A Review of the Upper Cretaceous-Cenozoic Geology of the Fuegian Andes
Eduardo B. Olivero1 and N. Malumián2
1Centro Austral de Investigaciones Científicas (CADIC-CONICET); B. Houssay 200; 9410 Ushuaia; Tierra del Fuego; Argentina; [email protected]
2SEGEMAR and CONICET; B. Lavaissé 1194; C1107BJD, Buenos Aires, Argentina
In this study the description of the complex geology of the southernmost tip of South America and its continuation into the North Scotia Ridge is divided into four main intervals, the rocks of which record evidence of dramatic changes in tectonic regimes and paleogeographical configurations. The geological observations in the region started with Darwin in 1833 and the following description of pre-Late Cretaceous intervals is mainly based on the fundamental studies by Kranck (1932) and Dalziel and colleagues (see Dalziel, 1989) and those of the Late Cretaceous-Cenozoic, which represents the main subject of this review, mainly on Olivero and Malumián (1999, 2002, 2007), Malumián and Olivero (2005, 2006), and Olivero et al. (2002, 2003, in press).
The oldest interval includes a pre Mid Jurassic metamorphic basement interpreted as an accretionary prism developed along the panthalassic margin of Gondwana. The highest metamorphic grade, with staurolite, kyanite, and sillimanite is in Cordillera Darwin; elsewhere they correspond mainly to greenschists. An unconformity separates the basement from the Jurassic volcanics. However, as peak-metamorphism was reached during the mid-late Cretaceous, basement and cover rocks are difficult to separate in the field.
The second interval includes complex successions of plutonic, volcanic, and sedimentary rocks that reflect Late Jurassic and Early Cretaceous extension and rifting. These include a Mid to Late Jurassic regional silicic volcanic field, which also covers a large area of Patagonia, and related plutonic granites in Cordillera Darwin. Continuation of the extensional regime during the Late Jurassic-Early Cretaceous opened in southern Patagonia the Rocas Verdes Marginal Basin, which is partially floored by ophiolites. The regional late Albian transgression in the Austral and Malvinas basins is related to subsidence during a sag phase. In the northern part of these basins, the Aptian to Maastrichtian strata representing platform, slope, and deep basinal settings are thought as originated during an interval of tectonic quiescence. Conversely, in the southern Rocas Verdes Marginal Basin the basal Late Cretaceous marks the inception of a compressional tectonic regime, which originated the ductile deformation, isoclinal folding, and metamorphism that characterize the Paleozoic to Mesozoic rocks of the southern Fuegian Andes. Peak metamorphism, reaching the amphibolite grade was attained between 100 and 90 Ma. The closing of the Rocas Verdes Marginal Basin was completed around 70 Ma and the Fuegian Andes were already uplifted by the late Campanian.
In the third interval, subsequent propagation of the compressional deformation and subsidence by tectonic loading along the northern orogenic margin originated the Austral and Malvinas foreland basins. The Turonian-lower Campanian “Estratos de Buen Suceso” represents the final stages of the closure of the marginal basin and/or the beginning of the foreland basins. During the late Campanian-Oligocene, propagation of compressional deformation originates three main depocenters. These are located within the thrust and fold belt of the Fuegian Andes and include: 1) the Bahía Thetis (Upper Campanian-Maastrichtian), Policarpo (Upper Maastrichtian/Danian), and Tres Amigos (Upper Paleocene) Formations, mostly turbidite settings with cosmopolitan agglutinated foraminifers; 2) the Río Claro Group, Upper Paleocene-Lower Eocene; and 3) the La Despedida Group, representing the extended upper mid Eocene-upper Eocene transgression with endemic foraminifers. A fourth depocenter, the Oligocene-mid Miocene Cabo Domingo Group mostly deposited below the calcite compensation depth and characterized by widespread agglutinated foraminifers, represents the last and deepest foredeep, originated just north of the fold belt during the waning compressional phase. Within the fold belt there are reduced exposures of mid Eocene bryozoan limestones of the Río Bueno Formation, and fluvial upper Eocene-lower Oligocene of the Punta Cactus and Sloggett Formations. During the late Campanian to mid Miocene, the foraminiferal assemblages allow precise dating of the main tectonic events and coupled with the trace fossils and sedimentary facies, the general characterization of the depositional settings.
The fourth interval is associated with the activity of the left-lateral Magallanes-Fagnano fault system, which presently defines the transcurrent boundary between the South America and Scotia plates. In Argentinean Tierra del Fuego, transcurrency apparently started in the Oligocene-Miocene and it is associated with small pull-apart basins. One of these basins is located within the folded belt and it is filled with late Miocene-Pliocene shallow marine deposits.
This review highlights a rather complete marine Upper Cretaceous to Mid Miocene stratigraphic column, which includes an aggregate thickness in excess of 3500 m of sedimentary rocks. It constitutes one of the few available onshore records of the paleoclimatic and paleobiogeographic events that occurred in southern high latitudes.
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Olivero, E.B., Malumián, N., Palamarczuk, S., 2003. Estratigrafía del Cretácico superior-Paleoceno del área de bahía Thetis, Andes Fueguinos, Argentina: acontecimientos tectónicos y paleobiológicos. Revista Geológica de Chile, 30, 245-263.
Olivero, E.B., Malumián, N., Palamarczuk, S., Scasso, R., 2002. El Cretácico superior-Paleógeno del área del Río Bueno, costa atlántica de la Isla Grande de Tierra del Fuego. Revista de la Asociación Geológica Argentina, 57, 199-218.
Financial support from CONICET PIP 5100, Argentina
AAPG Search and Discovery Article #90079©2008 AAPG Hedberg Conference, Ushuaia-Patagonia, Argentina