Neogene continental denudation and the beryllium conundrum

2021 ◽  
Vol 118 (42) ◽  
pp. e2026456118
Author(s):  
Shilei (李石磊) Li ◽  
Steven L. Goldstein ◽  
Maureen E. Raymo
Keyword(s):  
Fold Increase ◽  
Silicate Weathering ◽  
Late Cenozoic ◽  
Glacial Cycles ◽  
Denudation Rates ◽  
Geological Processes ◽  
Basalt Weathering ◽  
Beryllium Isotopes ◽  
Continental Weathering ◽  
Pyrite Weathering

Reconstructing Cenozoic history of continental silicate weathering is crucial for understanding Earth’s carbon cycle and greenhouse history. The question of whether continental silicate weathering increased during the late Cenozoic, setting the stage for glacial cycles, has remained controversial for decades. Whereas numerous independent proxies of weathering in ocean sediments (e.g., Li, Sr, and Os isotopes) have been interpreted to indicate that the continental silicate weathering rate increased in the late Cenozoic, beryllium isotopes in seawater have stood out as an important exception. Beryllium isotopes have been interpreted to indicate stable continental weathering and/or denudation rates over the last 12 Myr. Here we present a Be cycle model whose results show that variations in the 9Be weathering flux are counterbalanced by near-coastal scavenging while the cosmogenic 10Be flux from the upper atmosphere stays constant. As a result, predicted seawater 10Be/9Be ratios remain nearly constant even when global denudation and Be weathering rates increase by three orders of magnitude. Moreover, 10Be/9Be records allow for up to an 11-fold increase in Be weathering and denudation rates over the late Cenozoic, consistent with estimates from other proxies. The large increase in continental weathering indicated by multiple proxies further suggests that the increased CO2 consumption by continental weathering, driven by mountain-building events, was counterbalanced by other geological processes to prevent a runaway icehouse condition during the late Cenozoic. These processes could include enhanced carbonate dissolution via pyrite weathering, accelerated oxidation of fossil organic carbon, and/or reduced basalt weathering as the climate cooled.

scholarly journals Denudation systematics inferred from in situ cosmogenic <sup>10</sup>Be concentrations in fine (50–100 µm) and medium (100–250 µm) sediments of the Var River basin, southern French Alps

2019 ◽  
Vol 7 (4) ◽  
pp. 1059-1074 ◽  
Author(s):  
Apolline Mariotti ◽  
Pierre-Henri Blard ◽  
Julien Charreau ◽  
Carole Petit ◽  
Stéphane Molliex ◽  
...  
Keyword(s):  
Glacial Cycles ◽  
Size Fractions ◽  
French Alps ◽  
Fine Grained ◽  
Denudation Rates ◽  
Variable Morphology ◽  
Cosmogenic 10Be ◽  
The Impact ◽  
Quartz Grains

Abstract. Marine sedimentary archives are well dated and often span several glacial cycles; cosmogenic 10Be concentrations in their detrital quartz grains could thus offer the opportunity to reconstruct a wealth of past denudation rates. However, these archives often comprise sediments much finer (<250 µm) than typically analyzed in 10Be studies, and few studies have measured 10Be concentrations in quartz grains smaller than 100 µm or assessed the impacts of mixing, grain size, and interannual variability on the 10Be concentrations of such fine-grained sediments. Here, we analyzed the in situ cosmogenic 10Be concentrations of quartz grains in the 50–100 and 100–250 µm size fractions of sediments from the Var basin (southern French Alps) to test the reliability of denudation rates derived from 10Be analyses of fine sands. The Var basin has a short transfer zone and highly variable morphology, climate, and geology, and we test the impact of these parameters on the observed 10Be concentrations. Both analyzed size fractions returned similar 10Be concentrations in downstream locations, notably at the Var's outlet, where concentrations ranged from (4.02±0.78)×104 to (4.40±0.64)×104 atoms g−1 of quartz. By comparing expected and observed 10Be concentrations at three major river junctions, we interpret that sediment mixing is efficient throughout the Var basin. We resampled four key locations 1 year later, and despite variable climatic parameters during that period, interannual 10Be concentrations were in agreement within uncertainties, except for one upper subbasin. The 10Be-derived denudation rates of Var subbasins range from 0.10±0.01 to 0.57±0.09 mm yr−1, and spatial variations are primarily controlled by the average subbasin slope. The integrated denudation rate of the entire Var basin is 0.24±0.04 mm yr−1, in agreement with other methods. Our results demonstrate that fine-grained sediments (50–250 µm) may return accurate denudation rates and are thus potentially suitable targets for future 10Be applications, such as studies of paleo-denudation rates using offshore sediments.

scholarly journals Do degree and rate of silicate weathering depend on plant productivity?

