The Geology of the Palen Mountains Gypsum Deposit, Riverside County, California. Oscillations in the Foraminifera of the Vicksburg Group from a Well in George County, Mississippi

Citation

Hoppin, Richard Arthur (1951) The Geology of the Palen Mountains Gypsum Deposit, Riverside County, California. Oscillations in the Foraminifera of the Vicksburg Group from a Well in George County, Mississippi. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/39JR-ZS98. https://resolver.caltech.edu/CaltechTHESIS:06152018-143736204

Abstract

[Thesis 1]. The Geology of the Palen Mountains Gypsum Deposit, Riverside County, California:

A large deposit of gypsum 5 square miles in area is located at the north end of the Palen Mountains. Interbedded gypsum, marble, quartzite, feldspathic quartzite, and lime silicate rocks, together with metamorphosed intrusives, are arranged in bands trending east-west. The rocks are intensely deformed and metamorphosed. Intense folding, faulting, brecciation, and shearing occurred as a result of strong deformation. These structures vary in magnitude from the large mappable units down to those microscopic in size. Along with the extreme deformation, the area has been subjected to regional, contact, and metasomatic and hydrothermal metamorphism in that order.

The gypsum occurs as massive beds of finely crystalline material of very high grade interbedded with marble or as thinly laminated gypsiferous epidotic schists. Little anhydrite is found at the surface and its presence at depth cannot be ascertained for no drilling has been done. Although the gypsum is of high quality, its value is lessened by the presence of large and small fragments of marble which are literally “floating” in the gypsum beds. These “Tectonic” impurities will increase the cost of mining.

The deposits have been variously dated as Precambrian and as Paleozoic. The lack of fossils and the small amount of geologic work done in the southeastern Mojave desert make dating and correlation difficult. The deposits are similar to those in the Little Maria and Maria Mountains to the east with an upper Paleozoic age designation probably the better alternative. The possibility should be considered that these gypsum, marble, schist, and quartzite beds are the deformed and meta-morphosed equivalents of the gypsum, limestone, shale and sandstone of the Kaibab and Moenkopi (Permian and Triassic) formations in Southern Nevada.

[Thesis 2]. Oscillations in the Foraminifera of the Vicksburg Group from a Well in George County, Mississippi:

An oscillation chart is presented based on the foraminiferal content of core samples of the Vicksburg Group (Middle Oligocene) from a well in southeastern Mississippi. The oscillations are due primarily to relative changes in depth at this geographic position during the deposition of the sediments. These changes are indicated by variations in the percentage distribution of the species of foraminifera.

Ten cubic centimeters of each sample were washed and then sieved through a 150 mesh screen. A count was made of the number of specimens of each species or closely related group of species in each sample. The percentage distribution of the benthonic calcareous and arenaceous forms were calculated separately because the benthonic calcareous foraminifera are the more delicate depth indicators. The relative depth significance of the benthonic calcareous foraminifera was determined by plotting their percentages against the percentage of Uvigerina spp., which are considered typically open-water elements.

The possible influence of modifications of other ecologic factors comprising the depositional environment must also be considered when interpreting faunal changes. However, as a sample covers an interval of several inches or several feet in thickness (equivalent to hundreds or thousands of years), these effects are probably insignificant. The interpretation of fossil material is further complicated by such processes as mixing, mechanical abrasion, solution, and recrystallization.

The chart reveals several transgressions and regressions in the Vicksburg Group, even though the section appeared at first glance to be made up of a monotonous, homogeneous foraminiferal fauna. A single chart could not be carried across the strong faunal break between the Red Bluff (Lower Oligocene) and the Vicksburg. By charting the two parts separately, the oscillations are more easily discerned.

The method shows promise as a correlation tool in sedimentary sections in which there were fairly rapid depth changes. An individual chart probably should not be extended over a period of time greater than an epoch because evolutionary development will tend to mask faunal changes caused by oscillations of depth.

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