Siwalik Group Research Articles

Morpho-tectonic control on the distribution of C3-C4 plants in the central Himalayan Siwaliks during Late Plio-Pleistocene

The Siwalik deposits of the Himalayan foreland basin (HFB) preserve the Late Miocene-Pleistocene record of the Himalayan tectonics, monsoonal variation and the expansion of C4 plants. Previous vegetation reconstructions emphasized the Late Miocene expansion of C4 plants with an implicit assumption that the vegetation thrived in the floodplain of lowland rivers. The coarsening-upward sequence of the Siwalik Group suggests deposition in an alluvial fan setting in which the Lower and Middle Siwaliks are deposits of distal region whereas the Upper Siwaliks represents a proximal region of the fan. The modern alluvial fans forming in the Himalayan foothills show a significant difference in elevation (ca. 300 m) and vegetational composition between their proximal and distal regions. In the HFB, the elevation difference is expected to be more pronounced due to the surface uplift of Siwalik deposits along the Himalayan Frontal Thrust (HFT). The increased elevation would have affected the vegetation distribution in the Upper Siwaliks which implies that the vegetation in the proximal part of the fan might not represent lowland floodplain. However, the vegetation composition is less understood from the Upper Siwaliks region due to the scarcity of conventional proxies in these younger foreland deposits.In this context, δ13C values of bulk soil organic matter (SOM), n-alkane and n-alkanoic acid in the paleosols were measured from Late Mio-Pleistocene Siwaliks at Surai Khola (Nepal) to comprehend the impact of elevation on vegetation distribution in the HFB. The results suggest most commonly observed expansion of the C4 plants at ca. 7 Ma, and a unique second phase of expansion of C3 plants post-3 Ma. The higher δD values of n-alkane and n-alkanoic acid suggest that the climate was drier in the last 4 Myr; most likely driven by the onset of the Northern Hemisphere Glaciation (NHG). The growth of C3 plants was favored due to cool climatic conditions induced by a higher elevation in the proximal part of the fan. Water-bearing conglomerates in the Upper Siwaliks may have helped the C3 plants to thrive in a relatively drier climate. This multi-proxy paleovegetation reconstruction demonstrates a morpho-tectonic control on the abundance of C3-C4 plants in the Siwaliks with the possible influence of NHG.

Miocene hyaenids (Hyaenidae; Carnivora) from Siwaliks of Pakistan

Newly discovered Miocene hyaenid specimens, recently collected from the Siwalik Group, are described and discussed. A careful comparison with the known material reveals that these specimens belong to the early hyaenid species Thalassictis cf. T. proava, Ictitherine indet. and Lepthyaena sivalensis. The stratigraphic range of T. proava extended up to the Dhok Pathan Formation (Middle Miocene to Early Pliocene). The stratigraphic range of T. proava comprises the Middle to Late Miocene, with the youngest record in Hasnot, Potwar Plateau in the Siwalik Group. The material is of great interest because Siwalik carnivoran material is rare.

New remains of Elephantidae from the Upper Siwalik subgroup (Plio-Pleistocene) of Pakistan

The Siwalik sequence saw the appearance and spread of the family Elephantidae in the Indian subcontinent during the Plio-Pleistocene epochs. Elephas flourished and underwent species turnover during the Plio-Pleistocene of the Siwalik Group. The newly discovered specimens include serially arranged M2-3 and partial maxillary fragment with M2 of Elephas planifrons, and M3 and partial dp4 of Elephas hysudricus from the Pinjor Formation (Pleistocene) of the Siwaliks. A tusk from the Tatrot Formation (Pliocene) of the Siwaliks, has been assigned to Elephantoidea indet. Based on the comparison with the stratigraphically well-dated mammalian fauna from the various Siwalik localities of the Indian subcontinent, the age of Sardhok, Panjan Sher Shahana and Kurla Sharif range is suggested to be from the Late Pliocene (Piacenzian) to Late Early Pleistocene (Calabrian), and a savannah like environment is suggested for these localities.

