Siwalik Sediments Research Articles

Calophyllum L.: An important tropical element in the monsoon-influenced ancient Siwalik Forest of eastern Himalaya

Calophyllum vegetative (leaves and woods) fossil remains have been widely reported from the Cenozoic sedimentary strata across the Northern and Southern Hemispheres. However, until now, no reproductive megafossil remains have been discovered. Here, we report and describe Calophyllum fossil fruits from the Siwalik (middle Miocene–Pliocene) sediments of Darjeeling foothills, eastern Himalaya for the first time. In addition, we also provide fossil materials of isolated leaves in appreciable numbers recovered from the same stratigraphic level. Our Siwalik fossils and extant members of Calophyllum are closely related morphologically by stalked, ball-shaped (spherical to ovoid) drupe with a thin, dark brown, smooth surfaced outer layer and a hard endocarp; and symmetrical, oblong-elliptic shaped entire margined lamina with numerous close parallel secondary veins, and obscure tertiary veins. Based upon morphology and epidermal anatomy, the fossil fruits are recognized as a new fossil-species Calophyllum ramthiensis sp. nov. The present Calophyllum leaf and fruit fossils, along with previous reports suggest that Calophyllum was an important forest element throughout the eastern Himalaya during the period of Siwalik sedimentation (Mio-Pleistocene time). We briefly discuss the fossil history of Calophyllum and palaeobiogeography in India and palaeoclimatic implications regarding the distribution and habitat of fossil and modern members of Calophyllum.

A new epifoliar melioloid fungus from the Siwalik (Miocene) of Himachal sub-Himalaya and its palaeoecological implications

A new fossil epifoliar ascomycete (Ascomycota), Meliolinites miocenicus nov. sp. (fossil Meliolaceae), occurs in situ on a compressed monocot leaf from middle Siwalik (Late Miocene, ca. 12–8 Ma) sediments of Himachal Pradesh, Western Himalaya. The fossil consists of a well-preserved mycelium of superficial, brown to dark brown, septate, thick-walled, branched hyphodiate hyphae; a sub-globose, dark brown putative ascoma, and an oblong to broadly cylindrical, five-celled, four-septate, mature germinating ascospore. The new fossil differs from earlier reported melioloid fossils primarily in the morphology of appressoria. Meliolinites miocenicus nov. sp. on its host is evidence of the existence of a biotrophic relationship at the time of deposition. Qualitative climate data using plant megafossils recovered from the same fossil locality indicate that M. miocenicus nov. sp. and its host thrived in a warm and humid tropical environment.

New records for the Middle Siwalik flora of eastern Nepal and their climatic significance

The Siwalik plant fossils are important in understanding the climate change caused by the uplift of the Himalaya. The plant fossil assemblages are abundantly known from Nepal's central and western Siwalik sediments. However, they are poorly known from the Siwalik of the eastern region from where the modern Indian Summer Monsoon (ISM) enters Nepal. That is why fossils of this region are important in understanding the evolutionary history of ISM in Nepal. In the present communication, we report four new fossil leaf impressions/ compressions, namely Thelypteridaceophyllum tertiarum Joshi and Mehrotra of the family Thelypteridaceae, Calophyllum suraikholaensis Awasthi and Prasad of the Calophyllaceae, Albizia siwalica Prasad of the family Fabaceae, and Daphnogene makumensis Mehrotra, Dilcher et Lott of the family Lauraceae from the well-dated Middle Siwalik (∼9.5 Ma) sediments of eastern Nepal. The aforementioned and previous fossil records suggest that seasonal or monsoonal rainfall was present during the deposition of the sediments.

Fossils can reveal a long-vanished combination of character states: Evidence from a mysterious foliicolous anamorphic fungus from the Middle Siwalik (Late Miocene) of Himachal Pradesh, India

ABSTRACT Fossils can unveil a long-vanished combination of character states that inform inferences about the timing and patterns of diversification of modern fungi. By examining the well-preserved stacked chained vesicular conidiophores developed in clusters from the basal stroma, we describe a new taxon of fossil Zygosporiaceae with a combination of characters unknown among extant taxa on compressed serrated-margined dicot leaf (cf. Fagaceae) recovered from the Siwalik sediments (Late Miocene; ca. 12–8 Ma) of Himachal Pradesh, western Himalaya. Based upon conidiophore morphology, our Siwalik fungal remains, similar to Zygosporium Mont. (Zygosporiaceae: Xylariales: Sordariomycetes), are recognized as a new fossil species, Z. stromaticum Kundu & Khan, sp. nov. Zygosporium stromaticum is the only known fossil anamorphic fungus that occurs on plant cuticles and has a cluster of stacked chained vesicular conidiophores arising from a poorly preserved basal stroma formed by irregular, thick-walled cells. Its combination of morphological characteristics is unknown in extant fungal taxa, so Z. stromaticum likely represents a new anamorphic foliicolous fungus that may now be extinct. This unique evidence may be essential for the calibration of divergence time estimations of fungal lineages.

