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This work considers the spatial distribution and ages of western MOZ basin siliclastic sediments prior to providing insights into the diagenesis of degraded dune and alluvial fan sands. Previously published and new TL/OSL ages imply that extensive over-washing of dune sands took place at least 100 ka ago while ages on Okavango floodplains imply that the fan was formed ca. 40 ka and has since undergone periods of higher and lower flood regimes. Sediment analyses indicate that both dune and fan sands contain a diagenetic matrix of clay-enhanced amorphous silica (CEAS) which bonds weakly formed aggregates. The time of formation of diagenetic matrix products is inconclusive but may have been accelerated during or shortly after events dated using OSL/TL techniques. Hence earlier dune over-washing may have led to greater porewater of an acidic to near neutral nature which in turn promoted smectite formation and silicic acid precipitation > 100 000 years ago. The relatively abundant CEAS matrix in floodplain sands implies more recent semi-continuous flood events again of an acidic-near neutral nature leading to the formation of smectite. In this case the floodplain sediments are dated as having been deposited around 40 and 11 ka, when porewater content may have accelerated clay formation and silica dissolution. The dual nature of the CEAS in the islands reflects a changing environment from smectite-dominated flooding events to sepiolite-dominated desiccation events. Flooding may also correspond to TL/OSL ages over the past 40 000 years which contributed to accelerated CEAS formation. The sepiolite is associated with a Ca-rich matrix implying desiccation which may relate to drying events over the 40 000 year period or to riparian tree root pumping and selective salt accumulation. This work shows that sedimentation in incipient rifts is complex and rarely explained totally in terms of primary depositional events. The implications of different stages of sand diagenesis may be significant in enhancing palaeo-environmental interpretations in semi-arid fluvial environments.

The Little Falls member of the Nepisiguit Falls Formation is situated in the northern part of the Brunswick Belt of the Bathurst Mining Camp and has been interpreted as the distal equivalent of proximal tuffaceous rocks that host the stratiform Brunswick No. 12 and No. 6 Pb-Zn massive sulfide deposits. It comprises fine-grained, greenish-gray tuffaceous sandstone in the lower part, and coarse-grained, crystal-rich tuffaceous sandstone in the upper part. Petrographic evidence suggests that these rocks have a turbiditic origin. The Little Falls member is underlain by the Vallee Lourdes member, mainly composed of relatively shallow-water calcareous rocks, and is conformably overlain by Mn-rich sedimentary rocks, mainly red argillites that host the Tetagouche Falls Mn-(Fe) deposit. All these rocks are considered to belong to the Nepisiguit Falls Formation, part of the Ordovician Tetagouche Group. Whole-rock geochemical data from the fine-grained tuffaceous sandstone and coarse-grained tuffaceous sandstone indicate that the two units of the Little Falls member are distinct. Zr and TiO 2 contents, and total rare earth element (REE) values are higher in the coarse-grained unit (average Zr/TiO 2 = 0.040, average ∑REE = 247 ppm, n = 6) than in the fine-grained unit (average Zr/TiO 2 = 0.048, average ∑REE = 158 ppm, n = 17), which can be attributed to the variation in crystal content between the two units. Both units are HREE-enriched and have elevated La/Yb relative to the typical Nepisiguit Falls Formation. Overall, the geochemical data combined with evidence from the bounding units suggest that the Little Falls member was deposited in relatively shallow water, possibly in a near-arc environment. The relationship of volcanic facies within the Nepisiguit Falls Formation and the geochemistry of these facies indicate strongly that fine grained, reworked tuffaceous rocks, regardless of whether they are the distal equivalents of proximal tuffaceous rocks, are not associated with the major ore-bearing horizons of the Bathurst Mining Camp.

