Textural and Petrographic Studies of Multistoried ...

Indexed in Scopus Compendex and Geobase Elsevier, Chemical Abstract Services-USA, Geo-Ref Information Services-USA, List B of Scientific Journals, Poland, Directory of Research Journals www.cafetinnova.org ISSN 0974-5904, Volume 06, No. 05

October 2013, P.P.1027-1046

Textural and Petrographic Studies of Multistoried Sand Bodies as Observed in Quarry Sections in West Godavari District, Andhra Pradesh, India S. RAMASAMY1, A. RAMACHANDRAN 1, DAVID LALHMINGLIANA CHAWNGTHU1, K.VELMURUGAN1, K. SELVARAJ 2, S. B HUVANESWARI1, AND S. CHANDRASEKAR1 1

School of Earth and Atmospheric Sciences, Department of Geology, Guindy Campus University of Madras, Chennai-600025, India 2 State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University 182 Dauxe Road, Xiamen 361005, China Email: [email protected], [email protected] Abstract: The unfossiliferous Rajahmundry Sandstone beds of Mio-Pliocene age from the Minanagaram and Gangolu quarry sections have been studied for their textural characteristics and petrographic variations. The lithological successions in these sections are dominantly made up of sandstones, and the associated argillaceous and conglomerate facies are secondary. Cyclic sandstone beds with erosional base and upward fining are characteristics of these sand bodies in the quarry faces. Grain size analysis of the Minanagaram quarry samples reveals that they are poorly to moderately sorted and very fine skewed, while the Gangolu samples are more fine-grained, poorly sorted and near symmetrically skewed. Petrographically, ferruginous argillaceous litharenite and ferruginous litharenite are identified in the Minanagaram quarry section and ferruginous argillaceous litharenite alone in the Gangolu quarry. The former quarry section reveals predominance of planar and trough cross-bedded sandstones interspersed with thin polymict type of conglomerate units. The petrofacies in Q-F-L ternary diagrams mainly suggest a continental and recycled orogen source of cratonic interior tectonic setting, in an intense chemical weathering which resulted in quartz-rich sediments formed in a humid climate. Qun-Qnun-Qp ternary plots of detrital quartz suggest plutonic to medium and high rank metamorphic source rocks. Gangolu sequences are fine- to medium-grained sandstones interbedded with thin conglomerate beds. The lithoclasts are fragments of schists, shales and rare sandstone and are deeply squashed. There is a total absence of polycrystalline quartz grains in these samples. Sedimentary structures such as trough and plane cross beds are common in Minanagaram quarry, where as plane beds dominate Gangolu quarry section indicating a moderate to high flow regime in the later. Diagenetic alteration of such unstable minerals as feldspars and ferromagnesian minerals resulted in the production of hematite and argillaceous cement. As sediments are coarse and partially cemented without showing any pressure solution effects, it is inferred that they have been subjected to shallow burial diagenetic environment. An attempt has been made to draw information on depositional, source area, weathering, transportational, and paleoclimate histories. Keywords: Minanagaram and Gangolu Quarry sections, Point-bar deposits, Primary sedimentary structures, Textural characteristics and petrography Introduction: The basics of point bar mechanisms, channel, channel margin and flood plain deposits are found in many text books (Friedman and Sanders, 1978; Reading, 1996; Bridge, 2003; Prothero and Schwab, 2004). Kraus (1987) attempted to use paleosols sandwiched between channel sandstones for interpreting depositional and subsidence history of the Bighorn Basin, Wyoming. Bridge and Mackey (1993) described the multistorey sand bodies as a sand body of one cycle superimposed upon one or more earlier sand bodies. Studies on internal three-dimensional complexities of fluvial sand

bodies are now becoming common and more sophisticated, and are being driven by the petroleum industry to understand the internal architecture of reservoir units (Miall, 1994; Lunt et al., 2004). Further, most of the studies now focus on identifying architectural elements and bounding surfaces (Miall, 1996). Plint (2002) explained the terminologies for describing three-dimensional forms of channel bodies. A detailed account on width and thickness of fluvial channel bodies and valley fills in the geological record was compiled by Gibling (2006). Turowski et al. (2007) modeled quantitatively the high sediment load that

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Textural and Petrographic Studies of Multistoried Sand Bodies as Observed in Quarry Sections in West Godavari District, Andhra Pradesh, India

mantle riverbeds and rate of river incision into bedrock. Johnson et al. (2009) explained how channel slopes are set by sediment load rather than bedrock properties, despite long-term incision into bedrock. The sequence of Rajahmundry Sandstone beds shows wide variation in texture and composition in Minanagaram and Gangolu quarries. The Minanagaram Quarry is situated to the south of the Chennai-Kolkata Highway (17°00′17°05′ N; 81°35′-80°40′ E), 16 km south-west of Rajahmundry. The study areas falls in the toposheet 65 G/12 (inch scale) (Fig. 1). The Gangolu Quarry is situated to the north of the same highway, on the western side of the Godavari River bank, 38 north-west of Rajahmundry. In the present study, two sandstone quarry sections in West Godavari District, Andhra Pradesh, have been studied in detail both in the field and laboratory. Grain size analysis and petrography have been employed to understand the variations in grain size and sediment characteristics. Geology and Stratigraphy: The litho-sequence observed in Minanagaram and Gangolu quarry sections belong to the Rajahmundry beds. King (1880) assigned a Mio-Pliocene age for the Rajahmundry Sandstones (Krishnan, 1960). However, most of the expanses of the study area are covered by the Deccan basalt. Vaidyanathan (1963) gave a short account on the economic potential of the sediments of Rajahmundry area. Raju et al. (1965) had undertaken a field study on Rajahmundry Sandstones towards establishing paleocurrents, and the general stratigraphic succession of the area is given below as presented by them: Minanagaram Quarry section: Minanagaram is a small hamlet situated about 500 m south of the Chennai-Kolkata Highway in West Godavari District. The sandstone is quarried south of the village for construction use, ostensibly for its color, since the entire region is covered by black-colored Deccan basalt. However, the sandstones are not very compact, though they are tough enough to be detonated by dynamite-triggered explosives for quarrying. The entire section was measured to be 15.75 m (Figs. 3a&b) comprising dominantly cross-bedded coarse sandstones that occasionally become conglomeratic (Fig. 3c). Both planar and trough cross beddings are found in the coarse sandstones; thin conglomerate beds are also noticed. It is also evident that the cross-bedded sandstones are repeated in the sequence (Fig. 2). The general pattern of sedimentation is cyclic. In the sequence, a number of shale clasts (Fig. 3.d) of local origin are found, especially in the conglomerate unit. The sandstones are porous and not compact and, in places, are friable. While fine-grained silt units are not encountered in the quarry, very thin, discontinuous shale units are noticed.

