The Holocene in the South-Eastern region of the Province Jujuy, North-West Argentina

The results reported are from three sedimentary sections bordering the Rio Grande and its tributary in San Salvador de Jujuy and surrounding areas. The prevailing precipitation in the area of investigation at 1200 m elevation, is about 900 mm/yr and increases with altitude to 1300 mm/yr at 1700 m elevation. On the basis of these sections it is possible to recognize two Holocene dry phases and two humid phases. A dry period, from the Late Pleistocene until 8900 yr BP, is evident in the section Los Perales, in the form of a 3 m loess bed, rich in Volcanic glass. The Hypsithermal period, beginning 8900 yr BP and ending 6400 yr BP or even later, is identified by two different fossil soil developments in the section Los Perales, as well as by several peat horizons in the section Rio Chico. In the first case, we can recognize intensive soil development in the Early Holocene levels, which can be separated into two soil development phases. These phases are represented by two B-horizons separated by a 15 cm thick loess bed, and are dated by C-14 to 8180 +/- 130 yr BP and 6470 +/- 100 yr BP. In the case of the Rio Chico section, the peat below a gravel bed was radiocarbon dated to 8930 +/- 130 yr BP 7610 +/- 130 yr BP, 6970 +/- 100 yr BP and 6470 +/- 110 yr BP. The middle Holocene in section Los Perales is characterized by a 45 cm thick loess deposit, which reflects predominantly dry conditions. The recurrence of moister conditions and corresponding soil development into vertisols is documented by several palaeosols, the older ones dating to 1340 +/- 50 yr BP. (C) 1999 INQUA/Elsevier Science Ltd. All rights reserved.