A new foliicolous fossil-species of Asterina Lév. (Asterinaceae; Asterinales) associated with Calophyllum L. from the Siwalik of Eastern Himalaya and its implications

The present study reports and describes a new foliicolous fossil-species of Asterina Lév. (Asterinaceae: Asterinales: Dothideomycetes) namely, A. siwalika sp. nov., on a compressed leaf assigned to modern Calophyllum L. (Calophyllaceae) recovered from the Siwalik sediments (early Miocene to Pliocene: Chunabati Formation) of Darjeeling, Eastern Himalaya. This epifoliar Siwalik fungal species is characterized by a dark brown, sub-dense mycelial mat; septate, branched, superficial, oppositely arranged hyphae with one to two-celled, alternate to oppositely arranged appressoria; flattened, circular, non-ostiolate thyriothecia, scutellum with radially arranged isodiametric to cylindrical cells; and bi-celled, one-septate, conglobate to ellipsoidal, striated ascospores. Here, we reconstruct for the first time a possible sexual life cycle of A. siwalika. The in-situ occurrence of Asterina on Calophyllum leaf cuticles suggests a warm and humid tropical climate and a possible host-parasitic relationship that might have existed in the ancient forest of the Darjeeling sub-Himalaya region during the time of deposition. The conclusion is supported by published qualitative and quantitative climatic data using plant megafossils recovered from the same fossil locality.

Fig leaf from the Middle Siwalik sediments of eastern Nepal with implication on biogeography and palaeoclimate

The Siwalik flora is important in understanding the orogeny of the Himalayas and the resulting climate change. Though the fossil records from the eastern Himalayan Siwalik of Nepal are sparse, we report a fossil leaf impression/ compression of Ficus precunea Lakhanpal from the Middle Siwalik (upper Miocene–lower Pliocene) sediments of eastern Nepal. The characteristic leaf venation pattern and morphological details suggest its strong affinity with the extant species of F. semicordata Buch.-Ham. ex Sm. The fossil assemblage indicates the presence of seasonal forests during the depositional period in the region.

The first evidence of saprophytic Tetraploa on Siwalik (Late Miocene) monocot leaf from western Himalaya and its role in palaeoecology reconstruction

Even though the records of Tetraploa spores from Mesozoic and Cenozoic sedimentary strata along with spore-pollen assemblages are numerous and well documented, no foliicolus Tetraploa macroconidia have been reported to date. Here, we report the first occurrence of conidia assignable to modern Tetraploa Berk. & Broome (Tetraplosphaeriaceae: Pleosporales: Dothideomycetes) on cuticular fragments of compressed monocot leaf recovered from the middle Siwalik sediments (Late Miocene; 12–8 Ma) of Himachal Himalaya, India. We determine their taxonomic position based on detailed macromorphological comparison with similar modern and fossil taxa and discuss their palaeoecological significance in terms of the present-day ecological conditions of modern analogues. This finding also represents an essential data source for understanding Tetraploa's evolution and diversification in deep time.

First report of fossil representative of Zygosporium mont. With stacked chained vesicular conidiophores from India

In the present manuscript, we describe and illustrate a novel foliicolous fossil-species of Zygosporium Mont. (Zygosporiaceae: Xylariales: Sordariomycetes) on compressed monocot leaf recovered from the Middle Siwalik sediments (Late Miocene) of Himachal Pradesh, western Himalaya. The new fossil-species characterized by macronematous, dark brown, unbranched or occasionally branched conidiophores with a chain of up to four integrated dark brown, curved, thick-walled, swollen, hook-like, alternately or sub-oppositely arranged vesicles is described here as Zygosporium himachalensis sp. nov. This is the first fossil evidence of Zygosporium having stacked chained vesicular conidiophores and is so significant data for both paleomycologists and mycologists. The in-situ occurrence of Z. himachalensis on monocot leaf cuticles suggests a possible host–saprophyte relationship that might have existed in the ancient forest of Himachal Pradesh during the Miocene.

