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Geoscience e-Journals





An International Year of Planet Earth-2008 Initiative

Current Issue Technical

Year 2017

Volume X

Sedimentological Characteristics of a Channel Bar Deposit of the Jiadhal River, Dhemaji District, Assam, India
Satyajit Sonowal and Jayanta Jivan Laskar

The present study aims to identify and interpret various bedform features and lithofacies and their textural characteristics found within a channel bar of the Jiadhal River in Dhemaji District, Assam. The channel bar has a length of approximately 8 km with a maximum width of 1.26 km. Various bedform features found in the area includes small and mega ripples, water level cut marks and track and trails. Six lithofacies types were identified from six vertical sections which were excavated within the channel bar. These are Horizontal laminated sand (Sh), Planar cross-bedded sand (Sp), Trough cross bedded sand (St), Massive sand (Sm), Laminated sand, silt and mud (Fl) and Massive mud (Fm). Texturally the sediments are medium to fine sand (Mz= 1.30 Ф to 2.80 Ф), moderately sorted (σi= 0.52 Ф to 0.90 Ф), near symmetrical to positive skewed (Ski= -0.01 to 0.22) and mesokurtic to very leptokurtic (Kg= 0.96 to 1.48). The CM plot of the bar sediments indicates rolling, graded suspension (saltation) and suspension modes of their deposition.


Keywords: Bedform features, Lithofacies, Texture, Channel bar, Jiadhal River, Dhemaji District, Assam.

Geochemical Modelling of Magma Evolution Process in Bodie Hills Volcanic Field, Nevada, USA
Liubomyr Gavryliv 1, Gogolev Konstantin 2 and Aleksieienko Anton

The middle to late Miocene Bodie Hills Volcanic Field (BHVF) represents one of the largest volcanic complexes of the ancestral Cascades magmatic arc. Though, the former volcanoes are known to contain geochemical imprints of tectonic regime, deep structure evolution and lithosphere characteristics, there are still virtually no links or correlations made between various volcanic suites of BHVF, which accounts for the necessity of their thorough analysis. The paper aims to improve petrologic and geochemical knowledge of magma evolution of four volcanic centers: Mount Biedeman, Aurora, Masonic and West Brawley Peak. There are used published whole-rock XRF (X-ray fluorescence), ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy) and ICP-MS (Inductively Coupled Plasma Mass Spectrometry) chemical analyses performed in analytical laboratories of SGS Minerals, Toronto, Canada. Many of the rocks show the effects of magma mixing, interaction with crustal rocks and open system crystallization. The results indicate that BHVF rocks contain a significant portion, at least 10% by mass, of granodiorite and volcanic sediment of Sierra Nevada. BHVF magmas rising from mid to shallow crustal levels and initiating assimilation processes in shallower reservoirs apparently had >1500 ppm Sr and 87Sr/86Sr <0.7040. The chemical composition of trace elements in BHVF indicate fractional crystallization with the accumulation of plagioclase, olivine, augite and magnetite. Conclusively, geochemical studies of BHVF rocks point out that magmas were variably contaminated, and that much of the rocks were recycled in a MASH (Melting, Assimilation, Storage, Homogenization) zone.


Keywords: Magma Evolution; Trace Elements; Fractional Crystallization with Assimilation; MASH zone; Geochemical Modelling; Bodie Hills Volcanic Field.

Hantkeninidae (Planktonic Foraminifera) from the Middle-Upper Eocene of Jabal Hafit, United Arab Emirates
Haidar Salim Anan

Six species of the planktonic foraminiferal Family Hantkeninidae belonging to the genera namely Cribrohantkenina and Hantkenina are recorded and described from the Middle- and Upper Eocene succession of Jabal Hafit, Al Ain area, United Arab Emirates. The species include Cribrohantkenina inflata, Hantkenina alabamensis, H. compressa, H. australis, H. liebusi and H. primitiva. The three species of Hantkenina named last are recorded for the first time from the UAE.


Keywords: Middle Eocene, Upper Eocene, Hantkeninidae   species, United Arab         Emirates