Geology of the area between Bardibas and Sindhuli Madi, Sub-Himalaya, Central Nepal

The Siwalik Group (Sub-Himalaya) is the east-west extending youngest mountain belt formed by the sediments derived from the rising Himalaya on the north. The Siwalik Group is separated from the Lesser Himalaya to the north by the Main Boundary Thrust (MBT), and the Indo-Gangetic Plain to the south by the Main Frontal Thrust (MFT). The study was carried out mainly along the Ratu Nadi, Kamala Nadi river sections and was lithostratigraphically divided into the Lower Siwalik, Middle Siwalik, and Upper Siwalik, from the bottom to the top section, respectively. The Lower Siwalik is composed of fine-grained greenish grey calcareous sandstone (subarkose and lithic arenite), variegated mudstone, and calcareous siltstone. The Lower Siwalik is exposed due to the Marine Khola Thrust in the Gadyauli Khola, and sandstone there is more indurated and non-calcareous. The Middle Siwalik is mainly comprised of the medium- to coarse-grained salt-and-pepper sandstone (arkose and subarkose) with large cross lamination, calcareous sand lenses, convolute bedding, dark grey siltstone and mudstone. Plant fossils are also present in the finely laminated clay bed of the Middle Siwalik along the Ratu Nadi section. The Upper Siwalik comprises of mud- to sand-supported pebble to cobble conglomerates.

Stress regime changes in the Main Boundary Thrust zone, Eastern Himalaya, decoded from fault-slip analysis

The Main Boundary Thrust (MBT) Zone in the Darjeeling foothills, Eastern Himalaya exhibits northerly dipping fault splays, named here as MBT-1 and MBT-2, with Proterozoic Daling Group in the MBT-1 hanging wall, Upper Paleozoic Gondwana rocks between the MBT-1 and the MBT-2, and Neogene Siwalik Group in the footwall of the MBT-2. On the basis of reduced stress tensors from fault-slip analysis and their grouping relative to different stratigraphic units in the MBT zone that crops out over a strike length of ∼20 km, the following successive stress regimes have been interpreted. The earliest brittle deformation recorded only in the basal part of the Gondwana succession was controlled by a pre-Himalayan NW-SE extensional regime. The Himalayan deformation under sustained N-S compressive regime developed in three stages: (a) thrust displacement along the MBT-1, juxtaposing folded Daling rocks against the Lower Gondwana rocks; (b) tilting and fracturing of Lower Gondwana succession and thrust transport over the Siwalik rocks along the MBT-2; (c) strike-slip regime with NW- and NE-trending faults affecting both the Lower Gondwana and Siwalik strata, developed possibly due to increased tectonic loading. The tensor solutions under N-S compressional regime are consistent with the modern plate convergence, supporting a foreland propagating thrust system in the Eastern Himalaya. In addition, an E-W extensional regime led to apparent orogen-parallel extension.

The youngest occurrence of Hexaprotodon Falconer and Cautley, 1836 (Hippopotamidae, Mammalia) from South Asia with a discussion on its extinction

The earliest hippopotamid fossils from the Indian Subcontinent come from the Miocene of the Siwalik Group. South Asian hippopotamidae are represented by the genus Hexaprotodon, and remains of these hippos are commonly found in Neogene and Quaternary sites. Here we report on the first directly dated specimen of Hexaprotodon sp. from the Narmada Valley of Central India and its associated paleoecological implications. The specimen, an upper right canine fragment, was dated to 16,467–15,660 cal BP using accelerator mass spectrometry radiocarbon dating method. This individual lived during Heinrich Event 1, a particularly arid period. Isotopes from dental enamel revealed this animal to have lived in a savanna environment, and likely experienced a shortage of water. Using other dated remains of Hexaprotodon from the Indian Subcontinent, we developed a tentative extinction chronology, which showed that Hexaprotodon likely survived into the Early Holocene. We hypothesize that a combination of climatic stress and anthropogenic impacts would have caused the species’ eventual extinction.

