Geoscience Reference
In-Depth Information
strata.Thesurfcrashedbehindus,givingusnochoicebuttoshoutatoneanotheras
we pointed out anything of geological interest. We also warily watched the sea for
anyroguewavesthatmightcatchusbysurprise.FieldworkalongtheVictoriacoast
istreacherousenoughtoencourageahealthycautioninitspractitioners—supported
by the inverted sign at the end of the trail down—and that day was no different.
Inretrospect,wewerefortunatetohavethewintersolsticeapproaching,which
meant the sun would begin to set close to
5:00 p.m., a constraint that urged us to use our time judiciously. Sure enough,
within less than ten minutes of our arriving, Greg and I started finding trace
fossils—invertebrateburrows—infine-grainedsandstonesandsiltstonesexposedin
theoutcrop.Onetypeofburrowwasastubbyverticalcylinder,someofwhichwere
U-shaped. Another was a thin, reddish J- or U-shaped structure, also oriented ver-
tically. Each burrow form was abundant in the thin strata.
These little trace fossils invoked an unprecedented excitement within me, as
they provided clues to the ancient ecosystems of the area. Both types of burrows
wereformerlyopentubes,filledwithsandverysoonaftertheyweremade.Further-
more, invertebrate burrows often act as sensitive indicators about the former eco-
logy of an area, and these were typical of what you might see in a modern river
floodplain. For instance, some aquatic insect larvae dig burrows in sediments un-
der very shallow water or on the surfaces of emergent sand bars, whereas other
insects—such as ants, bees, and wasps—can only make nests above water. These
trace fossils looked more like aquatic insect burrows to me, probably used for com-
bined feeding and dwelling.
The presence of these burrows alone was scientifically important, and when
put in the context of having been formed in a polar environment, they were doubly
significant. Insects and other invertebrates in polar environments cannot burrow in-
tofrozensediment.Rather,theywaituntillatespringorsummertomaketheirdom-
iciles or brooding burrows, after the uppermost layers of sediments have thawed
out. Or they wait until new, soft surfaces have been formed by sediment deposited
