An exceptional storm accumulation of nautilids, Lower Cretaceous, Neuquén Basin, Argentina

CICHOWOLSKY, MARCELA; PAZOS, PABLO; TUNIK, MAISA ANDREA; AGUIRRE URRETA, MARIA BEATRIZ

LETHAIA

WILEY-BLACKWELL PUBLISHING, INC

Año: 2011 vol. 45 p. 121 - 138

0024-1164

An exceptional accumulation of nautilid shells of the species Cymatoceras perstriatum(Steuer) is reported and described in the Lower Cretaceous Agrio Formation of the Neuque´n Basin (west-central Argentina). The bed represents a storm deposit in a shallowwaterenvironment within the mid-ramp. The evidences of a storm-related origin of thebed come from the petrographic analysis and taphonomic features of the shells, speciallythe sedimentary infill pattern. The shells are dispersed in patches within the stratum,without any orientation relative to the bedding plane. It is proposed that the shells werefloating after the death of the animals, although most of them have an almost completeliving chamber. The presence of some heavily encrusted shells suggests that there is amixing of specimens with different drift times. A variety of factors related to the originof such high number of nautilid shells are discussed, including a transgressive stand systemtract, the possible existence of a gregarious behaviour, changes in salinity and winddirections. h Lower Cretaceous,