Regional Scale Petrological Trends in Llandoverian Dolomites, Michigan Basin, USA

Recent studies frequently use vertical petrological trends to interpret the fluids and mechanisms of dolomitization. However, a spatial and lateral understanding of how these fluids and mechanisms change on a platform scale is largely unknown.

The current study integrates mineralogical, textural, geochemical, and elemental data from a series of cores along the dip profile of a Llandovery age carbonate ramp platform in the Michigan Basin to investigate platform scale dolomitization in the alternating limestones and dolostones of this succession. Previous research of the Llandovery succession in the Michigan Basin indicates a regional trend in dolomite abundance whereby the overall thickness of Llandovery dolomites decreases down-dip into the basin, pinching out towards the basin center.

Thin-section petrography and scanning-electron-microscopy from a core in northeastern Michigan suggest that dolomitization of some Llandovery intervals occurred very early and was likely driven by evaporative fluids in a restricted tidal setting. However, further investigations of these Llandovery dolomite intervals show that dolomites are moderately ordered, Ca-rich, and δ18O and δ13C values generally fall in the expected range of dolomites formed in Silurian marine fluids. By examining the spatial patterns and trends between dolomitic bodies along the dip profile, we hope to understand better the fluids and mechanisms associated with platform scale dolomitization of the Llandovery Series.