Silty Texture Research Articles

Paleontologic and Sedimentologic Character of Corell's Point Faunal Assemblage (Upper Devonian: Famennian), Southwestern New York State: ABSTRACT

The Corell's Point faunal assemblage of the lower Gowanda Shale Member, Canadaway Formation, represents a series of burrowed zones yielding biocoenoses of benthos, taphocoenoses of nektos, and wood fragments. Marine-transported animals and plants are generally pyritized, but many endemic organisms are not. The faunal assemblage occurs at various levels in the Gowanda Shale, and may recur in adjacent stratigraphic units. The Corell's Point faunal assemblage and associated pyrite nodules apparently formed in a starved shelf setting, influenced by sporadic influxes of sediment, possibly by distal turbidites. Cephalopods were added to the Corell's Point assemblage by postmortem pelagic drift; their attendant epizoans probably detached and gave rise to small, locally abundant auloporid mounds. Some organisms may have been rafted in attached to algal mats; these mats possibly carried ammonoids, nautiloids, wood fragments, pelmatozoans, bivalves, gastropods, and fishes, producing infrequent dense associations of these organisms. Mild bioturbation of surface muds was effected by Zoophycos and infaunal mollusks. Winnowing of fine muds by organisms may account for the consistent silty texture of sediment associated with the Corell's Point faunal assemblages; underlying and overlying strata are generally fine-grained with discrete siltstone beds. Zoophycos and other lebensspuren, plants, and some cephalopods are encountered in sections of the Gowanda Shale lacking the Corell's Point faunal assemblage. These shales and siltstones exhibit relatively little evidence of fauna-induced sediment mixing. End_of_Article - Last_Page 1164------------

The available-water capacities of North Auckland soils

Abstract Available-water capacities of the principal groups of soils of high clay content in North Auckland have been determined. Within each main soil group they are markedly uniform. Among the soils on sedimentary parent rocks podzolisation is accompanied by larger available-water capacities in the A horizons and smaller ones in some B horizons than are found for unpodzolised soils. Of the soils on volcanic parent rocks, the brown loams on basalt have small available-water capacities, and the brown granular soils, on andesitic rocks, large ones. The large available-water capacities of the A horizons of podzols are related to silty textures, but other differences in available-water capacity among soil groups are best explained by other physical properties. These include high dry bulk densities in the B horizons of some podzolised soils, low dry bulk densities in the B horizons of brown granular soils, and considerable volumes of large, easily drained pores in many brown loams.

Vegetation as a Soil-Forming Factor on the Quillayute Physiographic Unit in Western Clallam County, Washington

Several treeless areas (i.e., prairies) in an otherwise heavily forested locale are known in Clallam County, on the Olympic Peninsula in northwestern Washington (Wheeting 1936, Fowler and Wheeting 1941). These persistent elements of the landscape, in a region where the climate is extremely favorable for the growth of the surrounding forest, provide an opportunity to compare influences of prairie and forest vegetation upon the development of soil properties. The site of this study was the Quillayute Prairie and the immediately adjacent forested area in western Clallam County. Locally the soils of both prairie and forest have developed from the same deep sediments of silty texture. These soils lie within a terrain that exhibits a topographic unity suggestive of a single physiographic unit. Evident dissimilarities of soil morphology within this physiographic unit appear to be attributable largely to the influence of vegetation as a soil-forming factor. This work was done to provide some clarification of soil genesis as it is affected by vegetation, and to provide data for categorizing a local soil. The writers wish to acknowledge advice and assistance given by C. D. Campbell, H. S. Conard, R. Daubenmire, R. A. Gilkeson, R. A. McCreery, D. McKey-Fender, J. Rumely, W. F. Scott, L. H. Smith, W. A. Starr and R. Turner during the course of this work.

Petrography of Some Minnesota Tills

ABSTRACT Wisconsin tills in Minnesota may be assigned to different ice lobes depending primarily upon the color, texture, stone content, and other petrographic characteristics. These petrographic features have their origin chiefly in distinctive types of bedrock in Minnesota and adjacent areas. The Precambrian rocks that underlie the drift over most of the state include red sandstone and slate in a belt extending south-southwest from the head of Lake Superior; basalt, felsite, gabbro, anorthosite, and related rocks in the highland north of Lake Superior; iron formation; and various metamorphic and granitic rocks. Paleozoic carbonate rocks are found principally in southern Manitoba but also in southeastern Minnesota. Cretaceous shale occurs in the area of the Red River Valley and in southwester Minnesota. The configuration of the several ice lobes was determined partly by the presence of lowlands in the bedrock, notably one following the Red River-Minnesota River valleys (Des Moines lobe) and one following a lowland extension of the Lake Superior basin (Superior lobe). The central part of the state was occupied by the Wadena lobe and the Rainy lobe, and their directions of movement were probably controlled by mutual interference as well as by pre-existing topography. The Wisconsin glacial history in Minnesota was marked also by repeated advances of the several ice lobes. In the case of the Superior lobe the tills assigned to the Cary and Valders advances may be identified texturally because the Valders till was formed by the incorporation of lake clays deposited in the Lake Superior basin during the Two Creeks interstadial just preceding, whereas the Cary Superior till is sandy. A Mankato Superior till, identified on morphologic grounds, appears to have an intermediate (silty) texture. Of the two tills of western source, the Wadena is the more sandy, probably because the Des Moines till passed over Cretaceous shale. The tills of the Rainy lobe and its two sublobes (Pierz and Brainerd) are all sandy and are stonier than the tills of the other lobes. Stone counts are perhaps the most diagnostic petrographic characteristic of Minnesota tills. They are easily made and generally point to the correct assignment. Difficulties occur where tills contaminate one another in contact zones. Color distinctions, as measured by the Munsell color chart or in the laboratory by the Clark-Maxwell method, are also generally distinct. Heavy-mineral analyses and clay-mineral analyses are of limited use in differentiating tills. They are time-consuming and not particularly diagnostic.