Biology Reference
In-Depth Information
mostly low-lying, and often fl ooded land surfaces from the equatorial re-
gions north to the Arctic and south to the Antarctic.
In the Late Jurassic and Early Cretaceous a large fragment of land called
the Maya, or Yucatán, block was located in the developing Gulf of Mexico
(fi g. 2.17). It was on one of the microplates that were moving to the south-
west. It collided with southern Mexico in the Early Cretaceous and contin-
ued to slide to the southwest along a line marked by the Salina Cruz Fault
running from Tehuantepec to the Gulf of Mexico. Yucatán was sutured on
to southern Mexico by the end of the Early Cretaceous.
In the Middle and Late Cretaceous there was a volcanic island arc off
the coast of northwestern Mexico. With subduction of the Pacifi c plate
and movement of North America westward, it became accreted onto the
continent as present-day Baja California in the Oligocene (35-23 Ma). A
northward-spreading center developed between Baja California and the
mainland about 29 Ma and was completed by 5 Ma to form the Gulf of Cali-
Figure 2.16
Coniferous forest formation: montane coniferous forest association of
Pinus
ponderosa
and
P. montezumae
, Sierra Madre Occidental, El Salto, Durango, Mexico. Small,
isolated stands of
Picea
grow in the area. Photograph courtesy of Jesse Perry Jr.
