IDEAN   23403
INSTITUTO DE ESTUDIOS ANDINOS "DON PABLO GROEBER"
Unidad Ejecutora - UE
artículos
Título:
The genus Steinmanella Crickmay in the transition between the Vaca Muerta and Mulichinco formations, Early Valanginian, Neuquén Basin, Argentina
Autor/es:
LETICIA LUCI; DARÍO G. LAZO
Revista:
AMEGHINIANA
Editorial:
ASOCIACION PALEONTOLOGICA ARGENTINA
Referencias:
Año: 2012 vol. 49 p. 96 - 117
ISSN:
0002-7014
Resumen:
The genus Steinmanella Crickmay is recorded in
several Lower Cretaceous marine units of the Neuquén Basin. It is particularly
abundant at the transition between the Vaca Muerta and Mulichinco formations.
This paper presents a taxonomic revision of this fauna, discusses the
stratigraphic range of each species, and describes and interprets the associated
lithofacies based on detailed field sections, newly collected specimens and
revision of previous fossil collections. Four sections were measured in
northern Neuquén comprising the upper beds of the Vaca Muerta Formation and the
lower ones of the Mulichinco Formation. The Steinmanella
fauna was dated accurately on the basis of a precise ammonoid zonation. The
species were found in the Neocomites wichmanni and Lissonia riveroi zones of
early Valanginian age. Specimens were collected in situ from dark grey shales,
alternating siltstones, wackestones and mudstones, and rudstones. Three species
were identified: Steinmanella curacoensis
(Weaver), S. quintucoensis (Weaver),
and S. subquadrata sp. nov. Steinmanella curacoensis has an oval
outline, poor demarcation of carinae, flank and corselet ribs partially
intercalated at the median part of the valve, and oval escutcheon. Steinmanella quintucoensis has a furrow
below the marginal carina, subrectangular outline, robustly tuberculated flank
ribs, and lanceolate escutcheon. Steinmanella
subquadrata sp. nov. has a subquadrate outline, well-marked carinae, and
oval escutcheon ornamented with thin
ribs and small elongated tubercles.