Santa Marta Formation
| Santa Marta Formation Stratigraphic range: Upper Cretaceous |
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| Type | Geological formation |
| Unit of | Marambio Group |
| Underlies | Snow Hill Island Formation |
| Location | |
| Region | James Ross Island, Antarctica |
The Santa Marta Formation is a geologic formation in Antarctica. It, along with the Hanson Formation and the Snow Hill Island Formation, are the only formations yet known on the continent where dinosaur fossils have been found. The formation outcrops on James Ross Island off the coast of the northern tip of the Antarctic Peninsula. In its entirety, the Santa Marta Formation is on average one kilometer thick.
The Santa Marta Formation was deposited during the Santonian and Campanian ages of the Late Cretaceous. It overlies the Gustav Group laid down during the Barremian and Santonian ages and is succeeded by the Snow Hill Island Formation of late Campanian age. Together, the Santa Marta Formation, Snow Hill Island Formation, the overlying López de Bertodano Formation (deposited from the late Campanian age of the Late Cretaceous to the early Paleocene epoch of the early Paleogene), and the Sobral Formation (deposited during the early Paleocene) form the Marambio Group.
Originally the formation was subdivided into three informal members termed the Alpha, Beta, and Gamma members. The names were later changed to the Lachman Crags, Herbert Sound, and Rabot members. The Lachman Crags and Herbert Sound members, named after the areas in which they outcrop, are found in the northern part of James Ross Island. Both members are late Campanian in age. The Lachman Crags Member, the older of the two, is around 500 meters thick. The lower section of the member consists of tuffaceous mudstone while the upper section consists of tuffaceous turbidites formed by underwater avalanches. Bioturbation is evident in tuff beds throughout the member due to the disruption of sediments by benthic life during the time of deposition. The Herbert Sound member is also around 500 meters thick and also can be divided into two distinct sections. Channeled debris flows interbedded with turbides make up the lower portion of the member and are overlain by fine sandstones (followed by coarser sandstones and coquinas) that make up the upper portion of the member.
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