1,721,006 research outputs found
Erosion of Tortonian phosphatic intervals in upwelling zones. The role of internal waves
No full textDuring the Miocene, the upwelling is assumed to be important in the formation of many Mediterranean phosphate deposits in carbonate platform successions. There are different types of upwelling mechanisms such as equatorial upwellings, ice-edge upwellings and coastal upwellings. The carbonate platforms are mainly affected by wind-driven coastal upwelling systems. During upwelling season, the seawater in coastal areas is strongly density stratified and the permanent pycnocline rises inshore forming an inclined frontal layer. The liaison between upwellings and internal waves is widely documented in the literature. Internal waves result from perturbations of the hydrostatic equilibrium, where balance is sustained between the force of gravity and buoyant restoring force. Many perturbations of the pycnocline can propagate as an internal wave. In a coastal upwelling, a key role for wave propagation is played by permanent pycnocline. The run-up swash currents develop during the break of internal waves and produce erosional processes. In particular, the backwash return flow may induce the erosion of seafloor sediments and transport these sediments downslope as bedload. Erosion of phosphate-rich intervals has been extensively documented. The deposition of gravity-flow sediments is followed by intervals of non-deposition, incipient lithification, phosphogenesis and erosion. In this work, we evaluate the role of internal waves in the formation of the resedimented phosphate-rich intervals characterising the basal portion of the hemipelagic Orbulina marls. These marls are deposited on the low-angle Latium-Abruzzi carbonate ramp and represent deposition in a foreland basin during the initial stages of evolution of the Central Apennine Belt during the early Tortonian age
Petrographic and mineral-glass chemical dataset of igneous rock clasts from Early Oligocene Aveto-Petrignacola Formation (Northern Italy)
Full text linkThis dataset article contains petrographic and mineral-glass chemical data of igneous rock clasts from Early Oligocene Aveto-Petrignacola Formation (APF; Northern Italy). Meth- ods for obtaining the dataset include optical microscopy, scanning electron microscopy and electron probe microanal- ysis. The APF volcanic rocks are basalts, basaltic andesites, andesites, dacites and rhyolites. Rare gabbroic cumulate nodules complete the dataset. Basalts are porphyritic, with calcic plagioclase (An 72–92 Ab 7–27 Or 0–1 ), ferroan enstatite (En 59–68 Fs 29–37 Wo 3–4 ) and augite (En 38–39 Fs 18–20 Wo 41–44 ) phenocrysts, in a hypocrystalline groundmass made up of bytownite (An 71–85 Ab 14–28 Or 1 ), augite (En 37–38 Fs 19 Wo 43–44 ), ferroan enstatite (En 62–68 Fs 30–35 Wo 1–4 ) and rare pigeonite (En 46–50 Fs 37–42 Wo 7–17 ). The basaltic andesites are porphyritic to glomeroporphyritic with phenocrysts of zoned plagio- clase (An 44–67 Ab 32–55 Or 1 ), orthopyroxene, Mg-rich augite (En 38–42 Fs 15–17 Wo 43–45 ), rare pargasite to edenite amphibole (Mg# 69–59) and very rare biotite in a hypocrystalline to holohyaline groundmass. Andesites are highly porphyritic with phenocrysts of plagioclase (An 47–79 Ab 20–52 Or 0–1 ), pargasite to magnesio-hornblende (Mg# 72–67), Mg-rich augite (En 43–46 Fs 12–17 Wo 41–43 ), subordinate ferroan enstatite (En 68–74 Fs 23–29 Wo 3–4 ), biotite (Mg# 53) and Ti-magnetite (Usp 29–41 ). Dacites (massive lavas and ignimbrites) are porphyritic, with phenocrysts and phenoclasts of plagioclase (An 33–79 Ab 20–62 Or 0–4 ), calcic amphibole (Ti-pargasite, Mg-hornblende and edenite; Mg# 81–46), biotite (Mg#67–56), very rare Mg-rich augite (En 41–42 Fs 16–18 Wo 40–43 ) and resorbed quartz in hypohyaline to holohyaline groundmass with a dense mat of anhedral quartz, labradorite-andesine (An 36–66 Ab 33–61 Or 1–4 ) and rare anorthoclase (An 22 Ab 66 Or 12 ).
