Weekly Report 9 -- Sunday, 13 February 2011
Location
OPERATIONS
After Hole U1377A on Hadar Guyot (Prospectus Site LOUI-4B) needed to be abandoned the vessel was slightly offset and Hole 1377B was spudded on 6 February. Rotary coring advanced the hole to a final depth of 37.0 mbsf with an average recovery of 39% when time on site expired. After the drillstring was recovered, and the beacon retrieved, the vessel departed Site U1377 for Auckland at 0730 hr on 8 February. The time on Hole U1377B was 57.5 hours and the total time on site was 70.0 hours (2.9 days). Because of concerns of heavy wind and rough seas on the transit to Auckland, the vessel departed the location approximately 18 hours earlier than originally planned. Despite experiencing strong headwinds during the first half of the voyage (resulting in a drop of transit speed to ~9 knots) the vessel arrived in Auckland on 11 February about 12 hours earlier then originally planned. With the first line ashore at 17:09 Expedition 330 has ended. In total 1114 m of sediment and igneous basement were cored at 8 holes at 6 sites located on 5 different seamounts and 806 m of core was recovered corresponding to 72% recovery.
SCIENCE RESULTS
During the last week of Expedition 330 we finished coring operations on Hadar Guyot and started our transit to Auckland. All lab groups were busy with describing and analyzing the last cores and samples from Site U1377, preparing site reports and clearing their lab and working spaces.
The Sedimentology lab group finished the stratigraphic characterization of Site U1377. Although their observations were limited by a very poor recovery, the material obtained in Holes U1377A and U1377B defines a consistent sedimentary pattern on top of Hadar Guyot. Two units were recognized based on macroscopic and microscopic observations of the sediment. Unit I represents the uppermost sediment of Hadar Guyot and was recovered at Holes U1377A and B. The sediment is composed of a nannofossil foraminiferal ooze, which strongly resembles the soft sediment recovered in the uppermost part of Sites U1372 on Canopus Guyot, U1374 on Rigil Guyot, and U1375 on Achernar Guyot, and is considered to reflect recent pelagic sedimentation on top of the drilled seamount. Examinations by the Paleontology lab groups reveal that the ooze contains a mixed assemblage of calcareous nannofossils and planktonic foraminifers indicating an early Pliocene to Holocene age. Unit II corresponds to few cuttings recovered in Section 330-U1377A-3R-CC, and ten small-sized (<20 cm-thick) pieces recovered by drilling of in situ sediment (Holes U1377A and B). Unit II includes: (1) a middle-late Eocene foraminiferal limestone with abundant planktonic foraminifers, a few ferromanganese encrustations, and rare shallow-marine bioclasts (e.g. echinoderm fragments); and (2) a latest Paleocene-early Eocene, heterolithic multicolor basalt conglomerate with a few ferromanganese encrustations. The matrix of the conglomerate is composed of foraminiferal limestone with abundant plantkonic foraminifers and a few shallow-marine fossils (e.g. echinoderm fragments, larger foraminifera, shell fragments, and gastropod). Preliminary age assignments of the foraminifer content of the limestone (based on thin section observations) range from middle to late Eocene for Hole U1377A and late Paleocene-early Eocene for Hole U1377B. The faunal assemblages and sedimentary textures indicate that Unit II at Site U1377 represents a (or several) condensed section(s) likely to have deposited in a shallow-marine to hemipelagic-pelagic environment on top of Hadar Guyot.
Below the sedimentary Units I and II, Hole U1377B entered the igneous basement at 9.1 mbsf and cored a total of 27.9 m of igneous rocks that were first described by the Igneous Petrology lab group. The upper part of the succession consists of a single, 10.1 m thick unit of flow-banded trachybasalt similar to that in Hole U1377A, whereas the lower part consists of 17 small (up to 2.1 m thick) trachybasalt units with curved and glassy margins. These suggest that this lower part of the succession is composed of pillow lava or small lobate flows erupted in a submarine environment. The upper 3.8 m interval of this lower group contains small amounts of olivine, plagioclase and augite phenocrysts, sometimes in glomerophyric clusters, while the lower part is aphyric. A curious feature of this interval is that, in several instances, the inter-pillow space is filled with glass that connects with the more massive interior of the unit below. It appears that lava in the still-molten interior of a pillow has broken out as a protrusion that filled the space between overlying pillows. Alternatively, magma may have been injected into a stack of pillows, but the similarity in appearance between injected and pillow trachybasalt suggests that, in either case, both were part of the same eruptive event. The strong flow banding seen in both holes suggests that the rocks recovered at Site U1377 are generally alkalic and have probably the most evolved composition of all the rocks drilled during Expedition 330.
