PRELIMINARY LATE QUATERNARY SLIP HISTORY OF THE CARBONERAS FAULT, SOUTHEASTERN SPAIN

The Carboneras fault is one of three principal Cenozoic strike-slip fa ults in the Betic Cordillera of southeastern Spain. In this study, we characterize the paleoseismic history of the Carboneras fault by exami ning the evidence for lateral offset of 85-180 ka Tyrrhenian marine te rraces, by dating the left-lateral stream-channel offsets in La Serrat a, and by postulating a late Holocene coastal uplift event. We define three Quaternary alluvial-geomorphic units that assist in constraining rates of fault slip. Qfo deposits are pre-Tyrrhenian in age (> 100 ka ); Qf deposits are post-Tyrrhenian in age (<100 ka); and Qfy deposits are Roman or post-Roman (<1-2 ka) in age. Examination of the southern and northern segments of the Carboneras fault indicates that although Tyrrhenian marine terraces are vertically offset 5-10 m, no evidence f or large lateral offset of the marine terraces is visible. In La Serra ta, 80-100 In lateral stream-channel offsets are older than about 100 ka, and Wurmian-age alluvial fans were deposited within these offset c hannels. Along Rio Carboneras, mapping and topographical profiling of Qfy deposits indicate that stream deposits were previously graded to a sea level 3-5 m higher than that at present. The correlation of the Q fy terrace with upraised bedrock beach platforms along the coast sugge sts that a regional tectonic uplift event occurred during the last 1-2 ka. Based on a C-14 age on charcoal from Qfy deposits, this event mig ht have occurred since about AD 1475. The Quaternary slip history of t he Carboneras fault during the last 100 ka appears to be one of vertic al uplift rather than strike-slip movement, in agreement with contempo rary focal mechanisms. Maximum vertical slip rates during the last 100 ka are of the order of 0.05-0.1 mm/year. (C) 1997 Elsevier Science Lt d.