Postgraduate Report
UNESCO/IGCP 447 2ND INTERNATIONAL CONFERENCE ON
MOLAR-TOOTH CARBONATES AND THE EVOLUTION OF THE
EARTH IN THE PROTEROZOIC
Anne Gore
JCU, Qld
2003 AIG Postgraduate Bursary Winner
I wish to extend my gratitude to the Australian Institute of Geoscientists and their
generous sponsors for providing me with the Postgraduate Student Bursary Award for
2003. This fund contributed towards my attendance at the UNESCO/IGCP 447 2nd
International Conference on Molar-tooth Carbonates and the Evolution of the Earth in
the Proterozoic, held from 2-9th September 2003, in and around Missoula, Montana,
USA.
Being part of one of the working groups, I was able to present my latest investigations
and geochemical analyses of molar-tooth structure from the Loves Creek Member in the
Bitter Springs Formation, Central Australia. My evidence confirmed the carbonates in
the uppermost unit to be of marine origin, as well as
not having a high magnesium calcite precursor. My
attendance at this meeting, where an assemblage of
molar-tooth structure experts intensely compare and
discuss ongoing examinations, gave me a unique
opportunity to gain further knowledge and share
ideas, attain global visibility, as well as nurture old
and new contacts.
Research Summary
Molar-tooth structure is an enigmatic feature of
ancient sedimentary rocks that formed consistently
in mid to upper carbonate ramp settings between 2.6
and 0.75 billion years ago, then abruptly
disappeared.
This Precambrian structure
occasionally resembles the markings on elephants’
molar-teeth, hence the origin of the name, and is
described as ‘irregularly shaped, 5-15 microns,
microcrystalline, calcite blobs and ribbons that have
sharply defined walls against the surrounding
sediment’. The significance of molar-tooth structure
is its characteristic calcite crack fill, which has a
tendency to preserve seawater chemistry due to its
early diagenetic formation.
Until recently, little work had been done on molar-tooth structure outside of North
America, but through the IGCP Project 447 (2001-2006), it appears to be a universal
widespread occurrence, and is certainly more common in Australia than previously
thought. So far, molar-tooth structure has been described from the Bitter Springs
Formation of central Australia (Peter Southgate), Lawn Hill Platform in NW
Queensland (Peter Southgate, pers. comm.), and NW Tasmania (Clive Calver). This
project has innovatively mobilised a global network of colleagues in the collection of
samples and discussion of various analytical results, and aims to fill a major gap in our
knowledge of the Precambrian.
My PhD research into the fascinating puzzle of molar-tooth structure formation was
initiated by my supervisor Graham Shields. We are gradually building up a collection
of representative Proterozoic samples from around the world and especially Australia,
for comparative analyses. Construction of a such a detailed worldwide petrographic and
geochemical database has not previously been attempted, and will provide a unique
approach to recreating the chemical evolution of seawater and understanding the early
evolution of our planet’s surface environment.
The 2nd International Field-Conference in Missoula
This year’s field-conference hosted around twenty delegates from seven different
countries, with several anticipated representatives sadly unable to attend because of visa
difficulties. Due to the numerous forest fires in the district, investigations of outcrops
began in ‘hazy’ circumstances, and out-running the smoke across north-western
Montana became the catch-cry, with the theme for the week being “On a clear day…”.
Supposed ‘outstanding mountain views’ were constantly shrouded in smoke, so much
so, that the French contingent presumed we were on flat land! Several intended outcrop
visits had to be deleted from the itinerary due to fire closures and sighting of grizzly
bears. Even so, there were plenty of formations to be investigated and sampled, with
still never enough time to ‘crawl’ over each site.
We began the trip with a visit to the Revett Quartzite near Ravalli, moving upwards in
the geologic sequence through the Empire, Helena and Wallace Formations as we
traveled through Flathead Indian Reservation towards Kalispell. Molar-tooth structures
and stromatolites were found to be abundant in most formations, with sampling and
photographs aplenty. An accurate understanding of Belt Supergroup geology is
progressing but is still ambiguous in places, therefore various opinions were constantly
debated at each site and made interesting evening conversation. Scientific presentations
from all delegates were held throughout the week, with some interesting revelations,
and possible correlations with my own research, coming from the fields of geochemistry
and palaeogeography.
Glacier National Park was our next stomping ground, and from the views in the
postcards, the Going-to-the-Sun Road would have been an impressive sight (on a clear
day…)! Several locations were investigated along the way (some with ‘hair-raising’
pathways), from the Altyn and Appekunny Formations through to the younger Snowslip
Formation at the top of Logan Pass. Again intense discussions abounded, such as an
oolite bed being a redefined Helena-Wallace Formation boundary, but molar-tooth
structure horizons were plentiful, especially in the masonry rocks used to build the road
wall. Two nights were spent at St. Mary’s, a small town on the Blackfeet Indian
Reservation with picturesque views of the lake and low-hanging wisps of smoke
causing spectacular sunsets. A hike to Grinnel Glacier in Many Glacier Park was halted
midway due to a grizzly bear on the track, making interesting conversation, with a
redefined hike being hastily organised.
Continuing on our journey of north-western Montana, the next stop was outside of
Eureka where the Purcell Lava to younger Snowslip Member 6 stromatolites were
inspected. Further south, near Libby Dam, a large section of the Helena Formation
(~1500ft) produced numerous settings of molar-tooth structure within the dolomitic
beds. The younger Wallace Formation on the eastern side of the dam, revealed
stromatolitic units interspersed with molar-tooth structure in the lower units, and graded
upwards to thinning microlaminae cycles.
Our stay in Libby was complimented by the welcoming rain during the night, giving
relief to the firefighters and clearing the air. However, the rain curtailed our ongoing
outcrop investigations and the morning talks were abandoned due to a blackout.
Presentations were finalised in Missoula later in the day, and the conference concluded
with a late dinner and several speeches. All delegates deemed this an appropriate end to
what was an impressive (even though smoky) and highly successful 2nd international
field-conference.
Outcomes
Through attendance at this field-conference, I was able to collect numerous photos and a
quantity of Proterozoic samples from the Purcell-Belt Supergroup for my ongoing
geochemical analyses. Discussion times were especially encouraging, so much so that I
have begun to write an article on my Bitter Springs findings.
Next year, our 3rd international meeting will be a Topical Symposia (T-06.04) entitled
‘Molar-tooth structures and Precambrian carbonate facies’, and is a part of the 32nd
International Geological Congress held in Florence, Italy from August 20-28. I aim to
present further investigations, not only from Australia, but a global perspective of
molar-tooth structure analyses.
Graham Shields and myself at James Cook University, along with Peter Southgate from
Geoscience Australia in Canberra, are presently organising the 4th IGCP 447 fieldconference that will be held in Australia in 2005. Due to the vast distances between
sites, our current planning sees Alice Springs, Northern Territory as the main objective,
with daily excursions to molar-tooth structure sites within the area. Before we are
inundated by a swarm of global molar-tooth structure experts, we would like to compile
an atlas of all Australian Precambrian occurrences. We therefore invite you to drop us a
line if you know of any weird looking crack-like structures that you may have come
across in your travels.