States of biogenic bedding as records of the interplay of ecologic time and environment (a case study of modern siliciclastic sediments, Mellum Island, southern North Sea)

Abstract

Vertical sequences in modern siliciclastic sediments are used to document the intimate relationship between sedimentation rates and frequency and the development of microbial mats of different successional stages that correspond with hiatal intervals between the sedimentation events. Spatio-temporarily varying types of biogenic bedding developed from the former interaction of surface mats with sedimentation at water/sediment or air/sediment interfaces. Determinants of both surface mats and their bed-per-bed characteristics in the sedimentary record are local dominance changes between the two filamentous cyanobacterial speciesOscillatoria limosa andMicrocoleus chthonoplastes. Both represent different morphotypes and form mats of different consistency, biomass enrichment, structural complexity and thickness. Local dominance changes between both species proceed along an ecologie succession which starts withO. limosa-dominated pioneer mats and progressively continues towards thicker mats in whichM. chthonoplastes is abundant. Experiments have shown that both species are able to re-establish surface mats after burial, however, mats dominated by the one or other species require different time spans to return to their reference states before burial. These so-called ecologie time spans largely are controlled by the length of breaks in sedimentation. The spatial distribution of surface mats of different successional stages is converted into the sedimentary record which is characterized by different biolaminite types. The vertically variable buildups underline the importance of different time spans of hiatal intervals in biogenic bedding.