ESBOZO PALEOECOLOGICO DE LAS ASOCIACIONES FORAMINIFEROLOGICAS TERCIARIAS DE LA ARGENTINA

Norberto Malumian

Abstract


The majority of the Tertiary ingressions in Argentina can be identified by means of foraminiferal assemblages which are named by their dominant or typícal genera. A sequence mainly composed of low diversity faunas: the Boltovskoyella assemblage (Late Eocene-Early Oligocene); Hopkinsina - "Unicosiphonia'' assemblage (Late Eocene -Early Oligocene); Cribrorotalia assemblage (Late Oligocene) ; Martinottiella assemblage (Lower-Middle Miocene) and "Protetphidium" assemblage (Late Miocene-Early Pliocene), can be recognized, conforming a biostratigraphical standard for this mostly shallow water ingression of variable extend which usually lack diagnostic planktonic foraminifers from the chronological point of view. According to specific diversity, ecological features of dominant genera and the planktonic/benthonic ratio of each assemblage, the generalized ecological characteristics are: a) The Danian sea does not reach a deepness larger than outer shelf, the major part of its sediments were deposited in inner shelf with normal salinity ; b) The Boltovskoyella assemblage, related with limestones, represents one of the warmer seas in the Tertiary, and inhabited an inner shelf environment; e) The Hopkinsina- "Unicosiphonia" assemblage inhabited mostly inner shelf environments; d) The Cribrorotalia assemblage, of inner shelf environment, evidence a lowering temperature; e) The Martinottiella assemblage represents one of the deepest environments recorded in the Tertiary, corresponding to an outer shelf-epibatial environment; f) the "Protelphidium" assemblage represents shallow, mainly abnormal salinity waters.

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