The present Slovenian communities in the Italian borderlands have undergone extraordinary changes in the size and composition of their populations over the last century. After World War II, a large ...number of political refugees from Slovenia also settled there. Since the Italian authorities did not grant them Italian citizenship, most of them emigrated across the ocean after a few years. The rest became actively involved in the social and cultural life of the borderlands. Certainly, the refugees played a very prominent role in the culturally deprived Slovenian community in the Primorska region, which was the result of a quarter of a century of fascist oppression. This applies in particular to the education, media, cultural activities and religious life, where traces of their work are evident.
The Palaeoproterozoic Baraga Group (ca. 1850
±
1
Ma) of northern Michigan is a ∼
1200
m thick sedimentary succession of marine clastic, iron formation, chert, and phosphatic sedimentary rocks that ...accumulated at the peak of the world's first major phosphogenic episode. Lithofacies stacking patterns are interpreted to record the flooding of the Nuna continental margin during two sea-level cycles. The base of the first sequence is marked by a transgressive lag on Archean basement that is transitional into a highstand accumulation of sandstones deposited in peritidal environments. The bottom of the second sequence is characterized by a chert and carbonate unit with numerous subaerial exposure surfaces deposited in intertidal to supratidal environments. This chert grades upward into subtidal deposits composed of interbedded organic-rich mudstone and sandstone. The highstand and falling stage systems tracts are composed of progradational deltaic deposits. Sequences were framed using the newly discovered Sudbury impact ejecta horizon as a datum. Its emplacement approximately coincides with unrelated environmental changes that increased the delivery of river-borne sediment to the Nuna margin.
Iron bearing minerals ankerite, siderite, and pyrite show that ferrous iron was present in peritidal to deep marine environments. Ankerite dominates nearshore settings where pyrite is absent; pyrite occurs in deeper, progradational deltaic deposits where sulfide was produced by bacterial sulfate reduction. Phosphorite is restricted to shallow-water sediments of the first sequence and the lowstand of the second sequence. Precipitation is interpreted to be the result of Fe-redox pumping just below the sediment–water interface where photosynthetically-produced, nearshore oxygen oases impinged on the seafloor. Such shallow-water phosphorite accumulation is in stark contrast to many Phanerozoic depositional systems in which phosphogenesis occurs across the shelf. This difference likely reflects the dissimilarity in the oxygenation state of the seafloor. In the Precambrian, Fe-redox pumping and thus, phosphogenesis, was restricted to shallow-water settings with a suboxic seafloor. In the Phanerozoic, phosphorite forms in the full spectrum of shelf environments because the entire seafloor is generally well oxygenated. The concentration of bioavailable P in neritic environments during the Proterozoic may have played a major role in the development of benthic microbial ecosystems and evolving eukaryotes.
The Eagle Cu–Ni–(PGE) deposit is hosted by mafic to ultramafic intrusive rocks associated with the Marquette–Baraga dike swarm in northern Michigan. Sulfide mineralization formed in a conduit system ...during early stages in the development of the ∼1.1Ga Midcontinent Rift System. The conduit environment represents a prime location for melt–rock interaction. In order to better assess the extent of country rock contamination in the Eagle system, a combined trace element, Nd, Os, O and S isotope study of country rocks, sulfide-bearing igneous rocks and massive sulfide was undertaken.
Both the Eagle and the weakly mineralized East Eagle intrusion show trace element patterns that are similar to those of picritic basalts that formed during early stages of rift development. The trace element, Os, Nd, and O isotopic values of the igneous rocks are consistent with <5% of bulk contamination by Paleoproterozoic and Archean country rocks. Both the Re–Os and Sm–Nd system provide isochrons that are in agreement with the 1107Ma U–Pb baddeleyite age of the intrusive rocks. Calculated γOs(1100) and εNd(1100) values for the magmas are +34 and −2. δ18O values of pyroxene in feldspathic pyroxenite range from 6.5‰ to 6.6‰ and provide the only indication that bulk contamination may locally have exceeded 20%. Sulfur isotopic values of disseminated and massive sulfide in the Eagle intrusion range from 0.3‰ to 4.6‰. The δ34S values are much lower than those that characterize most of the country rocks, but could still be indicative of a contribution of S from country rocks of up to ∼50%. Δ33S values of the disseminated and massive sulfides range from −0.10‰ to 0.09‰ indicating a source in Paleoproterozoic country rocks. Semi-massive sulfide in the Eagle deposit has δ34S values between 2.2‰ and 5.3‰, and Δ33S values show a broad range between −0.86‰ and 0.86‰ indicating a major contribution from an Archean source. Isotopic data from the Eagle deposit strongly indicate that multiple sources of sulfur were involved in the generation of the Ni–Cu–(PGE) mineralization, and magmas which traversed variable paths through the mantle and crust were focused and utilized the same conduit at the level of the Eagle deposit. Our results emphasize the fact that the sulfur isotopic values of immediate country rocks may not be appropriate as end-member values for mixing calculations; sulfur derivation from deeper in the conduit system may have involved rocks with very different sulfur isotope ratios. In addition, sulfur isotopic exchange reactions between passing magma and accumulated crystals or sulfide liquid in the conduit may have led to decreased sulfur isotope variability and δ34S values near those of mantle sulfur.
