The Western North American Cretaceous-Tertiary (K-T) boundary interval and its content of shock-metamorphosed minerals: Implications concerning the K-T boundary impact-extinction theory

At 20 sites in the Raton Basin of Colorado and New Mexico, and at several other sites in Wyoming, Montana, and Canada, a pair of claystone units, an Ir abundance anomaly, and a concentration of shock-metamorphosed minerals mark the palynological K-T boundary. The K-T boundary claystone, which is composed of kaolinite and small amounts of illite/smectite mixed-layer clay, is similar in most respects to kaolinite tonstein layers in coal beds. At some, but not all, K-T boundary localities, the boundary claystone contains solid kaolinite and hollow and solid goyazite spherules, 0.05 to 1.2 mm in diameter. The upper unit, the K-T boundary impact layer, consists chiefly of kaolinite and various amounts of illite/smectite mixed-layer clay. The impact layer and boundary claystone are similar chemically, except that the former has slightly more Fe, K, Ba, Cr, Cu, Li, V, and Zn than the latter. The facts that the boundary claystone and impact layer contain anomalous amounts of Ir, comprise a stratigraphic couplet at Western North American sites, and form thin, discrete layers, similar to air-fall units (volcanic or impact), suggest that the claystone units are of impact origin. Significantly, the impact layer contains as much as 2 percent clastic mineral grains, about 30 percent of which contain multiple sets of shock lamellae. Only one such concentration of shocked minerals has been found near the K-T boundary. The type of K-T boundary shock-metamorphosed materials (quartzite and metaquartzite) in the impact layer and the lack of shock lamellae in quartz and feldspar of pumice lapilli and granitic xenoliths in air-fall pumice units of silicic tuffs, such as the Bishop Tuff, eliminate the possibility that the shock-metamorphosed minerals in the K-T impact layer are of volcanic origin. The global size distribution and abundance of shock-metamorphosed mineral grains suggest that the K-T impact occurred in North America

K/T boundary stratigraphy: Evidence for multiple impacts and a possible comet stream

A critical set of observations bearing on the K/T boundary events were obtained from several dozen sites in western North America. Thin strata at and adjacent to the K/T boundary are locally preserved in association with coal beds at these sites. The strata were laid down in local shallow basins that were either intermittently flooded or occupied by very shallow ponds. Detailed examination of the stratigraphy at numerous sites led to the recognition of two distinct strata at the boundary. From the time that the two strata were first recognized, E.M. Shoemaker has maintained that they record two impact events. We report some of the evidence that supports this conclusion

The Cretaceous-Tertiary boundary interval, Raton Basin, Colorado and New Mexico, and its content of shock-metamorphosed minerals: Implications for the Cretaceous-Tertiary boundary impact-extinction theory

Thesis (Ph.D.) University of Alaska Fairbanks, 1988In the Raton Basin and other Western North American Cretaceous-Tertiary (K-T) boundary sites, a pair of claystone beds, an overlying coal, an an iridium anomaly mark the boundary. The lower unit, the boundary claystone, is a 1- to 2-cm-thick kaolinitic tonstein that is generally free of quartz grains, has a micropherulitic texture, and contains a trace-element suite similar to average North American shale. Rare kaolinite and goyazite spherules in the claystone probably are not of impact origin. An equivalent of the boundary claystone does not occur at boundary sites outside of North America. The upper unit, the impact layer, is about 5 mm thick and consists chiefly of kaolinite; it is microlaminated and contains ubiquitous kaolinite pellets and vitrinite laminae. Its chemical composition is different than the boundary claystone, particularly its greater content of iridium. Shock-metamorphosed minerals are concentrated in the impact layer and generally are absent in subjacent rocks. The origin of the two units is seemingly closely related because they form a couplet at Western North American sites. However, evidence suggests that the claystone matrix of the units is not altered volcanic or impact-generated material. The impact layer contains up to 2 percent clastic mineral grains, 30 percent of which contain shock lamellae. Of these grains, quartzite, metaquartzite, and chert constitute about 60 percent and quartz the remainder. Grains of shocked feldspar and granite-like mixtures of quartz and feldspar are rare. The abundance of unshocked quartzite, metaquartzite, and chert in the impact layer and their paucity in underlying rocks suggests they are of impact origin. Evidence suggests that the shock-metamorphic minerals in the impact layer are not of volcanic origin. The Manson, Iowa, structure is proposed as the impact site because of the mineralogic similarity of Manson subsurface rocks and shocked K-T boundary minerals, the large size (35 km) of the impact structure, the compatible isotopic age of shocked granitic rock from the Manson impact structure and the K-T boundary (66 Ma), and the proximity of the Manson impact structure to North American boundary sites that contain relatively abundant and large shocked minerals

