Literatura académica sobre el tema "Carbonate weathering"

This study is the geochemical examination of mineral weathering and its path from hinterland, through sediment deposition and pedogenesis, to its dissolution and eventual uptake into plants or precipitation as carbonate minerals. The three papers examine the rate and character of carbonate and silicate mineral weathering over a wide range of climatic and tectonic regimes, time periods, and lithologies, and focus on very different questions. Examination of the 87Sr/86Sr ratios of architectural ponderosa pine in Chaco Canyon, New Mexico confirms a societally complex style of timber procurement from the 10th to the 12th centuries. In El Malpais National Monument, New Mexico, we measured the 87Sr/86Sr ratios in local bedrock and soils and compared them to the leaf/wood cellulose of four conifers (Pinus ponderosa, Pinus edulis, Juniperus monosperma, Juniperus scopulorum), a deciduous tree (Populus tremuloides), three shrubs (Chrysothamus nauseosus, Fallugia paradoxa, Rhus trilobata), and an annual grass (Bouteloua gracilis) and a lichen (Xanthoparmelia lineola). We found that plant 87Sr/86Sr ratios covaried with variations in plant physiognomy, life history, and rooting depth. In addition, the proportion of atmospheric dust and bedrock mineral contributions to soil water 87Sr/86Sr ratios varied predictably with landscape age and bedrock lithology. On the Himalayan floodplain, soils and paleosol silicate weathering intensities were measured along a climatic transect and through time. Overall, carbonate weathering dominates floodplain weathering. But, periods of more intense silicate weathering between 9 - 2 Ma, identified in soil profile and in the 87Sr/86Sr ratios of pedogenic carbonates, appear to be driven by changes in tectonic, rather than climatic, regime. All three papers are good examples of how 87Sr/86Sr isotopic tracer studies can shed light on pedogenic formation rates and internal processes. The complexity of each system warns against generalizations based on just one locale, one species or lithology, or a few isotopic ratios.

L'altération des lithologies himalayennes a potentiellement impacté le cycle global du carbone. Pour pouvoir contraindre et comprendre les processus qui se sont produits dans l'Himalaya et qui ont affecté ces cycles, nous devons être distinguer les signatures de l'altération du silicate et du carbonate dans la charge dissoute des fleuves de l'Himalaya. Des études antérieures ont tenté de le faire en utilisant diverses méthodes mais il n’existe toujours pas de consensus clair sur l’ampleur et le flux de l’altération du silicate dans l’Himalaya. Cette thèse propose l'utilisation du 40Ca comme traceur pouvant améliorer la quantification du flux d'altération du silicate et du carbonate dans la charge dissoute des rivières himalayennes. Des travaux antérieurs ont montré que le budget de l'eau de mer 40Ca est dominé par une source de manteau, de sorte que les carbonates marins ont une signature homogène de 40Ca indiscernable par rapport à la valeur du manteau. En revanche, la croûte supérieure de silicate devrait avoir développé une composition radiogénique. La différence entre la signature en Ca radiogénique des lithologies de carbonate et de silicate peut donc être utilisée pour différencier l’altération du carbonate et du silicate dans la charge dissoute des rivières. Nous présentons ici une étude géochimique comprenant des analyses de Ca radiogénique des rivières drainant les principales unités lithologiques de l'Himalaya, ainsi que des résultats provenant de sédiments, de substrat rocheux, de sol et de gravier. Nos résultats montrent que les carbonates de l’Himalaya ne présentent pas d’excès de 40Ca radiogénique malgré des signatures très variables 87Sr/86Sr, alors que les sédiments sont radiogènes (+0.9 à +4). Ceci suggère que pour Ca, contrairement à Sr, l'échange isotopique entre les lithologies silicate et carbonate a été minime. La composition en Ca radiogène de l'eau des rivières va de +0.1 dans les captages à prédominance carbonatée à +11 dans les rivières drainant des bassins versants silicatés. Pour les grandes rivières, les estimations du budget relatives à l’altération du silicate et du carbonate sur la base des éléments principaux et la composition en Ca radiogénique tendent à concorder. Cependant, pour certaines rivières plus petites, en particulier celles drainant des bassins à dominance silicatée dans les formations cristallines de HHC et du LH, certaines divergences sont observées. Celles-ci ne peuvent pas être attribuées à une définition imprécise de la composition chimique ou radiogénique en Ca des pôles de mélange