On the quarry face in the eastern part, a hematite-rich mudstone bed (Fig. 3.b) is observed but not extending on to the western side. However, in the top-level of the quarry section and just below the recent gravel bed, ~0.5 m-thick whitish shale bed is seen which is continual for most part of the entire length of the quarry section. These hematite-rich mudstone and shale beds are flood plain over bank deposits. The lithic fragments in the conglomeratic sandstones and conglomerate beds consist of assorted metamorphic derivatives of schist and quartzite, and shale pebbles (Fig. 3e). These pebbles are well rounded and polished. Gangolu Quarry section: The Gangolu Quarry section is located in a forest in the northern part of the study area near Hukumpeta. In fact, the section has been opened up at the top level of the hill exposing medium quality, compact to tough sandstones. The height of the quarry section is 12.60 m (Fig. 3d). Like Minanagaram, the sequence in this quarry section also consists of planar cross beds and moderately trough cross beds (Figs. 3.g & h), and thin conglomerate beds at the top level of the sequence of bedded sandstones. The size of the clasts in sandstones varies from fine- to medium-grained and occasionally coarse-grained. The rock fragments in the conglomerate bed are mostly schist fragments. They are rounded and polished. Other sedimentary features include locally derived shale chip conglomerate bed, hematite rinds and steep cross beddings (Fig. 3.i) and lenticular beds (Fig. 3.j). The trough cross beddings are much wider in scale. Sedimentary structures: The quarry-cut faces exhibit a number of sedimentary structures. Though the predominant structures are planar and troughs cross beddings, there are other minor structures restricted to certain segments in the quarry face. They are (i) hematite-rich clay nodules; (ii) slump features and soft sediment fold (Fig. 3f); and (iii) vertical vein fillings of clay. These structures are of immense help to discuss about the depositional environment. Kelling (1969), in his statistical analysis of sedimentary structures in the Rhondda Beds of South Wales, Great Britain, employed partition of current vector variability for accounting three-component flow systems (attitude or orientation, geometry or shape and dimensional characteristics of cross stratification) which has received earlier scant attention except in the work of Olson and Potter (1954) and Potter and Siever (1956). Most vector orientation studies are founded on the premise that a single drainage system was responsible for the aggregate distribution of current data in a fluvial sequence. But an examination of modern fluvial basins suggests that diverse subsidiary flow-systems may contribute substantially to the vector fields represented in the basin, especially in the more proximal headward

International Journal of Earth Sciences and Engineering ISSN 0974-5904, Vol. 06, No. 05, October 2013, pp. 1027-1046

S. R AMASAMY, A. R AMACHANDRAN , D AVID LALHMINGLIANA CHAWNGTHU, K.VELMURUGAN, K. SELVARAJ, S. B HUVANESWAR 1, AND S. CHANDRASEKAR regions. Hence, distinction between variably arising from such interaction of diverse sub-flow systems by tributaries in the fluvial basin, and that generated by the various hierarchically ordered sedimentary structures present in fluvial basins is important (Allen, 1965, 1966). The gross lithology, sedimentary structures, and cyclicity of the Rhondda Beds formation attest its fluvial character. They also indicate that most of the Rhondda Beds sediments were formed by continuous or intermittent current flow within migrating river channels in which bodies of standing water were presumably rare, as observed by Kelling (1964; 1968). Most of the cross-stratification encountered in the present study area was generated from migrating ripple and dune bedforms. Raju et al. (1965), in his studies on paleocurrents of the sandstones exposed around Rajahmudry, established the current direction as parallel to the present-day Godavari River flow (SE direction). Methodology: Thirty thin sections of sandstones were prepared to study the petrographic characteristics and modal composition under the microscope using ribbon counting method. For preparation of samples for sieve analysis, samples of consolidated sediments were separated using minimal force with a mortar and rubbercovered pestle. The sediments were treated with 30% dilute HCl to remove carbonate material and then dried and sieved. Seventeen samples from Minanagaram and ten from Gangolu quarry sections were selected for the present study and subjected to sieve analysis with a sieve interval of half phi (0.50φ). Weight percentages, cumulative percentages, mean (Mz). Inclusive Graphic Standard Deviation (σ1), Inclusive Graphic Skewness (SK1), Median (Md), One percentile (φ1), Graphic Kurtosis (KG) (Folk and Ward, 1957) were computed for all the samples. Moment statistics were also computed and tabulated. Discussion: Figures 4a-e show the cumulative frequency curves for the samples analyzed from Minanagaram and Gangolu sections. Spencer (1963) interpreted the porosity and permeability of sand-matrix mix sandstone based on grain size distribution curves and demarcated the logical cut off point to distinguish grains from matrix to be 0.03 mm (approx. 10th percentile = 5φ). However, it was Visher (1969) who did extensive analysis of log normal distribution of grain size curves and inferred several important transportational and depositional processes from the sub-populations within the curves, namely suspended, saltation and surface creep or rolling loads. The frequency curves of both Minanagaram and Gangolu quarry samples show some variations (compare the samples marked with M to G within frequency curves, M stands for Minanagaram and G for

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Gangolu) in their patterns and our comparison with Visher’s curves (op. cit, Figs. 2, 14, 15, 16) shows that these sediments were deposited largely in the main channel with more saltation population, followed by surface creep and suspension loads. However, the frequency curves of Minanagaram samples show three distinct populations, while in the Gangulu Quarry samples; saltation and supended loads are marked. Graphic Mean: The mean grain size of the Minanagaram sandstone ranges from 0.63 to 0.01φ; for Gangolu sandstone, it varies from 1.63 to 0.91φ (Table 1). Grain size contrasts occur within laminae and beds in the study area due to internal structures and inhomogenity. The general trend is the upward fining sequence that is evident in these fluvial deposits. Such trends were also observed by Basumallick (1966) and Grace et al. (1978) from their studies on size frequency distribution of samples taken from within the sand laminae. Graphic Standard Deviation: The inclusive graphic standard deviation values of Minanagaram samples range from 1.40 to 0.94φ and those of Gangolu vary between 1.71 and 1.19φ. Minanagaram samples fall in the poorly to moderately sorted category while Gangolu samples fall in poorly sorted class of Folk and Ward (1957). Russell (1939) divided sorting action into two types: local sorting involving assortment of particles at site deposition and progressive sorting consisting of an assortment in the direction of transportation. According to Inman (1949), medium sand could be transported both by saltation and in suspension, fine sand could be transported predominantly in suspension but partly by saltation, and very fine sand, silts and clays could be transported in suspension. Near the source where the stream is actively degrading its channel, the high values of friction velocity would cause the fine materials, including sand, to be mostly in suspension. However, to maintain a suspended load, a portion of fine material would be at the bottom. The bottom-load at this point would consist predominantly of coarse material with decreasing amounts of fines. Since the sample is near source, the friction velocity exceeds the threshold velocity for all but the coarsest material. It is to be expected that the samples will not be as well sorted as material farther downstream. Inclusive Graphic Skewness: The skewness values of Minanagaram samples range from 1.32 to 0.38φ implying that they are very fine skewed, while those of Gangolu range from 0.83 to 0.01φ fall largely in the near symmetrical to +0.3 to 0.1 fine-skewed category. Mason and Folk (1958), Friedman (1961) and Duane (1964) emphasized the


