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.
How to translate text using browser tools
1 March 2012
The Genus Steinmanella Crickmay (Bivalvia) in the Transition Between the Vaca Muerta and Mulichinco Formations, Early Valanginian, Neuquén Basin, Argentina
Leticia Luci,
Darío Gustavo Lazo
ACCESS THE FULL ARTICLE
Ameghiniana
Vol. 49 • No. 1
March 2012
Vol. 49 • No. 1
March 2012
Formación Mulichinco
Formación Vaca Muerta
Mulichinco Formation
Neuquén Province
Provincia de Neuquén
Steinmanella
Trigonioida