utilisés pour la modélisation budgétaire, car les valeurs requises pour résoudre le modèle ne sont pas raisonnables. Ils ne peuvent pas non plus être expliqués par la précipitation de carbonates secondaires dans les rivières car la composition non radiogénique de carbonates suggère que ce processus n'est que mineur. Au contraire, ces différences peuvent être dues à la dissolution des traces de calcite radiogénique contenues dans les lithologies de silicate HHC et LH. Le vieillissement de ce matériau, qui ne représente qu'une infime partie de la surface du captage du silicate, pourrait produire une proportion substantielle du Ca radiogénique et pourrait ainsi avoir une influence significative sur le calcul des budgets de ces bassins à partir des données isotopiques. Néanmoins, comme cet effet est observé principalement dans les bassins à faible taux d’érosion des silicates, son influence sur les estimations du flux global de vieillissement du silicate sera mineure. Plus généralement, les résultats de cette thèse impliquent que le système 40Ca permet une résolution de problématiques qui ne peuvent pas être approfondies avec succès à l'aide d'isotopes Sr dans l'Himalaya. Des travaux supplémentaires sont nécessaires pour définir la gamme complète des compositions de Ca radiogénique dans l’Himalaya afin de répondre clairement aux questions concernant les flux d’altération des silicates<br>Weathering of Himalayan lithologies has had a potential impact on the global carbon cycle. To be able to constrain and understand the processes that occurred in the Himalayas that affected these cycles, we must be able to distinguish the signatures of silicate and carbonate weathering in the dissolved load of Himalayan rivers. Previous studies have attempted to do this using a variety of methods but there is still not a clear consensus on the magnitude and flux of silicate weathering in the Himalaya. This thesis proposes the use of 40Ca as a tracer that could improve the quantification of the silicate and carbonate weathering flux in the dissolved load of Himalayan rivers. Previous work has shown that the 40Ca budget of seawater is dominated by a mantle source, such that marine carbonates have a homogeneous 40Ca signature indistinguishable from the mantle value. In contrast, the upper silicate crust is expected to have developed a radiogenic composition. The difference between the radiogenic Ca signature of carbonate and silicate lithologies can be therefore used to differentiate between carbonate and silicate weathering in the dissolved load of rivers. Here, we present a geochemical survey, including radiogenic Ca analyses, of rivers draining the main lithological units of the Himalaya, as well as results from sediments, bedrock, soil and gravel. Our results show that Himalayan carbonates exhibit no radiogenic 40Ca excesses despite highly variable 87Sr/86Sr signatures, whereas sediments are variably radiogenic (+0.9 to +4). This suggests that for Ca, unlike for Sr, isotopic exchange between the silicate and carbonate lithologies has been minimal. The radiogenic Ca composition of river water ranges from +0.1 in carbonate dominated catchments to +11 in rivers draining silicate catchments. For large rivers, silicate and carbonate weathering budget estimates based on major elements and radiogenic Ca compositions tend to agree. However, for some smaller rivers, especially those draining silicate dominated basins in the HHC and LH formations, some discrepancies are observed. These cannot be attributed to poor definition of the chemical or radiogenic Ca composition of the endmembers used for budget modeling, as the values required to bring the estimates into agreement are unreasonable. They also cannot be explained by precipitation of secondary carbonates in the rivers as the non-radiogenic composition of the carbonate fraction of sediments suggests that this process is only minor. Rather, these discrepancies may be due to the dissolution/weathering of trace amounts of radiogenic calcite contained within HHC and LH silicate lithologies. The weathering of such material, which represents only a tiny fraction of the area of the silicate catchment, could yield a substantial proportion of the radiogenic Ca and may thus have a significant influence on the isotopically based weathering budgets of these basins. Nevertheless, as this effect is observed primarily in basins with low silicate erosion rates, its influence on estimates of the overall silicate weathering flux will be minor. More generally, the results of this thesis imply that the 40K–40Ca system can resolve issues that cannot be successfully addressed using Sr isotopes in the Himalaya. Further work is needed to define the full range of radiogenic Ca compositions in the Himalaya in order to clearly answer questions regarding silicate weathering fluxes

