THE COMPARATIVE DEPOSITIONAL HETEROGENEITY OF MANCHHAR FORMATION (SIWALIK GROUP), SOUTHERN INDUS BASIN, PAKISTAN

Present study is carried out for detailed description, distribution and interpretation of lithofacies and textural analysis of Manchhar Formation from Gaj River, Manchhar Lake and Lal Bagh Sections of Southern Indus Basin Pakistan. Four different clastic lithofacies are identified during present study, which are conglomeratic sandstone (Gt), shale (Fm), fine to coarse grain flat bedded sandstone (Sh) and fine to coarse grain trough cross-bedded sandstone (St). These Facies suggest that Manchhar Formation is deposited in the Beach to shallow agitated water and fluvial system. Twenty-nine (29) unconsolidated loose and friable sandstone samples were selected for textural analysis. Grain-size parameters such as mean, median, standard deviation, Skewness and Kurtosis were used for transport history, mode and hydrodynamic energy condition to recognize the depositional environment. Stewart Diagram shows deltaic/wave water process takes active role under the influence of wave process. Linear discriminant functions analysis show that the fluvial environment of deposition dominates and influences shallows water and beach environment. Passega diagram reveals that transport mode was rolling and suspension by the tractive current that shows the fluvio-deltaic to deltaic wave with the influence of wave depositional environment of Miocene-Pliocene (Neogene) Manchhar Formation.

Various methods are used to measure the grain size of clastic sediments based on research and the extent of particle sizes to be measured.
Direct grain size analysis and point counting are the two extensively used approaches for   after [22,23].
The rifting of the Indian Plate from other Gondwanian fragments during the Mesozoic created various realms of Tethys Ocean along the western margin of the Indian Plate and geology of Indus Basin mainly based on the rocks deposited in these realms of Tethys Ocean along the western margins [24,25].The Indus basin is divided into the Upper and Lower Indus Basin, separated by the Precambrian shield element Sargodha High [21] (Fig. 1).
Jacobabad High is another basement zone of unwrap that divides the Lower Indus Basin into Central and Southern Indus Basin [21,23,26] (Fig. 1).The Precambrian crystalline basement rocks and sedimentary rocks of Mesozoic and Cenozoic are reported from the Southern Indus Basin [23,24] (Table 1

MATERIALS AND METHODS
Three stratigraphic sections of Manchhar Formation are measured through tape_brunton and Jacob's staff method [28,29] (Fig. 2).Thirty-five unconsolidated sandstone and shale samples were collected through random sampling method (one bed-one sample) [28,29].Four lithofacies have been recognized based on the field parameters, i.e., texture, sedimentary structure, grain size, and lithologic units.For the detailed textural analysis these three sections were logged and properly sampled, mostly from unconsolidated sandstone beds, and twenty-nine (29) samples were selected for grain size analysis (Fig. 3).Uden and Wentworth millimeter scale of sediments converted into Φ-scale [30].Cumulative

RESULTS AND DISCUSSION
The

Facies analysis
Depending on the grain size, sedimentary structures and vertical facies relationship, four facies were recognized in the Gaj, Manchhar and Lal Bagh sections of the Manchhar Formation.These lithofacies at studied sections showed variable thickness and were used to identify the depositional setting.Recorded lithofacies are described below.

Shale (Fm)
Shale facies is composed of fine-grain of silt and clay-size mineral.The color ranges from bluish grey, grey, greyish, brownish grey to grey pinkish to camel color (Fig. 5f).It is soft, loose, oxidized and contains mud-cracks and plant rootlets.
Iron oxide or iron hydroxide minerals such as hematite, goethite, or limonite are frequently found in shale deposited in oxygen-rich settings.
Many varieties of shale have red, brown, or yellow colors due to a small percentage of these minerals dispersed throughout the rock.
Red shale can be formed when hematite is and rootless [46][47][48].The sequence Manchhar Formation at Lal Bagh section is typical of a braided river system [49,50].Variability in the grain size reflects the difference in water stage fluctuations [31,51].

Medium-fine grained sandstone (Sh)
These facies recognized in the Manchhar Formation at Lal Bagh section are flatbed thick to very thick-bedded sandstone.These facies are smoky white, yellowish, brownish, greenish grey, greenish-yellow, yellowish-brown, and greyish.The grain size ranges from fine grain to medium-grained, which are rounded to sub-rounded and well-sorted to moderately well sorted and friable (Fig. 5d).They have no orderly variation of sedimentary structure, but

Interpretation of Graphic Mean
Graphic mean size represents the average grain size of sediments.The studied section indicates that fine sand was dominant over medium sand in Manchhar Lake and Gaj River sections.In contrast, medium sand was prevalent over the fine sand in the Lal Bagh Section.In the studied sections, the graphic mean size ranges between 1.34 to 3.09Φ.
The inclusive graphic standard deviation or sorting is one of the most valuable processes to find out the nature of the sorting or uniformity in sediments and indicate hydrodynamic conditions during transportation and deposition [2,13].The results of the studied section (Table 2) reveal that poorly sorted sediments are dominant over moderately sorted sediments indicative of moderate to high hydrodynamic energy conditions [12,59].
Kurtosis indicates sharpness or peakedness in the frequency distribution curve of grain size by measuring the ratios between the sorting in the "tails" of the curve and the sorting in the central portion.The results of Kurtosis for studied sections varied between 0.63 to 2.85Φ (Table 2).
Skewness depicts the consistency/uniformity in the supply of sediments in most fine or coarse proportions.Skewness results for study sections range from between -0.005 to 1.14 Φ (Table 2), indicating the dominance of fine skewed, followed by nearly symmetrical, strongly fine skewed, strongly coarse skewed and coarse skewed [6,13,58].

