A note of caution on the use of boulders for exposure dating of depositional surfaces

Schmidt, Silke; Hetzel, Ralf; Kuhlmann, Jan; Mingorance, Francisco; Ramos, Víctor A.

doi:10.1016/j.epsl.2010.11.039

Cited by 58 publications

(71 citation statements)

References 59 publications

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“…Hence, unit 2 was most likely deposited between ~10 and ~14 ka. This age interval is similar to the age of 11-13 ka that was obtained by 10 Be and 14 C dating of an alluvial terrace 30 km north of the study area (Schmidt et al, 2011a). Three alluvial surfaces near San Juan (150 km north of the study area) yielded also latest Pleistocene and Holocene ages by 10 Be dating (Siame et al, 2002).…”

Section: Ugams = University Of Georgia Accelerated Mass Spectrometrysupporting

confidence: 59%

“…OSL dating presumes the complete resetting of the optical signal during exposure to sunlight directly before the deposition. Although significant progress has been made on each of these approaches during the past decades, only six studies revealed consistent ages between OSL, 14 C, 10 Be and uranium series dating on alluvial, fluvial and playa sediments (Preusser et al, 2003;Anders et al, 2005;DeLong and Arnold, 2007;Magee et al, 2009;Kurth et al, 2011;Schmidt et al, 2011a). On the other hand, the alluvial sediments studied by Nissen et al (2009) Be depth profile compared to those obtained from OSL techniques, although both methods revealed internally consistent results.…”

Section: Introductionmentioning

confidence: 95%

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Optical dating of alluvial deposits at the orogenic front of the andean precordillera (Mendoza, Argentina)

et al. 2011

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Abstract:Well constrained numerical ages of alluvial fan sediments are key to understanding the chronology of alluvial episodes and tectonic activity at the front of the Andean Precordillera. We tested the application of radiocarbon and optically stimulated luminescence (OSL) dating in the distal part of an alluvial fan five kilometers north of Mendoza. For OSL dating a large number of aliquots (n > 70) -each composed of ~50 quartz grains -were measured in order to obtain reliable burial ages despite scattered dose distributions. Owing to a feldspar contamination in all samples, an infrared stimulation was inserted before each OSL measurement, which reduced the feldspar OSL signal successfully. By using the minimum age model we obtained stratigraphically consistent burial ages of alluvial deposits in a depth profile. The uppermost ~1 m of sediment is composed of debris flow deposits buried 770±76 years ago. Three plant remnants used for radiocarbon dating from the same layer, however, yielded ages younger than 350 years, which are interpreted to underestimate the depositional age. Underneath the debris flow, a major unconformity cuts a series of distal alluvial fan sediments with interstratified floodplain deposits, which are composed of sandy and calcite-rich silt layers, respectively. Three samples from this unit which were distributed over one meter of sediment thickness yielded statistically concordant OSL ages of 12.3±1.2 ka, 12.3±1.2 ka, and 11.7±1.1 ka. The deposition of these sediments during the latest Pleistocene coincides with a phase of cool and humid climate, which occurred before the alluvial fan propagated farther into the foreland. The overlying debris flow sediments are associated with alluvial fan incision during the arid Late Holocene.

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Section: Ugams = University Of Georgia Accelerated Mass Spectrometrysupporting

confidence: 59%

Section: Introductionmentioning

confidence: 95%

Optical dating of alluvial deposits at the orogenic front of the andean precordillera (Mendoza, Argentina)

et al. 2011

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“…While the relief on the paleo-landscape remnants is low (b1 km) and climate is arid, the region is tectonically active. Modern shortening is occurring in the adjacent Sierra de las Peñas system 15 km to the east of the study region (Ahumada and Costa, 2009;Schmidt et al, 2011aSchmidt et al, , 2011b. Erosion rates for the colluvium draped paleo-landscape remnants are near the median values reported for rock outcrops in the compilation by Portenga and Bierman (2011).…”

Section: Non-equilibrium Landscapementioning

confidence: 71%

“…There are few constraints on the onset of deformation in this region. Locally, the oldest constraint on faulting within the northern study area is 20 Ma (Reyna, 2011) with neotectonic activity occurring in the Sierra de las Peñas (Ahumada and Costa, 2009;Schmidt et al, 2011aSchmidt et al, , 2011b. The nearest age constraints are~100 km to the north and south.…”

Section: Deformation Historymentioning

confidence: 98%

Surface uplift and erosion of the southernmost Argentine Precordillera

Walcek

Hoke

2012

Geomorphology

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“…However, the significant scattering of CRN observed in distinct clasts of alluvial fans (e.g. Ritz et al, 2006;Owen et al, 2011;Schmidt et al, 2011) and along the fluvial system (Belmont et al, 2007) suggests that fluvial processes can contribute significantly and perturb the CRN signal in sediments.…”

Section: Introductionmentioning

confidence: 97%

Control of geomorphic processes on 10Be concentrations in individual clasts: Complexity of the exposure history in Gobi-Altay range (Mongolia)

2011

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International audienceThe dating of alluvial landforms by cosmogenic nuclides requires distinguishing the pre-deposition inheritance from the post-deposition history of the clasts in the studied marker. Moreover, estimating catchment-scale erosion rates from the concentrations of cosmogenic nuclides in active alluvia requires a good knowledge of the local/regional relationships between rock exhumation and transport through space and time. This is still poorly known for timescales of tens of thousand years. In order to document the evolution of clast exhumation and transport rates through time, we analyze in situ 10Be concentrations in boulders and cobbles from hillslopes to outlet of an arid mountainous catchment located in Gobi-Altay, Mongolia, strongly affected by global climatic changes during the Pleistocene-Holocene period. Samples were collected on bedrock, abandoned alluvial deposits, active colluvia and alluvia. Our results show a large 10Be scattering in the active river bed, consistent with a low and discontinuous catchment erosion rate dominated by mass wasting and fluvial incision. On the contrary, pre-exposure signal within abandoned terraces is much more homogeneous, consistent with climatic pulses responsible of strong erosional events on hillslopes and rapid fluvial transport. These results show that exhumation/transport processes at the catchment scale vary in style and intensity through time as a consequence of climatic oscillations. The occurrence of abrupt climatic changes during short periods of time recorded by 10Be concentrations in abandoned alluvia raise questions about the temporal applicability of catchment erosion rates derived from cosmogenic nuclide concentrations measured in sediments of active rivers. On the other hand, strong and short erosion events limit and homogenize the pre-exposure 10Be signal in associated deposits like debris-flows, making them particularly suitable markers for dating in active tectonic and paleoclimatic studies

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A note of caution on the use of boulders for exposure dating of depositional surfaces

Cited by 58 publications

References 59 publications

Optical dating of alluvial deposits at the orogenic front of the andean precordillera (Mendoza, Argentina)

Optical dating of alluvial deposits at the orogenic front of the andean precordillera (Mendoza, Argentina)

Surface uplift and erosion of the southernmost Argentine Precordillera

Control of geomorphic processes on 10Be concentrations in individual clasts: Complexity of the exposure history in Gobi-Altay range (Mongolia)

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