Triplinerved cinnamon from the Siwalik (middle Miocene) of eastern Himalaya: Systematics, epifoliar fossil fungi, palaeoecology and biogeography

Cinnamomum Schaeffer (avocado, family Lauraceae), commonly known as cinnamon tree, is a highly diverse, economically important evergreen element of tropical and subtropical regions of the world. In the present work, several compressed leaf remains similar to modern leaves of Cinnamomum are recovered from the lower part of the Siwalik strata (middle Miocene) of Darjeeling foothills, eastern Himalaya. The fossil specimens are characterized by an elliptic to ovate lamina, acute to short acuminate apex, round to acute base, basal as well as suprabasal acrodromous type of primary venation, and anomocytic type of stomata. Based on leaf architecture (macro- and micromorphological features) and using leaf epidermal anatomy, these Siwalik fossil leaves are confidently assigned to the genus Cinnamomum and are recognized as a new species: C. miocenicum Mahato, Hazra et Khan. The evidence of current Siwalik specimens and earlier-reported fossil species similar to thermophilic Cinnamomum in appreciable numbers from other Siwalik localities (Darjeeling, Uttarakhand, and Nepal) suggests that Cinnamomum was a common Siwalik element, pointing toward the existence of tropical, warm and humid climate conditions during the Siwalik sedimentation time. This conclusion is also supported by epifoliar fungal remains recovered from cuticular fragments of this lauraceous taxon. This finding also represents an essential source of data for understanding Cinnamomum’s evolution and deep time diversification. We review in detail the biogeographic history and suggest possible migratory routes of the genus from an Asian perspective.

The Potwar Siwaliks: an impressive Neogene record of terrestrial rocks and fossils

Abstract Outcropping sedimentary deposits of the Potwar Plateau in northern Pakistan comprise the most complete record of Neogene Siwalik rocks and faunas to be found in the Indian subcontinent documenting an extraordinary record of terrestrial vertebrate fossils for the Miocene Epoch. The Potwar Plateau is a portion of the Siwalik Hills, the mountainous terrane of the outer Himalayas extending over 2000 km across the northern margin of the Indian subcontinent. Siwalik strata accumulated as a molassic sedimentary wedge shed southward with the erosion of the rising crust as it was uplifted via plate tectonics. The long Potwar record of numerous superposed assemblages of fossil vertebrates preserves a history spanning many millions of years, and constitutes a unique geoheritage resource for Asia and for the world. The record can be dated and interpreted with a high degree of precision rarely achieved in terrestrial settings. The Potwar Siwalik sediments document 18 million years of change in the subtropical ecosystem of South Asia, in which global to regional climate change directly impacted terrestrial palaeofloras and palaeofaunas, forcing coevolution of elements of the terrestrial food web, and with that the modernization of mammalian groups. The potential to trace coincidence of abiotic changes with evolution within lineages is unusual.

Hyperconcentrated floods cause extreme gravel transport through the sandy rivers of the Gangetic Plains

The Gangetic Plains comprise steep gravelly river channels that transition to low gradient sandy channels 10-40 km downstream of the mountain front. This “gravel-sand transition" is characterized by an abrupt greater-than-one-order-of-magnitude drop in both gradient and sediment grain size, suggesting a degree of long-term stability. However, the stratigraphic record of the gravel-sand transition in the Miocene Siwalik Group demonstrates intermittent transport of coarse gravels tens of kilometres downstream of the transition; such events in contemporary channels would drive channel avulsion(s) and increase flood risk, devastating communities across the plains. We combine sedimentological analysis of Siwalik deposits with entrainment calculations which demonstrate that hyperconcentration is required to transport coarse bedload over low-gradient plains. Transport conditions are attainable when intense monsoon precipitation (a 200- to 1000-year event) is combined with increased suspended sediment concentrations in channels. Predicted climate change and ongoing seismicity increase the likelihood of such extreme events within this century.

