CAMEL TRACKS AND STROMATOLITES IN A MIO-PLIOCENE EPHEMERAL LAKE DEPOSIT, MUDDY CREEK FORMATION NEAR MESQUITE, NEVADA

A recently discovered camel tracksite near Mesquite, Nevada occurs in the Mio-Pliocene Muddy Creek Formation. Seventeen, variously oriented, Lamaichnum tracks are exposed. Additional tracks are probably concealed by a soil crust that partially covers the track-bearing surface. The tracks are preserved as impressions into a 4-cm-thick, gray, silty limestone which is cracked and rapidly eroding away. On the basis of size and orientation of the tracks, we infer that at least three individuals are represented, and possibly as many as five. We are using photogrammetry to study this tracksite, as well as to digitally capture and preserve its evanescent features.

Sixty-five meters from the camel tracks, the same gray, silty limestone is exposed as a much thicker (~90 cm) interval packed with unusual, cm-scale stromatolites. Individual stromatolites are separated from one another, and they are floating in the limey matrix. Bands of silt are interbedded with some of the stromatolitic laminae, presumably recording dust storms that deposited silt in the lake.

We interpret this camel-track-and-stromatolite-bearing interval to record an ephemeral lake that developed during a rare, high-water-table episode within the fluvial-and-eolian-dominated Muddy Creek Formation in the Mesquite region. No other carbonate beds have been reported in this region. Because stromatolites are slow-growing microbial structures, their presence in this deposit implies that the deeper portions of this lake existed continuously for decades, and possibly for a century or longer.