A method for the disaggregation of mudstones

We describe a method which effectively and gently disaggregates muds and mudstones by combining a saturation-freeze-thaw technique with treatment by ultrasonic probe. The method works well for samples containing <5% TOC and which have been buried to depths less than about 3500 m. It does not work for samples strongly cemented with carbonates or silicates. Scanning electron micrographs of size fractions and the strong mineralogical segregation between size fractions are offered as evidence of complete disaggregation.     

Optically Stimulated Luminescence (OSL) dating of glacial sediments from Arctic Russia - depositional bleaching and methodological aspects

Optical dating has been extensively used for stratigraphical correlation in the reconstruction of Eurasian ice-sheet dynamics and palaeoenvironmental changes during the last glaciation. In recent terrestrial studies in Arctic Russia, Optically Stimulated Luminescence (OSL) is the main chronological tool, and has been used across the whole of the Eurasian north. We report new OSL ages obtained on glaciofluvial and glaciolacustrine sediments from the Arkhangelsk and Taymyr regions of Arctic Russia and discuss the characteristics of the quartz OSL signal in terms of its saturation limit, variability among samples from the same location, and initial signal resetting in different depositional environments. It is shown that effect of partial bleaching in our mainly Weichselian samples is trivial because: modern analogues are well zeroed; there is good agreement between OSL and ¹⁴C ages in young samples; and skewness in the dose distribution of relatively older samples is mainly due to varying shapes of the growth curves. The overall reliability of the OSL ages from Arctic Russia, when compared with the limited independent age controls available, appears to be good.     

Time flies: the geological record of insects

Two recent databases show that the fossil record of insects is better than commonly supposed, comprising over 1000 families and 5000 genera. Insects (hexapods) first appeared in the Devonian, but by the Permian the number of orders present was similar to that of the present day. However, family data suggest an unsteady increase in diversity during the Phanerozoic, with four main peaks and troughs but no sudden change (supported by genera) at the Cretaceous/Tertiary transition.     

Palaeoclimatic inferences from upper Palaeozoic siltstone of the Earp Formation and equivalents, Arizona-New Mexico (USA)

The Late Palaeozoic configuration of Pangaea contributed to a palaeoclimatic extreme that was characterized by both icehouse and monsoonal conditions. This study uses sedimentological, geochemical, and provenance data from silty facies of the Earp and equivalent Supai Formations (Arizona, New Mexico) to shed light on atmospheric circulation and glacial–interglacial climate change in westernmost equatorial Pangaea. Five silt‐rich facies comprise both loessite and marine and fluvially reworked loessite. An initial aeolian origin for the silt is indicated by the remarkably invariant grain size and the laterally continuous, sheet‐like geometry of beds. The silt‐rich facies occur in repetitive facies associations (1–20 m scale) that form mixed continental‐marine (loess, marine‐reworked loess), shallow‐marine, and continental (loess, palaeosol) ‘sequences’. Facies repetitions of both mixed continental‐marine and shallow‐marine sequences reflect a linked glacioeustatic–glacioclimatic control, whereas the continental (loess–palaeosol) couplets reflect a primary glacial–interglacial climatic cyclicity linked to glacioeustasy. Stratigraphic interpretations suggest that aeolian silt flux maximized during glacial to incipient interglacial stages (lowstand to early transgression), and decreased significantly or ceased during interglacials (highstand to early falling stage). Detrital‐zircon geochronological data indicate a transition from dominantly north‐easterly winds during the Middle Pennsylvanian to north‐westerly and south‐easterly winds by the Early Permian, which trend is inferred to reflect the onset of monsoonal circulation in western Pangaea. Relative grain‐size data support the detrital‐zircon data, and exhibit a significant decrease from the Sedona arch/Central Arizona shelf (north) to the Pedregosa basin (south) sections. Whole‐rock geochemical data suggest a relatively unweathered source for the silt in the north, and detrital‐zircon data indicate significant silt was derived from the local basement. These large piles of silt(stone) preserve valuable information for reconstructing both long‐term evolution in atmospheric circulation and short‐term fluctuations in glacial–interglacial climate. Many such indicators for long have been applied to ‘recent’ (Plio‐Pleistocene) loess, but are equally applicable to ‘deep‐time’ strata.