RESEARCH FOR CONTINUOUS PALAEOCLIMATE RECORD OF ENSO IN SOUTHERN CHILE (LAKE DISTRICT)

A research for a continuous Holocene ENSO record is actually carried out in Lake District area in southern Chile. Our purposes are to understand the sedimentological model deposition and, to build-up an age-model based on varve-counting. Overlapping thin-sections were prepared from the short cores by freeze-drying method. Their microscopic observations allow micro-sedimentological investigation and varve-counts at high resolution. The two selected lakes (Icalma Lake, 38°50’S; Puyehue Lake 40°40’S) present high-resolution laminated deposits. The sediment of Puyehue Lake is composed of couplets (light spring/summer layer and dark autumn/winter layer). Numerous tephras are interbedded so that they can be dated using varve chronology, with a calibration study of tephra thickness. Tephras in Icalma Lake is much more developed than in Puyehue Lake. The core ICA-I contains about 26 tephra beds (interflow site), whereas only 3 tephra beds were recognized from the thin-sections in PUII (interflow site). Consequently, we focused on the Puyehue Lake interflow site (PUII), because this coring site shows a more continuous “varve” record along with a few tephra beds. In addition, PUII core also present a liquefied facies (between 3.5 and 8.5 cm depth) that has to be taken in consideration before to build-up an age-model. According to varve chronology this homogeneous event is related to the major regional 1960’s palaeoseismic event (9.5 magnitude), that reworked 5 cm sediment thickness (c.a.67 years). Based on this correction, an age-model was adjusted until AD 1330, and annual accumulation rates were calculated (0.4 to 1.2 mm.yr-1). Theses results have to be compared with those obtained by other dating methods (210Pb, 137Cs, 14C), and with the historic data.