Development of a soil chronosequence in late quaternary alluvium in Central Texas : a stable C isotope and mass balance approach /
This investigation evaluated a 15 000 yr soil chronosequence
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1996.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=739669081&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | This investigation evaluated a 15 000 yr soil chronosequence developed in loamy, carbonatic alluvium of Cowhouse Creek in Coryell County, Texas. The chronosequence was represented by four pedons that have been forming less than 600 yr, and for 2000, 5000, and 15 000 yr. objectives were to: (i) quantify rates of pedogenic carbonate accumulation using stable C isotopes; (ii) quantify mineralogical components of the clay fraction using mass balance calculations based on CEC and x- ray diffraction; (iii) determine the mass flux of total CaCO3, pedogenic carbonate, sand, silt, clay, iron oxide, and organic C using mass balance techniques; (iv) assess micromorphic transformations with petrographic thin sections; and (v) develop pathways of pedogenesis using a soil taxonomic scheme. Results showed that pedogenic carbonate gains and total CaCO3 losses were similar when calculated for the first 5000 yr of pedogenesis. However, by 15 000 yr total CaCO3 losses exceeded pedogenic carbonate gains. Consequently, pedogenic carbonate never morphologically evolves past the filamentous stage I category. Mineralogical transformations were minimal because moderately alkaline conditions persisted during pedogenesis. Mica, smectite, and mica-smectite randomly interstratified assemblages were the dominant clay minerals. Through time, free Fe oxides and clay increased, while carbonate sands and silts decreased. The only soil property reaching steady state was organic C, which occurred within 2000 yr. As a result of carbonate loss, the microfabric changed from crystic in the Holocene- aged soils to argillasepic and skelsepic in the upper part of the Pleistocene-aged soil. Results also showed ochric epipedons becoming mollic epipedons within 2000 yr, cambic horizons developing within 2000 yr, and calcic horizons forming within 5000 yr. Furthermore, Entisols transformed into Mollisols within 2000 yr, and Mollisols became Vertisols within 15 000 yr. The development of Vertisols from loamy parent materials occurred in response to the release of occluded clays from dissolution of sand- and silt-size carbonate particles. |
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| Item Description: | Vita. "Major Subject: Soil Science." |
| Physical Description: | xiii, 155 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references: pages 110-118. |