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D.R. Muhs

Publications and source records attributed to D.R. Muhs.

At least 55 records · Page 3Linked to original sources
USGS2000

Geochemical and mineralogical evidence from eolian sediments for northwesterly mid-Holocene paleowinds, central Kansas, USA

A prominent (4500 km2) dune field in the Great Plains is the Great Bend Sand Prairie of south-central Kansas. Dunes here overlie late Quaternary alluvium and were reactivated extensively in the late Holocene. Geomorphic and soil evidence suggests that the most likely eolian sand source is the Arkansas River valley to the northwest. Nevertheless, orientations of stabilized dunes indicate that the most recent dune-forming winds came from the south or southwest, in agreement with modern wind data. Mineralogy and trace element concentrations in eolian sands of the Great Bend Sand Prairie are similar to those to the Arkansas River, which permits the Arkansas River as a sediment source. Ca and Sr abundances, which reflect small amounts of carbonate minerals, are higher in Arkansas River sand compared to eolian sands and show a systematic depletion away from the Arkansas River to the southeast. These trends are likely due to carbonate mineral depletion downwind from abrasion and size reduction. Thus, paleowinds probably were northwesterly during initial deposition. Northwesterly winds occur today when dry, Pacific-derived air is dominant. We hypothesize that the residence time of this air mass was much greater while dunes initially formed, possibly during a warmer and drier mid-Holocene period.

Quaternary International↗
USGS1999

Late Quaternary loess in northeastern Colorado: Part II - Pb isotopic evidence for the variability of loess sources

Loess in eastern Colorado covers an estimated 14 000 km 2 , and is the westernmost part of the North American midcontinent loess province. Stratigraphic studies indicate there were two periods of loess deposition in eastern Colorado during late Quaternary time. The first period spanned ca. 20 000 to 12 000 14 C yr B.P. (ca. 20–14 ka) and correlates reasonably well with the culmination and retreat of Pinedale glaciers in the Colorado Front Range during the last glacial maximum. The second period of loess deposition occurred between ca. 11 000 and 9000 14 C yr B.P. This interval may be Holocene or may correlate with a hypothesized Younger Dryas glacial advance in the Colorado Front Range. Sedimentologic, mineralogic, and geochemical data indicate that as many as three sources could have supplied loess in eastern Colorado. These sources include glaciogenic silt (derived from the Colorado Front Range) and two bedrock sources, volcaniclastic silt from the White River Group, and clays from the Pierre Shale. The sediment sources imply a generally westerly paleowind during the last glacial maximum. New carbon isotope data, combined with published faunal data, indicate that the loess was probably deposited on a cool steppe, implying a last glacial maximum July temperature depression, relative to the present, of at least 5–6 °C. Overall, loess deposition in eastern Colorado occurred mostly toward the end of the last glacial maximum, under cooler and drier conditions, with generally westerly winds from more than one source.

Geological Society of America Bulletin↗
USGS1997

Holocene eolian activity in the Minot dune field, North Dakota

Stabilized eolian sand is common over much of the Great Plains region of the United States and Canada, including a subhumid area of ~1500 km 2 near Minot, North Dakota. Eolian landforms consist of sand sheets and northwest-trending parabolic dunes. Dunes and sand sheets in the Minot field are presently stabilized by a cover of prairie grasses or oak woodland. Stratigraphic studies and accelerator mass spectrometry radiocarbon dating of paleosols indicate at least two periods of eolian sand movement in the late Holocene. Pedologic data suggest that all of the dune field has experienced late Holocene dune activity, though not all parts of the dune field may have been active simultaneously. Similar immobile element (Ti, Zr, La, Ce) concentrations support the interpretation that eolian sands are derived from local glaciofluvial and glaciolacustrine sediments. However, glaciolacustrine and glaciofluvial source sediments have high Ca concentrations from carbonate minerals, whereas dune sands are depleted in Ca. Because noneolian-derived soils in the area are calcareous, these data indicate that the Minot dune field may have had extended periods of activity in the Holocene, such that eolian abrasion removed soft carbonate minerals. The southwest-facing parts of some presently stabilized dunes were active during the 1930s drought, but were revegetated during the wetter years of the 1940s. These observations indicate that severe droughts accompanied by high temperatures are the most likely cause of Holocene eolian activity.

