To the north of Chandigarh, the sector of the Siwalik Frontal Range called Chandigarh Hills, about forty kilometres long, is bounded to the northeast by the Sirsa Fault, to the southwest by the Himalayan Frontal Thrust, to the northwest by the Sutlej lineament and to the southeast by the Ghaggar fault (Fig. 1). Before the folding, the main streams flowed from the Himalayan mountains toward the southwest into the Indo-gangetic plain (Singh and Tandon, 2008). The uplift began during the Middle Pleistocene and was associated with the formation of large conglomeratic alluvial fans called the Boulder Conglomerate Formation. The progression of the Indian plate toward the north intensified the folding of the sub-Himalayan foreland basin, forming several parallel anticlines. Uplift of the Siwalik Range started with the Masol anticline that first arose in the south-eastern part and further spread toward the north-west. The southeastern part became an axis culmination, and at its south-eastern extremity, the Masol anticline became a fold culmination; moreover, it extended to the southeast in the Kohra anticline, a second axis (Fig. 1). The parallel Tandi anticline is less pronounced (Ranga Rao, 1993). The Siwalik Frontal Range (SFR) thus became an orographic barrier and diverted the stream flows toward the north-west for the Sirsa and Sutlej Rivers, and toward the south-east for the Ghaggar River (Singh and Tandon, 2008). Since this period, the streams flowing from the northern slopes of the SFR and from the Himalayas are collected in a wide corridor called dun drained by the Sirsa River “pinjaur dun” along the northern side of the Chandigarh Hills (Fig. 1).

The Masol inlier is strongly dissected by the erosion continuously activated by the uplift of the Siwalik Frontal Range and the monsoon, the lithostratigraphic study of the Quaranwala zone is easy (Fig. 2).

The topography of the SFR of Chandigarh is influenced by the geological structure due to the tectonics and the erosion process, and as a result presents a succession of synclinal and anticline dug by rivers or choes. One of these choes, the Patiali Rao, flows from the NE to the SW, crosses the Masol anticline and divides it on this both riversides in different reliefs, altitudes and structural dips. The western side corresponds to the dome of the anticline whose one sector is dug and drained by a short tributary, the Pichhli Choe (Fig. 2). Thus on this riverside the centre of the anticline is a narrow and flattened with hillocks capped by residual sediments of the upper layers of the trenched anticline. The eastern riverside of the Patiali Rao is a large anticline excavated in its centre where the relief is constituted by a bowl-shaped depression, steep slopes and cliffs truncated by vertical active gullies.

The Pichhli watershed is about 1 kilometre length and oriented NNW-SSE along the anticline axis. The Pichhli valley is formed by two short streams in its upstream part separated by several small hills. Several meanders occur in its downstream part before the confluence with the Patiali Rao. The changes of the directional flow are sometimes located at the same places than faults. These faults may have influenced the spatial organisation and growth of the choe. The topography of the Pichhli watershed is asymmetrical; the eastern slopes are abrupt with a set of cliffs whereas the topography of the western side is higher and characterized by massive sandstone bars and steps. Various erosion morphologies are present like cavities due to natural sand excavation, rock fall, landslide and river erosion (Gargani et al., 2016). The Pichhli Choe riversides show two alluvial terraces indexed T1 and T2 (Gargani et al., 2016).

The erosion is very active, outcrops of the geological formations and their colluviums are observed in all the areas. All the paleonto-archeological localities are in the Masol anticline, located in the both sides of the Patiali Rao valley.

Sahni and Khan, 1964 and Sahni and Khan, 1968 have drawn the first geological map of the Masol anticline. The oldest units of the Tatrot Formation are not exposed contrary to the youngest attributed to the Late Pliocene (Dambricourt Malassé et al., 2016a). The two geologists noted that grey and red clays are characteristic of the lower Tatrot and that the pink or yellow clays characterize the upper Tatrot rich in vertebrate fossils designated as the Quranwala fossiliferous zone or Quranwala zone. This zone ends with a series of claystone and sandstone devoid of fossils over 20 m thick, capped by a fossiliferous grey clay unit covered by pebbly sandstone. For the two geologists, the grey clay corresponds to the last deposit of the Tatrot, and the pebbly sandstone to the boundary between the Tatrot and Pinjor Formations. The fossiliferous deposits end a few meters above this sandstone rich in pebbles. Later, Ranga Rao et al. (1995) conducted new investigations and observed again an alternation of sandstone and claystone, brown, orange brown, grey-brown, yellow in color, in which the claystones are thicker than the sandstones. The latter are medium to coarse-grained and are gravely in their upper part. Beyond the inlier where the Pinjor Formation is exposed, coarse-grained sandstones become thicker and more frequent upwards than the claystones (Ranga Rao et al., 1995 and Sahni and Khan, 1964).

