Page 10 - Petroleum Geology

IX

The point is this: if your perspective is limited to one part of the world,
you are more likely to be led into erroneous ideas because the evidence that
would distinguish cause and coincidence might be lacking. A geologist who
has spent his career in the Western Canada basin would probably have totally
different ideas about the generation, migration and entrapment of petroleum
from one whose career had been spent in the US. Gulf Coast. Indeed, they
would probably have different ideas about the nature of geology in general.
Not the least of these contrasts would be the lack of deformation in the West-
ern Canada basin where, from the well-head, the Rocky Mountains can be seen;
while the Gulf Coast is deformed under the continental shelf with no land
in sight, let alone mountains. But our Canadian geologist would feel quite at
home in Mexico and Libya, while our Gulf Coast geologist would feel quite
at home in Nigeria and South-East Asia.
Geology, I believe, still suffers from one important, but unavoidable, fact:
it grew from studies of outcrop, which are necessarily confined to the land
areas, with the third dimension limited to the depths of mines and
the heights of mountains, and it is still practised by a majority of geologists
within these dimensions. The geology of what we can see and touch is the
geology of sedimentary basins that are no longer accumulating sediment, and
the geology of orogeny. Petroleum geology gives us a glimpse of sedimentary
basins that are still actively accumulating sediment, and are still being de-
formed in spite of the fact that they have not yet suffered orogeny. Petro-
leum geology, although not giving us a complete three-dimensional picture,
has given us a three-dimensional picture of some areas in great detail to
depths of two, three, and four kilometres. Who would have imagined that
there could be Mesozoic thrust faults beneath the horizontal Tertiary of the
north German plains? . . . or folds and faults in young Tertiary sediments in
many continental shelves? Our conception of an unconformity seems to
have been dominated by Hutton’s unconformity on the east coast of Scot-
land, and an assumption of subaerial erosion; yet there are extensive and im-
portant unconformities in the continental shelves that were never subaerially
formed, so far as we can determine, and the deformation, erosion and subse-
quent sediment accumulation were entirely submarine.
These matters affect our understanding of geology. There are others that
affect our understanding of petroleum geology. When people peer into our
science from another discipline, and speak with confidence, we tend to ac-
cept what they say. Lord Kelvin poured scorn on geologists of the last cen-
tury, and few rose to defend geology against him. A century later, we can
say with confidence that most of what he said about geology and geologists
was wrong. During the last 20 years or so, chemists have spoken with increas-
ing confidence about the generation of oil, and geologists have tended to
mould their concepts to fit the hypotheses of chemists. Some seem to have
forgotten that geology is also a science - even if an imprecise one compared
to chemistry, physics and mathematics, but nevertheless a science with its