Seaward dipping reflectors along the SW continental margin of India: Evidence for volcanic passive margin     

K. K. Ajay  A. K. Chaubey  K. S. Krishna  D. Gopala Rao  D. Sar 《Journal of Earth System Science》2010,119(6):803-813

Multi-channel seismic reflection profiles across the southwest continental margin of India (SWCMI) show presence of westerly dipping seismic reflectors beneath sedimentary strata along the western flank of the Laccadive Ridge — northernmost part of the Chagos-Laccadive Ridge system. Velocity structure, seismic character, 2D gravity model and geographic locations of the dipping reflectors suggest that these reflectors are volcanic in origin, which are interpreted as Seaward Dipping Reflectors (SDRs).  相似文献   

The Nature and Distribution of Particulate Matter in the Mandovi Estuary,Central West Coast of India     

Pratima Mohan Kessarkar  Venigalla Purnachandra Rao  Ranjan Shynu  Prakash Mehra  Blossom E. Viegas 《Estuaries and Coasts》2010,33(1):30-44

Systematic seasonal variations of suspended particulate matter (SPM) along a 44-km transect of the Mandovi estuary reveal that the concentrations of SPM are low at river-end stations, increase generally seaward, and are highest at sea-end stations of the estuary. An estuarine turbidity maximum (ETM) occurs at sea-end stations during June–September when river discharge is high and also in February–May when river discharge is low. These are the two windiest times of year, the former associated with the southwest monsoon and the latter characterized by a persistent sea breeze. The salinity vs. SPM plot shows that high SPM is a seaward deposit and skewed landward. Suspended matter comprised of floccules, fecal pellets, and aggregates that consist of clay and biogenic particles occur everywhere in the estuary. Diatoms are the most common and are of marine type at the sea-end and freshwater-dominated at river-end stations of the estuary. SPM is characterized by kaolinite- and smectite-rich clay mineral suites at the river- and sea-end stations, respectively. Smectite concentrations increase seawards with the increase in SPM content and are not influenced by salinity. Wind-driven waves and currents and biogeochemical processes at the mouth of estuary likely play an important role in the formation of ETM in resuspension and transformation of SPM into floccules and aggregates and in their upkeep or removal.  相似文献   

Indications of an extreme event deposits along the west coast of India: evidences from GPR investigations   总被引：1，自引：1，他引：0  

V. J. Loveson  A. R. Gujar  S. D. Iyer  P. Srivastava  G. M. Tirodkar  R. A. A. Luis 《Environmental Earth Sciences》2014,72(10):4155-4166

The ground-penetrating radar (GPR) was used to trace the subsurface details in the Palshet coastal zone (Maharashtra) as it exhibits an interesting array of geomorphological features. Furthermore, our main goal was to identify and locate features that might have formed during a reported extreme event and its effects on the flow of the nearby Sundri River. Two profiles (8 and 4 m depth) were collected across the beach and along the backshore, respectively. While the 8-m depth profile (west to east; across the beach) indicates a series of coastline regression in this area, the 4-m depth profile along the coastline (north to south) in the backshore zone reveals two significant incidents viz., (1) stages of development of the paleo-channels that indicate the migration of the Sundri River towards south and (2) huge sediment deposits up to 2.5-m thick in the backshore area. The erosional relict surface (~2.5 m depth) was traced along with various spells of sediments that perhaps occurred due to an extreme event. Sand samples were collected from two trial pits along the GPR profiles to understand the sedimentology and mineralogy in the backshore area. These data together with beach profiles and geomorphological maps suggest that the sands were deposited by an extreme event perhaps during the 1854 cyclonic storm. The sands were trapped in suitable geomorphological sites along the Palshet coast and these sand deposits of about 2.5 m thickness forced the River Sundri to shift its course towards the south. This new revelation facilitates a further study that could focus on the nearby coastal areas to document such extreme event deposits and their influence on the geomorphic set-up.  相似文献   

Sedimentary variations of geomorphic subenvironments at Al-Lith area,central-west coast of Saudi Arabia,Red Sea     