Distribution of δ34S values obtained from sulfide minerals in various portions of the Eagle intrusion traced along drill cores: EAUG0300 and EAUG0301. Colored shells indicate outer margins of ...different ore types. Red is massive, orange is semi-massive, and purple is disseminated. The δ34S ratios within the intrusion cluster within a tight range even though the ratios are widely variable in the surrounding country rocks.
Display omitted
•δ 34S in sulfide minerals from Eagle and Eagle East intrusions lie between 1 and 3‰.•δ 34S values from sulfides in the country rocks vary widely from −9 to 35‰.•Homogeneous mixing of sulfide liquid during magmatic uplift is evident.
The Eagle Ni-Cu magmatic sulfide deposit in the Upper Peninsula of Michigan is hosted in mafic-ultramafic rocks associated with the 1.1 Ga Midcontinent Rift event. The deposit consists of massive, semi-massive and disseminated sulfide textural zones located in two closely spaced funnel-shaped intrusive bodies, called the Eagle and Eagle East intrusions. The intrusions are surrounded by metamorphosed supracrustal Paleoproterozoic rocks of the Michigamme Formation and at depth by a Neoarchean migmatitic banded gneiss. δ34S values were obtained from sulfide minerals separated by micro-drilling from different parts of the intrusions and the surrounding rocks. The δ34S values from the intrusions cluster within a small range between 1 and 3‰ relative to V-CDT regardless of the mode of occurrence, textural type, mineral type and location of the sample. However, disseminated sulfide minerals in the metasedimentary country rocks of the Michigamme Formation show a substantially greater range in δ34S values between 4 and 35‰ with a median of 7.7‰ while disseminated sulfides in the basement granite-gneiss show values ranging from −9 to 13‰ with a median of 2.5‰. The narrow range of δ34S values within the intrusions despite wide variabilities in the surrounding country rocks can be explained by the incorporation of crustal sulfur by a mantle-derived magma, followed by a homogeneous mixing of the immiscible sulfide liquid, with a silicate liquid to sulfide liquid ratio (R-factor) of 200 or more. The assimilation of crustal rocks and the mixing of the resultant immiscible sulfide liquid must have been facilitated by the rapid movement of magma along a narrow conduit system.
► We investigated the origin of Nubian Sandstone (NSS) fossil aquifer in the Sinai Peninsula. ► NSS aquifer was largely recharged in wet climatic periods yet receives local recharge in dry periods. ► ...Results were validated using geophysical and isotopic data, and continuous rainfall runoff models. ► Groundwater isotopic compositions in recharge areas are similar to those of modern precipitation. ► Average annual modern recharge for Sinai’s NSS aquifers was assessed at ∼13.0 million m
3/yr.
The Nubian Sandstone (NSS) aquifer of northeast Africa is believed to have been recharged in previous wet climatic periods in the Quaternary Period. While this is largely true, we show using the Sinai Peninsula as our test site that the aquifer is locally receiving modern recharge under the current dry climatic conditions. The validity of the advocated model was tested using geophysical (conventional electrical resistivity ER) and isotopic (O, H) data, and estimates for modern recharge were obtained using continuous rainfall-runoff modeling over the period 1998–2007. Interpretations of ER profiles are consistent with the presence of unconfined NSS aquifers flooring recharge areas at the foothills of the crystalline basement in Sinai at Baraga (thickness: 20 to >188 m; resistivity: 16–130 Ω m) and Zalaga (thickness: 27 to >115 m; resistivity: 3–202 Ω m). The isotopic composition (
δD: −22.7 to −32.8‰;
δ
18O: −4.47 to −5.22‰) of groundwater samples from wells tapping the NSS aquifer underlying recharge areas is consistent with mixing between two endmembers: (1) fossil groundwater with isotopic compositions similar to those of the Western Desert NSS aquifer (
δD: −72 to −81‰;
δ
18O: −10.6 to −11.9‰), and (2) average modern meteoric precipitation (
δD: −9.84‰;
δ
18O: −3.48‰) in Sinai, with the latter endmember being the dominant component. A first-order estimate for the average annual modern recharge for the NSS aquifer was assessed at ∼13.0
×
10
6
m
3/yr using the SWAT (Soil Water Assessment Tool) model. Findings bear on the sustainable exploitation of the NSS aquifer, where the aquifer is being locally recharged, and on the exploitation of similar extensive aquifers that were largely recharged in previous wet climatic periods but are still receiving modest modern meteoric contributions.