With rising atmospheric CO2 concentrations, a detailed understanding of processes that impact atmospheric CO2 fluxes is required. While a sink of atmospheric carbon from the continents to the ocean from carbonate mineral weathering is, to some degree, offset by carbonate mineral precipitation in the oceans, efforts are underway to make direct measurements of these fluxes. Measurement of the continental sink has two parts: 1) measurement of the dissolved inorganic carbon (DIC) flux leaving a river basin, and 2) partitioning the inorganic carbon flux between the amount removed from the atmosphere and the portion from the bedrock. This study attempted to improve methods to measure the DIC flux using existing data to estimate the DIC flux from carbonate weathering within the limestone karst region of south central Kentucky. The DIC flux from the Barren River drainage basin upstream from Bowling Green in southern Kentucky and northern Tennessee, and the upper Green River drainage basin, upstream from Greensburg, Kentucky, was measured, each for a year, using U.S.G.S. discharge data and water-chemistry data from municipal water plants. A value of the (DIC) flux, normalized by time and area of carbonate rock, of 4.29 g km-3 day-1 was obtained for the Barren River, and 4.95 kg km-3 for the Green. These compared favorably with data obtained by Osterhoudt (2014) from two nested basins in the upper Green River with values of 5.66 kg km-3 day-1 and 5.82 kg km-3 day-1 upstream from Greensburg and Munfordville, respectively. Additional normalization of the values obtained in this study by average precipitation minus evapotranspiration over the area of carbonate rock, or water available for carbonate dissolution, resulted in values of 5.61x107 g C (km3 H20)- 1 day-1 (grams of carbon per cubic kilometer of water, per day) for the Barren, and 7.43x107g C (km3 H20)-1 day-1 for the Green River. Furthermore, a statistical relationship between the total DIC flux and time-volume of water available for dissolution has been observed, yielding an r2 value of 0.9478. This relationship indicates that the primary variables affecting DIC flux for these drainage basins are time and the volume of water available for dissolution.

Although karst processes in south central Kentucky have been studied extensively, the Haney Limestone Member of the Golconda Formation has not been studied in detail in contrast to limestones stratigraphically below it that are thicker. In addition, the relationship between petrographic features of the Haney Limestone and the formation of caves and karst features has not been studied extensively compared to lithographic, petrographic, or structural variables Petrographic data were collected using core and surface exposures across the study area of south central Kentucky from northern Logan and Warren counties up toward the Rough Creek Graben region, and stratigraphic columns were constructed. Twenty-three petrographic thin-sections were made from samples collected at these sites, described, and photo documented. These studies have revealed that grain size and silica content play a role in how the Haney weathers both in surface exposure and in a cave setting. Petrographic thin-section analysis suggests that the Haney possesses a complex diagenetic history that involves several generations of calcite cementation, dolomitization, silicification, and pressure-dissolution features in the form of microstylolites and stylolites. A basal shale in the Big Clifty occurs commonly at the Big Clifty/Haney contact and acts as a confining hydrogeologic unit, which is favorable for the development of springs and caves. Studying the Haney Limestone petrographically provides an opportunity not only to study a lesser known unit, but also in the context of relating petrographic influences or controls on the morphology of Haney cave-passage development under both vadose and phreatic hydrologic regimens. Heretofore, the vast majority of cave morphological studies have only linked the hydrologic regimen to formation of cave passages, but such studies have not considered petrographic variance. This study not only relates karst features to petrographic variance, but also provides a petrographical description of the Haney across south central Kentucky, whereas many previous studies focused on Illinois and Indiana. Understanding Haney petrographic characteristics also provides context for potential carbonate hydrocarbon reservoirs and groundwater resources in the Illinois Basin region.