A. S. Basaham  A. M. Gheith  A. A. A. Khawfany  R. Sharma  N. H. Hashimi 《Arabian Journal of Geosciences》2014,7(3):951-970

Sediment characteristics are the indicators of the intensity and geological history of the processes active in an area. Their association with different geomorphic features also signifies the present day conditions of deposition. In this study, variations in sediment characteristics associated with different geomorphic features, such as the coastal zone, two islands and a lagoon in the Al-Lith area of central-west coast of Saudi Arabia have been analysed. Whereas, the detrital sediments (sand?+?mud) are common (61–87 %) in most of the subunits of the coastal zone; the nondetrital (carbonate rich) sediments are more common (54–95 %) on the two islands as well as the lagoon; indicating distinct sources of sediments in these regions. The variation of sediment texture between sand and sandy silt in most geomorphic units, also shows that they are exposed to high-energy conditions, whereas occurrence of heavy minerals in small proportions (<7 %) indicates limited inputs from land-based igneous and metamorphic rocks. Sediment mean size vs. standard deviation shows that the sediment characteristics of a geomorphic unit (e.g. beach or sand bar) on the coast and on the island are different owing to different processes responsible for their formation.  相似文献   

GPR studies over the tsunami affected Karaikal beach,Tamil Nadu,south India     

V J Loveson  A R Gujar  R Barnwal  Richa Khare  G V Rajamanickam 《Journal of Earth System Science》2014,123(6):1375-1385

In this study, results of GPR profiling related to mapping of subsurface sedimentary layers at tsunami affected Karaikal beach are presented . A 400 MHz antenna was used for profiling along 262 m stretch of transect from beach to backshore areas with penetration of about 2.0 m depth (50 ns two-way travel time). The velocity analysis was carried out to estimate the depth information along the GPR profile. Based on the significant changes in the reflection amplitude, three different zones are marked and the upper zone is noticed with less moisture compared to other two (saturated) zones. The water table is noticed to vary from 0.5 to 0.75 m depth (12–15 ns) as moving away from the coastline. Buried erosional surface is observed at 1.5 m depth (40–42 ns), which represents the limit up to which the extreme event acted upon. In other words, it is the depth to which the tsunami sediments have been piled up to about 1.5 m thickness. Three field test pits were made along the transect and sedimentary sequences were recorded. The sand layers, especially, heavy mineral layers, recorded in the test pits indicate a positive correlation with the amplitude and velocity changes in the GPR profile. Such interpretation seems to be difficult in the middle zone due to its water saturation condition. But it is fairly clear in the lower zone located just below the erosional surface where the strata is comparatively more compact. The inferences from the GPR profile thus provide a lucid insight to the subsurface sediment sequences of the tsunami sediments in the Karaikal beach.  相似文献   

An appraisal of an iterative construction of the endmembers controlling the composition of deep-sea manganese nodules from the Central Indian Ocean Basin     

R M Renner  B N Nath  G P Glasby 《Journal of Earth System Science》2014,123(6):1399-1411

This paper describes an estimation of endmember compositions followed by the assessment of those results by log-ratio variance analysis. As an appraisal, it deals only with the first objective of an endmember analysis namely, to identify endmembers if they exist by estimating their compositions. Following the creation of the endmember estimates, the computation of an array of log-ratio variances was a key innovation in this type of study. Log-ratio variances revealed intrinsic linear associations between the dominant elements on each of the estimated endmember compositions, largely confirming the endmember analysis. The dataset under study contained the concentrations of 16 elements in 93 samples of deep-sea manganese nodules from the Central Indian Ocean Basin. Many previous analyses of these nodules were undertaken to assess the economic potential of the deposits. This study by contrast, quantified the inter-element associations that account for the nodule compositions. Four endmembers were identified. The elements loaded on each were: (1) Mn, Zn, Ni, Cu, Mn-rich, (2) Fe, Ti, P, Co, Fe-rich, (3) Si, Al, Na, K, clay minerals, (3) Mg, ultramafic material, possibly including Mn, Cr, V, Ca, Na. These latter elements were also detected by their log-ratio variances to be associated with Mg on the 4th endmember.  相似文献   

