Diagenetic K‐feldspar pseudomorphs in the Triassic Buntsandstein sandstones of the Iberian Range, Spain

Abstract

Early diagenetic K‐feldspar in the Triassic Buntsandstein of the Iberian Range (Spain) occurs as pseudomorphs after detrital K‐feldspar (Or<93) and plagioclase (Ab<96). These pseudomorphs are chemically pure (Or>99), untwinned, commonly heavily clouded by vacuoles and tiny inclusions, dark‐luminescing and are composed of numerous fine euhedral crystals of K‐feldspar. The latter property suggests that the pseudomorphs form via dissolution of detrital K‐feldspar and plagioclase and precipitation of authigenic K‐feldspar. X‐ray diffraction analysis shows that the authigenic K‐feldspar is intermediate microcline.

Diagenesis and reservoir quality of the Sherwood Sandstone (Triassic), Corrib Field, Slyne Basin, west of Ireland

“…The origin of early diagenetic K-feldspar has been much debated over the years (Morad, Marfil, & de la Pena, 1989) since it is a common, minor, early cement in aeolian and ephemeral river sandstones. K-feldspar precipitation requires high silica activities and high K þ /H þ ratios (Morad, Ketzer, & De Ros, 2000).…”

Atmospheric weathering and silica-coated feldspar: Analogy with zeolite molecular sieves, granite weathering, soil formation, ornamental slabs, and ceramics

“…Papers on natural feldspars include: crystallographic control on alteration of microcline perthite (33); formation of pits aligned along microcracks and twin planes, enlargement into honeycombs, and major increase in surface area per volume (34-38; forthcoming papers by M. Lee and I. Parsons); slower dissolution of natural than artificially weathered feldspars at comparable pH, etc., and absence of a protective surface layer of common weathering products (35,(39)(40)(41)(42)(43); interaction of feldspar minerals in soils with organic species and microbes (44)(45); and various geological factors for feldspars in sedimentary rocks (46)(47)(48).…”

Linking diagenesis to sequence stratigraphy in fluvial and shallow marine sandstones: Evidence from the Cambrian–Ordovician lower sandstone unit in southwestern Sinai, Egypt

“…Flux of meteoric water in the LST fluvial sandstones also resulted in the formation of abundant authigenic K-feldspar pseudomorphs and overgrowths (Morad et al, 1989) (Fig. 9a,b,f,g).…”

“…9a,b) that show patchy or blocky extinction patterns. Backscattered electron imaging shows the presence of abundant microporosity and tiny voids/pits aligned parallel to the cleavage and twin planes, that both are characteristic of diagenetic feldspar pseudomorphs (Land and Milliken, 1981;Morad et al, 1989;Milliken, 1989) (Fig. 9c).…”