Biology Reference
In-Depth Information
epic poem, and the area's prehistory surfaced in a real-life saga every bit
as dramatic as
Evangeline
's. On Thursday, 21 November 1980, Texaco was
drilling a well at Jefferson Island, unaware that below were the caverns of
the Diamond Crystal Salt Mine. At a depth of about 1228 feet, the rig be-
gan to tilt, and a whirlpool formed in the lake, eventually creating a crater
180 feet in diameter. Two Texaco oil rigs, several barges from the adjacent
Delcambre Canal, a loading dock, the Live Oak Botanic Gardens, assorted
greenhouses, a house trailer, trucks, and several tractors were pulled into
the crater. Miraculously no one was killed; indeed, the water drained so fast
that Leonce Viator Jr., who was fi shing on the lake, was able to climb out of
his grounded boat and run to shore.
As the continents continued to separate, the waters of the Gulf deepened
and the formation of salt domes waned. The subduction zone along the coast
of western Mexico was extending southward toward present-day Central
America. When ocean crust descends into the Earth's interior, it becomes
molten at a depth of about 200 km and may then rise to the surface through
fi ssures to form an arc of volcanoes or volcanic islands. These conditions
in the Late Cretaceous prepared the way for lands that would eventually
become the Greater Antilles. An early model by Malfait and Dinkleman
(1972) depicted a continuous or near-continuous stretch of land connecting
or nearly connecting the continents. This land supposedly moved relatively
eastward, encountered the stable Jurassic to Late Cretaceous Bahamas Plat-
form, and broke into early versions of the present-day Greater Antilles. This
geologic model has proved important to biologists because it is consistent
with one of the two principal means of plant and animal distribution: vicar-
iance and dispersal. Vicariance involves the separation of a once continuous
biotic range through plate tectonics (e.g., movement of South America away
from Africa) or the formation of an intervening barrier (e.g., rise of the An-
des Mountains). Distribution may also occur through gradual short-distance
or abrupt long-distance dispersal of seeds or other plant propagules. Thus,
one means is based on movement of the land (vicariance), and the other on
movement of the organism (dispersal). The early Malfait-Dinkleman model
of Antillean origin was most compatible with vicariance.
The scenario for the geologic development of the Greater Antilles around
which consensus is now developing is that of Pindell and Barrett (1990;
Pindell 1994), augmented by the geophysical research of Paul Mann and
others (e.g., Mann 1999). By this view, an arc of volcanic islands originated
off present-day Pacifi c Central America in the Cretaceous about 130 Ma.
From the beginning, the islands were separate and mostly submerged. They
attained their present position by the relative motion of the three regional