North Dakota↗
USGS1996

Origin of the late quaternary dune fields of northeastern Colorado

Stabilized eolian deposits, mostly parabolic dunes and sand sheets, cover much of the landscape of northeastern Colorado and adjacent parts of southwestern Nebraska in four geographically distinct dune fields. Stratigraphic and soil-geomorphic relations and accelerator radiocarbon dating indicate that at least three episodes of eolian sand movement occurred between 27 ka and 11 ka, possibly between 11 ka and 4 ka, and within the past 1.5 ka. Thus, eolian sand deposition took place under both glacial and interglacial climatic conditions. In the youngest episodes of eolian sand movement, Holocene parabolic dunes partially buried Pleistocene sand sheet deposits. Late Holocene sands in the Fort Morgan and Wray dune fields, to the south of the South Platte River, have trace element ratios that are indistinguishable from modern South Platte River sands, but different from Ogallala Formation bedrock, which has previously been cited as the main source of dune sand on the Great Plains. Sands in the Greeley dune field, to the north of the South Platte River, have trace element concentrations that indicate a probable Laramie Formation source. Measurements of parabolic dunes indicate paleowinds from the northwest in all dune fields, in good agreement with resultant drift directions calculated for nearby weather stations. Thus, paleowinds were probably not significantly different from present-day winds, and are consistent with a South Platte River source for the Fort Morgan and Wray dune fields, and a Laramie Formation source for the Greeley dune field. Sand accumulated downwind of the South Platte River to form the Fort Morgan duen field. In addition, sand was also transported farther downwind over the upland formed by the calcrete caprock of the Ogallala Formation, and deposited in the lee of the upland on the southeast side. Because of high wind energy, the upland itself served as a zone of sand transport, but little or no sand accumulation took place on this surface. These studies, which demonstrate the importance of fluvial-source sediments for dune fields in Colorado, may be applicable to other dune fields in North America. Because modern drift potentials in northeastern Colorado are among the highest in the world, the present stability of dunes in the region may be in part a function of the dunes being supply-limited rather than solely transport-limited. Extensive (∼ 7700 km 2 ) late Holocene dunes document that eolian sand in northeastern Colorado is very sensitive to small changes in climate or fluvial source conditions.

Geomorphology↗
USGS1996

Origin of Bermuda's clay-rich Quaternary paleosols and their paleoclimatic significance

Red clayey paleosols that are chiefly the product of aerosolic dust deposition are interbedded in the Quaternary carbonate formations of the Bermuda oceanic island system. These paleosols provide a basis for reconstructing Quaternary atmospheric circulation patterns in the northwestern Atlantic. Geochemical analyses were performed on representative paleosol samples to identify their parent dust source. Fine-grained fractions were analyzed by energy-dispersive X ray fluorescence to determine trace element (Zr, Y, La, Ti, and Nb) concentrations and to derive geochemical signatures based on immobile element ratios. These ratios were compared with geochemical signatures determined for three possible sources of airborne dust: (1) Great Plains loess, (2) Mississippi River Valley loess, and (3) Saharan dust. The Zr/Y and Zr/La ratios provided the clearest distinction between the hypothesized dust sources. The low ratios in the paleosol B horizons most closely resemble Saharan dust in the <2-μm size class fraction. Contributions from the two North American loessial source areas could not be clearly detected. Thus Bermuda paleosols have a predominantly Saharan aerosolic dust signature. Saharan dust deposition on Bermuda during successive Quaternary glacial periods is consistent with patterns of general circulation models, which indicate that during glacial maxima the northeast summer trade winds were stronger than at present and reached latitudes higher than 30°N despite lower-than-present sea surface temperatures in the North Atlantic.

