Alluvial stratigraphy and geochronology along the Duck River, Central Tennessee : a history of changing floodplain sedimentary regimes
AuthorBrakenridge, George Robert.
Geology -- Tennessee -- Duck River Region.
Committee ChairSmiley, T.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractFour lithostratigraphic alluvial formations and eight chronostratigraphic "accumulation phases" occur along the middle Duck River Valley. Each accumulation consists of about 2 m of sandy and gravelly bottom stratum facies overlain by 2.5-4 m of clayey and silty top stratum facies. An additional 1-2 m of clayey and silty terrace veneers blanket all but the youngest accumulation. Based on numerous excavations into this fill, and 14 radiocarbon dates, a history of floodplain sedimentation can be traced: 1) Yellowish brown clay loam was deposited during the late Pleistocene, above a bedrock thalweg 5 in higher than the present level. Severe bedrock and floodplain erosion then occurred. 2) During the early Holocene, aggradation of dark yellowish brown clay loam occurred, over a bedrock valley floor already as deep as that at present. Scattered within this unit are early Archaic (ca. 9000 yr B.P.) chert artifacts. 3) Following a brief interval of stability, brown silty clay loam accreted, but by 7200 ¹⁴C yr B.P. the floodplain surface was again stable and soil formation dominated over deposition. Abundant mid-Archaic chert artifacts as young as 6400 ¹⁴C yr B.P. in age were left behind by their makers on this fossil floodplain surface, and pollen analytical studies document an effectively drier climate in the region during this time. 4) By 6400 ¹⁴C yr B.P., renewed overbank accretion was underway and pollen analyses indicate an increasingly humid climate. Aggradation continued up to 4200¹⁴C yr B.P., by which time the older surface, artifacts, and soil were buried by veneers of dark brown silty clay loam, itself containing late Archaic artifacts. 5) Two periods of floodplain stability and soil formation, separated by aggradation, occurred during the past 4000 years. The last period of stability ended in the early 1800's; the introduction of row crop agriculture into the basin at this time probably caused the historic episode of renewed accretion which is still underway. In response to altered hydrologic regimes, the Duck River forms new floodplains by suspended load deposition on older floodplain surfaces, on vegetated channel banks, and on the higher portions of vegetated in-channel bars. In contrast, lateral accretion of point bar sands and gravels is not an important floodplain forming process along this river.
Degree NamePh. D.