Controls on Chemical Weathering and Physical Erosion in a Mixed Carbonate-Siliciclastic Orogen

High-resolution siliciclastic grain size and bulk mineralogy combined with clay mineralogy, rubidium, strontium, and neodymium isotopes of Core MD01-2393 collected off the Mekong River estuary in the southwestern South China Sea reveals a monsoon-controlled chemical weathering and physical erosion history during the last 190,000 yr in the eastern Tibetan Plateau and the Mekong Basin. The ranges of isotopic composition are limited throughout sedimentary records:87Sr/86Sr = 0.7206–0.7240 andεNd(0) = −11.1 to −12.1. These values match well to those of Mekong River sediments and they are considered to reflect this source region. Smectites/(illite + chlorite) and smectites/kaolinite ratios are used as indices of chemical weathering rates, whereas the bulk kaolinite/quartz ratio is used as an index of physical erosion rates in the eastern Tibetan Plateau and the Mekong Basin. Furthermore, the 2.5–6.5 μm/15–55 μm siliciclastic grain size population ratio represents the intensity of sediment discharge of the Mekong River and in turn, the East Asian summer monsoon intensity. Strengthened chemical weathering corresponds to increased sediment discharge and weakened physical erosion during interglacial periods. In contrast, weakened chemical weathering associated with reduced sediment discharge and intensified physical erosion during glacial periods. Such strong glacial–interglacial correlations between chemical weathering/erosion and sediment discharge imply the monsoon-controlled weathering and erosion.

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Supplementary material to "Vegetation and climate effects on soil production, chemical weathering, and physical erosion rates"

10.5194/esurf-2021-22-supplement ◽

2021 ◽

Author(s):

Mirjam Schaller ◽

Todd Alan Ehlers

Keyword(s):

Chemical Weathering ◽

Climate Effects ◽

Erosion Rates ◽

Soil Production ◽

Physical Erosion ◽

Supplementary Material ◽

Vegetation And Climate

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(U-Th-Sm)/He dating of supergene Fe duricrusts in NE French Guiana: implications of a multiproxy approach

10.5194/egusphere-egu2020-11900 ◽

2020 ◽

Author(s):

Beatrix Heller ◽

Silvana Bressan Riffel ◽

Cécile Gautheron ◽

Thierry Allard ◽

Guillaume Morin ◽

...

Keyword(s):

Chemical Weathering ◽

French Guiana ◽

X Ray Diffraction ◽

X Ray ◽

Weathering Processes ◽

Erosion Rates ◽

Large Dispersion ◽

Icp Ms ◽

Physical Erosion ◽

Geochemical Analyses

Laterites are developing under intense chemical weathering and low physical erosion rates. Despite their large extension at the Earth&#8217;s surface, there is still a lack of time constraints for their formation, evolution and relation with climatic change. Nevertheless, several chronological studies show that they represent a geological record at least all along the Cenozoic Era. Indeed, laterite samples often contain several coexisting generations of iron oxides and oxyhydroxides that indicate successive weathering processes due to the dissolution of previously formed phases followed by reprecipitation. This study focuses on the condition and chronology of weathering in Northeastern French Guiana which generated pedogenic iron crusts on Paleoproterozoic mafic and intermediate rocks. It offers the opportunity to document the evolution of this part of the Guyana Shield, known as a tectonically stable area since the Cretaceous. The two sampling sites, Kaw and Baduel, are paleosurfaces at 300m and 100m elevations, respectively, that have been dated previously by paleomagnetism, providing Eocene ages for both sites, albeit with some substantial uncertainties and dispersion [1].Since the duricrust (top layer) of the lateritic profile is enriched in hematite and goethite, we aim to date those mineral phases using the (U-Th-Sm)/He method. Older ages are from Oligocene and Miocene epochs for the Kaw and Baduel sites, respectively, with a large dispersion in the age values, as expected from the presence of several generations of Fe-minerals. Identification of petrological relationship between these different generations is hindered by their intimate mixing. In order to overcome this difficulty and to identify the episodes of weathering and mineral precipitation, we coupled a number of mineralogical and geochemical analyses, namely through powder and single grain X-ray diffraction, energy dispersive X-ray spectrometry (SEM-EDS) and solution- and LA-ICP-MS. Data on formation ages of secondary iron phases will be discussed by reference to literature, in terms of geodynamic and paleoclimatic forcing.[1] Th&#233;veniaut, H., and Freyssinet, P. (2002): Timing of lateritization on the Guiana Shield: synthesis of paleomagnetic results from French Guiana and Suriname. Palaeogeography, Palaeoclimatology, Palaeoecology (178) 91-117

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Recent Budget of Hydroclimatology and Hydrosedimentology of the Congo River in Central Africa

Water ◽

10.3390/w12092613 ◽

2020 ◽

Vol 12 (9) ◽

pp. 2613

Author(s):

Alain Laraque ◽

Guy D. Moukandi N’kaya ◽

Didier Orange ◽

Raphael Tshimanga ◽

Jean Marie Tshitenge ◽

...