Interpretation of Bivariate diagrams
The bivariate plot of sorting versus mean (Mz) indicates that the samples of studied sections are fine to medium sand size and poorly to moderately well sorted [59,60].Which most of the sample of Manchhar Formation poorly sorted to moderately sorted and are fine sand to medium sand.The samples of the Gaj River Section are primarily fine sand and moderately sorted, possibly due to grain to grain interaction perhaps grains decrease and moderately sorted.The samples of the Lal Bagh Section dominantly medium grain sand and poor to moderately sorted whereas, samples of the Manchhar Lake Section are primarily fine sand and poorly sorted (Fig. 7a).The dominance of poorly sorted to moderately sorted sandstones in the Manchhar Formation may point to a near-source region [11,14,61].to medium sand grain [13,59].Figure 7b indicates that most samples of studied sections clustered in inland dune field and some samples gathered in the beach environment.
The sorting plotted against graphic Skewness confirms that most Manchhar Formation samples are poorly sorted to moderately sorted and fine skewed to near-symmetrical are fall in coarse skewed [6,59] (Fig. 7c).
The plot of graphic kurtosis versus skewness reveals that almost all samples are leptokurtic to mesokurtic followed very leptokurtic to platykurtic and mostly near symmetrical to fine skewed (Fig. 7d).The excess and lowest values of kurtosis reveal that some samples acquire their sorting at somewhere else in the depositional environment [4,14,17].Interms of depositional environment scatter plot of graphic kurtosis versus skewness reveals that dominant influence of beach environment over riverine [59].
Various attempts have been made to set up a link between statistical parameters and depositional environment [8,16,17,60,62,63].
Scatter graphs are produced on the assumption that statistical parameters reliably indicates variation in hydrodynamic conditions of transportation and sedimentation [44].The discriminate diagram (Fig. 8) was proposed by Stewart [62] to understand the energy condition and deposition of sediments and differentiate among the river, wave, and slow water processes by producing a graph between the skewness versus median.It has been recognized that almost all Manchhar Formation sandstone samples fall between the river field and relatively slow water deposition and some samples fall in the wave field and river field (Fig. 8a).All the Manchhar Formation sandstone samples scattered in and around the wave field and river field, which reveals that they were deposited by the deltaic/wave process [6,59] (Fig. 8b).Sahu [8] produced and formulated the function known as LDF Y1, Y2, Y3 and Y4.LDF functions were used to discriminate among deposition mechanisms.LDF were computed from the calculated textural parameters (Table 3).

S. No
The scatter graph Y3 versus Y2 proposed by Sahu [8] (Fig. 9b) reveals that most sediments of the Manchhar Formation plummet in the field of "shallow marine/agitated environment".Some samples are huddled in the field of the "fluvial/agitated" depositional setting domain.
The bivariate plot of Y4 versus Y3 (Fig. 9a) shows that most sediments gathered in the field of "shallow marine/turbidity current" depositional setting.some samples occupy "turbidity currents/fluvial environment".This indicates that the sediments are deposited in a "fluvial to deltaic depositional environment" with the influence of "shallow marine environments" [1,59].

CONCLUSION
The Manchhar Formation (Neogene Molasses of Siwalik Group) in study area is mainly composed of clastic sediments.Facies evidences and grain size distribution diagrams suggest that Manchhar Formation have been deposited in shallow agitated water of beach to delta and fluvial system.Furthermore, diagrams also suggest that sediments of Manchhar Formation were mainly transported through rolling and suspension.
Depositional sedimentary environments provide vital constraints regarding paleo-geography, biodiversity and tectonic evolution.Different field and laboratory based approaches are being used to decipher the depositional environment of sedimentary rocks such as lithofacies, petrography, grain size analysis, mineralogy and geochemistry.Lithofacies and Grain size analysis are the essential techniques in sedimentology for extracting geological information from clastic sedimentary rocks to understand the paleo-climatic and environmental setting, hydrodynamics,

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. mt. area res., Vol. 9, 2024 particle size measurement[2,4,16].The Sedimentologists concentrate on (a) type of grain size measuring method, (b) technique of computing textural data, and (c) representing in mathematical and graphical methods.The graphical technique involves producing textural data on bivariate graphs, and the mathematical treatment/method uses arithmetic equation or grain size parameters to correspond to textural data.In environmental studies, two-factor difference graphs and "Linear Discriminate Function" (henceforth LDF) and log probability graphs are widely used as graphical plots in textural studies.Drawing of two-factor deviation graph helps to differentiate between the various depositional environment [9, 17-19].
frequency curves were produced from the cumulative weight percent of grain size data of each section.From these cumulative frequency curves, selected percentile values such as, 5, 16, 25, 50, 75, 84 and 95 were recorded and various grain size strictures, such as "mean, standard deviation, (sorting), skewness, and kurtosis" are computed.The software platforms of ArcGIS 10.3, Corel Draw X4, LogPlot 7 and Origin Pro 9 were used for maps, image annotations, lithofacies logs and grain size graphical plots respectively.

