INNOVATIVE AND CONVENTIONAL APPROACHES TO DETRITAL ZIRCON PROVENANCE ANALYSIS: LOOKING TO THE PAST, PRESENT, AND FUTURE

Detrital provenance analysis is an important tool in our understanding paleo-fluvial drainages, erosion of landscapes, paleogeographic reconstructions, and regional geologic and tectonic histories. Here, we examine the utility of multiple provenance analysis techniques through their application to paleo, modern, and synthetic detrital datasets. Zircon is a common accessory mineral found in most detrital sediments, primarily due to its refractory nature. During formation, zircon preferentially incorporates the element U and Th into its crystal lattice while excluding Pb, making it ideal for radiometric dating. Inexpensive and time-efficient U/Pb age acquisition techniques make zircon the mineral of choice for a majority of provenance studies. The sedimentary basins between the Yangtze River and Red River have long been used to argue for a Mississippi River-scale paleo-drainage. We examine the U/Pb zircon ages of Cenozoic deposits ranging from Eocene to Pliocene age from basins surrounding the first bend of the Yangtze River and upper reaches of the Red River. We combine this data with a comprehensive suite of zircon grain-ages from contemporaneous deposits, modern fluvial sediments, and bedrock source units from previously published literature. Using the new technique developed here, of combining age spectra deconvolution and age component interpolation maps, it becomes clear that Cenozoic deposits of the Southeastern margin of the Tibetan Plateau do not share provenance with offshore sediments associated with the Paleo Red River in the Yinggehai Song-Hong Basin. This, coupled with detailed stratigraphic measurements and interpretations, as well as paleoflow measurements strongly suggests that at least since the Eocene, there was no connectivity between the Yangtze and Red Rivers. In a modern setting, examination of provenance of fluvial sediments collected throughout a known catchment can provide insight into regional erosional patterns. The modern Yangtze River, the largest river in Eurasia, provides a perfect setting to apply detrital zircon provenance analysis. We use a previously published zircon U/Pb age distribution dataset of fifteen trunk stream samples and ten samples of the largest tributaries feeding the Yangtze. We apply a series of age-distribution analysis techniques to examine both downstream changes in provenance of trunk stream samples as well as identify the key bedrock and tributary sources of sediment to the trunk stream samples throughout the Yangtze\u27s reach. The original work using this dataset argued that increasing anthropogenic influences, primarily agricultural, lead to a greater than expected influence of the Han, Yuan, and Xiang Rivers, whose confluence with the Yangtze occur in the middle-to lower reaches. The quantitative analysis developed here, however, shows a consistent distribution of U/Pb ages for Yangtze River trunk stream sediments is established in the upper reaches of the Yangtze after the first bend and is maintained some 3000km downstream. The signal is most likely derived from the erosion of the geologic terranes of the Songpan Ganze Terrane and the Longmenshan range, which are sourced primarily by the Yalong, Min, and Dadu rivers. These sources of sediment are consistent with known areas of greater stream power due to higher slopes, exhumation rates, and tectonic activity. One technique that has recently been applied to detrital zircon datasets is multidimensional scaling, or MDS. MDS transforms pairwise dissimilarity measurements of sample U/Pb age distributions into Euclidian distances and then some optimal configuration, where greater distances between sample points represents greater dissimilarity between their respective age distributions. While MDS is not new, its application to detrital zircon datasets has never been rigorously tested. We examine several important issues in the application of MDS to detrital zircon research, including how intra-sample variation is represented as well as how dissimilarities are calculated; how random sampling associated with dating a limited number of zircon grain ages can and does affect the resulting MDS configuration; and how MDS differentiation is affected by samples containing either varying degrees of overlapping, shared, or unique age components. In application of MDS to both synthetic and real-world datasets, we illustrate the usefulness of the approach in the interpretation of detrital zircon age data; which suggests that thoughtful application of MDS mapping to detrital zircon data can afford significant advantages in the geologic interpretation of zircon grain ages

<i>Chirotherium barthii </i>Kaup 1835 from the Triassic of the Isle of Arran, Scotland

The mould of a track from SE Arran, and several in situ trackways and individual tracks, as well as a partial trackway on a loose block of Triassic sandstone, from western Arran, represent the first verifiable fossil tracks of Chirotherium from the Triassic of Scotland and support a Scythian (Lower Triassic) age for the base of the Auchenhew Beds. The grouping of the I–IV toes with toe V behind and lateral to the group is characteristic of Chirotherium-like tracks. A comparison with European and American Triassic trackways suggests that the tracks belong to the species Chirotherium barthii Kaup, 1835, first described from Hildburghausen, Germany

Disorder induced local density of states oscillations on narrow Ag(111) terraces

The local density of states of Ag(111) has been probed in detail on disordered terraces of varying width by dI/dV-mapping with a scanning tunneling microscope at low temperatures. Apparent shifts of the bottom of the surface-state band edge from terrace induced confinement are observed. Disordered terraces show interesting contrast reversals in the dI/dV maps as a function of tip-sample voltage polarity with details that depend on the average width of the terrace and the particular edge profile. In contrast to perfect terraces with straight edges, standing wave patterns are observed parallel to the step edges, i.e. in the non-confined direction. Scattering calculations based on the Ag(111) surface states reproduce these spatial oscillations and all the qualitative features of the standing wave patterns, including the polarity-dependent contrast reversals.Comment: 19 pages, 12 figure

