Nayyer Alam Zaigham

Prospect of hydrocarbon associated with fossil-rift structures of the southern Indus basin, Pakistan

The southern Indus basin (550 x 250 km) is characterized by tectonic upwarping on the western margin of the Indo-Pakistan subcontinent. Several hypotheses have so far been proposed to explain the origin of these crustal features, but these basement upwarps remain puzzling. Aeromagnetic data have been analyzed and interpreted, supplemented with seismicity and geological information. From the integrated study, we inferred basement configuration and developed models for tectonic evolution of these exotic crustal features and their impact on hydrocarbon potential associated with the southern Indus basin. The southern Indus basin is identified as an extension basin resulting from an inferred fossil-rift crustal feature overlain by a thick sedimentary sequence. Extension was a consequence of temporal divergence of the Indo-Pakistan subcontinent from Gondwanaland during the early Paleozoic. Based on magnetic-anomaly trends, the Indus basin fossil-rift feature is characterized by horst and graben structures, together with a system of transcurrent faults. The association of seismicity events and basement crustal features suggests that Tertiary reactivation of individual segments of the inferred rift structure has deformed overlying sequences of the Indus basin and also the surrounding areas, particularly the fold and thrust belt of Pakistan on the western side of the basin. The proposed geological models also illustrate the potential for appropriate environments for development of hydrocarbon source rocks, sufficient heat for thermal maturity, and structures for reservoirs and seals, suggesting more bright prospects in the southern Indus basin.

Heavy metal toxicity levels in the coastal sediments of the Arabian Sea along the urban Karachi (Pakistan) region

Heavy metals are stable and persistent environmental contam-inants since they cannot be degraded or destroyed. Therefore, theytend to accumulate in the soils and sediments. Excessive levels ofmetals in sediments affect marine biota and pose a risk to humanhealth through the consumption of seafood (Adams et al., 1992;Rowlatt and Lovell, 1994; Mucha et al., 2003; Feng et al., 2004;Zhang et al., 2007). The main anthropogenic sources of heavy met-als are various industrial point sources, including present and for-mer mining activities, foundries and smelters, and diffuse sourcessuch as piping, combustion by-products, traffic, etc. (NRC, 1989;Bryan and Langston, 1992; Long, 2000; Pekey, 2006; Hyun et al.,2007). Relatively volatile heavy metals and those that become at-tached to air-borne particles can be widely dispersed on very largescales. Heavy metals in aqueous and sedimentary transport (e.g.,river run-off) enter the normal coastal biogeochemical cycle andare largely retained within near-shore and shelf regions in propor-tion to geochemical controls (McAlister et al., 2005; Chaparro et al.,2005). Sediment analyses play a crucial role in assessing the degreeof heavy metal pollution and the resulting health risk associatedwith the food chain.Karachi is situated at the southern most part of Pakistan alongthe Arabian Sea and it is the largest business hub and the mostheavily populated urban centre in the vicinity. The coastal zoneof Karachi is about 167 km long. The estimated population of Kar-achiis morethan15 million.The rapidindustrializationandurban-ization of the city has altered the quality of the environment andcreated ecological disturbances and associated problems for the lo-cal community. Pollution in the Karachi coastal region is mainlyattributed to the Lyari and Malir rivers, which are served by vari-ous channels of untreated domestic and industrial waste, carryingmore than 300 million gallons per day (MGD) (1,125,000 m