ALBERT

Description: This study tested whether accurate dating by accelerator mass spectrometry (AMS) radiocarbon wiggle-matching of short tree-ring series (~30 annual rings) in the Medieval period could be achieved. Scientific dating plays a central role in the conservation of historic buildings in England. Precise dating helps assess the significance of particular buildings or elements of their fabric, thus allowing us to make informed decisions about their repair and protection. Consequently, considerable weight, both financial and legal, can be attached to the precision and accuracy of this dating. Dendrochronology is the method of choice, but in a proportion of cases this is unable to provide calendar dates. Hence, we would like to be able to use 14C wiggle-matching to provide a comparable level of precision and reliability, particularly on shorter tree-ring sequences (~30 annual growth rings) that up until now would not routinely be sampled. We present the results of AMS wiggle-matching five oak tree-ring sequences, spanning the period covered by the vast majority of surviving Medieval buildings in England (about AD 1180–1540) when currently we have only decadal and bidecadal calibration data.

Description: It is becoming increasingly clear that in order to generate accurate radiocarbon dates for bone collagen samples it is important to determine a sample-specific background correction to account for the greater complexity and higher number of steps in the pretreatment chemistry of this material. To provide suitable samples for the 14C community, 7 bone samples were obtained from contexts within British gravel quarries, which according to other dating techniques or stratigraphic information, should be of infinite age with respect to 14C. The bones were analyzed at the Oxford Radiocarbon Accelerator Unit (ORAU) and the Scottish Universities Environmental Research Centre (SUERC) to determine their suitability. In this paper, we show that 6 of the samples were indistinguishable from background. Both institutions measured finite ages for sample 387 from Oxey Mead that were statistically indistinguishable. Further work is required to establish whether this is because the bone was intrusive and of a younger age than expected or whether it is contaminated either postdepositionally or in the laboratory. We favor the former explanation because (1) the 2 chemistry laboratories use very different pretreatment schemes, (2) collagen yields were high, and (3) the laboratories produced ages that are in good agreement. The 6 “greater than” age samples will be made available to 14C laboratories to be used as background standards.

Description: In 2003, a National Electrostatics Corporation (NEC) 5MV tandem accelerator mass spectrometer was installed at SUERC, providing the radiocarbon laboratory with 14C measurements to 4–5‰ repeatability. In 2007, a 250kV single-stage accelerator mass spectrometer (SSAMS) was added to provide additional 14C capability and is now the preferred system for 14C analysis. Changes to the technology and to our operations are evident in our copious quality assurance data: typically, we now use the 134-position MC-SNICS source, which is filled to capacity. Measurement of standards shows that spectrometer running without the complication of on-line δ13C evaluation is a good operational compromise. Currently, 3‰ 14C/13C measurements are routinely achieved for samples up to nearly 3 half-lives old by consistent sample preparation and an automated data acquisition algorithm with sample random access for measurement repeats. Background and known-age standard data are presented for the period 2003–2008 for the 5MV system and 2007–2008 for the SSAMS, to demonstrate the improvements in data quality.

Description: A new National Electrostatic Corporation (NEC) 5MV accelerator mass spectrometer became operational at the Scottish Universities Environmental Research Centre (SUERC) in July 2002. It has 2 Cs sputter negative ion sources: a 134-sample source (S1) for the routine measurement of all species, and a hybrid source (S2) with 40 spaces for radiocarbon measurements with either graphite or CO2 samples. A number of performance tests on graphite samples have been carried out on both sources. A precison of better than 0.3% is feasible for modern samples on a routine basis. The 14C background of the machine and the graphite preparation process blank are 0.04 ± 0.01 and 0.16 ± 0.05 pMC, respectively, indicating that 14C dating back to ~50 kyr BP is possible. The normalized 14C values for a series of reference materials agree well with the IAEA, TIRI, and FIRI consensus values. Routine measurement of 14C has been underway since May 2003. Preliminary results of performance tests on the CO2 gas ion source are also reported.