Sediment samples from a continuous 4.6 m profile in the dry bed of Lake Ngami in NW Botswana were analysed for geochemistry and dated using both 14C and TL methods. Certain units in the profile were found to be diatom rich and these, with the geochemical results, were used as indicators of high and low lake levels within the basin. The Lake Ngami sediments contain a high proportion of SiO2 (51–92.5 wt%, avg. 72.4 wt%) and variable levels of Al2O3 (2.04–17.2 wt%, avg. 8.88 wt%). Based on elevated Al2O3 and organic matter (LOIorgC ) results, lacustrine conditions occurred at ca. 42 ka until 40 ka and diatom results suggest that relatively deep but brackish conditions prevailed. At 40 ka, the lacustrine sedimentary record was terminated abruptly, possibly by tectonic activity. At ca. 19 ka, shallow, aerobic, turbulent conditions were prevalent, but lake levels were at this time increasing to deeper water conditions up until ca. 17 ka. This period coincides with the Late Glacial Maximum, a period of increased aridity in the central southern Africa region. Generally, increasing Sr/Ca ratios and decreasing LOIorgC and Al2O3, from ca. 16 to 5 ka, suggest decreasing inflow into the basin and declining lake levels. Based on the enrichment of LREE results, slightly alkaline conditions prevailed at ca. 12 ka. Diatom results also support shallow alkaline conditions around this time. These lake conditions were maintained primarily by local rainfall input as the region experienced a warmer, wetter phase between 16 and 11 ka. Lake levels rose rapidly by 4 ka, probably in response to enhanced rainfall in the Angolan catchment. These results indicate that lake levels in the Lake Ngami basin are responding to rainfall changes in the Angolan catchment area and local rainfall. The results confirm that the present-day anti-phase rainfall relationship between southern Africa and regions of equatorial Africa was extant during the late Quaternary over the Angolan highlands and NW Botswana.

This work considers new evidence for palaeo-environmental change taking place during the Pleistocene in northern Botswana. Duricrusted strandlines along the northeastern margin of Sua Pan provide palaeo-environmental data pertaining to the Makgadikgadi subbasin (MSB) with inferences regarding the larger Makgadikgadi–Okavango–Zambezi (MOZ) rift depression. Field, XRD and geochemical data show that MSB strandlines comprise calcretes (LU1 type), MgO-rich calcretes with silica (LU2 type), sil-calcrete (LU3 type) and silcrete (LU4 type). Early freshwater episodes appear to have been followed by calcrete-dominated drying phases interspersed with repeated silcretisation. Calcretisation through pan littoral sediments may have been both biogenically and environmentally induced. Calcite precipitation was in part controlled by the Mg/Ca ratio of pore water in the pan littoral zone suggesting closed basin type evaporative conditions, which were followed by a major desiccation interval. Phases of silcrete precipitation appear to be related to periods when the geochemistry of the lake littoral more closely resembled present-day Na–CO 3 –SO 4 –Cl-type brines. Silica saturated acidic, moderately saline groundwater preceded Si precipitation which took place as the pH reduced. Si mobilisation occurred (inter alia) as a result of quartz grain dissolution enhanced by diatoms, bacteria and algal growth in the moist pan littoral. SiO 2 -rich pore waters migrated through cracked and desiccated calcrete into areas of lower salinity and lower pH resulting in preferential calcite removal and silcrete precipitation. Approximate TL dates imply that exposed littoral sand underwent calcretisation during the drying phases of extensive palaeo-lakes which occurred prior to 110 ka, 80–90 ka and 41–43 ka. These wet periods compare fairly well with Vostok core chronologies for southern Africa.

