Four 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.

The Mascot-Jefferson City zinc district of East Tennessee is the major source of zinc in the United States. Sphalerite mineralization which occurs as a breccia infilling in the Lower Ordovician Knox Group carbonates has been studied in detail at the Young Mine, located in the central portion of the district. The sphalerite occurs as fracture fillings and as rosettes between carbonate breccia blocks and displays well developed growth zoning characterized by variations in color, opacity, inclusions, and composition. Ore emplacement was preceded by two periods of solution brecciation. The first episode was related to a paleokarst terrain developed atop the Knox unconf orrni ty. The second episode was probably related to tectonic activity and expulsion of fluids from a sedimentary basin to the southeast. Episodic dolomitization in the vicinity of the ore bodies both predated and accompanied sphalerite deposition. Dolomite and other minor gangue phases deposited concurrently with sphalerite. Fluorite, calcite and quartz grew as postore, vug-filling phases. Sphalerite fluid inclusions reveal wide ranges in homogenization and freezing temperatures ( 81° to 199° C; -11.2° to -37.0° C) which may represent the mixing of two fluids--a hypersaline metal-rich brine with a less saline fluid resident in the host rocks. A geochemical model shows that Mg/Ca ratios and temperatures were such that dolomite was stable during ore deposition. Inclusions in post-ore gangue phases display an overall decrease in homogenization temperatures, are less saline, and show a narrower range of salinities. / M.S.