Tectonics and stratigraphy of the Late Paleozoic Paganzo basin of Western Argentina and its regional implications

  • Fernandez-Seveso F
  • Tankard A
  • 27

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Abstract

The Carboniferous-Permian Paganzo succession straddles the Pampeanas, Precordillera, and Chilenia terranes. Late Devonian-Early Carboniferous diastrophism of the Chañic event separated very different early and late Paleozoic histories of basin formation. The Paganzo basin was initiated in the Visean by reactivation of old terrane boundaries. The early Paganzo consisted of a suite of discrete fault-controlled depocenters interpreted as transtensional pull-apart basins linked to right-lateral displacement along major crustal faults. Younger phases of basin formation were characterized by amalgamation of these various depocenters into a single broad basin. The Paganzo succession is divided into four supersequences by major hiatuses. These are the Guandacol, Tupe, and lower and upper Patquía-De la Cuesta supersequences. Each is constructed by stacked unconformity-bounded depositional sequences. These four supersequences record the various stages of basin evolution. The Guandacol sediments were deposited in isolated basins. Fieldwork shows a pattern of rapid subsidence and stacking of coarse alluvial facies along basin-bounding faults. The characteristics of the finer grained strata indicate a periglacial influence. The overlying Tupe supersequence suggests a gradual cessation of fault activity as the various depocenters were yoked together. Tupe stratigraphy onlaps the Guandacol-Tupe unconformity and buries some of the previous interbasin highs. In Patquía-De la Cuesta time, the Paganzo basin had widened to its maximum extent. Significant transgressions are recorded in Tupe (Westphalian-Stephanian) and Patquía-De la Cuesta (Artinskian and Kazanian) stratigraphy. Extensive geochemical studies show that Patquía source rocks are oil prone. Although indications are that the Paganzo basin is prospective, it remains largely untested. Regional studies show that the strike-slip faults that controlled Carboniferous basin development in northwestern Argentina diverge northward where they become involved in the Chaco salient of the Bolivian Andes. The Tupambi-Tarija and Escarpment sequences of Bolivia are broadly contemporaneous with the Guandacol and Tupe stratigraphy of the Paganzo basin. They share similar depositional characteristics typical of rapidly subsiding transtensional basins, including stacked alluvial facies, thick debris flow diamictites, massive soft sediment deformation, and dewatering structures. The Escarpment Formation represents an expansion of the earlier Tupambi-Tarija depocenters and contains an anastomosing drainage system.

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Authors

  • F Fernandez-Seveso

  • A J Tankard

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