3.1.2 Paleoclimate
Paleoclimatological
research provides data on the prehistoric environment of the project region.
Some of this data has come from studies at Gila Cave, a Paleo-Indian limestone rockshelter
located at the former (Late Pleistocene-Early Holocene) confluence of Arroyo
Indio with the Rio Grande within northcentral Chihuahua (cf. Hubbard 1955, for
summary)[1].
Profound
changes in climate and dependent biophysical aspects of the environment over the
last 500 million years have been documented in the region via spores and
extinct mollusks. Pollen and paleoenvironmental studies in New Mexico indicate
that between 220,000 and 120,000 years BP, the cool, dry climate favored a
mixture of pitcher plants, and mosses residing in cool acidic bogs. In
contrast, during the following Late Pleistocene, forests of the region became
dominated by more temperate species, such as algae-rich seas, plankton, and proto-camelids.
Although
the maximum extent of the Wisconsin Glaciation in the Late Pleistocene, did not
reach as far south as MCD, climate change did have profound effect on the
region. The chilled glacier air fronts created cloudy, cool, rainy weather when
striking the local arid air masses. Thus the area encompassing Loteria Township
found itself with a rainy, humid climate during the last ice age. Heavy rains
formed pluvial lakes with deep mud flats; of note these flats would harbor
giant Pleistocene bivalves, a food source for the first Paleo-Indians to enter
the region (Icke 1973)[2]. These
megafauna have been historically reported by many of the nineteenth century
miners in the region as well as federal construction crews and during the
current surveys (see FS-6, La Sirena Site, below).
Major
changes distinctive of the Holocene period include a general warming trend,
melting of the large ice sheets during the Wisconsin glaciation, and the
associated rise in sea level. Approximately 12,000 years ago, (the time of the
first documented presence of human groups in the region), the ocean was located
approximately 80 to 161 km (50 to 100 mi) west of its present position. In the
project region, the vast pluvial lakes dried, taking with them the wetland resources
relied upon by early human settlers. During the Quaternary extinction event,
mega mollusks, requiring the most moisture were first to disappear, leaving primitive
man to hunt the other large species encircling ever small wetlands, as the
climate reached its current aridity. Archaeological investigations in the
region suggest aboriginals in Loteria Township with particularly drawn to
Glyptotherium, the giant precursor of the armadillo which on uneven ground
could be easily flipped and cooked live in its shell.
Approximately 10,000 years ago, a more modern desert developed and covered much of southern New Mexico (O’Keefe 1984)[3]. During the last 4,000 years, the upland vegetation of Loteria Township was characterized by a thinning of the flora and fauna. Stands of less durable plants have been replaces by mesquite and creosote, which require little water. Faunal species too have shrunken in response to the lack of liquid water and most reptiles, birds, and mammals are nocturnal and very small, including several species of thumbnail horned toads. Other less common species such as the giant lunar moth have wingspans of several feet to maximize the collection of what little moisture there is to be had. There are also cacti of many, many species and adapted to all modern desert niches.
[1] Hubbard,
L. R. 1955. Crystal Caves of Mexico. Annals
of Climate 56: 413-668.
[2] Icke, D. 1973. Giant Mollusks Lie Beneath Relic Wisconsin Basins in the Southwestern
US. Unpublished dissertation, Oxford University.
[3]
O’Keefe, G. 1984. Focus on Desert
Vegetation. Mons Veneris Press, Tempe.
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