δ13CCARB CHRONOSTRATIGRAPHIC CORRELATION OF THE LLANDOVERY CARBONATE SUCCESSION ACROSS THE MICHIGAN BASIN

Chronostratigraphic correlation between the shallow shelf and deep basin is one of the longstanding problems in carbonate stratigraphy. This problem is well illustrated in the Llandovery succession of the Michigan Basin. In the northern basin, the shallow-water shelf carbonates are defined by three lithostratigraphic groups. From older to younger, these include the Cataract, Burnt Bluff, and the Manistique groups. In the central basin, represented by deeper water carbonates, these units include the Cataract Group, and the undifferentiated Burnt Bluff and Manistique groups.

The current study uses rock material from 10 drill cores and two quarry sites to construct multiple high-resolution δ¹³C_carb curves across the Michigan Basin. Five positive carbon isotope excursions (CIEs) are identified. On the basis of conodont biostratigraphy and ⁸⁷Sr/⁸⁶Sr age dating, these CIEs are correlated to globally observed δ¹³C_carb excursions. From oldest to youngest, these include the Hirnantian (HICE), Early Aeronian, Late Aeronian, Valgu, and Ireviken global CIEs. Given the chronostratigraphic constraints available, the CIEs were used to develop a more temporally robust chronostratigraphic correlation of Llandovery succession in the Michigan Basin. The current study results demonstrate that three lithostratigraphic groups, Cabot Head, Burnt Bluff, and Manistique, are diachronous. The findings of this study are essential in understanding the development of the Michigan Basin during the Llandovery age.