•Report the age of the Belleview sill that intrudes the Negaunee Iron Formation.•Demonstrate that this sill is older than the Hemlock Volcanics.•Highlight that this sill is older than the onset of ...the Penokean orogeny.•Prove that the Negaunee is not coeval with the Animikie Iron Ranges.
The Belleview metadiabase sill crosscuts the Siamo Slate and the Negaunee Iron Formation of the Marquette Range Supergroup, Michigan. It is one of a series of metamorphosed diabase sills that intrudes the Menominee Group and possibly the Baraga Group. Chloritic sills within the Marquette Range Supergroup have yet to be officially grouped as one or more series or swarms and therefore stratigraphic correlations and temporal relationships between these sills remain speculative. The recovery of the first sensitive high-resolution ion mass spectrometry (ID-TIMS) U–Pb date of 6 baddeleyite grains from the Belleview sill yielding an age of 1891±3Ma is a positive step to classifying these chloritic metadiabases. This new date has three important implications: (1) it gives a definitive minimum age of Negaunee Iron Formation deposition; (2) it confirms recent stratigraphic correlations that suggest that the Negaunee Iron Formation is older than the Mesabi, Gunflint and Gogebic Iron Ranges and not contemporaneous; and (3) it does not support recent correlations of the Menominee Group chloritic sills with the 1874Ma Hemlock Formation within the Baraga Group of the Marquette Range Supergroup.
This new date does not support a more recently proposed synorogenic foredeep depositional environment for the deposition of the Negaunee Iron Formation. Instead, this age date supports an earlier interpretation that the Negaunee Iron Formation is part of continental shelf deposits laid down prior to onset of 1875–1835Ma collision. The age of the Belleview sill suggests that it is the result of extension-related magmatism that is prior to the currently defined Penokean orogenic event.
A forested dunefield covers the Baraga Plains in western upper Michigan. The ages of five dunes, from across the dunefield, were determined by optically stimulated luminescence (OSL), employing the ...single-aliquot regenerative-dose (SAR) method on quartz grains. The results indicate that sand mobilization was restricted to the middle Holocene, at around 7 ka. Four environmental variables, rapid climatic oscillations, fire, strong winds and a dry climate are invoked as a combined cause of dune formation. This study provides further evidence for the wide extent of aeolian activity in the upper Midwest of North America during the middle Holocene.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, OILJ, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The peneplaned Archean craton in the Lake Superior region was the platform upon which a continental margin assemblage was deposited. Extension resulted in localized rifts that received thicker ...accumulations of sediments and volcanic rocks than did adjacent parts of the platform. Seas transgressed onto the continent several times and an ocean basin opened south of the present-day Lake Superior. Island arcs that formed during subduction collided with the craton margin as the ocean basin closed; oceanic crust is poorly preserved as a dismembered ophiolite sequence. The arc volcanics are preserved as the Wisconsin magmatic terranes. The collision resulted in a fold-and-thrust belt known as the Penokean orogen. To the north of the fold-and-thrust belt, a northward-migrating foreland basin — the Animikie basin — developed. Thick turbidite successions were deposited along the basin axis, and terrigenous clastics and Lake Superior-type iron-formation were deposited on the shelf along the northern margin of the basin.
The primary paleoclimatic indicators are: (1) glaciogenic rocks at the base of the Paleoproterozoic succession in Michigan indicating ice-house conditions; (2) remnants of a paleosol on the glaciogenic rocks indicative of deep weathering, probably under subtropical conditions and therefore of greenhouse conditions; and (3) carbonate minerals after gypsum, halite, and anhydrite in stromatolitic dolomite, indicative of aridity.
