Sequences Stratigraphy of the Dupi Tila Formation, Lalmai Hills, Comilla, Bangladesh

-- Mrinal Kanti Roy, Syed Samsuddin Ahmed, Tapas Kumar Bhattacharjee,
Sultan Mahmud, Md. Moniruzzaman, Md. Masidul Haque, Sudip Saha,
Md. Ismail Molla and Pulin Chandra Roy

The present research work deals with the lithofacies analysis along with the sequence stratigraphy of the Dupi Tila Formation, Lalmai Hills, Comilla to infer the depositional environment and paleogeography. The Dupi Tila Formation consists of alternation of yellow to light brown medium to fine grained sandstones and siltstone, grayish black to bluish gray shale to siltyshale and mudstone with local conglomerate. Different sedimentary facies are genetically grouped into coarse grained facies association (FAC), tide dominated facies association (FAT), heterolithic facies association (FAHL) and shallow marine facies association (FASM). The study of sequence stratigraphy indicates a lowstand systems tract for the basal part, a transgressive systems tract for the middle to lower horizon of upper part and highstand systems tract for the uppermost part. The whole Dupi Tila Formation is a Type-I sequence, as the upper boundary with the Modhupur Clay Formation is erosive and unconformable and lower contact with the underlying Girujan Clay Formation is also erosive and unconformable, though not exposed here. The study of the facies, facies relationship, facies association, paleocurrent analysis and sequence stratigraphy indicates that the depositional environment was extended from shallow marine shore face to intertidal flat through estuarine to tidal channel except the basal part, where deposition was confined to the piedmont alluvial set up of alluvial fan to braid plain. At the latest time, the area was inundated by sea when black shale and black mudstone with Sll facies and glauconite were deposited. Tripura-Sylhet Hills in the east to northeast and Shillong Massif in the north acted as sources of sediment derivation.

© 2011 IUP. All Rights Reserved.

The Use of Geochemical Element to Classify Contrasting Crystallization/Magma Mixing in Lower Benue Trough, Nigeria: A Case Study of Ishiagu, Lokpaukwu and Uturu

-- T N Jowhar

Geochemical data of pyroclastics rocks from Ishiagu, Lokpaukwu and Uturu are presented. The occurrence of compositional variation in the samples indicates that high-level fractionation or alteration occurred. The data indicate that samples are Picrite to Basanite (GroupA), Hawaiite (Group B) and Nephelinite (Group C). Such variation would suggest that rocks of these three localities do not form part of continuous series and could have resulted from partial melting process generated from the mantle and later passed through the process of magma contamination/ assimilation. The rocks can be separated into three magmatic groups: mildly tholeiitic, transitional tholeitic and calcalkaline. Petrographic characterization shows that the rocks are composed of plagioclase (Labradiorite and andesine), clinopyroxene (cpx) (Augite), orthopyroxene (opx) (hypersthene), iron ores, olivine, nepheline and k-spar (in three samples) and quartz (in five samples). Major element geochemistry indicates that all the pyroclastics in the study areas are deficient in CaO and MgO and high in Na2O, TiO2 and LOi. K2O content is low in the pyroclastic rocks of Ishiagu and Uturu, while the pyroclastics in Lopkaukwu are exceptionally high in K2O, implying that the magma was eventually modified by high K-alkaline chemistry, probably from the widening of the proto-oceanic South Atlantic before final emplacement as volcanic in a sediment dominated continental rift setting.

© 2011 IUP. All Rights Reserved.

History of Seismic Events in Garhwal Himalaya, India

-- Arun K Shandilya, Anurag Shandilya and Anupam Shandilya

The studies on the history of the seismic events in the part of Garhwal, Himalaya has been carried out. On the basis of the seismic records of seismic events n Garhwal a review of the events has been done and probabilities of the earthquake has been workout in the part of Garhwal-Kumaun-Himalaya in Uttaranchal. In the southern part of outer Himalaya, thrust zones are expected to produce long-term probabilities of large earthquakes of magnitude more than 6, on Richter scale which have on and average 5 to 20 mm reactivation and neotectonic upliftments along the shear zones. These zones have been estimated to have future probabilities of earthquakes in these areas, which are based on the historical seismic records, the long-term slip rate and the displacement caused by the previous seismic events. The historical records of seismic events in these parts of the Himalaya have the earthquake intensities varying from 4 to 6.0 on Richter scale in the geological past. The Kangra earthquake (1905) recorded more than 7.0 on Richter scale, Garhwal Earthquake (1883) 6.0, Uttarkashi earthquake (1920 and 1991) 5.6 and 6.8 respectively, Chamoli earthquake (1999) 6.5, and the Dehradun earthquake (1970) 5.6. The approach followed for calculations of probabilities employs the estimated recurrence times with a model that assumes probability increases with elapsed time from the large earthquake on the fault/thrust zone areas. Through the calculated probabilities, the estimated natural disaster/ hazards in the newly born state of Uttaranchal in Himalayan belt can be reduced.

© 2011 IUP. All Rights Reserved.

Aquifer Parameter Evaluation of Upper Gadilam River Basin, Vizhupuram District, Tamil Nadu

-- S Aravindan and M Manivel

The study area, upper Gadilam River basin, is located in Vizhupuram district of Tamil Nadu. The number of energized wells in this area has increased manifold due to free supply of electric power until recently by the government of Tamil Nadu, which has resulted in a regional decline in groundwater piezometric heads in this water table aquifer. A hydrogeological study was carried out in the study area. This paper deals with aquifer parameters estimation based on the pumping test data generated in the field. Water level observations in the area indicated that aquifer has undergone less stress condition within the course of time from the yesteryears or early 1995 to June 2004. Transmissivity computed by Theis (1935) method ranges from 301.82 gpd/sq. ft at Ponniyandal to 19,910.14 gpd/sq. ft in Pallavadi towards south central part of the study area. The specific capacity has a range of 0.906 gpm/ ft. of dd in Ponniyandal to 121.91 gpm/ft of dd at Kottaiyampalayam in the eastern central part of the study area. Groundwater level in the basin by rainfall recharge and hydrodynamic method is estimated as 69 million cu.m of recharge and 33 million cu. m of groundwater storage.

© 2011 IUP. All Rights Reserved.