Diatom Analysis

Abstract

In this chapter we present the diatom analysis results from glacio- lacustrine and lacustrine sedimentary sequences (Laguna Cascada, 54° 45′51′′ S, 64° 20′20.7′′W and Lago Galvarne Bog, 54° 44′16′′S, 64° 19′37.9′′W). The deeper part of Laguna Cascada core was radiocarbon dated in 13.285 ± 80 14C B.P. (15.949–15.545 cal. years B.P.). Diatom analysis has showed the existence of significant climate and paleoenvironmental fluctuations around the end of the Late Glacial and beginning of the early Holocene. The deglacial period was dominated by fragilarioids species. However, diatom assemblages had changed during the Holocene due to different climate trends. Diatom analyses from Lago Galvarne Bog were carried out only in the section corresponding to the middle Holocene marine transgression. The base of the core was dated at 13,515 14C B.P. (16,260 cal. years B.P.). Between 8,000 and 7,400 cal. years B.P., the domi- nance of marine diatoms together with species of brackish waters has suggested a strong marine influence within the basin. Between 7,400 and 3,700 cal. years B.P., a coastal environment would have been developed at Lago Galvarne, or perhaps even a fjord-type environment, as suggested by the high frequency of brackish diatoms together with fresh waters.