HOLOCENE GLACIATION IN THE SIERRA NEVADA, CALIFORNIA

Multiple sediment cores from two paternoster lakes (First and Second lakes in ascending order) in North Fork Big Pine Creek, Sierra Nevada, preserve the most detailed and complete record of Holocene glaciation yet recovered in the range.  The lakes are fed by outwash from the Palisade Glacier, the largest (~1.3 km²) and presumably longest-lived glacier in the Sierra Nevada, and capture essentially all of the rock flour produced by the glacier.  Distinct late-Holocene (Matthes) and late-Pleistocene (Recess Peak) moraines lie between the modern glacier and the lakes.  The lakes have therefore received continuous sedimentation since the retreat of the Tioga glacier (Last Glacial Maximum) and capture rock flour related to all post-LGM advances.

A total of 6 long cores (up to 5.5m sediment depth) and 1 high resolution short core preserve a coherent record of increased and decreased rock flour flux to the lakes through the Holocene.  Age constraints on rock flour spikes in First Lake based on 13 ¹⁴C-dated macrofossils indicate Holocene glaciation began ~3200 cal. yr B.P., followed by glacier maxima at ~2800, ~1600, ~700 and ~100 cal. yr. B.P., the most recent peak being the largest.  ¹⁴C analysis of four additional macrofossils in a core from Second Lake are consistent with the glacial record in First Lake, thus provide further constraints on the onset and culmination of the Neoglacial events in the basin.

High resolution ²¹⁰Pb, magnetic susceptibility and loss-on-ignition analyses of the short (Glew) core indicate that rock flour flux to Second Lake began decreasing during the 1800's.  This result compares well with historical photos showing Sierran glaciers being near their Matthes maxima in the mid to late 1800's, and indicates that the rock flour record in the lakes responds rapidly (£ decade) to thinning or shrinkage of the glacier. 

Preliminary equilibrium line altitude (ELA) measurements from both North and South forks of Big Pine Creek drainage indicate that Matthes maximum ELAs were typically ~100m higher than those of the late-glacial Recess Peak advance in the same cirques.