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importance of skewness as an environmentally sensitive parameter, particularly in modern sediments and the same can be extended to older deposits where diagenesis has not much affected the sediment texture and composition. Negative skewness in general indicates winnowing effects of the depositional environments and positive skewness is associated with sheltered depositional environments. When sediment is moved by wind or river (Friedman, 1961), transportation is generally unidirectional, and this explains the positive skewness. Further, the maximum size of grains that can be transported in suspension or by saltation varies with the competency of the transporting medium, but transportation of fine particles remains unchanged. Graphic Kurtosis: Most of the samples from the Minanagaram Quarry are leptokurtic; few are platykurtic and mesokurtic. The analyzed samples from Gangolu Quarry are mostly platykurtic. According to Martins (1965), kurtosis is less sensitive to environment than skewness. Bivariate plots: Various bivariate plots such as median vs. one percentile (after Passega, 1964), and mean size vs. standard deviation (after Steward, 1958), and standard deviation vs. skewness (after Friedman, 1967) were plotted with a view to discriminate depositional environments and transportation modes. These are in fact energy process plots (Figs. 5a-e). The C-M patterns of Passega (1964) are a versatile means of disclosing the orderly arrangement of a number of geological factors. From Figs. 5a and 5d, it is very clear that most of the samples from both the quarries fall in the N-O segment implying rolling or tractive currents to be the principal transport mechanisms of these fluvial sediments. Friedman’s plots (Figs. 5b, 5e) reveal strong fluvial signatures in the deposition of sediments. The other bivariate plots of Steward (Figs. 5c, 5f) also strongly support a fluvial regime for Minanagaram, and scattering of samples in the fields are largely due to deposition of fine sediments in the Gangolu Quarry. Moment Statistics: One approach to the quantitative analysis of grain size data is to characterize each size analysis by a derived number or set of numbers, and then compare and contrast samples using the derived numbers. The descriptive statistics that can be used are mean size, standard deviation, skewness and kurtosis (Table 2) (Baker, 1968). Jaquet and Vernet (1976) emphasized on the similarity of grain parameters such as mean size, standard deviation and skewness calculated both from graphical and moment methods and, therefore, interpretation based on both these methods will not

show much difference. As for kurtosis, moment and graphic parameters provide different information and, therefore, both should be used separately as interpretive tools. Graphic kurtosis KG is ratio of sorting in the tails over sorting at the center of the distribution. It, therefore, measures the uniformity of sorting. Moment kurtosis is extremely sensitive to the tails of the distribution. Folk and Ward (1957) defined the geological meaning of the kurtosis: an extreme KG value means that part of the sediment achieved its sorting elsewhere in a high-energy environment, and was then transported unmodified into another environment, where it was mixed type of material. However, in the present study, sediments were largely processed afresh in the fluvial system and not modified elsewhere. Moment kurtosis was interpreted by Thomas et al. (1972, 1973) as an index of mixing of two endpopulations. Petrography & Modal Analysis: Thin sections were prepared for representative samples from both Minanagaram and Gangolu quarry sections. For clastic petrography, the classifications proposed by Dott (1964) and Pettijohn et al. (1987) were followed. Two petrographic types in the Minanagaram Quarry and a lone petrographic type in the Gangolu Quarry were identified and are described below: Modal Analysis: The counting of Q-F-R grains for the representative twenty-three samples from Minanagaram and Gangolu quarry sections was effected using a manual point counter set on the microscopic stage (Table 3). The modal compositions of the petrographic types are shown in Table 4, from which it is clear that quartz dominates and is more enriched in Gangolu Quarry than Minanagaram. Next in the order are feldspars, which are relatively less throughout the quarry sections. However, rock fragments are considerable in both Minanagaram and Gangolu quarry samples (Figs. 6a-j, Figs. 7a-j).The petrofacies in Q-F-L ternary diagram suggest mainly continental and recycled orogen source of craton interior and quartzose rock type in a humid climatic setting. Qun-Qnun-Qp ternary plot of detrital quartz suggests plutonic to medium and high rank metamorphic source. Minanagaram Sandstone Quarry Section: The Minanagaram sandstone samples were collected on the basis of minor lithological variation. a) Ferrugenous Litharenites: The bottommost sample is ferrugenous litharenite showing point contact (Fig. 8a, S.No:M1). It is coarse-grained and only stable quartz grains form the framework. The lithic fragments are mostly of schists and reworked sandstone granules. The quartz grains dominantly show unit extinction. Few grains exhibit


S. R AMASAMY, A. R AMACHANDRAN , D AVID LALHMINGLIANA CHAWNGTHU, K.VELMURUGAN, K. SELVARAJ, S. B HUVANESWAR 1, AND S. CHANDRASEKAR undulose extinction and few others display polycrystalline structures with curved boundaries. There are many mineral inclusions within the quartz grains such as augite, biotite, sillimanite and cordierite. The reworked sedimentary rock fragments show quartz grains with clay coats. The clay coats are found complete around certain framework quartz grains. This shows pre-depositional origin of clay (petromatrix or detrital clay). Further, only this petrographic type reveals at least the presence of ferromagnesian mineral inclusions as stated above within the quartz grains. The grains are angular and porosity is moderate. Perhaps the source sediments for this rock type as well as for the clasts within the reworked sandstone were one and the same as revealed by the identical mineralogy and clay coats. b) Ferrugenous argillaceous litharenite was identified at the bottom level. This rock type encloses two distinct populations of quartz grains – coarse and medium size (Fig. 8b). The lithic fragments include quartzite, and squashed shale pebbles. Packing is slightly tight. Above this rock type an identical petrographic type (S. No. M2) was identified. It also shows point contact and the framework grains are coarse quartz. It contains considerable number of lithic fragments consisting of schist, gneiss and a reworked large-sized tightly packed sandstone fragment (Fig. 8c). This sandstone fragment displays pressure solution effects. It is well rounded and, at one side of the fragment, siltstone is still intact suggesting derivation of the fragment from the bedding plane of the parent sequence. Most of the ferromagnesian minerals have been completely altered and dissolved in the diagenetic solution resulting in the development of argillaceous matrix and cements. Greenish tinge in the argillaceous matrix indicates the presence of authigenic chlorite. c) This rock type is overlain by argillaceous ferruginous litharenite (S. No.M4). It displays bimodal population and the coarse quartz grains are angular. Majority of quartz grains shows unit extinction; few display undulose extinction. Polycrystalline quartz grains are few revealing dominant, straight boundaries. It is moderately cemented and porosity is considerable. Percolation of hematite and argillaceous materials from the top of the sequence along linear pores was identified. This process suggests diagenetic alteration of ferromagnesian minerals in certain zones and then flowage of iron-rich materials through interconnected pores. The cement is a mixture of argillaceous and hematite components, but the latter prevails over the former. Complete clay coats are prevalent around many quartz grains. In such grains, shrinkage of clay due to dehydration resulted in separation of clay coats from the quartz grains (Fig. 8d). Next in the stratigraphic succession is argillaceous ferruginous litharenite (S. Nos. M7, M8). In this rock