Fossil Species of Lagerstroemia and Millettia from Miocene Strata of the Sarkaghat Region in the Sub-Himalayan Zone of Himachal Pradesh, India, and their Palaeobotanical Inferences

Palaeobotanical investigations were conducted on plant macrofossils obtained from the Middle Siwalik sediments of Sarkaghat, Mandi District, Himachal Pradesh, India as part of this current communication. This study discovered the existence of two previously unknownfossil species that correspond to the taxa that are now living, Lagerstroemia Linn. and Millettia Wight & Arn. of the families Lythraceae and Fabaceae, respectively. These modern comparable taxa of the macrofossils reported here are distributed in the tropical evergreen tomoist deciduous forests of the south-east Asian region which may suggest that tropical forests under moist conditions were prevalent during the Upper Miocene times in this region in contrast to mixed deciduous forest under the reduced precipitation at present. It alsoindicates the prevalence of a humid tropical climate during the Miocene in the Sarkaghat area.

Mio‐Pliocene exhumation of the hinterland and sediments provenance of the Neogene strata from Kumaun Himalaya of northwest India: Insights from detrital fission‐track thermochronology

Fission‐track (FT) thermochronological analysis of detrital apatite and zircon derived from the lower and middle Siwalik Group of the sub‐Himalaya allows the reconstruction of the long‐term exhumation history of the Higher Himalayan Crystalline (HHC) and Lesser Himalayan Sequence (LHS), and also the provenance of the Siwalik sediments. Here, we report 14 detrital apatite and zircon fission‐track (AFT/ZFT) ages of lower and middle Siwalik subgroups of the Kumaun region, northwest Himalaya. Detrital FT ages suggest that all sandstone samples were never buried below the temperature range of 90° to 100°C and remained as unreset to retain a signal of source‐area exhumation. A detrital AFT age from sandstone sample at close proximity to the Main Boundary Thrust (MBT) is 4.4 ± 0.5 Ma (Pliocene time) which is completely reset and younger than the depositional age, while the detrital ZFT ages of the same sample are unrest. The AFT age represents the time of reactivation of the MBT during which ZFT ages were not affected. This study revealed that the provenances of Siwalik sediments are located majorly in the MBT hinterland areas and the nearest sources are Amritpur granite, the outer Lesser Himalayan meta‐sedimentary (LHMS) zone, Almora klippe, Ramgarh thrust sheet, and the overlying Tethyan Himalayan Sequence. These source areas can be attributed to the development of local drainage networks in the Ramganga‐Kosi drainage basin during late Miocene to Pliocene (i.e., ~9 to 4 Ma). Based on detrital FT datasets, it has been envisaged that different tectonic activities in the MBT hinterland area between Miocene and Pliocene Periods cause the tectonic upliftment and exhumation of source areas and supply the sediment to the Siwalik foreland basin.

Fossil endocasts of two Pleistocene bovines (Bovidae, Mammalia) from the Upper Siwaliks of northern India

ABSTRACT Natural fossil endocasts are a direct source of information on palaeoneurology of extinct species and, in recent years, there has been a dramatic revival of interest in palaeoneurological investigations. Endocasts of bovines (family Bovidae), however, remain hitherto undescribed. Here we describe two well preserved natural endocasts of Pleistocene bovines from the Upper Siwalik deposits exposed near Panchkula (Haryana), in the vicinity of Chandigarh city, northern India. The two endocasts, referred here to cf. Bubalus platyceros and Bovini indet., are similar in gross morphology but differ significantly in several respects. Comparison with modern bovines reveals important similarities between the Siwalik endocasts and the brains of Bos taurus and Bubalus bubalis, especially in size of their cerebral hemispheres and placement of fissures. However, the Siwalik endocasts differ significantly in being less replete with gyri and sulci, suggesting that bovines have undergone an increase in complexity of their neuroanatomy during the later part of the Pleistocene. This study also supports the recently proposed hypothesis that mammalian taxa with relatively large brain size were more likely to survive the Pleistocene megafaunal extinctions.

