An upper Ordovician (upper Sandbian) benthic Paleozoic fauna at Langesund in the Oslo graben area has been reviewed. The study area consisted of the uppermost 13 meters of sediments in the Fossum Formation. A species/plot matrix retrieved in the formation has been analyzed with multivariate ordination techniques, extracting main gradients in species composition. The main gradient in species composition is correlated with sea level fluctuations already known. Results presented herein are interpreted as sea level fluctuations on a finer scale based on paleobiological evidence. Three fossil associations of importance are identified, with a decreasing abundance of primary producers correlated with increasing sea depths. The sea level fluctuation interpretation of a DCA ordination is supported by ecological assessment, including the abundance of primary producers, as well as the strength of the gradient, diversity patterns, occurrence of a superabundant culture of filter feeding Lepteana brachiopods, and a comparison of paleocurrents between lowstand and drowning events. These results are furthermore supported by sedimentological evidence.