Santa Marta formation

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James Ross Island

The Santa Marta Formation is a geological formation in Antarctica . Together with the Mount Kirkpatrick-formation and the Snow Hill Iceland lineup it is the only formation in the Antarctic, the dinosaurs - fossils were found. The formation emerges on James Ross Island , off the coast of the northern tip of the Antarctic Peninsula . On average, the Santa Marta formation is one kilometer thick.

stratigraphy

The Santa Marta formation was formed during the Santonium and Campanium ( Upper Cretaceous ). It lies above the Gustav group that formed during the Barremium and Santonium, and is in turn overlaid by the Snow Hill Island Formation of the late Campanium. Together with the Snow Hill Island Formation, the overlapping Lopez de Bertodano Formation and the Sobral Formation , the Santa Marta Formation forms the Marambio Group .

Originally the formation was divided into three informal members, the alpha, beta and gamma member. Later these were renamed Lachman-Crags-Member , Herbert-Sound-Member and Rabot-Member . The Lachman Crags and Herbert Sound members were named after the northern part of James Ross Island where they come to light. The Lachman Crags and Herbert Sound members come from the late Santonium and the lower Campanium.

The older Lachman Crags member is 500 meters thick. The layers in the reclining member consist of tuff and mudstone , while the upper layers are made up of tuff and turbidites - avalanche-like turbid currents. The tuff banks show bioturbation caused by benthic dwellers during the deposition .

The Herbert Sound Member is also around 500 meters thick and can be divided into two sections. Debris flows with embedded turbidites make up the lower section; this is then overlaid by fine sandstone .

The deposit environment of the two members was probably an underwater cone , which emanated from a large river delta . Rapid sediment infiltration in this step delta led to overstepping with occasional debris flow , which in turn triggered the turbidite flows . A high level of tectonic magmatic activity in this region during the Upper Cretaceous could explain the periodically occurring tuff banks.

The Rabot member of the Santa Marta Formation is limited to the southeastern part of James Ross Island and can be dated to the Campanium. Its future is spatially separated from the two other members that come to light in the northern areas of the island. Originally, the Rabot member was viewed as a separate formation, but is now classified as equal to the other two members. Like the Lachman-Crag-Member and the Herbert-Sound-Member, the Rabot-Member also consists of clay stones and tuff banks with often very strong bioturbation as well as very rare conglomerates .

Recently a fourth member was expelled, the Hamilton Point Member . The banks of this member were previously seen as the upper part of the Rabot member, but they are now an independent member.

Flora and fauna

The Antarctic coastal waters were home to large numbers of microorganisms during the deposition of the Santa Marta Formation. The microfossils mainly include ostracods and dinoflagellates .

Macrofossils invertebrates are also found in the formation. Even ammonites were found, often embedded vertically in the layers. Originally it was assumed that ammonites only assume this position in the sediment after their death if they are stored in shallow water under a certain pressure; However, there is evidence that under certain circumstances ammonites could also be stored vertically at greater depths. Many mussels were also found in the formation, such as Cucullaea , Panopea , Pinna and Pterotrigonia . There were also polychaeta , annelids such as Rotularia and snails such as Cerithioidea in the banks.

Taniwhasaurus

Fish were also present, including one of the first collar sharks , Chlamydoselachus thomsoni . Of particular note is a small marine vertebrate, the mosasaur Taniwhasaurus , formerly known as Lakumasaurus antarcticus . The close relationship of T. antarcticus to other species of the genus taniwhasaurus in New Zealand and Patagonia points to a Gondwana - endemics .

Antarctopelta , an ankylosaur , was discovered in 1986 in a northern part of James Ross Island, 2 kilometers south of the Santa Marta Bulge, in a bank that is part of the Santa Marta Formation. It was the first dinosaur found in Antarctica. It is possibly a nodosaurid , but an exact cladistics to check the relationship to other ankylosauriais still missing. Although the Santa Marta Formation was only formed by marine sediments, the bodies of these animals, along with other debris, may later have been washed into the water and then sink to the bottom and be buried by sediments.