Grassland fire ecology has roots in the late Miocene

That fire facilitated the late Miocene C4 grassland expansion is widely suspected but poorly documented. Fire potentially tied global climate to this profound biosphere transition by serving as a regional-to-local driver of vegetation change. In modern environments, seasonal extremes in moisture amplify the occurrence of fire, disturbing forest ecosystems to create niche space for flammable grasses, which in turn provide fuel for frequent fires. On the Indian subcontinent, C4 expansion was accompanied by increased seasonal extremes in rainfall (evidenced by δ18Ocarbonate), which set the stage for fuel accumulation and fire-linked clearance during wet-to-dry seasonal transitions. Here, we test the role of fire directly by examining the abundance and distribution patterns of fire-derived polycyclic aromatic hydrocarbons (PAHs) and terrestrial vegetation signatures in n-alkane carbon isotopes from paleosol samples of the Siwalik Group (Pakistan). Two million years before the C4 grassland transition, fire-derived PAH concentrations increased as conifer vegetation declined, as indicated by a decrease in retene. This early increase in molecular fire signatures suggests a transition to more fire-prone vegetation such as a C3 grassland and/or dry deciduous woodland. Between 8.0 and 6.0 million years ago, fire, precipitation seasonality, and C4-grass dominance increased simultaneously (within resolution) as marked by sharp increases in fire-derived PAHs, δ18Ocarbonate, and 13C enrichment in n-alkanes diagnostic of C4 grasses. The strong association of evidence for fire occurrence, vegetation change, and landscape opening indicates that a dynamic fire-grassland feedback system was both a necessary precondition and a driver for grassland ecology during the first emergence of C4 grasslands.

First record of the Miocene hominoid Sivapithecus from Kutch, Gujarat state, western India.

Hominoid remains from Miocene deposits in India and Pakistan have played a pivotal role in understanding the evolution of great apes and humans since they were first described in the 19th Century. We describe here a hominoid maxillary fragment preserving the canine and cheek teeth collected in 2011 from the Kutch (= Kachchh) basin in the Kutch district, Gujarat state, western India. A basal Late Miocene age is proposed based on the associated faunal assemblage that includes Hipparion and other age-diagnostic mammalian taxa. Miocene Hominoidea are known previously from several areas of the Siwalik Group in the outer western Himalayas of India, Pakistan, and Nepal. This is the first record of a hominoid from the Neogene of the Kutch Basin and represents a significant southern range extension of Miocene hominoids in the Indian peninsula. The specimen is assigned to the Genus Sivapithecus, species unspecified.

Palaeoclimatic estimates for a latest Miocene-Pliocene flora from the Siwalik Group of Bhutan: Evidence for the development of the South Asian Monsoon in the eastern Himalaya

Fossil leaf floras, from the latest Miocene-Pliocene Siwalik Group exposed in Bhutan, sub-Himalaya, are subjected to a CLAMP (Climate Leaf Analysis Multivariate Program) analysis using a high-resolution gridded climate calibration. The CLAMP analysis of 27 different morphotypes of fossil leaves indicates a mean annual temperature (MAT) of 24.1 °C ± 2.8 °C; a cold month mean temperature (CMMT) of 18.9 °C ± 4 °C and a warm month mean temperature (WMMT) of 27.8 °C ± 3.3 °C. The analysis also suggests a weak monsoonal climate (the monsoon index, MSI 46.7; present MSI 52) with growing season precipitation (GSP) of 1819 ± 916 mm (present GSP 2490 mm). Here we also compare palaeoclimate estimates of the latest Miocene-Pliocene Siwalik Group flora from Bhutan (c. 6 to 3.8 Ma) with those of previously investigated Siwalik Group floras from the Miocene-Pleistocene of Arunachal, India and Miocene Siwalik floras of Darjeeling, India which characterise the monsoon signature at the time of deposition. Since all the Siwalik floras of the eastern Himalaya (Darjeeling and Arunachal Pradesh) spanning the mid-Miocene to Pleistocene yield almost the same values we suggest that overall the eastern Himalayan Siwalik climate appears to have been remarkably uniform over the past 15 million years. The MAT result of the Bhutan Siwalik flora differs by just 0.6 °C from Arunachal and 1.2 °C from Darjeeling Siwalik floras. For all Siwalik fossil assemblages, WMMTs, CMMTs and LGSs (length of the growing season) are similar and consistent (WMMTs around 28 °C, CMMTs around 18 °C and LGSs around 12 months). Similarly, the mean annual relative humidity (RH) and specific humidity (SH) appear to have been uniformly around 80% and 14 g/kg respectively throughout the Neogene of the eastern Himalayan Siwaliks. Changes in the monsoon index suggest that in both Bhutan and Arunachal sub-Himalaya, there has been little change in the intensity of the monsoon since mid-Miocene time, while further west in the Darjeeling area precipitation seasonality has increased since the mid-Miocene.