The fluorescence and laser properties of ten aromatic compounds, specially chosen from the p-oligophenylenes (D(2) symmetry) or m-oligophenylenes (C(2) or D(3) symmetry) are studied experimentally (at 293 K) and quantum chemically. The quantum yields, gamma and the decay times, tau(f) of fluorescence are measured for deaerated and non-deaerated cyclohexane solutions. The oscillator strengths, f(e) of the S(0)--S(p) (1A--(1)L(a)) and S(0)--S(alpha) (1A--(1)L(b)) transitions, fluorescence, k(f) and intersystem crossing, k(ST), rate constants, and natural lifetimes, tau(0)(T) are calculated. The lowest 1L(b), 1L(a) and 3L(b) (77 K) levels are determined. It is found that all p-oligophenylenes from p-terphenyl onwards are excellent, photochemically stable laser dyes although the solubility in this series decreases dramatically. On the basis of trends observed in p-oligophenylenes (D(2)-series) and on the properties of the experimentally studied m-oligophenylenes of the C(2)- and D(3)-series, the fluorescence and laser properties of other compounds from these series are estimated/predicted. It is shown, for the first time, that m-oligophenylenes of the C(2)-series, from 1,3-di(p-terphenyl)benzene will acquire fluorescence of 1L(a)--(1)A nature and could be extremely effective laser dyes. It is also shown that m-oligophenylenes of the D(3)-series, from 1,3,5-tri(p-quaterphenyl)benzene will also acquire 1L(a)--(1)A nature fluorescence and laser ability, although this would not be as good as that of compounds in the C(2)-series. It is concluded that m-oligophenylenes can be used not only for passive mode locking but some may also be used as laser dyes and scintillators. The results obtained are important for various practical purposes and theoretical considerations.

Quaternary sedimentation in the Moshaweng dry valley of southeastern Botswana is evaluated on the basis of geomorphological evolution and sedimentological analyses. Stratigraphic evidence reveals an upper surface (1095 m) containing abundant sil-calcrete, an intermediate surface (1085 m) in which sil-calcrete underlies nodular calcrete and lower (1075 m) surface in which sil-calcrete and nodular calcrete are interbedded. This subdivision is reflected in the geochemical composition of the sediments which show an overall trend of decreasing SiO2 content (and increasing CaCO3 content) with depth from the highest to the lowest surface levels. The calcretes and sil-calcretes represent modifications of pre-existing detrital Kalahari Group sand and basal Kalahari pebbles which thinned over a Karoo bedrock high. Modification took place during wet periods when abundant Ca++-rich groundwater flowed along the structurally aligned valley system. With the onset of drier conditions, water table fluctuations led to the precipitation of nodular calcretes in the phreatic layer to a depth of about 20 m. A major geochemical change resulted in the preferential silicification of the nodular calcrete deposits. Conditions for silica mobilization may be related to drying-induced salinity and in situ geochemical differentiation brought about by pebble dissociation towards the top of the sediment pile. As calcretization and valley formation progressed to lower levels, silica release took place on a diminishing scale. Thermoluminescence dating infers a mid-Pleistocene age for sil-calcrete formation suggesting that valley evolution and original calcrete precipitation are much older. Late stage dissolution of CaCO3 from pre-existing surface calcretes or sil-calcretes led to the formation of pedogenic case-hardened deposits during a time of reduced flow through the Moshaweng system possibly during the upper or late Pleistocene. Copyright © 2002 John Wiley & Sons, Ltd.

Absorption. fluorescence and laser properties of perylene, benzo(ghi)perylene and coronene are studied experimentally (under the same conditions) and quantum chemically at room (293 K) and at low (77 and 4 K) temperatures and direct comparison is made between the results for each molecule. All the main absorption and fluorescence parameters such as oscillator strength, fe, quantum yield, gamma, decay time, tauf, fluorescence rate constant, kf (Einstein coefficient, A) and intersystem crossing rate constant, kST, are measured or calculated. The systems of singlet and triplet levels for these compounds are simulated and analyzed. Triplet states mixing with the lowest singlet S1 state are determined. The low values of kST found are explained. The possible vibronic coupling in the molecule coronene is discussed. The nature of the three fluorescence bands of coronene observed is interpreted. The change in the arrangement of the singlet and triplet levels of the studied compounds is interpreted quantum-chemically. It is found that at room temperature (293 K), only perylene shows laser action, while all three compounds show good laser oscillation at low temperature (100 K). The differences in the laser properties of these compounds are explained by the inversion of the Sp(1La) and Sinfinity(1Lb) levels which occurs in the transition from perylene to benzo(ghi)perylene. Chemical properties of the compounds studied are outlined. Linear and quasi-linear fluorescence spectra of perylene and benzo(ghi)perylene, obtained at 77 and 4 K. can be used in the identification of these compounds.

