A Climatic Sequence Stratigraphic Model in the Terrestrial Lacustrine Basin:A Case Study of Green River Formation,Uinta Basin,USA

In recent years,with the development of terrestrial sequence stratigraphy,more attention has been focused on the study of the terrestrial lacustrine sequence stratigraphic model globally. Different viewpoints are preferred by researchers.Under the guidance of the theory of sequence stratigraphy,the findings of this paper indicate that climate is a major factor controlling the formation of the fourth-order sequence,based upon the study of the sequence stratigraphy in the Green River Formation of the Uinta...     

Forensic geology at the International School Science Fair 2013

In July 2013 the International School Science Fair (ISSF) was hosted by Camborne Science and International Academy, Cornwall, UK. This meeting brings young talented scientists together from around the world to participate in workshops and activities highlighting current scientific developments. As part of ISSF 2013, a workshop on forensic geology was delivered to some of the international participants. This included the preparation of a map to show the mineralogical composition of the soils of the participating schools. The soil mineralogy was determined using automated mineral analysis based on scanning electron microscopy. In addition there were workshops on the recovery of geological trace evidence in a forensic context and the theory and practice of carrying out a geophysical search for hidden items. Data generated as part of this workshop are available to download from the International Union of Geological Sciences, Initiative on Forensic Geology website ( http://www.forensicgeologyinternational.com ).     

Metripol birefringence imaging of unconsolidated glaciotectonized and ice keel scoured sediments: identification of unistrial plasmic fabric

In unconsolidated sediments subject to strain, clays and silts are realigned into particular optical birefringent arrangements (plasmic fabrics), which provide information on the style and intensity of sediment deformation. A relatively new, non‐destructive, optical microscopy technique for automatically recording and quantifying birefringence (previously commercialized under the name ‘Metripol’) is pioneered in this study as a valuable and innovative micromorphological tool with which to examine deformation in unconsolidated sediments. Metripol is applied to unistrial plasmic fabric in glaciotectonized and ice keel scoured sediment from the Netherlands and former Glacial Lake Agassiz (Manitoba, Canada) respectively. Colour‐coded images are produced in which colour represents relative optical retardation and thus optical anisotropy through the quantity |sinδ| and optical orientation of anisotropy through the angle Ø (also indicated by linear azimuths). In this study Metripol typically demonstrates that the better developed the unistrial plasmic fabric is, the higher the |sinδ| values, the larger the areas of high |sinδ| values, and the longer and more densely populated the azimuths. In addition, some unistrial plasmic fabrics under Metripol demonstrate lower |sinδ| than previous examples and the surrounding sediment, despite being ‘perceived’ as demonstrating higher birefringence under a standard petrographic microscope. This is particularly true in clay‐rich sediments and has implications for the way we currently describe and interpret unistrial plasmic fabrics in unconsolidated sediment. Finally, the identification and quantification of additional structures that would otherwise have gone undetected using a standard petrographic microscope (e.g. linear and circular structures that are likely to represent discrete shears and skelsepic plasmic fabric, respectively) highlight the potential for Metripol to gather information on the deformation history of unconsolidated sediments that is unavailable to standard techniques.     

A Climatic Sequence Stratigraphic Model in the Terrestrial Lacustrine Basin: A Case Study of Green River Formation,Uinta Basin,USA

In recent years, with the development of terrestrial sequence stratigraphy, more attention has been focused on the study of the terrestrial lacustrine sequence stratigraphic model globally. Different viewpoints are preferred by researchers. Under the guidance of the theory of sequence stratigraphy, the findings of this paper indicate that climate is a major factor controlling the formation of the fourth-order sequence, based upon the study of the sequence stratigraphy in the Green River Formation of the Uinta basin in the USA. It also divides the fourth-order sequence in the terrestrial lacustrine basin into two system tracts: the wet (rising) half-cycle and the dry (falling) half-cycle, establishing a new-style fourth-order sequence stratigraphic model for the terrestrial lacustrine basin, that is, the climate-genetic sequence stratigraphic model. As a result, the theory of sequence stratigraphy is greatly enriched.     

