ammonites

Cerro la Isla: Early/Lower Cretaceous, Chile
collected by Bell

Where & when
Geology
Taphonomy & methods
Metadata & references
Geography
Country:Chile State/province:Atacama
Coordinates: 27.4° South, 69.5° West (view map)
Paleocoordinates:27.7° South, 36.0° West
Basis of coordinate:estimated from map
Geographic resolution:local area
Time
Period:Cretaceous Epoch:Early/Lower Cretaceous
Key time interval:Early/Lower Cretaceous
Age range of interval:145.5 - 99.6 m.y. ago
Stratigraphy
Formation:Quebrada Monardes
Lithology and environment
Primary lithology:"cross stratification" conglomeratic sandstone
Secondary lithology:planar lamination mudstone
Includes fossils?Y
Lithology description: "The pterosaur horizon fines upward from cross-bedded pebbly sandstone and intraclast breccia at the base to parallel-bedded mudstone at the top. The base is an irregular erosion surface cut 50 cm or more into the underlying sediments. There is no distinctive basal lag gravel"
Environment:"floodplain" Tectonic setting:intermontane basin
Geology comments: "Intra-arc extensional basin. The fault-bounded basin formed a deep, but narrow, north-south elongated trough within an andesitic volcanic chain. Warm and arid climate with a low and seasonal rainfall. Intermontane desert basin flanked by volcanoes and floored by dune fields, saline lakes, mudflats, alluvial fans and floodplains. The pterosaur horizon is interpreted as the traction and debris-flow deposits of a rapidly flowing sheet of water. Represents an exceptional flood event"
Taphonomy
Modes of preservation:body
Size of fossils:macrofossils
Spatial orientation:random
Preservation of anatomical detail:poor
Abundance in sediment:few
Disassociated major elements:some
Disassociated minor elements:many
Fragmentation:extreme
Spatial resolution:allochthonous
Taphonomy comments: Layer (covering at least 1 km2) deposited by a single extreme flood event and containing remains of thousands of pterosaurs. Horizon includes thousands of scatted pterosaur bone fragments, sparsley scattered through the sediment. The bones are not concentrated as a basal lag but are scattered throughout the horizon. "The distribution and orientation indicates that the bones are derived clasts...it may be that many of the fossils represent long-term bone accumulations reworked and redeposited by the flood"
Collection methods and comments
Collection methods:field collection,observed (not collected)
Reason for describing collection:paleoecologic analysis
Collectors:Bell
Metadata
Database number:92314
Authorizer:R. Butler Enterer:R. Butler
Modifier:R. Butler Research group:vertebrate
Created:2009-11-06 00:13:45 Last modified:2009-11-06 00:18:33
Access level:the public Released:2009-11-06 00:13:45
Reference information
Primary reference:
31118 C. M. Bell and K. Padian. 1995. Pterosaur fossils from the Cretaceous of Chile: evidence for a pterosaur colony on an inland desert plain. Geological Magazine 132:31-38 [R. Butler/R. Butler]

Secondary references:

31119 D. M. Martill, E. Frey, C. M. Bell and G. C. Diaz. 2006. Ctenochasmatid pterosaurs from Early Cretaceous deposits in Chile. Cretaceous Research 27:603-610 [R. Butler/R. Butler]