Tectonic control on deltaic sediment dispersal in the middle to upper Turonian Western Cordilleran Foreland Basin,USA

Tectonic forcing of delta progradation is increasingly being invoked to explain stratal stacking patterns in foreland basins. Nonetheless, the recognition of different types of tectonic forcing and their consequences for the spatial and temporal distribution of accommodation often rely on incomplete data sets and indirect sequence stratigraphic criteria. Previous work has concluded that the Cenomanian–Turonian Frontier Formation of northern Utah, north‐west Colorado and south‐west Wyoming (‘Vernal Delta’) owes its origin largely to tectonic overprinting of depositional patterns, although the lack of a comprehensive sequence stratigraphic framework for the unit has hampered evaluation of this claim. This study provides detailed facies and sequence stratigraphic analyses based on outcrop sections and wireline log suites from the Uinta, Piceance and Green River basins. Four genetically related intervals were defined and mapped by using regionally traceable stratigraphic horizons (flooding surfaces and sequence boundaries). Internally, intervals are composed of distal and proximal delta front lithologies, and coastal plain facies. Overall, Intervals 1 to 4 form a major basinward projection of coarse clastic strata generated in response to four separate, high‐frequency regressions. Furthermore, a change through time from southward projection of elongate lobes (Intervals 1 and 2) to eastward dispersal and development of a broad, arcuate planform (Intervals 3 and 4) can be explained in terms of changes in prevailing tectonic forcing mechanisms. North–south trending Sevier Orogeny forebulge structures controlled Intervals 1 and 2. West–east progradation (Intervals 3 and 4) was probably controlled by Proterozoic basement lineament reactivation due to Laramide foreland uplifts. Therefore, this study provides direct geological evidence for the initiation of local Laramide deformation as early as 90 Ma. These findings contribute to a more complete understanding of tectonic forcing of coastal to shallow marine successions in foreland basins and the tectonic evolution of the western USA.     

The structural and tectonic evolution of a Rodinian continental fragment in the Mawson Escarpment,Prince Charles Mountains,Antarctica

Part of East Antarctica's shield collided with Greater India during assembly of the Rodinia supercontinent. The pre-Rodinia continental margin of the Antarctic landmass is represented by Palaeoproterozoic basement rocks of the Lambert Complex, which are best exposed in the North Mawson Escarpment area of Antarctica's Prince Charles Mountains. Having investigated the structure of this escarpment, we conclude that rocks of the Lambert Complex were stacked by oblique northward overthrusting motions while deforming pervasively in the infrastructure zone of a convergent orogen, i.e. when this continental fragment of pre-Rodinia Antarctica collided with India around 960–905 m.y. ago. This resulted in exhumation to shallower, but still deep, crustal levels, so that the deformation was accompanied by Barrovian-type metamorphism that evolved to high-temperature, low-pressure conditions. The metamorphism outlasted most of the ductile deformation with temperatures reaching 750 °C, though potentially greater, under pressure conditions of about 5 kbar. In this paper we outline the structures and, from a plate tectonics viewpoint, consider their likely association with Rodinian and Gondwanan orogens in East Antarctica, i.e. the Rayner and Prydz Belts.     

Hydrological heterogeneity of an alpine stream–lake network in Switzerland

Water source and lake landscape position can strongly influence the physico‐chemical characteristics of flowing waters over space and time. We examined the physico‐chemical heterogeneity in surface waters of an alpine stream‐lake network (>2600 m a.s.l.) in Switzerland. The catchment comprises two basins interspersed with 26 cirque lakes. The larger lakes in each basin are interconnected by streams that converge in a lowermost lake with an outlet stream. The north basin is primarily fed by precipitation and groundwater, whereas the south basin is fed mostly by glacial melt from rock glaciers. Surface flow of the entire channel network contracted by ～60% in early autumn, when snowmelt runoff ceased and cold temperatures reduced glacial outputs, particularly in the south basin. Average water temperatures were ～4 °C cooler in the south basin, and temperatures increased by about 4–6 °C along the longitudinal gradient within each basin. Although overall water conductivity was low (<27 µS cm^?1) because of bedrock geology (ortho‐gneiss), the south basin had two times higher conductivity values than the north basin. Phosphate‐phosphorus levels were below analytical detection limits, but particulate phosphorus was about four times higher in the north basin (seasonal average: 9 µg l^?1) than in the south basin (seasonal average: 2 µg l^?1). Dissolved nitrogen constituents were around two times higher in the south basin than in the north basin, with highest values averaging > 300 µg l^?1 (nitrite + nitrate‐nitrogen), whereas particulate nitrogen was approximately nine times greater in the north basin (seasonal average: 97 µg l^?1) than in the south basin (seasonal average: 12 µg l^?1). Total inorganic carbon was low (usually <0·8 mg l^?1), silica was sufficient for algal growth, and particulate organic carbon was 4·5 times higher in the north basin (average: 0·9 mg l^?1) than in the south basin (average: 0·2 mg l^?1). North‐basin streams showed strong seasonality in turbidity, particulate‐nitrogen and ‐phosphorus, and particulate organic carbon, whereas strong seasonality in south‐basin streams was observed in conductivity and dissolved nitrogen. Lake position influenced the seasonal dynamics in stream temperatures and nutrients, particularly in the groundwater/precipitation‐fed north‐basin network. Copyright © 2007 John Wiley & Sons, Ltd.     