Journal of Geophysical Research D: Atmospheres↗
USGS1994

New uranium-series ages of the Waimanalo Limestone, Oahu, Hawaii: implications for sea level during the last interglacial period

The Waimanalo Formation (limestone) of Oahu has been correlated with the last interglacial period based on U-series dating of corals by T.-L. Ku and colleagues. The limestone consists of growth-position corals and overlying coral conglomerate. An apparent bimodal distribution of ages for the growth-position corals (mean age = 133 ka) and the overlying coral conglomerate (mean age = 119 ka) has been interpreted to represent two distinct high stands of sea that occurred within the last interglacial period. Both growth-position corals and overlying, conglomerate coral occur in an outcrop east of Kaena Point and consist mainly of Pocillopora and Porites. U-seriesages of growth-position corals that show closed-system conditions are 120 &plusmn; 3 ka and 127 &plusmn; 4 ka; overlying conglomerate corals have U-seriesages that range from 120 &plusmn; 3 ka to 138 &plusmn; 4 ka. At Kahe Point, conglomerate corals have ages of 120 &plusmn; 3 ka and 134 &plusmn; 4 ka. These data show that the growth position corals are not systematically older than the conglomerate corals; thus, there is no evidence for two distinct high stands of sea. Waimanalo deposits at Kahe Point and Mokapu Point (new U-seriesages of 134 &plusmn; 4 ka and 127 &plusmn; 3 ka) have beach deposits as high as 12.5 m and, at Mokapu Point, growth-position corals as high as 8.5 m. A last-interglacial sea-level stand of +8.5 to +12.5 m conflicts with estimates of +6 m from a number of tectonically stable coastlines and islands in the western Atlantic Ocean. We infer, therefore, that Oahu may be undergoing uplift at a low rate. This uplift may be due to compensatory lithospheric flexure, because the island of Hawaii has been subsiding throughout much of the Quaternary from volcanic loading. Because of this possible uplift, Oahu and islands like it elsewhere in the Pacific cannot be used as reference points for sealevel during the last interglacial period.

Hawai'i↗
USGS1994

Thorium-230 ages of corals and duration of the last interglacial sea-level high stand on Oahu, Hawaii

Thorium-230 ages of emergent marine deposits on Oahu, Hawaii, have a uniform distribution of ages from ∼114,000 to ∼131,000 years, indicating a duration for the last interglacial sea-level high stand of ∼17,000 years, in contrast to a duration of ∼8000 years inferred from the orbitally tuned marine oxygen isotope record. Sea level on Oahu rose to ≥1 to 2 meters higher than present by 131,000 years ago or ∼6000 years earlier than inferred from the marine record. Although the latter record suggests a shift back to glacial conditions beginning at ∼119,000 years ago, the Oahu coral ages indicate a near present sea level until ∼114,000 years ago.

Hawaii↗
USGS1993

The potential response of eolian sands to greenhouse warming and precipitation reduction on the Great Plains of the U.S.A.

Sand dunes and sand sheets are extensive on the semi-arid GreatPlains but are at present stabilized by a sparse vegetation cover. Use of a dune mobility index, which incorporates wind strength and the ratio of mean annual precipitation to potential evapotranspiration, shows that under predicted greenhouse climate effects of increased temperature and reduced precipitation, sand dunes and sand sheets on the GreatPlains are likely to become reactivated over a significant part of the region.

Great Plains↗
USGS1991

U and Sr Isotopes in ground water and calcite, Yucca Mountain, Nevada: Evidence against upwelling water

Hydrogenic calcite and opaline silica deposits in fault zones at Yucca Mountain, Nevada, have created considerable public and scientific controversy because of the possible development of a high-level nuclear waste repository at this location. Strontium and uranium isotopic compositions of hydrogenic materials were used to test whether the veins could have formed by upwelling of deep-seated waters. The vein deposits are isotopically distinct from ground water in the two aquifers that underlie Yucca Mountain, indicating that the calcite could not have precipitated from ground water. The data are consistent with a surficial origin for the hydrogenic deposits.

Nevada↗