Structures and textures in Triassic braided stream conglomerates ('Bunter' Pebble Beds) in the Sherwood Sandstone Group, North Staffordshire, England

ABSTRACT In the northern parts of the Needwood and Stafford/Eccleshall Basins, England, the Pebble Beds of the Sherwood Sandstone Group contain thick successions of texturally mature, fluvial pebble/cobble conglomerates which are organized into either horizontal or cross-stratified sets. The horizontally lying sets, generally coarser grained and more poorly sorted than the cross-bedded sets, are usually disorganized and either matrix- or clast-supported, although thin lenses of well-sorted, occasionally openwork units, interpreted as falling stage phenomena, are often present. The cross-stratified conglomerates have foresets exhibiting remarkable textural organization, with a coarse, bimodal (sometimes matrix-supported) part grading upwards or being abruptly overlain by a finer, well-sorted (occasionally openwork) part and finally capped by sandstone. These rhythmic textural changes are attributed partly to an avalanche process at high stage and partly to falling stage conditions. The most common types of vertical association are thick successions of horizontally bedded conglomerates (up to 20 m) and sequences of an upwards coarsening nature (2-12 m) in which cross-stratified sets are overlain by flat-lying sets. The environment of deposition of the gravels is interpreted as one in which water depths at high stage were greater than depths in most modern braided stream plains (proglacial or alluvial fan) but shallower than depths associated with the Pleistocene catastrophic floods from which texturally mature, giant gravel bars have been recorded. Recent braided streams with relatively confined channels and considerable bar/channel relief are better analogues. In particular, medial or mid-channel bars with a two-tier structure (subaqueous and partly emergent portions) may explain the upward-coarsening sequences in which horizontally lying conglomerates overlie cross-stratified conglomerates. The thicker sequences of horizontally stratified conglomerates represent proximal, longitudinal bar deposits. Sheets of pebbly sandstone and argillaceous sandstone lying between the conglomerates, and commonly occurring towards the top of the succession, largely represent deposition from sandwaves and dunes. Finer, interbedded, argillaceous sandstones, siltstones and mudstones are interpreted as overbank and waning-flood deposits. Basin-forming tectonism of increasing intensity probably caused the initial coarsening upwards of the lower part of the succession, whilst more stable tectonic conditions and decreasing relief on the margins of the basins and in the areas of provenance in the Midlands and the Hercynides, account for the upwards-fining of the upper part of the succession.     

Edentulous pterosaurs from the Cambridge Greensand (Cretaceous) of eastern England with a review of Ornithostoma Seeley, 1871

A re-examination of fossil material from the Late Cretaceous Cambridge Greensand Member (CGM) of the West Melbury Marly Chalk Formation revealed a number of new specimens of edentulous pterosaur jaw fragments previously identified as shark fin spines and fish jaws and accessioned under the epithet ‘cestraciontid finray’ and ‘jaws of fish’. These are now recognised as pterosaurian jaw tips and referred to Ornithostoma sedgwicki Seeley, 1891 and Azhdarchoidea indet. This material increases the diversity of edentulous pterosaurs from the CGM.The edentulous pterosaur Ornithostoma sedgwicki Seeley, 1891 from the Cretaceous Cambridge Greensand of eastern England is reviewed. The holotype specimen is confirmed as a fragment of a premaxilla/maxilla of a non-tapejarid azhdarchoid on account of the conspicuous curvature of the dorsal and occlusal margins posteriorly and the presence of small neural foramina on the lateral margins. Neural foramina are not seen on jaws of members of the Pteranodontia, a group to which O. sedgwicki was included previously. The referral of O. sedgwicki to Azhdarchoidea eliminates the single known Lower Cretaceous occurrence of Pteranodontidae, restricting the temporal range of this taxon to the Upper Cretaceous. Postcranial material referred to O. sedgwicki from the type horizon is regarded as indeterminate Pterosauria.     

Using stable isotopes to estimate travel times in a data‐sparse Arctic catchment: Challenges and possible solutions

