Geochemistry of garnet xenocrysts and garnet-bearing xenoliths in Ordovician bentonites

Within outcrops of the black Utica shales south of the Mohawk Valley narrow re-entrants parallel with stratification are visible, often accompanied -by a marked orange-staining of the underlying strata. These rentrant features indicate the presence of bentonites weathered back faster then the enclosing shales. These bentonites are presumably magmatic ashes related to extensive volcanism when an island arc collided with the North American continent in the late Ordovician about 450 million years ago (Taconic orogeny). Bentonites are good stratigraphic markers because of the short time-interval they represent and the large area they cover. Therefore they are commonly used as correlation tools. In this study an attempt was made to use the minerals (i.e. garnets) as a correlation tool in contrast to earlier attempts to correlate bentonites by chemical fingerprinting using bulk chemistry (Huff, 1986; Kolata et al., 1986, 1987). The mineral content of these bentonites was separated and analyzed. In this study special attention was paid to the garnets and garnet-bearing rock fragments. The garnets were analyzed using an electron microprobe for major elements and trace elements, i.e. Ti, Sc, Zn and Y. In the single crystals as well as in the rock fragments two groups of garnets are observed: (1) pink grains containing 0.4-5 mol.% grossular, 56-79 mol.% almandine, 12-40 mol.% pyrope, 1-5 mol.% spessartine, and \u3c2.2 mol.% andradite; and (2) dark grains containing 14-24 mol.% grossular, 48-76 mol.% almandine, 2-35 mol.% pyrope, 1-9 mol.% spessartine, and \u3c7 mol.% andradite. For the trace elements some general trends are observed, especially a positive correlation of TiO2 with CaO, with up to 1150 ppm TiO2 in the CaO-rich garnets. A negative correlation of Sc and CaO is observed, leading to higher amounts of Sc (100-200 ppm) in the CaO-poor garnets compared to the CaO-rich garnets which contain generally less than 100 ppm Sc. Yttrium does not show a distinct behavior with changing CaO content, but it appears to favor slightly garnets with higher CaO content. Geothermobarometry calculations (Berman and Perkins, 1987; Lindsley and Anderson, 1983; Ellis and Green, 1979; Fuhrman and Lindsley, 1988; Ghent, 1976; Kohn and Spears, 1990) were attempted on rock fragments with suitable mineral assemblages. Calculated temperatures and pressures included: (1) 600ºC on pyroxene pairs; (2) 605-625ºC and 6.5-7.5 kbar on a rock fragment containing garnet-hornblende-quartz-plagioclase; (3) 450-550ºC on feldspars; (4) 600-650ºC on clinopyroxene-garnet pairs; and (5) pressures of 4.5 kbar at 600ºC for the assemblage garnet- plagioclase-aluminosilicate and quartz, which support the view that the garnets and rock fragments are derived from a metamorphic source of about granulite-facies grade. The incorporation of xenocrysts and xenoliths into the bentonites can be explained by the disruption and integration of Grenville-like crust into the ash during eruption. This explanation is consistent with the ages derived from a K-feldspar aliquot of one of the bentonites using the Ar/Ar method of dating, which shows a thermal history similar to Grenville crust K-feldspars and an age of 550-750 million years. This is too old to be derived from metamorphism during the Taconic event, nor can these feldspars be explained as authigenic phases; therefore, the best explanation is a different source than the volcanism at 450 million years, and a minimum age for this source of 750 million years, and probably older. The subject of this investigation is split into two parts: (1) Garnets as means of correlation and (2) garnets as indicators for the source of the magmas creating the bentonites. Both lines of investigation were unsuccessful. The xenocrystic garnets in the bentonites cannot be used for correlation purposes and are also of very limited use to define a source area because of their metamorphic character

Measurement of calcium isotopes (δ44Ca) using a multicollector TIMS technique

We propose a new“multicollector technique” for the thermal ionization mass spectrometer (TIMS) measurement of calcium (Ca) isotope ratios improving average internal statistical uncertainty of the 44Ca/40Ca measurements by a factor of 2–4 and average sample throughput relative to the commonly used “peak jumping method” by a factor of 3. Isobaric interferences with potassium (40K+) and titanium (48Ti+) or positively charged molecules like 24Mg19F+, 25Mg19F+, 24Mg16O+ and 27Al16O+ can either be corrected or are negligible. Similar, peak shape defects introduced by the large dispersion of the whole Ca isotope mass range from 40–48 atomic mass units (amu) do not influence Ca-isotope ratios. We use a 43Ca/48Ca double spike with an iterative double spike correction algorithm for precise isotope measurement

