Microbial signatures in peritidal siliciclastic sediments: a catalogue

Abstract

A catalogue of microbial structural signatures is presented, based upon the coupling of fundamental biogeochemical–microbial processes and local morphogenetic 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 cyanobacteria Microcoleus 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/binding 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 erosional and overthrust structures. (5) Post‐burial processes: textural fabrics that evolve from 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. In 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 siliciclastic tidal settings.

Remarkable preservation of microbial mats in Neoproterozoic siliciclastic settings: Implications for Ediacaran taphonomic models

“…Gehling, 1999), as well as other sedimentary structures of putative microbial origin, including pustules, sinuous cracks and sand chips (Fig. 2, Schieber, 1999;Gerdes et al, 2000;Noffke et al, 2001;, have been recognised from siliciclastic bedding planes ranging from the Archean (Noffke et al, 2003;2006, a, b;Noffke, 2007;Noffke et al, 2008;Noffke, 2009 this volume) to the present day (Gerdes et al, 2000;Noffke et al, 2001;Noffke, 2009 this volume). As applied here, the term 'microbial' refers to organisms ranging from bacteria and archaea, to protozoans, algae (protoctists) and fungi (e.g.…”

“…These predictions are examined by means of a review concerning the distinctive phenomenon of bedding plane wrinkle structures or MISS (sensu Noffke et al, 2001), which are often used to infer the presence of widespread microbial mats (biofilms) on the Ediacaran seafloor (e.g. Seilacher & Pflüger, 1994;Seilacher, 1999;Gerdes et al, 2000;Noffke et al, 2001;2002;Noffke, 2009 this volume). Also considered is the emerging evidence for the preservation of microbial components of the mats themselves, in a variety of taphonomic modes (e.g.…”

A case study of microbial mat-related features in coastal epeiric sandstones from the Paleoproterozoic Pretoria Group (Transvaal Supergroup, Kaapvaal craton, South Africa); The effect of preservation (reflecting sequence stratigraphic models) on the relationship between mat features and inferred paleoenvironment

“…However, the pervasive large palimpsest ripple fields complemented by a rich variety of associated MRS observed at most extensive outcrops of the latter unit (Parizot et al, 2005;Bosch and Eriksson, 2008;Eriksson et al, 2010), contrast strongly with the near-absence of MRS in the Daspoort outcrops. As has been discussed in section 2 of this paper, for both modern and ancient mats (including Precambrian examples) growing on clastic substrates, a school of thought supports a bias in the occurrence of MRS in the shallow marine -tidal flat-supratidal setting-sabkha environmental continuum (e.g., Schieber, 1998;Gerdes et al, 2000;Noffke et al, 2001b;Schieber et al, 2007a;Gerdes, 2007;Bose and Chafetz, 2009;Noffke, 2010). The widespread occurrence of MRS in the Magaliesberg Formation supports the view that these mat-related features might be partially diagnostic of such coastal palaeoenvironmental settings, but the paucity of Daspoort MRS does not.…”

“…salt works and laboratory models; Schneider, 1995;Gerdes and Klenke, 2003). Gerdes et al (2000) and Noffke et al (2001b) provide further examples of the perceived shallow marine -coastal bias in clastic mat studies in Pleistocene-modern tidal flats, as do Parizot et al (2005) for Palaeoproterozoic equivalents where they related MRS to inferred water depths and wave heights. In the Precambrian record, where the absence of grazers enhanced preservation and abundance of MRS, most marginal shallow marine settings formed part of preserved epeiric seas (e.g., Eriksson et al, 2008); as an example, Schieber (1998) relates MRS in the c. 1450-850 Ma Belt Supergroup of North America to a palaeoenvironmental spectrum ranging from calm offshore -shallow nearshore -sea-marginal sandflats -shallow nearshore lagoons.…”

Neoproterozoic substrate condition vis-à-vis microbial mat structure and its implications: Sonia Sandstone, Rajasthan, India

“…Noteworthy is that these structures show close association with a wide spectrum of microbial mat-related structures (Gerdes et al, 2000;Parizot et al, 2005;Sarkar et al, 2008;Samanta et al, 2011), but do not share morphological similarities with any of them.…”