Keyword(s):

Chemical Weathering ◽

Central Africa ◽

Hydrological Regime ◽

Organic Production ◽

Congo Basin ◽

Congo River ◽

Physical Erosion ◽

Hydrological Regimes ◽

Material Fluxes

Although the Congo Basin is still one of the least studied river basins in the world, this paper attempts to provide a multidisciplinary but non-exhaustive synthesis on the general hydrology of the Congo River by highlighting some points of interest and some particular results obtained over a century of surveys and scientific studies. The Congo River is especially marked by its hydrological regularity only interrupted by the wet decade of 1960, which is its major anomaly over nearly 120 years of daily observations. Its interannual flow is 40,500 m3 s−1. This great flow regularity should not hide important spatial variations. As an example, we can cite the Ubangi basin, which is the most northern and the most affected by a reduction in flow, which has been a cause for concern since 1970 and constitutes a serious hindrance for river navigation. With regard to material fluxes, nearly 88 × 106 tonnes of material are exported annually from the Congo Basin to the Atlantic Ocean, composed of 33.6 × 106 tonnes of TSS, 38.1 × 106 tonnes of TDS and 16.2 × 106 tonnes of DOC. In this ancient flat basin, the absence of mountains chains and the extent of its coverage by dense rainforest explains that chemical weathering (10.6 t km−2 year−1 of TDS) slightly predominates physical erosion (9.3 t km−2 year−1 of TSS), followed by organic production (4.5 t km−2 year−1 of DOC). As the interannual mean discharges are similar, it can be assumed that these interannual averages of material fluxes, calculated over the longest period (2006–2017) of monthly monitoring of its sedimentology and bio-physical-chemistry, are therefore representative of the flow record available since 1902 (with the exception of the wet decade of 1960). Spatial heterogeneity within the Congo Basin has made it possible to establish an original hydrological classification of right bank tributaries, which takes into account vegetation cover and lithology to explain their hydrological regimes. Those of the Batéké plateau present a hydroclimatic paradox with hydrological regimes that are among the most stable on the planet, but also with some of the most pristine waters as a result of the intense drainage of an immense sandy-sandstone aquifer. This aquifer contributes to the regularity of the Congo River flows, as does the buffer role of the mysterious “Cuvette Centrale”. As the study of this last one sector can only be done indirectly, this paper presents its first hydrological regime calculated by inter-gauging station water balance. Without neglecting the indispensable in situ work, the contributions of remote sensing and numerical modelling should be increasingly used to try to circumvent the dramatic lack of field data that persists in this basin.

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Cosmogenic nuclide methods for measuring long-term rates of physical erosion and chemical weathering

Journal of Geochemical Exploration ◽

10.1016/j.gexplo.2005.08.060 ◽

2006 ◽

Vol 88 (1-3) ◽

pp. 296-299 ◽

Cited By ~ 13

Author(s):

James W. Kirchner ◽

Clifford S. Riebe ◽

Kenneth L. Ferrier ◽

Robert C. Finkel

Keyword(s):

Chemical Weathering ◽

Cosmogenic Nuclide ◽

Physical Erosion

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Non-residual Sr of the sediments in Daihai Lake as a good indicator of chemical weathering

Quaternary Research ◽

10.1016/j.yqres.2012.11.010 ◽

2013 ◽

Vol 79 (2) ◽

pp. 284-291 ◽

Cited By ~ 15

Author(s):

Yan Zeng ◽

Jingan Chen ◽

Jule Xiao ◽

Liang Qi

Keyword(s):

Climate Change ◽

Lake Sediments ◽

Lake Water ◽

Chemical Weathering ◽

Environmental Processes ◽

Daihai Lake ◽

Variation Patterns ◽

Potential Indicator ◽

Physical Erosion ◽

Different Sources

AbstractThe Rb/Sr ratio of lake sediments has been demonstrated to be a potential indicator of chemical weathering by increasing work. However, Rb and Sr in lake sediments are derived from both chemical weathering and physical erosion. Rb and Sr of different forms in lake sediments may record different environmental processes and information. In this study, the variation patterns of Rb and Sr of different forms in sediments of Daihai Lake were investigated. The results show that Rb and Sr of different forms display noticeably different variation patterns due to their different sources and associated environmental processes. Using the Rb/Sr ratios of bulk lake sediments to reflect chemical weathering is not accurate. The non-residual Sr of the sediments without detrital carbonates, representing the Sr leached from the catchment, can be used as an index of chemical weathering because the weathering of Sr minerals is very sensitive to climate change, and the non-residual Sr content of the sediment is determined more by Sr2 + influx than by the physicochemical conditions of lake water. The correspondence between the non-residual Sr and TIC/TOC in Daihai Lake also indicates that the non-residual Sr of the sediments is a good indicator of chemical weathering in the catchment.

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Rapid response of silicate weathering rates to climate change in the Himalaya

10.31219/osf.io/r2gwv ◽

2021 ◽

Author(s):

Anthony Dosseto ◽

Nathalie Vigier ◽

Renaud Joannes-Boyau ◽

Ian Moffat ◽

Tejpal Singh ◽

...

Keyword(s):

Climate Change ◽

Carbon Dioxide ◽

Atmospheric Carbon Dioxide ◽

Chemical Weathering ◽

Tight Coupling ◽

Weathering Rates ◽

Fluvial Terraces ◽

Physical Erosion ◽

Atmospheric Carbon ◽

Earth’S Climate

Chemical weathering of continental rocks plays a central role in regulating the carbon cycle and the Earth’s climate (Walker et al., 1981; Berner et al., 1983), accounting for nearly half the consumption of atmospheric carbon dioxide globally (Beaulieu et al., 2012). However, the role of climate variability on chemical weathering is still strongly debated. Here we focus on the Himalayan range and use the lithium isotopic composition of clays in fluvial terraces to show a tight coupling between climate change and chemical weathering over the past 40 ka. Between 25 and 10 ka ago, weathering rates decrease despite temperature increase and monsoon intensification. This suggests that at this timescale, temperature plays a secondary role compared to runoff and physical erosion, which inhibit chemical weathering by accel-erating sediment transport and act as fundamental controls in determining the feedback between chemical weathering and atmospheric carbon dioxide.

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