Intensional Polymorphism in Type-erasure Semantics

Intensional polymorphism, the ability to dispatch to different routines based on types at run time, enables a variety of advanced implementation techniques for polymorphic languages, including tag-free garbage collection, unboxed function arguments, polymorphic marshalling, and flattened data structures. To date, languages that support intensional polymorphism have required a type-passing (as opposed to type-erasure) interpretation where types are constructed and passed to polymorphic functions at run time. Unfortunately, type-passing suffers from a number of drawbacks: it requires duplication of constructs at the term and type levels, it prevents abstraction, and it severely complicates polymorphic closure conversion.We present a type-theoretic framework that supports intensional polymorphism, but avoids many of the disadvantages of type passing. In our approach, run-time type information is represented by ordinary terms. This avoids the duplication problem, allows us to recover abstraction, and avoids complications with closure conversion. In addition, our type system provides another improvement in expressiveness; it allows unknown types to be refined in place thereby avoiding certain beta-expansions required by other frameworksEngineering and Applied Science

The origin of micrograins

Using ultraviolet and infrared techniques, researchers investigated the origins of the tiny (approx. 10A) grains whose presence in the interstellar medium (ISM) is inferred from near-infrared photometry (Sellgren, Werner, and Dinerstein 1983; Sellgren 1984). The authors consider two possibilities: (1) that the grains are formed by condensation in stellar atmospheres; or (2) that they are formed by fragmentation of larger grains in interstellar shocks. They searched for evidence of very small grains in circumstellar environments by analyzing ultraviolet extinction curves in binaries containing hot companions, and by searching for the 3.3-micron emission feature in similar systems. The ultraviolet extinction curve analysis could be applied only to oxygen-rich systems, where small carbonaceous grains would not be expected, so these results provide only indirect information. Researchers find a deficiency of grains smaller than 800A in oxygen-rich systems, consistent with theoretical models of grain condensation which suggest that grains grow to large sizes before injection into the interstellar medium. More direct information on carbonaceous micrograins was obtained from the search for the 3.3-micron feature in carbon-rich binaries with hot companions, whose ultraviolet flux should excite the tiny grains to emit in the infrared. No 3.3-micron feature was found, suggesting that the micrograins are absent in these systems. In addition to the negative search for micrograins in circumstellar environments, researchers have also studied the possible association of these grains with shocks in the diffuse interstellar medium. Using Infrared Astronomy Satellite (IRAS) colors as indicators of the presence or absence of the small grains (e.g., Ryter, Puget, and Perault 1987 and references cited therein), researchers systematically searched for them in regions (reflection nebulae) expected to have sufficient ultraviolet flux to make them glow in the infrared. They found that the distribution is not uniform. The researchers propose that production of micrograins by fragmentation of larger grains in shocks could explain this uneven distribution

The challenges of diagnosing osteoporosis and the limitations of currently available tools

Abstract Dual-energy X-ray absorptiometry (DXA) was the first imaging tool widely utilized by clinicians to assess fracture risk, especially in postmenopausal women. The development of DXA nearly coincided with the availability of effective osteoporosis medications. Although osteoporosis in adults is diagnosed based on a T-score equal to or below − 2.5 SD, most individuals who sustain fragility fractures are above this arbitrary cutoff. This incongruity poses a challenge to clinicians to identify patients who may benefit from osteoporosis treatments. DXA scanners generate 2 dimensional images of complex 3 dimensional structures, and report bone density as the quotient of the bone mineral content divided by the bone area. An obvious pitfall of this method is that a larger bone will convey superior strength, but may in fact have the same bone density as a smaller bone. Other imaging modalities are available such as peripheral quantitative CT, but are largely research tools. Current osteoporosis medications increase bone density and reduce fracture risk but the mechanisms of these actions vary. Anti-resorptive medications (bisphosphonates and denosumab) primarily increase endocortical bone by bolstering mineralization of endosteal resorption pits and thereby increase cortical thickness and reduce cortical porosity. Anabolic medications (teriparatide and abaloparatide) increase the periosteal and endosteal perimeters without large changes in cortical thickness resulting in a larger more structurally sound bone. Because of the differences in the mechanisms of the various drugs, there are likely benefits of selecting a treatment based on a patient’s unique bone structure and pattern of bone loss. This review retreats to basic principles in order to advance clinical management of fragility fractures by examining how skeletal biomechanics, size, shape, and ultra-structural properties are the ultimate predictors of bone strength. Accurate measurement of these skeletal parameters through the development of better imaging scanners is critical to advancing fracture risk assessment and informing clinicians on the best treatment strategy. With this information, a “treat to target” approach could be employed to tailor current and future therapies to each patient’s unique skeletal characteristics.https://deepblue.lib.umich.edu/bitstream/2027.42/143867/1/40842_2018_Article_62.pd