Thomas Klenke

Microbially Induced Sedimentary Structures: A New Category within the Classification of Primary Sedimentary Structures

ABSTRACT Cyanobacterial films and mats syndepositonally influence erosion, deposition, and deformation of sediments. The biomass levels surface morphologies, and microbial mats stabilize depositional surfaces and shelter the sediment against erosion or degassing. Growing microbial mats dredge grains from their substrate upwards, whereas cyanobacterial filaments that are oriented perpendicular to the mat surface reach into the supernatant water and baffle, trap, and bind suspended particles. These and similar biotic-physical interactions are reflected in syndepositional formation of microbially induced sedimentary structures. We distinguish structures on bedding planes (leveled bedding surfaces, wrinkle structures, microbial mat chips, erosional remnants and pockets, multidirectional ripple marks, and mat curls) and internal bedding structures (sponge pore fabrics, gas domes, fenestrae structures, sinoidal laminae, oriented grains, benthic ooids, biolaminites, mat-layer-bound grain sizes). We propose to place this group of microbially mediated structures as a fifth category (bedding modified by microbial mats and biofilms) in Pettijohn and Potters (1964) existing classification of primary sedimentary structures.

Benthic cyanobacteria and their influence on the sedimentary dynamics of peritidal depositional systems (siliciclastic, evaporitic salty, and evaporitic carbonatic)

Abstract Peritidal sedimentary systems are widely colonized by benthic cyanobacteria that form biofilms and microbial mats. The bacterial communities interfere with physical and chemical sedimentary dynamics, which is documented by the formation of Microbially Induced Sedimentary Structures (MISS). The structures form a new fifth category in the existing Classification of Primary Sedimentary Structures. Siliciclastic depositional systems are dominated by physical dynamics. By biostabilization, cyanobacteria shelter their substrata against erosion during periods of intensive hydraulic reworking, or they permit flexible deformation of sandy sediments. During low hydrodynamic disturbance, the bacteria enhance deposition of sediments by baffling, trapping, and binding. Such biotic-physical interference is recorded by MISS such as erosional remnants and pockets or planar stromatolites. Chemical depositional systems include (i) evaporitic salty environments characterized by evaporation and dissolution and (ii) evaporitic carbonatic environments that include evaporation, dissolution, and in situ lithification of organic matter. Here, cyanobacterial mats experience periodical desiccation or evaporation of crystals and mat-related structures such as petees, and polygonal patterns of cracks are formed. Cyanobacteria and heterotrophic bacteria provide a chemical microenvironment that supports in situ lithification of organic matter. In thin-sections, carbonate precipitates as ooids or lines of decaying filaments are visible. MISS occur in modern and ancient depositional systems. They record (i) biological abilities of benthic cyanobacteria to cope with sedimentary dynamics and (ii) paleoclimate and paleoenvironmental conditions during Earth history. Similar structures are also expected in extraterrestrial (paleo)environments.

A microscopic sedimentary succession of graded sand and microbial mats in modern siliciclastic tidal flats

Microscopic studies of thin sections from modern siliciclastic tidal flat sediments in the southern North Sea demonstrate the significant role of microbial mats in the buildup of sedimentary sequences. This is documented by a unit only a few millimetres thick. It starts at the base with a fine- to medium-grained quartz sand often containing secondary pores (‘fenestrae type’) merging gradually into finer sediments. The lower siliciclastic part is superposed by an upper organically dominated layer built by microbial mats. Within the organic material, single quartz grains without any contact to each other are oriented with their long axes parallel to the bedding planes. Each siliciclastic part in the lower section of the unit indicates the initial deposition of coarser grains in a stronger flow regime followed by gradually decreasing flow velocities. Each microbial mat in the upper part essentially represents a period of low sedimentation rate. During its growth, grains still settle down onto the mat and become bound in the organic matrix. The orientation of these grains with their long axes parallel to the bedding plane points to an energetically suitable position to gravity achieved by the friction reduction of the soft organic matter. Repeated depositional events followed by low-rate deposition cause the buildup of various units. There is no visible reworking of the former surfaces, since the microbial mats prevent erosion during periods of increased flow. The buildup is characteristic of siliciclastic sediments repeatedly occupied, stabilized, and fixed by microbial films or mats.

