Dt. Rodbell, THE TIMING OF THE LAST DEGLACIATION IN CORDILLERA ORIENTAL, NORTHERN PERU, BASED ON GLACIAL GEOLOGY AND LAKE SEDIMENTOLOGY, Geological Society of America bulletin, 105(7), 1993, pp. 923-934
The degree of soil development on moraines and radiocarbon ages indica
te that the Cordillera Oriental, a part of the eastern Andes in northe
rn Peru (7-degrees 30'-7-degrees 55'S; 77-degrees 20'-77-degrees 35'W)
, was last glaciated during the last glacial maximum (marine isotope s
tage 2). This glaciation was the most extensive late Quaternary glacia
tion in the area. Radiocarbon-dated sedimentological changes in six se
diment cores from three lakes and one bog reveal that the last deglaci
ation is marked by a two-stepped transition from rhythmically laminate
d inorganic sediment to massive, organic-rich sediment. The first step
of this transition commenced before 12.1 +/- 0.2 ka (+/- 1 sigma) and
probably by ca. 13.5 ka. Glaciers covered less than 50% of their last
glacial maximum area by 12.1 +/- 0.6 ka, and cirques west of the main
divide were probably ice-free by this time. A return to rhythmically
laminated inorganic sediment in the lakes and the bog occurred between
12.1 +/- 0.6 and 10.3 +/- 0.4 ka. This may reflect an episode of incr
eased stream discharge and glacier expansion during which glaciers reo
ccupied cirques above approximately 3,800 m. This glacier expansion ad
ds to widespread evidence of a late-glacial readvance in the tropical
Andes. All cirques have been ice-free since between 10.3 approximately
0.4 and 9.7 +/- 0.5 ka.