Quaternary Sedimentary Structures at Monterey Dunes, California, Imaged By Ground Penetrating Radar
Chan, J. and Craig, M. S.
Numerous coastal dune studies have successfully used ground penetrating radar (GPR) to image sedimentary structures and correlate them with climatic variations and depositional history during the late Pleistocene and Holocene. The Monterey Dunes complex spans approximately 18 km of coastline at Monterey Bay and is the largest coastal dune complex in Central and Northern California. In order to study the internal structure of the Monterey Dunes, we conducted GPR surveys at three locations. A 100 m2 survey grid consisting of 14 GPR profiles was recorded at the former location of Stilwell Hall using 50 MHz antennas. Additional GPR surveys were recorded at Marina Dunes Preserve and near Lake Court using 100 MHz antennas. Topography along the profiles was surveyed using differential GPS and used to apply elevation corrections to the GPR profiles. GPR data were bandpass filtered, spatially filtered, and migrated. Theoretical vertical resolution of the data is approximately 0.3 to 0.63 m. All profiles exhibit southeast (leeward) dipping, foreset laminations that appear to correspond to relict slipfaces, and the reflections correlate closely with observed dune outcrops. Two well-indurated layers with soil horizons, each approximately 1 m thick, are observed along the bluff which separate dune deposits approximately 8 to 20 m thick. The Monterey Dunes have been interpreted in other studies to be Holocene and late Pleistocene in age. We interpret the soil horizons as having formed during highstands when sand input from the shoreface ceased and the dunes were stabilized by vegetation. The main episodes of dune building occurred during periods of low sea level, as sands from the exposed shoreface were blown inland to form coastal dune fields by the prevailing northwest wind. Holocene dunes probably formed from reworked Pleistocene dunes eroded by storm waves and subsequent winds.
AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013