New chronostratigraphy for a Lower to Upper Carboniferous strike-slip basin of W-Precordillera (Argentina): Its paleogeographic, tectonic and glacial importance.

JUAN PABLO MILANA; DI PASQUO, M.M.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2019 vol. 96 p. 1 - 24

0895-9811

Milana, J.P., di Pasquo, M.M. 2019. New chronostratigraphy for a Lower to Upper Carboniferous strike-slip basin of W-Precordillera (Argentina): Its paleogeographic, tectonic and glacial importance. Journal of S Am Earth Sciences, Submission 29/07/2019- approved September 2019. available online: 11-OCT-2019 DOI information: https://doi.org/10.1016/j.jsames.2019.102383New biostratigraphic ages and the stratigraphic revision of a c. 4 km thick succession of Lower and UpperCarboniferous beds, exposed in the Del Salto creek, in the western Precordillera (San Juan, Argentina) are presented.Detailed mapping and analysis of the vertical and lateral variations of the sedimentary systems of the three units weare redefining here (El Planchón, Churupatí and Del Salto formations) allowed us to modify many pre-existingconcepts. The palynological data provided for the El Planchón Formation corroborate it is not Devonian butCarboniferous, (mid-late Visean), since it conformably overlies the Del Ratón Formation (Early Visean). A distal glacialinterval in El Planchón lower member, distal turbidites and hemipelagites in the middle member and non-glacialshallow-water heterolithics with small slumps and proximal turbidites for the upper member are interpreted. An angularunconformity defines the base of the alluvial conglomeratic Churupatí Formation (redefined herein), that showsdramatic lateral variations from a dominantly alluvial conglomeratic sequence to the north (green- purpleconglomerates) and sandier fluvial to swampy sequences to the south. Chrupati palynological content suggests its lateVisean ? early Serpukhovian age. A new erosive unconformity separates Churupatí from Del Salto formations with aninterpreted glacial origin, while the palynological content of basal Del Salto Fm indicates a Pennsylvanian (Bashkirian)age, not Permian. A dextral strike-slip basin is interpreted to explain this Carboniferous succession, based ongeological, stratigraphical and sedimentological data. Evidence supporting this interpretation are: (1) its thickness (c. 4Km) in a restricted geographical place as no traces of these units are found east or westwards except for Del Saltoformation equivalents. (2) the amount of active-tectonically fed gravel, important lateral changes, and fast transitions tofrom gravel- to mud-dominated sequences, (3) the southward displacement of the entry-point from hinterland of coarsesediment observed between Churupatí and Del Salto formations, (4) the partial rotation of local structures, (5) itscoincidence with the modern dextral Del Tigre fault. The entire sequence supports the existence of three main glacialepisodes and does not support the existence of the Protoprecordillera, but a surrounding hummocky positive terrainthat did not obstruct the drainage systems moving sediment eastwards