The late Pleistocene glaciation in the Bogchigir Valleys (Pamir, Tajikistan) based on ¹⁰Be surface exposure dating

Abstract

Glacial chronologies from the Pamir may not only provide insights into past changes in temperature, but also into past changes in precipitation related to the northern-hemispheric westerlies and the monsoonal circulation. We present 18 new exposure ages from the Bogchigir Valleys that complement and refine our previous studies in these valleys. The most extensive dated glaciation in the area occurred ~ 100 ka, during Marine Oxygen Isotope Stage (MIS) 5, and indicates increased precipitation likely from both the westerlies and the monsoonal circulation. A subsequent glacier advance, which deposited characteristic ‘chukur’ moraine lobes, occurred at ~ 80–75 ka. Circumstantial evidence points to glacial advances at ~ 65 and 40 ka, the latter likely also documenting increased monsoonal moisture supply during MIS 3. Less extensive glacial advances occurred during MIS 2 at ~ 28 and 24 ka and reflect the aridization trend during the course of the last glacial cycle. Deglaciation started ~ 21 ka, interrupted by minor stillstands or readvances at ~ 16 and 12 ka. Local calibration sites and glacier-climate modeling would be very helpful to reduce the systematic methodological uncertainties (still at least 10%) and to draw more detailed paleoclimatic conclusions.

Rates of river incision across the main tectonic units of the Pamir identified using optically stimulated luminescence dating of fluvial terraces

“…Additional scattered younger ages are interpreted as prolonged ice degradation and/or glacial recession (Zech et al, 2005b). Two less extensive glacial advances between 37 -30 kyr (MIS 3/2) and 24 -22 kyr (MIS 2) pre-date the LGM (Zech et al, 2005a;Abramowski et al, 2006;Röhringer et al, 2012). Minor glacial advances have been identified at ∼16 kyr and ∼12 kyr during an overall period of glacial retreat (Röhringer et al, 2012).…”

“…Glacial advances particularly during the Late Quaternary likely affected the drainage evolution by changing transported sediment volumes and river discharge and therefore may have triggered the development of river terraces along the Panj. Information regarding the Quaternary glacial chronology of the Pamir is limited to few study sites on the Pamir Plateau (Zech et al, 2005a;Abramowski et al, 2006;Röhringer et al, 2012). A chronology for local glacial landforms at lower altitudes in west-trending valleys has yet to be established.…”

“…Cosmogenic nuclide dating of the moraine yielded two age clusters of 136 -93 kyr and 86 -60 kyr (Zech et al, 2005a;Abramowski et al, 2006;Röhringer et al, 2012). The oldest glacial moraine from the Lake Yashilkul, the Southern Alichur Range and the Ailuitek Pass indicates the presence of paleo-glaciers down to the intra-plateau valley floors at ∼3600 m a.s.l.. Hummocky moraines accompanied by two lateral moraine ridges indicate a glacial advance during MIS 3, which is synchronous with an increased influence of the ISM (Zech et al, 2005a;Röhringer et al, 2012) as reported from the Hindu Kush, Karakoram Range and Tibet (e.g., Owen et al, 2002bOwen et al, ,a, 2008Owen et al, , 2012. Additional scattered younger ages are interpreted as prolonged ice degradation and/or glacial recession (Zech et al, 2005b).…”

“…The dated time range spans the period since the last glacial advance during early MIS 2 on the Pamir Plateau (Zech et al, 2005a;Abramowski et al, 2006;Röhringer et al, 2012). The oldest dated terraces of (23 ± 2.9) kyr to (19 ± 2.9) kyr coincide exposure ages of moraines from the last glacial advance (cf.…”

“…Feedbacks with topography result in climatic gradients between the margins and the plateau of the Pamir. Glacial moraines on the Pamir Plateau provide evidence for multiple glacial advances during the Late Quaternary (Zech et al, 2005a;Abramowski et al, 2006;Röhringer et al, 2012).…”