The Volcanic Ash Soils of Northern Chilean Patagonia (44°– 48°S): Distribution, Weathering and Influence on River Chemistry
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FACULTEIT WETENSCHAPPEN Opleiding Master of Science in de geologie The volcanic ash soils of Northern Chilean Patagonia (44°– 48°S): Distribution, weathering and influence on river chemistry Elke Vandekerkhove Academiejaar 2013–2014 Scriptie voorgelegd tot het behalen van de graad Van Master of Science in de geologie Promotor: Dr. Sebastien Bertrand Leescommissie: Prof. Dr. Eric Van Ranst, Dr. Maarten Van Daele Cover picture: View on Cerro Castillo near Puerto Ibáñez (Photo: J.-Y. De Vleeschouwer). Acknowledgements Before reading the thesis, I would like to thank some people who helped me during this study. Above all, my greatest thanks go out to my promotor, Dr. Sebastien Bertrand, for his great support and supervision on my thesis. I would like to thank him for giving me the opportunity to do this highly interesting research and for all the sharing of thoughts, his good advice and suggestions regarding the subject. Moreover, many times he helped with explaining everything and assisted me during my investigation. Based on the data obtained by Dr. Sebastien Bertrand, Zakaria Ghazoui and Astrid Bartels, I was able to perform this study so therefore I would like to express gratitude for them for the expeditions to Chile to collect all samples. I would also like to thank the Renard Centre of Marine Geology for the usage of the equipment at their laboratory. With regards to the support in the laboratory during the measurements, my thanks go out to Daniëlle Schram who was always present to answer my questions in the sedimentology lab. For the assistance during the XRD analysis and the possibility for the usage of the equipment, I would like to thank Ir. Joël Otten and Dr. Nathalie Fagel from Liège University in Belgium. Furthermore I would like to thank the staff from the UC Davis Isotope Facility and the NOSAMS Facility for performing the analyses on bulk organic geochemistry and the radiocarbon dating analyses on the samples, respectively. Finally, I really would like to thank my parents, Filiep Vandekerkhove and Anneke Demuynck, and my friend Arne very much for their endless support and constant encouragement during my student years. Since they were my greatest supporters I would like to dedicate this thesis to them. Thank you and enjoy reading! List of figures Figure 2.1: Elevation map indicating the location of the study area. Figure 2.2: Annual precipitation and temperature maps of South America. Figure 2.3: Vegetation changes within the study area. Figure 2.4: Tectonic map of the southeast Pacific and southern Chile. Figure 2.5: Geological map of Northern Chilean Patagonia with the statigraphical succession. Figure 2.6: Schematic cross-section of the study area during the late Triassic. Figure 2.7: Map of South America indicating the active volcanic zones. Figure 2.8: Overview on several studies for glacier advance after the LGM. Figure 2.9: Soil map of Patagonia. Figure 3.1: Map indicating the location of the andosol profiles. Figure 3.2: Rectified isopach map (6700 BP Hudson eruption event) on top of SRTM images. Figure 3.3: Precipitation map with the location of the three selected profiles. Figure 3.4: Pictures of the three selected profiles AP13-11, AP12-02 and AP12-04. Figure 3.5: Schematic overview of the selected profiles with the indication of the analyzed subsamples. Figure 3.6: Representation of the elemental and isotopic composition of organic matter. Figure 3.7: Polynomial relationship between TOC and LOI550 on soil sample measurements. Figure 3.8: Schematic diagram of the EA-IRMS. Figure 3.9: Ring holders for XRD-analyses and the diffractometer instrument. Figure 3.10: Accelerated mass spectrometer at NOSAMS. Figure 4.1: Volcanic ash soil thickness map. Figure 4.2: Validation of the volcanic ash soil thickness map. Figure 4.3: Results of the LOI550 measurements and bulk organic geochemistry conducted on the subsamples. Figure 4.4: δ13C versus C/N atomic ratio of the soil samples from the three profiles. Figure 4.5: Calibration plots for samples AP13-11-0, AP12-02-0 and AP12-04-10. Figure 4.6: Results of the XRD analysis on AP13-11, AP12-02 and AP12-04. Figure 5.1: Relationship between TOC and LOI550 results of profiles AP13-11, AP12-02 and AP12-04 and comparison with the measurements of Bartels (2012) and Paesbrugge (2013). Figure 5.2: Linear correlation between annual precipitation and kg of organic carbon per m². Figure 5.3: Plotted δ13C vs C/N atomic ratios of the soil samples from the three profiles and fresh vegetation samples. Figure 5.4: Comparison between the C/N atomic ratios, TOC (%) and TN (%) of the three profiles. Figure 5.5: Volcanic soil thickness map with indication of the sediment core locations in the fjords. Figure 