Stratigraphy
The Pungo River Formation is divided into two members, the Early Miocene-aged Belhaven Member and the Middle Miocene-aged Bonnerton Member. It stretches from southern North Carolina north to southeastern Virginia, being replaced northwards by the roughly coeval Calvert Formation. [1] However, it largely lies buried underground throughout much of this range, generally at depths of 120 to 170 feet (37 to 52 m) below the surface. [2] The only major terrestrial exposure is at the Aurora mine, although offshore exposures are also known on the continental shelf of Onslow Bay, which were likely redeposited via sea-level changes over the Pliocene and Pleistocene. [3]
The deposition of the Pungo River Formation is thought to be linked to a major marine transgression from the Mid-Miocene Climactic Optimum, which inundated the Onslow and Aurora embayments. [3] Deposition of the Pungo River Formation would have ended following a recession of the sea level, exposing more land. Later, the ocean would have again submerged the land, depositing the Yorktown Formation over it. [2]
The highly fossiliferous and phosphorus-rich deposits in Beaufort County, which are now mined, are thought to have been formed by a large back eddy that formed behind a predecessor to Cape Lookout. The eddy would have caught many marine organisms that used up all the dissolved oxygen in the water, forming a large dead zone that allowed organic materials to easily fossilize due to the lack of decomposition. [3]
Economic significance
The Pungo River Formation is mined extensively for its phosphorite deposits, including at one of the largest phosphate mines in the world, the Aurora mine. The deposits were discovered during exploratory efforts in 1955 by Texas Gulf, with the mine being established by 1965. Due to the highly fossiliferous nature of the Pungo River formation and the overlying Yorktown Formation, both of which are exposed at the mine, numerous fossils have been discovered at the mine, and the sediments from it are a prime target for fossil collecting. Some of the mine's most notable fossils are displayed at the Aurora Fossil Museum. [2]
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