Fossiliferous methane-seep deposits from the Cenozoic Talara Basin in northern Peru

摘要

Thirteen fossiliferous limestone deposits from Cenozoic strata in the Talara Basin in northern Peru are identified as ancient methane-seep deposits. Planktonic foraminifera and the existing stratigraphical framework of the Talara Basin indicate an early Oligocene, or possibly late Eocene, age of these deposits. They are found in three distinct areas - Belen, Cerro La Salina and Cerros El Pelado - and differ in their petrography, stable isotope signatures, and lipid biomarker and macrofaunal contents. At Belen, the carbon stable isotope signature of the carbonate and the abundance of n-alkanes indicates the possibility of oil seepage in addition to methane seepage; for Belen and Cerro La Salina the high abundance of the biomarker crocetane indicates a dominance of anaerobic methane-oxidizing archaea of the ANME-2 group, whereas the rather small combined crocetane/phytane peak of a Cerros El Pelado limestone agrees with mixed ANME-1/ANME-2 input. The macrofauna consists mainly of molluscs; the Cerro La Salina sites include mostly infaunal thyasirid and lucinid bivalves and only few vesicomyid bivalves; gastropods include Provanna antiqua, the limpet Pyropelta and several vetigastropods. The Belen site is dominated by the elongate vesicomyid bivalve Pleurophopsis lithophagoides. The most common bivalve at the Cerros El Pelado sites is an undetermined, possible vesicomyid, and a smooth provannid gastropod. Biogeographically the faunas are most similar to those of the northwestern United States, as indicated by two joint species; similarities on the genus level (Conchocele, Lucinoma, Pleurophopsis, Provanna, Colus) exist also with Japan and the Caribbean region.