Paleoclimatic Variation in the Valley of Guatemala during Precolumbian Times

Samples recovered from the bed of the extinct Lake Miraflores (6-11 March, 2000)

In preparation for soliciting funds from FAMSI, we had opened a test pit in the dry bed of the ancient Lake Miraflores. In September of 1999, Dr. Brenner had removed samples of the sediments down to a depth of 200 cm (for profile of the test pit, see Figure 2). His subsequent analysis of the samples revealed the presence of diatoms of the genus Pinnularia and a few of the genus Aulacoseira, beginning at a depth of 145 cm, indicating the ancient presence of standing water. Upon receiving the funding we hired two workers in March, 2000, to re-open the pit. This time it was taken down to 315 cm where the sedimentary deposits became extremely hard and difficult to excavate. Dr. Brenner employed the same methodology as that of the previous September, extracting by trowel a sample of soil at 5 cm intervals from the side wall of the pit (Figure 3). The samples were extracted from the west profile, beginning at 50 cm below surface and continuing down to 315 cm. Sub-samples from 170 to 315 cm in the profile were transferred to labeled Whirl-pak bags to be transported to the U.S. by Brenner and Curtis (samples above these levels had already been removed and taken for analysis in September, 1999).

Figure 3: Photographs of excavation in the bed of extinct Lake Miraflores.

Sufficient soil was removed to provide stratigraphic samples for Ingeniero Franklin Matzdorf to carry out an analysis of physical properties in the Civil Engineering Laboratory at the Universidad del Valle de Guatemala. Based on his analysis, the contents of the pit fall into three major strata: 50 – 100 cm; 100 – 210 cm; 210 – 315 cm. Stratum 1 corresponds roughly to layers 1 to 6 in Figure 2, Stratum 2 to level 7, the third stratum to the excavation carried out in March 2000. He reports that Strata 2 and 3 show extreme impermeability which would be characteristic of lake bottom sediments. The details of the physical characteristics will have relevance when view in light of the pollen and microfossil analysis.

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