--> --> Alunite in Tyler Formation, Late Carboniferous Deposits of Williston Basin North Dakota

AAPG Rocky Mountain Section Meeting

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Alunite in Tyler Formation, Late Carboniferous Deposits of Williston Basin North Dakota

Abstract

Hyperspectral core scanning of Tyler Formation of mid-Pennsylvanian deposits reveals the possible occurrence of alunite group of minerals that occur as pebble to granule-sized clasts in a massive mudstone to shale containing halloysite and kaolinte. Preliminary XRD analysis of two samples has confirmed the presence of multiple mineral phases of alunite group. Modern occurrences of alunite are rare and restricted to arid environments with groundwater that contains high dissolved sulfate concentrations and very low pH. These minerals may form under the influence of an extremely acidic syndepositional environment or shallow postdepositional diagenetic processes. Alunite minerals have been identified in Permian red beds across Wyoming, Utah and in the Permian Opeche Formation in North Dakota. The existence of these minerals satisfies one diagnostic feature associated with extremely acidic lakes and groundwater. This study is able to conclude that alunite minerals identified by hyperspectral imaging and confirmed by XRD are present in the red beds found in the upper portion of the Tyler Formation. Additional work will be needed to identify other mineral associations that would further define a conceptual framework consistent with the depositional settings and early diagenetic chemistries that may extend across the Pennsylvanian-Permian boundary in the Williston Basin.