TIMING OF LATE QUATERNARY GLACIAL ADVANCES IN THE CENTRAL PERUVIAN ANDES (10°-11°S) SUGGESTS A LINK TO HEINRICH EVENTS

Seven cosmogenic ¹⁰Be ages from boulders on a moraine in the Santuario Nacional Bosque de Piedras de Huayllay (BP) in the Western Cordillera of the central Peruvian Andes (10°59'S, 76°20'W, ~4180-4200 masl) are consistent with ¹⁰Be ages on moraines in both the Eastern Cordillera (40-45 km to the east) and the Nevado Jeulla Rajo (NJR) massif (10°00'S, 77°16'W) at the southern end of the Cordillera Blanca (150 km to the northwest). In the BP, ¹⁰Be ages are ~14-15 ka on four ignimbrite boulders, ~26 and ~20 ka on two quartz boulders, and ~45 ka on ignimbrite bedrock below the trimline in the valley wall. In the Eastern Cordillera bordering Lake Junin, the most extensive glaciations are >150 ka, but end moraine loops farther upvalley date to the local last glacial maximum (LLGM; ~26-30 ka) and a late-glacial stillstand or readvance (~14-18 ka). In NJR, ¹⁰Be ages indicate that the largest lateral moraines were deposited during similar intervals: the LLGM (~27-32 ka) and late-glacial (~13-18 ka). Avulsion of a glacial valley preserved an older, smaller pair of lateral moraines (ca. 56-65 ka) in NJR; correlative moraines were apparently not preserved in the Junin valleys. We have found no moraines in NJR that date to the global LGM (~19-24 ka), but see some evidence for an advance ~40-48 ka. Three cobbles provide a minimum age of ~50 ka for lodgement till that extends ~6 km across the Conococha Plain beyond the termini of the NJR moraines. The wide distribution of till suggests that at least one older glaciation was far more extensive than any of the late Quaternary NJR advances that we have dated by ¹⁰Be (ages calculated using CRONUS-Earth Online Calculator v. 2.2, Lal/Stone time-dependent scaling, and zero erosion). The timing of glacial advances in the central Peruvian Andes since 70 ka suggests a correlation to Heinrich events and associated southward shifts of the Intertropical Convergence Zone (ITCZ) in the Atlantic Ocean. We propose that Peruvian glaciers typically expanded when southward migration of the ITCZ resulted in increased precipitation in the tropical Andes during colder intervals.