Geoscience Reference
In-Depth Information
pools that were left scattered across the desert. Our normally peace-
ful evenings of relaxed conversation quickly degenerated into long
hours of swatting and slapping as we tried to fend off the buzzing,
bloodsucking hordes. Our only advantage was that they slept during
the day, which allowed our work to proceed without these annoying
interruptions.
The next two days were spent wrapping up odds and ends, espe-
cially around the egg quarry. Frankie precisely documented the posi-
tion of more than two hundred eggs using the system of grids laid out
in the quarry. In addition, Luis, Gerald, and Gareth built plaster
jackets around several clusters of eggs so that we could collect them
for further study. One was huge, containing forty or fifty eggs and
probably weighing almost a thousand pounds. Natalia Klaiselburd,
who was released from her duties in the quarry to prospect, found
three more fragments of eggs that contained patches of fossilized skin.
Another embryo was found in an egg near the quarry. Throughout this
period, the mosquitoes were still on the rampage.
With the eggs in the quarry now completely exposed, Lowell and
his geological team spent most of the morning of the thirteenth
examining the site. We focused our attention on a puzzling geologi-
cal phenomenon: the mudstone in the egg layers was laced with
smooth, shiny, grooved surfaces that looked similar to slickensides, the
surfaces one sees in fault zones where blocks of rock slip past one
another as movement occurs along the fault. However, the slickensides
in the mudstone at Auca Mahuevo were not large and continuous, the
way one would expect if they had been created by a large fault that
extended for hundreds of yards or miles across the countryside. These
were only a few inches to a foot long. Some of the magnetic samples
from the mudstone that we had collected in 1997 were yielding
screwy results, which we thought might have resulted from the move-
ment of the mudstone blocks along the small slickensides. But we
didn't have any idea what had caused the slickensides, since they
weren't large enough to be major faults.
Fortunately, David Loope, a geology professor from the University
of Nebraska, had arrived the previous evening, and we described
what we had been seeing to him. Dave possesses a calm and consid-
ered demeanor, as well as an entertaining sense of humor that is as dry
as the Patagonian desert, and he is a widely recognized expert on