Bathymetric preference of four major genera of rectilinear benthic foraminifera within oxygen minimum zone in Arabian Sea off central west coast of India     

ABHIJIT MAZUMDER  RAJIV NIGAM 《Journal of Earth System Science》2014,123(3):633-639

Fifty two surface sediment samples collected from the region off Goa, central west coast of India from water depths of 15–3300 m were analyzed with special emphasis on foraminiferal content. Rectilinear benthic foraminiferal morphogroup shows a high relative abundance within Oxygen Minimum Zone (OMZ), both shallow marine (50–60 m water depth) and intermediate to deep water (150–1500 m water depth). We gave special emphasis on four rectilinear foraminiferal genera, namely Fursenkoina, Bolivina, Bulimina and Uvigerina to observe their individual distribution among OMZ. We found genus Fursenkoina predominates at the shallow water OMZ, within the water depth zone of 50–60 m. Within 150–1500 m water depth, which is considered as intermediate to deep water OMZ in this region, genus Uvigerina shows its highest abundance above 1000 m water depth, whereas genus Bulimina shows its affinity with deeper water environment (>1000 m water depth). Genus Bolivina does not show any such depth preference, except its higher abundance in only intermediate to deep water OMZ. This depth differentiation among four rectilinear benthic foraminiferal genera presents the basic data for palaeoclimatic study based on the extent and intensity of OMZ along with the palaeobathymetry study.  相似文献   

Beach dynamics and oscillations of shoreline position in recent years at Miramar Beach,Goa, India: a study from a GPR survey     

V. J. Loveson  A. R. Gujar  Sridhar D. Iyer  P. Udayaganesan  R. A. A. Luis  S. S. Gaonkar  P. Chithrabhanu  G. M. Tirodkar  A. K. Singhvi 《Natural Hazards》2014,73(3):2089-2106

Consideration of human influences is crucial to understanding the coastal sediment supply and associated shoreline responses prior to undertaking coastal hazard management studies. Observation of the widening of some selected Indian beaches, especially over the last 6 decades, is of significance. From this perspective, Miramar Beach, Goa, India, was studied using three ground-penetrating radar shallow subsurface profiles (4 m depth). Based on a series of depositional siliciclastic packages, six progradational packages were recognised, which were interrupted by sharp erosional boundaries. These erosional boundaries represent transgressive phases of the shoreline migration. It was observed that the shoreline migration is coupled with the deposition and erosion of sediments, and this is supported by the historical admiralty charts. The optically simulated luminescence dating of the sediments collected at the first progradation period reveals that the age corresponds to the years 1952–1957, which also corroborates the information provided by the local populace. In the past 6 decades, the shoreline growth has been rapid because of the heavy sediment influx from the Mandovi River caused by increased mining activities (since the 1950s) in upstream areas. Since the 1950s, the shoreline has prograded rapidly, building a beach from ~40 to ~280 m wide (average rate of 4 m/year) in response to enhanced sediment supply from the Mandovi River created by mining activities upstream. Superimposed on this overall regressive trend is a series of deposition and erosion cycles. Perhaps, if a similar trend continues, then there will possibly be a further widening of the beach in the future. A close monitoring network is needed to understand the causes of the cycles in shoreline position and to predict their future behaviour. The present investigation on the nature of the coastal response to anthropogenic activities in a river basin as well as the role of short-time cycles on shoreline behaviour in the last 6 decades could be an ideal reference study and motivate the search for similar areas along other coastal locations.  相似文献   

The contribution of deep-sea macrohabitat heterogeneity to global nematode diversity   总被引：1，自引：0，他引：1  

《Marine Ecology》2010,31(1):6-20

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Disseminated sulphides in basalts from the northern Central Indian Ridge: implications on late-stage hydrothermal activity     

Ranadip Banerjee  Dwijesh Ray 《Geo-Marine Letters》2015,35(2):91-103

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