Fibrous gypsum veins as diffuse features and within fault zones: the case study of the Pisco Basin (Ica desert, southern Peru)

Abstract

New knowledge on patterns of fibrous gypsum veins, their genetic mechanisms, deformation style and weathering is provided by a field-and laboratory-based study carried out on the Neogene to Quaternary Pisco Basin sedimentary strata exposed in the Ica desert, southern Peru. Gypsum veins vary considerably in dimensions, attitudes and timing, and can develop in layered and moderately fractured rocks also in the absence of evaporitic layers. Veins occur both as diffuse features, confined to certain stratigraphic levels, and localized within fault zones. Arrays formed by layer-bounded, mutually orthogonal sets of steeply dipping gypsum veins are reported for the first time. Vein length, height and spacing depend on the thickness of the bed packages in which they are confined. Within fault zones, veins are partly a product of faulting but are also inherited layerbounded features along which faults are superimposed. Owing to the different petrophysical properties with respect to the parent rocks and their susceptibility to textural and mineralogical modifications, water dissolution and rupture, gypsum veins may have a significant role in geofluid management. Depending on their patterns and grade of physical and chemical alteration, veins may influence geofluid circulation and storage, acting as barriers to flow and possibly also as conduits.

Lithological control on fracture cementation in the Keuper Marl (Triassic), north Somerset, UK

“…The presence of gypsum veins in non-nodular beds has been reported in previous studies (Shearman et al 1972; Gustavson, Hovorka & Dutton, 1994; Mohamed El Tabakh & Warren, 1998; Cosgrove, 2001; Rustichelli et al 2016). Gypsum-filling of fractures has been largely attributed to externally sourced gypsum (Shearman et al 1972; Machel, 1985; Gustavson, Hovorka & Dutton, 1994).…”

“…Although fractures can reduce or block fluid flow after complete sealing (e.g. Laubach, 2003; Hooker et al 2016; Rustichelli et al 2016), sealed fractures as mineral veins are prone to reactivation and reopen due to the weak chemical bonds between cement and wall rocks (Gale & Holder, 2008, 2010). In mudrocks, fracture systems commonly exhibit a heterogeneous distribution which can be described as discrete units in fracture stratigraphy with different rock compositions, textures diagenesis, and also the intrinsic tendency for fractures to remain open or to seal (Laubach, Olson & Gross, 2009; Gale et al 2014).…”

Allostratigraphy and paleontology of the lower Miocene Chilcatay Formation in the Zamaca area, East Pisco basin, southern Peru

“…The onshore portion of the East Pisco Basin (Figure 1) is over some 30 km wide and about 200 km long, extending approximately from Pisco to Nazca (Dunbar, Marty, & Baker, 1990;León, Aleman, Torres, Rosell, & De la Cruz, 2008;Thornburg & Kulm, 1981). The basin started to form not later than the early Eocene (DeVries, 2017) with crustal extension, subsidence, and sediment accommodation probably being driven by subduction-related tectonic erosion (Clift, Pecher, Kukowski, & Hampel, 2003;Hampel, Kukowski, Bialas, & Huebscher, 2004), which also accounts for two major NW-SE and NE-SW trending normal and transtensional fault systems (Rustichelli, Di Celma, Tondi, & Bianucci, 2016a;Rustichelli, Di Celma, Tondi, Baud, & Vinciguerra, 2016b;Viveen & Schlunegger, 2018). Rapid uplift and inversion of the basin started around the latest Pliocene following the subduction of the Nazca Ridge beneath the South America and has persisted to this day (Hsu, 1992;Macharé & Ortlieb, 1992;Saillard et al, 2011).…”

Insights into the diagenetic environment of fossil marine vertebrates of the Pisco Formation (late Miocene, Peru) from mineralogical and Sr-isotope data

“…Gypsum is fibrous and grows inwards orthogonally to the vein sides. In the studied area we did not find veins with deformed gypsum, which are present elsewhere in the region (Rustichelli et al, 2016). The XRPD data reported in Table 2 indicate that anhydrite is present together with gypsum in all vein samples.…”