The Tres Cruces Formation is a sedimentary and fossiliferous geological formation that crops out across Paihuano in the Coquimbo Region of Chile. It dates back to the Early Jurassic period (Sinemurian through Pliensbachian stages). The lithology of the formation comprises clastic rocks, such as sandstone, conglomerate, and fossil-rich limestone, formed in marine settings. As such, the Tres Cruces Formation preserves a marine fossil record represented by brachiopods, molluscs (ammonites, bivalves, gastropods), and marine reptiles (ichthyosaurs). The formation is named after Quebrada Tres Cruces, whhich is an important fossiliferous locality.
Paleobiota of the Tres Cruces Formation
Ammonites Genus Species Material Locality Unit Notes Images Acanthopleuroceras Indeterminate Not specified. Quebrada Dolores A polymorphitid ammonite. Amaltheus Indeterminate Not specified. Quebrada Dolores A amaltheid ammonite. Arieticeras? Indeterminate Not specified. Quebrada Tres Cruces A hildoceratid ammonite. Radstockiceras? Indeterminate Not specified. Quebrada Dolores A oxynoticeratid ammonite.
Bivalves Genus Species Material Locality Unit Notes Images Cardinia Indeterminate Not specified. Quebrada Tres Cruces A cardiniid bivalve. Exogyra Indeterminate Not specified. Quebrada Tres Cruces A gryphaeid bivalve. Gryphaea Indeterminate Not specified. Quebrada Dolores A gryphaeid bivalve. Ostrea Indeterminate Not specified. Quebrada Tres Cruces A ostreid bivalve. Panopea Indeterminate Not specified. Quebrada Tres Cruces A hiatellid bivalve. Pholadomya Indeterminate Not specified. Quebrada Tres Cruces A pholadomyid bivalve. Weyla W. alata Not specified. Quebrada Tres Cruces, Quebrada Dolores, Quebrada Matahuaico A pectinid bivalve.
Brachiopods Genus Species Material Locality Unit Notes Images Spiriferina S. rostrata Not specified. Quebrada Tres Cruces, Quebrada Dolores A spiriferinid brachiopod. Terebratula Indeterminate Not specified. Quebrada Dolores A terebratulid brachiopod. Zeilleria Indeterminate Not specified. Quebrada Tres Cruces A zeilleriid brachiopod.
Gastropods Genus Species Material Locality Unit Notes Images Lithotrochus L. humboldtii Not specified. Quebrada Tres Cruces, Quebrada Dolores A trochid gastropod. Nerinea Indeterminate Not specified. Quebrada Tres Cruces A nerineid gastropod. Pleurotomaria Indeterminate Not specified. Quebrada Tres Cruces A pleurotomariid gastropod.
Ichthyosaurs Genus Species Material Locality Unit Notes Images Ichthyosauria indet. Indeterminate Twelve vertebrae centra. Quebrada Tres Cruces An ichthyosaur.
See also Lautaro Formation
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