Diagenetic analysis in limestones of the Upper Cretaceous, southwest of Rio Negro Province, Argentina

Abstract

The diagenetic traits present in the calcareous succession of the Upper Cretaceous in the southwest of Rincon de Colitoro Grande (40 ° 56 '30' 'SL and 68 ° 55' 45 '' WL), Patagonia, Argentina, are described by means of high petrography resolution (catodoluminiscence). It is framed in the Maastrichtian lower-Danish transgression (the latter generally represented by the Roca Formation). At a microscale, the fossil fauna is composed of abundant fragmented remains of bivalves, gastropods, echinoderms and cephalopods, whose characteristics and association allow it to be preliminarily assigned as cold water carbonates. The cementation present in the grainstones and packstones facies under study is typical of a shallow marine environment, in which took place an excellent development of scalenohedral calcite, with very well-zoned crystals (up to 9 cementing events). The highly variable tenors of activating elements (Mn, Ce, Pb) and inhibitors (Fe, Co, Ni) of the luminescence in carbonates allow the development of an excellent stratigraphy of cements. Oxygen and carbon isotopic shows average values of -8 %o dO18 and -2 %o dC13 PDB respectively of the same, allow to establish have a high degree of diagenetic alteration for these limestones, with typical compositional characteristics of water carbonates cold, very similar to those recorded previously towards the east of the North Patagonian Massif.