Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.

Through the interplay of a stabilising cold-water coral framework and a dynamic sedimentary environment, cold-water coral carbonate mounds create distinctive centres of bio-geological accumulation in often complex (continental margin) settings. The IODP Expedition 307 drilling of the Challenger Mound (eastern Porcupine Seabight; NE Atlantic) not only retrieved the first complete developmental history of a coral carbonate mound, it also exposed a unique, Early-Pleistocene sedimentary sequence of exceptional resolution along the mid-latitudinal NE Atlantic margin.In this study, a comprehensive assessment of the Challenger Mound as an archive of Quaternary palaeo-environmental change and long-term coral carbonate mound development is presented. New and existing environmental proxy records, including clay mineralogy, planktonic foraminifer and calcareous nannofossil biostratigraphy and assemblage counts, planktonic foraminifer oxygen isotopes and siliciclastic particle-size, are thereby discussed within a refined chronostratigraphic and climatic context.Overall, the development of the Challenger Mound shows a strong affinity to the Plio-Pleistocene evolution of the Northern Hemisphere climate system, albeit not being completely in phase with it. The two major oceanographic and climatic transitions of the Plio-Pleistocene the Late Pliocene/Early Pleistocene intensification of continental ice-sheet development and the mid-Pleistocene transition to the more extremely variable and more extensively glaciated late Quaternary mark two major thresholds in Challenger Mound development: its Late Pliocene (>2.74 Ma) origin and its Middle Late Pleistocene to recent decline. Distinct surface-water perturbations (i.e. water-mass/polar front migrations, productivity changes, melt-water pulses) are identified throughout the sequence, which can be linked to the intensity and extent of ice development on the nearby British Irish Isles since the earliest Pleistocene. Glaciation-induced shifts in surface-water primary productivity are thereby proposed to fundamentally control cold-water coral growth, which in turn influences on-mound sediment accumulation and, hence, coral carbonate mound development throughout the Pleistocene. As local factors, such as proximal ice-sheet dynamics and on-mound changes in cold-water coral density, significantly affected the development of the Challenger Mound, they can potentially explain the nature of its palaeo-record and its offsets with the periodicities of global climate variability. On the other hand, owing to this unique setting, a regionally exceptional, high-resolution palaeo-record of Early Pleistocene (ca 2.6 to 2.1 Ma) environmental change (including early British Irish ice-sheet development), broadly in phase with the 41 ka-paced global climate system, is preserved in the lower Challenger Mound. All in all, the Challenger Mound record highlights the wider relevance of coral carbonate mound archives and their potential to capture unique records from dynamic (continental margin) environments. (C) 2013 Elsevier Ltd. All rights reserved.

During IODP Expedition 307, the first (and so far only) complete sequence through a cold-water coral carbonate mound was successfully drilled. After decades of research on contemporary to sub-recent coral carbonate mound environments, the complete recovery of the Challenger Mound record, sampling one of the large mounds along the Irish sector of the NE Atlantic continental margin (eastern Porcupine Seabight; Belgica mound province), allowed for the first time the investigation of long-term mound development, from mound initiation to decline. Here, we present an overview of the palaeo-environmental (i.e. hydrodynamic, oceanographic and climatic) signal captured in the entire Challenger Mound sequence (Hole U1317E). A high-resolution multi-proxy characterisation of the ca. 155m long mound matrix sediment record was conducted, encompassing a wide array of sedimentological, mineralogical, geochemical and stratigraphic techniques. These included, amongst others, siliciclastic particle-size analysis, X-ray diffraction phase quantification, isotopic fingerprinting of target elements for provenance purposes, calcareous nannofossil and planktonic foraminifer biostratigraphy and assemblage counts. In this way we aimed to (1) identify the controls on Challenger Mound development throughout the different phases of its entire Plio-Pleistocene to recent build-up, and (2) assess the unique character of coral carbonate mounds as recorders of Quaternary palaeo-environmental change at intermediate water depth in the NE Atlantic. Overall, Challenger Mound development shows a strong affinity to the general climate variability of the Northern Hemisphere, although not being completely in phase with it. The major oceanographic and climatic rearrangements of the Plio-Pleistocene, such as those associated with the Late Pliocene/Early Pleistocene intensification of continental ice-sheet development (ca. 2.75 – 2.55 Ma)1 or the orbital frequency changes during the mid-Pleistocene climate transition (ca. 1.2 – 0.6 Ma)2, seem responsible for the two significant thresholds in Challenger Mound development: its Late Pliocene origin and its Middle-Late Pleistocene to recent decline. However, local influences such as proximal (British-Irish) ice-sheet dynamics and on-mound changes in cold-water coral density seem to have a stronger control on Challenger Mound development and may have induced the offset between global climate and Challenger Mound proxy record variability. On the other hand, owing to this, a unique, high-resolution palaeo-record of regional Early-Pleistocene environmental change (including early British-Irish ice-sheet development3) is preserved in the lower Challenger Mound, covering a period that is not recorded in the general sedimentary sequence of the area. The Challenger Mound record, albeit with restricted Late Quaternary preservation, highlights the potential of coral carbonate mounds as excellent palaeo-recorders, providing us with unique records from ‘complex’ continental margin environments.

Sr isotope stratigraphy provides a new age model for the first complete section drilled through a deep-water coral mound. The 155-m-long section from Challenger Mound in the Porcupine Seabight, southwest of Ireland, is on Miocene siliciclastics and consists entirely of sediments beating well-preserved cold-water coral Lophelia pertusa. The Sr-87/Sr-86 values of 28 coral specimens from the mound show an upward-increasing trend, correspond to ages from 2.6 to 0.5 Ma, and identify a significant hiatus from ca. 1.7 to 1.0 Ma at 23.6 m below seafloor. The age of the basal mound sediments coincides with the intensification of Northern Hemisphere glaciations that set up the modern stratification of the northeast Atlantic and enabled coral growth. Mound growth persisted throughout glacial-interglacial fluctuations, reached a maximum rate (24 cm/k.y.) ca. 2.0 Ma, and ceased at 1.7 Ma. Unlike other buried mounds in Porcupine Seabight, Challenger Mound was only partly covered during its growth interruption, and growth restarted ca. 1.0 Ma.

The discovery of mounds and reefs hosting cold‐water coral ecosystems along the northeastern Atlantic continental margins has propelled a vigorous effort over the past decade to study the distribution of the mounds, surface sediments, the ecosystems they host, and their environments [Hovland et al., 1994; Freiwald and Roberts, 2005].This effort has involved swath bathymetry, remotely operated vehicle deployments, shallow coring, and seismic surveys.Global coverage is difficult to gauge, but studies indicate that cold‐water corals may cover as large an area as the better known warm‐water corals that form shallow reefs (284,300 square kilometers) [Freiwald et al., 2005]. Cold‐water corals occur in a variety of forms and settings, from small isolated colonies or patch reefs to giant mound structures such as those found west of Ireland.

Challenger Mound, a putative carbonate mound structure covered with dead deepwater coral rubble and located in Porcupine Seabight on the southwest Irish continental margin, was the focal point of twelve days of scientific drilling aboard the JOIDES Resolution during Integrated Ocean Drilling Program Expedition 307.Specific drilling objectives included the following:1. Establish whether the mound base rested on a carbonate hardground of microbial origin and whether past geofluid migration events acted as a prime trigger for mound genesis.