quinta-feira, novembro 05, 2009

Paleogeografia de Africa durante o Cretácico

A paleontologia de vertebrados pode dar bons contributos à paleogeografia. No artigo publicado no Buletim da Sociedade Geológica de França, usamos os nossos conhecimentos adquiridos no trabalho desenvolvido em Angola para melhor compreender o ambiente e geografia de África durante o Cretácico Superior.

A, Late Turonian (90 Ma) lowstand paleogeography of the South Atlantic region; B, Late Turonian upwelling in the South Atlantic region (blue areas = upwelling; size of blue dots represents volume of upwelling X persistence); C, Late Turonian rainfall and runoff pattern the South Atlantic region (green = land runoff; size of cyan squares represents average annual rainfall); D, Late Turonian salinity (red = more salty; blue = less salty; arrows = summer surface ocean currents). Blue dashed lines = lowstand; brown dashed lines = highstand [Scotese, 2008].
After Jacobs et al., 2009.

L L Jacobs, O Mateus, M J Polcyn, A S Schulp, C R Scotese, A Goswami, K M Ferguson (2009) Cretaceous paleogeography, paleoclimatology, and amniote biogeography of the low and mid-latitude SouthAtlantic Ocean Bull. Soc. géol. Fr. 180: 4. 333-341.

Key-words. – Paleobiogeography, Angola, South Atlantic, Cretaceous, Mosasaur, Angolasaurus, Turtles, Chelonians, Squamates.

Abstract. – The Cretaceous tropical Atlantic Ocean was the setting for an initial tectonically controlled late Aptian shallow water ( 300 m) connection between the northern and southern portions of the Atlantic, followed by a deep-water connection by the Turonian. Ocean currents changed with deepening of the South Atlantic and progressive widening of the Equatorial Atlantic Gateway. Aptian evaporite deposition came to a halt. The Albian-Turonian interval includes atrend toward increasing sea level and was characterized by globally warm sea surface temperatures. Productive areas of coastal upwelling led to the deposition of organic-rich sediments varying in position along the African coast with time, culminating in the Benguela Upwelling that commenced in the Miocene. The drift of Africa in the Late Cretaceous indicatesthat throughout most of this period, the coastal area around the fossil locality of Iembe, north of Luanda, Angola, lay in arid latitudes (15o S to 30o S), which are generally characterized by sparse vegetation. This presumption is consistent with the utter lack of macroscopic terrestrial plant debris washed into near shore sedimentary environments and indicates that organic rich marine shales have a minimal terrestrial carbon component. The connection of the North and South Atlantic oceans severed a direct terrestrial dispersal route between South America and Africa, but opened a north-south dispersal route for marine amniotes. This seaway was used by late Turonian mosasaurs and sea turtles as evidenced by Angolasaurus and a new turtle taxon close to Sandownia, both found at Iembe and derived from northern clades. The presence of a sauropod in late Turonian sediments, also from Iembe, suggests that this animal was tolerant of warm, arid conditions as the desert elephants of Namibia are today. Further, it suggests that the waning terrestrial dispersal route between South America and Africa was situated in a region where high temperature, low rainfall, and sparse vegetation would be expected to restrict the movement of more mesic and ecologically sensitive species..

1 comentário:

Ricardo Araújo disse...

Haja alguem que faca alguma coisa pela paleo de vertebrados em Portugal! Parabens OM por mais uma!