Macrofossils of Artocarpaceae and Lauraceae from Siwalik (Upper Miocene) Sediments of Himachal Pradesh, India and their Climatic and Biogeographic Significance

Macrofossils of Artocarpaceae and Lauraceae from Siwalik (Upper Miocene) Sediments of Himachal Pradesh, India and their Climatic and Biogeographic Significance

Diversity of hipparionines (Perissodactyla: Equidae) from the late Miocene–Pliocene Siwalik deposits at Haritalyangar, India

The present work is focused on the hipparionine remains from the late Miocene to early Pliocene deposits of the Haritalyangar areas, Himachal Pardesh, India. These remains are taxonomically ranked to five genera (Plesiohipparion, Proboscidipparion, Cormohipparion, Sivalhippus, and Eurygnathohippus) and seven species. The described taxa are predominantly known from China, Africa and the Indian subcontinent. Among these, Proboscidipparion is reported for the first time from the Siwaliks; the material assigned to Plesiohipparion sp. is a potential candidate for a new species. Hipparionines from this area have long been poorly known and are helpful to understand the palaeontological context of the Indian Siwalik mammalian fauna. The hipparionines suggest a wide variety of environmental conditions ranging from grasslands to forests.

Evidence of the oldest extant vascular plant (horsetails) from the Indian Cenozoic

Equisetum (Equisetaceae) has long been a focus of attention for botanists and palaeontologists because, given its extensive and well-documented fossil record, it is considered the oldest extant vascular plant and a key element in understanding vascular plant evolution. However, to date, no authentic fossil evidence of Equisetum has been found from the Indian Cenozoic. Here, we describe a new fossil species, namely, E. siwalikum sp. nov., recovered from the middle Siwalik (Late Miocene) sediments of Himachal Pradesh, western Himalaya. We identified fossil specimens based on morphological and epidermal characters. In addition, X-Ray diffraction (XRD) analysis was used to determine the mineral composition of compressed stems of Equisetum. The close affinity of our recovered Siwalik fossils to Equisetum is supported by the presence of both macromorphological and epidermal characters. Because Equisetum generally grows in wet conditions around water reservoirs, our findings indicate that the fossil locality was humid and surrounded by swamp and lowland regions during deposition. Ample fossil evidence indicates that this sphenopsid once existed in the western Himalaya during the Siwalik period. However, at present Equisetum is confined to a particular area of our fossil locality, probably a consequence of severe environmental changes coupled with competition from opportunistic angiosperms. Our discovery of Equisetum fossils in appreciable numbers from the Siwalik sediments of the Himachal Himalayas is unique and constitutes the first reliable recognition of Equisetum from the Indian Cenozoic.

Leaf Impression of Amesoneuron (Arecaceae) from the Lower Siwalik Sediments of the Kankai Mai River Section, Eastern Nepal

A leaf impression of Amesoneuron (Arecaceae) is reported from the Lower Siwalik sediments of the Kankai Mai River section, eastern Nepal. The overall habit, habitat and modern distributions and climatic conditions show the existence of tropical to sub-tropical wet evergreen forests with humid swampy lowland areas during the deposition of the sediments.

PALYNOSTRATIGRAPHIC STATUS AND DEPOSITIONAL ENVIRONMENT OF GIRUJAN CLAY AND DUPITILA FORMATION EXPOSED ALONG SHARI RIVER (DIGRAIL) AND DUPIGAON, SYLHET, BANGLADESH

The Girujan Clay Formation is demarcated as Bangladeshopollenites barishalensis Zone, which is equivalent to middle-upper Siwalik sediments of Punjab Basin. The mangrove and coastal palynotaxa present in this formation indicate that these sediments have been deposited under the delta condition in a supratidal environment. The Girujan Clay Formation is considered to be of Mio-Pliocene in age. The DupiTila Formation is recognized here as Corrugatisporites sp. Zone. This formation is equivalent to Namsang bed of Assam-Meghalaya region. The palynological assemblage of this formation is suggestive of a high degree of precipitation and the presence of rainfed river system prevailing in the basin of deposition. It is of Plio-Pleistocene in age.

First Record of Fossil parthenocissus (Vitaceae) Leaf from Siwalik Sediments of Sarkkaghat, Himachal Pradesh, India and its Biogeographic Implications

A non- entire fossil leaf, Parthenocissus miocenica n. sp. is reported for the first time from the Upper Miocenesediments of Sarkaghat area in the Himalayan foot hills of Himachal Pradesh, India. It shows closeresemblance with an extinct taxon, Parthenocissus semicordata (Wall.) Planch. of the family Vitaceae. This isone of the biogeographically important taxa which is native to Himalaya and presently distributed intropical and subtropical regions of N.W. India, Nepal to central China and western Malaysia. The presentrecovered fossil along with other known fossils from Sarkaghat area suggest a tropical humid climate inthe area during Miocene epoch.