Magnetic polarity stratigraphy of the Mio-Pliocene mammal-bearing Big Sandy Formation of western Arizona

The Big Sandy Formation in western Arizona consists of up to 65 m of clays, silts, sands and volcanic ashes that were deposited in a lacustrine paleoenvironment. Three paleomagnetic samples were collected from each of 54 sites spaced at stratigraphic intervals of no more than 5 m. After laboratory studies of pilot samples to determine their paleomagnetic characteristics, all other samples were measured for their NRM and then demagnetized in alternating fields of 150 Oe. After statistical filtering and a hierarchical site classification, 48 sites were used to interpret the magnetic polarity zonation.Vertebrate fossils from the Big Sandy Formation are collectively termed the Wikieup Local Fauna, and indicate a late Hemphillian Land Mammal “Age”. Three fission-track (zircon) dates from the Big Sandy Formation yielded a mean age of 5.5 ± 0.2 m.y. B.P. Using these radiometric data to calibrate the magnetic polarity zonation, it appears that the Big Sandy Formation spans late Epoch 6 to early Gilbert time (late Miocene to early Pliocene). The Wikieup Local Fauna is compared to two other roughly contemporaneous mammalian assemblages from New Mexico and Texas. Faunal differences previously thought to represent a very late Hemphillian age for the Wikieup Local Fauna are apparently related to ecogeographic variation and not time.     

The development of slaty cleavage, fleurieu peninsula, south australia

In low grade, biotite-rich metasiltstones and slates from the western side of Fleurieu Peninsula, the slaty cleavage is defined by elongate deformed old biotites and by the coincident elongate dimensions and (001) planes of thin, well aligned new biotites. Histograms of frequency versus (001)-S₁ angle (S₁ defined by aligned thin muscovite used as the reference plane) were determined in thin section for both populations. The old biotites show a symmetrical bimodal distribution of (001) about S₁, with maxima at around 20° either side ofS₁. This distribution, together with the preserved intracrystalline strain, indicates that these old grains deformed largely by slip on (001) with some modification of grain boundaries by diffusive transfer. The new biotite grains are very well aligned (standard deviation 3.8°) and show no sign of mechanical deformation. They have not been mechanically rotated into alignment but must have nucleated and grown in a specific orientation. The proportion of new to old grains increases with metamorphic grade, causing a rapid strengthening of the crystallographic alignment. In slates and phyllites with similar microstructure, the mica fabric determined by X-ray texture goniometry cannot be used as a quantitative measure of the geometry and magnitude of the bulk strain, as the intensity of the crystallographic fabric will be strongly influenced by the proportion of new mica, which is itself greatly affected by the metamorphic grade during slaty cleavage formation.     

Tidal triggering of deep moonquakes

Matching signals have previously been identified from about eighty repeating deep moonquake sources. These moonquakes clearly display tidal periodicities in their histories of origin times and signal amplitudes; they are presumably triggered by the solid-body tide in the moon, raised primarily by the earth. The A1 hypocentre has been the most active and has also produced seismograms with signals of reversed polarity. In an attempt to deduce focal mechanisms for these events, we calculated various tidal stress functions at the Al hypocentre using a homogeneous moon model, and correlated them with the origin times of events. No good correlation was found, either for tidal stress peaks of consistent polarity, or for tidal stress peaks of opposite polarity at the times of “inverted” events. This could be due to an inaccurate moon model, but it has also been noted that the relative amplitudes of signals recorded at different seismic stations vary between events from the same hypocentre. Earthquake swarms often contain events with fault-plane solutions in very different orientations. A similar variation between events from each deep moonquake hypocentre would explain the different amplitude ratios and also the “inverted” events.     

