Biology Reference
In-Depth Information
ternary, and dunes and loess originating during dry conditions correlated
with cold phases of the many glacial maxima.
22. Volcanism since 930 kyr along the coast of central Chile, Plio-Pleistocene
deposits near Antofagasta, Chile, elevated 240 mm per thousand years
since 330 kyr, a 7.8 magnitude earthquake in northern Chile on 30 July
1995, and a 7.6 earthquake in central Peru on 15 August 2007—all these
events have the potential of altering subterranean aquifers, surface drain-
age patterns, and vegetation.
23. Dry periods on the Altiplano of Bolivia linked with dry intervals in the
Amazon Basin and reduced transport of moisture.
The cumulative ancillary evidence, combined with the direct albeit scat-
tered paleobotanical information, gives strong support for changing cli-
mates, landscapes, water tables, and vegetation in the tropics and adjacent
regions in the lower latitudes. The data from the High Plain of Bogotá fi lls
in the details for one locality at 2 Ma (Hooghiemstra 1984).
The Bogotá site is ideal for the study of environmental and vegetation
history. First, as a slowly sinking basin, it has accumulated sediments more
or less continuously since about 3.5 Ma. Second, it is located at 2550 m in
the eastern cordillera of the Colombian Andes, so the sediments preserve
a variety of vegetation types moving up and down the slope. Third, being
distributed along a steep altitudinal gradient, these zones of vegetation
move rapidly and clearly in response to even moderate changes in climate.
The locality is in the Andean forest belt at 2300-3200 m, situated between
the subpáramo above 3200 m and the subandean forest at 1000-2300 m
(chap. 8).
The plant record begins at 3.2 Ma. Between 3.2 and 2.7 Ma, conditions
are warm. Between 2.7 and 2.2 Ma, the area turns colder above 2600 m
by 5°C-9.5°C, with an overall regional cooling of 8°C. The onset of colder
termperatures at the Bogotá site corresponds to the beginning of signifi cant
global cooling and expanding glaciation. For about the past 800,000 years,
changes on the High Plain have followed the 100,000-year periodicity of
the Milankovitch eccentricity cycle. In glacial times, the grass-shrubland
páramo is prominent, while in warmer times it is the subandean forest. In
postglacial times, there is evidence for a reversal to temperatures cooler by
3°C-4°C at the time of the Younger Dryas, 10.8-9.5 kyr. Thus, the vegeta-
tion at the high altitudes in northern South America at 2 Ma, and in sub-
sequent times, follows patterns and subpatterns generally similar to those
farther north, and the effects extend downslope, for example, a cooling of
5°C-6°C and drying in the Amazon lowlands at the glacial maxima.