Excavations conducted at the White Paintings Rock Shelter (WPS) have uncovered 7 m of deposits ranging in age from the historic period to at least 100,000 years at the base. Eleven stratigraphic units are described in relation to palaeoenvironmental conditions inferred from sediments and other data. These units contain seven major divisions in the cultural sequence highlighted by a lengthy record of Later and Middle Stone Age deposits. A wide variety of mammals as well as other animals were found in the upper 3 m. Numerous fish bones, wetland mammals and barbed bone points make this site especially interesting because of its desert location. The highest frequencies of fish bones are found between c . 80/90–130 cm (Upper Fish deposits) and between 210–280 cm below the surface (Lower Fish deposits). Most of the barbed bone points were recovered in the Upper Fish deposits. The Lower Fish deposits contain extinct Equus capensis and a microlithic industry as well as some bone points. A large blade industry is found beneath the Lower Fish deposits. This blade industry shows continuity with the underlying Middle Stone Age.

Fluorescence properties of 36 specially chosen aromatic compounds are experimentally studied at a temperature of 293 K. The compounds are arranged in pairs so that even numbered compounds, because of symmetrical substitutions, are designated a higher symmetry group than those of odd numbered compounds. The pairs are, however, family-related in π-structure. The quantum yield of fluorescence γ, and decay times τf, of deaerated and nondeaerated cyclohexane solutions are measured. The oscillator strength fe, the fluorescence rate constants Kf, natural lifetimes τ0T and intersystem crossing rate constants Kst, are calculated. Investigations showed that transition from a lower to higher symmetry, but family-related in π-structure molecule depending on the nature of the S1 excited state, has different effects on parameters such as γ, τf, fe, Kf and Kst. If the S1 excited state has the nature of the Sp(1La) state, then the value of ν00 decreases. This is accompanied by an increase in the values of γ and τf. Parameters fe and Kf may change unpredictably. However, if the development of π-structure occurs in the direction of polarization of the S0 → S1 transition, the values of fe and consequently Kf are also found to increase. If the S1 excited state has the nature of the Sα(1Lb) state then generally, γ, fe and Kf are found to decrease, with τf increasing. Furthermore, the Kst value in most cases of symmetrical substitution, decreases, sometimes very significantly, though the energy gap between S1 and T1 states becomes less. For example, the transition from 9-phenylanthracene (C2 symmetry group) to 9,10-diphenylanthracene (D2 symmetry group) is accompanied by a decrease in the value of Kst, by a factor of 18. This phenomenon is qualitatively treated using the first-order spin-orbit coupling theory and simulation of singlet and triplet levels.

Egmont volcano is the most westerly expression of volcanic activity in the North Island of New Zealand and is located 180 km above a westward-dipping subduction zone. Lava flows from the main cone Taranaki, and a parasitic cone Fanthams Peak, were sampled for palaeomagnetic analyses. Palaeomagnetic directions obtained from lava flows mostly from the upper northeast flanks of the main cone and Fanthams Peak were compared with an already established palaeosecular variation curve for the region. The palaeomagnetic evidence suggests that the lava flows covering the main peak were extruded during two eruptive phases. An older phase occurred between 2800 and 7000 years B.P. and a younger phase between 400 to 700 years B.P. Some of the eruptive activity of Fanthams Peak may have occurred during the same time interval as the emplacement of the lavas of the northeast flank of Taranaki.