Late Quaternary palaeohydrology of the Konya Basin, Turkey, based on isotope studies of modern hydrology and lacustrine carbonates

The Konya plain in south central Anatolia, Turkey, which is now largely dry, was occupied around the time of the Last Glacial Maximum by a fresh-oligosaline lake covering more than 4000 km². Sediment cores from three residual water bodies (Pinarbai, Akgöl and Süleymanhaci) within the larger Pleistocene lake basin, have been analysed using a multidisciplinary approach. The sediment sequences are dated as spanning the last 50 Ka years, although breaks in sedimentation mean that there is only partial chronological overlap between them. Carbon and oxygen isotope analyses on lacustrine carbonate from the three cores give contrasting isotope profiles which reflect the different ages and independent hydrological behaviour of different sub-basins through the late Quaternary. Distinguishing changes that are regional from local effects is aided by modern isotope hydrology studies and by comparing the carbonate ¹³C and ¹⁸O values to diatom and other analyses undertaken on the same cores.     

Stable isotopic investigations of early development in extant and fossil chambered cephalopods I. Oxygen isotopic composition of eggwater and carbon isotopic composition of siphuncle organic matter in Nautilus

Eggwaters from the chambered cephalopod Nautilus are depleted in both ¹⁸O and deuterium relative to ambient seawater. Eggwaters from six other species, including the related chambered cephalopod Sepia, do not show such depletion. These observations indicate that the previously observed step towards more positive $\text{δ}{}^{18}\text{O}$ values in calcium carbonate laid down after Nautilus hatches, relative to carbonate precipitated prior to hatching, can be explained by equilibration of the carbonate with water in the egg before hatching and with seawater after hatching. The presence of an oxygen isotope difference between eggwater and seawater for Nautilus and its absence for Sepia suggest that hatching will be recorded in the $\text{δ}{}^{18}\text{O}$ values of shell carbonates for some but not all extinct and extant chambered cephalopods.The $\text{δ}{}^{13}\text{C}$ values of the organic fraction of the siphuncle in Nautilus do not show any consistent pattern with regard to the time of formation before or after hatching. This observation suggests that the minimum in $\text{δ}{}^{13}\text{C}$ values previously observed for calcium carbonate precipitated after Nautilus hatches is not caused by a change in food sources once the animal becomes free-swimming, as has been suggested.     

Winds in southeast Queensland and rain in Australia and their possible long-term relationship with sunspot number

Wind records at Brisbane indicate past changes in ambient weather systems that appear to be confirmed by observed changes in Australian rainfalls. Both wind and rainfall data support geological field evidence of a climatic change in southeast Queensland in the 1930s. At Brisbane the numbers of calms observed in January and July declined from 1887 to 1935, and then increased again. This variation was associated with changes in wind patterns, particularly in winter (July) from 1933 to 1937 and afterwards, but also in summer (January) during the 1930s. The changes in circulation were enough to explain the movement of beach and dune sands at that time. The changes in windiness show a close connection with the 80-year trend in sunspot number: the initial period of below average sunspot number coincided with increasing wind strength and more southeasterly winds. Rainfall trends show similar associations with sunspot trends, but the direction of rainfall change is different in different regions. In southeast Australia changes in rainfall are positively correlated with trends in sunspot number over the last 80 years, while the opposite holds for the far southwest and Cape York Peninsula. On the north coast negative correlations occur in summer, and positive correlations in winter, but in Queensland and western New South Wales the correlations are positive in summer and negative in winter. It is too soon to tell whether the connection between sunspots and weather is accidental or functional.     

Quantitative evaluation of crosshole seismic reflection images using physical model data1

Physical models give us a known geometry with which to compare our processed reflection images and therefore our imaging techniques. We show how this comparison may be quantified in order to evaluate processed images properly. A crosshole data set was acquired through a model interrogated at ultrasonic frequencies using Durham University's physical modelling system. Various reflectivity images were obtained using processing sequences which include deconvolution, wavefield separation and migration. An error-energy scheme was used to assess the quality of these images, by comparing them against a best-fit depth model. A synthetic data set was also used to evaluate the imaging capability of the crosshole geometry and the effectiveness of the different processing schemes.