Autigenic chlorite and chlorite-smectite mixed layer as indicator of increasing reducing condition in the Huincul Formation, Neuquén Basin, Argentina

JOSEFINA PONS; ANA LAURA RAINOLDI; DANIEL BEAUFORT; PATRICIA PATRIER; AGNES IMPICCINI,; MARTA FRANCHINI

Edinburgo

Congreso; Euroclay2015; 2015

he Clay Minerals Group of the Mineralogical Society of Great Britain & Ireland and The Clay Minerals Society.

The Huincul High (HH) and Los Chihuidos High (ChH) are morpho-structures of the Neuquén Basin characterized by the occurrence of hydrocarbon fields regional structures at depth and impregnations of bitumen in the sedimentary rocks of the Upper Cretaceous Neuquén Group. The Huincul Formation is a red-bed sequence of the Neuquén Group deposited in a fluvial environment. Some of the structures of the HH and ChH, reactivated during the Andean orogeny, acted as vertical channels connecting the reservoir fluids with the paleo-channels of the Huincul Formation. The reaction of hydrocarbons with red beds generated bleached sandstones (white) and gray- greenish gray and brown sandstones at the redox front, between the red and the bleached sandstones.This presentation establishes the relationship between diagenetic processes, hydrocarbons migration, and their implication in the origin of chlorite and chlorite-smectite mixed-layers coatings in the greenish grayand brown sandstones of the Huincul Formation.The greenish gray and brown sandstones and conglomerates document hydrocarbon migrations in the Huincul Formation where previous kaolinite and hematite coating were transformed to dioctahedral smectite, chlorite-smectite mixed layer or chlorite and pyrite, respectively. The transformation of smectite to chlorite in some of the greenish gray rocks located at the lower part of the Huincul Formation at NHH, involved fast rate of growth nucleation at expense of previous smectite and suggests a high fluid/rock ratio. This condition prevailed in the permeable layers of the sedimentary unit with low channel/floodplain ratio. The partial transformation of dioctahedral smectite to chlorite-smectite mixed layer or trioctahedral chlorite produced excess of silica and precipitation of micro quartz. Addition of Mg is required to form chlorite-smectite mixed layer or chlorite from the dioctahedral smectite and could be taken from the alteration of detritus mafic minerals and/or Mg-rich water formation that migrated with hydrocarbons.