Regional fluid migration in the Illinois basin: Evidence from in situ oxygen isotope analysis of authigenic K-feldspar and quartz from the Mount Simon Sandstone

摘要

Oxygen isotope compositions of widespread, authigenic K-feldspar and quartz over-growths and cements in the Upper Cambrian Mount Simon Sandstone were measured by ion microprobe in 11 samples distributed across the Illinois basin and its periphery. Average K-feldspar δ~(18)O values increase systematically from + 14‰ ± 1‰ in the southern-most and deepest samples in Illinois to +24‰ ± 2‰ in the northernmost outcrop sample in Wisconsin. A similar trend was observed for quartz overgrowths (22250L?± 2‰ to 28‰ ± 2‰). Constant homogenization temperatures (100-130 ℃) of fluid inclusions associated with quartz overgrowths throughout the basin suggest that the geographic trend in oxygen isotope compositions is a result of diagenetic modification of a south to north migrating basinal fluid.