Soil Development, Relative Dating, and Correlation of Late Quaternary Marine Terraces in Southwestern Oregon

Abstract

AbstractFlights of tectonically uplifted, late Quaternary marine terraces are preserved at several localities along the Oregon coast. Intervening coastal areas without marine terraces reflect net subsidence. These gaps in the coastal terrace record make it difficult to correlate terraces along the Pacific coast. To test the utility of soils in relative dating and correlation, two flights of marine terraces near Cape Blanco and Cape Arago were investigated. The terraces could be distinguished in each area from soil morphological properties and a quantitative index of soil development derived from field descriptions. The soils in the two areas show a progression in development from spodosols to spodosols underlain by clayey material to ultisols. The lowest two terraces at Cape Blanco, which have reported age estimates of 80,000 and 105,000 yr, are correlative with the lowest two terraces at Cape Arago. The fifth and oldest terrace at Cape Blanco has no equivalent at Cape Arago. Soil development indices for the third and fourth terraces at each area allow two alternative sets of correlations.