The Masol 1 locality (M1) is at the top of the narrow and flattened mount corresponding to the anticline culmination; to the west it extends on the slopes up to the bed of the Picchli choe and to the east, up to the steep ravine that limits the plateau and dominates the village (Fig. 2). The locality is characterized by several residual hillocks from the Quranwala zone, some of them capped by colluvium (Fig. 3A and B).

To draw the most complete lithostratigraphic log, it was necessary to walk fifty metres north-westward of M1 where the outcrops continue with the youngest units at Masol 2 (M2) (Fig. 4). The latter is a bowl-shaped depression dominated by cliffs which form the northern slope of the plateau. The locality is divided in two sectors: Masol 2-east is a first depression at the top of the anticline and Masol 2-west is a second depression located very abruptly on the slope towards the Picchli Choe (Fig. 3C, number 5). By locations the outcrops are topped by colluviums resulting from the dismantling of the upper strata; their thickness varies between several centimetres to more than one meter (Gargani et al., 2016) (Fig. 3B).

Lithostratigraphic description

Four lithostratigraphic sections were necessary to establish the composite sequence of Masol 1 and 2, which totals 36 m of thickness. These sections are located in the upper part of the mount and along its western slope accessible through the gullies (Fig. 4): i) the section of Masol 1, with lithologic units B, C, D, E and F; ii) the section of Masol 1, upstream of the west-south-west ravine with lithological units G and H; iii) the section of Masol 1, downstream of the west-south-west ravine with lithological units I, J, K and L; iv) the section of Masol 2 west, with lithological units A, B+, C+, D+ and E+. The composite log totalizes 16 lithostratigraphic units characterized by alternation of medium-grained sandstones including gravelly lenses and siltstones usually brown in color (Table 1, Fig. 5). The latter are thicker than the sandstones. The sedimentology and mineral composition of Masol 1 are described in Abdessadok et al. (2016).

Fossils remains and artefacts of the Masol 1 locality:

Masol 1 locality yielded the highest number of fossil bones due to its configuration along the 150 m long southern scarps of the plateau and its extension from the Pichhli Choe to the west up to the extremity of the flattened mount to the east (Figs. 3A and C). These fossiliferous scarps are composed of the silts D–E and the sandstones B and C (Fig. 5). They form an erosional front in the Quranwala faunal zone facing south-east in this sector of the mount (Fig. 3A). The fossils are regularly unearthed from silts and sandstones due to the intensive rain during the monsoon. A few fossils have been collected in the silts D–E or in the sandstone blocks of this unit B, the majority recovered in and on recent colluviums resulting from the dismantlement of the silts and sandstones B–C.

The faunal list of Masol 1 (387 fossils) is given in Moigne et al. (2016) and includes a lot of dermal plates from the turtles Colossochelys and Geoclemys, a few from Crocodylus, one fossil of carnivore (Hyena), many bones of Bovidae, Cervidae, Proboscidae such as Hexaprotodon, Stegodon and Suidae. The cut-marked shaft Masol 1 R10084, discovered in 2009, is yellow with remains of a thin crust of micaceous sand; its cortical bone is well preserved, like two hemi-mandibles of an antelope collected directly in the yellow silts D, and its medullary cavity is lined with calcite crystals. Its local origin was definitely confirmed by two splinters collected within a perimeter of 2 m², the first in 2011 very similar to the shaft but without connection, and the second one in 2013 which was reattached to the shaft during the study of the materials (Dambricourt Malassé et al., 2016a and Moigne et al., 2016). Its stratigraphic origin is very likely the boundary between the yellow silt D and the base of the micaceous sandstone C.

The stone tools in quartzite were recovered in the same conditions; they always occur with fossil bones. The first chopper was collected in 2008 (Dambricourt Malassé et al., 2016a), 30 m from the tibia shaft Masol 1 R10084, in a small butte of redeposited sandstone blocks and silts rich in turtle bones located at the limit of the eastern ravine, named the “Turtle hillock” (Fig. 3A, numbers 1 and 2). Some samples were extracted from this colluvium to be dated by Electron Spin Resonance.