Substrate control of C4 plant abundance in the Himalayan foreland: A study based on inter-basinal records from Plio-Pleistocene Siwalik Group sediments

Data from different parts of the globe including the Himalayan foreland suggest that the expansion of C4 plants was not synchronous and hence invoke influences of regional factors on C4 plants evolution. The disparity in the abundance of C4 plants across different regions of the Kangra sub-basin, NW Himalaya, has been attributed to variation in grain size of the substrate and its moisture content. In the absence of vegetation and climate data from the Upper Siwaliks of the Kangra sub-basin, the present study considers the adjacent Subathu sub-basin. The δ13C values of soil carbonate nodule (SC) from the Ghaggar and Moginanda regions and fossil tooth enamel from the Haripur Khol region of the Subathu sub-basin have been measured and compared to data from the other Siwalik regions to assess the spatio-temporal distribution of C4 plants. Additionally, the δ18OSC values have been evaluated to reconstruct local climatic conditions. Stable carbon and oxygen isotope data from SC across the Siwaliks indicate that climate was not the only driver influencing the C4 plant abundance.Comparison of the sedimentary architecture among the different Siwalik regions indicates that the abundance of overbank fine sediments is higher in the western Siwaliks than the central and eastern Siwaliks. The δ13C values and abundance of overbank fine sediments across different Siwaliks suggest a significant influence of substrate on the abundance of C4 plant in the Himalayan foreland.

Formation of a Rain Shadow: O and H Stable Isotope Records in Authigenic Clays From the Siwalik Group in Eastern Bhutan

AbstractWe measure the oxygen and hydrogen stable isotope composition of authigenic clays from Himalayan foreland sediments (Siwalik Group), and from present day small stream waters in eastern Bhutan to explore the impact of uplift of the Shillong Plateau on rain shadow formation over the Himalayan foothills. Stable isotope data from authigenic clay minerals (<2 μm) suggest the presence of three paleoclimatic periods during deposition of the Siwalik Group, between ∼7 and ∼1 Ma. The mean δ18O value in paleometeoric waters, which were in equilibrium with clay minerals, is ∼2.5‰ lower than in modern meteoric and stream waters at the elevation of the foreland basin. We discuss the factors that could have changed the isotopic composition of water over time and we conclude that (a) the most likely and significant cause for the increase in meteoric water δ18O values over time is the “amount effect,” specifically, a decrease in mean annual precipitation. (b) The change in mean annual precipitation over the foreland basin and foothills of the Himalaya is the result of orographic effect caused by the Shillong Plateau's uplift. The critical elevation of the Shillong Plateau required to induce significant orographic precipitation was attained after ∼1.2 Ma. (c) By applying scale analysis, we estimate that the mean annual precipitation over the foreland basin of the eastern Bhutan Himalayas has decreased by a factor of 1.7–2.5 over the last 1–3 million years.

