Dinosaur Dreaming
2001 Excavation report
Nicholas Van Klaveren
The Flat Rocks fossil locality was excavated for a period
of six weeks, from late January to early March 2001. This was one week later than
the previous year and was chosen to coincide with the university holidays and
to avoid the tourist season at Inverloch.
All the fossil material was collected under permit No. 10001158
of the Department of Natural Resources and Environment Victoria.
The excavation this year was moved up the beach about five metres
westward toward the cliff because of the discovery of two well-preserved mammalian
jaws at 185 metres East, 100 metres North during a one-day field trip during December
2000. The relative shallowness of the overlying sand at the site higher up the
beach meant that the construction of girders and tarpaulins was unnecessary.
Excavation Methods
The excavation method this year continued with the use of large
iron wedges and sledgehammers to remove the bulk of the fossil layer from the
targeted area. Exposed specimens were removed with a diamond sawblade-equipped
Stihl TS460 Cutquik. The technique of removal used last year was continued with
wedges driven into the semi-continuous coal layer at the base of the Middle Sandstone
Unit, then a second level extracted with the wedges driven into the Lower Sandstone
Unit.
The unfossiliferous, overlying sandstone overburden was removed
with two Cobra petrol-driven jackhammers. Once the majority of the overburden
was removed the method, was then switched to sledgehammers and wedges so as to
provide greater control to protect the underlying fossil layer from damage.
Equipment
Due to its location, the Flat Rocks fossil locality presents
a number of difficulties with regard to the difference in elevation, and large
waves at high tide.
For the previous three years, a construction consisting of packing
material, plastic tarpaulins, steel mesh and rock bolted down iron beams was built
to help exclude sand and thereby increase access time to the fossiliferous units.
A number of innovations were to be tried this year to improve
the system introduced three years ago.
Solar Power Unit and Pump
In expectation of the use of the construction this year, a solar
power unit and small salt-water pump were constructed.
A continuous trickle of salt-water draining from the sand surrounding
the excavation area has usually necessitated the unpleasant task for a volunteer
to scoop and bucket this water throughout the day.
To dispense with this onerous (and odorous) task, a 12-watt,
8-volt, photovoltaic array coupled with 18 D-cell Nickel - Cadmium batteries form
a solar power unit, which is battery assisted in cloudy times and self-charging
in times of low use.
This unit powers a 12-volt salt water pump housed in a filter
with a stabilizing steel base plate with a total output of around 5 litres per
minute, depending upon the height of the head.
Splines
An ever-present problem with the construction used in previous
years is the surge of waves driving sand and seaweed beneath the edge of the tarpaulins.
Borrowing from the method of securing fly-wire netting in windows
with rubber splines, large wooden splines fitted into grooves cut into the surrounding
rock around the construction were to be used to secure the heavy truck tarpaulin.
Previously, heavy sandbags were used which were unreliable, being
swept away and also potentially back-damaging when moved each day.
The splines were to be held down by rock bolt washers fitted
over the rock anchors used to secure the girders.
Without the use of the construction this year, this new innovation
will have to be tested at a future date.
Excavated Areas
A small excavation west of the fault at 185 metres East, 99 metres
North, which had always been characterised by frequent jointing and small scale
faults with strongly sericitised gouge, has been worked sporadically since 1997.
This site was once thought to contain mostly turtle and fish remains, unexpectedly
yielded two mammal jaws in a single day in December 2000.
Area A
With the decision to concentrate on this area it was necessary
to remove the overlying sandstone with the petrol driven jackhammers. During the
process a thin (5 centimetre) brown, oxidized carbonaceous clay layer of limited
extent (40 centimetres wide) was encountered. This new unit located at 183 metres
East, 101 metres North probably represents a small pool or puddle, which was exposed
for some time between the major flooding events. A number of small bones were
unexpectedly found in this unit and consisted of a small hollow limb and a shard
of turtle carapace. A possibility that entire small animals may be preserved in
this unit due to the different environment and energy of deposition warrant further
investigation next year as the majority of this small layer is still exposed in
the northern face of this year's excavation.
The main fossiliferous conglomerate produced specimens at a rate
and quality equal to the down-slope excavations of previous years, including a
further three mammal jaws.
A major development from this year's excavation was the recognition
of micro-channelling within the major conglomerate units. The deeper parts of
these small channels were found to yield bone concentrations ten times that of
the surrounding rock. Numerous other small channels could then be discerned all
throughout the fossil layer including the lower units, in which material left
behind in previous years was thought to be substandard because of the paucity
of specimens.
Area B & C
Minor amounts of rock were excavated at these two points and
were found to contain adequate amounts of fossil material of a medium grade.
Future Excavations
In consultation with Doris Seegets-Villiers, the units containing
the mammal jaws excavated this year will be pursued westward next year.
These units again outcrop at the surface and are untouched except
for a few exposed bones, which have already been cut out. It is notable that these
bones are found in the base of the microchannels mentioned previously.
Excavation next year will concentrate upon the wedge-shaped lower
units already exposed and then follow the main units subsurface, with some removal
of sandstone overburden. The problem of inflow of water from the mass of sand filling
the previous year's hole will be countered with the building of a small sandbag
wall and the placement of a slotted drainage pipe with a geotextile sock. The
sandbag wall will be only two or three bags in height so it is not exposed above
the sand between daily excavations next year. It has also been proposed (by Marion
Anderson) that the sandbags be armoured by hessian on the west side to protect
against the daily shovelling out of the excavation. |
