Date of Award
Doctor of Philosophy (PhD)
The present sedimentary environment of Devils Lake, a Closed brackish lake in northeastern North Dakota, was investigated, and changes in the Holocene lacustrine environment are interpreted. Sediment samples from Main Bay of Devils Lake were analyzed for their physical, chemical and mineral ogical properties. Analytical data on surface sedimer.t were used to delineate the present sedimentary environment, while data on sediment from three cores were used to reconstruct the Holocene lacustrine history.
The dominant physical processes affecting the surface sediment are wave action and intermittent sediment influx through Big Coulee. The dominant chemical process, precipitation of calcium carbonate, is a result of high super saturation of lake water during periods of active phyto-plankton photosynthesis. High-magnesian calcite and aragonite are precipitated directly from the lake water; they account for 60 percent of the carbonate material deposited in Devils Lake. Biologic productivity in Devils Lake is the main source of organic matter deposited annually to the sediment. Calculations indicate that at least 50 percent of this organic matter is regenerated to the aquatic environment by oxidation and anaerobic decay.
Factor analysis of analytical data from sediment cores showed that calcium and carbonate are intimately associated in various carbonate minerals, while only 50 percent of the magnesium originates in these minerals. The excess magnesium originates partly in clay minerals and partly in organic matter. Most of the iron originates in clay minerals. Depositional rates of major sediment components in Devils Lake have generally decreased with increasing age of the lake.
Approximately half of the recently deposited high magnesian calcite is alt9red to low-magnesian calcite in less than 200 years time. This solution alteration of hlgh magnaslan calcite results in an increase in the magnesium calcium ratio of interstitial water that reacts with calcite or aragonite to form dolomite.
The relative abundance of diatom frustules, the presence of gypsiferous spheres, the interstitial sulfate content, the sedimentary calcium-iron ratio, the high-magnesian calcite calcite ratio, and the occurrence of peat and organic silt layers interstratified with beach sands are the most significant parameters for reconstructing the Holocene sediment ary history of Devils Lake.
The lake level has fluctuated considerably during the past 6000 years in response to shifting climatic and hydro logic conditions. The lake was dry during the latter part of the Hypsithermal interval. The level rose and declined several times between 6000 and 2500 years ago. A peat was formed in Creel Bay around 1340 years ago. Several subsequent minor fluctuations in lake level culminated in a saline, low-water stage at 500 years before present when oak trees grew on the dry surface sediment of East stump Lake. The level subsequently rose until 1800 A.D., declined to a low-water stage in 1940 A. D., and has been rising inter mittently from that time to the present. Salinity data indicate that the lake was fresh approximately i50 years ago. Comparison of the Devils Lake chronology with those from other regions indicates that major climatic changes which caused significant fluctuations in the lake level may have extended beyond the northern Great Plains region.
Callender, Edward, "The postglacial sedimentology of Devils Lake, North Dakota" (1968). Theses and Dissertations. 46.