Kentucky’s Upper Green River Basin has received significant attention due to the area’s high biodiversity and spectacular karst development. While carbonate bedrock is present throughout the watershed, it is more extensive and homogenous along the river between Greensburg and Munfordville than upstream from Greensburg where the geology is more heterogeneous. This research quantitatively evaluated how lithological differences between the two catchment areas impact hydrochemistry and inorganic carbon cycling. This first required correcting catchment boundaries on previous US Geological Survey Hydrologic Unit Maps to account for areas where the boundaries cross sinkhole plains. Basin boundaries using existing Kentucky Division of Water dye trace data differed from the earlier versions by as much as three kilometers. The river at the downstream site is more strongly influenced by carbonate mineral dissolution, reflected in higher specific conductance (SpC) and pH. The SpC at Munfordville ranges from 0.9 to 4.8 times that at Greensburg, averaging 2.0 times higher. Although rainfall is impacted by sulfuric acid from coal burning, river pH is buffered at both sites. The pH is higher at Munfordville 91% of the time, by an average of 0.28 units. Diurnal, photosynthetic pH variations are damped out downstream suggesting interactions between geologic and biological influences on river chemistry. River temperature differences between the two sites are at least 4oC higher at Greensburg under warm season conditions, but there is a clear trend of temperature differences diminishing as the river cools through the fall and winter. This results from a relatively stable temperature at Munfordville, impacted by large spring inputs of groundwater within the karst region downstream. Although weak statistical relationships between SpC and HCO3 - create uncertainties in high resolution carbon flux calculations, measurement of these fluxes is more highly impacted by discharge variations than concentration variations, which resulted in average daily atmospheric flux estimates within 34% between the two basins using weekly concentration data (3.3x108 vs. 2.2x108 gkm-2 d-1, where km2 is the outcrop area of carbonate rocks), and within only 12% using 15-minute concentration data from regressions (2.6x108 vs. 2.3x108 gkm-2 d-1) for Greensburg and Munfordville, respectively.

The Savannah River Site (SRS) deposits in the Southeastern US between 30-45 m of depth are calcium carbonate-rich, marine-skeletal, Eocene-aged sediments with varying clastic content and extensive diagenetic alteration, including meter-sized caves that coexist with brittle and hard limestone. An experimental investigation including geotechnical (P- and S-wave velocities, tensile strength, porosity) and geochemical (EDS, XRD, SEM, N2-adsorption, stable isotopes, K-Ar age dating, ICP-assisted solubility, groundwater) studies highlighted the contrast between hard and brittle limestones, their relationship with cave formation, and allowed calculation of parameters for geochemical modeling. Results demonstrate that brittle and hard limestones bear distinct geochemical signatures whereby the latter exhibits higher crystallinity, lower clastic load, and freshwater-influenced composition. Results also reveal carbonate diagenesis pathways likely driven by geologic-time seawater/freshwater cycles, microorganism-driven micritization, and freshwater micrite lithification. The second section of this investigation dealt with SRS surface soils which are largely coarse-grained and rich in iron oxides with various degrees of maturity. These soils were simulated in the laboratory using Ottawa sands that were chemically coated with goethite and hematite. Surface (SEM, AFM, N2-adsorption) and geotechnical properties (fabric, small-strain stiffness, shear strength) were investigated on the resulting "soil analog". Results indicate that iron-oxide coated sands bear distinct inherent fabric and enhanced small-strain stiffness and critical state parameters when compared to uncoated sands. Contact mechanics analyses suggest that iron oxide coatings yield an increased number of grain-to-grain contacts, higher surface roughness, and interlocking, which are believed to be responsible for the observed properties.

