During February and March of 2015, Jamie Gleason (Associate Research Scientist) participated as a shipboard inorganic geochemist on Expedition 354 of the International Ocean Discovery Program (IODP), which drilled a 7-site E-W transect at ~8°N across the Bay of Bengal (northern Indian Ocean). The goals of the 8-week cruise (Singapore to Colombo, Sri Lanka) were to 1) recover a long-term record of submarine fan sedimentation from the middle Bengal Fan, and 2) capture details of the erosional, uplift and weathering history of the evolving Himalayan Orogen and its impact on global and monsoonal climate. 17 years in the making, Expedition 354 focused on answering several related and long-standing questions regarding 1) long-term carbon storage in tectonically active remnant ocean basins, 2) models for submarine fan migration, evolution, and hydrocarbon potential, 3) tectonic uplift history of the Himalayas and timing of India-Asia collision, and 4) Late Cenozoic interplay between mountain building and the Indian monsoon cycle. The scientific goals of Expedition 354 were designed to overlap with those of Expedition 353 (Indian Monsoon) and the recently concluded Expedition 355 (Arabian Sea), maximizing the scientific payoff of these time- and cost-intensive expeditions [http://iodp.tamu.edu/scienceops/expeditions/bengal_fan.html].
The drill ship used for Expedition 354 was the JOIDES Resolution (“JR” for short), which is leased to the US National Science Foundation and IODP for scientific investigation and sample return from the world’s ocean basins [click here for video with sound: https://www.youtube.com/watch?v=pJ_9Vnc0y8c]. Science operations are coordinated through Texas A&M University, which provides the onshore and offshore technical staff and instrumentation to carry out a wide variety of scientific research aboard the JR. Altogether, the ship accommodates over 100 people, with about half being the ship’s crew (including drillers, engineers etc.). Technical staff and scientists make up the remainder, with 34 scientists from 14 different countries participating in Expedition 354.
Preliminary research results generated by Expedition 354 have already been published online [http://publications.iodp.org/preliminary_report/354/], even as the on-shore phase of research is just getting underway. Several major findings and surprises were revealed during the course of describing the nearly 1.7 km of core recovered by Expedition 354. These findings are being presented at a host of upcoming international meetings including Goldschmidt (Prague, Czech Republic) and Fall AGU (San Francisco, CA), and include the discovery of 1) an unexpected hiatus in mid-Pleistocene, mid-fan turbidite sedimentation, 2) evidence for high rates of organic carbon burial in the Neogene, 3) downhole termination of fan deposits in the deepest hole drilled, and 4) well-preserved Pleistocene tephra layers from several Toba (Sumatra) ultraplinian volcanic eruptions.
Depth to seafloor in this environment averaged 3.6 kilometers, and the deepest hole we drilled reached 1.2 km below seafloor. Recovery of sediments proved to be a significant challenge, as the loosely consolidated turbidite sands were exceptionally resistant to recovery by conventional drilling and advanced piston coring (APC) operations normally employed on the JR. The solution was to employ a half-length APC (4.5 meter long core barrel) combining drilling without recovery every ~10 meters, a strategy which yielded superior recovery without losing significant drilling time. Primary sedimentary features were beautifully captured this way, an important key to the success of the expedition. Additional strategies were employed on the rig floor/catwalk area to capture loosely consolidated sands from spilling out of the core barrels (especially during our frequent encounters with buried, sand-rich channel deposits).Gleason’s IODP-supported post-cruise research will be conducted with colleagues at the University of Arizona’s LaserChron Center (ALC) in Tucson, focusing on provenance of the heavy mineral fraction in turbidite sands of Neogene age. Following separation of thousands of individual detrital zircon grains, we will subject them to laser age-dating (U-Pb geochronology) using the mass spectrometers housed in the ALC NSF-supported facility. Our goal is to assemble a record of Himalayan uplift using a variety of provenance tools including zircon single grain U-Pb geochronology, Hf isotope geochemistry and fission track thermochronology, single grain muscovite Ar-Ar thermochronology, and a host of other provenance techniques that will, through our collaborations, utilize nearly all mineral fractions (e.g., quartz, apatite, feldspar, clays and oxides, as well as a complex suite of metamorphic minerals). When the standard 1-year, post-cruise moratorium placed on sample access is lifted, scientists from any institution will be allowed full access to the rich inventory of sediment cores recovered by IODP Expedition 354.