Geology topics

C.A. Holmgren

Publications and source records attributed to C.A. Holmgren.

4 recordsLinked to original sources

USGS2017

Holocene vegetation history from fossil rodent middens near Arequipa, Peru

Rodent (Abrocoma, Lagidium, Phyllotis) middens collected from 2350 to 2750 m elevation near Arequipa, Peru (16??S), provide an ???9600-yr vegetation history of the northern Atacama Desert, based on identification of >50 species of plant macrofossils. These midden floras show considerable stability throughout the Holocene, with slightly more mesophytic plant assemblages in the middle Holocene. Unlike the southwestern United States, rodent middens of mid-Holocene age are common. In the Arequipa area, the midden record does not reflect any effects of a mid-Holocene mega drought proposed from the extreme lowstand (100 m below modern levels, >6000 to 3500 yr B.P.) of Lake Titicaca, only 200 km east of Arequipa. This is perhaps not surprising, given other evidence for wetter summers on the Pacific slope of the Andes during the middle Holocene as well as the poor correlation of summer rainfall among modern weather stations in the central AndesAtacama Desert. The apparent difference in paleoclimatic reconstructions suggests that it is premature to relate changes observed during the Holocene to changes in El Nin??o Southern Oscillation modes. ?? 2001 University of Washington.

Quaternary Research↗

USGS2017

A 16,000 14C yr B.P. packrat midden series from the USA-Mexico Borderlands

A new packrat midden chronology from Playas Valley, southwestern New Mexico, is the first installment of an ongoing effort to reconstruct paleovegetation and paleoclimate in the U.S.A.-Mexico Borderlands. Playas Valley and neighboring basins supported pluvial lakes during full and/or late glacial times. Plant macrofossil and pollen assemblages from nine middens in the Playas Valley allow comparisons of two time intervals: 16,000-10,000 and 4000-0 14C yr B.P. Vegetation along pluvial lake margins consisted of open pinyon-juniper communities dominated by Pinus edulis, Juniperus scopulorum, Juniperus cf. coahuilensis, and a rich understory of C4 annuals and grasses. This summer-flowering understory is also characteristic of modern desert grassland in the Borderlands and indicates at least moderate summer precipitation. P. edulis and J. scopulorum disappeared or were rare in the midden record by 10,670 14C yr B.P. The late Holocene is marked by the arrival of Chihuahuan desert scrub elements and few departures as the vegetation gradually became modern in character. Larrea tridentata appears as late as 2190 14C yr B.P. based on macrofossils, but may have been present as early as 4095 14C yr B.P. based on pollen. Fouquieria splendens, one of the dominant desert species present at the site today, makes its first appearance only in the last millennium. The midden pollen assemblages are difficult to interpret; they lack modern analogs in surface pollen assemblages from stock tanks at different elevations in the Borderlands. ?? 2003 University of Washington. Published by Elsevier Inc. All rights reserved.

Quaternary Research↗

USGS2008

Late-Holocene fossil rodent middens from the Arica region of northernmost Chile

Identification of >40 taxa of plant macrofossils in 14 rodent (Abrocoma) middens collected from 2800 to 3590 m elevation at the latitude of Arica, Chile (18??S) provide snapshots of vegetation in the northernmost Atacama Desert over the past 3000 years. Midden floras show considerable stability throughout the late Holocene, which may be due in part to the broad elevational ranges of many perennial species and midden insensitivity to changes in plant community structure. The greatest variability is found in annuals in the Prepuna, a climatically sensitive zone. This variability, however might also arise from the brevity of midden depositional episodes. As the first midden record from the Arica-Parinacota Region (Chile's northernmost administrative region), this study demonstrates the potential for future midden research in this area. ?? 2007 Elsevier Ltd. All rights reserved.

Journal of Arid Environments↗

USGS2008

Late-Holocene fossil rodent middens from the Arica region of northernmost Chile

Identification of >40 taxa of plant macrofossils in 14 rodent (Abrocoma) middens collected from 2800 to 3590 m elevation at the latitude of Arica, Chile (18°S) provide snapshots of vegetation in the northernmost Atacama Desert over the past 3000 years. Midden floras show considerable stability throughout the late Holocene, which may be due in part to the broad elevational ranges of many perennial species and midden insensitivity to changes in plant community structure. The greatest variability is found in annuals in the Prepuna, a climatically sensitive zone. This variability, however might also arise from the brevity of midden depositional episodes. As the first midden record from the Arica-Parinacota Region (Chile's northernmost administrative region), this study demonstrates the potential for future midden research in this area.

Arica-Parinacota Region↗