Patterns of attachment and reflective functioning in families of adolescents with eating disorders

This study investigated attachment patterns and mentalising capacity of adolescent girls with eating disorders, their mother’s reflective capacity, and family functioning. Girls with eating disorders scored higher rates of insecure attachment, lower attachment coherence and higher hypermentalising than non-clinical girls. Although mothers’ reflective functioning did not differ between groups, a proportion of clinical mothers scored very low reflective functioning compared to controls. Clinical families presented with higher depression, anxiety, communication difficulties and conflict

Irradiance and nutrient-dependent effects on photosynthetic electron transport in Arctic phytoplankton: A comparison of two chlorophyll fluorescence-based approaches to derive primary photochemistry.

We employed Fast Repetition Rate fluorometry for high-resolution mapping of marine phytoplankton photophysiology and primary photochemistry in the Lancaster Sound and Barrow Strait regions of the Canadian Arctic Archipelago in the summer of 2019. Continuous ship-board analysis of chlorophyll a variable fluorescence demonstrated relatively low photochemical efficiency over most of the cruise-track, with the exception of localized regions within Barrow Strait, where there was increased vertical mixing and proximity to land-based nutrient sources. Along the full transect, we observed strong non-photochemical quenching of chlorophyll fluorescence, with relaxation times longer than the 5-minute period used for dark acclimation. Such long-term quenching effects complicate continuous underway acquisition of fluorescence amplitude-based estimates of photosynthetic electron transport rates, which rely on dark acclimation of samples. As an alternative, we employed a new algorithm to derive electron transport rates based on analysis of fluorescence relaxation kinetics, which does not require dark acclimation. Direct comparison of kinetics- and amplitude-based electron transport rate measurements demonstrated that kinetic-based estimates were, on average, 2-fold higher than amplitude-based values. The magnitude of decoupling between the two electron transport rate estimates increased in association with photophysiological diagnostics of nutrient stress. Discrepancies between electron transport rate estimates likely resulted from the use of different photophysiological parameters to derive the kinetics- and amplitude-based algorithms, and choice of numerical model used to fit variable fluorescence curves and analyze fluorescence kinetics under actinic light. Our results highlight environmental and methodological influences on fluorescence-based photochemistry estimates, and prompt discussion of best-practices for future underway fluorescence-based efforts to monitor phytoplankton photosynthesis

On the Value of Certain Physical Efficiency Tests for Assessing Endurance in Soldiers

Abstract Not Provided

Safety and efficacy of non-absorbable mesh in contemporary gynaecological surgery

Mesh-augmented pelvic floor surgery evolved to address the limitations of native tissue repair in reconstructive surgery. The development of the synthetic mid-urethral tape signalled a revolution in the treatment of stress urinary incontinence, whilst the use of mesh in abdominal apical prolapse repair may confer benefits over native tissue alternatives. However, these procedures can be associated with mesh-specific complications, underlining the need for shared decision-making between physicians and patients prior to mesh surgery. Transvaginal non-absorbable mesh implants for pelvic organ prolapse are associated with a high risk of serious adverse events, leading to withdrawal or restricted use in many countries. Increased scrutiny has led to growing concerns about complications associated with all types of mesh-augmented reconstructive surgery, attracting widespread media attention. National and international reports have been commissioned examining the safety and efficacy of mesh surgery in gynaecology. They have all highlighted systemic failures in the development, regulation and clinical adoption of medical devices. The widespread application of novel devices prior to the availability of reliable safety and efficacy data, and delayed recognition of adverse events, is of serious concern. Notwithstanding, the available data continue to support a role for mesh augmentation. This review outlines the evolution of gynaecological mesh, the safety and efficacy of pelvic floor surgery using non-absorbable mesh materials, and an overview of specific complications