Re: Precambrian geology (1)

Jonathan Clarke (
Fri, 30 Apr 1999 07:19:21 +1000


Allen Roy wrote in part:

> One can say OVER 200 YEARS! or One can say ONLY 200 years. On the global
> scale, the total area where strata is exposed at the surface is very small.
> And the number of wells drilled does not begin to give a complete picture
> of the hidden strata. There is a lot of extrapolation based upon a
> reletively small quantity of evidence.

Biostratigraphy has been steadily refined in more than 200 years, but the
overall pattern has remained the same. This indicates to me that it is very
robust concept, even though based on a small sample of the whole fossil record.
One would expect the robustness of biostratigraphy to be decreasing with time,
not increasing, if it were based on an inadequate sampling of the fossil

> If biostratigraph is that good, why don't they hit oil each time they
> drill?

Biostratigraphy is simply a way to correlate geological formations. The
presence or absence of economic oil accumulations is dependent on a whole range
of factors. Things like suitable source rocks, appropriate oil migrations
paths, and an appropriate trap. The confluence of these factors can only be
tested by drilling. These factors are not dependent on biostratigraphy.

God Bless