Chronology and paleoenvironmental interpretation of talus flatiron sequences in a sub‐humid mountainous area: Tremp Depression, Spanish Pyrenees

Abstract

Talus flatirons are debris-covered relict slopes, disconnected from the source area, which are relatively common in arid and semi-arid areas. Talus flatiron sequences record the alternation of accumulation and incision phases. These chronosequences may be used for infer temporal changes in the morphogenetic processes acting on the slopes as well as information on the local paleoclimatic history. Talus flatiron sequences developed in the Tremp Depression, eastern Spanish Pyrenees, are analysed from the geomorphological, chronological and paleoenvironmental perspective. The two groups of relict slopes differentiated by means of detailed geomorphological mapping have been dated by optically stimulated luminescence (OSL) and radiocarbon dating at 25-20 kyr (S3) and 5Á4-1Á7 cal kyr (S2). The talus flatiron group S3 is correlated with a fluvial terrace of the Noguera Pallaresa River (c. 23 kyr BP). The comparison of the ages obtained in the Tremp Depression with chronologies published for talus flatiron sequences in semi-arid areas and other paleoclimatic proxies suggests that the aggradation phases in the slopes occurred during periods with higher humidity and vegetation cover. The chronological differences observed between semi-arid Spain and the Tremp Depression may be partly related to the more humid climate of the latter mountain area.

Reconstructing Mousterian landscapes in the southeastern Pyrenees (Roca dels Bous site, Pre-Pyrenees ranges, Spain)

“…Rockfall and stratified slope deposits are commonly associated with cold conditions in periglacial and mountain environments. Nevertheless, similar sedimentological characteristics have also been described in temperate upland environments (García-Ruiz et al, 2001;Van Steijn, 2011), and aggradation on slopes located to the north of the study area have been related to vegetation cover and humidity conditions (Roqué et al, 2013). There is some evidence in the RB sequence to suggest that a non-extreme cold climate prevailed during the site formation period, namely: (1) the site is located at a low altitude (278 m asl), (2) the rock shelter has a southern orientation with a high insolation degree, and (3) the sequence is capped by a flowstone unit, denoting the existence of warm and wet conditions at the top of the sequence.…”

Late Pleistocene talus flatiron formation below the Coal Cliffs cuesta, Utah, USA

“…These ages constrained deposition of individual flatiron aprons, but the incision and abandonment of those deposits could only be inferred by the depositional age of the next youngest flatiron. Later datasets incorporated optically‐stimulated luminescence and cosmogenic nuclide dating techniques alongside radiocarbon to both address this issue and obtain more precise depositional ages (Gutiérrez et al ., , ; Boroda et al ., , ; Gutiérrez‐Elorza et al ., ; Roque et al ., ). Although very few chronologies have been assembled at present, many suggest a strong temporal correlation between talus flatiron formation and late Quaternary climate changes.…”

“…While some aprons are active depositional settings, others have been dissected by gullies and disconnected from the escarpment, quarantining them from sediment sources and creating relict surfaces called talus flatirons. These landforms have been recognized since the mid‐20th century (Koons, ; Ahnert, ), and yet only in recent years have a small number of flatiron sequences been quantitatively dated (Gutiérrez et al ., , ; Gutiérrez‐Elorza and Martinez, ; Boroda et al ., , ; Gutiérrez‐Elorza et al ., ; Roque et al ., ). Though they are few in number, some available datasets reveal a link between talus flatiron formation and global climate (Gutiérrez et al ., , ), demonstrating that numerically dated flatirons can be used both to quantify rates of cuesta evolution and interpret the driving mechanisms.…”

Sedimentological and palaeohydrological characterization of Late Pleistocene and Holocene tufa mound palaeolakes using trenching methods in the Spanish Pyrenees

“…The tufa complex developed in association with non‐thermal artesian springs (14 to 19°C; Linares et al ., ) of calcium‐bicarbonate‐rich waters, perched above the local drainages. The elevation of both the base level of erosion and the groundwater outlets has changed throughout the evolution of the system in relation to the episodic entrenchment of the drainage network, as recorded by stepped sequences of fluvial terraces and mantled pediments (Linares et al ., ; Roqué et al ., ). Calcium carbonate precipitation around the artesian springs induced by CO 2 degassing, aided by biogenic activity and local increase in turbulence (Ford & Pedley, ; Keppel et al ., ), resulted in the progressive upward growth of tufa mounds topped by annular rimstones enclosing quasi‐circular lakes (Fig.…”