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type, the predominance of hematite cement is evident. Flowage of fine sand and hematite material from overlying sequence along connected pores is distinct. The lithic clasts are both coarse- and fine-grained metamorphics. Few squashed pelitic grains are also found. The coarse quartz grains show number of inclusions/vacuoles and weak lines. They are highly corroded and etched. The overlying petrographic type, ferruginous litharenite (S. No. M10) is very similar to the previous one. Among litho clasts in the sequence, few metamorphic fragments with granular texture are also interspersed. Gangolu Sandstone Quarry Section: Ferrugenous argillaceous litharenite, representing a sandstone sample (G3) from the bottom-level stratigraphic sequence, reveals the identity of the petrographic type as ferruginous argillaceous litharenite. The framework is constituted by angular fine sand-sized quartz grains. They show point contact under the microscope. The only other mineral grain present is muscovite mica. The lithic fragments are of fine-grained schist. They are highly squashed No detrital hematite is found around clastic grains. Therefore, it is believed that the hematite cement belongs to late diagenetic origin. Most probably, it was derived as an alteration product of such ferromagnesian minerals as pyroxene, olivine, hornblende etc. These minerals are not found intact even in trace level. In the quarry section, many hematite halos are noticed which attest to derivation of hematite from enrichment zones of ferromagnesian minerals alteration. Later, the present-day climate-induced soil forming process in the litho-section has also partly helped to generate hematite cement due to alteration of such iron-bearing minerals. Few well rounded fine sand grains are also found. Either these grains could have been derived through eolian action or the rounding of angular grains would have been possible due to soilforming processes. Almost all the quartz grains are monocrystalline. Perhaps originally these quartz grains were polycrystalline in the parent metamorphic rock, which later became disaggregated by the combined effects of transportation and diagenetic alteration. A good number of quartz grains display undulose extinction. The succeeding sample (S. No. G4) from the stratigraphic horizon is of the same petrographic type (Ferruginous argillaceous litharenite) and no distinct petrographic feature is found. The overlying sample (S. No. G6) has a framework of medium- to fine-grained quartz grains. Equal number of quartz grains show undulose and unit extinctions. The cement consists of both argillaceous and hematite materials (Fig. 8e). Both of them are largely diagenetic in origin. Scarce amount of protomatrix (detrital clay) is observed. The accessory


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minerals include muscovite and doubtful twinned feldspar. Hematite cement is formed in patches. The diffused rock fragments are of schist types (Fig. 8f). The samples from middle level stratigraphic section (S. No. G7) in the quarry show enhanced grain size (mediumsized quartz grains). These quartz grains are highly angular, etched and corroded due to soil forming process. The green tinge seen in the argillaceous matrix is probably due to chlorite. Hematite pervades in patches in the field of view indicating its origin from late diagenetic process from alteration of ferromagnesian minerals. Even vestiges of these minerals are not recorded. Muscovite mica flakes are found but do not show stress effect pointing to shallow burial and mild compaction. No identifiable feldspars could be recorded and in all probability they were completely altered in the diagenetic environment. A sample selected from higher level (S. No. G8) shows many linear quartz grains derived from schists. Some quartz grains display thin clay coats implying detrital clay generation in an intense weathering profile. No overgrowth layers are found over the quartz grains. Very few altered feldspar grains (orthoclase) along with muscovite flakes could be identified. The cement is a mixture of authigenic argillaceous and ferrugenous materials. Further, the top level samples (S. No. G9 and G10) have assorted framework of quartz grains. Very few rounded quartz grains are found among the dominant angular quartz grains. Percentage of lithic fragments is reduced and the unstable gradients in those fragments are completely altered. The rounded fine quartz grains found in these rock types are most likely derived from an eolian source. Few undeformed muscovite flakes are also recorded. Inferred depositional and diagenetic environments Minanagaram Quarry Section: The stratigraphic sequence of the quarry section reveals predominance of planar and trough crosses bedded sandstones. There are thin conglomerate beds and shale chips among other detrital coarse clastics. The conglomerate is of polymict type. Fine clastics are minor and they are thin and discontinuous. These fine clastics are hematite-rich clay (red bed) at the middle level and kaolinitic at the top of the sequence. This overall unfossiliferous coarse clastics sequence points out that these sediments were deposited in a of a pointbar system of moderate fluvial energy. Occasionally, the river overflowed and flooded the valley floor resulting in the deposition of fine clastics. These overbank fine clastics have become ferrugenized in due course of time due to alteration of ferro-magnesium-rich minerals, which imparts a red color to hematite-rich mudstone beds. These upward fining deposits are point bar deposits of a high gradient moderate energy river as

