Recent stratigraphic analysis of the Wenlock strata within the type sections of the Welsh Borderlands and eastern Laurentia has revealed the presence of numerous K-bentonite horizons. Through the analysis of geophysical logs, measured cores and outcrops preliminary correlations within the Wenlock of the Midland Platform (UK) have been made. Within the eastern Laurentian sections of North America there is little reference to the presence of Wenlock age K-bentonites. However, preliminary field studies have determined the presence of potentially correlative packages of K-bentonites. Analysis of clay layers collected from the Osgood Shale (upper Telychian-lower Wenlock) and Louisville Limestone (upper Wenlock) of Indiana and adjacent Kentucky, Williamson Shale (upper Telychian) of New York State, the Estill Shale (upper Telychian-lower Wenlock) and Bisher Formation (?upper Wenlock) in east central Kentucky and Ohio indicate the presence of illite-smectite clays, P-form quartz, apatite and zircon in most samples. It is significant that these K-bentonite horizons appear to be non-randomly clustered near the lower and upper boundaries of the Wenlock and occur in biostratigraphically similar positions within the eastern Laurentian and Welsh Borderlands, suggesting the possibility of intercontinental correlation. The pulsed pyroclastic outpourings responsible for these K-bentonites occur during the early phase of Salinic Orogeny (late Telychian extending through the Wenlock). Furthermore eastern Laurentian K-bentonites are coarser grained in nature compared to their Avalonian stratigraphic equivalents suggesting a Laurentian source region.
AAPG Search and Discovery Article #90925©1999 AAPG Foundation Grants-in-Aid