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vol.41 número1ALCANCES SOBRE LA PRESENCIA DE CHAETOPHRACTUS VILLOSUS (DESMAREST, 1804) (DASYPODIDAE) EN EL PARQUE NACIONAL TORRES DEL PAINE, MAGALLANES, CHILEREVISION DE LOS CERAMBYCIDAE (COLEOPTERA) DE LA REGION DE MAGALLANES: LISTA ILUSTRADA índice de autoresíndice de materiabúsqueda de artículos
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Anales del Instituto de la Patagonia

versión On-line ISSN 0718-686X

Resumen

MALUMIAN, Norberto; HROMIC, Tatiana  y  NANEZ, Carolina. THE PALEOGENE OF THE MAGALLANES BASIN: BIOSTRATIGRAPHY AND UNCONFORMITIES. Anales Instituto Patagonia (Chile) [online]. 2013, vol.41, n.1, pp.29-52. ISSN 0718-686X.  http://dx.doi.org/10.4067/S0718-686X2013000100003.

The Magallanes or Austral Basin is shared by Argentina and Chile; both countries developed the knowledge on foraminifera in different timing and ways. These differences delayed the integration of the stratigraphical information from both parts of the Basin. In Chile, the studies began in the ’40s in the national oil company ENAP and most of its reports remained unpublished until 1974, when a system of stages for correlation was proposed. This system, particularly for the Paleogene, was based on benthonic foraminifera because of the scarcity of planktonic forms. In Argentina, a first study on the Paleogene foraminifera from the Austral Basin is published in the late 60s, and after several years devoted to publish and illustrate the Cretaceous foraminifera, the research has been again focused on the Paleogene since the end of the century. The integration of the knowledge from both sides of the international boundary, and particularly the gathering of the data on the scarce planktonic forms, have helped to correlate Argentinean and Chilean formations, pointing out the great difference between the thick Paleogene sequences in the Chilean Peninsula Brunswick and the reduced Paleogene sequence, including more manifest and amplified unconformities, in the Argentinean Atlantic Fuegian coast. The contact between the Maastrichtian and the Danian by means of foraminifera is recognized in the northern part of the Basin (Cerro Dorotea Formation), whereas in the southern part is not evident due to an unconformity in the mid-Paleocene and the dominant, not age diagnostic, flysch type assemblages. The Paleocene/Eocene turnover in calcareous assemblages exhibits a contrast between a cosmopolitan Midway type assemblage in the upper Paleocene (La Barca/Chorrillo Chico formations) and an endemic early Eocene Austral assemblage that includes the first appearance of the genus Elphidium (Punta Noguera/lower Agua Fresca), and the genus Cribrorotalia in the Punta Noguera Formation. The lower Middle Eocene unconformity separates disaerobic and turbiditic paleoenvironments of the Paleocene-lower Middle Eocene (La Barca, Punta Torcida/Chorrillo Chico, Agua Fresca) from the aerobic shallow marine settings of the late Middle Eocene (Leticia/Tres Brazos, Boquerón). The sediments underlying the unconformity were deposited in a turbiditic marine paleoenvironment, with both restricted circulation and connection with the open sea, which was dominant from the Campanian up to the lower Eocene. The paleoenvironmental turnover is clearly reflected by the dominance of agglutinated and generally small foraminifera in the Campanian-lower Eocene in contrast with dominant large Nodosariidae foraminifera associated to a bloom of crinoids in the late Mid Eocene. This turnover reveals changes in the morphology of the basin that may have promoted the aeration of its bottom. The Eocene/Oligocene transition is nearly coincident with an unconformity, and a good biostratigraphical resolution is attained by means of the small tenuitellids that together with serial planktonics have good penetration in marginal basins. A proxy to the boundary is the disappearance of Globigerinatheka index, which apparently coincide with the last occurrence of the benthonic taxon "Kolesnikovella" severini. The unconformity, expressed by the Tchat Chii/Santa Clara formations, separates in the Tierra del Fuego Island very shallow water sediments (Cerro Colorado/Discordia), from deep and corrosive marine water sediments (María Cristina-Herminita/Puerto Nuevo).This tectonically deepening is coeval with uplift in the Peninsula Brunswick and Última Esperanza-Río Turbio areas. The Oligocene/Miocene boundary in high latitudes is not recognizable by means of foraminifera at present, and its location could be preliminary estimated at the contact between La Desdémona Formation and Cabo San Pablo/Cabo Ladrillero beds.

Palabras clave : Magallanes Basin; Paleogene; biostratigraphy; foraminifera.

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