Evidence for rapid environmental changes in low latitudes during the Late Silurian Lau Event: the Burgen-1 drillcore, Gotland, Sweden

Erosional outliers are an important component of the Ludlow (Late Silurian) stratigraphy of Gotland, Sweden. However, due to the poor degree of exposure, outcrop studies have not revealed a detailed section from any of these outliers. The first complete stratigraphy of such an erosional remnant, the Burgen outlier, is presented here, based on the recently recovered Burgen-1 drillcore. Stratigraphical units encountered are, from oldest to youngest, the uppermost Hemse Group (>35 m), Eke Formation (0.4 m), Burgsvik Formation (3.4 m) and the basal Hamra Formation (12 m preserved). Based on carbon stable isotopes and lithological correlation to nearby outcrops that are zoned by conodonts, it can be concluded that the most profound late Ludlow sedimentary changes took place shortly after the onset of the globally recognized Lau Event (δ13C values reach 8.7 ‰ in the lower Hamra Formation). Sedimentary changes include development of discontinuity surfaces, widespread occurrence of an intraclastic conglomerate, increased microbial activity (Rothpletzella and Wetheredella), and influx of clastics to the basin. These changes are linked to substantial base-level changes during the event. A general comparison with the Prague basin suggests contemporaneous sedimentary changes on Baltica and on cratonic elements from peri-Gondwana during the event.