Amounts Of K-feldspar Research Articles

The Exquisite Comparison of Shale Mineralogical-Geochemical Characteristics between Chang 7 Member and Chang 9 Member in Yanchang Formation, Ordos Basin

Significant amounts of unconventional oil and gas resources have been discovered in the Yanchang Formation of Ordos Basin. Shale layers deposited in Chang 7 member (divided into Chang 7-2 submember (C7-2SM) and Chang 7-3 submember (C7-3SM) and Chang 9 member (C9M)) are the main source rocks. Based on the comparison of mineralogical and geochemical characteristics, it is concluded that (1) in terms of mineralogical characteristics, the C7-3SM shale possesses the largest content of illite/smectite mixed layer and reducing minerals and the least quantity of quartz. The C9M shale shows the highest percentage of quartz and illite and the least amount of K-feldspar and Kaolinite. In C7-2SM and C9M shale, amorphous silica surrounded tightly by clay minerals is easily observed by the scanning electron microscopy. Besides the drilling orientation, the small content of quartz contributed to the lowest porosity for the C7-3SM shale. (2) In terms of geochemical characteristics, the C7-3SM shale exhibits high productivity due to type II1 kerogen. The organic matter in the C7-2SM and C9M shale contains mainly type II2 and possibly type III kerogen. The C9M shale exhibits the highest organic thermal maturity. The C7-3SM shale was formed in a relatively higher salinity of sedimentary water.

Early Cretaceous redbeds from the Minle Basin, Hexi Corridor, northwest China: Mineralogy and geochemistry implications for paleoweathering, provenance, and tectonic settings

Redbeds with a large thickness in the lower Cretaceous record abundant geologic information in the Minle Basin. We have conducted the paleoweathering conditions, provenance, and tectonic settings based on mineralogy and geochemistry. Our results indicate that mudstone samples are characterized by abundant illite with negligible amounts of K-feldspars and analcime. The lower part of the lower Cretaceous is rich in quartz, whereas the upper part is dominated by dolomite and analcime. We suggest that this is caused by the decreasing input of the clastic influx during the middle-late early Cretaceous. High index of compositional variation values (average 1.33) indicate first-cycle sediment supply, suggesting an overall compositional immaturity and short-distance transportation. These characteristics are consistent with an active regional extension tectonic setting. The [Formula: see text] system ([Formula: see text];[Formula: see text];[Formula: see text]) and Th/U versus Th consistently reveal that the lower Cretaceous experienced a positive gradient in chemical weathering from young to old formations. Although the patterns of trace elements in three formations of the lower Cretaceous are different, those of the rare earth elements (REEs) tend to be consistent. The significant enrichment of light REEs, heavy REEs fractionation, and distinctive negative Eu anomalies suggest derivation from an old, upper continental crust composed of predominantly felsic sediments. This interpretation is supported by several discrimination diagrams such as titanium dioxide-nickel ([Formula: see text]), which shows the characteristics of immature recycled sediments. A few sensitive elements, ratios, and normalized REE patterns indicate a provenance of an active continental margin and a continental island arc (CIA). The La-Th-Sc, Th-Co-Zr/10, and Th-Sc-Zr/10 discrimination plots further confirm the CIA signature. Thus, we conclude that the early Cretaceous redbeds in the Minle Basin, Hexi Corridor, were deposited in a dustpan-shaped half-graben basin in a CIA setting when northwest China was influenced by intense regional extension.

