Small-pebble and heavy-mineral composition of glacial deposits in northeastern Kansas.

Abstract

Continental glaciation in Kansas was demonstrated beyond doubt more than a century ago. Deposition rather than erosion was the predominant effect of glaciation in Kansas. The composition of these glacial deposits was investigated and is described in this thesis. Core samples from a buried valley in northeastern Kansas were provided by the Kansas Geological Survey. Subsurface samples from thirteen localities were analyzed for small-pebble (4-8 mm) and heavy-mineral (.0625-.125 mm) content. Fourteen samples were analyzed for pebbles and fifty-one samples were analyzed for heavy minerals. Surficial samples were collected from along the buried valley and the glacial border zone. Samples from ten localities were analyzed for small-pebble and heavy-mineral content. Thirty seven samples were analyzed for pebbles and fifteen samples were analyzed for heavy minerals. The samples were separated into their respective grade sizes by wet sieving. The small pebbles were identified by using a binocular microscope, counted, and put into the following categories: quartz, quartzite, felsic crystalline, mafic crystalline, limestone, chert, sandstone + shale, and ironstone. The heavy minerals were identified by using a petrographic microscope, counted, and put into the following categories: opaque, amphibole, epidote, garnet, kyanite, pyroxene, rutile, sphene, spinel, tourmaline, and zircon. Depositional environment is, aside from weathering, the most significant factor in determining the composition of the tills, sands, and gravels. The tills were deposited directly by glacier ice, and contain a considerable percentage of limestone plus sandstone and shale and of unstable heavy minerals. The sands were deposited in proglacial lakes, thus they underwent enough transportation to remove some of the limestone plus sandstone and shale and some of the unstable heavy minerals. The gravels have been deposited by outwash streams, and most samples have lost most of the limestone plus sandstone and shale and most of the unstable heavy minerals as a result of longer stream transportation.