revealed by the existence of very coarse fluviatile materials including rock fragments. A good proportion (>15%) on interpretive part could be obtained from associated lithoclasts, which would be direct evidences on provenance interpretation. The source area must predominantly be a nearby metamorphic schist terrain subjected to high intensity chemical weathering under a tropical climate. Thus, high intensity weathering has altered almost all the unstable minerals such as ferromagnesian and feldspar minerals in the weathering soil-forming profile. This is also supported by the occurrence of detrital clay coats around quartz grains, and since the sequence is enriched in angular, coarse clastics with considerable amount of lithoclasts, it can be safely inferred that the source must have been be a proximal one. Few reworked sedimentary grains of identical lithology might have been derived from the older sequence of the Rajahmundry sandstones. The schist fragments being highly unstable among the metamorphics, only smaller-sized fragments could be expected. It seems that the provenance continually experienced a moderate uplift supplying enough coarse clastics to be deposited in the fluvial environment. The quartzose sands were most likely derived from broad positive areas in the interior of the stable craton. The few sedimentary structures seen in the quarry section – slump features and folded soft sediment layers – all reveal local instability of the depositional site at places. Perhaps less than 10% of feldspars were deposited along with coarse clastics as evident from the altered relicts of such feldspars in thin sections. Since these sediments are coarse and partially cemented without showing any pressure solution effects, it is certain that they were subjected to shallow burial diagenetic environment. Further, the cement consists of a mixture of argillaceous and hematitic components revealing the production of such materials in the diagenetic realm (late diagenetic stage) by complete alteration of detrital feldspars and ferromagnesian minerals. That is the reason wiping out completely such unstable mineral grains. There are hematite-rich clay bands and nodules which further support that ferrous oxide released from diagenetic alteration sites of ferromagnesian minerals was easily absorbed by clay minerals present in the shale sequence. Very late in diagenetic stage is the soil-forming process of the sequence, which caused considerable flow of hematitic material associated with fine clastics along the interconnected forces. The highly corrosive action of such fluids was also responsible for the corrosion and leaching of many quartz grains. Gangolu Quarry Section: The difference from Minanagaram is only in grain size and minor shale sequence – Gangolu sequences are medium- to fine-grained sandstones interbedded with conglomerate beds. The lithoclasts are same but are


S. R AMASAMY, A. R AMACHANDRAN , D AVID LALHMINGLIANA CHAWNGTHU, K.VELMURUGAN, K. SELVARAJ, S. B HUVANESWAR 1, AND S. CHANDRASEKAR deeply crushed. While majority of the quartz grains are angular, considerable number show undulose extinction. There is total absence of polycrystalline quartz grains unlike in Minanagaram. This is due to the fact that the rock fragments and quartz grains being fine- to mediumgrained, all aggregated polycrystalline quartz grains were disaggregated later by the combined effect of transportation and diagenesis. In all probability, the same source area that supplied coarse clastics for the deposition of Minanagaram sequence, also supplied the fine clastics of same mineralogy but in a subdued relief that allowed greater retention of clasts in the weathering profile with a sluggish erosion rate through a tributary. However, plane beds and other cross-bedded structures in the sandstones support the prevalence of a moderate to high flow regime during deposition of the clastics in the main channel. The thickening of a clastic unit in the direction of the current as noticed in these sandstones may be quite possible along basin margins, particularly when sediments are derived from distal, low-yield source areas (Potter and Pettijohn, 1963). The locations of these quarry sections are also almost along the same longitude, sub-parallel to the Godavari River. The sandstone sequence of Gangolu Quarry is finegrained and, therefore, looks much more compacted. However, a closer study revealed that this difference lies in grain size parameters. They contain small amount of matrix. Naturally, compaction of such fine-grained clastics leads to an improved packing index and relatively reduced porosity. Other diagenetic aspects of Minanagaram hold good for this quarry section, too. Conclusions: The unfossiliferous Rajahmundry Sandstones exposed in the Minanagaram and Gangolu quarry sections are part of the point bar deposits of Godavari River. The sandstones show erosive bases followed by thin conglomeratic units. The multistoried sand bodies seen in both quarry sections are interpreted as point-bar deposits showing fining upward sequence. The clasts in the conglomerate units include highly polished gneissic and locally derived mud chips. These quarry sections also host many primary sedimentary structures, which clearly reveal moderate to high energy conditions (floods) at the time of deposition of the Gangolu sandstone. During the deposition of clastics in the Minanagaram area, a lower flow regime was largely maintained. The trough and planar cross beds show a paleocurrent direction along that of the present-day Godavari River course. The Minanagaram Quarry exhibits largely planar and trough cross beds, while Gangolu dominantly displays plane beds of fine sands. The red mudstone sandwiched in the Minanagaram Quarry is an overbank deposition with enrichment of hematite. The source area must have been

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predominantly a metamorphic schist terrain subjected to high intensity chemical weathering under tropical climate as revealed by the petrography of these sandstones. Acknowledgements: The authors are thankful to the authorities of the University of Madras for various help during the investigations. The first author specially thank the UGC for partially supporting the work through the sanctioned Projects (No. 41-1032/2012(SR) Dt. 23.7.2012 and UGC- CPEPA F. No. 8-2/2008 (NS/PE) Dt. 14.12.2011).We thankfully acknowledge the support and encouragement received from the Professor and Head, Department of Geology, University of Madras. References: [1] J.R.L. Allen, on bed-forms and paleocurrents. Sedimentol. Vol.6, (1966) pp.153-190. [2] R.A. Baker, Kurtosis and Peakedness. J. Sed. Pet., 38, (1968) 679-680. [3] S. Basumallick, Size differentiation in a crossstratified unit. Sedimentol., Vol.6, (1966) pp.35-68. [4] J.S Bridge, Rivers and Floodplains: Forms, Processes and Sedimentary Record. Blackwell Science, New York (2003). [5] D.J. Doeglas, Interpretation of the results of mechanical analysis. Jour. Sediment. Petrol., V.16, (1946) pp19-40. [6] R.H.JR. Dott, Wacke, Graywacke and Matrix- what approach to immature sandstone classification? Jour. Sed. Petrology, 34, (1964). pp 625-632. [7] D.B. Duane, Significance of Skewness in recent sediments, Western Pamlico Sound, North Carolina. Jour. Of Sed. Petrol., Vol.34, No.4, (1964) pp.864-874. [8] R.L. Folk, W.C.Ward, Brazos river bar: a study in the significance of grain size parameters Jour. Sed. Petrol. V.27, (1957) p.3-2. [9] R.L. Folk, A review of grainsize parameters, Sedimentology V.6, (1966) p.73-93. [10] G.M. Friedman, Distinction between dune, beach, and river sands from their textural characteristics. Jour. Of Sed. Petrol., Vol.31, (1961) pp. 514-529. [11] G.M. Friedman, Dynamic Processes and Statistical Parameters Compared for size frequency distribution of beach and river sands. Jour. Sed. Petrol. V.70, (1967) p.327- 354. [12] G.H. Friedman, J. E. Sanders, Principles of Sedimentology, John Wiley & Sons, New York., (1978) pp 792. [13] M.R. Gibling, Width and Thickness of fluvial channel bodies and Valley fills in the Geological Record: A literature complication and classification. Jour. of Sed. Res., Vol.76, (2006) p.731-770.


