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

Abstract

Bleaching of red beds by the migration of reducing pore fluids is a widespread phenomenon, 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 on widespread bleaching of Cretaceous red beds in the Neuquén Basin and the relationship of this bleaching to hydrocarbon migration. In the Cerro Granito area of the Huincul High, Neuquén Basin, the basal deposits of the Neuquén Group (Candeleros and Huincul Formations) are bleached. This alteration was apparently controlled by fluid and host-rock composition as well as by the intensity and span of the fluid-rock interaction. Red, fine-grained sandstones and mudstones of the Candeleros Formation were deposited in fluvial and swamp environments and contain authigenic hematite, Na-rich corrensite, micro-and mesoquartz, calcite, and analcite. Coarse-grained sandstones and mudstones of the Huincul Formation, which overlie the Candeleros Formation, were deposited in a braided fluvial system, 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 both formations contain bitumen and clusters of calcite + bitumen concretions, and partially dissolved detrital clasts and most cements, including early Fe-oxides, which resulted in an increase in secondary porosity and bleaching of the red beds. Alteration of the Candeleros Formation is confined to medium-to coarse-grained sandstone in which corrensite is partially dissolved and its interlayer charge is satisfied by Ca instead of Na, as in corrensite from the red sandstones. Extensive dissolution occurred in the Huincul Formation, which favored 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 higherpermeability portions of the Candeleros and Huincul Formations. The seal provided by the Lisandro Formation was breached during uplift driven by Tertiary tectonism, resulting in the exhumation of the Huincul and Candeleros Formations. This study highlights the importance of a variety of alterations, including complex clay mineral paragenesis, contemporaneous with bleaching of the red beds. Such alterations can potentially be used to provide evidence for the passage of chemically reducing fluids associated with hydrocarbons in other regions, including cases where the original red color has been completely removed. Chachil Plutonic Complex+ + 39° 09′ 39° 09′ S S 1m Figure 4. (A) Geological map of the area showing the location of altered and unaltered levels in the Candeleros and Huincul Formations. (B) Orientation of fractures, faults, and elongated carbonate concretions within the Cerro Granito area. (C) Panoramic view showing the unconform...

Alteration halos in the Tordillos sediment-hosted copper deposit of the Neuquén Basin, Argentina

“…Tubes and clusters of concretions formed by poikilotopic calcite2 with red luminescence are similar to calcite pipes described in the Candeleros and Huincul Formations at El Porvenir area (Rainoldi et al, 2015) and in other reservoir rocks associated with faults (e.g., Entrada Sandstone, Utah; Garden et al, 2001). These concretions indicate a change in partial pressure of CH 4 and/or CO 2 rather than signaling fluid mixing.…”

“…During the Andean orogeny, reactivations of previous Triassic and Jurassic structures at the Huincul High (Maretto and Pángaro, 2005) triggered subsurface fluid seepage (formation water + hydrocarbons), breaking seals (Vaca Muerta Formation), and producing the up-flow of oil and formation water from the Lotena, Mulichinco, and Centenario reservoir rocks (Cabaleiro et al, 2002;Montagna et al, 2010) to the Neuquén Group. Evidence of this process is the conspicuous bitumen impregnations in the most permeable strata of the Neuquén Group described in the study area, in the Los Chihuidos High (e.g., Sapo Sur and Grillo Cu deposits, Rainoldi et al, 2014), and in other regions of the Huincul High (e.g., Barda González, La Cuprosa, and El Porvenir SHC deposits; Giusiano et al, 2006Giusiano et al, , 2008Pons et al, 2009;Paz et al, 2014;Rainoldi et al, 2015). Additional evidence for oil emplacement in the Huincul Formation at Tordillos is found in the numerous organic-rich fluid inclusions hosted in the micro-quartz overgrowths, calcite3, 4, and barite2 cements (see also Pons et al, 2015a).…”

Uranium Traps in Phreatic Sandstone-type Prospect, Taunsa Area, Dera Ghazi Khan, Eastern Sulaiman Range, Pakistan: Evidences from Autoradiography and Optical Microscopy

“…The organic matter in Taunsa uranium ore is possibly related with dead oil (solidified HC). This observation is supported by the extensive bleaching visible in the host sandstone on the outcrop which is generally considered an effect of petroleum migration into oxidized rocks (Schumacher and Abrams., 1996;Petrovic et al, 2008;Rainoldi et al, 2015).…”

Basic chemical compositions combination rules and quantitative criterion of red beds

“…Among them, the research of geomorphic characteristics and mineral compositions mostly adopts qualitative or semi quantitative methods, and there are many such studies. For example, Rainoldi et al (2015) identified red beds by studying the color of geomorphic characteristics and hematite in mineral compositions, and studied the mechanism of red beds bleaching. Uchida et al (2000) distinguished red sandstone, yellowish brown sandstone, and green sandstone according to the content https://doi.org/10.5194/egusphere-2023-2590 Preprint.…”