Articles | Volume 12, issue 8
https://doi.org/10.5194/bg-12-2301-2015
https://doi.org/10.5194/bg-12-2301-2015
Research article
 | 
16 Apr 2015
Research article |  | 16 Apr 2015

Fossilized bioelectric wire – the trace fossil Trichichnus

M. Kędzierski, A. Uchman, Z. Sawlowicz, and A. Briguglio

Abstract. The trace fossil Trichichnus is proposed as an indicator of fossil bioelectric bacterial activity at the oxic–anoxic interface zone of marine sediments. This fulfils the idea that such processes, commonly found in the modern realm, should be also present in the geological past. Trichichnus is an exceptional trace fossil due to its very thin diameter (mostly less than 1 mm) and common pyritic filling. It is ubiquitous in some fine-grained sediments, where it has been interpreted as a burrow formed deeper than any other trace fossils, below the redox boundary. Trichichnus, formerly referred to as deeply burrowed invertebrates, has been found as remnant of a fossilized intrasediment bacterial mat that is pyritized. As visualized in 3-D by means of X-ray computed microtomography scanner, Trichichnus forms dense filamentous fabric, which reflects that it is produced by modern large, mat-forming, sulfide-oxidizing bacteria, belonging mostly to Thioploca-related taxa, which are able to house a complex bacterial consortium. Several stages of Trichichnus formation, including filamentous, bacterial mat and its pyritization, are proposed to explain an electron exchange between oxic and suboxic/anoxic layers in the sediment. Therefore, Trichichnus can be considered a fossilized "electric wire".

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Short summary
In our study we propose new interpretation of commonly found trace fossil of genus Trichichnus which can be regarded as a fossilised bacterial mat system produced by giant sulphur bacteria related to genus Thioploca. We suggest that the bioelectrical processes may occur during some stages of live and/or post-mortem history of Thioploca-housed bacterial consortium. This greatly improves our understaniding of initial colonization of the marine sea floor after improvements of oxygenation.
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