Aragonite and calcite cementation in “boulder-controlled” meteoric environments on the Fern Pass rockslide (Austria): implications for radiometric age dating of catastrophic mass movements

Abstract

On the Fern Pass rockslide (Eastern Alps, Austria), projecting boulders collected surface runoV and delayed percolation of water into the rockslide mass, leading to decimetre-scale, Xuctuating, phreatic/ vadose diagenetic systems along their contact. In these systems, aragonite and calcite precipitation were nourished mainly by dissolution of carbonate-rock Xour. Cement precipitation was limited to southern-and eastern-exposed "runoV haloes" of boulders and mainly resulted in cemented breccias. Aragonite precipitation was related to dissolved Mg 2+ and/or to high CaCO 3 supersaturation in evaporative-concentrated pore waters. Early aragonite cement yielded a 234 U/ 230 Th age of 4,150 § 100 years. Relative to other radiometric ages ( 36 Cl, 14 C; by other authors) for the rockslide event, the U-Th age of the aragonite is the most precise proxy of depositional age. Carbonate cements are present in other rockslide and rockfall deposits also. U-Th dating of such cements is thus a comparatively rapid and inexpensive method of minimum-age dating catastrophic mass movements.

Quaternary carbonate-rocky talus slope successions (Eastern Alps, Austria): sedimentary facies and facies architecture

“…Talus slopes that shed into detachment scars of age-dated rockslides in the NCA (cf. Patzelt and Poscher 1993;Ostermann et al 2007;Prager et al 2007) record similar aggradation rates. In the NCA, the preservation of lithified talus successions ranges from practically complete to erosional relicts a few tens of meters in size.…”

“…Cut and polished rock slabs and a total of 128 thin sections provided documentation of facies and diagenesis. For the method of age determination of cement by 234 U/ 230 Th disequilibrium dating, see Ostermann et al (2006Ostermann et al ( , 2007. Definitions of technical terms of geomorphology and sedimentology can be viewed in the electronically supplemented material.…”

Age distribution of fossil landslides in the Tyrol (Austria) and its surrounding areas

“…Further data were gained from the curiously, strongly deflected southern rockslide branch, where post-depositional carbonate cements are encountered. They were dated using the 230 Th/ 234 U-disequilibrium method and yielded a minimum age of 4150±100 yrs for the accumulation of the rockslide debris (Ostermann et al, 2007). Based on these data, a temporal differentiation between two failure events, one making up the northern rockslide branch, and another, making up the southern branch, is not yet possible.…”

Hydrogeological Significance of Secondary Terrestrial Carbonate Deposition in Karst Environments

“…According to Pedley (1990) tufas can be described as 39 either autochthonous (forming in-situ), e.g. phytoherm framestone (anchored) and 40 phytoherm boundstone (dominated by the heads of skeletal stromatolites), or clastic (not 41 anchored). Clastic tufas include: phytoclasts, oncoids, detritus, peloids and palaeosols.…”

“…Additionally, maximum evapotranspiration associated with the 12 summer months concentrates constituents entering the ground to as much as twice that 13 measured in the atmospheric precipitation (Edmunds, 1971 Genty 39 and Quinif (1996) varied both between and within stalagmites, in the range 0.47 to 2.17 mm. 40 Laminae were defined by variations in the density of the intercrystalline pores and 41…”