Abstract
A radiolarian assemblage found in the lowermost strata of the Rio Mayer Formation, as exposed at Estancia La Federica in Santa Cruz Province, Argentina, is described. The biostratigraphic markers of this assemblage indicate a late Berriasian-early Barremian age (early Early Cretaceous). The radiolarians have faunal affinities with early Cretaceous assemblages reported from offshore northwestern Australia and the western Pacific, northeast of New Zealand. A cool-water affinity is suggested for the Patagonian assemblage. Ten meters below the levels with radiolarians sediments bearing continental palynomorphs are found. They are referred to the Springhill Formation of Berriasian to Valanginian age.
Highlights
The Patagonian Austral Basin stretches over a large area offshore and onshore of Southern Argentina in Santa Cruz and Tierra del Fuego provinces (Fig. 1 A)
The formation is mostly continental as shown with palynological data, but in the upper sector it grades to marine environments that are attributed to the basal part of the Río Mayer Formation
The age of the Springhill Formation varies according to its location in the basin, being older (Late Jurassic, Kimmeridgian to Tithonian) in the southernmost area of the basin, but becoming younger (Early Cretaceous, Hauterivian to Aptian) towards the northernmost outcrops (Arbe, 1989; Kraemer & Riccardi, 1997)
Summary
The Patagonian Austral Basin stretches over a large area offshore and onshore of Southern Argentina in Santa Cruz and Tierra del Fuego provinces (Fig. 1 A). The age of the Springhill Formation varies according to its location in the basin, being older (Late Jurassic, Kimmeridgian to Tithonian) in the southernmost area of the basin (where it is found in the subsurface), but becoming younger (Early Cretaceous, Hauterivian to Aptian) towards the northernmost outcrops (Arbe, 1989; Kraemer & Riccardi, 1997). The Springhill Formation was dated as Berriasian, based on Pelecypoda, Perisphinctidae and Belemnoidea (Riccardi, 1977), to Valanginian, based on foraminifera and ostracoda (Kielbowicz et al, 1984).
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