A 250ka sedimentary record from a small karstic lake in the northern Levant (Yammoûneh, Lebanon) – Paleoclimatic implications

The Levant, influenced by both the Mediterranean Sea and the Saharan–Arabian deserts, is a key region for understanding climatic changes in response to glacial/interglacial boundary conditions that have greatly affected regional hydrology. Here, we present the first long-term paleoenvironmental record from the northern Levant, presently much wetter than the southern Levant. Our record derives from the multi-proxy study of a sediment core (36 m long) retrieved from the small intra-mountainous, tectonic basin of Yammouneh (Lebanon), which is mainly supplied by karstic springs.Sediments consist of a thick accumulation of brownish to greenish clayey silts, interrupted by intervals of whitish marls composed of CaCO3 rich material. The core chronology is based on radiometric dating (14C and U/Th) and paleomagnetic techniques. The sedimentary sequence spans approximately the last two glacial–interglacial cycles (~ 250 ka). Carbonate content is relatively high throughout the profile due to a perennial input of detrital calcite from the watershed, but varies significantly. The marls are mostly composed of authigenic and biogenic calcite and reflect lacustrine environments with high carbonate productivity during peaks of interglacial periods. Their occurrence suggests low physical erosion of the basin slopes which were covered by arboreal vegetation, and intense karstic water circulation under warm and relatively wet conditions, in agreement with pollen data. The clayey silts are dominated by quartz and clay minerals, and a few amounts of K-feldspars and dolomite. They are characterized by high concentration in magnetic particles, and high relative concentrations of Si, Al, K and Fe considered as strictly of detrital origin. Due to the carbonated nature of the watershed, quartz and K-feldspars are attributed to eolian origin from a distal source. The clayey silt intervals generally suggest palustrine conditions with abrupt flows responsible for runoff-derived material, or subaerial environments and low local water availability in particular during the Last Glacial Maximum. High Si/Al and K/Al ratios, during interglacials, are attributed to relatively high eolian dust contribution due to the decrease of local detrital inputs.Our study reveals significant differences between Yammouneh and lake records from the Dead-Sea basin (southern Levant), the latter showing high/low levels during glacial/interglacial periods. These hydrological differences might reflect either changes in the North–South (NS) rainfall gradient in response to the development of the northern ice sheet and the southward migration of the westerly belt, or local factors, i.e., a decrease in efficient precipitation and water availability at Yammouneh during the coldest glacial periods (e.g., the Last Glacial Maximum), due to water storage by ice caps on the Mount Lebanon range and frozen soils in the Yammouneh basin.

A 250 ka sedimentary record from a small karstic lake in the Northern Levant (Yammoûneh, Lebanon) : Paleoclimatic implications

The Levant, influenced by both the Mediterranean Sea and the Saharan–Arabian deserts, is a key region for understanding climatic changes in response to glacial/interglacial boundary conditions that have greatly affected regional hydrology. Here, we present the first long-term paleoenvironmental record from the northern Levant, presently much wetter than the southern Levant. Our record derives from the multi-proxy study of a sediment core (36 m long) retrieved from the small intra-mountainous, tectonic basin of Yammoûneh (Lebanon), which is mainly supplied by karstic springs. Sediments consist of a thick accumulation of brownish to greenish clayey silts, interrupted by intervals of whitish marls composed of CaCO 3 rich material. The core chronology is based on radiometric dating ( 14 C and U/Th) and paleomagnetic techniques. The sedimentary sequence spans approximately the last two glacial–interglacial cycles (~ 250 ka). Carbonate content is relatively high throughout the profile due to a perennial input of detrital calcite from the watershed, but varies significantly. The marls are mostly composed of authigenic and biogenic calcite and reflect lacustrine environments with high carbonate productivity during peaks of interglacial periods. Their occurrence suggests low physical erosion of the basin slopes which were covered by arboreal vegetation, and intense karstic water circulation under warm and relatively wet conditions, in agreement with pollen data. The clayey silts are dominated by quartz and clay minerals, and a few amounts of K-feldspars and dolomite. They are characterized by high concentration in magnetic particles, and high relative concentrations of Si, Al, K and Fe considered as strictly of detrital origin. Due to the carbonated nature of the watershed, quartz and K-feldspars are attributed to eolian origin from a distal source. The clayey silt intervals generally suggest palustrine conditions with abrupt flows responsible for runoff-derived material, or subaerial environments and low local water availability in particular during the Last Glacial Maximum. High Si/Al and K/Al ratios, during interglacials, are attributed to relatively high eolian dust contribution due to the decrease of local detrital inputs. Our study reveals significant differences between Yammoûneh and lake records from the Dead-Sea basin (southern Levant), the latter showing high/low levels during glacial/interglacial periods. These hydrological differences might reflect either changes in the North–South (NS) rainfall gradient in response to the development of the northern ice sheet and the southward migration of the westerly belt, or local factors, i.e., a decrease in efficient precipitation and water availability at Yammoûneh during the coldest glacial periods (e.g., the Last Glacial Maximum), due to water storage by ice caps on the Mount Lebanon range and frozen soils in the Yammoûneh basin.

