Facies architecture, palaeoecology and biotic spatial self-organization of a Devonian, sediment-impacted carpet reef

• Applicant: Professor Dr. Adrian Immenhauser
• Subject Area: Palaeontology
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449929798

The Middle and Late Devonian time interval witnessed the perhaps largest Palaeozoic expansion of epeiric platform carbonates. Here, we present an exceptionally exposed Devonian reefal biostrome in the Klutert Cave, Western Germany. We argue that this cave represents a compelling test case to investigate the facies architecture, palaeoecology and biotic spatial self-organization of a Givetian (387-382 Ma) sediment-impacted reef. The Klutert Cave is intriguing for several reasons: (i) the reefal body is stratigraphically thin (<12.3 metres) and qualifies as a ‘carpet-reef’, not unlike many Holocene reefs. The reef is intercalated between clastic units and its core and flanks are exposed laterally for about 450 x 200 m within the cave. The extremities of the reef flanks pinch out in road cuts in the vicinity of the cave. (ii) The reef is extremely well-exposed both laterally as well as stratigraphically. The recently-cleaned cave walls provide access to 26,000 m2 of continuous rock surfaces exposing the base, core, flanks and top of the reefal body in exquisite detail. (iii) The host matrix sediment indicates significant clastic input (turbidity) onto the shelf during the comparably short interval of reef growth. Based on detailed facies maps of cave walls, we intend to numerically test these outcrops for the hallmarks of intrinsic biotic self-organization arising out of the interaction between consumers (here stromatoporoids, tabulate and rugose corals) and their resources (nutrients, illumination, space etc.). This is particularly interesting, as upsection increasing levels of sediment influx along with sea-level change can be placed within the context of patterns in biotic self-organization during reef initiation, acme and demise. We will further test the work hypothesis that self-organization processes allow for a comparison between Devonian and Holocene biostromal successions from marginal locations, such as the Persian/Arabian Gulf, where reef systems develop with a relatively low faunal diversity. The analysis of the clay mineral spectrum and provenance of fine-grained clastic material in the matrix will shed light on sediment influx. An important component of this project is a detailed taxonomic framework of reefal biota, providing evidence on biotic diversity in a sediment-stressed environment. We will compare and contrast biotic (calcite) archives (corals, stromatoporoids, brachiopods) for the response of their ultrastructure and geochemical properties exposed to diagenetic alteration. By this we intend to provide benchmarks for proxy data in Devonian palaeoenvironmental research. We have deliberately chosen to focus on one study area and will work in great spatial resolution. It is, at present, unclear to what degree this carpet reef is exceptional or, alternatively, serves as a benchmark against which other coeval (generally, sediment-impacted carpet-reefs) reefs can be compared. Research presented here aims to answer these questions.

• DFG Programme: Research Grants
• International Connection: France, United Kingdom, USA
• Cooperation Partners: Professor Dr. Markus Aretz; Professor Dr. Stephen W. Lokier; Professor Dr. Samuel Purkis