2020 ◽  
Vol 17 (19) ◽  
pp. 4883-4917 ◽  
Author(s):  
Ralf A. Oeser ◽  
Friedhelm von Blanckenburg
Keyword(s):  
Primary Productivity ◽  
Net Primary Productivity ◽  
Nutrient Recycling ◽  
Fold Increase ◽  
Critical Zone ◽  
Mineral Nutrient ◽  
Silicate Weathering ◽  
Weathering Rates ◽  
Novel Strategy ◽  
The Impact

Abstract. Plants and their associated below-ground microbiota possess the tools for rock weathering. Yet the quantitative evaluation of the impact of these biogenic weathering drivers relative to abiogenic parameters, such as the supply of primary minerals, water, and acids, is an open question in Critical Zone research. Here we present a novel strategy to decipher the relative impact of these drivers. We quantified the degree and rate of weathering and compared these to nutrient uptake along the “EarthShape” transect in the Chilean Coastal Cordillera. These sites define a major north–south gradient in precipitation and primary productivity but overlie granitoid rock throughout. We present a dataset of the chemistry of Critical Zone compartments (bedrock, regolith, soil, and vegetation) to quantify the relative loss of soluble elements (the “degree of weathering”) and the inventory of bioavailable elements. We use 87Sr∕86Sr isotope ratios to identify the sources of mineral nutrients to plants. With rates from cosmogenic nuclides and biomass growth we determined fluxes (“weathering rates”), meaning the rate of loss of elements out of the ecosystems, averaged over weathering timescales (millennia), and quantified mineral nutrient recycling between the bulk weathering zone and the bulk vegetation cover. We found that neither the degree of weathering nor the weathering rates increase systematically with precipitation from north to south along the climate and vegetation gradient. Instead, the increase in biomass nutrient demand is accommodated by faster nutrient recycling. In the absence of an increase in weathering rate despite a five-fold increase in precipitation and net primary productivity (NPP), we hypothesize that plant growth might in fact dampen weathering rates. Because plants are thought to be key players in the global silicate weathering–carbon feedback, this hypothesis merits further evaluation.

scholarly journals Denudation systematics inferred from in situ cosmogenic <sup>10</sup>Be concentrations in fine (50–100 μm) and medium (100–250 μm) sediments of the Var River basin, southern French Alps

2019 ◽  
Author(s):  
Apolline Mariotti ◽  
Pierre-Henri Blard ◽  
Julien Charreau ◽  
Carole Petit ◽  
Stéphane Molliex ◽  
...  
Keyword(s):  
River Basin ◽  
Glacial Cycles ◽  
French Alps ◽  
Denudation Rates ◽  
Cosmogenic 10Be ◽  
Quartz Grains

Abstract. Marine sedimentary archives are well dated and often span several glacial cycles; cosmogenic 10Be concentrations in their detrital quartz grains could thus offer the opportunity to reconstruct a wealth of past denudation rates. However, these archives often comprise sediments much finer (

Denudation response of the Mediterranean Alpine Ranges to the Quaternary glacial cycles

2021 ◽  
Author(s):  
Pierre-Henri Blard ◽  
Stéphane Molliex ◽  
Apolline Mariotti ◽  
Julien Charreau ◽  
Gwenaël Jouet ◽  
...  
Keyword(s):  
High Resolution ◽  
Southern Alps ◽  
Special Focus ◽  
Glacial Cycles ◽  
Climatic Fluctuations ◽  
Denudation Rates ◽  
Original Dataset ◽  
Climatic Transition ◽  
The Mediterranean ◽  
Glacier Flow

