Selected Publications

Abstract:   A catalogue of microbiaI structural signatures is presented, based upon the
coupling of fundamental biogeochemical-microbial processes and local
merphogenetic determinants. It summarizes a collection of sedimentary
structures obtained from two modern siliciclastic peritidal environments in
different climatic zones [temperate humid: Mellum Island, southern North Sea;
subtropical arid: coast of southern Tunisia). Textural geometries reveal a high
structural diversity, but their determinants are primarily based upon six major
parameters: (1) intrinsic biofactors: structural diversification of sedimentary
microbial films and mats inherent: in the organisms, i.e. their construction
morphology, growth, taxis and behaviour, and local abundance of specific
morphotypes. Most prominent are the ensheathed filamentous cymobacteria
MicrocoIeus chthonoplastes and Lyngbya aestuarii, and the sheathless
filamentous cyanobacterium Oscillatoria limosa. (2) Biological response to
physical disturbances: sediment supply, erosion and fracturing of surface
layers resulting from desiccation cause growth responses of biofilms and
microbial mats. (3) Trapping/biniding effects: physicobiological processes give
rise to grain orientations and wavy to lenticular lamina, lamina-specific grain
arrangements and 'sucrose' calcium carbonate accumulations. (4) Secondary
physical deformation of biogenic build-ups: mechanical stresses acting upon
sediments overgrown and biostabilized by biofilms and mats produce erosionaI
and overthrust structures. (5) Post-burial processes: textural fabrics that evolve
horn mechanical effects of gas formation from decaying mats, and features
related to the formation of authigenic minerals (calcium carbonates, calcium
sulphates, pyrite). (6) Bioturbation and grazing: post-depositional structures,
such as Skolithos-type dwellings, traces of burrowing insects, gastropod
grazing traces and faecal pellets. h synopsis, the catalogue firstly comprises
a sound set of ubiquitous signatures. This uniformity in architectural
characteristics is attributed to the presence and local, dominance of certain
microbes throughout the different settings. The catalogue secondly documents
signatures that are extremely sensitive to tidal position, hydrodynamic regime
and overall climatic conditions. These kinds of signature indicate narrow facies
zones, which often coincide with the activity or dominance zones of certain
organisms. An overview of structures of microbial origin from the fossil record
underlines the potential of many of the signatures included in this catalogue to
become fossilized and provide strong indicators of former siIiciclastic tidal
settings.

Keywords:   Noffke, Biofilms, biostabilization, condensed fibrillar meshworks, microbial
mats, sedimentaq structures, thrombolitic fabrics

PDF