Use of isotopes to quantify the temporal dynamics of the transformation of precipitation into run‐off has revealed fundamental new insights into catchment flow paths and mixing processes that influence biogeochemical transport. However, catchments underlain by permafrost have received little attention in isotope‐based studies, despite their global importance in terms of rapid environmental change. These high‐latitude regions offer limited access for data collection during critical periods (e.g., early phases of snowmelt). Additionally, spatio‐temporal variable freeze–thaw cycles, together with the development of an active layer, have a time variant influence on catchment hydrology. All of these characteristics make the application of traditional transit time estimation approaches challenging. We describe an isotope‐based study undertaken to provide a preliminary assessment of travel times at Siksik Creek in the western Canadian Arctic. We adopted a model–data fusion approach to estimate the volumes and isotopic characteristics of snowpack and meltwater. Using samples collected in the spring/summer, we characterize the isotopic composition of summer rainfall, melt from snow, soil water, and stream water. In addition, soil moisture dynamics and the temporal evolution of the active layer profile were monitored. First approximations of transit times were estimated for soil and streamwater compositions using lumped convolution integral models and temporally variable inputs including snowmelt, ice thaw, and summer rainfall. Comparing transit time estimates using a variety of inputs revealed that transit time was best estimated using all available inflows (i.e., snowmelt, soil ice thaw, and rainfall). Early spring transit times were short, dominated by snowmelt and soil ice thaw and limited catchment storage when soils are predominantly frozen. However, significant and increasing mixing with water in the active layer during the summer resulted in more damped steam water variation and longer mean travel times (~1.5 years). The study has also highlighted key data needs to better constrain travel time estimates in permafrost catchments.     

Modelling suspended sediment discharge in a glaciated Arctic catchment–Lake Peters,Northeast Brooks Range,Alaska

Seasonal suspended sediment transfer in glaciated catchments is responsive to meteorological, geomorphological, and glacio-fluvial conditions, and thus is a useful indicator of environmental system dynamics. Knowledge of multifaceted fluvial sediment-transfer processes is limited in the Alaskan Arctic – a region sensitive to contemporary environmental change. For two glaciated sub-catchments at Lake Peters, northeast Brooks Range, Alaska, we conducted a two-year endeavour to monitor the hydrology and meteorology, and used the data to derive multiple-regression models of suspended sediment load. Statistical selection of the best models shows that incorporating meteorological or temporal explanatory variables improves performances of turbidity- and discharge-based sediment models. The resulting modelled specific suspended sediment yields to Lake Peters are: 33 (20–60) t km⁻² yr⁻¹ in 2015, and 79 (50–140) t km⁻² yr⁻¹ in 2016 (95% confidence band estimates). In contrast to previous studies in Arctic Alaska, fluvial suspended sediment transfer to Lake Peters was primarily influenced by rainfall, and secondarily influenced by temperature-driven melt processes associated with clockwise diurnal hysteresis. Despite different sub-catchment glacier coverage, specific yields were the same order of magnitude from the two primary inflows to Lake Peters, which are Carnivore Creek (128 km²; 10% glacier coverage) and Chamberlin Creek (8 km²; 23% glacier coverage). Seasonal to longer-term sediment exhaustion and/or contrasting glacier dynamics may explain the lower than expected relative specific sediment yield from the more heavily glacierized Chamberlin Creek catchment. Absolute suspended sediment yield (t yr⁻¹) from Carnivore Creek to Lake Peters was 27 times greater than from Chamberlin Creek, which we attribute to catchment size and sediment supply differences. Our results provide a foundational understanding of the current sediment transfer regime and are useful for predicting changes in fluvial sediment transport in glaciated Alaskan Arctic catchments.     

Micromorphology of ice keel scour in pebbly sandy mud and fine‐grained sands: Scarborough Bluffs,Ontario, Canada

The keels of icebergs and ice‐pressure ridges plough through unconsolidated sea/lake sediments gouging out long grooves known as ice keel scour marks. Although the surface and (more recently) subsurface morphology of scours are well‐documented, little is known of the effect of grain size on the detectability, style and intensity of sub‐scour deformation. This investigation macroscopically and microscopically (two‐dimensional thin sections) examines suspected ice keel scour in: (i) glaciolacustrine pebbly sandy mud and (ii) fine‐grained sands at Scarborough Bluffs, Ontario, Canada. In this investigation, there is an almost identical suite of deformation structures (individual structures and overprinted structural patterns) to those identified in iceberg‐scoured clays from former Glacial Lake Agassiz (Manitoba, Canada); this confirms that deformation in the pebbly sandy mud and fine‐grained sands at Scarborough Bluffs is likely to be indicative of ice keel scour. Discrete differences in the detectability, style and intensity of deformation between the Scarborough Bluffs and Glacial Lake Agassiz sediments are probably a function of grain size in response to ice keel scour. This research provides additional information on the types of structures that are associated with sediment deformation by processes of ice keel scour in a variety of grain sizes. This information is particularly valuable to inform palaeoenvironmental reconstruction and offshore engineering in areas where ice keel scour occurs in a variety of grain sizes. It also demonstrates the potential value of micromorphology where, for example, the study of cores is necessary.