An ichnofossil assemblage from the fluvial deposits of the Upper Pliocene–Pleistocene Pinjor Formation (Siwalik Group), northwestern Himalayas, India: Palaeoenvironmental implications

Continental (fluvial) strata of the Pinjor Formation (Siwalik Group), northwestern Himalayas, India, contain an invertebrate trace fossil assemblage containing Planolites beverleyensis, Palaeophycus isp., Scoyenia gracilis, Taenidium barretti and other undifferentiated traces. The traces are found in an \(\sim \)26 m thick interval of alternating pinkish red siltstone, which is intercalated with mudstone, and thickly-bedded buff and greenish coloured sandstone. These sediments are interpreted as the deposits of floodplains and channel-bars of fluvial environments and low-energy overbank floodplain deposits. The trace fossils studied here are the first well documented ichnofossil assemblage from the vast, late Cenozoic Siwalik depositional system. They are not only of palaeoenvironmental significance, but they add to the growing ichnofossil database in facies of fluvial origin and should be an impetus to further ichnological studies of the Siwalik Group.

Landslide susceptibility assessment of the Chure Khola Catchment area of the Siwalik region, Central Nepal

Landslide susceptibility analysis is carried out in the Chure Khola Catchment, between Amlekhganj and the Churia Mai Range of the Bara District, covering area of 20 sq. km. The catchment lies in the Siwalik Hills composing the Siwalik Group of rocks of Middle Miocene to Early Pleistocene age. Owing to the week and fragile geology, the Siwalik Hills are prone to the gully erosion, shallow landslide and debris flow, during the heavy rain storms in monsoon seasons. In the present study, landslide susceptibility assessment was carried out using two methods, rapid field-based assessment and statistical index methods. For the susceptibility mapping of the river bank slopes, field- based method was used. The seven parameters such as slope angle, slope material, reduction to groundwater, effect of drainage, effect of past failure, effect of vegetation cover and effect of land use were used to calculate the factor of safety in the field. The slope areas were classified as highly susceptible (FS<0.7), susceptible (0.7<FS<1), marginally stable (1<FS<1.2) and stable (FS>1.2) categories, and finally, a susceptibility map was prepared. For the total 4.179 sq. km area where rapid field-based assessment was carried out, the areas covered by highly susceptible, susceptible, marginally stable and stable zones are respectively, 21.56%, 22.11%, 17.37% and 38.95%. Among the highly susceptible and susceptible zones identified, 71% sites have experienced recent slope failures. Landslide susceptibility mapping of the whole catchment area was prepared using statistical index method, and considering seven causative parameters such as elevation, slope, slope aspect, curvature, river proximity, stream density and lithology, which were determined and prepared from DEM using Arc GIS. Eighty percent landslides were used as the training sample for the spatial analysis, whereas 20% landslides were used for the validation of the study. The landslide susceptibility map exhibits the areas covered by very high, high, moderate, low and very low susceptibility zones are 47.18%, 25.28%, 19.77%, 3.60% and 4.16%, respectively. Validity of the study was determined using Riemann Sums method. Success Rate Curve shows that 78.04 % of the areas lie under the curve. Evaluating susceptibility in small watershed is important to mitigate shallow landslide related problems and in rehabilitating forest areas in the Churiya Hills of Nepal.

Fossil wood flora from the Siwalik Group of Arunachal Pradesh, India and its climatic and phytogeographic significance

The plant fossil records from the Siwalik Group of Arunachal Pradesh, India are far from satisfactory due to remoteness and dense vegetation of the area. We report seven fossil woods of which three belong to the Middle Siwalik (Subansiri Formation), while the rest are from the Upper Siwalik (Kimin Formation). The modern analogues of the fossils from the Middle Siwalik are Lophopetalum littorale (Celastraceae), Afzelia-Intsia and Sindora siamensis (Fabaceae) and from the Upper Siwalik are Miliusa velutina (Annonaceae), Calophyllum tomentosum and Kayea (Calophyllaceae) and Diospyros melanoxylon (Ebenaceae). The dominance of diffuse porosity in the fossil woods indicates a tropical climate with low seasonality (little variation) in temperature, while a high proportion of large vessels and simple perforation plates in the assemblage infer high precipitation during the deposition of the sediments. The aforesaid inference is in strong agreement with the previous quantitative reconstruction based on fossil leaves. Several modern analogues of the fossil taxa are now growing in low latitudes possibly due to an increase in seasonality (increased variation) in temperature caused by the rising Himalaya.