Over millions of years, atmospheric CO2 concentrations, and Earth’s climate, are regulated by continental silicate weathering and associated marine carbonate deposition. On this geological timescale, carbonate weathering has no net effect on CO2 drawdown. However, over the coming decades-to-centuries, accelerated weathering of carbonate rocks may provide a sink for anthropogenic CO2 emissions and increase alkalinity flux to the oceans to counteract ocean acidification. Recent experimental evidence strongly supports trees and their associated mycorrhizal fungi as key drivers of silicate mineral weathering; however, their role in the context of carbonate weathering is largely unknown. Carbonate lithology is abundant globally and underlies many boreal and temperate forest ecosystems in the northern hemisphere. If biological enhancement of carbonate weathering by forests occurs, this might presents a new opportunity for CO2 sequestration. This thesis presents results from a 14-month field experiment at the UK's national pinetum investigating carbonate rock weathering under a common climate. Overall, I find original evidence for biotic enhancement of calcite- and dolomite weathering by an evolutionary diverse range of trees that host either arbuscular (AM) or ectomycorrhizal (EM) root-associating fungal symbionts. Recent soil analyses are integrated with a re-interpretation of historic data to provide an 85-year record of in-situ soil development under different forestry species. This study challenges the classic dogma that divergence of properties is driven by the major tree functional groups, angiosperms and gymnosperms. Instead, we find that over decades, mycorrhizal functional type plays a dominant role in determining soil physico- chemical characteristics, and conditions generated by EM fungi are likely to enhance mineral weathering. Field trials next investigated the impact of tree-mycorrhizal functional group on weathering of the four main carbonate rock types (chalk, limestone, marble and dolomite) and a quartz silicate. Under EM trees carbonate rock grain dissolution was 12 times faster that silicate weathering. In the initial 3 months, calcite weathering intensity increased from gymnosperm to angiosperm species and from AM to later, but independently-evolved EM fungal partnerships. More extensive weathering after 6 months, especially within EM forest soils, confirms the importance of these fungi for carbonate mineral dissolution and nutrient mobilisation. This effect is linked to rhizosphere acidification by EM fungi and is confirmed by a parallel study of tree species’ influence on soil chemistry. Both AM and EM fungi facilitate the mobilisation of nutrient elements, which are provided to their host plants in exchange for carbon from photosynthesis. I applied a suite of nanoscale surface analysis techniques (VSI, SEM) to quantify mineral alteration and provide direct evidence for mycorrhizal involvement in carbonate weathering in the field. Fungal hyphae preferentially colonised chalk and quartz silicate grains, which contained the highest concentrations of phosphorus (P), a growth limiting elemental nutrient. P was selectively depleted from silicate grains, especially in EM forest soils, but accumulated on carbonates. Although the origin of this accumulated P remains uncertain, extensive analyses of different potential P-pools indicated it is likely to be inorganic, but accumulated via active microbial import. These findings lead to new insights linking carbonate weathering with phosphorus biogeochemical cycling in soils. Results show that P from the surrounding environment is concentrated on carbonate grains and this potentially provides a renewable P resource accessible to host trees. Overall, this thesis builds new support for the role of mycorrhizal partnerships in shaping soil properties important for accelerating carbonate rock weathering (Chapter 2); presenting the first field-based evidence for the enhancement of carbonate dissolution by tree roots and their associated mycorrhizal partners (Chapters 3-5) and generating new insights into biogeochemical P cycling in soils (Chapter 4). More broadly, these findings suggest targeted reforestation/afforestation with EM-tree taxa on carbonate-rich terrain as a possible regional-scale land management strategy for promoting short-term anthropogenic CO2 sequestration and perhaps helping ameliorate ocean acidification.

Rising atmospheric CO2 concentrations have motivated efforts to better quantify reservoirs and fluxes of Earth’s carbon. Of these fluxes from the atmosphere, one that has received relatively little attention is the atmospheric carbon sink associated with carbonate mineral dissolution. Osterhoudt (2014) and Salley (2016) explored new normalization techniques to improve and standardize a process for measuring this flux over large river basins. The present research extends this work to the 490,600 km2 Ohio River drainage basin and 11 subbasins. The study estimated the DIC flux leaving these basins between October 1, 2013, and September 30, 2014, based on secondary hydrogeochemical, geologic, and climatic data. The total annual DIC flux for the Ohio River basin was estimated to be 7.54 x 1012 g carbon (C). The time-volume normalized value of DIC flux for the Ohio basin was 3.36 x 108 g C/km3 day, where the km3 refers to the amount of water available during the year. This was within 71.4% agreement with the Barren River data (Salley, 2016) and within 63.9% agreement with the Green River data (Osterhoudt, 2014). In general, normalized DIC flux values of sub-basins containing at least modest amounts (more than 8%) of exposed carbonates (Tennessee, Cumberland, Green, Kentucky, Licking, Monongahela, and Allegheny) were in strong agreement with the normalized DIC flux of the Ohio River basin, whereas inclusion of basins with little or no near surface carbonates (Wabash, Great Miami, Scioto and Kanawha) yielded poor agreement. Regression analysis yielded strong agreement between DIC flux and the normalization parameters for the carbonate-bearing sub-basins (R2 = 0.97, p =