Partial melting of deeply subducted continental crust and the formation of quartzofeldspathic polyphase inclusions in the Sulu UHP eclogites

Two types of quartzofeldspathic inclusions hosted by omphacite and garnet were identified in the Sulu UHP eclogites. The first consists of albite, quartz, and various amounts of K-feldspar. In contrast, the second consists predominantly of K-feldspar and quartz without any albite. The presence of quartzofeldspathic inclusions within the UHP mafic eclogites indicates that partial melting occurred in deeply subducted continental crust via mica dehydration melting reactions at an early stage of rapid exhumation. Such a melting event generated hydrous Na-K-Al-Si melts. These melts infiltrated into the mafic eclogite and were captured by recrystallizing garnet or omphacite, which together followed by dehydration and crystallization to form feldspar-bearing polyphase inclusions. Formation of silicate melts within the deeply subducted continental slab not only provides an excellent medium to transport both mobile (LILE) and immobile (HFSE) elements over a large distance, but also induces effective changes in the physical properties of the UHP slab. This process could be a major factor that enhances rapid exhumation of a deeply subducted continental slab.

Mineralogy and potassium release from some Western Australian soils and their size fractions

Seven surface horizon soils and their sand, silt, and clay fractions were characterised for mineralogy, and K release by extracting samples with 1 mM CaCl 2 solution daily for 10 days. The low silt content is characteristic of many Western Australian soils, which may provide a partial explanation of the paucity of available K in soils that contain little silt-size primary minerals. The sand and silt fractions were dominated by quartz and contained significant amounts of K-feldspars. The clay fraction was dominated by kaolinite, and some samples contained illite/mica, inhibited vermiculite, and gibbsite. On a per unit weight basis the clay-fraction released the largest amount of K followed in sequence by the silt and sand. The contribution of size fractions to total K release by the soil ranged from 50 to 87%, 2 to 7%, and 10 to 44% for the clay, silt, and sand, respectively. Linear plots of K release versus time 1/2 for the soils, and the sand and silt fractions, indicated that a parabolic diffusion equation adequately describes the K release process. For some clay samples this diffusion controlled kinetic is not strictly obeyed during the initial period of K desorption due to rapid exchange of adsorbed K at sites on external surfaces. The Elovich equation plots show a discontinuity in slope and support the hypothesis of the multireactive nature of K exchange sites for these soils. The parabolic diffusion rate constant closely predicted K supply to plants as it has a close positive relationship (r = 0.99) with total K uptake by ryegrass for 260 days of growth.

Quaternary gabbro-anorthosites as effusives in Kamchatka

Holocrystalline gabbro-anorthosites and anorthosites have been found in the thick interformational veins of the upper portions of the Pliocene-Quaternary Nikolka volcano in Kamchatka. The gabbro-anorthosites contain a marked amount of K-feldspar, and on the basis of their chemistry, they have been assigned to the tephrite-basalts. They are identical to the megaplagiophyre basalts, which are widely distributed in the Central Kamchatka depression. It has been suggested that the magma of subalkaline gabbro-anorthosites occurred in signifcant depths at the base of the crust during emanation differentiation of a saturated tholeiite. Further fractionation of this magma could have led to the formation of autonomous anorthosites and alkaline gabbroids associated with them in natural assemblages. —Authors.