Modelling suspended sediment flow in arid upland basins

Abstract

A conceptual basin model of the instantaneous unit sediment graph was developed for sediment graph prediction from arid upland basins by routing mobilized sediments through a series of linear reservoirs. The sediment graphs generated by convolution of the instantaneous unit sediment graph compared reasonably well with the observed ones for four representative arid upland sub-basins in the Luni basin, India. The mobilized sediment during a storm was related to effective precipitation and the parameters of the model were estimated from observed events. The model can be applied to ungauged flow events through parameterization.     

Crustal structure and rift tectonics across the Cauvery–Palar basin,Eastern Continental Margin of India based on seismic and potential field modelling

The Cauvery–Palar basin is a major peri-cratonic rift basin located along the Eastern Continental Margin of India (ECMI) that had formed during the rift-drift events associated with the breakup of eastern Gondwanaland (mainly India–Sri Lanka–East Antarctica). In the present study, we carry out an integrated analysis of the potential field data across the basin to understand the crustal structure and the associated rift tectonics. The composite-magnetic anomaly map of the basin clearly shows the onshore-to-offshore structural continuity, and presence of several high-low trends related to either intrusive rocks or the faults. The Curie depth estimated from the spectral analysis of offshore magnetic anomaly data gave rise to 23 km in the offshore Cauvery–Palar basin. The 2D gravity and magnetic crustal models indicate several crustal blocks separated by major structures or faults, and the rift-related volcanic intrusive rocks that characterize the basin. The crustal models further reveal that the crust below southeast Indian shield margin is ～36 km thick and thins down to as much as 13–16 km in the Ocean Continent Transition (OCT) region and increases to around 19–21 km towards deep oceanic areas of the basin. The faulted Moho geometry with maximum stretching in the Cauvery basin indicates shearing or low angle rifting at the time of breakup between India–Sri Lanka and the East Antarctica. However, the additional stretching observed in the Cauvery basin region could be ascribed to the subsequent rifting of Sri Lanka from India. The abnormal thinning of crust at the OCT is interpreted as the probable zone of emplaced Proto-Oceanic Crust (POC) rocks during the breakup. The derived crustal structure along with other geophysical data further reiterates sheared nature of the southern part of the ECMI.     

A NOTE ON MAGNETIZED SPHERES*

The interpretation of total field anomalies becomes somewhat complicated, especially when an arbitrarily magnetized spherical ore mass happens to be the causative body. Even though some attempts have been made to analyze total field anomaly maps, they are often too complicated and their underlying assumptions in respect of permanent and induced components of magnetism are far from realistic. In this note, an attempt has been made to show that vertical magnetic anomalies are capable of yielding interpretation with ease and precision as far as magnetized spheres are concerned. An empirical method has been outlined for computing the magnetization inclination in the plane of the profile using the measured distances between principal maximum, principal minimum, and zero anomaly positions on a magnetic anomaly profile.     

INTERPRETATION OF LANDSAT MSS DATA IN AN IRON-ORE-BEARING ZONE IN GOA,INDIA*

In South and Central Goa iron ore occurs in two parallel belts with the general NW-SE Dharawar trend. The ore occurrence, however, is not continuous. There are barren zones as well as zones of very high concentration in some of which there are mining activities. Landsat MSS data have been interpreted over a zone covering both mineral belts in order to delineate the ore occurrences. As a guide line a known ore-bearing area has been considered along with the unknown zones. On the basis of two-dimensional plotting of gray level values it has been found that the MSS bands 4 and 7 are most suitable for the studies over iron-rich areas in Goa. Two techniques are described here for the processing of the MSS data; the separation of residual from the regional and MSS band-ratioing. It is observed that (i) the gray level residual maps of MSS bands 4 and 7 are of use in demarcating the iron-ore-bearing zones, and (ii) an existing mine, an abandoned mine, and a proved iron ore zone could be delineated by MSS band-ratioing. On the basis of the latter technique, a few areas with ore occurrence potential have been indicated.