Then, in 2009, the team collected flakes and a few choppers in the perimeter between the cut-marked tibia shaft Masol 1 R10084 and the “Turtle hillock” and one chopper on the slope of the ravine below this hillock. Later two choppers were found in the perimeter of the tibia shaft Masol 1 R10084 (5 and 8 meters) and another one 40 m to the west of this locality on colluviums from the same silts D and E. Among 3 small pieces of quartzite, 2 are flakes and one is a retouched fragment; the 14 heavy-duty tools are various types of choppers (Gaillard et al., 2016).

There is no layer or lense of quartzite cobbles/pebbles along the 150 m of outcrops but an important concentration of cobbles is visible 80 m beyond to the north at Masol 2, in the colluviums of the silts E and D among blocks of the dismantled units B and C (sandstones). Their sizes vary from 10 to 20 cm long, two trial trenches were open in these colluviums and in their substratum to test the presence of artefacts.

Fossils remains and artefacts of the Masol 2 locality:

The fossils of Masol 2 show little displacement since their exhumation. The most remarkable sublocality is Masol 2-east with a very large, segmented and incomplete tusk, associated to a large fragmented scapula of a proboscid covered by cemented gravel (Moigne et al., 2016). At this place, there is just a fragile residual relief forming a sort of wall composed of silt units D–E, with a very thin layer of C at the top and gravel of the sandstone B (Fig. 6). The fossils were deposited on the silts since the erosion of the gravels. One chopper was recovered near the scapula on the wine-colored silt of unit E. Fossils, flakes and choppers were collected on the other side of this wall where the Masol 2 depression follows the direction of the dip from the east to the west (Fig. 6). These fossils and artefacts were lying along the foot of the small plateau which separates Masol 1 (south side) and Masol 2 (north side). Year after year several specimens were collected: one flake collected directly on the silt of the “wall”; two diaphyses of proboscid in the colluviums; again choppers and flakes, either in the silt, on the slopes or on the surface, a maxillary of Hexaprotodon, many splinters of tusks and in the western sector, the important accumulation of quartzite cobbles. Other fossils complete the collection of Masol 2 (Moigne et al., 2016).

Two trial trenches A1 and B1 have been dug in this sector in order to verify whether choppers and flakes could be in situ near the Hexaprotodon (trench A1) and nearby the quartzite cobbles occurring on the surface (trench B1) (Fig. 6 and Fig. 7).

The trial trench A1 (1 × 2 m) was dug in silt E and excavated to the top of sandstone F. The lithostratigraphic sequence comprises 5 levels, from the top to the bottom: the humic surface, the silt E divided into 3 sublayers, and the top of the unit F (Fig. 8). The layer L1 is rich in blocks of sandstone. The layer L2 is the silt E in situ with many gravels and provided two quartzite cobbles, one with a broken surface (Fig. 8); downwards the silt becomes lumpy and compact until the grey sandy silts F. The trench provided 10 fragmented fossils in each layer but no artefact. Details are given in Fig. 9. The significant observation is the presence of quartzite cobbles in silt E.

The trench B1 (2 × 2 m) (Fig. 10) was excavated a few meters beyond trench A1, by following the dip toward the western limit of the depression, in a small bank of silt E covered by blocks of sandstone and many quartzite cobbles. The lithostratigraphic sequence is visible along the south-north section on 60 cm high, whereas along the west-east section the layers are beveled by the slope. The trench shows two layers: the upper layer L1 with blocks and nodules of sandstone and quartzite cobbles/pebbles in a silty matrix; the lower layer L2 is a wine-colored silt with some coarse elements in its upper part, while its lower part is lumpy and compact (Fig. 10). The latter corresponds to the silt unit E, the same as in the trench A1, and the layer L1 corresponds to the mixed sediments of the dismantled silt of unit D and sandstone of units C and B. The high concentration of quartzite cobbles and pebbles in L1, in the upper part of L2 and around the small bank, originates very probably from a dismantling of a localized lens of cobbles deposited during the silty phase D–E.

The trench B1 provided 10 very fragmented fossils and artefacts in quartzite in both layers described in Gaillard et al. (2016). In the layer L2, the artefacts are an end-chopper (Masol 2–17), a simple chopper with chipped edges (Masol 2–166), an obliquely broken cobble with chipped cutting edge (Masol 2–43) and a flake (Masol 2–133). Among the 10 fossils (Fig. 9), one is a fragment of upper molar from Hexaprotodon and another one is an abraded tooth of Equidae (Masol 2–B1–28) recorded in the lumpy silt (Fig. 11). As in the trench A1, the silt in situ is the base of the unit E with the unit F visible just below. Quartzite cobbles and the four artefacts were collected in the altered part of L2 capped by the colluviums (Fig. 10).

