Late Quaternary solifluction sheets in the British uplands

Solifluction sheets are large-scale and extensive valley-floor and valley-side landforms developed widely in the British Isles from mass-wasting of glacial and periglacial sediments during late-glacial times. We describe their geographical distribution and review the processes that have led to their development. We use data from the Cheviot Hills, the one site in the British Isles where sedimentology and optically stimulated luminescence dating have been combined, to assess their age and nature of deposition. We also present data from central Wales where a new mapping and resistivity survey has reconstructed the nature of valley-side solifluction sheets. We explore the relative lack of recent research on these landforms and argue that solifluction sheets represent a clear example of how upland geomorphological systems have responded to late-glacial climate change. We end by identifying a number of areas where research on these enigmatic features could be focussed, including better understanding of their distribution, sedimentology and age.     

The onset of coronal mass ejections

This study addresses the onset of coronal mass ejections. From examination of sensitive X-ray images from the Solar Maximum Mission around the projected onset time of coronal mass ejections we identify two important new features: (1) there is usually a weak, soft X-ray enhancement 15–30 min prior to the linearly extrapolated chromospheric departure time of the ejection; (2) this activity is generally from two widely separated ( 10⁵ km) parts of the Sun. Possible physical mechanisms for these phenomena are examined and it is concluded that a plausible explanation is that the initial energy release is converted first into kinetic energy of suprathermal protons, 10²–10³ keV. The protons are trapped in a large magnetic loop which later breaks open as the mass ejection; Coulomb losses are the destabilizing agent but the mass ejection is probably magnetically driven. Protons that escape into the loss cone will impact the loop footpoints to heat the upper chromospheric material to a sufficiently high temperature to generate the weak soft X-ray emission. There will also be an H signature, and this is observed in a number of events. There is in general no radio emission or hard X-ray emission accompanying the soft X-ray precursor. When the coronal mass ejection is followed by a flare, then this is generally from a point close to, but not identical to, one of the points with the earlier soft X-ray enhancement.NCAR is sponsored by the National Science Foundation.     

Identification and quantification of carbonyl-containing α-pinene ozonolysis products using <Emphasis Type="Italic">O</Emphasis>-<Emphasis Type="Italic">tert</Emphasis>-butylhydroxylamine hydrochloride

The yields of carbonyl-containing reaction products from the ozonolysis of α-pinene have been investigated using concentrations of ozone found in the indoor environment ([O₃] ≤ 100 ppb). An impinger was used to collect gas-phase oxidation products in water, where the derivatization agent O-tert-butylhydroxylamine hydrochloride (TBOX) and gas chromatography-mass spectrometry were used to identify carbonyl-containing species. Seven carbonyl-containing products were observed. The yield of the primary product, pinonaldehyde was measured to be 76 %. Using cyclohexane as a hydroxyl radical (?OH) scavenger, the yield of pinonaldehyde decreased to 46 %, indicating the influence secondary OH radicals have on α-pinene ozonolysis products. Furthermore, the use of TBOX, a small molecular weight derivatization agent, allowed for the acquisition of the first mass spectral data of oxopinonaldehyde, a tricarbonyl reaction product of α-pinene ozonolysis. The techniques described herein allow for an effective method for the collection and identification of terpene oxidation products in the indoor environment.     

Channel change and the significance of floodplain stratigraphy: 1990 flood event,lower river Tay,Scotland

During February 1990 a flood event on the River Tay with an estimated recurrence interval of 70 years in its lower reaches caused extensive flooding and geomorphological change. The most extensive area of flooding and dramatic geomorphological change, the erosion of two new channels across the floodplain, was in the vicinity of the village of Caputh, Perthshire. The location of the eroded channels relates to the position of former river courses, identifiable by depressions in the floodplain surface and floodplain stratigraphy. The lower floodplain surface elevation and occurrence of gravel and sand deposits along the line of the former river courses caused the area to be more vulnerable to erosion and controlled the morphology of the eroded channels.     

