Revision of Valanginian Steinmanellinae bivalves from the Neuquén basin, West-central Argentina, and their biostratigraphic implications

• Valanginian trigonioids of the genus Steinmanella are revised.
• Steinmanella caicayensis is newly described based on 261 precisely dated specimens.
• The Valanginian of the Neuquén Basin is divided into three trigonioid zones.
• An integrated biostratigraphic zonation is proposed based on trigonioids and ammonoids.

We present a new species of Steinmanella Crickmay from the Valanginian of the Neuquén Basin, west-central Argentina, and at the same time update a Valanginian–earliest Barremian bivalve zonation which is integrated into the local, Chilean and European standard ammonoid zonations. Steinmanella caicayensis sp. nov. presents a moderately inflated shell, a subtriangular outline, well-developed carinae and a straight to moderately convex anterior margin. Steinmanella is very abundant in the Tithonian–Barremian interval in the basin and thus provides an ideal opportunity to perform detailed taxonomic and stratigraphic studies; a former zonation based on these trigonioids is here revised and expanded with a thorough revision of Valanginian occurrences based on new material. Two new zones are proposed, namely the S. quintucoensis and S. caicayensis zones, encompassing Valanginian times. The proposed bivalve zonation encompassing the Valanginian–earliest Barremian time interval can be useful in correlating with other southwestern Gondwanan regions, such as Perú, Chile, South Africa, Tanzania, and India, where Steinmanella has been recorded.