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[14] J.T. Grace, B.T Grothaus, R. Ehrlich, Size frequency distributions taken from within sand laminae. Jour. Of Sed. Petrol., Vol.48, No.4, (1978) pp. 1193-1202. [15] D.L. Inman, Sorting of sediments in the light of fluid mechanics. Jour. Of Sed. Petrol., Vol.19, No.2, (1949) pp.51-70. [16] J.M Jaquet, J.P Vernet, Moment and Graphic size parameters in the Sediments of Lake Geneva (Switzerland). Jour. Of Sed. Petrol., Vol.46, No.2, (1976) pp. 305-312. [17] J.P.L. Johnson, K.X. Whipple L.S. Sklar, T.C Hanks, Trasnport slopes,sediment cover, and bedrock channel incision in the Henry Mountains, Utah. Jour. Of Geophy. Res., Vol.114, F02014. (2009). [18] G. Kelling, The environmental significance of cross stratification parameters in an Upper Carboniferous Fluvial Basin. Jour. Of Sed. Petrol., Vol. 39, No.3, (1969) pp. 857-875. [19] W. King, the Upper Gondwana and Other formations of the Coastal region of the Godavari District. India Geol. Surv., Mem., 16(3), (1880) p.195-264. [20] M.J. Kraus, Integration of channel and floodplain suites II. Vertical relations of Alluvial Paleosols.Jour. Sed. Petrol, Vol. 57, No.4, (1987) p.602-612. [21] M.S. Krishnan, Geology of India and Burma: Madras Higginbothams (Private) Ltd., (1960) p 604. [22] R.D. Lima, D.D.F.Rosetti Depositions, Facies in Late Cretaceous-? Lower Tertiary Deposits from Northwestern Maranhao State, Brazil. Revista Brasileira de Geosciences, Vol.29, No.2, (1999) pp.237-244. [23] I.A. Lunt, J.S Bridge, R.S Tye, A Quantitative three dimensional depositional models of gravelly braided rivers. Sedimentol., Vol.5 No:3, (2004) pp.377-414. [24] S.D Mackey, J.S Bridge, Three dimensional model of alluvial stratigraphy: theory and application. Jour. Of Sed.Res.Vol.B65 (1995) pp.7-31. [25] L.R Martins, Significance of Skewness and Kurtosis in environmental interpretation. Jour. Of Sed. Petrol. (1965). [26] C.C. Mason, R.L. Folk, Differentiation of beach, dune, and Aeolian flat environment by size analysis, Mustang Island, Texas. Jour. Of Sed. Petrol., V.28, (1958) pp.211-226. [27] A.D Miall, Reconstructing Fluvial Macroform Architecture from Two Dimensional Outcrops: Examples from the Castlegate Sandstone, Book Cliffs. Utah. Jour. Sed. Res., Vol.B64, No.2, (1994) p.146-158.

[28] R. Passega, Grain Size representation by C-M. Parameters as a Geological tool. Jour. Sed. Petrol. V.34, (1964) pp. 830-847. [29] F.J. Pettijohn, P.E. Potter, R. Siever, Sand and Sandstones. Springer-Verlog Berlin Heildelberg, New York Publication, (1987) pp.571. [30] A.H. Plint paleo-valley systems in the upper cretaceous Dunvegon formation, Alberta and British Colmbia: Bulletin Canadian Pertoleum Geology, V.50, (2002) pp 277-296. [31] P.E. Potter, F.J Pettijohn, Paleocurrents and Basin Analysis: Berlin, Gottingen, Heidelberg, SpringerVerlag, (1963) p. 296 [32] P.E. Potter, R. Siever, Sources of basal Pennsylvanian sediments in the Eastern Interior Basin, 1, Crossbedding. Jour. Geol., Vol.64, (1956) pp. 225-244. [33] D.R Prothero, F. Schwab, Sedimentary Geology: an Introduction to Sedimentary rocks and Stratigraphy. 2nd Edition W.H. Freeman and Company, New York (2004). [34] D.S.N. Raju, C.N. Rao, B.K Sengupta, Paleocurrents in the Miocene Rajahmundry Formation, Andhra Pradesh, India. Jour. Sed. Petrol., Vol.35, No.3 (1965) pp. 758-762. [35] T.S. Raju, M.P.C. RAO. Sedimentology of Tertiaries and Upper Gondwanas of parts of west Godavari District. A.P. Q.J. Geol. Min. Metallic Society of India, 40, (1968) p.73-88. [36] H.G. Reading, Ed. Sedimentary Environments and Facies. #rd Ed. Oxford; Nlackwell Scientific Publications (1996). [37] D.W Spencer, The Interpretation of grain size distribution curves of clastic sediments. Jour. Of Sed. Petrol., Vol. 33, No.1, (1963) pp. 180-190. [38] H. B. JR. Steward, Sedimentary reflections of depositional Environments in San Higuel Lagoon, Baja, California, Mexico, Am.Assoc. Petrol. Geol. Bull, V.42, (1958) p.2567-2618. [39] R .L. Thomas, Kemp, A.L.W. Lewis, G.F.M Distribution, composition and characterisitics of the surficial sediments of Lake Ontario. Jour. Of Sed. Petrol., Vol.42, No.1, (1972) pp. 66-87. [40] R.L. Thomas, A.L.W Kemp, G.F.M Lewis, The surficial sediments of Lake Huron. Canadian Jour. Earth Sci., Vol.10, (1973) pp. 226-265 [41] J.M. Turowski, D. Lague, N. Hovius. Cover effect in bedrock abrasion: a new derivation and its implications for the modeling of bedrock channel morphology, J. Geophys. Re., 112, F04006, (2007). [42] R. Vaidyanathan, Economic significance of studies on sedimentation in Rajahmundry area, Andhra Pradesh: Current Sci., Vol.32, (1963) pp. 119-120. [43] G. S Visher, Grain size distribution and depositional process. Jour. Of Sed. Petrol., Vol.39, No.3, (1969) pp. 1074-1106.


S. R AMASAMY, A. R AMACHANDRAN , D AVID LALHMINGLIANA CHAWNGTHU, K.VELMURUGAN, K. SELVARAJ, S. B HUVANESWAR 1, AND S. CHANDRASEKAR [44] C. K. Wentworth, A Scale of grade and class terms for clastic sediments, Jour. Geol. V.30, (1922)

P.377-392.

Fig1: Location map of the study area

Fig2: Sandstone Quarry Sections


1035

1036


Fig3a: Photograph showing a full view of Minanagaram Quarry section

Fig3b: A thin ferruginous (hematite) clay bed in the eastern side of the Minanagaram Quarry 15.75m

Fig3c: Photograph shows polished rounded metamorphic rock fragments in the coarse sandstone bed- Minanagaram Quarry section

Fig3d: Horizontal bedding features in the Gangolu Quarry section

Fig3e: Shale-chips amidst metamorphic rock fragments in the Minanagaram Quarry

Fig3f: Soft sediment structures and hematite rinds in the same locality (Minanagaram)


S. R AMASAMY, A. R AMACHANDRAN , D AVID LALHMINGLIANA CHAWNGTHU, K.VELMURUGAN, K. SELVARAJ, S. B HUVANESWAR 1, AND S. CHANDRASEKAR

1037

Fig3g: High angle cross-bedded sandstones at the bottom level of the Gangolu Quarry section

Fig3h: Wide-size trough cross-beds in Gangolu Quarry section; note peculiar ‘drop’ features perhaps caused by pebble droppings during deposition

Fig4a: Cumulative frequency curve of Minanagaram quarry samples M1-M6

Fig3i: A bed of mud chip conglomerate facies at the bottom level of the Gangolu Quarry section.

