Chitinozoan Biostratigraphy of the Lusklint 1 Section (Gotland, Sweden) a Potential Replacement for the GSSP for the Base of the Wenlock Series (Silurian)

New chitinozoan biostratigraphy of the Lusklint 1 outcrop and complementary Lusklint-1 core (Gotland, Sweden), provides an improved level of chronostratigraphic resolution to the Silurian Ireviken Event and the position of the Llandovery-Wenlock boundary. The Lusklint 1 outcrop section is famous as the reference section for its formalized conodont extinction ‘datums 1 to 6’ and is currently under scrutiny as a potential replacement for the GSSP for base of the Wenlock Series. The nearby Lusklint-1 core extends another 18 meters below the lowest level of the outcrop, doubling the accessible Llandovery succession. The Margachitina margaritana Biozone is one of four chitinozoan biozones (two global, two local) that are recognized. Consistent with other sections worldwide, it is identified by its morphologically highly distinct index fossil, M. margaritana, and spans the Llandovery-Wenlock boundary.However, the intermittent occurrence of the tiny marker fossil across this series of closely spaced samples, raises some questions as to the precision with which the boundaries of this biozone can be drawn in routine studies that rely on less closely-spaced sampling. Chitinozoan species disappear stepwise throughout the Lusklint 1 composite section, even below the lowest conodont extinction datum, but show the most pronounced decline at datum 4, which is also the level at which scolecodonts and conodonts were most affected at Lusklint 1. Chitinozoans at Lusklint 1 are well-preserved, abundant, and their stratigraphic ranges match well with those of the current Wenlock GSSP and other Llandovery-Wenlock sections around the globe. If the Lusklint 1 outcrop is selected as the new GSSP of the base of the Wenlock Series, chitinozoans have the potential to act as a helpful auxiliary marker.