Santa-Marta-Formation
The Santa Marta Formation is a geological formation in Antarctica. Together with the Mount Kirkpatrick Formation and the Snow Hill Iceland formation it is the only formation in the Antarctic, were found in the dinosaur fossils. The formation occurs on the James Ross Island to days off the coast of the northern tip of the Antarctic Peninsula. On average, the Santa Marta Formation is one kilometer powerful.
Stratigraphy
The Santa Marta Formation formed during the Santoniums and Campanian ( Upper Cretaceous ). It is located on the Gustav Group, which was formed during the Barremiums and Santoniums, and is in turn overlain by the Snow Hill Iceland lineup of the late Campanian. Along with the Snow Hill Iceland formation, the overlying Lopez -de- Bertodano lineup and the Sobral Formation forms the Santa Marta Formation, the Marambio Group.
Originally, the formation was divided into three informal members, the alpha-, beta - and gamma - members. Later, these were renamed Lachman Crags Members, Herbert Sound members and Rabot Members. The Lachman Crags and the Herbert Sound members were named after the northern part of James Ross Island, where they come to light. The Lachman Crags and the Herbert Sound members from the late Santonian and lower Campanian.
The older Lachman Crags Members is 500 meters thick. The layers in the footwall of the member consist of tuff and mudstone, while the upper layers of tuff and turbidites - avalanche-like turbidity currents - are built. The Tuff- benches show bioturbation, caused during the deposition by benthic dwellers.
The Herbert Sound members is also about 500 meters thick and can be divided into two sections. Debris flows with intercalated turbidites make up the lower portion; this is then overlaid by fine sandstone.
The depositional environment of the two members was probably an underwater cone emanating from a large river delta. Rapid sediment loads in this stage Delta led to over -sharing with occasional debris flow, which in turn caused a release of Turbiditströme. A high degree of tectonic -related magmatic activity in this region during the Late Cretaceous could explain the Tuffbänke intermittent.
The Rabot Member of the Santa Marta Formation is restricted to the southeastern part of the James Ross Island and can be dated to the Campanian. His Imminent is spatially separated from the other two members that have come to light in the northern areas of the island. Originally, the Rabot Member was considered as a separate formation, but it is now classified as equal with the other two members. As the Lachman Crag Members and the Herbert Sound Member is also the Rabot Member of mudstones and Tuffbänken often with very strong bioturbation and very rare conglomerates.
Recently, a fourth member was expelled, the Hamilton Point Member. The banks of this member were formerly not considered upper part of Rabot Members, but they are now a separate member.
Flora and Fauna
The Antarctic coastal waters harbored a large number of microorganisms during the deposition of the Santa Marta Formation. Among the microfossils are found mainly ostracods and dinoflagellates.
Invertebrate macrofossils are also to be found in the formation. Even ammonites were found embedded often perpendicular to the layers. It was originally thought that ammonites only accept after her death this position in the sediment when they are stored in shallow water under a certain pressure; but there is evidence that show that in certain circumstances Ammonites could be stored vertically also in greater depth. There also many shells were found in the formation, as Cucullaea, Panopea, Pinna and Pterotrigonia. Furthermore, were Polychaeta, Annelida as Rotularia and snails as the Cerithioidea available in the pews.
Fish were also present, among others, one of the first collar sharks, Chlamydoselachus thomsoni. Particularly noteworthy is a small marine vertebrate, the mosasaurs Taniwhasaurus, formerly known as Lakumasaurus antarcticus. The close relationship of T. antarcticus to other species of the genus Taniwhasaurus in New Zealand and Patagonia indicates a Gondwana - endemics.
Antarctopelta, a Ankylar, 1986 was discovered in a northern part of James Ross Island, 2 miles south of the Santa Marta curvature in a bank that is part of the Santa Marta formation. It was the first dinosaur discovery in Antarctica. It possibly is a Nodosauriden, however, still lacks an accurate cladistics to verify the relationships to other Ankylosauria. Although the Santa Marta formation was only by marine deposits, the bodies of these animals may have been purged along with other debris later into the water, and then sink to the bottom and become buried by sediments.
Leaves and fragments of plants are often preserved in the fossil entire formation found in the lower layers and whole tree trunks. This is a proof of forest biotopes that covered Antarctica during the Late Cretaceous period on the basis of a warmer global temperatures and milder climate. The former vegetation of the river deltas could certainly feed large herbivores, such as Antarctopelta.