Mineral reactions associated with hydrocarbon paleomigration in the Huincul High, Neuquén Basin, Argentina

RAINOLDI ANA; FRANCHINI MARTA; DANIEL BEAUFORT; PETER MOZLEY; ADOLFO GIUSIANO; CESARETTI NORA; PATRICE PATRIER; AGNES IMPICCINI,; PONS, JOSEFINA

GEOLOGICAL SOCIETY OF AMERICA BULLETIN

GEOLOGICAL SOC AMER, INC

Lugar: Boulder; Año: 2015 vol. 127 p. 1711 - 1729

0016-7606

Bleaching of red beds by the migration of reducing pore fluids is a widespreadphenomenon, with most previous work on the topic focused on detailed studies in the southwestern United States, and to a lesser extent Germany. Herein, we report onwidespread bleaching of Cretaceous red beds in the Neuquén Basin and the relationship ofthis bleaching to hydrocarbon migration. In the Cerro Granito area of the Huincul High,Neuquén Basin, the basal deposits of the Neuquén Group (Candeleros and HuinculFormations) are bleached. This alteration was apparently controlled by fluid and host-rockcomposition as well as by the intensity and span of the fluid-rock interaction. Red, finegrained sandstones and mudstones of the Candeleros Formation were deposited in fluvialand swamp environments and contain authigenic hematite, Na-rich corrensite, micro- andmesoquartz, calcite, and analcite. Coarse-grained sandstones and mudstones of the HuinculFormation, which overlie the Candeleros Formation, were deposited in a braided fluvialsystem, under more humid and acidic conditions than the Candeleros Formation.Sandstones are similar in composition and texture to the Candeleros sandstones, except they contain less basic volcanic detritus and lack corrensite. Bleached facies in bothformations contain bitumen and clusters of calcite + bitumen concretions, and partiallydissolved detrital clasts and most cements, including early Fe-oxides, which resulted in anincrease in secondary porosity and bleaching of the red beds. Alteration of the CandelerosFormation is confined to medium- to coarse-grained sandstone in which corrensite ispartially dissolved and its interlayer charge is satisfied by Ca instead of Na, as in corrensitefrom the red sandstones. Extensive dissolution occurred in the Huincul Formation, whichfavored the precipitation of new authigenic minerals such as smectite, mixed-layer chloritesmectite, and pyrite. Bleaching and associated alteration most likely resulted from interaction of hydrocarbons with the red beds. Hydrocarbon paleomigration in the Cerro Granito area occurred in higher-permeability portions of the Candeleros and HuinculFormations. The seal provided by the Lisandro Formation was breached during upliftdriven by Tertiary tectonism, resulting in the exhumation of the Huincul and CandelerosFormations. This study highlights the importance of a variety of alterations, includingcomplex clay mineral paragenesis, contemporaneous with bleaching of the red beds. Such alterations can potentially be used to provide evidence for the passage of chemicallyreducing fluids associated with hydrocarbons in other regions, including cases where theoriginal red color has been completely removed.