Opaline Cements of the Altamaha Formation in Central Georgia: a petrographic analysis
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Authors
West, Travis M.
Issue Date
2020
Type
Presentation
Language
en_US
Keywords
Alternative Title
Abstract
The Altamaha Formation of central Georgia consists of well-indurated Miocene sandstones. Previous workers, as well as this study, have documented opaline and silica cements in these rocks. The origin of these cements and their associated depositional environment is unclear. This study is an attempt to better characterize these cements through petrographic analysis and hand sample examination. Various samples have been collected from the Central Georgia Coastal Plain region including locations from Ashburn, Georgia to Soperton, Georgia. These rocks are poorly sorted, angular, well-indurated, feldspathic to sub-feldspathic sandstones. They generally show significant volumes of matrix and silica cements. Minor amounts of clay and carbonate cements have also been observed. The previously mentioned matrix is problematic because these rocks are not graywackes. The formation is interpreted to be terrestrial due to the presence of terrestrial fossils along with terrestrial depositional features. Initial analysis of thin sections revealed that some of the cement is true opaline though other portions of cement appear to be chalcedonic quartz or in transition from opaline to chalcedonic quartz. In hand sample, these cements are opaque white with conchoidal fracture and do not show opaline luster.