The Pisco Formation is a geologic formation located in Peru, on the southern coastal desert of Ica and Arequipa. The approximately thick formation was deposited in the Pisco Basin, spanning an age from the Middle Miocene up to the Early Pleistocene, roughly from 15 to 2 Ma. The tuffaceous sandstones, diatomaceous siltstones, conglomerates and dolomites were deposited in a lagoonal to near-shore environment, in bays similar to other Pacific South American formations as the Bahía Inglesa and Coquimbo Formations of Chile. Several specialists consider the Pisco Formation one of the most important Lagerstätten, based on the large amount of exceptionally preservedmarine fossils, including sharks, penguins, whales, dolphins, birds, marine crocodiles and aquatic giant sloths. Famous fossils found in these layers include the giant raptorial sperm whaleLivyatan, the aquatic slothThalassocnus, the sperm whaleAcrophyseter, and the walrus-like dolphin Odobenocetops.
Description
The Pisco Formation of the Pisco Basin consists of tuffaceous sandstones, diatomaceous yellow to gray siltstones and a basal conglomerate. The formation is deposited from Pisco in the north to Yauca in the south. The northern portion is known as the Ocucaje Area and the southern part as the Sacaco Area. The total thickness of the formation is estimated at. The formation unconformably overlies the Chilcatay and Caballas Formations.
Fauna
The Pisco Formation has provided a rich resource of marine fauna, including marine mammals like cetaceans and seals, large fishes, reptiles, and penguins. It is also one of the richest sites in the world for fossil cetaceans, with close to 500 examples being found in the formation. The oldest fossils of the aquatic sloth Thalassocnuscome from the Aguada de Lomas horizon of the Pisco Formation and were dated at roughly 7 Ma. The youngest specimen was found in the Sacaco horizon and dated to approximately 3 Ma. Thalassocnus was preyed upon by the probable apex predators of the environment, Livyatan and megalodon. The youngest strata belonging to the formation have been dated at 2 Ma, corresponding to the Early Pleistocene. Fossils of the Humboldt penguin were found in these deposits at the Yauca locality.
