Deposition and preservation of fluvio-tidal shallow-marine sandstones: A re-evaluation of the Neoproterozoic Jura Quartzite (western Scotland)

The 2 to 5 km thick, sandstone‐dominated (>90%) Jura Quartzite is an extreme example of a mature Neoproterozoic sandstone, previously interpreted as a tide‐influenced shelf deposit and herein re‐interpreted within a fluvio‐tidal deltaic depositional model. Three issues are addressed: (i) evidence for the re‐interpretation from tidal shelf to tidal delta; (ii) reasons for vertical facies uniformity; and (iii) sand supply mechanisms to form thick tidal‐shelf sandstones. The predominant facies (compound cross‐bedded, coarse‐grained sandstones) represents the lower parts of metres to tens of metres high, transverse fluvio‐tidal bedforms with superimposed smaller bedforms. Ubiquitous erosional surfaces, some with granule–pebble lags, record erosion of the upper parts of those bedforms. There was selective preservation of the higher energy, topographically‐lower, parts of channel‐bar systems. Strongly asymmetrical, bimodal, palaeocurrents are interpreted as due to associated selective preservation of fluvially‐enhanced ebb tidal currents. Finer‐grained facies are scarce, due largely to suspended sediment bypass. They record deposition in lower‐energy environments, including channel mouth bars, between and down depositional‐dip of higher energy fluvio‐ebb tidal bars. The lack of wave‐formed sedimentary structures and low continuity of mudstone and sandstone interbeds, support deposition in a non‐shelf setting. Hence, a sand‐rich, fluvial–tidal, current‐dominated, largely sub‐tidal, delta setting is proposed. This new interpretation avoids the problem of transporting large amounts of coarse sand to a shelf. Facies uniformity and vertical stacking are likely due to sediment oversupply and bypass rather than balanced sediment supply and subsidence rates. However, facies evidence of relative sea level changes is difficult to recognise, which is attributed to: (i) the areally extensive and polygenetic nature of the preserved facies, and (ii) a large stored sediment buffer that dampened response to relative sea‐level and/or sediment supply changes. Consideration of preservation bias towards high‐energy deposits may be more generally relevant, especially to thick Neoproterozoic and Lower Palaeozoic marine sandstones

The effectiveness of Theraplay for children under 12 – a systematic literature review

Background Theraplay is a relationship‐focused model of treatment based on attachment theory involving both adult and child. The study aims to review the quality of Theraplay research and Theraplay’s effectiveness for children aged 12 years and under with a range of presenting difficulties, to inform future practice and identify areas for further research. Methods A systematic literature search was conducted using PsycINFO, CINAHL, MEDLINE and Web of Science. Quantitative studies using Theraplay only as a treatment for children aged 12 years and under with any presenting difficulty were identified. Additional manual searching was conducted, including eligible studies’ reference lists. Critical appraisal tools were used to provide a narrative synthesis of Theraplay’s effectiveness and research quality. Results Only six eligible articles were identified, meaning there was a lack of rigorous evidence eligible to offer conclusions into Theraplay’s effectiveness. The review highlighted the small evidence base, mixed quality research methodology and high levels of heterogeneity in how Theraplay is practiced and evaluated. Of the eligible studies, Theraplay was found promising in its effectiveness when used with internalising and externalising difficulties, dual diagnoses and developmental disabilities. Conclusions Theraplay is regularly practiced across the world; however, the evidence base of rigorous research to inform Theraplay’s effectiveness and mechanisms of change is lacking. Firm conclusions could not be offered, although Theraplay was shown to be promising intervention for some presentations. Further research into Theraplay’s effectiveness and key mechanisms of change are recommended to enhance the quality and depth of Theraplay literature

Supplemental material: Cambrian–Ordovician orogenesis in Himalayan equatorial Gondwana

GSA Data Repository Item 2016215, GSA Bulletin. File size: about 126 KB

Tectonic model for development of the Byrd Glacier discontinuity and surrounding regions of the Transantarctic Mountains during Neoproterozoic-Early Paleozoic

The Byrd Glacier discontinuity us a major boundary crossing the Ross Orogen, with crystalline rocks to the north and primarily sedimentary rocks to the south. Most models for the tectonic development of the Ross Orogen in the central Transantarctic Mountains consits of two-dimensional transects across the belt, but do not adress the major longitudinal contrast at Byrd Glacier. This paper presents a tectonic model centering on the Byrd Glacier discontinuity. Rifting in the Neoproterozoic producede a crustal promontory in the craton margin to the north of Byrd Glacier. Oblique convergence of the terrane (Beardmore microcontinent) during the latest Neroproterozoic and Early Cambrian was accompanied by subduction along the craton margin of East Antarctica. New data presented herein in the support of this hypothesis are U-Pb dates of 545.7 ± 6.8 Ma and 531.0 ± 7.5 Ma on plutonic rocks from the Britannia Range, subduction stepped out, and Byrd Glacier. After docking of the terrane, subduction stepped out, and Byrd Group was deposited during the Atdabanian-Botomian across the inner margin of the terrane. Beginning in the upper Botomian, reactivation of the sutured boundaries of the terrane resulted in an outpouring of clastic sediment and folding and faulting of the Byrd Group

Cambrian rocks and faunas of the Wachi La, Black Mountains, Bhutan

The Pele La Group in the Wachi La section in the Black Mountains of central Bhutan represents the easternmost exposure of Cambrian strata known in the Himalaya. The group contains a succession of siliciclastic rocks with minor amounts of carbonate, the uppermost unit of which, the Quartzite Formation, bears age-diagnostic trilobite body fossils that are approximately 493 Ma old. Trilobite species include Kaolishania granulosa, Taipaikia glabra and the new species Lingyuanaspis sangae. A billingsellid brachiopod, Billingsella cf. tonkiniana, is co-occurrent. This fauna is precisely correlated with that of a specific stratigraphic horizon within the upper part of the Kaolishania Zone, Stage 9 of the Cambrian System, Furongian Epoch of the North China block, and thus represents the youngest Cambrian sedimentary rocks yet known from the Himalaya. The faunal similarity suggests proximity between North China and the Himalayan margin at this time. This unit was deposited in a predominantly storm-influenced shelf and shoreface environment. U-Pb geochronological data from detrital zircon grains from the fossil-bearing beds of the Quartzite Formation and strata of the underlying Deshichiling Formation show grain age spectra consistent with those from Cambrian rocks of the Lesser and Tethyan Himalaya in Tibet, India and Pakistan. These data support continuity of the northern Gondwanan margin across the Himalaya. Prominent peaks of approximately 500 Ma zircons in both the Quartzite and Deshichiling formations are consistent with the Furongian (late Cambrian) age assignment for these strata. The presence of these relatively young zircon populations implies rapid post-cooling erosion of igneous bodies and subsequent deposition which may reflect the influence of a widespread Cambro-Ordovician orogenic event evident in the western Himalaya. © 2010 Cambridge University Press.Link_to_subscribed_fulltex