DOI: 10.5281/zenodo.15524838
title: No major increase in erosion rates in Central Himalayas during the late Cenozoic, revealed by 10Be in the newly dated Valmiki Siwalik section. Supplementary tables.

description: This dataset is used as support for the manuscript "Supplementary Information forNo major increase in erosion rates in Central Himalayas during the late Cenozoic, revealed by 10Be in the newly dated Valmiki Siwalik section."

Tab. S1. Measurements of bedding strike and dips, and their location along the three subsections of the composite EVF Section.

 

Tab. S2. Location, stratigraphic depths and ages of all collected samples from the composite EVF and WVF Sections. Type indicates whether we collected the sample for paleomagnetism (Mag), or isotopic measurements (Sandy). We calculated stratigraphic depth from tape-meter measurements and GPS coordinates. We derived ages from the magnetostratigraphic age model (see § 4). Arbitrary one-sigma age uncertainty of 0.1 Ma. Note that (1) not all samples for cosmogenic measurements (i.e. below Dwcos25) were analysed in this study, (2) some samples have duplicates (e.g. T501 and T502), and some samples, without being duplicates, belong to the same strata (e.g. Dwcos8 and Dwcos44). Stratigraphic positions of sandy and paleomagnetic samples having reliable results are displayed in Fig. 8.

 

Tab. S3. Paleomagnetic directions. Composite EVF Section only. D: magnetic declination, I: magnetic inclination, g: geographic coordinates, s: stratigraphic coordinates, a95: radius of the fan in which the mean direction lies within 95% confidence, N: normal polarity, R: reverse polarity, Int: intermediate direction, GC: remanent direction trajectories that follow great circle paths, unstable: unstable directions, which cannot be interpreted.

 

Tab. S4. Major elements for our sandy samples. Elemental ratios normalized by Si. Measurement below the detection limit indicated by < D.L. Samples Ggcos1, Ggcos3, Dwcos7, Dwcos9, Dwcos13, Dwcos17, Dwcos20 without major and trace element measurement, nor Sr-Nd isotopic measurement.

 

Tab. S5. Trace elements for our sandy samples. Measurement below the detection limit indicated by < D.L.

 

Tab. S6. Sr-Nd isotopes for our sandy samples. The 143Nd/144Nd are reported as εNd(0), using CHUR(0) = 0.512638 (Goldstein et al., 1984), and relative contributions of the main geological units. The ~40% of the TSS contribution originating from carbonates is not included. Sample Dwcos32 falls outside the ternary diagram defined by the three main Himalayan lithologic unit poles (HHC, TSS and LH), so that its projection on the HHC-LH mixing curve is an approximate value.

 

Tab. S7. 10Be blank-corrected modern concentrations. Mass of quartz decontaminated from the atmospheric contribution, with 1.5% 1-sigma uncertainty. Measurement of 9Be before dissolution was calculated from the 9Be carrier concentration, with 2.92% 1-sigma uncertainty. Measurement of 9Be after evaporation determined by CRPG-SARM, with 12.5% 1-sigma uncertainty. The two 9Be measurements are distinct, because of the potential enriched Be content due to the large mass of dissolved quartz. The 10Be concentration was computed using the maximum of these two values. 10Be/9Be measured by CEREGE-ASTER. We extracted Be from samples in several series, each of them having average chemical blanks indicated here. The blank is 13% of the 10Be/9Be ratio on average (“Proportion of the correction of the blank”) and up to 52% for Dwcos8 which was analyzed in a series with a higher blank close to 10-14. The 10Be concentrations presented here were only corrected from the blank. Some samples are duplicates and indicated by * and **. Two sets of two samples were sampled in the same sandstone layer and indicated by # and ##. Both duplicates and samples from the same strata are pooled and averaged for paleoerosion rate calculation.

 

Tab. S8. 10Be Himalayan paleoconcentrations and paleoerosion rates. The paleoconcentrations are corrected for recent exposure during Siwalik exhumation (Crex), transfer and burial through the plain (Cfp), and radioactive decay. Correction for recent exposure is calculated according to 36Cl calibrated model (Eq. 3 § 11), height and approximate slope of the sampled cliff or river bank, and a qualitative coefficient for evidence of very recent erosion. Correction for transfer and burial through the plain are calculated according to the model parameters presented in Tab. S9 and to the depth of the sample below the top of the stratigraphic layer, in which we sampled. The field “Proportion of corrections” indicates which proportion of the concentration represents the transfer and exhumation corrections. The average erosion rate for duplicates (*,**) and samples taken in the same strata (#,##) is calculated from the weighed average of the paleoconcentrations. We reported for information apparent paleoerosion rates for samples younger than 1.25 Ma. However, we do not consider or discuss these rates since we presume that the sediment of these young samples is not directly issued from the erosion of the paleo-Narayani Catchment. 

 

Tab. S9. Parameters used for the flood plain transfer model. We determined these parameters from our observations on the modern channel using satellite imagery (Google Earth©) (sinuosity including average obliquity of the river relative to a radial direction) or from published studies, 1: (Lupker et al., 2012b); 2: (Morin et al., 2018); 3: (Jain and Sinha, 2003); 4: (Dubille and Lavé, 2015); 5: (Pati et al., 2019).

 

Tab. S10. Feldspar fraction chemical and 36Cl AMS results. All variables required for calculating a 36Cl cosmogenic and radiogenic production using CREp Chlorine-36 exposure age calculator (Schimmelpfennig et al., 2022) are also provided: porosity, major and trace elements of the whole rocks, major elements and [Cl] content in the feldspars fraction. Chemical measurement below the detection limit is indicated by < D.L.

 

Tab. S11. Recent 10Be exposure computation based on 36Cl results, and steady erosion model. We determined the 36Cl cosmogenic and radiogenic contributions using the CREp Chlorine-36 exposure age calculator (Schimmelpfennig et al., 2022), and the variables given in Tab. S10. For the recent exposure model, we took the outcrop-dependent parameters from Tab. S8.