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Australasian IODP Regional Planing Workshop (2017. Sidney), Instituto Geológico y Minero de España, España, Instituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Científicas, España, Istituto Nazionale di Oceanografia e Geofisica Sperimentale, Italia, San Diego State University, Estados Unidos

Marine diatoms are sensitive to water-mass distribution and their physical-chemical and biotic preferences affect their biogeographical distribution. In sedimentary records, although altered by secondary processes such as dissolution, they track the primary signal formed in surface water. This make them the major biostratigraphic and environmental markers in the Southern Ocean as they record sea-surface temperatures, sea ice and other parameters usefull for paleoceanographic and paleoclimatic reconstructions (Jordan et al. 2010; Leventer et al., 2010; Crosta, 2011; Escutia et al., 2011). We present three case studies of diatom biostratigrapy and paleoceanographic reconstructions performed on Antarctic sediments recovered from: 1) Pleistocene-Holocene sequences in the Ross Sea and Wilkes Lands, with evidences of glacial/deglacial-interglacial phases (PNRA and IMAGES-CADO Projects in Atlantic and Australian Sectors) (Caburlotto et al., 2010; Tolotti et al., 2013) and 2) Late Eocene-Early Miocene sequences in Prydz Bay, with preliminary micropaleontological results and biostratigraphy related to the greenhouse/ice-house transition (ODP Project in the Indian Sector) (Lagabrielle et al., 2009; Suto et al., 2012). Jordan W.J. & Stikley C.E. 2010. Diatoms as indicators of paleoceanographic events. In: Smol J.P. & Stoermer E.F. Eds., The Diatoms: Applications for the Environmental and Earth Sciences., II Edition., 424-452. Escutia C., Brinkhuis H., Klaus A. & IODP Expedition 318 Scientists. 2011. IODP Expedition 318: From Greenhouse to Icehouse at the Wilkes Land Antarctic Margin. Scientific Drilling, 12, 15-23. Caburlotto A., Lucchi R.G., De Santis L., Macrì P. & Tolotti R. 2010. Sedimentary processes on the Wilkes Land continental rise reflect changes in glacial dynamic and bottom water flow. International Journal of Earth Sciences, 99(4), 909 – 926. Crosta X. 2011. Marine diatoms in polar and sub-polar environments and their application to Late Pleistocene paleoclimate reconstruction. IOP Conf. Series: Earth and Environmental Science, 14, 1-18. Leventer A., Crosta X. & Pike J. 2010. Holocene marine diatom records of environmental change. In: Smol J.P. and Stoermer E. F. Eds., II Edition., 401-423. Lagabrielle Y., Goddéris Y., Donnadieu Y., Malavieille J. & Suarez M. 2009. The tectonic history of Drake Passage and its possible impacts on global climate. Earth and Planetary Science Letters, 279, 197–211. Suto I., Kawamura K., Hagimoto S., Teraishi A. & Tanaka Y. 2012. Changes in upwelling mechanisms drove the evolution of marine organisms. Palaeogeography, Palaeoclimatology, Palaeoecology, 339-341, 39–51. Tolotti R., Salvi C., Salvi G. & Bonci M.C. 2013. Late Quaternary climate variability as recorded by micropalaeontological diatom data and geochemical data in the western Ross Sea, Antarctica. Antarctic Science, 25(6), 804–820.

The DRAKE-SCOTIA SEA GATEWAYS is a new multidisciplinary International Ocean Discovery Program (IODP) drilling proposal aimed at determining the time of opening and pattern of development of gateways in the Drake Passage and the adjacent Scotia Sea, and their influence on global ocean circulation, biotic evolution and climate. The Drake Passage with the adjacent Scotia Sea represent one of Earth’s most important oceanic gateways, between the southern tip of South America and the Antarctic Peninsula, a crucial area for water mass exchange between the Pacific Ocean, the Atlantic Ocean and the Weddell Sea, the importance of which is evidence by in many multinational studies. Nevertheless, the region has not been yet drilled for scientific purposes. The objective of this work is to present the main scientific goals of this drilling proposal and its link with the IODP Science Plan for 2013-2023., Department of Earth Sciences, Royal Holloway University, Reino Unido, British Antarctic Survey, Reino Unido, Department og Geology and Geophysics, Yale University, Estados Unidos, Geophysical Department, Geological Survey of Denmark and Greenland, Dinamarca, Alfred Wegener Institute, Helmholtz for Polar and Marine Research, Alemania, Instituto Geológico y Minero de España, España, Ocean and Earth Science, University of Southampton, Reino Unido, University Texas at Austin, Estados Unidos, Institute of Petroleum Engineering, Heriot-Watt University, Reino Unido, Instituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Científicas, España, Instituto Andaluz de Ciencias de la Tierra, Universidad de Granada, España, College of Earth, Ocean and the Environment, University of Delaware, Estados Unidos, University New South Wales, Australia, University Nebraska-Lincoln, Estados Unidos, Universidad de Buenos Aires, Argentina

The Izabal Basin is a spindle shaped pull apart basin, 100 km long and 20 km wide, trending ENE. It is located along the Polochic fault at the transform boundary between the North American and the Caribbean plates. Multichannel migrated seismic sections reveal that the basin is asymmetric both in cross and along strike directions, the deepest side (3.2 sec t.w.t.) being to the north, close and parallel to the northern bend of the Polochic fault. Notwithstanding the absence of a direct correlation with a well, analysis of the seismostratigraphic and structural features, along with consultation of the existing literature, permit the recognition of four main stages of evolution since the middle Miocene, and a rough correlation of the sedimentary infilling with the Tertiary and Quaternary formations that outcrop around the lake.