Figure 2 .
Figure 2. Geological map of the study area, modified after [27].
present study has successfully recognized four principle types of lithofacies (Gt, St, Sr, Fm) in the Manchhar Formation in the studied sections (Fig. 4).Studied sections show the principally clastic sedimentary rock lithology ranges from Conglomerate, Sandy Conglomerate, Sandstone and Shale.During present study the facies nomenclature is adopted as recommended by Miall [31].

Figure 5 .
Figure 5. Field photographs showing (a) sandstone and conglomerate (b) sandstone and conglomerate (c) Trough cross bedded sandstone (d) planner cross-bedded sandstone (e) parallel-laminated sandstone and conglomerate (f) shale present.Yellow or brown shale can result from the presence of limonite or goethite.The fine-grain components imply that a large amount of the sediment was accumulated in the flood plain area, based on the interpretation of lithological properties of this type of facies.Because of the abundance of burrows and calcareous concretion, the sandy silt and clay units are most likely levee-associated small terminal splay deposition [42-45].The migration of calcareous solutions was facilitated by numerous burrows

3 . 1 . 4 .
burrows and rootlets tend to occur near the top.These lithofacies belong to weakly confined, and distributaries splay association/environment [34, 42, 52].These facies are regarded as channel fill sediments and conceived as the depositing of crevasse splay channels in connected flood plains of a distant, sand-dominant braided fluvial system [32, 41, 53].The crevasse splay channels were formed by repeated crevassing and incision, and the channel base encountered recurrent scouring, bed-load transportation, and sedimentation [38, 39].The upward movement of shaly lenses, burrows, and root traces could be related to abandoning crevasse channels and diminishing current energy [31, 38, 50, 53-56].Trough cross-bedded sandstone (St) Fine to coarse grained trough cross-bedded sandstone facies are mostly repeated common in Manchhar Formation.It is generally greenish yellow, yellowish brown, greenish brown, dark brown, yellowish grey, greyish grey.It is thick-bedded and show fining upward pattern.Grains are angular to sub-round and moderate to poorly sorted (Fig. 5c).The facies is friable characterized by dominantly cross-bedded sandstone that is underlying conglomerate facies (Gt).This facies has clayey matrix having calcareous cement and become in places friable.Individual beds show limited fining-upward characteristics, which could be attributable to a lack of particle sizes heterogeneity.The accumulation of a distal sand influential braided fluvial system is construed as fine-coarse grain trough cross-bedded sandstone facies.The lateral movement generated the large-scale inclined strata, which are channel bar deposits.The absence of mud cracks and roots evidence in the lowermost part of the channel deposits demonstrated perennial river flow [11, 57].Trough and planer cross-stratification indicate the existence of a moving sinuous crested dune and a moving straight crested dune, respectively.The latter was discovered in the presence of higher flow velocities.The erosive power of many simultaneously active changing channels is likely to responsible for the failure of vertical accretion of sediments [41, 42, 51].

Figure 6 .
Figure 6.Grain-size distribution frequency curves (a, c & e) and cumulative frequency curves (b, d & f) for the Manchhar Formation.
cumulative frequency curve usually creates an S-shaped curve and the gradient of the cumulative frequency curves at the middle reflects the sorting of sediments.Gentle or broad slop of curve indicates the poor sorting and reveals low hydrodynamic conditions, and steep slope indicates well sorting of sediments and indicates high hydrodynamic energy condition (Fig 6).Cumulative frequency curves indicates dominance unimodality around 2.5Φ , few samples indicate the bimodal with various frequency distribution around 0.5Φ.The dominance of the unimodal nature of sediments indicates the little bit of mixing of clay particles and suggests a relatively steady depositional mechanism.Some samples of studied sections indicates bimodality peaks at around 1.5Φ (Fig. 6a, c & e).The bimodal nature of sediments is characterized by a mixture of various grain sizes and depositional processes and the change in transportation mode.Grain size parameters of clastic sedimentary rocks, such as, mean size, median,

Figure 8 .
Figure 8.(a) Bivariate plot of graphic median versus standard deviation.(b) Bivariate plot of Skewness versus median.

Figure 9 .
Figure 9. (a) Discrimination of environments based on Linear Discrimination functions plot of Y4 against Y3, (b) Discrimination of environments based on Linear Discrimination functions plot of Y2 against Y3.

Figure 10a&b .
Figure 10a&b.C-M plots showing the transporting mechanism of the Manchhar Formation.

Table 1 .
Stratigraphy of the Southern Indus Basin,