Abstract
A new ammonoid species of the Andean endemic genus Andiceras Krantz is here described from upper Tithonian-lower Berriasian levels of the Vaca Muerta and Chachao Formations of the Mendoza Group, in north-western Mendoza Province, Argentina. Andiceras planulatus sp. nov. lies between the last beds with representatives of the Substeueroceras koeneni Assemblage Zone of late Tithonian age and the first bed yielding elements of the Argentiniceras noduliferum Assemblage Zone of early Berriasian age, according to the traditional Andean ammonoid zonation scheme. The particular stratigraphic position of Andiceras planulatus together with its easily recognizable morphology makes this species a good potential biostratigraphic marker for the Jurassic-Cretaceous boundary beds in the Andean region.
Highlights
The Neuquén Basin of west-central Argentina is located between 32 and 40o South and comprises a nearly continuous sedimentary infill from Late Triassic to Cenozoic (Fig. 1a)
During the Tithonian the Vaca Muerta Formation was deposited over a homoclinal carbonate-siliciclastic ramp system that probably turned into a distally steepened ramp during the Berriasian (Mitchum and Uliana, 1985; Kietzmann et al, 2008; Kietzmann and Vennari, 2008)
Andiceras planulatus sp. nov. is here proposed as a new form of Andiceras Krantz, a genus firstly described from upper Tithonian-lower Berriasian sedimentites in Mendoza Province (Krantz, 1926)
Summary
The Neuquén Basin of west-central Argentina is located between 32 and 40o South and comprises a nearly continuous sedimentary infill from Late Triassic to Cenozoic (Fig. 1a). The Mendoza Group (Groeber, 1946), in the study area, includes the Tordillo (Kimmeridgian), Vaca Muerta (lower Tithonian-lower Berriasian), Chachao (lower Berriasian-lower Valanginian), and the Agrio (upper Valanginian-Hauterivian) Formations. From upper Tithonian to lower Berrisian levels of the top of the Vaca Muerta Formation and the base of the Chachao Formation, some ammonoid specimens assignable to a new species have been recovered. Is here proposed as a new form of Andiceras Krantz, a genus firstly described from upper Tithonian-lower Berriasian sedimentites in Mendoza Province (Krantz, 1926). This new species may have a high biostratigraphic potential as it is located between the late Tithonian Substeueroceras koeneni and the early Berriasian Argentiniceras noduliferum Assemblage zones. Dimension of the specimens are indicated in mm: D: diameter; H: whorl height; W: whorl width and U: umbilical diameter
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