Petrography and geochemistry of Palaeozoic quartz-rich sandstones from Saudi Arabia: implications for provenance and chemostratigraphy

The Arabian Peninsula hosts a thick Palaeozoic succession, ranging from the Cambrian through the Permian. It not only contains deposits of the two major Palaeozoic glaciations but also holds both the major Palaeozoic hydrocarbon source and reservoir rocks. In addition, Palaeozoic sandstones serve as important aquifers. The succession is dominated by highly mature quartz arenites, as seen in thin sections. It is starved of fossils and very uniform in lithology. In order to better understand provenance, tectonic setting and stratigraphic relationships, the petrography as well as major and trace element geochemistry of sandstones were studied. Samples were taken from two study areas in southern (Wajid area) as well as central and northern (Tabuk area) Saudi Arabia. The dataset we present here is the first comprehensive study to cover the entire Palaeozoic succession in both the southern and northern part of the Arabian Peninsula. The collisional signal from some samples is a relic from the last stages of the amalgamation of Gondwana, carried into the basin by glaciogenic sediments. Major and trace element geochemistry indicate the Neoproterozoic basement of the nearby Arabian Shield as the most likely source for the detritus. Tectonic discrimination diagrams suggest that deposition of sandstones took place in an intracratonic setting, which is in accordance with the established model for the evolution of the Arabian Plate. An influx of fresh material, probably sourced from the Shield, did occur in the late Palaeozoic units of the Wajid area but did not reach the Tabuk area. Geochemical methods have shown some success in characterising the provenance of both study areas but were unable to reliably assess sedimentary recycling. A (meta‐)sedimentary source for the Palaeozoic sandstones could therefore neither be proven nor refuted. Multivariate cluster and principal component analysis of geochemical data revealed significant differences between the two study areas

New insights into the provenance of Saudi Arabian Palaeozoic sandstones from heavy mineral analysis and single-grain geochemistry

Saudi Arabian Palaeozoic siliciclastics cover a stratigraphic range from the Cambrian to the Permian. They crop out along the eastern margin of the Arabian Shield and are comprised of highly mature sandstones. Their heavy mineral assemblage reflects their mineralogical maturity and is dominated by the ultra-stable phases zircon, tourmaline and rutile. Less stable accessories are apatite, staurolite and garnet. Standard heavy mineral analysis of samples from two study areas in central/northern (Tabuk area) and southern (Wajid area) Saudi Arabia reveals distinct changes in provenance. Cambrian–Ordovician sandstones are first-cycle sediments, probably sourced from the ‘Pan-African’ basement. The overlying Hirnantian glaciogenic deposits consist of recycled Cambrian–Ordovician material. Devonian–Permian sandstones show a significant influx of fresh basement material, as attested by an increase of meta-stable heavy minerals. Single-grain geochemical analysis of rutile and garnet has proven to be a powerful supplementary technique. Rutile varietal studies reveal distinct differences in host rock lithologies between the two study areas: the Tabuk area contains predominantly felsic rutiles, whereas the Wajid area has more mafic input. Zr-in-rutile thermometry identified granulite-facies detritus in the lower Palaeozoic of the Tabuk area and has the potential to further define source areas. The distribution patterns of garnet host rock lithologies are remarkably similar in both study areas. They are dominated by amphibolite-facies metasediments and intermediate to felsic igneous rocks. Garnets derived from granulite-facies metasediments, which are scarce in the Arabian–Nubian Shield, also occur. Possible source rocks for high-grade garnets can be found in Yemen or farther south in the Mozambique Belt

Transition to marine ice cliff instability controlled by ice thickness gradients and velocity

Funding: This work is from the DOMINOS project, a component of the International Thwaites Glacier Collaboration (ITGC). Support came from NSF grant 1738896 and Natural Environment Research Council (NERC) grant NE/S006605/1. Logistics were provided by NSF–U.S. Antarctic Program and NERC–British Antarctic Survey. This study is ITGC contribution no. ITGC-044.Portions of ice sheets grounded deep beneath sea level can disintegrate if tall ice cliffs at the ice-ocean boundary start to collapse under their own weight. This process, called marine ice cliff instability, could lead to catastrophic retreat of sections of West Antarctica on decadal-to-century time scales. Here we use a model that resolves flow and failure of ice to show that dynamic thinning can slow or stabilize cliff retreat, but when ice thickness increases rapidly upstream from the ice cliff, there is a transition to catastrophic collapse. However, even if vulnerable locations like Thwaites Glacier start to collapse, small resistive forces from sea-ice and calved debris can slow down or arrest retreat, reducing the potential for sustained ice sheet collapse.PostprintPeer reviewe

Structural and environmental controls on Antarctic ice shelf rift propagation inferred from satellite monitoring

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102662/1/jgrf20163.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/102662/2/SupplementaryFigures_052513.pd