Ar/Ar dating of the Bandelier Tuff and San Diego Canyon ignimbrites, Jemez Mountains, New Mexico: Temporal constraints on magmatic evolution

The Jemez Mountains volcanic field (JMVF), located in north-central New Mexico, has been a site of basaltic to rhyolitic volcanism since the mid-Miocene with major caldera forming eruptions occurring in the Pleistocene. Eruption of the upper Bandelier Tuff (UBT) is associated with collapse of the Valles Caldera, whereas eruption of the lower Bandelier Tuff (LBT) resulted in formation of the Toledo Caldera. These events were previously dated by K-Ar at 1.12 ± 0.03 Ma and 1.45 ± 0.06 Ma, respectively. Pre-Bandelier explosive eruptions produced the San Diego Canyon (SDC) ignimbrites. SDC ignimbrite “B” has been dated at 2.84 ± 0.07 Ma, whereas SDC ignimbrite “A”, which underlies “B”, has been dated at 3.64 ± 1.64 Ma. Both of these dates are based on single K-Ar analyses.⁴⁰Ar/³⁹Ar dating of single sanidine crystals from these units indicates revision of the previously reported dates. Isochron analysis of 26 crystals from the UBT gives a common trapped ⁴⁰Ar/³⁶Ar component of 304.5, indicating the presence of excess ⁴⁰Ar in this unit, and defines an age of 1.14 ± 0.02 Ma. Isochron analysis of 26 crystals from the LBT indicates an atmospheric trapped component and an age of 1.51 ± 0.03 Ma. An age of 1.78 ± 0.04 Ma, based on the weighted mean of 5 individual analyses, is indicated for SDC ignimbrite “B”, whereas 3 analyses from SDC ignimbrite “A” give a weighted mean age of 1.78 ± 0.07 Ma. Evidence for xenocrystic contamination in the SDC ignimbrites comes from analyses of a correlative air-fall pumice unit in the Puye Formation alluvial fan giving ages of 1.75 ± 0.08 and 3.50 ± 0.09 Ma. The presence of xenocrysts in bulk separates used for the original K-Ar analyses could account for the significantly older ages reported.Geochemical data indicate that SDC ignimbrites are early eruptions from the magma chamber which evolved to produce the LBT, as compositions of SDC ignimbrite “B” are virtually identical to least evolved LBT samples. Differentiation during the 270-ka interval between eruption of SDC ignimbrite “B” and the LBT produced an array of high-silica rhyolite compositions which were erupted to form the LBT. Mixed pumices associated with eruption of the LBT indicated an influx of more mafic magma into the system which produced shifts in some incompatible trace-element ratios. Lavas and tephras of the Cerro Toledo Rhyolite record the geochemical evolution of the Bandelier magma system during the 370-ka interval between eruption of the LBT and the UBT.The combined geochronologic and geochemical data place the establishment and evolution of the Bandelier silicic magma system within a precise temporal framework, beginning with eruption of the SDC ignimbrites at 1.78 Ma, and define a periodicity of 270–370 ka to ash-flow eruptions in the JMVF. These intervals are comparable to those in other multicyclic caldera complexes and are a measure of the timescales over which substantial fractionation of large silicic magma bodies occur.     

Palygorskite as a sediment dispersal tracer in the eastern Mediterranean

Palygorskite is a clay mineral widely distributed in late Quaternary deposits of the eastern Mediterranean, where, locally, it proves an ideal tracer of sediment dispersal. This study shows that the origin of this mineral is not limited to African sources. Cores containing late Pleistocene to recent sediment record the transport of palygorskite from the Plain of Helos on the Peloponnesus to specific deep basins along the Hellenic Arc. Palygorskite, commonly concentrated in the silt size fraction, may be overlooked in studies that focus only on the <2 μm fraction. In this region we find that the detrial palygorskite distribution is partially controlled by size-sorting effects related to gravity-induced transport processes. In consequence, comprehensive compositional analyses should be made both on the silt and clay fractions.