INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
Tithonian ammonoids (Cephalopoda, Ammonoidea) from the Vaca Muerta Formation, Neuquén Basin, West-Central Argentina
E SCHWEIZERBARTSCHE VERLAGS
Lugar: Stuttgart; Año: 2016 vol. 306 p. 85 - 85
Ammonoids are the most abundant and diverse group of marine invertebrates present in the Vaca Muerta Formation (early Tithonian- early Valanginian) of the Neuquén Basin (west-central Argentina). A modern systematic review of the late early Tithonian - earlymiddle Tithonian ammonoids of the Vaca Muerta Formation was conducted, focusing on perisphinctids (Superfamily Perisphinctoidea)the main components of the ammonoid assemblages. This revision was based on new fields collections and the assessing of referencetype material. As a result, nine species included in four genera are identified, described and grouped into one family (Ataxioceratidae)and two subfamilies (Lithacoceratinae and Virgatosphinctinae). Subfamily Lithacoceratinae is represented by the monospecific genusIndansites (gen. nov.) and the species I. malarguensis Spath, 1925. Subfamily Virgatosphinctinae includes the genus VirgatosphinctesUhlig, 1910b with V. andesensis (Douvillé, 1910a) and V. (?) densistriatus (Steuer, 1897); the genus Pseudinvoluticeras Spath,1925 with P. douvillei Spath, 1925 and Pseudinvoluticeras primordialis n. sp.; and the genus Choicensisphinctes Leanza, H. 1980 withCh. choicensis (Burckhardt, 1903), Ch. erinoides (Burckhardt, 1903), Ch. n. sp. aff. Ch. erinoides and Ch. aconcaguensis n. sp. Thenew name Virgatosphinctes andesensis Assemblage Zone is here proposed to replace the former Virgatosphinctes mendozanus AssemblageZone of the Andean Tithonian. Also, a tentative biostratigraphic subdivision of this biozone into two consecutive Interval Subzones,Pseudinvoluticeras primordialis to the base and Indansites malarguensis to the top, is proposed. Both Interval Subzones can be partiallycorrelated with Darwini and Semiforme Zones of the European standard, indicating a late early Tithonian - early middle Tithonianage for the V. andesensis Assemblage Zone. In addition, synchronicity of the Tithonian transgression in the Neuquén Basin is sustainedthrough the existence of a taxonomically homogeneous ammonoid assemblage in the lower portion of all the Vaca Muerta Formationsections studied.