SMS On-Ice Report #2 - Oct. 28, 2007

October 28, 2007
Drill Site from Helo
Helicopter view of the ANDRILL drilling rig and science laboratories with the Transantarctic Mountains in the distance. Under the white tent is the drilling rig tower and rig floor, where all rig operations take place (photo: H. Godfrey).

 

The first phase of ANDRILL sediment coring is proceeding very well and the sea-riser has been successfully and firmly anchored into the sea-floor. The sea-riser is a long tube which allows for drilling fluids to be circulated from the drill rig down to the drilling bit, which is cutting through the sedimentary rocks. The current depth of penetration is about 229 meters below the sea floor.


Different sizes of PQ, HQ and NQ size drill bits
used by the ANDRILL system. The size of
the core produced by these bits decreases from
83 mm diamter (PQ) to only about 45 mm (NQ)
(photo: F. Florindo).

The drilling rig operates from the floating sea-ice over 380 meters of the ocean. A fabric ‘skin’ covers the drill rig and maintains a relatively comfortable working environment, keeping the drilling team, the equipment, and hydraulic hoses warm. The ANDRILL drilling system uses three sizes of drilling pipe that nestle together and allow recovery of more than 1000 meters of sedimentary core. When the largest drill string reaches its depth limit, or when the drilling team needs to secure a problem within the drillhole, the largest size pipe is cemented into the hole by sending a blob of cement to the base of the hole. Then, the next smaller drilling string with a smaller drill bit (see right) is lowered through the center of the cemented pipe and drilling continues. We just finished cementing the largest drill string at the base of the hole and are re-entering the hole with a new drill bit to continue coring through the cement and into new rock layers below. The target depth to reach our science goals is more than 1000 meters below the sea floor (mbsf), so we are one-quarter of the way there! We are very confident in the ability, experience and dedication of the drilling team to reach this target depth.


Alex Pyne, ANDRILL's Drilling Science
Manager (left) and Tim Paulsen, Drillsite Science
Team Leader (right) at the drill site, marking
the orientation of a newly recovered core
interval (photo: L. Reichelt).

Sediment cores, filled with a variety of rock types and fossils, are brought to the surface in 3 or 6 meter-long core sections, each within a tube that is pulled upwards by a wire through the center of the drill string. Right now, at 229 meters core depth, it does not take much time for the next core to be pulled up to the surface, but when we are down 800 to 900 meters, it may take more than 3 hours to recover the next 6 meter core section, reload the inner core tube, and send it back down the drill string to start drilling again.

The cores we are recovering have something for every geologist on the project science team. The scientific interests of the 56 on-ice geologists, technicians, students and educators are diverse, given that the science team comprises folks who refer to themselves as sedimentologists, lithostratigraphers, biostratigtraphers, chronostratigraphers, structural geologists, geochemists, paleomagnetists, physical properties specialists, downhole loggers, petrologists, volcanologists, clastologists, micropaleontologists, macropaleontologists, palynologists, curators, and other scientists from several other geological specializations that join together to study this unique drillcore. In addition to the 7 scientists at the drillsite, 25 other people - - drillers, core technicians, engineers, camp staff, and drilling scientists - - live on site and work 12 hour shifts to recover and prepare the core, and support the drilling crew (left).

Within the upper c. 229 meters, the drilling program cored through and recovered many types of rocks from different geological settings that existed at the SMS site in the past: sands from a shallow beach, lava from a local volcanic vent, diamictite or glacial till deposited below a glacier or ice sheet, and diatomaceous sediment made from the glassy remains of one celled algae called diatoms that lived in the open ocean.

The drilling team started the PQ cementing activities on October 26 when the drill bit was at c. 229 meters below the sea floor (mbsf). Coring activities were resumed on October 28, to drill through the cement and then into the sediments below.

The recovered section is telling us a very interesting environmental story. The uppermost 37 m of the core consist of a thick mafic lava flow and volcanic sediments including pumice clasts, which indicates a complex interplay between sedimentary and local volcanic processes. The volcanic sediments and the lava flow have been sampled for radiometric dating in Ar-Ar laboratories. In addition, samples for the paleomagnetism group and palynologists (studying fossil pollen and spores) have been sent to laboratories off-ice.


Photograph of a split core section of a
diamictite, a common rock type recovered in the
SMS Project drill core. This sedimentary rock,
deposited beneath glacier ice, contains a mixture
of large and small sedimentary particles,
surrounded by a field of muddy material (photo
from SMS digital data files).

Our current age control, developed on-ice, relies on diatom biostratigraphy, which indicates a mid-Pliocene age for the cored interval at c. 47 mbsf. This is based on the presence of a thin diatom-bearing unit within a c. 60 meter-thick diamictite unit (see right).

These glacial sediments contain abundant pebbles derived from the oldest crystalline basement rocks that are most likely sourced from the Transantarctic Mountains to the west and south of the drillsite. The nature of these sediments points to a rather extended period when an ice sheet was present at or in the proximity of the drill site. Another thick diamictite is present below c.124 mbsf (and extends to c.225 mbsf), most likely indicating similar environmental conditions, but with more abundant volcanic clasts. This change provides evidence for ice flow from a different direction that brought rocks from other locations to the SMS Project drillsite. Interestingly, between deposition of the two diamictite sedimentary units, there is a period of time when a different, largely non-glacial environment led to the deposition of fine grained sediments (e.g., sandstones and granule conglomerates), most likely in a shallow marine setting, perhaps just below a beach shoreline.

This drillhole has already started to confirm its high potential to identify different environmental changes that occurred during the last 17 million years as a consequence of climatic and/or tectonic processes.

Please watch this space for future updates as we track changing environmental conditions down the drillhole and back in time. The ANDRILL drilling rig is a “time machine” that allows us to explore Antarctica’s geological past, exploring one meter at time, deeper and deeper. We expect to encounter geological evidence that will indicate changes in climate and life in Antarctica during the warmer middle Miocene Epoch, c. 14 to 17 million years ago. An outstanding team of scientists is working with us to tell this tale of Antarctica’s past. The past may guide our understanding of how this region will respond to Earth’s warmer future.

Stay tuned for more…

David Harwood and Fabio Florindo
Co-Chief Scientists

Franco Talarico
Acting on-ice Co-Chief Scientist