Taxonomy and paleoecology of a new gastropod fauna from dysoxic outer ramp facies of the Lower Cretaceous Agrio Formation, Neuquén Basin, west-central Argentina

CATALDO, C.S., LAZO, D.G.

CRETACEOUS RESEARCH (PRINT)

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Año: 2015 vol. 57 p. 165 - 189

0195-6671

Four gastropod species are described from dysaerobic biofacies of the lower part of the Agua de la Mula Member of the Agrio Formation, Neuquén Basin: Metacerithium turriculatum (Forbes, 1845), Nerineopsis acutecarinatum (Behrendsen, 1891) and the new species Ampullina pichinka and Mesalia? kushea. They were active epifaunals and possibly deposit-feeders and/or browsers, and epifaunal to semi-infaunal possibly suspension- or deposit-feeder in the case of M.? kushea, thriving in soft to firm substrates. These gastropods, together with two aporrhaid species, are largely the dominant component of a typically small-sized, low-diversity macrobenthic fauna that occurs in dark coloured, organic-rich shales. The facies associations in which this fauna is recorded are thought to represent a transition from lower to upper outer ramp marine settings, in the context of a second order TST and early stages of a HST. The bearing facies are also interpreted as recording a transition from lower dysoxic conditions in the lowest part of the Agua de la Mula Member, and then upper dysoxic conditions up to almost the top of the unit. Two gastropod biofacies were recognized corresponding to the two stages: biofacies A, dominated by P. neuquensis and N. acutecarinatum, more tolerant to dysoxic conditions, and biofacies B, dominated by M. turriculatum and M.? kushea, less tolerant to dysoxia.