Checklist for the use of potassium concentrations in siliciclastic sediments as paleoenvironmental archives

Abstract

Weathering indices quantify the release of mobile elements from source units of soils and sediments. They have been employed in geosciences for more than three decades, but their performance in sedimentary archives can still be improved by deciphering other forcing factors than climatic. From the most common alkali and alkaline earth metals included in the weathering indices, K seems to be most suitable for deciphering paleoclimate records of temperate to subtropical non-arid climates, assuming the interpretation respects the complex of controlling factors on sediment geochemistry. As a case study, normalised K concentrations in siliciclastic sediments of the Most Basin (Miocene period, central Europe) are revisited here and variations compared with modern fluvially transported solids. Existing knowledge on manifold controls of K concentrations in sediments is summarised and used to propose list of possible controlling factors, in particular Al/Si and Zr/Rb as grain-size proxies, Ti/Al as provenance proxy relevant for K concentration in parent rocks,

Biotic and environmental changes in the Panthalassa Ocean across the Norian (Late Triassic) impact event

“…Potassium, Rb, and Al contents are attributed to aluminosilicates, especially clay minerals. Given that Al is resistant to chemical weathering (Nesbitt and Young 1982), Al-normalized K and Rb can be used as chemical weathering indicators (Tanaka and Watanabe 2015;Grygar et al 2019;Liu et al 2019). In the present study, the enrichment factors of K and Rb show similar trends.…”

Local to global controls on the deposition of organic-rich muds across the Late Jurassic Laurasian Seaway

“…Al-normalized values of Si, Ti and Zr can be used as grain size indicators, and Al-normalized K and Rb can be used as weathering and sediment provenance indicators (e.g. Sageman et al 2003;Brumsack 2006;Grygar et al 2019). Aluminium-normalized Si, Ti, Zr, K and Rb range from 2.0-3.8, 0.04-0.07, 8.2-33.2, 0.2-0.3 and 16.5-24.0 in ORB 4, respectively (Fig.…”

“…In contrast to the coarse grain size-/heavy mineral-bound elements Si, Ti and Zr, the abundance of K and Rb in marine sedimentary rocks is related to sediment provenance and/or weathering rates on the adjacent sediment because they are (like Al) commonly associated with fine-grained/lower-density terrigenous minerals like K-feldspar and clay minerals (Calvert & Pedersen 2007;Grygar et al 2019). Sediment routing systems and weathering rates are both affected by climate-driven processes, so K/Al and Rb/ Al ratios can be used to infer changes in climatic conditions and processes on landmasses adjacent to depositional basins.…”

“…To mitigate this challenge, ratios of elements with biogeochemically and hydrodynamically conservative behaviour must be used instead. Potassium and rubidium are strong candidates for this as changes in the Al ratios of both elements are dependent upon weathering on adjacent hinterlands (Grygar et al 2019).…”

Beginning of the Miocene Climatic Optimum in Central Europe in sediment archive of the Most Basin, Czech Republic

“…To fully take advantage of the stratigraphic uniqueness of the basin, a detailed study of stratigraphic correlation of the chemo-, cyclo-, and magnetostratigraphic records from the basin was performed. Chemo-and cyclostratigraphic studies of the Most Basin have mainly been based on geochemically normalised K concentrations (Matys Grygar et al 2019b), which potentially carry information on chemical weathering intensity in the sediment source area (Buggle et al 2011, Garzanti et al 2013, but which also bear certain grain-size contributions (Matys Grygar et al 2019b). Recently, normalised Mg concentrations have also been proposed as a weathering proxy (Dinis et al 2017).…”