Microbially induced sedimentary structures indicating climatological, Hydrological and depositional conditions within recent and pleistocene coastal facies zones (Southern Tunisia)

SummaryExtensive tidal areas of the Recent coast of southern Tunisia are overgrown by microbial mats. Different mat types of which each are dominated by distinct and well adapted cyanobacterial species develop. Ecological response of the mat-forming microorganisms to climatological hydrological and sedimentological factors produce characteristic sedimentary structures (=microbially induced sedimentary structures).A suecession of Pleistocene rocks crops out near the lagoon El Bibane, southern Tunisia. The stratigraphic section comprises structures that we regard as fossil equivalents to those microbially induced structures we observe in the Recent coastal area. Preservation of the structures is result of lithification of the microbial mats. This we conclude from fossil filaments of cyanobacteria visible within the rock matrix.The Recent microbially induced sedimentary structures indicate facies zones within the modern tidal environment. Comparison of the Recent structures with the fossil analogues recorded in the stratigraphic section aids to identify the same distinct facies zones within the Pleistocene coastal environment also.Erosion by water currents forms step-like cliffs, and the microbial mat is undermined and ripped off piece by piece. shallows within the supratidal area are overgrown by copious microbial mats comprising structures like biolaminites and—varvites, as well as polygons of cracks. The features originate from effects triggered by seasonal variations of climate. Tufts and reticulate pattern of bulges indicate supernatant water films covering the mat surfaces. Morphologically higher parts of the Recent tidal area are overgrown by single-layered mats forming petees, induced by microbial mat growth and evaporitive pumping.The study demonstrates that microbially induced sedimentary structures can be used to reconstruct small-scaled facies zones within coastal environments. The also include hints on paleoclimatological, hydrological and sedimentological conditions.

Effect of anoxia and high sulphide concentrations on heterotrophic microbial communities in reduced surface sediments (Black Spots) in sandy intertidal flats of the German Wadden Sea

Abstract Black reduced sediment surfaces (Black Spots) in sandy intertidal flats of the German Wadden Sea (southern North Sea) are characterised by elevated sulphide concentrations (up to 20 mM) and low redox potentials. It is assumed that the appearance of Black Spots is linked to elevated levels of organic matter content within the sediments. In order to establish the effect of high substrate and sulphide concentrations on the heterotrophic microbial communities in Black Spot sediments, bacterial abundances and the potential C-source utilisation patterns of microbial communities were compared in natural and artificially induced Black Spots and unaffected control sites. Bacterial numbers were estimated by direct counts and the most probable number technique for different physiological groups, while patterns of C-substrate utilisation of entire aerobic microbial communities were assessed using the Biolog sole-carbon-source-catabolism assay. Bacterial abundances at Black Spot sites were increased, with increases in mean cell numbers, more disperse data distributions and more extreme values. Substrate utilisation patterns of aerobic microbial communities were significantly different in Black Spot sediment slurries, showing diminished richness (number of C-sources catabolised) and substrate diversity (Shannon diversity index) in comparison to unaffected sites. Principal component analysis clearly discriminated Black Spot utilisation patterns from controls and indicated that microbial communities in individual Black Spot sites are functionally diverse and differ from communities in oxidised surface sediments and reduced subsurface sediments at control sites. This work suggests that potentially negative effects on microbial communities in Black Spot sediments, through anoxia and high sulphide concentrations, are balanced by the stimulating influence of substrate availability, leading to comparable or higher bacterial numbers, but lower functional microbial diversity of aerobic microbial communities.