Submarine mass-wasting deposits as an indicator of the onset of foreland thrust loading—Late Permian Bowen Basin, Queensland, Australia

In the eastern part of the Permo-Triassic Bowen Basin of Queensland, Australia, a transition from passive, thermal subsidence to flexural (foreland basin) subsidence is recorded within the Upper Permian stratigraphy. Two coarse-grained intervals containing deposits of mass-wasting processes occur within an otherwise siltstone-dominated succession over 1500 m thick (the Moah Creek Beds and equivalents). These intervals can be traced over at least 350 km north–south, along the structural eastern margin of the basin. The lower of the coarse-grained intervals is spectacularly exposed in the banks of the Fitzroy River, west of Rockhampton. Here, interbedded sandstones and siltstones of marine shelf origin are abruptly truncated by a mudrock succession containing evidence of slumping and contemporaneous magmatic activity. This unit passes up-section into packages of mass-flow conglomerates and diamictites, interpreted to have formed on an unstable submarine slope. The character of the mass-flow deposits, their stratigraphic position and lateral extent are interpreted in terms of destabilization of a sloping marine surface by pulsed, subsurface thrust propagation.     

Long-term coexistence of non-indigenous species in aquaculture facilities

Non-indigenous species (NIS) are a growing problem globally and, in the sea, aquaculture activities are critical vectors for their introduction. Aquaculture introduces NIS, intentionally or unintentionally, and can provide substratum for the establishment of other NIS. Little is known about the co-occurrence of NIS over long periods and we document the coexistence over decades of a farmed NIS (a mussel) with an accidently introduced species (an ascidian). Both are widespread and cause serious fouling problems worldwide. We found partial habitat segregation across depth and the position of rafts within the studied farm, which suggests competitive exclusion of the mussel in dark, sheltered areas and physiological exclusion of the ascidian elsewhere. Both species exhibit massive self-recruitment, with negative effects on the industry, but critically the introduction of NIS through aquaculture facilities also has strong detrimental effects on the natural environment.     

Comprehensive examination of large mineral and rock fragments in Stardust tracks: Mineralogy,analogous extraterrestrial materials,and source regions

Abstract– Transmission electron microscopy examination of 87 large fragments from 16 carrot‐shaped and bulbous Stardust (SD) tracks was performed to study the range and diversity of materials present in comet Wild 2. Olivines and low‐Ca pyroxenes represent the largest proportions of fragments observed; however, a wide range of minerals and rocks were found including probable ferromagnesian, Al‐rich and Si‐rich chondrule fragments, a refractory inclusion, possible matrix mineral/lithic clasts, and probable condensate minerals. These materials, combined with fine‐grained components in the tracks, are analogous to components in unequilibrated chondrite meteorites and cluster interplanetary dust particles (IDPs). Two unusual lithologies in the bulbous tracks are only observed in chondritic porous IDPs and may have direct links to IDPs. The absence of phyllosilicates indicates that comet Wild 2 may be a “dry” comet that did not accrete or form significant amounts of hydrated phases. Some large mineral fragments in the SD tracks are analogous to large mineral IDPs. The large variations of the coarse‐grained components within and between all 16 tracks show that comet Wild 2 is mineralogically diverse and unequilibrated on nearly all scales and must have accreted materials from diverse source regions that were widely dispersed throughout the solar nebula.     

Unlocking deep geothermal energy in the UK using borehole heat exchangers

In the wake of COP 26, the international community is aiming to reduce carbon emissions by adopting alternative and renewable energy sources. Deep geothermal energy can help to achieve this as it represents a low carbon-emitting energy resource that can provide a constant base load of energy. In the United Kingdom, the development of deep geothermal has been limited due to high geological uncertainty and risk. Past exploration has focused on hot sedimentary aquifers and hot dry-rock granites, with limited success. To mitigate risk and extract heat with a lower reliance on geological properties, such as permeability, new development methods have been conceived using deep borehole heat exchangers, where fluid is circulated in a closed-loop system. Feasibility studies have been undertaken through modelling of deep borehole heat exchangers with the hope that these novel technologies can be used to exploit geothermal energy.     

Calcified microbial mats date prehistoric canals—Radiocarbon assay of organic extracts from travertine

A methodology for radiocarbon dating of calcified microbial mats has been developed and successfully applied in establishing a preliminary chronology for the prehistoric carbonate-encrusted canals of the Tehuacán Valley of Puebla, Mexico. In contrast to traditional carbonate dating techniques, this method focuses on the organic carbon component of the calcareous sediments. This method is based on the assumptions that (1) the carbon being dated is derived from the organisms associated with travertine buildup on canals, (2) these organisms are incorporated into the travertine contemporaneous with calcite precipitation, and (3) this carbon is then sequestered from most subsequent contamination and secondary fractionation. Evidence supporting these assumptions includes δ¹³C values, cultural chronologies, and stratigraphic relationships consistent with expectations. © 1996 John Wiley & Sons, Inc.