Massive cryptic microbe-sponge deposits in a Devonian fore-reef slope (Elbingerode Reef Complex, Harz Mts., Germany)

Abstract

A massive occurrence of microbial carbonates, including abundant sponge remains, within the Devonian Elbingerode Reef Complex was likely deposited in a former cavity of the fore-reef slope during the early Frasnian. It is suggested that the formation of microbial carbonate was to a large part favored by the activity of heterotrophic, i.e., sulfate-reducing bacteria, in analogy to Quaternary coral reef microbialites. The Elbingerode Reef Complex is an example of an oceanic or Darwinian barrier reef system. In modern barrier reef settings, microbialite formation is commonly further facilitated by weathering products from the central volcanic islands. The Devonian microbialites of the Elbingerode Reef Complex occur in the form of reticulate and laminated frameworks. Reticulate framework is rich in hexactinellid glass sponges, the tissue decay of which led to the formation of abundant micrite as well as peloidal and stromatactis textures. Supposed calcimicrobes such as Angusticellularia (formerly Angulocellularia) and Frutexites, also known from cryptic habitats, were part of the microbial association. The microbial degradation of sponge tissue likely also contributed to the laminated framework accretion as evidenced by the occurrence of remains of so-called “keratose” demosponges. Further typical textures in the microbialite of the Elbingerode Reef Complex include zebra limestone, i.e., the more or less regular intercalation of microbial carbonate and cement. Elevated concentrations of magnesium in the microbialite as compared to the surrounding metazoan (stromatoporoid-coral) reef limestone suggests that the microbialite of the Elbingerode Reef Complex was initially rich in high-magnesium calcite, which would be yet another parallel to modern, cryptic coral reef microbial carbonates. Deposition and accretion of the microbialite largely occurred in oxygenated seawater with suboxic episodes as indicated by the trace element (REE + Y) data.

Chemotrophy-based phosphatic microstromatolites from the Mississippian at Drewer, Rhenish Massif, Germany

“…Many Frutexites have been interpreted as stromatolites dwelling in deep-water or cryptic habitats that show no preferred phototactic growth direction (Böhm & Brachert, 1993; Gischler et al . 2021). Although the morphology and size of the Drewer microstromatolites are similar to reported Frutexites , the lack of iron oxides in the samples and the formation environment of the concretions argues against this interpretation (cf.…”

Identification and current palaeobiological understanding of “Keratosa”-type non-spicular demosponge fossils in carbonates: with a new example from the lowermost Triassic, Armenia

“…Although occurrence data of "Keratosa"-type sponge fossils in carbonates are accumulating [3], most studies either only briefly mention the existence of these fossils or focus on their palaeoecological roles (e.g., [7,10,11,55]). The basic understanding of the diversity, taxonomy, and evolution of these fossil organisms has not yet been established.…”

Contrasting morphology and growth habits of Frutexites in Late Devonian reef complexes of the Canning Basin, northwestern Australia

“…The uncertainties related to this problematic microfossil Frutexites are reflected in the variety of terms used to describe its morphology and interpretations of its origin/s. Currently ‘ Frutexites ’ serves as an umbrella term for a range of dendritic features enriched in Fe and Mn including dendritic microfossil (Maslov, 1960; Rodríguez‐Martínez, Heim, Simon, et al., 2011), shrubs (Playford et al., 1976), arborescent Frutexites ‐like microstructure (Guido et al., 2016), dendritic ‘ Frutexites microstructure’ (Awramik & Grey, 2020) and bushy digitate calcimicrobe (Gischler et al., 2021). Other synonyms used are Frutexites crusts, Frutexites ‐like forms, haematitic/ferruginous/iron digitate/pillar‐shaped Frutexites microstromatolites, colloform limonitic crusts and iron dendritic aggregates (Rodríguez‐Martínez, Heim, Quéric, & Reitner, 2011; and references therein).…”