Geological Study of Dasht-e-Top Sedimentary Basin, Wardak Province, Afghanistan

This study is conducted to investigate the occurrence of various geological features, and to study the geology and soil characteristics of the study area. To achieve the objective of this research collection, different samples from different locations in study area were collected, analyzed in laboratory, and the results are compared with each other. The main rock types found in the study area were metamorphic rock (Gneiss) and igneous rock (Granite), and the main soil types found were Loam, sandy and silty soils with different soil structures (e.g. crumbling, platy, single grain, granular and prismatic). Calcium carbonate, Iron oxides and different sizes of sediments were also seen in the soil profile, where the size of sediments were changing as it was course size sediments and gravels near the mountain range and as going far from the mountain it was changed to fine size sediments like sand, silt and clay. The river terraces present in the area cover different geological structures such as angular and erosional unconformities, thinning out of strata and potholes. The mountain range surrounded the study area contains different observable tectonic structures such as anticline, syncline, vines (dyke, sill and apophasis). Furthermore, different types of valleys also existed in this area.

mountains have need of both sedimentary and pedologic research with details [4]. The accumulated sediments are mostly clay, loam, sand and gravels, which are deposited in plane parts of the basin. The thickness of sediments depends on slope and distance from the mountains, and the basin has located at the two sides of Kandahar-Kabul highway and both sides are plane up to two km, but close to the mountain there are hills and sloppy areas. All materials from different points of mountains are transported by floods and deposited at different parts in this basin [5] [6]. The age of sediments in this basin is Neogene-Pleistocene, and the sediment are in their normal position in the basin, where the lower layers are Neogene and the upper layers have Pleistocene age [7]. The Quality of sediments are directly referred to the type of mother rocks which eroded in the mountains. The size of materials also related to the distance of transportation from mountain ranges around the basin, where generally near to the mountains the sediments have very course to course sizes which include boulder, cobble, pebble and granules and with distance from mountains the size of material changes from fine to very fine and includes Sand, Silt and Clay. In mountainous area and its skirts, the grains are angular and sub angular but as getting far from mountains the grains become sub round and rounded [8] [9] [10]. In the soil profiles and river terraces different layers of materials can be seen, which is mainly due to oxidation, reductions and presence of CaCO 3 and organic materials. Where, the red color shows oxidation and solution of iron oxide, white color is due to reduction and CaCO 3 and the dark color is because of organic materials, that decomposed at the different periods of geology [11] [12] [13].

Materials and Methods
Generally, this research includes two parts.

Field Work
Field works are generally consisting the selection of points, collecting of the samples from the mountains (from different rock types present), field study of the sediments and all unconsolidated materials, study of the river terraces, Soil profiles, and existent structures of the area.

Laboratory Works
The laboratory works include the following procedures: Air drying and oven drying of the collected sedimentary samples at 30˚C for 24 hours, sieve analysis for determination of grain sizes of the soil samples, determination of CaCO 3 by using calcimeter, and using of Polarized light microscopes for microscopic studies of the rock samples.

Description of Site Studies
This study was carried out in Dasht-e-top sedimentary basin ( Figure 1

Results and Discussion
Generally the mountain ranges surrounding this sedimentary basin are consisting from metamorphic rock (Gneiss) and Igneous rock (Granite), and the ac-

Geomorphology of Dasht-e-Top
Generally, Dasht-e-top basin consists three types of relief, where the first type is sloppy areas, second is Skirt areas and hills and the third type is plain areas which are located at about 1 km at the two sides of Kabul-Kandahar road [20] [21]. The surrounding mountains of this basin is like ring (bowel) which is an inter mountains back basin [22].

Geology
The surrounding mountains of Dasht-e-top are formed from plutonic and me-  (Figure 3). Furthermore, different types of sedimentary features like alluvial fans and alluvial aprons were also seen in the area ( Figure 5).

Country Rocks and Rock Boundaries
The

Alluvial Fans
Dasht-e-Top sedimentary basin is relatively plane with many and different types of alluvial fans, these sedimentary features contains different types and sizes of sediments such as gravels, sands, silts and clay, whereas the grain size of sediments are related to the their transportation distance from mountains range, generally as we get close to the mountains range the grain size changes from Course to very Course (boulder, cobble, pebble and granule) and as we get away from mountains the grain sizes change from fine to very fine sediments (sands, silt and clay) ( Figure 5).

River Terraces and Soil Profiles
The soil profile studied in the study area include different layers of soil which