Three second-order depositional sequences are bounded by major unconformities, and can be correlated throughout the Lake Superior region.
Paleoproterozoic strata in northern Michigan, Wisconsin, and Minnesota were deposited between 2.3 and 1.75
Ga within the rifted margin and subsequent foreland basin of the Penokean orogen. These ...strata show evidence for multiple regional metamorphic events previously attributed entirely to the Penokean orogeny (1875–1835
Ma). Metasandstones from the Marquette Range Supergroup and the Animikie, Mille Lacs, and North Range Groups were sampled at multiple localities across Minnesota, Wisconsin and Michigan for metamorphic xenotime suitable for
in situ SHRIMP U–Pb geochronology. All samples are from the northern Penokean foreland basin where the metamorphic grade is greenschist to sub-greenschist and the strata are virtually undeformed. Xenotime U–Pb ages in these samples have a bimodal population with means of 1786
±
4
Ma (
n
=
32) and 1861
±
10
Ma (
n
=
9). Xenotime of both ages are contained in metasandstones from the basal Chocolay Group in Michigan and Wisconsin and the Mille Lacs Group and North Range Groups in Minnesota. The older age records a regional low-temperature thermal event that is slightly older than the overlying Menominee Group in Michigan and the Animikie Group in Minnesota and Ontario. This 1861
Ma event coincides with regional uplift that led to the formation of the unconformity between the Menominee Group and the overlying Baraga Group in Michigan; hence xenotime growth must have occurred at shallow burial depths. Younger units from the Menominee and Baraga Groups in Michigan and the Animikie Group in Minnesota, record only the 1786
Ma event.
A dominant 1800–1790
Ma metamorphic monazite population that overprints Penokean-interval monazite has been documented within amphibolite- to granulite-facies rocks immediately north of the Niagara Fault Zone within the vicinity of gneiss domes and granitic plutons. In contrast, the 1786
Ma xenotime ages are from low-grade, virtually undeformed rocks 50–150
km from the high-grade zones and thus do not appear to reflect a local thermal imprint. Rather, the geographic extent of the 1786
Ma xenotime growth event suggests that it reflects a basin-wide, subtle thermal pulse. It is proposed that the xenotime ages record widespread subtle heating triggered by renewed subduction along the orogen due to Yavapai-interval convergence. The 1800–1700
Ma Yavapai terrane forms an accretionary belt throughout the central and southwestern U.S. and truncates the southern part of the Penokean orogen in central Wisconsin and southeastern Minnesota, about 200
km south of the sample sites. Alternatively, an 1800–1765
Ma interval of gravitational collapse of overthickened crust of the Penokean orogen immediately north of the Niagara Fault Zone may have driven a northward flow of hydrothermal fluids which subtly but pervasively altered the northern parts of the Penokean foreland and resulted in xenotime growth.
Many of Michigan's loamy soils exhibit varying degrees of fragipan expression, which may be variously influenced by their parent materials. We examined three soils in northern Michigan with varying ...degrees of fragipan expression to assess development of fragipans formed in acidic and calcareous glacial drift. To accomplish this, soil characterizations were made through field, physical, chemical, and micromorphological observations and analyses. The soils have bisequal horizonation: an upper sequum associated with podzolization processes arid lower sequum associated with lessivage. Protofragipans and fragipans are found only in the lower sequum. The soils experience periodic episaturation and contain at least one lithologic discontinuity, often near the protofragipan or fragipan. The protofragipan and fragipans have loamy sand to loam textures, weak platy to subangular blocky structure, higher bulk densities (1.5-1.9 g cm^sup -3^) and lower pH values (4.8-6.8) than adjacent horizons, brittle failure, and fine vesicular pores. Eluvial protofragipan and fragipan horizons contain albic materials that tongue into underlying argillic horizons. Illuvial fragipans exhibit clay coats, flows, and bridging. Thin-section characterizations confirm the presence of closely packed fabrics, intergrain bridging by clays, and void pedofeatures. Scanning electron microscopy (SEM) provides evidence of eluviation, reorganization of silt and clay, fluctuating redox conditions, degraded void pedofeatures, and the presence of surficially amorphous (bonding) materials in the protofragipan and fragipans. Soil extraction data do not preclude the presence of a fragic-property (brittleness) agent. Results, therefore, indicate that these protofragipans and fragipans are pedogenic and can form, with variable expression, in both acidic and calcareous glacial parent materials. PUBLICATION ABSTRACT
