Christina Black, Emily Fleming, Sean Mulcahy, Megan Murphy,
Jennifer Philippe, Rebekah Shepard, Maris Tabor, Tatia Taylor

Geology Department, University of California, Davis

This web page is the culmination of a geology graduate course, GEL 281 Instrumental Techniques, taught by Dr. Peter Schiffman at the University of California, Davis. In October, 2002, under the guidance of Dr. Schiffman, Dr. Rob Zierenberg, and Dr. Dawn Sumner, eight graduate students collected travertine and water samples from active spring deposits on the McLaughlin Reserve in the California Coast Range. These samples were subjected to different analytical techniques with the primary goal of introducing students to different geological techniques and their applications to scientific research. These techniques include petrography and cathodoluminescence, x-ray diffraction, electron microprobe, neutron tomography, magnetics, ICPMS of water and solids, S and C-O-H isotopes, and analysis for microbial organisms. The results and highlights of this project are presented here. For information of the geology of the area please refer to the McLaughlin website.

[ Field Images ] [ Petrography and Microbiology ] [ Mineralogy and Magnetics ] [ Isotopes and Major & Minor Elements ]

The travertine mounds are composed of aragonite with lesser amounts of calcite, dolomite, and sepiolite. This sequence of precipitation is common throughout the samples.

• Low temperature dolomite is precipitating abiotically in these mounds.
• The travertines contain enough magnetite to retain a stable magnetic direction.
• Endolithic coccoidal bacteria have been identified in the samples.
• All of the waters show a d¹⁸O shift due to water-rock interactions at temperatures considerably greater than ambient surface conditions.
• Fluid composition is consistent with derivation from the Great Valley sequence.
• The composition and mineralogy are controlled by evaporative processes and the presence of serpentinite.

We thank the following people for their contributions to this project: Peter Schiffman, Dawn Sumner, Rob Zierenberg, Peter Green, Karen Kalenetra, John Meeks, John Neil, Howie Spero, Ken Verosub, Dave Winter, Norm Winter, and Janice Fong.

[ Field Images ] [ Petrography and Microbiology ] [ Mineralogy and Magnetics ]
[ Isotopes and Major & Minor Elements ]

schiffman@geology.ucdavis.edu