The Structural Geology lab group found a single geopetal structure in rocks from Hole 1377B indicating that this part of Hadar seamount experienced no tilting after deposition. Veins, vein networks, and vesicle bands are present in both holes, while chilled contacts were only observed in Hole U1377B. Vesicle bands in Hole U1377A have either moderate or sub-horizontal dips. Vesicle bands and chilled contacts in Hole U1377B are moderate to steep, with dips ranging from 45 to 90º. In Hole U1377B glass occurs on chilled pillow margins, along the edge of a small intrusion, and in the matrix of a breccia. These last two glass occurrences indicate forceful intrusion and rapid cooling of new magma into already solidified rocks.
The Geochemistry lab group completed data reduction and interpretation for the 15 igneous samples analyzed last Sunday by ICP-AES. Due to time constraints at the end of this expedition only a single sample could be analyzed from Site U1377. Its basaltic trachyandesitic composition confirms the evolved nature of the volcanic rocks drilled at this site. No samples were collected or analyzed for determination of carbonate, organic carbon, or organic nitrogen content during this week.
As done at the previous sites, all archive half-cores from Holes U1377A and U1377B were measured and alternate-field (AF) demagnetized using the cryogenic magnetometer, and principal component directions have been automatically picked. In addition, 10 discrete samples from Hole U1377A have been AF or thermally demagnetized, but only natural remanent magnetizations were obtained for seven samples from Hole U1377B due to a malfunction of the AF demagnetizer. Both the archive half-core and discrete sample remanent magnetizations in Hole U1377A provided generally consistent, moderate to steep positive inclinations, reflecting southern hemisphere reversed polarity. The archive half-cores of Hole U1377B also yielded reversed polarity remanent magnetizations.
The Physical Properties group finished running tests on whole-core and discrete samples from Holes U1377A and U1377B this week. Whole-round and split-half measurements were completed for all sections from Hole U1377-B, as was natural gamma ray radiation testing. The last group of discrete samples was chosen from Hole U1376B (through Core U1376B-5R-3) in collaboration with the Paleomagnetism group. The entire set of paleomagnetic, compressional wave velocity, and moisture and density measurements have been completed for all samples from Site U1377B. The Physical Properties group spent the remainder of the expedition preparing the data filtering program for future expedition use.
The Downhole Logging team gave their U1376 site presentation this week and has been working on corrections to site reports for Sites U1374 and U1376. Additionally, post-logging tests have been performed on the GBM with the main wireline.
One final sample was taken by the Microbiology lab group from Core 330-U1377B-4R and processed for cell counts, molecular biology and in situ stable isotopes. In addition, 18 incubations were started with nine media targeting growth of sulfur oxidizers, iron cycling microbes and general heterotrophs. A stable isotope addition bioassay was also initiated for studying growth rates of subsurface microbes of Hadar Guyot. Sampling of previously initiated stable isotope addition bioassays from Sites U1373 to U1376 continued as the ship transited back to Auckland and the microbiology lab was cleaned and samples prepared for shipment.
EDUCATION AND OUTREACH
Both the education officer and the videographer continued blogging and conducting video broadcasts during the last week of this expedition. Over the course of the expedition, the education officer has posted photos, links and status reports daily, as well as a weekly trivia contest, to the JR facebook page. During this time, the facebook page has had 746,979 post views and gained 139 fans. He has also maintained the Expedition 330 outreach content on the joidesresolution.org website, including posting 37 blog posts using three different blog accounts, JR junior (for kids age 8-12), Educator Ideas (for classroom teachers and informal educators) and Kevin Kurtz (for high school students and adults). The JR website has had over 10,339 visits during the course of the expedition with 4,943 new visitors. He also coordinated and facilitated, with the help of videographer and the expedition scientists, 27 successful webcasts with schools and museums. Fifteen of the scientists in the science party participated in question and answer periods. Just over 1000 children and adults participated in the live webcasts, and one school recorded the webcast to show to the rest of their students, adding 750 viewers to the total. The videographer finished recording and editing her last videos “Leavin’ Louisville” and an official Exp 330 wrap up video.
TECHNICAL SUPPORT AND H&S ACTIVITES
Technical staff engaged in providing full support for coring operations on Site U1377 and end of expedition activities.
Other support technical activities:
- Minor software upgrades to various applications continues.
- Deployed magnetometer for the transit into Auckland.
- Prepared labs for STP visit.
No HSE incidents to report.
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