APPLICATION OF HIGH RESOLUTION ED-XRF DATA TO ESTABLISH A SEQUENCE STRATIGRAPHIC FRAMEWORK OF HOMOGENEOUS CARBONATE ROCKS, MICHIGAN BASIN, USA

Sequence stratigraphic interpretations using conventional geologic datasets from outcrop, core, and wire-line logs are routinely applied to carbonate rocks. The vast majority of published work on this subject has investigated shallow water carbonates where facies shifts are readily observable. This standard approach is more difficult in deep water deposits, particularly when the rocks are texturally homogeneous.

In siliciclastic mudrocks, geologists have tackled the problem of textural homogeneity by applying elemental chemostratigraphy whereby changes in elemental concentrations are used to infer temporal variations in environmental conditions, such as redox and water depth. In this study, a chemostratigraphic approach using ED-XRF elemental data is applied to a collection of Silurian homogeneous lime mudstones in the Michigan Basin. Particular focus was given to the continental proxy elements (e.g., Al, Si, K, Ti, Zr), which are interpreted to reflect terrigenous material input into the basin. Continental proxy elements exhibit systematic variations that can be correlated between five wells in central basin within the Michigan Basin suggesting that elemental variations do not reflect local changes, but rather changing basin wide conditions. Positive correlation (R²>0.8) between Al-K, Ti-Zr, Al-Si, and Al-Zr are consistent with a detrital, continental origin for the proxy elements. Shifts in siliciclastic input into the carbonate system is interpreted to reflect sea level fluctuations. These fluctuations in sea level used to identify depositional cycles within a homogenous carbonate rocks that can be correlated throughout the basin.