Author

Al-Musawi

Date of Award

6-2019

Degree Name

Master of Science

Department

Geological and Environmental Sciences

Department

Geosciences

First Advisor

Dr. Stephen Kaczmarek

Second Advisor

Dr. William B. Harrison III

Third Advisor

Dr. Peter Voice

Keywords

Burnt Bluff Group, chronostratigraphy, carbon isotopes excursions, Llandovery, chemostratigraphy

Access Setting

Masters Thesis-Open Access

Abstract

In the Michigan Basin, the Burnt Bluff Group (BBG) is lower Middle Silurian in age (Llandovery), and is composed of limestones and dolostones. The BBG is bounded above by the Schoolcraft Formation and below by the Cabot Head Shale. The BBG in northern Lower Michigan is composed of three formations, including the Lime Island, Byron, and Hendricks, which reflect deposition on a broad shallow marine shelf. In contrast, the BBG in central Michigan is composed of a single lithologic unit called informally the “undifferentiated BBG (UD-BBG),” which reflects deposition in a deeper marine basin. Lithostratigraphically, the three formations in the north have been historically correlated to the UD-BBG in the south. The above lithostratigraphic model was evaluated in this study through integration of conodonts, stable carbon isotopes, and 87Sr/86Sr data, which were extracted from 5 cores in the Michigan Basin. These data were used to constrain the ages of the BBG in the Michigan Basin in order to establish a chronostratigraphic correlation from shelf to basin. In the shelf position, one positive, +4‰ VPDB, carbon isotope excursion (CIE) was identified. Conodont biostratigraphy constrains the age of this excursion to the global Late Aeronian excursion. In the slope position, which lies between the shelf and basin-center, three positive excursions (2.2-2.5‰, 5‰, +3‰ VPDB) were identified. Conodont age dates and 87Sr/86Sr data constrain these three positive excursions to the global Early Aeronian excursion, Late Aeronian excursion, and Valgu excursion, respectfully. In the basin-center position, two positive excursions were identified, +2-2.2‰, +3‰. Based on 87Sr/86Sr, these excursions were identified as the global Early Aeronian excursion, and the Late Aeronian excursion, respectfully. The age-constrained CIEs were used to correlate rock units between the three positions. These correlations imply that the existing lithostratigraphic model is not accurate, and that the BBG was deposited at different times in the different locations in the basin.

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