Changes in fossil assemblage in sediment cores from Mingulay Reef Complex (NE Atlantic): Implications for coral reef build-up

• Published in: Deep-sea research. Part 2. Topical studies in oceanography 2014-01, Vol.99, p.286-296
• Main Authors: Douarin, Mélanie, Sinclair, Daniel J., Elliot, Mary, Henry, Lea-Anne, Long, David, Mitchison, Freya, Roberts, J. Murray
• Format: Article
• Language: English
• Subjects: Accumulation; Biodiversity; Cold-water coral reef build-up; Computer aided tomography; Coral reefs; CT scan; Density; Earth sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Fossils; Lophelia; Lophelia pertusa; Marine and continental quaternary; Marine geology; Mathematical models; Physics of the oceans; Reefs; Scleractinia; Sediments; Surficial geology
• ISSN: 0967-0645; 1879-0100
• DOI: 10.1016/j.dsr2.2013.07.022

CT scanning and descriptions of sedimentary sequences have been conducted to describe the internal structure and define the evolutionary sequence of events leading to the build-up of cold-water coral reef constructed by the azooxanthellate scleractinian Lophelia pertusa. Two vibrocores containing coral clasts and associated fauna embedded in a matrix of marine sediment were taken at the Mingulay Reef Complex, an inshore (~120–190m water depth) L. pertusa reef off western Scotland. The cores were scanned using computed x-ray tomography (CT scan) with the aim of (1) reconstructing and quantifying the relative abundance and preservation of coral fragments in the cores, (2) identifying distinct reef facies, and hence (3) providing data that could lead to a conceptual model of reef growth. U-series dates were obtained on L. pertusa clasts from the two sediment cores to provide a temporal framework of the reef build-up. After exploring a range of methods for processing CT scans, three simple parameters were used to classify different strata within the cores: the overall density of the cores, the number of fossil clasts, and the sum of the area of clasts detected by the CT scan. These parameters were validated by comparing with density measurements from a multi-sensor core logger (MSCL) and physical dissection and analysis of fossils in the cores. From the CT scan analyses, three distinct reef facies were evident: Coral-Rich, Sediment-Rich and Shelly-Coral Hash Layers. The succession and rapid cycle of reef framework-forming L. pertusa development, disturbance and recovery allow us to provide a model of cold-water coral reef build-up including shifts in biodiversity, physical/chemical/biological processes and the sedimentary regime.