Lateral facies changes in the Lower Ordovician of northern Öland, Sweden

A method of presence/absence analysis of insoluble residues, in combination with correspondence analysis, was used in order to establish a microlithological zonation for the Lower Ordovician limestone sequence at Hälludden, northern Öland. The results from the correspondence analysis were applied to five neighbouring profiles in which similar presence/absence analyses were made. The procedure allowed unbiased comparisons between the profiles. The microlithological zones distinguished in the profile at Hälludden, were recognized also in the other profiles, and available data regarding the depositional environments at Hälludden could thus be applied to a larger area. Based on this analysis, an environmental interpretation for the Lower Ordovician of northern Öland was made. The regression in the lower part of the Hälludden sequence affected the whole of northern Öland, and the sea-floor was situated slightly higher in the northwest than in the east and south. This difference in sea-floor elevation did not, however, have any major influence on the general facies pattern produced by the regression. The relief may have been of the order of a few meters, while the regression may have been of a magnitude of up to 150 m.