Der Kreuznimbus auf sogenannten koptischen Textilien

Bis auf den „Londoner Mosestoff“, einem großformatigen, zweifärbigen Textil, das in Reservetechnik gefärbt wurde, und zeitlich schon dem 5. Jahrhundert zugerechnet werden kann, ist die Mehrzahl der sog. koptischen Textilien mit Kreuznimbusdarstellungen in spätere Zeit zu datieren. Die chronologische Einordnung kann jedoch nur auf Grundlage stilistischer Überlegungen erfolgen, da die gegebenen Fundumstände eine genaue Datierung im Regelfall unmöglich machen. Bei den Darstellungen handelt es sich des Weiteren ausschließlich um die Gruppe der polychrom gewirkten Gewandbesätze auf rotem Grund. Ab dem sechsten Jahrhundert treten Exemplare dieser Gattung vermehrt auf. Die Wahl der Farbe hatte eine triftige Ursache, galt Rot doch als Farbe des Lebens. Das Repertoire der dargestellten Szenen korreliert mit der attributiven Bedeutung des Kreuznimbus: Episoden wundersamer Begebenheiten bei der Geburt Christi, die explizite Formulierung der Gottsohnschaft bei seiner Taufe, Huldigungsszenen, ikonenhafte Darstellungen und nicht zuletzt die Wiedergabe von vollbrachten Wundern sollen vor allem die messianische Allmacht Christi zum Ausdruck bringen. Persönliche Intentionen und die Bezugnahme der Träger der in solcher Art dekorierten Kleidungsstücke auf die einzelnen Szenen spielten ebenso eine Rolle bei der Motivauswahl. Spezielle Aufmerksamkeit gebührt der quantitativ kleinen Gruppe der typologischen Darstellungen, zumal dieses Phänomen auch auf Textilien mit kleiner Fläche, etwa dem Oxforder orbiculus auftritt. Weiters kann anhand der vorliegenden „koptischen“ Textilien mit Kreuznimbusdarstellungen der Nachweis von Mustervorlagen für neutestamentarische Motive erbracht werden

Is river Ghaggar, Saraswati? Geochemical constraints

The identity of the river along which the famous Harappan Civilization developed and the causes of the demise of this culture are topics of considerable debate. Many of the Harappan sites are located along the ephemeral Ghaggar river within the Thar Desert in the northwestern India and adjacent Pakistan. The Ghaggar was also thought to be the mythical river Saraswati, which was described as glacial-fed river. Sr and Nd isotopic composition of the Ghaggar alluvium as well as Thar Desert sediments suggests a Sub-Himalayan sediment source, with no contribution from the glaciated regions. The development of extensive Harappan Civilization all along the Ghaggar suggests a catchment with high monsoon rainfall. It is likely that with the changes in the monsoon scenario after 3500 BC could have gradually dried up the Ghaggar river and resulted in the migration and/or extinction of the Harappan Civilization on this river

Is Rhiver Ghaggar, Saraswati? Geochemical constraints

The identity of the river along which the famous Harappan Civilization developed and the causes of the demise of this culture are topics of considerable debate. Many of the Harappan sites are located along the ephemeral Ghaggar river within the Thar Desert in the northwestern India and adjacent Pakistan. The Ghaggar was also thought to be the mythical river Saraswati, which was described as glacial-fed river. Sr and Nd isotopic composition of the Ghaggar alluvium as well as Thar Desert sediments suggests a Sub-Himalayan sediment source, with no contribution from the glaciated regions. The development of extensive Harappan Civilization all along the Ghaggar suggests a catchment with high monsoon rainfall. It is likely that with the changes in the monsoon scenario after 3500 BC could have gradually dried up the Ghaggar river and resulted in the migration and/or extinction of the Harappan Civilization on this rive

Ca & Sr dynamics in the Indogangetic plains: different sources and mobilization processes in northwestern India