Description: The dune of Oitavos, the underlying paleosol, and Helix sp. gastropod shells found within the paleosol were dated using a combination of radiocarbon and blue optically stimulated luminescence (OSL). The organic component of the paleosol produced a significantly older age (∼20,000 cal BP) than the OSL age measurement (∼15,000 yr), while 14C age measurements on the inorganic component and the gastropods produced ages of ∼35,000 yr and ∼34,000 yr, respectively. Rare-earth element analyses provide evidence that the gastropods incorporate geological carbonate, making them an unreliable indicator of the age of the paleosol. We propose that the 14C age of the small organic component of the paleosol is also likely to be unreliable due to incorporation of residual material. The OSL age measurement of the upper paleosol (∼15,000 yr) is consistent with the age for the base of the dune (∼14,500 yr). The younger OSL age for the top of the dune (∼12,000 yr) suggests that it was built up by at least 2 sand pulses or that there was a remobilization of material at the top during its evolution, prior to consolidation.

Description: It is becoming increasingly clear that in order to generate accurate radiocarbon dates for bone collagen samples it is important to determine a sample-specific background correction to account for the greater complexity and higher number of steps in the pretreatment chemistry of this material. To provide suitable samples for the14C community, 7 bone samples were obtained from contexts within British gravel quarries, which according to other dating techniques or stratigraphic information, should be of infinite age with respect to14C. The bones were analyzed at the Oxford Radiocarbon Accelerator Unit (ORAU) and the Scottish Universities Environmental Research Centre (SUERC) to determine their suitability. In this paper, we show that 6 of the samples were indistinguishable from background. Both institutions measured finite ages for sample 387 from Oxey Mead that were statistically indistinguishable. Further work is required to establish whether this is because the bone was intrusive and of a younger age than expected or whether it is contaminated either postdepositionally or in the laboratory. We favor the former explanation because (1) the 2 chemistry laboratories use very different pretreatment schemes, (2) collagen yields were high, and (3) the laboratories produced ages that are in good agreement. The 6 “greater than” age samples will be made available to14C laboratories to be used as background standards.

Description: The present paper reports on three sets of experiments exploring the persistence of seeds of oilseed rape (Brassica napus). The first, where known numbers of seeds were buried in September 1991 in two field experiments, demonstrated substantial initial losses of seeds, such that only 0·2 and 3·8% of seeds were still present after 4 months. In these experiments, which were not disturbed by mechanical cultivation, there was little evidence of further decline over the following 13 months. In the second of the two experiments, seeds were then left undisturbed for a further 136 months. A mean of 1·8% of seeds were still present after this period, providing further confirmation of the lack of decline in seed numbers in these undisturbed conditions. In the second pair of experiments, known numbers of seeds of three rape cultivars were broadcast onto plots and then either ploughed into the soil immediately after the start of the experiments, or were exposed to weekly shallow tine cultivation followed by ploughing after 4 weeks. The former created a larger seedbank than the latter. The experiments were then ploughed, annually (Expt 1) or at less frequent intervals (Expt 2); appreciable numbers of seeds survived for 65 months in both. Calculations based on exponential decline curves indicated that 95% seed loss would take 15–39 months, depending on the site, cultivar and initial post-harvest stubble treatment. The third part of the paper is based on more detailed studies of persistence of seeds of six cultivars in Petri dishes and buried in 25 cm pots. This work confirmed that cultivars differed in their persistence, as Apex was confirmed as highly persistent, whereas Rebel was short-lived. There were inconsistencies in the response of cultivar Synergy between the Petri-dish and pot experiment, which need further study. This experiment also reinforced the conclusion of the initial field experiments that little seed loss occurs in the absence of cultivations. Appreciable numbers of rape seeds will persist up to 4 years, in normal cropping conditions and in the absence of cultivation one experiment has confirmed persistence for over 11 years.

Description: SummaryDuring 1970–3 three experiments with winter wheat, three with spring barley, two with permanent grass and one with perennial ryegrass measured the effects of a liquid N-fertilizer (26% N) sprayed over the leaves either alone or with a herbicide added to it. ‘Nitro-Chalk’ (21% N) was used as the standard for comparison. The liquid N-fertilizer was made from urea and ammonium nitrate; the herbicide was a mixture of dichlorprop and MCPA. Each experiment tested all combinations of the two N fertilizers applied to give 38, 75 or 113 kg N/ha without the herbicide and with either 2·8, 5·6 (recommended dose) or 8·4 1/ha of herbicide. The 24 treatments were applied to winter wheat at growth stages 4–5 of the Feekes scale, to barley at growth stage 5 and to grass in late spring and again to regrowth after cutting.Herbicide alone sometimes scorched the leaves but seldom badly. Liquid N-fertilizer nearly always scorched the leaves and the amount of scorch was increased by adding herbicide; scorch also was increased by increasing the amount of either and so was most severe when most liquid fertilizer and most herbicide were sprayed together; this damage did not decrease yields appreciably except when only 38 kg N/ha was given.Spraying the herbicide with the liquid fertilizer always gave slightly better weed control than herbicide alone in the wheat, but not always in the barley; in the grass, weed control was no better than from herbicide alone.‘Nitro-Chalk’ gave larger yields of wheat grain than the liquid N-fertilizer did in seven of nine comparisons without herbicide and in 20 of 27 with it, of barley grain in five of nine comparisons without herbicide and in 15 of 27 with it, of permanent grass in 25 of 27 comparisons without herbicide and in 70 of 81 with it, and of perennial ryegrass in nine of nine comparisons without herbicide and in 25 of 27 with it. Thus herbicide did not alter the advantage that ‘Nitro-Chalk’ had.Percentages of N in the crops were larger with ‘Nitro-Chalk’ than with the liquid N-fertilizer but were changed little by herbicide.

