摘要
the stratigraphy of the gran bajo del gualicho formation is explained by the identification of the new saladar and arri車la members. the molluscan fauna comprises 38 genera and 44 species, 17 of which are new: anadara australis sp. nov, cubitostrea delrioi sp. nov., amusium rorii sp. nov, zygochlamys rizzoloi sp. nov,pododesmus (monia) atl芍ntica sp. nov, tawera canalei sp. nov,dosinia (dosinia) salarensis sp. nov., %26apos;spirocolpu芍 adapicis sp. nov., torcula magna sp. nov, magnatica hansi sp. nov, eudolium lissiei sp. nov, sconsia magdai sp. nov, chicoreus (chicoreus) guadalupei sp. nov., penion patagonensis sp. nov., mitra (fusimitra) carlosi sp. nov, austroimbricaria brugnii sp. nov. y polystira cingula sp. nov. the nvg (nodipecten sp.-venericor abasolensis- glycymerita camaronesia) molluscan assemblage in the saladar member nov. indicates an age of late early miocene-earliest middle miocene. the saladar member correlates with the upper section of the chenque formation and with the venericorbeanng horizons of the gaiman and vaca mahuida formations. the fauna of this member constitutes another evidence with respect to the weather stripes stated for patagonia since the late oligocene-early mocene. the assemblage recorded in the arri車la member nov. indicates the probable presence of the aequipecten parenensis zone and a stratigraphic relationship with the puerto madryn formation of a late mocene age, extending the covered 芍rea along the valdesian province to the salinas del gualicho. the fauna of the saladar member shows more affmity with that in the monte le車n and chenque formations, while the fauna in the arri車la member shares more resemblance with the paran芍 and puerto madryn formations. the chilean navidad and guadal formations have 30% and 10% of genus in common with fauna of the saladar member, respectively.