Sankaran Rajendran

ASTER mapping of limestone formations and study of caves, springs and depressions in parts of Sultanate of Oman

Caves, springs, and large depressions of limestone karst formations are becoming more attractive tourist places and have potential importance on socio-economic development. The present study is a multi-scale point of view on limestone karst, from the space images to microscopic fabric. Here, the karst features consist of limestone formations of Cretaceous (Albian–Cenomanian) age of Tanuf Valley and Tertiary (Late Paleocene–Middle Eocene) age of Sur region of parts of Sultanate of Oman which are mapped in the visible near-infrared and shortwave infrared spectral bands of advanced spaceborne thermal emission and reflection radiometer (ASTER) using decorrelated stretch image processing technique and the occurrences of caves, springs, and depressions of the formations in the field were studied. The decorrelated RGB images of ASTER spectral bands 8, 3, and 1 discriminated well the limestone formations and associated lithology. The limestone formations of Tanuf valley (Natih formations of Hajar unit) are thick-bedded, massive, shallow marine limestone and clayey limestone, which have caves and springs. Large depressions are studied as collapsed structures at the boundary between Abat formations; they consist of gray to white marly or micritic limestone with chert nodules and Seeb Formation of bioclastic limestone, calcarenite, marl, and sandstone of Sur region. Interpretations of limestone formations, their occurrences and distributions of caves, springs and depressions of these regions are verified and confirmed in the field and studied in the laboratory. Occurrences of more springs and depressions in the limestone formations of the study sites are interpreted and located on the Google Earth image. The study proved the capability of ASTER sensor in mapping of limestone formations and recommends the technique to other geographical regions where similar geological questions need to be resolved.

ASTER spectral analysis of ultramafic lamprophyres carbonatites and aillikites within the Batain Nappe, northeastern margin of Oman: a proposal developed for spectral absorption

We developed a scientific proposal on spectral absorption in remote sensing and a new image-processing method that is purely based on multispectral satellite image spectra to map ultramafic lamprophyre and carbonatite occurrences. The proposed method provides a simple, yet efficient, tool that will help exploration geologists. In this proposal, in which the spectral absorption is applicable to all satellite images obtained in visible, reflected infrared, and thermal infrared spectral wavelength regions, we found that the carbonatites appear white in colour on a greyscale or RGB thermal infrared image obtained in the thermal infrared wavelength region (3–15 μm) due to molecular emission of thermal energy by such carbonate content, particularly the wavelength recorded by the sensor and that the variation of absorption in spectral bands of an outcrop is due to the differences in percentage of carbonate content or the spectral, spatial, radiometric, or temporal resolution of satellite data or the occurrences of carbonatites to incident energy. The results were confirmed by studying the spectral absorption characteristics of carbonatites in selected world occurrences including parts of Batain Nappe, Oman; Fuerteventura (Canary Islands), Spain; Mount Homa, Kenya; Ol Doinyo Lengai, Tanzania; Mount Weld region, (Laverton), Australia, and Phalaborwa region, South Africa, using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Landsat Thematic Mapper (TM) satellite data. A subsequent study of visible near-infrared (VNIR) and shortwave infrared (SWIR) ASTER spectral bands of Early Cretaceous alkaline ultramafic rocks of Batain Nappe, along the northeastern margin of Oman to map for the occurrences of carbonatite and aillikite (ultramafic lamprophyres) dikes and plugs, showed their detection mainly by the diagnostic CO3 absorption (2.31–2.33 μm) in ASTER SWIR band 8. The results of image interpretations were verified and confirmed in the field and were validated through the study of laboratory analyses. A few more carbonatite dike occurrences were interpreted directly over the greyscale image of ASTER bands and true-colour interpretations of a Google Earth image along this margin. The carbonatites and aillikite occurrences of the area are rich in apatite, iron oxide, phlogopite, and REE-rich minerals and warrant new exploration projects.

