Reconstruction of the Miocene western Amazonian aquatic system using molluscan isotopic signatures.

摘要: Abstract Strontium isotopic ratios and Sr contents of molluscs from the Miocene Pebas Formation in Colombian Amazonia indicate that bulk was deposited a freshwater environment, predominantly draining Andes, with minor contribution shield regions. The molluscan oxygen carbon composition does not provide palaeosalinity proxy, but points to lacustrine palaeoenvironment. faunal character confirms such an interpretation. further suggest marine incursion reached area composed mixture shield-derived seawater, maximum salinity about 5 psu. Faunistic components this incursion-level support shield–seawater mixing. most likely western north, probably along Guyana shield.