Lord Howe Rise
Geoscience Australia and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) are undertaking collaborative research to better understand the geology of the central Lord Howe Rise (Figure 1).
The Lord Howe Rise (LHR) is an elongate ribbon of submerged and extended continental crust that separated from Australia during the Late Cretaceous (~74-52 million years ago). Present knowledge of the LHR geology is based on widely-distributed marine and satellite geophysical data, limited dredge samples, and sparse shallow (<600m below-sea floor) drilling into Cenozoic pelagic sediments.
Existing data provide a broad understanding of the LHR's crustal structure and sedimentary basin architecture. However, building more detailed knowledge of the LHR geology, and the geological evolution of the southwest Pacific more broadly, requires drilling into rocks that record the >100-million-year geological, tectonic and climatic history of the region. To this end, Geoscience Australia and JAMSTEC are leading an international effort to drill a deep stratigraphic hole on the LHR that will core Cretaceous and older (>65 million years) sediments and basement rocks.
A proposal for drilling up to 3500m below the sea floor into a LHR rift basin using the JAMSTEC drilling vessel CHIKYU was submitted to the International Ocean Discovery Program (IODP) in October 2015. After international peer review, the IODP proposal was rated "excellent" by the IODP Science Evaluation Panel in January 2017 and forwarded to the Chikyu IODP Board for approval and implementation.
The IODP deep stratigraphic drilling is supported by a program of data acquisition to define the geological framework of the proposed drill site(s) and to acquire the geotechnical data necessary to successfully drill a deep stratigraphic hole.
The objectives of the IODP deep stratigraphic drilling are to: 1) define the role and importance of continental crustal ribbons, like the LHR, in plate tectonic cycles and continental evolution; 2) recover new high-latitude data in the southwest Pacific to better constrain Cretaceous palaeoclimate and linked changes in ocean biogeochemistry; and 3) test fundamental evolutionary concepts for sub-sea floor microbial life over a 100-million-year timeframe. These objectives are aligned with the IODP 2013-2023 Science Plan. In addition, the drilling will enable assessments of the regional resource potential of the LHR by contributing samples and data from its sedimentary basins.
A summary of the IODP proposal is available for download [PDF 59 KB].
The Project commenced on 1 July 2015 and, if fully funded, will run for up to five years. The project includes four main activities, two of which, the pre-drilling surveys, are in progress.
1. Deep Seismic Survey for Crustal Structure and Tectonic Framework (March-May 2016)
JAMSTEC and Geoscience Australia, together with participants from the University of Sydney and GNS Science (New Zealand), successfully completed the first of two pre-drilling site surveys on 11 May 2016. This seven-week survey acquired 2D seismic reflection data and seismic refraction data, recorded by 100 ocean-bottom seismometers, along an east-west transect across the LHR to map regional crustal structure (Figure 1).
Additional data acquired during the survey includes ~600 line km of high-resolution multi-channel seismic over the proposed drill sites (Figure 2), multibeam sonar bathymetry, sub-bottom profiles, gravity and magnetics. A report on the Deep Seismic Survey is available for download from the JAMSTEC website.
2. Detailed Site Survey at Proposed Riser Drilling Site (November - December 2017)
The Detailed Site Survey will involve high-resolution seabed and shallow sub-sea floor mapping, collection of shallow (<60 m below-sea floor) sediment cores and underwater video at the site(s) being considered for drilling. The information from this detailed mapping and sampling will be used to understand the geotechnical properties of the seabed affecting drilling operations. These data will also contribute valuable baseline environmental information describing deep-water habitats in a remote area of Australia's maritime jurisdiction.
3. Deep Stratigraphic Drilling (possibly 2019 or 2020)
If funded, the proposed Deep Stratigraphic Drilling program will include a single deep hole designed to intersect the full stratigraphic succession in a LHR rift basin (Figure 2). A second priority is to drill one or two shallow holes into basement horst blocks. Drilling will incorporate full core recovery and extensive down-hole logging.
4. Processing and Storage of Data and Samples
All data and samples collected during the project will be made publicly available. Survey data will be available from Geoscience Australia and JAMSTEC, while core samples will be accessible from the IODP. The archival portion of the cores will be located at Geoscience Australia.