|
GREAT SALT LAKE AND BEAR LAKE
The Great Salt Lakein Utah represented one of the most exciting targets for scientific drilling in North America. A long history of scientific inquiry, beginning with the pioneering work of G.K. Gilbert, provided a solid framework of knowledge to identify promising locations for drilling activities.
The initial drilling leg of the GLAD800 system on the Great Salt Lake was funded by the National Science Foundation. This project collected a total of 371 m of core with a recovery of up to 96 %. The maximum penetration was a continuous core to a depth of 121 m, the longest continuous core from the lake (Core #4).
The preliminary analysis of the longest core record obtained by the GLAD drilling project at Great Salt Lake was based on subsamples of the core catcher samples, obtained at the base of each 3 m run. Major lithofacies changes observed throughout the core are mirrored by a variety of sedimentary indicators. These include diagenetic (usually acicular) selenite crystals, indicative of highly saline pore (and probably lake) waters, pulses of siliciclastic sands (indicative of episodic and probably proximal stream inputs to this site), and both replacement and framboidal pyrite (indicative of reducing conditions and high organic carbon accumulation, generally associated with marsh deposition).
Invertebrate fossils occur throughout Core #4, although their abundances are quite erratic. Brine shrimp fossils are indicative of saline or hypersaline conditions. The other metazoan which occurs in Great Salt Lake today, the larvae of the brine fly, has been recovered for the first time as a fossil in this study. This finding is extremely exciting because these insects are potentially very diagnostic of salinity conditions and the nearby occurrence of stromatolite hardgrounds, which they require as attachment surfaces for filter feeding. Many horizons yielded mollusks and various species of planorbids, indicative of shallow littoral or marsh conditions. Fish bones occur at several horizons, although they have not been identified yet. Discoidal alagal mat fragments occur abundantly throughout the core except in the more saline intervals. Ostracodes occur in relatively low abundances throughout most of the core.
Correlation with the existing low-resolution ostracode, brine shrimp and palynological record of the Great Salt Lake indicates that Core 4 reaches the stage 6 - stage 7 boundary (ca. 175 ka). However, the preservation of Core 4 is much better than in previously available samples. To realize the full potential of this record our ultimate goal is to analyze samples at much higher resolution. Initially this will be at ca. 1000-year intervals (175 samples). Then an additional 100 samples will be studied to resolve sub-millennial events.
In addition to paleoclimate information, the Great Salt Lake records the history of tectonic events along the Wasatch Front. This area is undergoing active extension at rates of 0.4-0.7 mm/yr and possibly up to ~1.5 mm/yr. Seismic reflection data suggest that more displacement has been accommodated on the East Lake fault (ELF) to the west of Antelope Island than on the Wasatch fault itself. A high-resolution seismic reflection survey of the southwestern Great Salt Lake produced ~325 km of high-quality profiles, including 31 crossings of the ELF and related subsidiary faults west of Antelope and Fremont Islands. These high-resolution profiles provide extraordinarily detailed images of stratigraphic and structural geometries in the hanging wall of the ELF that can be directly related to several seismogenic slip events on that structure.
Detailed dating studies (AMS dating of hand-picked charcoal) are presently being completed by Holly Godsey, a graduate student at the University of Utah who is in part supported by a DOSECC student internship. In addition, Debbie Balch, a graduate student at the University of Arizona is conducting a paleoclimate study of Core #4. She is also partially supported by a DOSECC internship.
Below summarizes the locations and depths of all holes cored on the GSL:
GREAT SALT LAKE HOLES DRILLED AUG. 12 - SEPT 7, 2000:
|