Petrography of the Neogene Siwalik Group sandstones, Khutia Khola section, Nepal Himalaya: implications for provenance, paleoclimate and tectonic setting

The Neogene fluvial sediment (Siwalik Group) forming the southernmost foothill in the Himalaya is one of the best archives of climate history and uplift of the Himalaya. The petrographic composition of these fluvial sandstones provides information on source rocks, depositional climate of the Siwalik sediments and tectonic setting of the Himalaya. This study presents the petrographical results of the Siwalik sandstones from the Khutia Khola section, Nepal Himalaya. Petrographically, these sandstones are lithic arenites (30%) to sub-litharenites (70%). Provenance analyses show that sediments were mainly derived from recycled orogenic and transitional recycled areas in the recycled orogen block provenances. The climatic indexes suggest the semi-humid to humid climate during sedimentation of the Khutia Khola sandstones. The stratigraphic trend of the lithic components show that metamorphic lithic grains are increasing and sedimentary lithic grains are decreasing in up section, and the Lesser and Higher Himalayas are the mixed source of these Siwalik sandstones.

Middle Miocene small mammals from the Siwalik Group of Northwestern India

The freshwater Siwalik deposits of the Himalayan foreland basin have long been known to yield prolific Miocene-Pleistocene mammalian fauna. Overwhelming of this data comes from the Siwalik sequence of Pakistan, where good palaeomagnetic control is available for various Siwalik lithounits. In contrast limited data on fossil mammals, more so on small mammals, is available from the Indian side of the Siwalik, where even most of the Siwalik formations lack palaeomagnetic and or radiometric calibration, despite the fact that several fossil yielding localities are known in India since long. In the present research work, small mammals discovered from a Lower Siwalik locality near Ramnagar town in Jammu province, Jammu and Kashmir State, India are reported and their age implication is discussed. The mammal fauna from the study area contains four species of rodents belonging to four subfamilies. These include Rhizomyinae represented by Kanisamys indicus, Ctenodactylinae by Sayimys sivalensis, Myomiminae by Myomimus sp. and Xerinae by Tamias urialis. The recovered biotas improve our knowledge on the rodent diversity of the Indian Lower Siwalik Subgroup and contribute to further constrain the age of the fossiliferous horizon between 13.6 and 13.2 Ma. The new fauna suggests a humid, forested palaeoecological setting.

Siwalik-age faunas from the Himalayan Foreland Basin of South Asia

The Himalayan foreland basin is characterised by three principal sedimentary successions. These are the Subathu Group (Palaeocene-Eocene), the Murree or Dharamsala Group (Oligocene-Miocene) and the Siwalik Group (Miocene-Pleistocene). The basin was linked in the east to the Bay of Bengal through the Bengal Basin and its western part was connected to the Arabian Sea through Rajasthan and Kachchh, Gujarat. The Himalayan foothills have long been known for yielding rich mammalian fossil occurrences and significant localities in the Indian Siwaliks include Kalagarh, Ramnagar, Haritalyangar, Chandigarh and Jammu regions. The Bugti Basin and Zinda Pir area of Sulaiman Range of Pakistan were also part of the foreland basin, as Lower and Middle Siwalik fossils are known from the Vihowa and Litra formations, respectively. The Marwat Formation of Bhittani and Marwat Ranges, Pakistan have also yielded Pinjor-age vertebrate fossils. The Middle and Upper Siwalik-age fossils are also known from the Irrawaddy Formation of Myanmar, where older Pegu beds have also yielded scanty Lower Siwalik-age fossils. This faunal succession in the Irrawaddy Valley may have geologically and biogeographically belonged to the Himalayan foreland basin in the past. Additional mammalian fossils having an affinity with the Lower and Middle Siwaliks are known from the Khari Nadi Formation of Kachchh. The Bokabil Formation of Tripura also yielded scanty Lower to Middle Siwalik fossils. A younger Siwalik late Miocene assemblage is known from Piram Island of Gujarat. These areas are also part of the foreland basin. Most recently, a late Miocene suid species was discovered and reported from near Baripada, Odisha. The paper discusses the respective faunal lists of the various successions mentioned above. Finally, the paper discusses the implications of the foreland faunas. The faunas of Lower and Middle Siwaliks of foreland basin have links with Europe, Turkey, Africa and Central Asia and throw light on the uplift of the Himalaya. The post-Siwalik faunas of central and Peninsular India and Indo-Gangetic Plains have also yielded remnant Siwalik taxa, including Stegodon insignis, Elephas hysudricus and Potamochoerus theobaldi. The Kurnool Cave Fauna and Recent Fauna of India have also generic resemblance with the foreland faunas.

