Chachao Coquina, Taphofacies 1a (Cretaceous of Argentina)

Where: Mendoza, Argentina (35.8° S, 69.9° W: paleocoordinates 34.9° S, 33.3° W)

• coordinate stated in text

When: Chachao Formation (Mendoza Group), Early/Lower Valanginian (140.2 - 136.4 Ma)

• "Valanginian limestones of Chachao Formation are included in the Mendoza Mesosequence.

•two informal members in the Chachao Formation, the lower one with Lissonia riveroi (Lower Valanginian) and the upper one containing Olcostephanus curacoensis."

• group of beds-level stratigraphic resolution

Environment/lithology: graded packstone

• "By Late Jurassic to Early Cretaceous times the Neuquen basin was a typical back-arc basin related to the Pacific South American convergent plate margin. Early in the Late Cretaceous, it became a foreland basin as a result of the beginning of the Andean uplift. Before Late Jurassic the basement of the basin had suffered an initial rift phase, which led to western marine flooding and the formation of a series of half-grabens which controlled the sedimentation.

•

•During Late Jurassic to Neocomian times the generalized thermal subsidence expanded the original sedimentation area and during this time more than 2500 m of sediments were deposited. The sedimentation ended with Late Cretaceous to Tertiary synorogenic continental deposits, closely related to the uplift of the Andean fold and thrust belt (Manceda and Figueroa 1995, Zapata et al. 1999).

•

•Late Jurassic-Early Cretaceous succession comprises a thick pile of marine and non-marine siliciclastics, volcanics and volcaniclastic sediments as well as carbonates and evaporites."

• "a normally graded, densely packed packstone-grainstone up to 1.80 m thick"

Collection methods: A typical feature of the Chachao Formation is the dominance of oysters, many of them quite large e.g. Aetostreon latissimun, and others small, e.g. Ceratostreon minos. Different kinds of semi-infaunal and infaunal soft bottom-dwellers and swimming bivalves were recognized (Table 1). Additional forms are represnted by gastropods, ammonites (Olcostephanus curacoensis), and ichnofossils such as Thalassinoides isp. Serpulids are reprsented by the colonial Sarcinella sp. and the solitary form Parsimonia sp. (Table 1). The highy diverse fauna of the analyzed sucession, made up with numerous stenohaline elements such as echinoderm, bryozoa, ammonite as well as serpulids and typical marine pelecypods indicate a fully marine environment (Palma 1996).

Primary reference: R. M. Palma and S. G. Lanes. 2001. Shell Bed Stacking Patterns in the Chachao Formation (Early Valanginian) in Malargue Area, Mendoza Province, Neuquen Basin, Argintina. Carbonates and Evaporites 16(2):168-180 [L. Ivany/P. Wall/P. Wall]more details

Purpose of describing collection: taphonomic analysis

PaleoDB collection 44669: authorized by Linda Ivany, entered by Patrick Wall on 16.09.2004

Creative Commons license: CC BY (attribution)

Taxonomic list

• Taken from Text
Show authors, comments, and common names
Polychaeta
 Sabellida - Serpulidae
Parsimonia sp.
Bivalvia
 Ostreida - Pinnidae
Pinna sp.
Pinna sp. Linnaeus 1758 oyster
 Ostreida - Gryphaeidae
Ceratostreon minos, "Aetostreon latissimun" = Exogyra (Aetostreon)
Ceratostreon minos Coquand 1869 oyster
"Aetostreon latissimun" = Exogyra (Aetostreon) oyster
 Pectinida - Pectinoidae
Pecten sp.
Pecten sp. Müller 1776 scallop
 Carditida - Crassatellidae
Ptychomya sp.
 Ichnofossils -
Thalassinoides sp.
Thalassinoides sp. Ehrenberg 1944