Rhyolitic compositions have been found both as volcanic clasts (massive lava and ignimbrites) with andesine to oligoclase phenoclasts (An 25–38 Ab 61–71 Or 1–4 ), quartz, biotite (Mg# 55–53) and Ti-magnetite (Usp 18–77 ), and as interstitial glasses (residual melt drops) in other APF volcanic rocks. The cumulate nodules are olivine-gabbro and amphibolegabbro/gabbronorite with a mineral paragenesis dominatedby plagioclase (An 41–73 Ab 26–57 Or 1–3 ), olivine (Fo 68–72 ), Mg rich augite to ferroan diopside (En 41–45 Fs 12–15 Wo 42–45 ; Mg#79–74), ferroan enstatite (En 65–74 Fs 24–33 Wo 2–3 ; Mg# 76–68), magnetite (Usp 15–28 ) and titanian pargasite (Mg# 67–65). The main cumulus phases are plagioclase, olivine and pyroxene, while intercumulus/postcumulus phases are titanian pargasite and magnetite. The dataset can be used to compare petrographic features and chemical compositions of calcalkaline rocks emplaced in other subduction-related settings. Above all, it can represent a useful contribution in solving the problem linked to the identification of a hidden Early-Oligocene source of the thick volcaniclastic APF succession in the Alpine-Apennine belt geodynamic evolution
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
REACTIVITY OF SECONDARY METAL-ALKYLS IN CATALYTIC PROPENE POLYMERIZATION: HOW DORMANT ARE "DORMANT CHAINS"?
No full textn this communication, we report on the direct measurement of dormant chain concentration and of the relative reactivity of authentic primary and secondary Zr-polymeryls toward propene, ethene, and H2 under practical conditions for a new highly regio- and stereoselective postmetallocene polymerization catalyst with controlled kinetic behavior. The results, in particular, confirm the poor reactivity toward propene of secondary M-polymeryls and the possible accumulation of dormant chains in propene homopolymerization
The First Molecularly Characterized (Isotactic Polypropylene)-block-Polyethylene Obtained via “Quasi-Living” Insertion Polymerization
No full textVELOCIMETRIA DOPPLER: ALTERAZIONI VELOCIMETRICHE IN GRAVIDANZE COMPLICATE DA GESTOSI ED ESITO PERINATALEVELOCIMETRIA DOPPLER: ALTERAZIONI VELOCIMETRICHE IN GRAVIDANZE COMPLICATE DA GESTOSI ED ESITO PERINATALE
No full textImproving the performance of bis(phenoxyamine) Group 4 metal olefin polymerization catalysts
No full textOn the occurrence of kalsilite in melilite-bearing ultrapotassic lavas from the Roman Province (Vulsini Mts., central Italy)
Full text linkThe Montefiascone Volcanic Complex belongs to the Vulsini Mts. volcanic district, one of the several leucite-bearing ultrapotassic Pleistocene volcanoes of the Roman Province (Central Italy). It is characterized by abundant pyroclastic successions and minor lava flows emplaced during a caldera formation phase occurred similar to 0.3-0.2 Ma. The volcanic products span from leucite-basanites and leucite-tephrites to rarer leucitites and melilitites, occasionally associated with very rare kalsilite melilitolite ejecta. Here we report for the first time the presence of primary kalsilite in two lava flows in Forcinella and Feltricci localities, identifying a kamafugitic component among the Montefiascone volcanics. Detailed petrographic, SEM and EPMA studies on ten samples from the two localities revealed, in addition to kalsilite, variable amounts of clinopyroxene, melilite, leucite and nepheline plus rarer olivine coupled with carbonate-bearing segregation pockets in the groundmass. Geochemical and isotopic data confirm the exotic nature of the analysed rocks, showing ultrabasic/basic (SiO2 = 42.15-45.94 wt%) and ultrapotassic (K2O = 6.17-8.48 wt%; K2O/Na2O = 5.3-8.7) compositions, as well as strongly radiogenic Sr-87/Sr-86 (0.71038-0.711068), poorly radiogenic Nd-143/Nd-144 (0.512057.512091) and uniform middle radiogenic Pb-206/Pb-204 (18.76-18.78). Boron isotopes (delta B-11 ranges from 7.36 to 8.82 parts per thousand) almost overlaps the typical MORB-OIB range values. These geochemical features recall those of the nearby kamafugite rocks from the Intra-Apennine Province. Major oxide and trace element modelling support fractionation links among the Italian kamafugite types. The overall geochemical and isotopic signatures speak for a common strongly subduction-metasomatized and orthopyroxene-free lithospheric mantle source. As already proposed for some nearby kamafugite centres in central Italy, limestone assimilation during magma ascent is a viable option to explain the mineralogical and whole-rock composition of Montefiascone lavas (i.e., the presence of carbonate plagues in the lava groundmass). This is particularly relevant considering the thick sedimentary sequence pierced by the limited volume of the upwelling magma. On the other hand, many other key features (such as the general lack of crustal xenoliths, the overall incompatible element fractionation and the radiogenic Sr isotopic ratios) clearly require also derivation from subduction-modified mantle sources
The First Molecularly Characterized (Isotactic Polypropylene)-block-Polyethylene Obtained via “Quasi-Living” Insertion Polymerization
No full text- …