5.6: Plotted δ13C and C/N atomic ratios of the samples from the three profiles and river samples. Figure 5.7: Locations for the water samples and correlation between the average DSi concentrations of the river water samples and average volcanic ash soil thickness for the different watersheds in the study area. Figure 5.8: Comparison of the geological map of the study area, the concentration of dissolved silicic acid (DSi) and the volcanic ash soil thickness map. Figure 5.9: Vegetation map of the study area. List of tables Table 3.1: Several minerals with the corresponding peaks and correction factor for X-Ray diffractograms. Table 4.1: Calculated volcanic ash volumes in the different watersheds. Table 4.2: Calibrated radiocarbon ages. Table 5.1: Average δ13C values and C/N atomic ratios for the soil samples, surface soil samples and fresh vegetation samples. Table 5.2: Overview of TOC and TN values for the three profiles. Table 5.3: Overview of the sediment accumulation rates from fjords based on age models obtained from radiocarbon ages and from the excess 210Pb distribution. Table 5.4: Summary δ13C values and C/N atomic ratios for different samples. Table 5.5: Overview of the average dissolved Si concentrations for the river water samples and the average soil thickness in the watersheds. Nomenclature NPI: Northern Patagonian Icefield SPI: South Patagonian Icefield PIS: Patagonian Ice Sheet CTJ: Chile Triple Junction EAMC: Eastern Andes Metamorphic Complex CMC: Chonos Metamorphic Complex SRTM: Shuttle Radar Topography Mission NPB: North Patagonian Batholith NVZ: Northern Volcanic Zone CVZ: Central Volcanic Zone SVZ: Southern Volcanic Zone AVZ: Austral Volcanic Zone SSVZ: Southern Southern Volcanic Zone LOFS: Liquiñe-Ofqui Fault System LGM: Last Glacial Maximum YD: Younger Dryas ACR: Antarctic Cold Reversal AP: Andosol Profile LOI: Loss On Ignition TOC: Total Organic Carbon TN: Total Nitrogen EA-IRMS: Elemental analyser-isotope ratio mass spectrometer V-PDB: Vienne PeeDee Belemnite XRD: X-Ray Diffraction NOSAMS: National Ocean Sciences AMS AMS: Accelerated Mass Spectrometer DSi: Dissolved silica Table of contents 1. Motivation and research questions ................................................................................1 2. General setting ...............................................................................................................3 2.1 Location ..............................................................................................................................3 2.2 Present-day climate and vegetation ...................................................................................4 2.3 Tectonic and geological setting ...........................................................................................5 2.4 Volcanic setting ...................................................................................................................8 2.4.1 Melimoyu................................................................................................................... 10 2.4.2 Mentolat .................................................................................................................... 10 2.4.3 Cay ............................................................................................................................ 10 2.4.4 Maca ......................................................................................................................... 11 2.4.5 Hudson ...................................................................................................................... 11 2.5 Quaternary evolution and paleoclimate ........................................................................... 12 2.6 Soils .................................................................................................................................. 13 3. Materials and methods .................................................................................................15 3.1 Field measurements and sampling.................................................................................... 15 3.2 Isopach mapping ............................................................................................................... 16 3.3 Analytical techniques ........................................................................................................ 17 3.3.1 Sample preparation ................................................................................................... 19 3.3.2 Loss on ignition .......................................................................................................... 19 3.3.3 Bulk organic geochemistry ......................................................................................... 20 3.3.4 Bulk mineralogy ........................................................................................................