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might be termed orogenic regressive sequences (there was apparently no winn-
owing), so normal faulting is the main cause of traps.
If the post-unconformity sequence proceeds to regression, it acquires the
characteristics of the normal transgressive-regressive sedimentary basin that
were discussed early in this chapter, and petroIeum may be trapped in growth
structures in the “terminal” regressive sequences.

A remarkable feature of petroleum geology, when viewed in this broad
perspective against the current hypotheses of plate tectonics, is that the major
petroleum provinces are areas that were extensional over great spans of geol-
ogical time, with not the slightest evidence for regionally-compressive struc-
tures, and the tectonics was vertical within, and in the immediate neighbour-
hood of , the sedimentary basins of many major petroleum provinces. Vertical
movements were the dominant control on stratigraphy and structure. We do
not yet understand the significance of these broad patterns of world geology
and geological history, but we may rest assured that they are significant and
that full understanding of the processes of the Earth can only follow under-
standing of these great areas. This will involve understanding the petroleum
geology of these regions, because that is the economic incentive for their in-
vestigation.

REFERENCES

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