MAGNETIC SUSCEPTIBILITY OF THE LATE DEVONIAN ANTRIM SHALE OF THE MICHIGAN BASIN

This study utilizes the magnetic susceptibility (MS) of sedimentary strata to correlate the Late Devonian Antrim Formation black shale and calcareous mudstone within the Michigan Basin as well as the Antrim with previously published MS profiles from contemporaneous, shale-dominated strata from the Illinois Basin. MS can be used as a proxy for changes in material composition, which is linked to paleoclimate-controlled sediment fluxes and depositional environments.

In the Michigan Basin, MS profiles through the basin-margin State Chester Welch 18 and the more basinal Krocker 1-17 cores show that MS patterns correspond to lithostratigraphic units. For some of these units the MS patterns are similar among the cores, though not for all units. Preliminary interpretation is that MS patterns are a result of proximity to sediment source (Acadian Orogeny versus Transcontinental Arch) as well as intrabasinal early diagenetic processes (pyrite). Furthermore, the lithostratigraphic units in these cores may not be chronostratigraphically equivalent.

This study also compares the Michigan Basin MS basinal profile (Krocker 1-17 core) with previously published data from the “Bullitt County Core” from Kentucky, in the southern Illinois Basin. Within a biostratigraphic framework, the Michigan and Illinois Basin cores appear to show similar MS patterns. This is possibly because sediment input to these two locations is primarily sourced from the Acadian Orogeny, and the depositional environment and therefore early diagenetic processes, are similar. Future work will combine mineralogical analysis with the MS profiles to decipher the source of magnetic susceptibility, currently hypothesized to be driven by ilmenite concentration.