Santa Marta Formation

Coordinates: 63°00′S 57°00′W / 63.0°S 57.0°W / -63.0; -57.0
Source: Wikipedia, the free encyclopedia.
Santa Marta Formation
Approximate paleocoordinates
60°54′S 67°36′W / 60.9°S 67.6°W / -60.9; -67.6
RegionJames Ross Island
Country Antarctica
Santa Marta Formation is located in Antarctica
Santa Marta Formation

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.

Stratigraphy

The Santa Marta Formation was deposited during the

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.[1]

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.

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.[3]

The

depositional environment is thought to have been a system of abyssal fans radiating out from a large river delta. The rapid aggradation of sediments from the delta produced a steep delta slope,[3]
which may have resulted in occasional debris flows that formed the turbides. A high degree of tectonic activity in the region at the time may explain the intermittent tuff beds throughout the formation.

The Rabot Member of the Santa Marta Formation is confined to the southeastern part of James Ross Island and dates back to the early to late Campanian. Outcroppings of the member are separated from those of other members in the northern part of the island. Originally the member was regarded as its own formation, and now it is considered to be the lateral equivalent of both the Lachman Crags and Herbert Sound members.[4] Like the Lachman Crags and Herbert Sound members, the Rabot member consists of mudstones and beds of tuff that are often highly bioturbated, and also consists of rare conglomerates. Recently a fourth member has been assigned to the formation called the Hamilton Point Member. The beds of this member used to be considered part of the upper portion of the Rabot member, but now are considered to be their own distinct member.[1]

Flora and fauna

A wide variety of microorganisms inhabited the coastal waters at the time of the deposition of the Santa Marta Formation. Microfossils include ostracods[5] and dinoflagellates.[4]

Invertebrates were also common. Fossils of

gastropods such as the cerithiid sea snail Cerithium
have also been discovered in beds within the formation.

Numerous

Trackways thought to belong to decapods have also been found.[7]

Taniwhasaurus

Fish were present, including one of the first

Lakumasaurus antarcticus.[9] The close relation of T. antarcticus to other species of Taniwhasaurus found in New Zealand and Patagonia provides evidence for a Gondwanan endemism.[10]

Antarctopelta oliveroi, an ankylosaur, was discovered in 1986 on the northern part of James Ross Island about 2 kilometers south of Santa Marta Cove in beds that were part of the Santa Marta Formation.[11] It was the first dinosaur found in Antarctica. It may be a possible nodosaur but there has been no formal phylogenic analysis to prove its relationship with other ankylosaurs. Although the formation is made up of only marine deposits, the bodies of these animals along with other debris may have frequently been washed out to sea to later sink to the bottom and be buried by sediment.

Leaves and fragments of plants are commonly found as fossils throughout the formation as well as large tree trunks in the lower members. This is evidence of the forested environment that covered Antarctica during the Late Cretaceous due to the overall warmer global temperature and milder climate. At that time the river delta had much vegetation, and was able to support large herbivores such as Antarctopelta.

See also

References

  1. ^
    doi:10.1006/cres.1996.0052
    .
  2. S2CID 130244948
    .
  3. ^
    S2CID 131316915
    .
  4. ^
    S2CID 129854861
    .
  5. doi:10.2113/49.1.95
    .
  6. S2CID 131436435
    .
  7. doi:10.1111/j.0031-0239.2004.00343.x
    .
  8. S2CID 140650195
    .
  9. S2CID 129446036
    .
  10. S2CID 128429649
    .
  11. ISBN 978-0-521-37266-4
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