Charles Darwin, extending the already sophisticated ideas of
Lyell, became the first person to arrive at a modern
understanding of atoll formation. Darwin reasoned that
atolls developed from slowly subsiding coral reef-fringed
volcanic islands; but he could not understand why large
areas of the western Pacific appeared to have a history of
subsidence. Knowledge of hot spots and seafloor spreading
along mid-oceanic ridges had not then dawned.
Leg 144 of the Ocean Drilling Program (ODP) began with the
JOIDES Resolution sailing from Majuro in the southern
Marshall Islands in late May (right). By August it had completed
two months drilling on atolls and guyots in the western Pacific:
its mission, essentially, to refine Darwin's synthesis by deep-sea
drilling.
This was my second cruise as a palynologist on the JOIDES
Resolution. Having served on Leg 105 Baffin Bay and
the Labrador Sea back in 1985 I was surprised how little
the ship had aged despite its rigorous schedule.
Of course, many improvements have been introduced over the years.
The most notable of these is the computer system. No longer
bound to the centralized VAX, we could write all our reports
and do publication-ready diagrams entirely on PCs and Macs
and these are all linked together by an intuitive network system.
Many of the more automated measuring devices (e.g., down-hole
logging and physical properties) are now also driven by Macs.
The Paleontology Lab has been enlarged by ditching the SEM and
merging two rooms. Modifications to one of the fume hoods now
means that HF digestion can be done easily. Nevertheless, with
cores coming up sometimes at a rate of one an hour (right),
standard processing becomes reduced to HCl, swirling in a
watch glass, sieving, glycerin jelly slide-making, and hoping
there won't be too many diatoms to dilute the dinoflagellates
(there weren't).
Very few atolls or guyots have actually been drilled.
Most of what we know about their geologic histories comes
from seismic stratigraphy and dredging. Leg 144 targeted a
series of drowned atolls along a north-south transect extending
from the Marshall Islands on the equator to Seiko Guyot off Japan.
All the guyots we drilled began life in the southern hemisphere
before drifting northwards so an important aim was to recover
basement basalt for age and paleo latitude determinations.
Other major objectives were to assess the nature of carbonate
platform development on the subsiding volcanic edifice and to
date final drowning of the platform. Pelagic sediments capping
the drowned guyots were of interest because, being above the
water depth at which carbonates substantially dissolve, the
contained nannofossils and foraminifers survive as a unique
bio- and isotope record of surface water carbonate production
in the remote western Pacific.
Drilling gave us some surprises. True reef facies are much less
common than we had anticipated. Platform carbonates were unexpectedly
difficult to core and we averaged well below 10% recovery.
The pelagic caps were also difficult to core because the sediments
turned soupy and had a tendency to slosh around in the core-liners
on deck until a piglet (far right) was designed to curtail this misbehaviour.
It was also found that stacking the cut sections of coreliner
vertically before moving them into the corelab helped to compact
the sediments and reduce disturbance during splitting (right).
Unfortunately, the pelagic sediments are mainly winnowed foraminifer
sands and we now know that guyot tops have been persistently swept
by intermediate-depth water currents during much of the late Cenozoic.
From a palynological point of view there were some exciting
discoveries including Neogene and early Quaternary dinoflagellates
in some of the less winnowed pelagic caps, and Cretaceous dinoflagellates
from dark platform limestones on one of the guyots. At several sites,
spores and pollen were recovered in paleosols (right) sandwiched
between weathered basalts and the overlying carbonate platform.
These spore-pollen assemblages provide a fascinating glimpse into
the Cretaceous vegetation of these volcanic islands. Visual
kerogen and palynofacies studies proved to be helpful for
interpreting nearly all sedimentary intervals but results
became especially critical when the temperamental Rockeval
machine (used for geochemical typing of organic matter) blew
its CPU early in the cruise.
Of course, Leg 144 wasn't all work. July 4th was celebrated
by a home-made kite flying contest on the helideck. Prizes
were awarded for various categories including the "and they
thought it would never fly" category which was won by the
Euro-air-sausage, coaxed into the air by Peter Hobbs of the
British Geological Survey (right). We celebrated Bastille Day
by having an extravagant ball in the science lounge. The
birthday of Isabella Premoli-Silva, one of our two co-chiefs,
was marked by an elegant served dinner in the galley: everyone,
of course, dressed to the nines. In fact the food was pretty
good throughout the cruise and the atmosphere extremely congenial
despite frustrations over low core recovery.
The cruise ended in Yokohama, Japan, where various officials
presented the captain and co-chiefs Isabella Premoli-Silva
(Universite de Milano) and Janet Haggerty (University of Tulsa)
with bouquets and mementos of the portcall (left).
Co-chiefs Isabella and Janet gained everyone's respect with their
enthusiasm and gentle leadership. Staff scientist Frank Rack did a
tremendous job in keeping all our reports within ODP's stringent
editorial guidelines. It is finally just worth noting that despite
low recovery, enough sedimentary rock was found to break the ODP
record for thin-sections made on ship: about 500 slides in total!
In fact a very large collection of data was assembled on ship, and a new synthesis concerning atoll and guyot evolution has begun to emerge from this and follow-up shore-based activities. An official overview of ODP Leg 144 drilling, authored by the shipboard party, is soon to be published in Nature,
Geotimes, and EOS.
Martin J. Head, ODP Leg 144 Shipboard Palynologist, Department
of Geology, University of Toronto, Toronto, Ontario, M5S 3B1.
*Present address: Department of Earth Sciences, Brock University, St. Catharines, Ontario
(Martin's travel expenses were covered by a grant from
the Canadian Petroleum Association).
This article first appeared in CAP Newsletter 15(2):12-15, 1992.