Masol 2-west is a depression leading the dip of the anticline towards the west at around meters 70 m below the trench B1 of Masol 2, (Fig. 3, number 5); many choppers and splinters, a few very well preserved bones in blocks of sandstone were collected on the outcrops composed of the yellow and brown silts D–E. This is the same configuration than Masol 2 but without clusters of quartzite.

The Masol 6 locality (M6) is located on the western side of the Pichhli watershed (Fig. 12). This sector of the Masol anticline presents one of the most complete sedimentary sequences. The topography is characterized by a succession of steps formed by cliffs capped by sandstone in alternation with silty series containing occasional sandy lenses. The lithostratigraphy described here includes Masol 6 and parts of the sequence below and above the locality proper on around 70 m thick after the combination of three sections: the lower is divided into 19 lithostratigraphic units, the middle in 26 units and the upper in 15 units.

Lithostratigraphic description of the lower section:

The lower section of 25 m thick begins at the Pichhli Choe and contains 19 lithostratigraphic units indexed from A+ to S+. It is characterized by an alternation of fine-grained sandstone and silts (Table 2, Fig. 13). The latter are thicker than the sandstones.

Lithostratigraphic description of the middle section:

The middle section 18 m thick is divided into 26 lithostratigraphic units and indexed from Z to A. From the units Z to T, the sequence is an alternation of sandstone benches and silts of pink, yellow, orange or brown color while the units from S to A are essentially silts where the subdivision is based on the colorimetry (Table 3, Fig. 14). The sedimentology and mineral composition are described in Abdessadok et al. (2016) and Tudryn et al. (2016).

Lithostratigraphic description of the upper section:

The upper section, 26.5 m in thickness, is divided into 17 lithostratigraphic units ranging from AA to AO and characterized by alternation of fine-grained grey sandstone with sedimentary structures, and pink and yellow silt. The silty sequence is thicker than the sandstone sequence (Table 4, Fig. 15).

Finally the composite log of Masol 6, 94 m thick, presents a recurrence of pink and yellow silts (Table 4). The lithostratigraphic units comprise thick silty layers intercalated with fine to medium-grained sandstones.

Fossil remains and archeology of Masol 6 Locality:

Masol 6 is the richest fossiliferous locality after Masol 1/Masol 2 due to its SE-NW extension along the silty plateau which borders the slopes below the crest. This narrow plateau is mainly composed of the silts of units D to U yielding fossils in situ such as the giant turtle Colossochelys recently unearthed, sometimes in block of sandstone. The fauna list includes many dermal plates of turtles Colossochelys, Geoclemys, Gavialis and three bones of Crocodylus, one of Hyena and one hemi-mandible of Panthera, broken tusks and long proboscid bones, Hexaprotodon, Sivatherium, bovids, cervids, one Equus, one tragulid Dorcatherium nagrii and two genera of Suidae (Moigne et al., 2016). The archeological material is quite abundant at Masol 6 with 50 large artefacts and 16 smaller ones (Gaillard et al., 2016). They were scattered on a highly dissected topography wider than Masol 2. They have been collected on the silty units from I+ to U (Fig. 13 and Fig. 14). One chopper was collected on the oldest silts F+ and G+.

The Masol 13 locality (M13) is a small hill on the eastern riverside of the Patiali Rao at the northern limit of the large bowl-shaped depression described above; the stratigraphic section has been drawn at the exact locality where the bovid splinter Masol 13 R10298 with cut-marks and stone tools have been collected in 2011 (Fig. 16). The 7 m thick section is subdivided into 4 units: unit A is a fine-grained sandstone rich in silt (4 m thick); unit B is a brown silt without lamination (0.60 m); unit C is a brown clay with greenish-grey marks without lamination (1.10 m) and unit D is a grey medium-grained sandstone, crumbling in ball-shaped lumps without structure of sedimentation (0.80 m). The sedimentology and mineral composition are described in Abdessadok et al. (2016).

Fossils remains and archeology of the Masol 13 locality

The cut-marked bovid splinter was collected on the silt C among blocks of the sandstone D and scattered quartzite cobbles. The list of faunal remains collected around the small mount includes 37 fossils with very few reptiles, crocodiles are missing, the majority are bovids (17) including Hemibos, and then Sivacapra, Stegodon, Hexaprotodon, Sivatherium and Cervus punjabiensis (Moigne et al., 2016).