Fig4b: Cumulative frequency curve of Minanagaram quarry samples M7-M12 Fig3j: Lenticular beds (enriched in coarse clastics) and horizontal and trough cross beddings in the Gangolu Quarry section. International Journal of Earth Sciences and Engineering ISSN 0974-5904, Vol. 06, No. 05, October 2013, pp. 1027-1046

1038


Fig4c: Cumulative frequency curve of Minanagaram quarry samples M14-M18

Fig4e: Cumulative frequency curve of Gangolu quarry samples G6-G10

Fig5a:

Fig4d: Cumulative frequency curve of Gangolu quarry samples G1-G5

Fig5b: International Journal of Earth Sciences and Engineering ISSN 0974-5904, Vol. 06, No. 05, October 2013, pp. 1027-1046


Fig5c:

1039

Fig5f:

Fig6a: Triangular plot of QFR of the Minanagaram quarry (after Pettijohn et al., 1972). Fig5d:

Fig5e:

Fig6b: Triangular plot of QFR of the Minanagaran quarry, (after folk, 1980).


1040


Fig6c: Triangular plot of QFR of the Minanagaram quarry (after James et al., 1986)

Fig6f: Triangular plot of QFR Provenance field boundaries Minanagaram quarry (after Dickinson and Suczek, 1979).

Fig6d: Triangular plot of QFR of the Minanagaram, (after Dickinson et al., 1983). Fig6g: Triangular plot of Qm FRt of the Minanagaram quarry (after Dickinson 1985).

Fig6e: Triangular plot of QmFRt of the Minanagaram quarry (after Dickenson et al., 1983) Fig6h: Triangular plot of QtFRt of the Minanagaram quarry, (after Dickinson, 1985).



Fig6i: Triangular plot of QFR in regard to evaluation of paleoclimate from the Minanagaram quarry (after Suttner and Dutta, 1986). Provenance field boundaries are taken from Dickinson and Suczek, (1979).

1041

Fig7b: Triangular plot of QFR of the Gangolu quarry (after folk, 1980).

Fig7c: Triangular plot of QFR of the Gangolu (after James et al., 1986) Fig6j: Ternary plot of detrital quartz types of the Minanagaram samples (after Basu et al., 1975). Qp, Quartz polycrystalline; Qnu, Quartz nonundulatory (monocrystalline; Qu; Quartz undulatory (monocrystalline).

Fig7d: Triangular plot of QFR of the Gangolu, (after Dickinson et al., 1983).

Fig7a: Triangular plot of QFR of the Gangolu, (after Pettijohn et al., 1972).


1042


Fig7e: Triangular plot of QmFRt of the Gangolu quarry (after Dickenson et al., 1983)

Fig7f: Triangular plot of QFR Provenance field boundaries Gangolu, (after Dickinson and Suczek, 1979)

Fig7g: Triangular plot of QmFRt of the Gangolu quarry (after Dickinson 1985)

Fig7h: Triangular plot of QtFRt of the Gangolu, (after Dickinson, 1985)

Fig7i: Triangular plot of QFR in regard to evaluation of paleoclimate from the Gangolu quarry (after Suttner and Dutta, 1986). Provenance field boundaries are taken from Dickinson and Suczek, (1979).

Fig7j: Triangular plot of detrital quartz types of the Gangolu samples (after Basu et al., 1975). Qp, Quartz polycrystalline; Qnu,Quartz nonundulatory monocrystalline); Qu; Quartz undulatory (monocrystalline).



Fig8a: Photomicrograhp of a ferruginous litharenite showing a fine-grained metamorphic rock fragment and angular quartz grains embedded in hematite cement (crossed nicols) Minanagaram quarry.

Fig8b: Photomicrograph of ferruginous argillaceous litharenite exhibiting a squeezed pelitic fragment at the center; also seen are angular coarse quartz grains cemented in a ferruginous clay mixture Minanagaram quarry (Minanagaram).

Fig8c: Photomicrograph of same petrographic type displaying a well rounded reworked sandstone fragment with tight packing as evident from pressure solution feature; also seen underneath the rock fragment a sticky portion of siltstone suggesting derivation of this fragment from the bedding plane of the parent rock (crossed nicols) Minanagaram.

Fig8d: Photomicrograph of ferruginous argillaceous litharentie displaying detrital clay coats around coarse quartz grains and their separation at place from the host grains due to shrinkage by dehydration phenomena (crossed nicols; Minanagaram).

Fig8e: Photomicrograph of a medium-grained ferrugenous argillaceous litharenite showing precipitation of argillaceous and hematite cements in the void spaces (Gangolu Quarry).

1043

Fig8f: Photomicrograph of a medium-grained ferrugenous argillaceous litharenite showing precipitation of argillaceous and hematite cements in the void spaces (Gangolu Quarry).


1044

Textural and Petrographic Studies of Multistoried Sand Bodies as Observed in Quarry Sections in West Godavari District, Andhra Pradesh, India Table1: Grain size statistical parameters (graphical methods)

S. No

Sample No

Mean Mz

Standard Deviation δ1

Skewness SK1

Kurtosis KG

Median

Standard Deviation Class

Skewness Class

Kurtosis Class

1

G1

1.48

1.37

0.26

1.11

1.7

Poorly Sorted

Fine Skewed

Leptokurtic

2

G2

1.13

1.71

0.25

0.81

1.6

Poorly Sorted

Fine Skewed

Platykurtic

Near Symmetrical Very fine Skewed

3

G3

1.56

1.57

0.03

1.07

1.9

Poorly Sorted

Mesokurtic

4

G4

0.91

1.19

0.83

0.47

0.3

Poorly Sorted

5

G5

1.14

1.62

0.24

0.87

1.5

Poorly Sorted

Fine Skewed

Platykurtic

6

G6

1.20

1.64

0.15

0.90

1.7

Poorly Sorted

Fine Skewed

Platykurtic

Very Platykurtic

Near Symmetrical Near Symmetrical Near Symmetrical Near Symmetrical Very fine Skewed

