Geologic map of the Islamabad-Rawalpindi area, Punjab, northern Pakistan

Abstract

Stream-channel alluvium (Holocene)-Unconsolidated gravel, sand, and silt that is subject to stream transport each year. Poorly to moderately sorted and low-angle crossbedding. Generally without soil or vegetation. Forms low islands and bars within braided ard meandering stream channels. Maximum thickness about 3 m Qfp Flood-plain and fan alluvium (Holocene)-Moderately bedded and sorted, sand and gravel channel and debris-flow deposits overlain by thin veneer of sandy silt and clay fro~a overbank flooding and slope-wash deposition. Typically deposited adjacent to streams or in fan-shaped bodies at mouth of canyons or gullies. Maximum thickness beneath flood plains about 6 m and beneath fans about 20 m Qas Alluvium and windblown silt, undifferentiated (Holocene and upper Pleistocene)~Eolirn silt and stream-channel, flood-plain, terrace, and slope-wash alluvium intermixed in small areas that cannot be depicted separately at map scale. Such deposits typical'" 7 occupy small depressions in the Margala Hills. Less than 10m thick Qp Potwar Clay (Holocene and Pleistocene)-Windblown silt and clay and subordinate amounts of alluvial gravel. Sediment is light brown to gray, very fine grained, hard, compact, and calcareous. Windblown sediment averages 71-74 percent silt-size and 15-16 percent clay-size material. Unit is 14-18 percent calcium carbonate. Mineral composition is predominantly quartz, but subordinate amounts of feldspar and clay minerals, such as kaolinite and illite, are present (Rendell, 1988, p. 392). The welldeveloped vertical partings and lack of bedding suggest that much of the sediment is atmospheric dust, but stratification of some of the sediment indicates partial reworkir 7 by surface wash and streams. Locally, silt is intercalated with crossbedded lenses of sand and gravel and with the Lei Conglomerate. Thermoluminescence ages of loers from the Rawat area range from 20 to 132 thousand years (ka) from near the surface to 11-m depth, and greater than 170 ka for more deeply buried loess beneath a gravel facies. Calculated accumulation rates range from 6 to 27 centimeters per thousand years (cm/1,000 yr)(Rendell, 1988, p. 393). The silt and clay beds are very erodibh; hence deep, steep-sided gullies and badlands are extensive. Unit subject to loss of bearing strength when wet. Thickness is highly varied, depending on relief of underlying unconformity. Exposed thickness 1-35 m. Similar deposits intercalated with Lei Conglomerate extend to a depth of 152 m (Ashraf and Hanif, 1980) Terrace alluvium (Holocene and Pleistocene) Gravel, clay, and silt locally cemented by calcium carbonate. Includes clast-supported boulders, cobbles, and pebbles of sedimentary rocks in a sandy and clayey matrix. These former stream-channel and flood-plain deposits no longer receive sediment because subsequent downcutting by streams has left them high above flood level. Repeated episodes of uplift or climate change and erosion have left terrace deposits at several levels. Unit resembles Lei Conglomerate but is younger and retains d...

Site Characterization Using Integrated Imaging Analysis Methods on Satellite Data of the Islamabad, Pakistan, Region

“…The terrain of this region consists of plains and mountains with a general physiography that trends east-northeast (Williams et al, 1999). The city of Islamabad is adjacent to a mountainous terrain known as the Margala Hills, part of the lower and outer Himalaya Range consisting of a series of ridges with altitudes reaching approximately 1600 m near Islamabad.…”

“…The Margala Hills are an intensely deformed tectonic belt that represents the uplift of the Peshawar Basin that is part of the active Himalayan foreland where fold and thrust belts form the collision zone between the Indian and Eurasian plates (Coward et al, 1987;Baker et al, 1988;Bender and Raza, 1995;Pivnik and Wells, 1996). South of the Margala Hills is a southward sloping piedmont bench (Williams et al, 1999) where the Islamabad and Rawalpindi urban developments are situated. Farther south, the Soan River Valley extends outward to the plains of the Potwar Plateau beyond the study area (Baker et al, 1988).…”

“…The lithology of the Islamabad and Rawalpindi area has been broadly classified by Williams et al (1999) as follows: (1) the northern mountainous Margala Hills consist of folded and thrust limestones and shales (Pivnik and Wells, 1996;Munir and Butt, 2007); (2) the piedmont bench consists of truncated and folded sandstones and shales, in addition to buried and exposed ridges of sandstones and shales west of Rawalpindi; and (3) the asymmetric syncline of the Soan River Valley consists of beds of fluvial sandstone, mudstone, and conglomerate. As a depositional system, the piedmont accumulates silt and alluvial gravel from the Margala Hills, which eventually spreads and fills the wide plains of low relief (Williams et al, 1999).…”

“…As a depositional system, the piedmont accumulates silt and alluvial gravel from the Margala Hills, which eventually spreads and fills the wide plains of low relief (Williams et al, 1999). Because of the dry climate, welldeveloped soils are scarce in the Islamabad area (Williams et al, 1999).…”

“…Our study area is denoted by the footprint of the true-color image. Additional information includes selected cities and physiography, the epicenter of the M 7:6 Muzaffarrabad earthquake, and our generalization of the selected thrust fault systems in the region based on Coward et al (1987), Baker et al (1988), Williams et al (1999), and MonaLisa et al (2004. Abbreviations: HTFZ denotes the Hazara thrust fault zone, MBT denotes the main boundary thrust, and PKF denotes the Panjal-Khairabad fault.…”