Leaves and fragments of plants are often found preserved in fossil form in the entire formation, and also whole tree trunks in the lower layers. This is evidence of forest biotopes that covered Antarctica during the late Cretaceous period due to the overall warmer global temperatures and milder climate. The vegetation of the river delta at that time could certainly feed large herbivores such as the Antarctopelta .

Individual evidence

  1. ↑ a b D. Pirrie, Crame, JA, Lomas, SA, and Riding, JB: Late Cretaceous stratigraphy of the Admiralty Sound region, James Ross Basin, Antarctica . In: Cretaceous Research . 18, No. 1, 1997, pp. 109-137. doi : 10.1006 / cres.1996.0052 .
  2. ^ JM Keating: Palynology of the Lachman Crags Member, Santa Marta Formation (Upper Cretaceous) of north-west James Ross Island . In: Antarctic Science . 4, No. 3, 1992, pp. 293-304. doi : 10.1017 / S0954102092000452 .
  3. ↑ Eduardo B. Olivero, Buatois, Luis A., and Scasso, Roberto A .: Paradictyodora antarctica: a new complex vertical spreite trace fossil from the Upper Cretaceous-Paleogene of Antarctica and Tierra del Fuego, Argentina . In: Journal of Paleontology . 78, No. 4, 2004, pp. 783-789. doi : 10.1666 / 0022-3360 (2004) 078 <0783: PAANCV> 2.0.CO; 2 .
  4. ^ A b Paul W. Sumner: Dinoflagellate cysts from the Rabot Member (Santa Marta Formation) of eastern James Ross Island . In: Antarctic Science . 4, No. 3, 1992, pp. 305-310. doi : 10.1017 / S0954102092000464 .
  5. ↑ Gerson Fauth, Seeling, Jens and Luther, Axel: Campanian (Upper Cretaceous) ostracods from southern James Ross Island, Antarctica . In: Micropaleontology . 49, No. 4, 2003, pp. 95-107. doi : 10.2113 / 49.1.95 .
  6. ↑ Eduardo B. Olivero: Taphonomy of ammonites from the Santonian-Lower Campanian Santa Marta Formation, Antarctica: sedimentological controls on vertically embedded ammonites . In: PALAIOS . 22, No. 6, 2007, pp. 586-597. doi : 10.2110 / palo.2005.p05-118r .
  7. ^ Martha Richter, Ward, David J .: Fish remains from the Santa Marta Formation (Late Cretaceous) of James Ross Island, Antarctica . In: Antarctic Science . 2, No. 1, 1990, pp. 67-76. doi : 10.1017 / S0954102090000074 .
  8. ↑ MW Caldwell, Konishi, T., Obata, I., and Muramoto, K .: New species of Taniwhasaurus (Mosasauridae, Tylosaurinae) from the upper Santonian-lower Campanian (Upper Cretaceous) of Hokkaido, Japan . In: Journal of Vertebrate Paleontology . 28, No. 2, 2008, pp. 339-348. doi : 10.1671 / 0272-4634 (2008) 28 [339: ANSOTM] 2.0.CO; 2 .
  9. ↑ JE Martin, Fernández, M .: The synonymy of the Late Cretaceous mosasaur (Squamata) genus Lakumasaurus from Antarctica with Taniwhasaurus from New Zealand and its bearing upon faunal similarity within the Weddellian Province . In: Geological Journal . 42, No. 2, 2007, pp. 203-211. doi : 10.1002 / gj.1066 .
  10. ↑ Olivero EB, Gasparini Z., Rinaldi CA and Scasso R. (1991) First record of dinosaurs in Antarctica (Upper Cretaceous, James Ross Island): paleogeographical implications , in Thomson MRA, Crame JA and Thomson JW (eds), Geological Evolution of Antarctica. Cambridge University Press, Cambridge: 617-622. ISBN 978-0-521-37266-4