The origin of the
Gulf of Mexico has been a long-standing point of controversy between
geologists, several theories have been presented to explain the
"hole" in the Bullard-type jigsaw fit of the continental
masses.
All involve plate tectonic reconstructions — but none have proven
fully satisfactory.
I propose that the origin was not due to traditional mechanisms
from below, but to a huge cosmic impact from above.
This may seem improbably to most geologists, but there are many
features favoring such an event, including morphology, geophysics,
metamorphic gradient, possibly orogenic tectonism, faulting and
an ideal focus of deposition for the Louann Salt. The lack of pre-Late
Triassic information leaves room for speculation.
Plate tectonic reconstructions fail to explain the lack of magnetic
signature expected in a rift basin, nor the Tethyan space problems
imposed by rotation of South America to fill the Gulf.
An impact origin would answer both of those difficulties. The "hole"
in the mosaic has been there from the moment of impact.
I'm suggesting that a huge cosmic impact (asteroid or comet) struck
the area of the present gulf in latest Permian time, creating an
immense saucer-like crater, fracturing the crust, metamorphosing
the underlying Paleozoic rocks (impact melt?) and causing an uplifted
Moho due to rebound tectonics.
This impact is seen as responsible for the world's greatest extinction
crisis at the close of the Permian, some 250 million years ago.
It also may have contributed to Permian glaciation of southern Pangea.
It's interesting that extinction crises also occurred at the Cambro/Ordovician,
Ordo/Siluiian, Devonian/Mississippian and Triassic/Jurassic boundaries
— and it is tempting to suggest that these crises also were triggered
by asteroid/comet impacts.
If one accepts the possibility of cosmic origin, then the following
speculative scenario is proposed:
- The Gulf of Mexico area was hit by a huge asteroid or comet
at the close of the Permian. It accounted for the great Permian
extinction crisis and perhaps contributed to Permian glaciation.
- It created an immense crater and resulted in an uplifted Moho
due to rebound tectonics.
- Impact metamorphosed underlying Paleozoic sediments and created
down to basin faulting and basinal grabens.
- The hot impact basin with a silled outlet to the open ocean
offered an ideal evaporating pan for deposition of the Louann
salt.
- Impact ruptured crustal integrity, caused an uplifted Moho by
rebound tectonics and probably induced deep-seated radially-outward
motions in the ductile mantle. This area of impact may have been
the trigger that initiated tripartite continental separation (similar
to a triple junction).
The Gulf was continental land area prior to the Pangean breakup,
and the "hole" in the Bullard mosaic did not exist until
impact. There is no need for plate tectonic reconstruction to fill
the gap. The Gulf of Mexico was formed by impact from above, not
by traditional plate tectonics from below.
The 35-million-year-old Chesapeake Bay area has now been identified
as a large impact structure. How many others have gone unrecognized?
Are we overlooking the obvious because of the immense size of the
Gulf of Mexico?
Look again at a map or a satellite image of the Gulf — and think
"impact crater." It would solve many perplexing problems
of the Gulf's origin.