Description: Three experiments have investigated the effect of the timing of control of infestations of volunteer barley (Hordeum vulgare), Stellaria media and Galium aparine on the growth and yield of winter oilseed rape (Brassica napus). Although the experiments used conventional herbicides to achieve the different timings of control, the work was done in the context of the commercialization of herbicide-tolerant oilseed rape, where treatments could be applied at any time from autumn to spring. In the three seasons studied, oilseed rape growth was particularly vigorous in the autumn and, as a consequence, the competitive impact of the weeds was lower than anticipated. Untreated volunteer barley and G. aparine reduced yields in one and two experiments, respectively. However, in all experiments volunteer barley reduced crop growth in winter and spring severely, even though January treatments prevented yield loss in these vigorous crops. Delayed control of this weed would not be advisable if the weed was particularly dense or the crop less vigorous. In contrast, the G. aparine had no effect on crop growth and was only really apparent in the crop in late summer, so delaying treatment until even March would not put yields at risk. In one year, S. media markedly reduced crop growth in late winter but in the second experiment this did not occur. Consequently, as with the G. aparine, delayed autumn control would be unlikely to jeopardize yields. Thus, if herbicide-tolerant crops are commercialized in Europe, there will be flexibility in timing of application of herbicides to control broad-leaved weeds in winter rape but there would be a risk of yield loss from delayed control of volunteer cereals.

Description: Combined structural, geochemical and isotopic studies have allowed an understanding of the timing and nature of an orogen-scale fault array. The results indicate that the deformation loci within the internal western Alps, during the Alpine collision, occurred as a foreland propagating thrust sequence. The east to west deformation migration within the internal zones is apparently in-sequence in relation to the external zones. Rb–Sr white mica dating of syn-kinematic greenschist-facies mineral assemblages from the Basal Briançonnais Thrust indicate that thrusting ceased between 27 and 32 Ma, several million years after shearing in the hinterland and several million years prior to shearing in the foreland. The Briançonnais Domain, which constitutes the hanging wall to the Basal Briançonnais Thrust, preserves two major shearing episodes. The first, with a top-to-the-northwest overshear, has been tentatively dated at 45 Ma. The second, a very pervasive, east–west orientated, greenschist-facies event was previously dated at 34 Ma on the hinterland margin of the Briançonnais Domain and has now been dated at 27–32 Ma on the foreland margin of the Briançonnais Domain. The period between 34 and 27 Ma apparently dates the migration of deformation through the relict European passive margin, represented by the Briançonnais Domain. This is believed to be in response to overthrusting of Adria/Africa and its associated subduction complex. Structural mapping indicates that the present Basal Briançonnais Thrust in the Col du Petit St Bernard region, Franco-Italian Alps, is a break-back thrust which cuts through an already imbricated pile. Geochronological evidence suggests that the early imbrication of the Briançonnais stratigraphy occurred prior to full interaction of the European and Adria/African plates, that is, during subduction, docking and escape from the subduction complex under Adria. Therefore, although the present Basal Briançonnais Thrust is a break-back thrust in terms of local structural geometries, it is an in-sequence foreland-propagating structure. Geochronological, micro-structural and micro-chemical data indicate that the Briançonnais Domain in the Col du Petit St Bernard zone is formed from granitoid material which intruded and cooled at approximately 320 Ma. During the Alpine event, deformation and metamorphism were insufficient to affect the Sr isotopic system. This suggests that this portion of the Briançonnais Domain was probably subducted to much shallower depths and underwent much less pervasive deformation than the other internal European basement material.