The North Scotia Ridge (NSR) is the submerged morpho-structural expression of the Scotia plate northern edge. It is constituted by the Tierra del Fuego continental margin, isla de Los Estados, Burdwood (BB), Davis and Aurora banks, and the Georgias islands shelf (Parker et al., 1996; Barker, 2001; Giner-Robles et al., 2003; Pandey et al., 2010). About 40 Ma these blocks were grouped forming a continental link between Tierra del Fuego and Antarctica. Afterwards, with the development of the Scotia plate, the blocks drifted towards the east to their actual position (Barker, 2001; Pandey et al., 2010). Several authors have established that the actual movement of the South America - Scotia plate boundary is left-lateral (Forsyth, 1975; Pelayo and Wiens, 1989; Giner-Robles et al., 2003; Thomas et al., 2003; Smalley et al., 2007). In the Tierra del Fuego region, the plate boundary is represented by a mostly transtensional fault system known as Magallanes-Fagnano (Lodolo et al., 2002, 2003, 2006, Tassone et al., 2008; Menichetti et al., 2008). Towards east, the boundary is located in the Malvinas trough, at the north of the BB and it would be transpressive (Cunningham et al., 1998; Giner-Robles et al., 2003; Bry et al., 2004). The change of the tectonic regime (transtensional to the W to transpressional to the E) would occur at 63.5 ºW (Lodolo et al., 2003; Yagupsky et al., 2003). As part of a study of the evolution of the SW Atlantic continental margin, we analyze and describe the morpho-structure of the western sector of the North Scotia Ridge. Fil: Esteban, Federico Damián. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Tassone, Alejandro Alberto. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Lodolo, E.. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale; Italia Fil: Menichetti, M.. Università di Urbino; Italia

A synthesis of the structural geology of the Tierra del Fuego Island, which integrates a new data set derived from field surveys and literature data of the last few years, is presented here. The main geological features of the region developed during the Mesozoic-Cenozoic Andean orogenic cycle that started in the Middle to Late Jurassic with a back-arc extension, crustal stretching and widespread volcanism, related to the break-up of Gondwanaland. An extensional fault system deriving from the mechanical and thermal subsidence led the evolution of the Rocas Verdes marginal basin, which hosts the upper Jurassic volcanoclastic rocks, the lower Cretaceous turbiditic sequences and few isolated elongated ophiolitic complexes. From the Late Cretaceous onward, the orogenic cycle of the Fuegian Andes continued with the shortening and inversion of the back-arc margin through horizontal contraction and crustal thickening. The uplift of the Cordillera, the emplacement of plutonic rocks, and the intercontinental polyphase deformation resulted from thick-skinned tectonics. The thrust system developed from its deeper roots, where the Palaeozoic basement was involved in compressive deformation, and propagated to the shallower stratigraphic levels of the northward verging Magallanes fold-and-thrust belt. The Magallanes foreland basin developed in front of the orogenic wedge that records at least four syntectonic angular unconformities from Late Cretaceous to Lower Miocene. During the Late Cretaceous Andean compression, three distinct phases of penetrative ductile deformation defined by low-greenschist facies assemblages took place, both in the basement and in the cover units. These deformations are related to a single metamorphic event with foliation development, as observed from microscopic analysis of the schist in the Ushuaia area. The first foliation S1 is preserved either as relic sericite microfolds between microlithons of the dominant S2, or as early refolded veins of recrystallized quartz. The S2 foliation is defined by oriented white mica. The crenulation of S2, which is related to D3 and occurs in most strained zones, becomes a pressure solution S3 spaced foliation, lined by opaque minerals. From the Palaeogene to the present, EW sinistral wrench tectonics affected the region as a component of the relative motion between South America and the Antarctic Peninsula. This strike-slip activity is well documented from the Carbajal valley to the Canal de Beagle region south of the Magallanes-Fagnano transform fault system. Restraining bends and overlapping step-over geometry characterize few sectors of the strike-slip faults with pop-ups, pressure ridges and uplifted slivers of crust. Releasing step-over along the transform fault system, both in on-shore and off-shore zones, formed several elongated pull-apart basins with many tens of km in length and a few km in width. The Lago Fagnano represents the main morphotectonic expression of this structural setting. A N-S geological cross-section through the Fuegian Andes synthesizes all the geological and geophysical data. The major stacks of internal thick skinned basement involved in the thrusting are high-grade Upper Palaeozoic to Lower Tertiary metamorphic rocks. The geometry of the thrust complex is an upright, south plunging monocline of moderately tilted sedimentary cover strata, as well as related thrusts, faults and chevron folds involving the Upper Jurassic and Cretaceous rocks. The orogenic shortening of the Fuegian Andes, including the Cordillera and the Magallanes fold-and-thrust belt, reaches few hundred kilometres with a left-lateral wrenching component of many tens of meters. The Tierra del Fuego Island is characterized by low seismicity (M