Title

Geochemical Analysis of the Marginal Facies of the Bear Gulch Limestone, Central Montana

Presentation Type

Poster

Abstract

There are a limited number of late Mississippian age deposits with soft bodied preservation like the Bear Gulch Limestone (BGL) in central Montana to study the End Mississippian mass extinction, the Serpukhovian Biodiversity Crisis. Understanding units like the BGL might illuminate this important time period, and expand our understanding of current global climate change.

Geochemical techniques never before applied to the BGL, have provided data that can be used reconstruct the paleoenironment of this fossil-bearing formation. The BGL holds an abundance of well-preserved soft-body fossils from the late Mississippian, including carbon films of organs, worms, and fish. The depositional setting is a restricted marine basin containing five biologic and lithological facies. The marginal facies within the study area is composed of three meters of dark brown fissile laminae.

During the summer of 2012 a 220 cm2 area of 50 successive layers of the marginal facies was excavated. The fossils in each layer were compared to literature for species identification. Of the 50 samples, ten fossil bearing samples were selected for geochemical and mineralogical analysis. The samples were ground to 150 microns and examined using X-ray diffraction (XRD), coulometry, and the ferrozine method. XRD provides basic analysis of the mineralogy, used to assist in lithology identification. Coulometry measures total organic carbon content (TOC). TOC is used to assess the potential for petroleum and productivity of the basin. The TOC ranged from 0.72 to 4.17%. The ferrozine method provides data for the determination of the depositional setting. Our initial research has provided a series of methods that can be adapted for the study of additional BGL facies.

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Apr 12th, 3:00 PM Apr 12th, 4:00 PM

Geochemical Analysis of the Marginal Facies of the Bear Gulch Limestone, Central Montana

UC Ballroom

There are a limited number of late Mississippian age deposits with soft bodied preservation like the Bear Gulch Limestone (BGL) in central Montana to study the End Mississippian mass extinction, the Serpukhovian Biodiversity Crisis. Understanding units like the BGL might illuminate this important time period, and expand our understanding of current global climate change.

Geochemical techniques never before applied to the BGL, have provided data that can be used reconstruct the paleoenironment of this fossil-bearing formation. The BGL holds an abundance of well-preserved soft-body fossils from the late Mississippian, including carbon films of organs, worms, and fish. The depositional setting is a restricted marine basin containing five biologic and lithological facies. The marginal facies within the study area is composed of three meters of dark brown fissile laminae.

During the summer of 2012 a 220 cm2 area of 50 successive layers of the marginal facies was excavated. The fossils in each layer were compared to literature for species identification. Of the 50 samples, ten fossil bearing samples were selected for geochemical and mineralogical analysis. The samples were ground to 150 microns and examined using X-ray diffraction (XRD), coulometry, and the ferrozine method. XRD provides basic analysis of the mineralogy, used to assist in lithology identification. Coulometry measures total organic carbon content (TOC). TOC is used to assess the potential for petroleum and productivity of the basin. The TOC ranged from 0.72 to 4.17%. The ferrozine method provides data for the determination of the depositional setting. Our initial research has provided a series of methods that can be adapted for the study of additional BGL facies.