A DIFFERENT PERSPECTIVE ONTO EARLY LIFE: SEDIMENTARY STRUCTURES RISING FROM PHYSICAL-MICROBIAL INTERACTION IN SILICICLASTIC TIDAL FLATS

Early life on Earth has been predominantly recognized from sturdy stromatolites or filigrane bacterial body fossils preserved in precipitated lithologies. Complex laboratory analyses detected biomolecules, and isotopes of biological origin, and give insight into the evolution of ancient microorganisms.

Recently, a different set of sedimentary structures has been detected that independent from stromatolites, or other biosignatures indicate the presence of microbial mats in Earth's oldest era. Tidal sandstones of early Archean age include a great variety of so-termed “microbially induced sedimentary structures (MISS)”. The structures include wrinkle structures, erosional remnants and pockets, multidirected ripple marks, and many other features.

Actualistic investigations conducted in modern, siliciclastic tidal flats showed that the MISS rise from the interference of microbial mats with the physical sedimentary dynamics of waves and currents. The microbial mats respond to erosion by biostabilization, or react by baffling, and trapping to the deposition of sediment. Only during calm dynamic conditions, microbial mat layers form by binding and growth.

The interference of the physical-biological parameter creates MISS. Due to their so different modes of formations, and their so different appearances and morphologies, the MISS have been included as own category in the Classification of Primary Physical Sedimentary Structures sensu Pettijohn & Potter 1964.

In the fossil record, the MISS can be found in shallow-marine settings not only in the early Archean, but in equivalent sandstones throughout Earth history. Thus their modern counterparts serve as valuable tools for the reconstruction of past microbial worlds.

Introductionary references:

Noffke, N., Hazen, R., Eriksson, K., & Simpson, E. (2006a): A new window into early life: Microbial mats in a siliciclastic early Archean tidal flat (3.2 Ga Moodies Group, South Africa). Geology, 34, p. 253-256.

Noffke, N., Gerdes, G., & Klenke, Th. (2003a): Benthic cyanobacteria and their influence on the sedimentary dynamics of peritidal depositional systems (siliciclastic, evaporitic salty and evaporitic carbonatic).- Earth Science Review, 62/1-2, 163-176.