&lt;p&gt;It is important to better understand how climatic fluctuations modified denudation, in particular during the large amplitude glacial cycles of the Quaternary, not only because denudation is thought to be a long-term climate pacer, but also because available denudation records are contradictory and sometimes underconstrained. To make progress on this question, we present here a compilation of &lt;sup&gt;10&lt;/sup&gt;Be-derived denudation rates from 6 boreholes and cores drilled in offshore sediments from two alpine massifs of the Mediterranean Sea: Southern Alps (Var River) and Corsica (Golo River). This original dataset of 60 &lt;sup&gt;10&lt;/sup&gt;Be samples from well-dated sedimentary archives documents at high resolution (1 kyr in some sections) the denudation variability over the last 3 million years of the alpine reliefs, with a special focus on the last five 100 kyr glacial cycles. Our new record brings two main results:&lt;/p&gt;&lt;p&gt;1) At the million years timescale, the appearance of the Quaternary glaciations at the Plio-Pleistocene transition (2.6 Ma) had a negligible impact on the mean &lt;sup&gt;10&lt;/sup&gt;Be-derived denudation rates of Mediterranean Alpine reliefs. This observation is in good agreement with other &lt;sup&gt;10&lt;/sup&gt;Be-denudation rates records from Asia (Tianshan and Himalaya) that report a limited impact of the Pleistocene climatic transition (Puchol et al., 2017; Charreau et al., 2020; Lenard et al., 2020), but at odds with other regions of the American Cordilleras, where tectonic may have played a role (Stock et al., 2004; Granger and Schaller, 2014).&lt;/p&gt;&lt;p&gt;2) At the glacial-interglacial cycles timescale, our high resolution &lt;sup&gt;10&lt;/sup&gt;Be data over the last 500 kys reveal that glacial maxima enhanced denudation compared to interglacial periods. However, this impact is variable in space and time, different denudation responses being observed between Southern Alps and Corsica. This contrasted behavior appears to be controlled by the velocity of paleoglaciers. Glacier flow being determined by the combined impact of paleoclimate and basin reliefs, this mechanism is responsible for a non-linear response of denudation to glacier fluctuations. This may explain why glaciations had regionally variable impacts on denudation (Mariotti et al., 2021).&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Charreau, J. et al. (2020) Basin Research. doi: 10.1111/bre.12511; Granger, D. E. and Schaller, M. (2014) Elements, doi: 10.2113/gselements.10.5.369; Lenard, S. J. P. et al. (2020) Nature Geoscience, doi: 10.1038/s41561-020-0585-2; Mariotti, A. et al. (2021) Nature Geoscience, doi: 10.1038/s41561-020-00672-2; Puchol, N. et al. (2017) Bulletin of the Geological Society of America, doi: 10.1130/B31475.1; Stock, G. M., et al. (2004) Geology, doi: 10.1130/G20197.1.&lt;/p&gt;

scholarly journals Temporal evolution of surface processes inferred from cosmogenic nuclides in a slow erosion setting, insights from the Sera do Cipo range, Brazil

2020 ◽  
Author(s):  
Vincent Godard ◽  
André Salgado ◽  
Lionel Siame ◽  
Jules Fleury ◽  
Team Aster
Keyword(s):  
High Resolution ◽  
Frequency Component ◽  
Cosmogenic Nuclides ◽  
Surface Processes ◽  
Tectonic Activity ◽  
High Frequency Component ◽  
Strong Positive Correlation ◽  
Late Cenozoic ◽  
Denudation Rates ◽  
Small Catchments

&lt;p&gt;Understanding the degree of sensitivity of the Earth Surface to past climate changes is key to assess the strength of postulated links between weathering, denudation, rock uplift and climate. Numerous studies have investigated the response of surface processes to the evolution through time of temperature and precipitation, in various settings and over different time periods. In particular, an important question still actively debated concerns whether or not Late Cenozoic climate change had an effective impact on denudation rates. It is noteworthy that this Late Cenozoic climatic evolution is often described as a long-term cooling over several Ma. However, although it has been postulated to be an important control on this response, the impact of its orbitally-controlled high-frequency component has been less investigated.&lt;/p&gt;&lt;p&gt;Studies focusing on climate-denudation links have often been carried out in regions of high tectonic activity. Therefore, they encountered associated significant limitations, such as: (1) high denudation rates that reach the analytical limits of many measurement methods; (2) stochastic events introducing a high degree of variability in the denudation signal; and, (3) high rates of tectonic uplift that can limit the sensitivity to the low-frequency component of the climatic boundary condition. Less active tectonic settings with lower denudation rates may thus provide conditions allowing to focus specifically on the coupling between climate variations and surface processes. Additionally, approaches combining different cosmogenic nuclides have proven to be very effective to unravel changes in surface processes over several time scales.&lt;/p&gt;&lt;p&gt;We present a new cosmogenic nuclides dataset from the Sera do Cipo range in Minas Gerais, Brazil. The core of the range is made of resistant quarzite bedrock with a relief of 500 m with respect to the surrounding low lands, and reported denudation rates are &lt;10 m/Ma. Streams sediments from small catchments near the summit divide, as well as clasts derived from massive quartz veins at hilltop locations, were sampled. Both &lt;sup&gt;10&lt;/sup&gt;Be and &lt;sup&gt;26&lt;/sup&gt;Al concentrations were measured in the collected samples, as in such slow denudation settings the ratio between the two nuclides is sensitive to changes in denudation rates through time. A high-resolution (1 m) Digital Elevation Models was also produced from tri-stereo Pl&amp;#233;iades satellite images. This allows to compute high resolution metrics such as hilltop curvature at the sampling sites. Hilltop denudation rates display a strong positive correlation with curvature. &lt;sup&gt;26&lt;/sup&gt;Al/&lt;sup&gt;10&lt;/sup&gt;Be values significantly departing from the theoretical steady state denudation ratio are interpreted at hilltop sites as reflecting the fluctuation of denudation through time. Concerning the catchments samples, the determined ratio can also be impacted by the sediment transport history along hillslopes. Combining cosmogenic nuclides and high-resolution topographic datasets, the measured concentrations were inverted to constrain the variation of denudation over the last 2 Ma. We observe a significant change in the denudation regime at 1 Ma, with different kind of responses between ridges and small catchments across the landscape.&lt;/p&gt;

scholarly journals Two-stage fluid pathways generated by volume expansion reactions: insights from the replacement of pyrite by chalcopyrite

