Chlorite-rich clay associations in interbedded tuffs and mudstones: diagenetic implications

FERNANDA CRAVERO; ROBERTO SCASSO; DIEGO KIETZMANN; IGNACIO CAPELLI

Granada

Conferencia; XVI International Clay Conference; 2017

Sociedad Española de Arcillas-SEA

The Upper Jurassic of two basins in southern South America and the Antarctic Peninsula is characterized by blackshale/mudstone-dominated marine successions with interbedded tuff beds milimetric to decimetric thick. Anoxicenvironment precluded bioturbation and sediment mixing, and favoured organic matter preservation (TOC 2-8%).Some of these successions may form unconventional oil reserves, such as the VacaMuerta Formation, and thereforethe study of clay mineralsis critical for the fracking process. As the clay mineral association developed ontuffs is totally diagenetic it may be regarded as a good tracer for the diagenetic grade. It is also remarkably differentfrom the clay mineral association in the background sediments.Most tuff beds in our case studies (the Ameghino Formation in the Larsen Basin, northeastern Antarctic Peninsulaand the VacaMuerta Formation in the Neuquén Basin, western Argentina) are massively replaced by carbonate,chlorite andillite-smectite interlayers (I/S). In the localities selected for this study both units underwent deep burialin the context of high geothermal gradient basins. Chlorite is more abundant than I/S in the tuffs and the oppositeis true for the background shales and mudstones.XRD studies (bulk rock and fraction