Field Trip. The geology of the Fuegian Andes: Cenozoic stratigraphy and ichnology.

E. B. OLIVERO; J. J. PONCE; N. B. CARMONA; M. I. LÓPEZ CABRERA; D. R. MARTINIONI

Fifth Argentinean Ichnologic Meeting and Third Ichnologic Meeting of the MERCOSUR. Field Trip Guidebook.

Laboratorio de Geología Andina (CADIC-CONICET)

Lugar: Ushuaia; Año: 2007; p. 27 - 44

FIELD TRIP SUMMARY:   From Ushuaia city to the north of Lago Fagnano, the National Route 3 offers an excellent opportunity to observe the landscape and the main geological features of the Fuegian Andes. Just north of the Beagle Channel, the highest peaks of the Fuegian Andes in the Argentinean part of Tierra del Fuego are located in the Sierra Sorondo and Sierra Alvear, where they reach about 1500 m above sea level. These two sierras, separated by the major tectonic depression of Tierra Mayor, are mainly composed of low-grade metamorphic Upper Jurassic volcanics and Lower Cretaceous mudstones and turbidites, which are typical for the Rocas Verdes Marginal Basin. North of Lago Fagnano, the landscape consists of lower relief mountain systems, such as the Sierra de Las Pinturas, which typifies the basal Paleogene fold-thrust belt of the foreland basin. North of Estancia María Cristina, subhorizontal sedimentary rocks that typify the youngest foredeep (Oligocene-Miocene) of the foreland basin characterize the low relief transition to the Fuegian steppe. Starting in Ushuaia and traveling along the National Route 3, during the first excursion day we will study the geological features of the Rocas Verdes Marginal Basin, including the ichnology and sedimentary facies of the Lower Cretaceous Yahgan Formation and the general geology of the Sierra Alvear, which is mainly composed of the Upper Jurassic Lemaire Formation. At Paso Garibaldi, Lago Escondido, we will have the rare opportunity to observe on land a major plate tectonic boundary, in this case the Magallanes-Fagnano Fault that separates the Scotia Plate from the South American Plate. After this, we will move across the Paleogene fold-thrust belt of the foreland basin up to the subhorizontal strata of the youngest foredeep, which are characterized by a dense injection of sandstone dykes. During the second and third days of the excursion, we will study the superb exposures of Cenozoic sedimentary rocks along the Atlantic coast. The second day will be devoted to study the Eocene sedimentary rocks that typify the fold-thrust belt, including the ichnology and facies transition from shallow marine sandstones of the Leticia Formation (upper Middle Eocene) to deeper turbidites of the Cerro Colorado Formation. During the third day of the excursion, we will see the frontal fault, separating the fold-thrust belt from subhorizontal foreland strata, and the general ichnological and sedimentological features of deep-marine Oligocene-Miocene sedimentary rocks, exposed from Punta Gruesa to Cabo San Pablo.