Fracturing and Near-Surface Diagenesis of a Silicified Miocene Deltaic Sequence: The Montjuïc Hill (Barcelona)

Abstract

Near-surface diagenesis has been studied in the Langhian siliciclastic rocks of the Montjuïc Hill (Barcelona Plain) by means of petrographical (optical and cathodoluminescence) and geochemical (electron microprobe, δ18O, δ13C, δ34S and 87Sr/86Sr) analyses. In the hill, these rocks are affected by strong silicification, but the same unit remains non-silicified at depth. The results reveal that fracturing took place after lithification and during uplift. Fracture cementation is clearly controlled by the previous diagenesis of the host rock. In non-silicified areas, cementation is dominated by calcite, which precipitated from meteoric waters. In silicified areas, fractures show multiepisodic cementation produced firstly by barite and secondly by silica, following the sequence opal, lussatite, chalcedony, and quartz. Barite precipitated only in fractures from the mixing of upflowing seawater and percolating meteoric fluids. The presence of silica stalactites, illuviation, and geopetal structures, and δ18O values indicate that silica precipitation occurred in the vadose regime from low-temperature percolating meteoric fluids, probably during a glacial period. Moreover, the presence of alunite suggests that silica cement formed under acidic conditions. Karst features (vugs and caverns), formed by arenisation, reveal that silica was derived from the dissolution of surrounding silicified host rocks.

Petroarcheológiai tanfolyam a szilicit nyersanyagokról – elméleti és gyakorlati képzés a Schelde és a Rajna közötti terület kőzetein

“…A kőeszközök nyersanyagainak nevezéktana régóta ismert probléma, melyre vonatkozóan számos konferencia-, gyűjteményes kötet és célzottan a terminológiai változatokra összpontosító kiadvány jelent már meg (lásd a teljesség igénye nélkül: Balogh 1991; Brandl 2010, 183-190;Cantarero et al 2020;Caux et al 2018, 210-219;Götze 2010, 163-176;Kostov 2010, 209-214;Mateiciucová 2008;Mester & Faragó 2016;Milnes & Thiry 1992, 349-377;Přichystal 1997;Přichystal 2010, 177-182;Přichystal 2013;Rácz 2010, 203-208;Šošić Klindžić 2010, 191-194;Szekszárdi 2005;Szekszárdi et al 2010;Szilasi 2019, 91-97;T. Biró 1998;T.…”

Tracking the Origin and Evolution of Diagenetic Fluids of Upper Jurassic Carbonate Rocks in the Zagros Thrust Fold Belt, NE-Iraq

“…The evolution of the seawater 87 Sr/ 86 Sr ratio curve during the Jurassic-Cretaceous is widely driven by variation in continental weathering rates (riverine) and predominant oceanic fluxes of non-radiogenic strontium sporadically during the Jurassic [5]. Silica hosted carbonates are another source that impacted the seawater radiogenic composition curve [38]. These sources of radiogenic strontium isotopes had a different effect on the seawater strontium isotope record (Figure 8, [5,9]).…”

Petrographic Markers for Archaeometric Identification of Montjuïc Sandstone, the Flagship Stone of Barcelona (NE Spain)

“…During Pliocene times Montjuïc was uplifted and faulted [55] and the sandstones were pervasively affected by joints that were subsequently silicified. In the lower parts of the series (i.e., within the Morrot unit) the joints appear only filled with thin amounts of chalcedony, but at the upper part (i.e., the Castell unit and above) the joints exhibit a complex filling, which can be observed in the widest open joints, usually formed by amorphous opal (sometimes with barite), then chessboard chalcedony and microquartz, and finally fibrous chalcedony towards the center of the joint ( Figure 4); for details of such late silicification see [56]. It is worth noting that chalcedony is predominantly of the length-fast (LF) type [57].…”