Author ORCID Identifier
Date Available
9-15-2023
Year of Publication
2023
Document Type
Doctoral Dissertation
Degree Name
Doctor of Philosophy (PhD)
College
Arts and Sciences
Department/School/Program
Earth and Environmental Sciences (Geology)
Advisor
Dr. Michael M. McGlue
Abstract
Large back-bulge retro-arc basins have limited information about the sediment composition, yet they comprise important parts of the stratigraphic rock record. The exorheic Pantanal Basin is the world's largest continental wetland that regulates many valuable ecosystem services (water storage, nutrient cycling, agriculture, ranching, tourism, and transportation). This dissertation is composed of three studies that utilize a suite of tools to examine the most fundamental basin-wide source-to-sink sediment processes and controls that affect the characteristics and distribution of modern sediments.
The first paper consists of a metadata analysis of 76 shallow tropical floodplain lakes in the literature with bathymetric data and age models developed from 210Pb, 14C, or optically stimulated luminescence. The assessment revealed an exponential increase in sediment accumulation rate since the 1960s, sometimes by as much as an order of magnitude compared to the historical sedimentation. Short-term sedimentation showed that the average lake infill time is 100-1,000 years, well within the time span of a few human generations. We highlighted the importance of lake bathymetry surveys because computing lake volume based on average depth tends to overestimate the true volume of the lake. Tropical lakes with steeper slopes and higher population density are at risk of more rapid infill rates, which implies accelerating sedimentation rates resulting from anthropogenic land use change.
The second paper presents a petrographic investigation of 97 modern fluvial sands across the Pantanal, coupled with a pour point analysis for each sampling station. The sands were prepared as grain mount thin sections, and 500 grains were counted for every sample following the Gazzi-Dickinson point counting method. We defined six provenance regions across the Pantanal Basin: lowlands, Amazon craton, Rio Apa craton, plateau, Southern Paraguay Belt, and Northern Paraguay Belt. The most commonly occurring grain was non-orogenic quartzose detritus (%Quartz\Feldspar\Lithic 88\5\7). Lithic grains were most concentrated in rivers draining the Paraguay Belt highlands, whereas K-feldspars were frequently observed in sands in rivers of the Rio Apa craton. Finer K-feldspar sands were found in the medial Taquari River megafan caused by channel avulsion and exhumation of more feldspar-rich floodplain deposits. The main control on sand is bedrock lithology, followed by mean annual precipitation.
The third paper is a study of the mineralogy and geochemistry of 74 distinct modern fluvial clays in the Pantanal Basin to assess the controls on clay composition. We used wavelength-dispersive X-ray fluorescence to measure major elemental abundance in silt + clay samples, and we used X-ray diffraction to obtain semi-quantitative clay proportions. The abundance of clay is as follows: kaolinite > vermiculite > illite > smectite. We identified the Taquari River weathering hinge, where kaolinite is most abundant in northern Pantanal muds and vermiculite is most abundant in southern Pantanal muds. The controls on clay compositions are as follows: hydroclimate > soils > lithology. The geochemistry of the silt + clay reveals the influence of quartz addition from parent rocks. In the context of the Plata River watershed, the kaolinite-dominant fluvial clays from the Pantanal Basin are diluted by illite-dominant clays from the sub-Andean foreland basin.
Digital Object Identifier (DOI)
https://doi.org/10.13023/etd.2023.405
Funding Information
This dissertation is based upon work supported by the National Science Foundation (NSF) Graduate Research Fellowship Program under Grant No. 1839289. This work was partially supported by a Southern Regional Education Board Doctoral Scholars Program Dissertation Award, two Ferm Fund awards from the Department of Earth and Environmental Sciences at the University of Kentucky, and a National Science Foundation/Geological Society of America Graduate Student Geoscience Grant #12743-20, which was funded by NSF Award #1949901 to E. Lo. Chapter 2 received support from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq - Process: 447402/2014-5) and a Bolsa PQ to A. Silva (Process: 314986/2020-0) and the Fundação de Apoio ao Desenvolvimento do Ensino, Ciência e Tecnologia do Estado de Mato Grosso do Sul (FUNDECT – Process: TO 063/2017). A generous grant from the University of Kentucky Student Sustainability Council facilitated the publication of Chapter 2 in an open-access journal. Chapters 3 and 4 received support from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq - Processes: 314986/2020-0 and 431253/2018-8) and a Bolsa PQ to A. Silva (Process: 314986/2020-0). The Fundação de Apoio ao Desenvolvimento do Ensino, Ciência e Tecnologia do Estado de Mato Grosso do Sul (FUNDECT - Processes: TO 267/2022 and 063/2017) financed fieldwork and research development. This study was supported by the Fundação Universidade Federal de Mato Grosso do Sul – UFMS/MEC – Brazil.
Recommended Citation
Lo, Edward L., "A Source-to-Sink Analysis of the Pantanal Basin (Brazil): Implications for Weathering, Erosion, and Landscape Evolution in the World's Largest Wetland" (2023). Theses and Dissertations--Earth and Environmental Sciences. 103.
https://uknowledge.uky.edu/ees_etds/103
XRD clays K-saturated.csv (348 kB)
XRD clays MgGly-saturated.csv (369 kB)
XRD clays K550-saturated.csv (340 kB)
Bulk calibrated XRF silt plus clay.csv (1 kB)
