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Conglomerate sequences over 700 m thick were deposited subsequent to ophiolite emplacement during Late Cretaceous time in north Oman. The conglomerates were deposited by streams draining the allochthonous ophiolite and Hawasina complex after their obduction onto autochthonous Mesozoic and older Oman shelf sequences and subsequent uplift. The conglomerates belong to the Qahlah Formation of Late Cretaceous age, which is sandwiched between the Semail Ophiolite/Hawasina complex and Maastrichtian-Palaeogene carbonate rocks. The siliciclastics of the Qahlah Formation are the first sediments deposited over the obducted oceanic crust sequence of ophiolite and Hawasina lithologies. In five locations studied in north Oman, the thickness of the formation varies from 140 m to over 700 m and comprises interbedded conglomerate, sandstone and siltstone. The sediments were deposited in isolated segmented depressions each characterized by its source terrain depending on lithologies exposed in the source area. Lithofacies associations, clast sorting and grain roundness suggest deposition in stream-dominated alluvial fans. Clasts in the conglomerates range from subangular to subrounded pebbles to boulders with both grain and matrix (sandstone) support. Cross-bedded fining-upwards sequences in channelized conglomerate and sandstone suggest deposition by high-energy flows in the proximal to distal reaches of alluvial fans. High proportions of chert and ophiolite fragments in the conglomerates suggest rapid erosion of obducted oceanic crust. The presence of Loftusiabearing carbonate beds and bivalve-bearing conglomerate beds in different sections indicates occasional interruption of alluvial deposition by marine transgressions.

The present study demonstrates the capability of multi-spectral data acquired from advanced spaceborne thermal emission and reflection radiometer (ASTER) satellite to explore the areas of massive carbonate deposits and associated rock formations for geological application. The extent of interdependence among VNIR, SWIR and TIR bands of ASTER spectral regions has been studied for discrimination of rock formations and identification of minerals of eastern mountain region (Saih Hatat window) of Sultanate of Oman and processed through digital image analysis and classification. Visual interpretation techniques have been employed to discriminate major quartz-rich silicates, carbonates and mafic ophiolite rock formations on the satellite image by carrying out subsequent image enhancement technique and principal component analysis (PCA). Color composite using nine VNIR and SWIR ASTER spectral bands by exposing the results of band ratios of (band 7 ? band 9)/band 8 for limestone (CaCO 3 ); (band 6 ? band 8)/band 7 for dolomite (CaMgCO 3 ); and band 2/band 1 for mafic-rich (Fe 3? ) rock formations differentiated the carbonates and ophiolite formations of the study region. The band ratios of 6/8 developed for quartz-rich silicates (shale, schist, sandstone, graywackes) of autochthonous Unit 'A' of Late Proterozoic to Early Ordovician and Tertiary age, 9/7 for the carbonates (limestone and dolomite) of Autochthonous rock Unit 'B' of Late Permian to Triassic age and 1/2 for mafic ophiolites (harzburgite, harzburgite with dunite) of Samail Nappe discriminated the different rock formations and increased the visual interpretations. It has well delineated the gray limestone and yellow dolomite of Autochthonous Unit 'A'. The subsequent PCA realized on the 6 SWIR spectral bands enables very good validation and discrimination of quartz-rich silicates, carbonates and mafic ophiolite rock formations defined on previous image rationing techniques and existing geological map, and provides information comparable to surficial formations previously not well recognized. It is capable of distinguishing the ancient and recent alluvial fans consisting of clay, silt, sand and conglomerate formations of Tertiary age from the Autochthonous Unit 'A'. Furthermore, the ASTER TIR spectral indices have been applied for assessing the effectiveness of TIR spectral bands on identification of quartz-rich silicates, carbonates and mafic-rich minerals and to evaluate the discriminated rock formations. The results agree well with existing geological maps and other published data. The study results show that the combination of visual interpretation, previous field knowledge and digital image processing techniques applied on the ASTER spectral regions have proved beneficial in studying carbonates and associated rock formations of eastern mountain region of Sultanate of Oman and can thus be used as a powerful tool to explore massive carbonate deposits or for geological mapping of other geographical regions where similar geological questions need to be resolved.

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