The nasal cavity microbiota of healthy adults

Abstract Background The microbiota of the nares has been widely studied. However, relatively few studies have investigated the microbiota of the nasal cavity posterior to the nares. This distinct environment has the potential to contain a distinct microbiota and play an important role in health. Results We obtained 35,142 high-quality bacterial 16S rRNA-encoding gene sequence reads from the nasal cavity and oral cavity (the dorsum of the tongue and the buccal mucosa) of 12 healthy adult humans and deposited these data in the Sequence Read Archive (SRA) of the National Center for Biotechnology Information (NCBI) (Bioproject: PRJNA248297). In our initial analysis, we compared the bacterial communities of the nasal cavity and the oral cavity from ten of these subjects. The nasal cavity bacterial communities were dominated by Actinobacteria, Firmicutes, and Proteobacteria and were statistically distinct from those on the tongue and buccal mucosa. For example, the same Staphylococcaceae operational taxonomic unit (OTU) was present in all of the nasal cavity samples, comprising up to 55% of the community, but Staphylococcaceae was comparatively uncommon in the oral cavity. Conclusions There are clear differences between nasal cavity microbiota and oral cavity microbiota in healthy adults. This study expands our knowledge of the nasal cavity microbiota and the relationship between the microbiota of the nasal and oral cavities.http://deepblue.lib.umich.edu/bitstream/2027.42/109547/1/40168_2014_Article_56.pd

Systems Analysis of complex glaciological processes and application to calving of Amery Ice Shelf, East Antarctica

Calving is a complex process subject to several cooperating atmospheric, oceanographic and glaciological forcings that vary in space and time, and whose relative effects are challenging to separate. Statistical ‘Systems Analysis’ is commonly used in engineering and economics to extricate complex ‘force–response’ relationships. Here we apply Systems Analysis to the Amery rift system, East Antarctica. We develop a scalable ‘System Model’ driven by a coarsely-sampled dataset characteristic of glaciological observations in remote locations, and validate it using rift lengths observed in 2000–06 and 2012. In this initial demonstration, we forecast a detachment date of ∼2019 ± 5 years for the large tabular iceberg colloquially known as the ‘Loose Tooth’, for which relative humidity surprisingly emerges as the best statistical predictor. RACMO2 climate modelling reveals that relative humidity correlates best with surface albedo and snowmelt, both of which are intimately linked to firn compaction and ice shelf temperature and flow. We postulate that relative humidity can therefore serve as a proxy for internal stress, a known key control of ‘Loose Tooth’ calving. Although no physical causality is implied in Systems Analysis, postulates such as this can aid in setting priorities in studies of complex glaciological processes

Seismicity within a propagating ice shelf rift: The relationship between icequake locations and ice shelf structure

Iceberg calving is a dominant mass loss mechanism for Antarctic ice shelves, second only to basal melting. An important process involved in calving is the initiation and propagation of through‐penetrating fractures called rifts; however, the mechanisms controlling rift propagation remain poorly understood. To investigate the mechanics of ice shelf rifting, we analyzed seismicity associated with a propagating rift tip on the Amery Ice Shelf, using data collected during the austral summers of 2004–2007. We apply a suite of passive seismological techniques including icequake locations, back projection, and moment tensor inversion. We confirm previous results that show ice shelf rifting is characterized by periods of relative quiescence punctuated by swarms of intense seismicity of 1 to 3 h. Even during periods of quiescence, we find significant deformation around the rift tip. Moment tensors, calculated for a subset of the largest icequakes ( M w  > −2.0) located near the rift tip, show steeply dipping fault planes, horizontal or shallowly plunging stress orientations, and often have a significant volumetric component. They also reveal that much of the observed seismicity is limited to the upper 50 m of the ice shelf. This suggests a complex system of deformation that involves the propagating rift, the region behind the rift tip, and a system of rift‐transverse crevasses. Small‐scale variations in the mechanical structure of the ice shelf, especially rift‐transverse crevasses and accreted marine ice, play an important role in modulating the rate and location of seismicity associated with the propagating ice shelf rifts. Key Points Rift‐related seismicity controlled by mechanical heterogeneity Back projection reveals that seismic deformation is continuous in region Spacing of rift‐transverse crevasses controls the timing of seismic swarmsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106935/1/jgrf20203.pd

Influence of age, reproductive cycling status, and menstruation on the vaginal microbiome in baboons (Papio anubis)

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111197/1/ajp22378.pd

Strategies to build a positive and inclusive Antarctic field work environment

Support from National Science Foundation (NSF: Grants 1738913, 1738896, 1738942, 1738992, 1738896, 1738934) and Natural Environment Research Council (NERC: Grants NE/S006788/1, NE/S006605/1, NE/S00677X/1). This research was supported in part by the NOAA cooperative agreement NA17OAR4320101. Logistics provided by NSF-U.S. Antarctic Program and NERC-British Antarctic Survey. ITGC Contribution No. ITGC-084.To increase inclusivity, diversity, equity and accessibility in Antarctic science, we must build more positive and inclusive Antarctic field work environments. The International Thwaites Glacier Collaboration (ITGC) has engaged in efforts to contribute to that goal through a variety of activities since 2018, including creating an open-access 'Field and Ship Best Practices' guide, engaging in pre-field season team dynamics meetings, and surveying post-field season reflections and experiences. We report specific actions taken by ITGC and their outcomes. We found that strong and supported early career researchers brought new and important perspectives regarding strategies for transforming culture. We discovered that engaged and involved senior leadership was also critical for expanding participation and securing funding to support efforts. Pre-field discussions involving all field team members were particularly helpful for setting expectations, improving sense of belonging, describing field work best practices, and co-creating a positive work culture.Publisher PDFPeer reviewe