carbon into the atmosphere, much of it from the intense volcanic activity of the NAIP.
The black shales contain the chemical evidence of this ancient global warming. Isotope analysis of the sediments reveals a sharp negative excursion in carbon-13, the signature of a massive injection of carbon into the atmosphere. Geochemists also study molybdenum and osmium isotopes within these layers to trace ocean-wide anoxia and continental weathering rates. The ocean itself became inhospitable in many areas. Widespread anoxia, or the complete lack of oxygen, is evident from the laminated shales, which lack the typical burrows and tracks of seafloor organisms. The combination of volcanism, continental breakup, and climate change recorded in the Vaigat Formation helps researchers understand understanding how Earth's systems respond to large-scale carbon release.