The magnetic properties of unwelded, poorly consolidated Quaternary tephra from Thera, Greece, are examined for the evidence on their emplacement, particularly the extent to which individual clasts have been reworked after initial deposition. Most samples have stable remanences with single component magnetization acquired between 350–450°C (some from 540°C) and 100/150°C, indicating that each of these samples was in a fixed position, relative to the ambient geomagnetic field, when they originally cooled over these temperature ranges. The between-sample directions within each tephra layer are either: (a) mutually consistent, i.e. within measurement and collection error; (b) grouped but more scattered than expected; or (c) randomly scattered. These groupings are interpreted in terms of hot emplacement followed by respectively: (a) no re-working; (b) cold, internal settlement of individual clasts; and (c) extensive cold, reworking. In each case, the percentage of reworked material within any given layer can be estimated from the scatter of the directions of remanence of individual clasts. Such estimates are consistent with some, but not all, volcanological appraisals. This magnetic method provides a simple, inexpensive method for establishing the degree of cold reworking in such unwelded tephra.

Absorption, fluorescence and laser properties of ten selected aromatic compounds from the oligophenylene family are studied experimentally at room temperature (293 K). The first eight compounds are arranged in such way that odd numbered compounds reveal 1Lb --1A fluorescence, while even numbered compounds show 1La --1A fluorescence. All compounds are family related in pi-structure and are of the same degree of planarity and rigidity. The quantum yield of fluorescence, gamma, and the decay times, tau(f), of non-deaerated and deaerated cyclohexane solutions are measured. The oscillator strength, f(e), the fluorescence rate constant, Kf, natural lifetimes, tau(o)T, and intersystem crossing rate constant, K(ST), are calculated. The lowest 1Lb and 1La singlet and 3La, triplet (77 K) levels are determined. Investigations showed that transition from a polyphenyl molecule which shows 1La --1A fluorescence to a family related in the pi-structure molecule which reveals the 1Lb --1A fluorescence is accompanied by certain changes in all the fluorescence parameters. This indicates that gamma decreases, tau(f) increases, Kf and the FWRE of the fluorescence spectrum decrease. Moreover, K(ST) also decreases, sometimes very significantly. The decrease in the K(ST) value is explained by the fact thatpsiS alpha/H(SO)/psiTimatrix elements of the spin-orbit coupling of the S alpha and Ti states are much lower in value than analogous elements of the spin-orbit coupling of Sp and Ti states. It is shown that all p-polyphenyles exhibit excellent laser action, while m-polyphenyles do not produce laser oscillation under any conditions. The values of K(ST) and other fluorescence parameters measured can be used for various practical purposes and theoretical considerations.

(The Journal of Cultural Studies: 2000 2(1): 318-325)

Archaeomagnetic dating on the Minoan ash horizons of the Santorini volcano and on fired destruction levels at late Minoan sites on Crete demonstrates that the basal (Plinian) air-fall ash of the first ‘Minoan’ pumice is contemporaneous with the destruction levels on central Crete, while the higher ‘Minoan’ ashes are contemporaneous with the destruction levels in extreme eastern Crete. These destruction levels were almost certainly caused by seismic activity, rather than the ash fall The determination of a time gap between these events lead to a reappraisal of the archaeological evidence and is important volcanologically.

Early studies of kiln structures suggested that magnetic refraction could be a major source of error in archaeomagnetic studies of large, strongly magnetized structures. Recent studies of the directions of magnetization of samples from four British and two Cretan kilns and furnaces do not show clear evidence for such effects, although only two show the level of scatter predicted from an assessment of the errors in orientation and measurement. There is also some evidence for systematic distortion of either declination or inclination around the circumference of some of these structures. These systematic deviations do not appear to be related to the intensity of magnetization, and the magnitude of scatter tends to decrease with increasing intensity of magnetization of the structure. The magnitude of scatter appears to be largest where the magnetic materials are inhomogeneous, but it is not clear how this can account for systematic variations. Evaluation of both earlier and newer observations indicates that floors are not necessarily the optimum parts of a structure for sampling, but instead walls can be considered at least as reliable if not more so. In both cases, differential subsistence may be the main source of error. It is recommended that, until more is known about the cause of scatter, sampling should incorporate both floors and walls, and that the azimuth of the sampling relative to the structure should be noted.

Archaeomagnetism, Santorini volcanic eruptions and fired destruction levels on Crete (reply)