Sprecher
Beschreibung
In recent years, variations in acritarch morphotypes and morphological parameters, particularly process (appendage) length, have been studied to understand the palaeoecology of acritarchs and environmental changes, for example, salinity, temperature, and oxygenation. The acritarchs from the Early-Middle Ordovician of the island of Öland, Sweden, have been studied with a focus on taxonomy and biostratigraphy. Recently, Calero-Gordon et al. (2025) investigated the palaeoecological distribution of acritarch assemblages from two Middle Ordovician sections on the island. Following these studies, several open questions remain. In this study, based on the same sections, changes in the morphology of selected acritarch morphotypes are analyzed across a regressive event recorded in the Öland shelf sequence. Our dataset includes investigations on additional morphotypes, in particular the fusiform acritarchs, the sphaeromorphs and the baltisphaerids, that are here subdivided into two groups with the presence or absence of basal plugs. Measurements of the process length and the central body diameter across these groups, combined with statistical analysis, reveal distinct patterns, most probably related to water depth: baltisphaerids without basal plugs and fusiforms dominate in shallower water settings (Hälludden section), while baltisphaerids with basal plugs are more abundant in deeper water settings (Hagudden section). Process length increases with water depth, whereas small-sized forms become rare in deeper water environments. The presence of basal plugs possibly represents an adaptation for flotation and water-column stability. Sphaeromorph acritarchs appear palaeoecologically widespread and are morphologically stable. Overall, this study confirms that detailed acritarch morphometrics can refine palaeoenvironmental reconstructions beyond their traditional biostratigraphic role.