The sedimentology, stratigraphy, and chemistry of playa lake deposits resulting from hurricane Nora in the Chapala basin, Baja California, Mexico

by Shoffner, Liselotte Rachel.

THE SEDIMENTOLOGY, STRATIGRAPHY, AND CHEMISTRY OF PLAYA LAKE DEPOSITS RESULTING FROM HURRICANE NORA IN THE CHAPALA BASIN, BAJA CALIFORNIA, MEXICO by Liselotte Rachel Shoffner Laguna Chapala, Baja California, Mexico is a closed basin containing a playa lake and presumably a proxy record of climate. On September 25, 1997, hurricane Nora crossed the Chapala basin, causing flooding in Laguna Chapala and providing the unique opportunity to examine the sedimentological impacts of a hurricane on the playa stratigraphy. Runoff from hurricane Nora formed a lake that locally reached depths up to 1.2 m. The lake did not completely evaporate until February of 1998. The playa was surveyed to determine the lake hypsometry and samples were examined by particle size analysis and x-ray diffraction. The mean grain size was 5.7 phi units. The dominant clay minerals were smectite, illite, and kaolinite. The dominant evaporite mineral was halite. The evaporite crust, vegetative debris at the flooding boundary, and large-scale mudcracks were unique to flooding and provide the most useful indicators of a storm event in Laguna Chapala’s sediments.