Chachao Coquina - Taphophacies 3: Early Valanginian, Argentina

List of taxa
Where & when
Geology
Taphonomy & methods
Metadata & references
Taxonomic list
Cephalopoda - Ammonitida - Olcostephanidae
Olcostephanus curacoensis
Bivalvia - Pectinida - Pectinidae
Pecten sp. Müller 1776
Bivalvia - Ostreida - Gryphaeidae
Ceratostreon minos (Coquand 1869)
Aetostreon latissimun
Bivalvia - Ostreida - Pinnidae
Pinna sp. Linnaeus 1758
Bivalvia - Arcida - Cucullaeidae
Cucullaea sp. Lamarck 1801
Bivalvia - Trigoniida - Trigoniidae
Trigonia sp. Bruguière 1789
Bivalvia - Cardiida - Kalenteridae
Myoconcha sp. Sowerby 1824
Bivalvia - Carditida - Astartidae
Eriphyla sp. Gabb 1864
unclassified
Thalassinoides sp. Ehrenberg 1944
see common names

Geography
Country:Argentina State/province:Mendoza
Coordinates: 35.8° South, 69.9° West (view map)
Paleocoordinates:34.9° South, 33.3° West
Basis of coordinate:stated in text
Time
Period: Cretaceous Epoch: Early Cretaceous
Stage: Valanginian 10 m.y. bin: Cretaceous 1
Key time interval: Early Valanginian
Age range of interval: 139.8 - 132.6 m.y. ago
Stratigraphy
Geological group:Mendoza Formation:Chachao
Stratigraphic resolution:group of beds
Stratigraphy comments: "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."
Lithology and environment
Primary lithology:tabular,grading,shelly/skeletal lithified wackestone
Secondary lithology: packstone
Includes fossils?Y
Includes fossils?Y
Lithology description: a massive, loosely packed, matrix-supported packstone-wackestone. The skeletal concentrations are tabular or slightly lenticular, from 25 to 40 cm thick. Lower and upper contacts of the shell accumulations may be gradational or sharp.
Environment:offshore ramp Tectonic setting:back-arc basin
Geology comments: "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."
Taphonomy
Modes of preservation:body
Size of fossils:macrofossils
Articulated whole bodies:some
Disassociated major elements:many
Size sorting:poor
Fragmentation:frequent
Bioerosion:frequent
Feeding/predation traces:drill holes
Spatial resolution:parautochthonous
Collection methods and comments
Collection excludes:some macrofossils
Collection methods:field collection
Reason for describing collection:taphonomic analysis
Collection method comments: “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 soft bottom dwellers and swimming bivalves were recognized (Table 1). Additional forms are represented by gastropods, ammonites (Olcostephanus curacoensis), and ichnofossils such as Thalassinoides isp. Serpulids are represented by the colonial Sarcinella sp, and the solitary form Parsimonia sp. (Table 1). The highly diverse fauna of the analyzed succession, 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)."
Taxonomic list comments:Taken from text
Metadata
Database number:44711
Authorizer:L. Ivany Enterer:P. Wall
Modifier:P. Wall Research group:marine invertebrate
Created:2004-09-16 12:17:38 Last modified:2007-12-03 16:28:03
Access level:the public Released:2004-09-16 12:17:38
Creative Commons license:CC BY
Reference information

Primary reference:
11680. 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]