The genus Steinmanella (Bivalvia, Trigonioida) in the Agrio Formation (Lower Cretaceous), Neuquén Basin, Argentina

LAZO, D.G.

JOURNAL OF PALEONTOLOGY

Paleontological Society

Lugar: Lawrence; Año: 2003 vol. 77 p. 1069 - 1085

0022-3360

Myophorellid bivalves (Trigonioida, Myophorellacea) with conspicuously tuberculate shells are abundant in Lower Cretaceous rocks of the Neuque´n Basin represented by the Gondwanian genus Steinmanella Crickmay, 1930. Publications concerning Neuque´n trigonioids deal only with taxonomy, and until now the sedimentary environments of the Steinmanella bearing facies have not been interpreted. The present study analyzes morphology, taxonomy, stratigraphy, and paleobiology of Steinmanella species collected from five sections of the Lower Member of the Agrio Formation, including the type locality. Two species are differentiated: Steinmanella pehuenmapuensis (Leanza, 1998) from the lower part of the member (Pseudofavrella angulatiformis Zone) and Steinmanella transitoriaSteinmanella Crickmay, 1930. Publications concerning Neuque´n trigonioids deal only with taxonomy, and until now the sedimentary environments of the Steinmanella bearing facies have not been interpreted. The present study analyzes morphology, taxonomy, stratigraphy, and paleobiology of Steinmanella species collected from five sections of the Lower Member of the Agrio Formation, including the type locality. Two species are differentiated: Steinmanella pehuenmapuensis (Leanza, 1998) from the lower part of the member (Pseudofavrella angulatiformis Zone) and Steinmanella transitoriaSteinmanella bearing facies have not been interpreted. The present study analyzes morphology, taxonomy, stratigraphy, and paleobiology of Steinmanella species collected from five sections of the Lower Member of the Agrio Formation, including the type locality. Two species are differentiated: Steinmanella pehuenmapuensis (Leanza, 1998) from the lower part of the member (Pseudofavrella angulatiformis Zone) and Steinmanella transitoriaSteinmanella species collected from five sections of the Lower Member of the Agrio Formation, including the type locality. Two species are differentiated: Steinmanella pehuenmapuensis (Leanza, 1998) from the lower part of the member (Pseudofavrella angulatiformis Zone) and Steinmanella transitoriaSteinmanella pehuenmapuensis (Leanza, 1998) from the lower part of the member (Pseudofavrella angulatiformis Zone) and Steinmanella transitoria(Leanza, 1998) from the lower part of the member (Pseudofavrella angulatiformis Zone) and Steinmanella transitoria (Steinmann, 1881) from the middle and upper part of the member (Holcoptychites neuquensis, Hoplitocrioceras gentilii, and Weavericeras vacaensis Zones). Specimens of both species have been recorded in intermediate to high-energy shoreface and low-energy offshore deposits. The inferred paleoecologic model is that Steinmanella lived semi-infaunally and burrowed on sandy substrates in the shoreface and on muddy substrates in the offshore. Colonization of low-energy subenvironments in the offshore probably occurred during increased seafloor oxygenation and reduced net sedimentation or brief omission periods.Holcoptychites neuquensis, Hoplitocrioceras gentilii, and Weavericeras vacaensis Zones). Specimens of both species have been recorded in intermediate to high-energy shoreface and low-energy offshore deposits. The inferred paleoecologic model is that Steinmanella lived semi-infaunally and burrowed on sandy substrates in the shoreface and on muddy substrates in the offshore. Colonization of low-energy subenvironments in the offshore probably occurred during increased seafloor oxygenation and reduced net sedimentation or brief omission periods.Zones). Specimens of both species have been recorded in intermediate to high-energy shoreface and low-energy offshore deposits. The inferred paleoecologic model is that Steinmanella lived semi-infaunally and burrowed on sandy substrates in the shoreface and on muddy substrates in the offshore. Colonization of low-energy subenvironments in the offshore probably occurred during increased seafloor oxygenation and reduced net sedimentation or brief omission periods.Steinmanella lived semi-infaunally and burrowed on sandy substrates in the shoreface and on muddy substrates in the offshore. Colonization of low-energy subenvironments in the offshore probably occurred during increased seafloor oxygenation and reduced net sedimentation or brief omission periods.