‘Resurrected’ concretions – their resumed cementation after exhumation, transport, re-deposition and exploitation by producers of the trace fossil Chondrites when still being soft
Year: 2025
Type: article
Abstract: Incipient concretions having argillaceous matrix and methane-derived cement were exhumed from a low-oxygenated muddy setting, transported and embedded in a fine-sandy tempestite. They were still soft after deposition of the tempestite because subsequently they were preferentially exploited by producers of the trace fossil Chondrites ; its tubes are wide-spaced and rare in the tempestite but abundant and narrow-spaced in the concretions. The tubes are filled with fine sand taken from the tempestite. The stable isotope signature of the concretions (δ 13 C −39 to −22 ‰) markedly differs from that of the tempestite (δ 13 C −3 to −2‰). Organoclastic sulfate reduction (OSR) and anaerobic oxidation of methane (AOM) dominated the initial cementation of the concretions. During OSR and AOM, sulfate was reduced to sulfidic phases, including H 2 S being toxic to animals. Nonetheless, Chondrites producers exploited the incipient concretions. Because around their tubes are no haloes that would indicate flushing with oxygenated water, the Chondrites producers likely lived in symbiosis with microbes utilizing and detoxicating sulfides and hence, followed a chemichnial behavior. After burrowing ceased, resumed precipitation of early diagenetic micrite filled the remaining porosity of concretions, whereas the tempestite sand was cemented by late diagenetic carbonate. Burrowing of the displaced incipient concretions documents their still soft-to-stiff consistency, since they were only partly cemented but resistant to compaction although still in a plastic state, so that they could be burrowed. This fact explains why early diagenetic concretions are rarely found in modern muddy sediments because they are hardly recognized and easily overlooked in modern sediment cores. Since coarse near-shore components are lacking, sediment reworking occurred distant from shore on a local swell. There, waves and currents enriched sand while concretions formed in mud underneath/nearby from where they became eroded and displaced by a stronger-than-average storm depositing them in a somewhat deeper area of restricted spatial extent.
Source: Marine and Petroleum Geology
Authors: Andreas Wetzel, Maciej Bojanowski
Language: English
Subfield: Paleontology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $3,440
Awards: G4496720776, G7470377620
OpenAlex ID: W4413119497