Tertiary and quaternary marine terraces and planation surfaces of northern Oman: Interaction of flexural bulge migration associated with the Arabian-Eurasian collision and eustatic sea level changes

The northeastern Arabian passive margin is being subducted beneath the Zagros and Makran of Iran. A flexural bulge related to the weight of the Makran has migrated at 4 cm/a through the previously uplifted Hajar Mountains of Oman as this active convergence and collision between Arabia and Eurasia progresses, adding approximately another 500 meters of relief, and forming a series of uplifted marine terraces, alluvial terraces, and planation surfaces that record the passage of the bulge. We use a combination of field studies, remote sensing and GIS to map and better-understand these terraces, and elucidate how the tectonics of bulge migration, down-to-trench normal faulting, and eustatic sea level changes have interacted to produce the extant geomorphic features on the inner slope of the flexural bulge as it sinks into the foredeep of the Gulf of Oman. We speculate those terraces that were uplifted on the outer slope of the forebulge as it initially migrated through the passive margin (affected by ophiolite obduction in the Cretaceous) 3.75–7.5 Ma ago are now sinking on the inner slope of the forebulge (corresponding to the outer trench slope in the foredeep), and have been partly covered by Quaternary marine terraces related to a Weichselian sea level high stand. Both the Tertiary and Quaternary terraces are cut by faults related to the active collision, confirming that there is a significant risk of moderate earthquakes in the region.

Assessment of heavy metal distribution pattern in the sediments of Tamirabarani river and estuary, east coast of Tamil Nadu, India

The present study aims to investigate the concentration and spatial distribution of trace metals in Tamirabarani river and estuary located in the southeast coast of India. Sediment samples collected from sixteen locations were analysed for Cu, Ni, Cr, Pb, Zn and Cd. The extent of pollution in these sediments was assessed using enrichment factor (EF), contamination factor (CF), geo-accumulation index (Igeo). The EF shows enrichment of Ni in the northern part of the estuary and that of Cu in the south and it is mainly due to the process of weathering. The contamination factor indicates Cd is more highly contaminated than other metals. Igeo index shows that Cd is moderately polluted and its spatial distributions clearly indicate that it is found in estuarine region. The comparison of metal concentration with other estuaries of India indicates that these metals are well below the permissible limit. The metals in the estuary of the study area indicate more of the predominance of natural process than other estuaries in India. It is evident that the samples of river and estuary area are dominantly due to the natural process rather than anthropogenic activity.

Capability of L-band SAR data in mapping of sedimentary formations of the Marmul region, Sultanate of Oman

This study demonstrates the capability of the longer wavelength (L-band) and fine mode images of the Phased Array type L-band Synthetic Aperture Radar (PALSAR), and the optical spectral bands of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) to map sedimentary formations and structures of the Marmul region, Central Oman. Results of study shows that the principal components image of the visible and near infrared–shortwave infrared (VNIR-SWIR) spectral bands of the ASTER have potential to discriminate the occurrence and distribution of marine and Quaternary sedimentary formations of the region. The color composite image developed using PALSAR data (R:HH + HV; G:HH; B:HV) has capable to differentiate the occurrence of the sedimentary formations and structures of the region. We developed ratios images by summing the HH intensity as a numerator and the HV intensity as a denominator (R:HH+(HH + HV)/HV, G:HH + HV, B:HH/HV), and by summing the HV intensity as a numerator and the HH intensity as a denominator (R:HV+(HH + HV)/HH, G:HV + HH, B:HV/HH) to study better the sedimentary formations and structures. The images discriminated well the occurrence of the limestones and shale formations of the marine deposits, the wadi alluvium of the Quaternary deposits and the manmade building structures of the region. We studied the minerals of the sedimentary formations using VNIR-SWIR spectral bands of the ASTER by spectral angle mapper (SAM) image processing method. The study showed presence of carbonates, silicates and OH bearing aluminosilicate minerals in the formations. The image interpretations are verified in the field and confirmed by the laboratory studies.