Weathering in the Himalaya, an East-West Comparison: Indications from Major Elements and Clay Mineralogy

Studying past weathering regimes is important for a better understanding of the influence of climate on weathering, erosion, and runoff. The Himalayan foreland basin contains a record of tectonics and paleoclimate since Miocene times. Spanning the entire mountain range, the Mio-Pliocene detrital Siwalik Group allows studies to directly compare the western and eastern Himalaya within similar sedimentary settings. In this study, we use major elements and clay mineralogy to reconstruct the weathering regime along strike since Miocene times. We studied previously dated Dharamsala (pre-Siwalik) and Siwalik sections in the western (Joginder Nagar, Jawalamukhi, and Haripur Kolar) and eastern (Kameng) Himalaya in order to constrain variations in weathering regimes along strike. The compilation of the three sections in the west makes for one of the longest continuous sedimentary records in the Himalaya, spanning over 20 My. The K/Al ratio is used as a reliable weathering proxy and shows a trend toward more intense weathering over time in both the west and the east, but with sediments in the western Himalaya generally more weathered than those in the east, despite higher precipitation in the east. Clay minerals and major elements indicate similar lateral variations in weathering. More intense weathering in the west is linked to a more seasonal climate, permitting weathering of sediments during the dry season, whereas higher runoff in the east leads to more rapid erosion and sediment transport, inhibiting extensive weathering.

Early Late Miocene Murine Rodents from the Upper Part of the Nagri Formation, Siwalik Group, Pakistan, with a new fossil calibration point for the Tribe Apodemurini (Apodemus/Tokudaia)

Abstract The early late Miocene is an interval of increased diversification for murine rodents. Whereas the genus Progonomys became widespread throughout Eurasia by 10 Ma, it appears from the known paleontological record that southern Asia is the arena of evolution and diversification at the base of the Murinae. The Siwalik fossil record of the Potwar Plateau in northern Pakistan preserves fossil evidence relevant to unraveling this history. Murine rodents are recorded there throughout the middle Miocene, and diversification began in Siwalik assemblages before 11 Ma. The well-established Progonomys and Karnimata lineages were already present between 11 and 10 Ma, and these represent extant murine crown groups. Here we document diversity in Siwalik murines dating to 10.5 to 10.1 Ma, and clarify their recognition by naming a new species of Karnimata and referring specimens of Progonomys from this interval to P. hussaini. In addition, we define at least two other uncommon murine species that coexist with them. One of these is an early record of Parapodemus, a fossil genus of Tribe Apodemurini, which constitutes a calibration point for the Apodemus/Tokudaia split. Together, these fossil taxa provide further evidence bearing on the major split among murines leading to the clades Murini and Arvicanthini.

Freshwater Ostracods from the Siwalik (Churia) Group of Nepal

Freshwater Ostracods from the Siwalik (Churia) Group of Nepal