Diagenetic migration of sulfides in sediments accumulated in different sedimentation settings

The Weathering-Modified Iridium Record of a New Cretaceous—Palaeogene Site at Lechówka Near Chełm, SE Poland, and Its Palaeobiologic Implications

“…1988;Hansen et al 1989;Tredoux et al 1989;Ebihara and Miura 1996;Of− ficer and Page 1996;Schmitz and Asaro 1996;Kramar et al 2001;MacLeod et al 2007;Premović 2009;Gavrilov 2010); conjectural explanations include a long−term volcanic activ− ity signature, bioturbation reworking, dissolution of carbon− ates, compactional squeezing of interstitial waters and/or chemical diffusion of metalloorganic compounds. Nanophase iron grains were suggested by some workers as the original iridium carrier in the K-Pg sites (e.g., Wdo− wiak et al 2001), although this interpretation is not univer− sally accepted (see e.g., Schuraytz et al 1997;Gabrielli et al 2004).…”

“…The mechanism of PGE leaching from decomposed extraterrestrial matter and transport in low−temperature aque− ous media, especially PGE host phases, has been insuffi− ciently known Chai et al 1995). Iridium, which, in some rare circumstances might also behave as a chalcophile element, may be bound at the surface of growing sulfide crystals and polycrystalline aggregates (see Gavrilov 2010), and the release of iridium was recently found at a py− rite−dominated mine tailing due to oxidative weathering in the soil profile (Martín−Peinado and Rodríguez−Tovar 2010). On the other hand, the connection of iridium with organic matter was highlighted by Schmitz et al (1988), and effective sorp− tion on humic acids is well proved (Varshal et al 2000).…”

“…In the K-Pg boundary strata at Stevns Klint, iridium is mostly asso− ciated with humic kerogen (Premović 2009), but this link is doubtful for the majority of coeval sites (see also Chai et al 1995). Secondary iridium re−concentration in neighbouring deposits may occur during mobilisation and re−precipitation due to decomposition of metalloorganic compounds at the trapping boundary, probably between reduced and oxidised sediments (Schmitz 1985;Crocket et al 1988;Tredoux et al 1989;Wallace et al 1990;Sawlowicz 1993;Colodner et al 1992;Evans and Chai 1997;Martinez−Ruiz et al 1999;Varshal et al 2000;Gavrilov 2010). Other factors may also be important, and e.g., Martín−Peinado and Rodríguez−Tovar (2010) demonstrated the dominant control of the clay fraction texture on the iridium redistribution in the soil matrix.…”

Nonpyrogenic charring of Late Pleistocene large mammal remains in northeastern Russia

“…Burial in the seasonally active layer access for moisture and microorganisms which led to the superficial blackening of the human remains. The main factor of the colour changes, probably, was the gel‐type hydrotroilite (FeS n • H 2 O) mineral, which formed under anoxic conditions due to microbial activity (Gavrilov 2010).…”