Direct graphite furnace atomic absorption spectrometric determination of metals in sea water : application of palladium modifiers and a fractal approach to their analytical support

Abstract Sea water, like other high-salinity matrices, causes severe interferences in the direct determination of metals by graphite furnace atomic absorption spectrometry (GFAAS), even when Zeeman-effect background corrections is applied. A method for eliminating these interferences by the application of mixed modifier system of ammonium oxalate and tetraamminepalladium(II) chloride is presented. In particular these modifiers optimize the direct GFAAS determination of lead and manganese. For cadmium, however, only ammonium oxalate should be used as a modifier. The geometry of the microdistribution of palladium on the palladium-conditioned graphite platform was investigated in order to elucidate possible stabilizing effects of palladium on the analytes which were observed with the different modifiers. Fractal characteristics of the palladium elemental distribution were ascertained by a scanning electron microscope-energy-dispersive x-ray spectrometer image box-counting analysis. The fractal dimension [ D B (0) = 1.77 ± 0.04 and 1.81 ± 0.04] and electron microscopic investigations indicated differences in the structure of palladium deposits on the platform. These variations in the palladium geometry affect the analytes to a certain extent.

Multifractal analysis of the microdistribution of elements in sedimentary structures using images from scanning electron microscopy and energy dispersive X ray spectrometry

A novel method for the quantitative characterization of density distributions of elements in sedimentary geosystems is presented. This general technique is based on the multifractal analysis of image-processed elemental maps obtained by scanning electron microscopy combined with energy dispersive X ray spectrometry. Applications to microdistributions of Si, Fe, and Al in recent bioactive siliciclastic marine sediments are reported. Inhomogeneous scaling behavior of these elemental distributions is observed in all cases. Two main conclusions can be drawn: (1) The sedimentary matrix exhibits true fractal geometry and (2) the processes allocating and rearranging the elements are not of pure stochastic type. Therefore the identification of genetic processes may be possible on the basis of their “multifractal fingerprints”.

Multifractal characterization of microbially induced magnesian calcite formation in Recent tidal flat sediments

Abstract Structures resulting from biogenic carbonate cementation of microbial mats in Recent siliciclastic tidal flat sediments of the North Sea are analyzed quantitatively by a novel combination of scanning electron microscopy and energy-dispersive X-ray spectrometry (SEM/EDX) imaging and subsequent multifractal analysis. Evaluation of calcium distribution patterns and their links to sediment-intrinsic mineralization processes show that the applied geometrical technique is an efficient tool for detecting microscopic variations in elemental distributions and related minerals within sedimentary matrices. Two main conclusions can be drawn: (i) magnesian calcite is a rapidly formed product of the early diagenesis of organic matter in Recent bioactive marine sediments; and (ii) multifractal spectra are measures for the spatial inhomogeneity of authigenic calcification processes acting on the sedimentary structure. This implies that elemental distribution patterns in a sedimentary system are scale-independent phenomena. Processes causing such patterns have occurred over certain periods with varying rates and on different scales. The detection of multifractal measures also opens a way towards a systematic survey of dynamic processes occurring in sedimentary structures.

Early European Experience in Marine Spatial Planning: Planning the German Exclusive Economic Zone

Marine spatial planning is emerging as an integrated, resource management-led approach to governing the use of the seas. Recent initiatives include those of some north European countries, including Germany, which has now completed a plan for its federal offshore territory. In this article, an analysis is presented of this pioneering plan and the consultation process behind its production, with a particular emphasis on the treatment of different sectoral interests around which the plan was structured. This revealed the attempts to coordinate not only the different demands at sea by means of allocation of areas and cross-sectoral considerations, but also the uneven representation of activities with certain interests gaining strongly and others effectively marginalized. This study provides early empirical evidence of the tensions involved in the attempt to adopt a spatial approach to marine governance. This new domain for planning is situated in the overlapping, but distinct domains of marine management and spatial planning. The conceptual backgrounds of both are drawn upon in assessing the strengths and weaknesses of the plan and in suggesting how marine plans might gain by giving close attention to the broader principles of marine and strategic planning.

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)

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 écologie 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 écologie 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.