The leachable fraction of the sediments from the Thar Desert fringe and the adjacent Ganges alluvial plains, has been studied to determine the sources and the processes responsible for the mobilization of Ca and Sr using Sr isotopes and Ca/Sr ratios. In the desert the leachable fraction of the soil/sediments is probably derived from mixing of old marine carbonates, microfossils with the sea-spray of the Arabian Sea and rainwater. Aeolian reworking of soil carbonates of this mixed origin could have provided the carbonate found at the desert fringe. The sub-humid zone of the Gangetic plains, just outside the desert fringe, has relatively higher 87Sr/86Sr ratios with lower Ca/Sr ratios, indicating silicate weathering as the major contributor of leachable fraction. The spatial geochemical differences could also be related to the ineffectiveness of dust transport and accumulation processes in the humid Ganga plain. The 87Sr/86Sr ratio of the present-day dust leachate from the polluted city of Delhi indicates that its Sr source is petroleum burnt residues

Proposal for International Agreement on Ca Notation resulting from discussion at workshops on stable isotope measurement held in Davos (Goldschmidt 2002) and Nice (EGS-AGU-EUG 2003)

A proposal is made to standardise the reporting of Ca isotope data to the δ44Ca/40Ca notation (or δ44Ca/42Ca) and to adopt NIST SRM 915a as the reference standard

Alloimmunization in dogs after transfusion: A serial cross-match study

Background Cross-matching is performed to determine the serological compatibility of donor and recipient blood. Current guidelines recommend that cross-matching should be performed in dogs when an initial transfusion was performed more than 4 days ago or when the transfusion history is unknown. Hypothesis Determination at what time point alloantibodies are detected in dogs after transfusion. The hypothesis was that dogs would form alloantibodies within 4 days after a transfusion. Animals Twenty-one anemic dogs were transfused and monitored for at least 4 subsequent days. Exclusion criteria were persistent red blood cell (RBC) agglutination and a previous transfusion. Methods Prospective observational study. Cross-matching was performed before the initial DEA 1-compatible transfusion and on days 1, 2, 3, and 4 and if possible, between day 5 and 28, using the tube method without enhancement (major cross-match, recipient controls); recipients were monitored for transfusion reactions. Results In 12/21 dogs a positive cross-match (microscopic degree of agglutination [AD] 1+ to 2+) was observed within 4 days after the transfusion. In a nonlinear regression model, no significant association was detected between type of anemia (P = .41), RBC storage time (P = .44), immunosuppressive treatment (P = .75) nor transfusion volume (P = .70) and the occurrence of positive cross-matches within 4 days after transfusion. Another 4 dogs developed a positive cross-match (microscopic AD 1+ to 2+) after 6 to 13 days. Conclusions and Clinical Importance Because production of alloantibodies was detected as early as 1 day after transfusion, cross-matching should be performed before every subsequent transfusion

Postoperative recovery of accelerometer-based physical activity in older cancer patients

Introduction: Recovery of physical activity is an important functional outcome measure after cancer surgery. However, objective data on physical activity for older cancer patients is scarce. The aims of this study were to quantify perioperative physical activity levels, assess recovery of physical activity three months after surgery, and characterise patients who achieved recovery. Materials and methods: This observational cohort study analysed physical activity data collected from patients aged >65 who were scheduled for cancer surgery between May 2018 and July 2019. Perioperative daily step count was measured using a Fitbit device. The primary outcome measure was the percentage of patients who returned to (>90% of) their preoperative (baseline) physical activity levels three months after surgery. Results: Fifty patients (mean age 73) were recruited, and available Fitbit data was analysed. Median daily step counts at baseline (n = 40), before hospital discharge (n = 40), and three months postoperative (n = 37) were 5,974 (IQR 4,250-7,922),1,619 (IQR 920-2,839), and 4,674 (IQR 3,047-7,592), respectively. The 15/37 (41%) patients who had reached baseline levels three months after surgery seemed to have more preoperative self-reported physical activity, better anaesthesiologists' physical status classification, and fewer in-hospital complications compared to patients who had not, although the differences were statistically non-significant. Conclusion: Perioperative physical activity was quantified for older cancer patients, and 41% returned to baseline levels within three months. Accelerometer-based physical activity provided a valuable outcome measure for postoperative physical recovery. Future studies using objective physical activity measures are needed to evaluate effects of interventional studies aimed at improving physical activity. (C) 2020 The Authors. Published by Elsevier Ltd