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Yang Zhang ◽  
Yuanfeng Cai ◽  
Yang Qu ◽  
Qin Wang ◽  
Lixin Gu ◽  
...  
Keyword(s):  
Volume Expansion ◽  
Silicate Weathering ◽  
Retrograde Metamorphism ◽  
Pyrite Surface ◽  
Two Stage ◽  
Geological Processes ◽  
Induced Fractures ◽  
Fluid Interactions

AbstractVolume expansion reactions involved in mineral–fluid interactions are linked to a number of geological processes, including silicate weathering, retrograde metamorphism, and mineralization. However, the effect of volume expansion on replacement reactions remains unclear. Here, we demonstrate that reactions associated with volume expansion during the replacement of pyrite by chalcopyrite involve two competing processes. The reaction is initially augmented because of the development of reaction-induced fractures in the pyrite. However, these fractures are subsequently filled by compacted products, which ultimately disrupts the contact and interaction between bulk fluids and the pristine pyrite surface. These competing processes indicate that replacement reactions are both augmented and inhibited by volume expansion reactions during pyrite replacement.

scholarly journals Continental weathering using combined Hf-Nd isotope system and clay mineralogy: new insights for the Late Cretaceous climate

2021 ◽  
Author(s):  
Pauline Corentin ◽  
Emmanuelle Puceat ◽  
Pierre Pellenard ◽  
Nicolas Freslon ◽  
Michel Guiraud ◽  
...  
Keyword(s):  
Clay Mineral ◽  
Late Cretaceous ◽  
Chemical Weathering ◽  
Clay Mineralogy ◽  
Global Scale ◽  
Climatic Conditions ◽  
Silicate Weathering ◽  
Nd Isotope ◽  
Continental Weathering ◽  
The Impact

&lt;p&gt;The Late Cretaceous period records a pronounced decrease in marine temperatures at a global scale initiating the last greenhouse-icehouse transition, whose origin still remains enigmatic. Continental weathering represents a major sink of atmospheric CO&lt;sub&gt;2&lt;/sub&gt; through silicate weathering reactions yet the importance of this process in the Late Cretaceous cooling has only been scarcely explored.&lt;/p&gt;&lt;p&gt;In this study we explore the impact of the eastern South American margin uplift, concomitant to the long-term Late Cretaceous cooling, on the evolution of chemical weathering of the Brazilian margin, using a new proxy of silicate weathering based on the coupled Lu-Hf and Sm-Nd isotope systems in clays. This proxy, expressed as &amp;#916;&amp;#949;&lt;sub&gt;Hf&lt;/sub&gt;, has been recently calibrated in modern environments (Bayon et al., 2016) but has only been scarcely applied to deep-time environments. This proxy, applied on sediments from DSDP site 356 on the S&amp;#227;o Paulo Plateau, highlights a marked increase in silicate chemical weathering of the southeastern Brazilian margin from the Santonian to the Maastrichtian, also supported by the evolution of the chemical index of alteration (CIA) and clay mineralogy.&lt;/p&gt;&lt;p&gt;This increase follows an episode of enhanced mechanical erosion of the margin revealed in the Turonian to Santonian by an increase of primary clay mineral (illite, chlorite) and Ti/Al ratio, linked to the tectonic uplift of the margin. Clay mineral assemblages additionally point to an evolution of local climatic conditions from arid to a more hydrolysing climate following this episode, that we link to a &amp;#8220;rain shadow effect&amp;#8221; affecting the eastern side of the newly formed relief that would have enhanced chemical weathering of the margin.&lt;/p&gt;&lt;p&gt;Importantly the temporal coincidence of the increase in chemical weathering depicted here with the marked acceleration of the global cooling recorded worldwide during the Campanian points to a potentially important role of this process on the overall climate decline initiating the descent into our icehouse climate mode. Although records from additional sites are needed to establish the spatial extent of the margin affected by this process, our new dataset brings new insights about the impact of tectonic forcing on climate.&lt;/p&gt;&lt;p&gt;Bayon et al. (2016) EPSL 438, p. 25-36.&lt;/p&gt;

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