Leptokurtic

7

G7

1.10

1.26

0.05

0.83

1.5

Poorly Sorted

8

G8

1.56

1.25

-0.01

0.69

1.7

Poorly Sorted

9

G9

1.63

1.35

-0.03

1.23

1.9

Poorly Sorted

10

G10

1.40

1.47

0.08

1.25

1.6

Poorly Sorted

11

M1

0.13

1.20

1.32

1.16

0.1

Poorly Sorted

12

M2

0.31

1.45

0.79

1.01

0.3

Poorly Sorted

Fine Skewed

Mesokurtic

13

M3

0.36

1.00

1.00

0.55

0.4

Poorly Sorted

Fine Skewed

Very Platykurtic

14

M4

0.01

1.18

1.18

0.74

0.3

Poorly Sorted

15

M5

0.03

1.06

1.06

0.60

0.1

Poorly Sorted

16

M6

0.38

0.68

0.68

1.50

0.3

Moderately Sorted

17

M7

0.50

0.60

0.60

1.32

0.5

Poorly Sorted

18

M8

0.16

1.20

0.79

0.71

0.3

Poorly Sorted

19

M9

0.33

1.01

0.66

1.33

0.4

Poorly Sorted

20

M10

0.46

1.01

0.62

1.19

0.4

Poorly Sorted

21

M11

0.18

0.94

0.90

1.53

0.1

Moderately Sorted

22

M12

0.05

1.32

1.18

1.75

0.3

Poorly Sorted

23

M14

0.08

1.11

1.06

0.67

0.1

Poorly Sorted

24

M15

0.16

1.21

0.86

1.12

0.2

Poorly Sorted

25

M16

0.63

1.20

0.38

1.30

0.9

Poorly Sorted

26

M17

0.31

1.05

0.79

1.21

0.3

Poorly Sorted

27

M18

0.26

1.13

0.83

1.62

0.20

Poorly Sorted

Very fine Skewed Very fine Skewed Very fine Skewed Very fine Skewed Very fine Skewed Very fine Skewed Very fine Skewed Very fine Skewed Very fine Skewed Very fine Skewed Very fine Skewed Very fine Skewed Very fine Skewed Very fine Skewed

Table2: Grain size data calculated from moment statistics Sample No

Mean Size (Mz)

Standard Deviation (σ)

Skewness (SK1)

Kurtosis (KG)

M1

1.55

2.40

0.10

0.27

M2

1.92

3.68

0.01

0.05

M3

1.80

3.57

0.05

0.07


Platykurtic Platykurtic

Leptokurtic Leptokurtic

Platykurtic Very Platykurtic Very Leptokurtic Leptokurtic Platykurtic Platykurtic Leptokurtic Very Leptokurtic Very Leptokurtic Very Leptokurtic Leptokurtic Leptokurtic Leptokurtic Very Leptokurtic

S. R AMASAMY, A. R AMACHANDRAN , D AVID LALHMINGLIANA CHAWNGTHU, K.VELMURUGAN, K. SELVARAJ, S. B HUVANESWAR 1, AND S. CHANDRASEKAR M4

2.22

4.92

0.02

0.02

M5

1.95

3.80

0.04

0.06

M6

1.04

1.08

0.64

3.42

M7

1.46

1.46

0.19

1.60

M8

2.04

4.16

0.02

0.04

M9

1.16

1.34

0.34

2.00

M10

1.14

1.29

0.38

1.96

M11

1.05

1.10

0.99

4.03

M12

1.77

3.13

0.09

0.13

M14

1.90

3.61

0.04

0.07

M15

1.49

2.22

0.10

0.31

M16

1.46

2.13

0.07

0.36

M17

1.24

1.53

0.38

1.10

M18

1.43

2.04

0.21

0.51

G1

1.87

3.49

-0.03

0.06

G2

2.83

8.00

-0.003

0.003

G3

2.41

5.80

-0.007

0.01

G4

3.69

13.61

0.0009

0.0007

G5

2.55

6.50

-0.004

0.007

G6

2.60

6.76

-0.006

0.007

G7

2.76

7.61

-0.002

0.004

G8

1.63

2.65

-0.06

0.16

G9

1.96

3.84

-0.02

0.04

G10

2.19

4.79

-0.007

0.02

1045

Table3: Modal analysis derived from thin sections of Minanagaram and Gangolu Quarry samples Sl. No

Sample No

Quartz (Mono+ Poly)

Feldspar (Plag+ Micro)

1

GU-1

95.62

0.00

Rock fragments (Quartzite+ Chert) 4.37

2

GU-2

86.7

1.26

12.02

3

GU-3

87.5

1.29

4

GU-4

81.77

0.00

5

GU-7

93.06

0.81

6

GU-8

98.74

7

GU-9

98.1

8

GU-10

98.75

9

M-1

85.27

10

M-2

93.71

0.00

11

M-3

93.3

12

M-4

87.3

13

M-6

14

M-7

15

M-8

Quartz undulose

Quartz nonundulose

Quartz polycrystalline

TQ/ (F+R.F)

PQ/ (F+R.F)

67.48

20.86

11.65

37.30

4.35

44.16

34.31

21.53

20.63

4.44

11.2

57.14

23.65

19.21

16.25

3.12

18.22

39.58

33.85

26.56

10.54

2.80

6.12

39.47

43.42

17.1

32.90

5.63

0.00

1.11

45.05

41.89

13.04

227.93

29.73

0.63

1.26

45.98

52.41

1.6

164.55

2.65

0.5

0.75

51.39

46.33

2.27

316.00

7.20

0.00

14.72

50.91

27.27

21.81

7.47

1.63

6.28

32.79

39.89

27.32

29.14

7.96

0.83

5.85

30.49

33.18

36.32

33.38

12.13

0.00

12.69

21.82

41.82

36.36

8.67

3.15

86.75

0.85

12.39

24.63

48.77

26.6

15.33

4.08

95.62

0.00

4.37

48.11

33.51

18.37

42.33

7.78

80.41

0.00

19.58

49.35

31.17

19.48

3.93

0.77


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16

M-9

91.82

0.00

8.17

34.93

31.51

33.56

17.87

6.00

17

M-10

91.72

0.00

8.27

27.07

38.35

34.58

16.08

5.56

18

M-11

91.77

0.00

8.22

20.69

54.48

24.82

17.64

4.38

19

M-12

83.33

0.00

16.66

20.34

40.68

38.98

7.08

2.76

20

M-14

90.04

0.86

9.09

37.98

24.04

37.98

20.90

7.94

21

M-15

92.6

0.00

7.39

27.70

44.13

28.16

28.82

8.12

22

M-16

92.72

0.00

7.27

24.02

46.57

29.41

28.06

8.25

23

M-17

91.3

0.00

8.69

16.35

42.77

40.88

18.30

7.48
