Pablo J. Torres Carbonell

Progressive deformation of a Coulomb thrust wedge: the eastern Fuegian Andes Thrust-Fold Belt

Abstract Time-calibrated balanced-cross sections of the eastern Fuegian Thrust–Fold Belt reveal many complex pro- and retro-vergent structures, rooted at the base of Cretaceous and within Paleocene rocks. These structures involve the unconformity-bounded syntectonic sequences of the Austral foreland basin, and accommodate a minimum shortening of c. 41.8 km. The complex kinematics of the thrust–fold belt are recorded by: (1) propagation of the basal décollement into the foreland, and forward-directed thrusting during the Ypresian; (2) out-of-sequence thrusting in the Lutetian; (3) subsidence and sedimentation from the Late Lutetian to the Oligocene; (4) backthrusting during the Oligocene; and (5) a renewed stage of forward-directed thrusting between the latest Oligocene and the Early Miocene, probably related to accretion below the sole fault in the hinterland. This thrust sequence is interpreted as the result of critical Coulomb wedge behaviour during the first stage of thrust–fold belt expansion, with accretion of new material that led to a taper decrease. The subsequent period of internal deformation corresponds to a subcritical stage, during which backthrusting accommodates significant shortening (c. 15%). After growth and taper increase, the last period of forward thrusting at the wedges front marks the inception of a new critical stage.

Geometry and kinematics of the Fuegian thrust‐fold belt, southernmost Andes

Fil: Torres Carbonell, Pablo Juan. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Austral de Investigaciones Cientificas; Argentina

Calcareous Nannofossils from the La Barca Formation (Paleocene/Eocene Boundary), Tierra Del Fuego, Argentina

The La Barca Formation, an organic-carbon rich sedimentary succession exposed along the Atlantic coast of Peninsula Mitre (Tierra del fuego, Argentina), was initially assigned to the late Paleocene, based on foraminifera and dinocysts. Planktonic foraminifera or calcareous nannofossils were not previously recorded in the two members of this formation. New samples of the upper member provided calcareous nannofossils that correlate with the late Paleocene-early Eocene assemblages in the Southern Hemisphere, spanning nannofossil zones NP9a/NP9b. The Paleocene/Eocene boundary in the La Barca Formation could be placed between the last occurrences of Fasciculithus richardii group and F. alanii, and the first occurrence of Romboaster cf. R. cuspis.