Biostratigraphic History of Dead Man Lake, Chuska Mountains, New Mexico

Dead Man Lake (elevation 2,800 m) is one of several hundred shallow lakes on the flat, rolling crest of the Chuska Mountains. The lacustrine sediments consist of 7 to 10 m late—Pleistocene sandy silt or fine sand beneath only 0.1 to 0.3 m Holocene organic mud. Five faunal zones in the Pleistocene sediments contain distinctive assemblages of Cladocera and larval Chironomidae. The Chydoridae were the dominant Cladocera during Wisconsin glaciopluvial time, but only two or three species occurred in any of the zones. Tanytarsini and Procladius (Tanypodinae) were usually the dominant Chironomidae; populations of Orthocladiinae and Chironomini were smaller and chronologically discontinuous. The Pleistocene fauna is an impoverished as in other Pleistocene lake sediments and in modern arctic lakes. Therefore the faunal assemblages support the palynological evidence for alpine conditions on the crest of the Chuska Mountains during Wisconsin glaciopluvial time. The organic mud deposited since the end of the Pleistocene contains a more diversified fauna; 12 species of Cladocera occur at one level. As in the Pleistocene sediments the Chydoriae are the most abundant Cladocera. The absence of planktonic Cladocera, the oxygen requirements of the dominant Chironomidae, and the stratigraphic relationships of the faunal zones all indicate that the lake has probably never been deeper than 5 m, even though the oldest lacustrine sediments now lie 16 m below an abandoned outlet. During Wisconsin time the floor of the basin was probably only a few meters below the outlet, and excess water spilled into the canyon west of the lake. A shallow lake was maintained by an equilibrium between sedimentation and bedrock subsidence. Precipitation was insufficient to fill the basin when the pluvial period ended, so the outlet was abandoned.