A long-lived middle Pleistocene lake formed in the Valle Grande, a large moat valley of the Valles caldera in
northern New Mexico, when a post-caldera eruption (South Mountain rhyolite) dammed the drainage out of the caldera. The
deposits of this lake were cored in May 2004 (GLAD5 project, hole VC-3) and 81 m of mostly lacustrine silty mud were
recovered. A tentative chronology has been established for VC-3 with a basal tephra Ar-Ar date of 552 +/- 3 ka, a correlation
of major climatic changes in the core with other long Pleistocene records (deep sea oxygen isotope records and long Antarctic
ice core records), and the recognition of two geomagnetic field polarity events in the core which can be correlated with globally
recognized events. This record spans a critical interval of the middle Pleistocene from MIS 14 (552 ka) to MIS 10 (~360 ka), at
which time the lacustrine sediments filled the available accommodation space in the caldera moat. Multiple analyses, including
core sedimentology and stratigraphy, sediment density and rock magnetic properties, organic carbon content and carbon isotope
ratios, C/N ratios, and pollen content reveal two glacial/interglacial cycles in the core (MIS 14 to MIS 10). This record includes
glacial terminations V and VI and complete sections spanning interglacials MIS 13 and MIS 11. In the VC-3 record, both of
these interglacials are relatively long compared with the intervening glacials (MIS 14 and MIS 12), and interglacial MIS 13 is
significantly muted in amplitude compared with MIS 11. These features are similar to several other mid-Pleistocene records.
The glacial terminations are quite abrupt in this record with notable changes in sedimentation, organic carbon content, C/N
ratios and watershed vegetation type. Termination V is the largest climate change evident in this part of the middle Pleistocene.
The glacial inceptions tend to be more gradual, on the order of a few thousand years.
|Title||Two middle Pleistocene glacial-interglacial cycles from the Valle Grande, Jemez Mountains, northern New Mexico|
|Authors||Peter J. Fawcett, Jeff Heikoop, Fraser Goff, R. Scott Anderson, L. Donohoo-Hurley, John William Geissman, Giday WoldeGabriel, Craig D. Allen, Catrina M. Johnson, Susan J. Smith, Julianna Fessenden-Rahn|
|Publication Type||Conference Paper|
|Publication Subtype||Conference Paper|
|Record Source||USGS Publications Warehouse|
|USGS Organization||Fort Collins Science Center|