42-4 A Silurian Basin Across the Famatinian-Cuyania Suture: Stratigraphic and Tectonic Implications from the Villacorta Formation

Session: Paleozoic Events and Processes: Sedimentary Geology, Paleontology, and Geochemistry (Posters)

Poster Booth No.: 12

Presenting Author:

Delfina Milanesio

Authors:

Milanesio, Delfina¹, Armas, Paula², Biddle, Julian³, Edgington, Anthony⁴, Otamendi, Juan⁵, Fosdick, Julie⁶, Cristofolini, Eber⁷

(1) Departamento de Geología, Universidad Nacional de Río Cuarto, Río Cuarto, , (2) Departamento de Geología, Universidad Nacional de Río Cuarto, Río Cuarto, , (3) Department of Earth Sciences, University of Connecticut, Storrs, , (4) Department of Earth and Environmental Sciences, Boston College, Boston, , (5) Departamento de Geología, Universidad Nacional de Río Cuarto, Río Cuarto, , (6) University of Connecticut, Storrs, , (7) Departamento de Geología, Universidad Nacional de Río Cuarto, Río Cuarto, ,

Abstract:

The Villacorta Formation is a Paleozoic sedimentary succession exposed in the Sierra de Famatina, central-western Argentina. Its geological significance lies in preserving a unique upper Silurian depositional record formed during the mature stage of collision between the Laurentia-derived Cuyania terrane and the autochthonous Famatinian orogen. The unit is bounded by well-defined angular and erosional unconformities, resting on the Lower Ordovician Suri Formation and overlain by the Pennsylvanian Agua Colorada Formation. As such, it provides an exceptional record of sedimentation between the Famatinian Orogeny and the onset of the Gondwanan Cycle. We present new sedimentology and detrital zircon U-Pb geochronology data from the Villacorta Formation to better understand the provenance and sediment routing of the Silurian basin. Detailed facies analysis identifies five facies associations that record a progradational trend from subtidal sandbars and tidal channels to a tide-dominated deltaic system. Detrital zircon U-Pb geochronology from a sandstone sample yields a nearly unimodal age distribution dominated by Lower Ordovician ages (ca. 470 ± 18.92 Ma), indicating a dominant sediment source in the Famatinian batholith. This age signature closely resembles Early Ordovician zircon populations documented in coeval Silurian–Devonian units of the adjacent Precordillera, such as the Los Espejos Formation. The Villacorta Formation is interpreted as a syn-orogenic sedimentary succession deposited during crustal shortening and mountain building following the collision of the Cuyania microplate with the Famatinian arc. Unroofing and tilting of the underlying Suri Formation indicate tectonic contraction before Villacorta deposition, while the westward extent of the Silurian Sea into the present-day Famatinian belt supports the existence of a broad Silurian basin system linking the orogen and the Cuyania terrane. By the Late Devonian, this basin became progressively compartmentalized and isolated from marine conditions due to the uplift of Grenvillian-age basement highs, including Sierra de Maz, El Espinal, and Umango. Together with low-temperature thermochronology (⁴⁰Ar/³⁹Ar hornblende and ⁴⁰Ar/³⁹Ar micas) and metamorphic ages from the Cuyania basement, the progradation of deltaic deposits sourced from an actively uplifting Famatinian belt supports a syn-orogenic depositional setting and documents shoreline regression.

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