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Millennial-scale dynamics of valley fills over the past 12,000 (super 14) C yr in northeastern New Mexico, USA

Daniel H. Mann and David J. Meltzer
Millennial-scale dynamics of valley fills over the past 12,000 (super 14) C yr in northeastern New Mexico, USA
Geological Society of America Bulletin (December 2007) 119 (11-12): 1433-1448

Abstract

We studied the alluvial histories of eight small (<40 km (super 2) ) watersheds in the uplands of northeastern New Mexico. The data come from radiocarbon-dated sections exposed in the banks of arroyos and permanent-channel streams. Results show that nine periods of valley aggradation separated by incision episodes occurred over the past 12,000 (super 14) C yr. These millennial-scale cycles occurred in rough synchrony within different drainages. Parts of some cycles coincided with well-known climatic fluctuations. For example, aggradation occurred during the Younger Dryas chronozone, 11,000-10,000 (super 14) C yr B.P., and valley fills persisted in incised states during the early Holocene peak in Milankovitch summer insolation. Incision occurred early in the Medieval Warm Period (ca. A. D. 1000-1300), aggradation during the Little Ice Age (A.D. 1300-1880), and incision during the last century. Changes in precipitation tied to the strength of the North American Monsoon system probably drive these cycles of aggradation and incision: when the system is strong, more frequent summer thunderstorms cause increased flooding in these small watersheds. Wetter summers over periods of decades to centuries allow forest vegetation to spread, which reduces sediment input from hillslopes at the same time floods are eroding valley fills. Aggradation of valley fills probably occurs when summer thunderstorms are less frequent, and large floods are correspondingly rare. Prolonged summer drought reduces forest cover, which increases erosion from slopes and causes sediment to accumulate in valleys. In turn, the strength of the North American Monsoon system is probably controlled by fluctuating sea-surface temperatures. The geomorphic cycles we describe may reflect a previously unrecognized, millennial-scale climate oscillation that is important in shaping the landscapes of the southern Great Plains.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 119
Serial Issue: 11-12
Title: Millennial-scale dynamics of valley fills over the past 12,000 (super 14) C yr in northeastern New Mexico, USA
Affiliation: University of Alaska, Institute of Arctic Biology, Fairbanks, AK, United States
Pages: 1433-1448
Published: 200712
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 93
Accession Number: 2007-128485
Categories: Quaternary geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 1 table, sketch maps
N36°49'60" - N37°00'00", W104°15'00" - W103°49'60"
Secondary Affiliation: Southern Methodist University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200724
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