The effects of source lithology, transport, deposition and sampling scale on the composition of southern California sand

The Transverse Ranges of southern California represent an uplifted and variably dissected Mesozoic magmatic arc, and Mesozoic to Holocene sedimentary and volcanic strata deposited in convergent and transform tectonic settings. Modern sand within part of the Western Transverse Ranges represents: first-order sampling scale of the Santa Monica and the San Gabriel Mountains; second-order sampling scale of the Santa Clara River draining both mountain ranges; and third-order sampling scale of the beach system between the mouth of the Santa Clara River and the eastern Santa Monica Mountains, and turbidite sand of the Hueneme-Mugu submarine fan. Source lithology includes plutonic and metamorphic rocks of the San Gabriel Mountains, and sedimentary and volcanic rocks of the Santa Monica Mountains. First-order sands have large compositional variability. Sand from local coastal drainage of the Santa Monica Mountains ranges from basaltic feldspatholithic to quartzofeldspathic. Sand of the San Gabriel Mountains local drainages has three distinct petrofacies, ranging from metamorphiclastic feldspatholithic to mixed metamorphi/plutoniclastic and plutoniclastic quartzofeldspathic. Second-order sand is represented by the main channel of the Santa Clara River; the sand has an abrupt downstream compositional change, from feldspathic to quartzofeldspathic. Third-order sand (beaches and deep-sea turbidite samples) of the Santa Monica Basin is quartzofeldspathic. Beach sand is more quartz-rich than is Santa Clara river sand, whereas turbidite sand is more feldspar-rich than is beach sand. Deep-sea sand has intermediate composition with respect to second-order samples of the Santa Clara River and third-order samples of the beach system, suggesting that (1) the Santa Clara River is the main source of sediments to the marine environment; and (2) local entry points from canyons located near local drainages may generate turbidity currents during exceptional flood conditions. Petrologic data of modern sand of the study area are highly variable at first- and second-order scale, whereas third-order sand is homogenized. The homogenized composition of deep-marine sand is similar to the composition of most ancient sandstone derived primarily from the Mesozoic dissected magmatic arc of southern California. This study of the Western Transverse Ranges illustrates the effects of source lithology, transport, depositional environment, and sampling scale on sand composition of a complex system, which provides insights regarding actualistic petrofacies models.     

TEMPERATURE VARIATIONS DURING THE LAST CENTURY AT HIGH ELEVATION SITES

Differential temperature changes with altitude can shed light on the relative importance of natural versus anthropogenic climatic change. There has been heightened interest in this subject recently due to the finding that high-elevation tropical glaciers have been retreating and that significant melting from even the highest alpine regions has occurred in some areas during the past 20 years or so, as recorded in ice core records, which do not reveal any similar period during previous centuries to millennia. In this paper we find evidence for appreciable differences in mean temperature changes with elevation during the last several decades of instrumental records. The signal appears to be more closely related to increases in daily minimum temperature than changes in the daily maximum. The changes in surface temperature vary spatially, with Europe (particularly western Europe), and parts of Asia displaying the strongest high altitude warming during the period of record. High-elevation climate records of long standing taken at a number of mountain tops throughout the world, but primarily in Europe, are available from a number of countries. In some cases, meteorological observations at these unique mountain sites have been discontinued for a variety of reasons, usually budgetary. It is hoped that the papers published in this special issue of Climatic Change can contribute to a reassessment of the value of continuing climate measurements at these mountain observatories by the appropriate entities, so that we may continue to have access to climate information from the tops of the world.