Siwalik Synopsis: a Long Stratigraphic Sequence for the Later Cenozoic of South Asia

Siwalik synopsis: A long stratigraphic sequence for the Later Cenozoic of South Asia The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters Citation Flynn, Lawrence J., David Pilbeam, John C. Barry, Michèle E. Morgan, and S. Mahmood Raza. 2016. “Siwalik Synopsis: A Long Stratigraphic Sequence for the Later Cenozoic of South Asia.” Comptes Rendus Palevol (January). doi:10.1016/j.crpv.2015.09.015. Published Version 10.1016/j.crpv.2015.09.015 Citable link http://nrs.harvard.edu/urn-3:HUL.InstRepos:26507534 Terms of Use This article was downloaded from Harvard University’s DASH repository, and is made available under the terms and conditions applicable to Other Posted Material, as set forth at http:// nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of- use#LAA 1 Siwalik Synopsis: A long stratigraphic sequence for the later Cenozoic of 2 South Asia 3 4 SYNOPSIS SIWALIK: LONGUE SUCCESSION STRATIGRAPHIQUE DU CÉNOZOÏQUE 5 MOYEN ET TARD AU SUD DE L’ASIE 6 7 Lawrence J. Flynna,*, David Pilbeama, John C. Barrya, Michèle E. Morgana,b, S. Mahmood 8 Razaa 9 10 a Department of Human Evolutionary Biology, Harvard University, 11 Divinity Avenue, 11 Cambridge, MA 02138, USA 12 13 b Peabody Museum of Archaeology and Ethnology, 11 Divinity Avenue, Cambridge, MA 14 02138, USA 15 16 *corresponding author [email protected] 17 18 19 20 Abstract 21 The Tertiary sediments of northern Pakistan are an exceptional record of terrestrial 22 sedimentation and represent most of Neogene time. Foremost is the Siwalik Group of the 23 Potwar Plateau, for which multiple, superposed fossil levels span ~18 – 6 Ma. Well- 24 developed magnetostratigraphic control provides secure dating so that Siwalik fossil 25 horizons may be interpolated into a time scale with resolution to 100,000 years. We 26 describe the geographic setting of the Potwar, give an overview of the temporal 27 distribution of faunas, and discuss changes in paleohabitat and paleoecology with 28 coinciding faunal change, as seen from the Siwalik viewpoint. The long Siwalik 29 biostratigraphy of many successive assemblages with its resolved time scale may be 30 compared directly with other well-dated sequences. Immigrant arrival and timing of 31 faunal change may be traced. The basins of the Iberian Peninsula show somewhat 32 different timing of introduction of hipparionine horses, and faunal turnover in the Siwaliks 33 precedes significantly the Vallesian crisis in Spain. In contrast to the increasingly seasonal 34 precipitation of the late Miocene Potwar, the paleohabitat of coeval North China appears 35 to have been moist and equable, with high diversity faunas. Continued development and 1 36 comparison of resolved Neogene records allows increasing resolution of the patterns of 37 faunal change on regional to global levels. 38 2 39 Key Words: Neogene; Siwaliks; mammals; paleoecology; biostratigraphy; 40 magnetostratigraphy1. Introduction 41 The Indian Subcontinent presents a special setting for paleobiologists. The uplift along 42 the northern margin of the land mass, as its leading edge subducts under the 43 mountainous terrain of the Tibetan Plateau, supplies clastic wedges of terrestrial 44 deposits to the south via major river systems. The relatively continuous process of 45 sediment accumulation under conditions favorable for vertebrate fossil preservation has 46 created a series of fossil horizons, superposed and laterally extensive, spanning much 47 of the second half of the Cenozoic Era. Many fossils represent successive samples of 48 the past biota. The most continuous series of superposed fossil horizons is contained in 49 the Siwalik deposits of the Potwar Plateau, Pakistan. This dense biotic record spanning 50 much of the Neogene can be compared with well-dated biostratigraphies from other 51 biogeographic regions to evaluate mammalian dispersal and turnover, timing of high or 52 low rates of appearance and disappearance events, and response to abiotic factors of 53 temperature, moisture, and tectonics. Research is beginning to address direct 54 comparisons of sequences in Spain and China, for example, because their records 55 comprise increasingly well-dated and resolved faunas. 56 Sedimentary formations of the Indian Subcontinent include primarily the classical 57 Siwalik Group rocks of northern Pakistan, Nepal and India, of late early Miocene 58 through Pliocene age. Also relevant and preserving similar faunal assemblages are the 59 Manchar Formation of southern Pakistan (Sindh), and coeval to older Zinda Pir Dome 60 and Bugti sediments of western Pakistan (Baluchistan) (Figure 1). The oldest of the 3 61 latter deposits are Oligocene in age (Welcomme et al., 2001). Together they produce a 62 rich record of successive faunas that can be studied for questions on lineage evolution, 63 community structure, and faunal change. 64 The Siwaliks and related formations have been the subject of field exploration for 65 almost 200 years. Early collecting was sporadic, with little attention paid to provenance, 66 but it provided impetus for later expeditions. Two of these were collecting campaigns 67 under the direction of Barnum Brown of the American Museum of Natural History in the 68 1920s and G. Edward Lewis of Yale University in the 1930s. Their collecting (Lewis, 1937) 69 was geographically controlled and today we can reconstruct in general where many of 70 their collections were made. Richard Dehm (Dehm et al., 1958), Universität München 71 expeditions of 1939 and 1955-56, and G.H.R. von Koenigswald, Rijksuniversiteit, 72 Universiteit Utrecht (1966-67), also recorded data for fossils recovered by their groups. 73 However, the potential for biostratigraphic study of long sections in defined areas was still 74 largely unrealized. 75 It is now feasible to record precisely the level of occurrence of superposed 76 stratigraphic horizons that produce fossils. The sequence of sites records the local 77 histories of organisms during much of the Miocene Epoch, both changes among members 78 in associated faunas as well as evolution within lineages. The fossil horizons of the Potwar 79 Plateau can be dated relative to one another, and ages can generally be resolved on the 80 scale of 100,000 years for the interval of approximately 18 to 6 Ma (Barry et al., 2013). 81 The record can be extended to about 22 Ma by paleomagnetic correlation of deposits of 82 the Zinda Pir area, and into the Pliocene Upper Siwaliks of the southeastern margin of the 4 83 Potwar Plateau. Sampling density for fossils is not constant throughout this time, which is 84 critical to note when interpreting recorded faunal change. Figure 2, based mainly on 85 Potwar records and supplemented by Zinda Pir and Upper Siwalik localities, shows the 86 uneven temporal distribution of Neogene sites in Pakistan. 87 The Siwaliks present a special geobiological case in which many successive and 88 dated levels can be sampled for their often abundant vertebrate fossils and ecological 89 proxies, affording an excellent opportunity to document changes in landscapes, habitats, 90 and faunas through time. The dimensions of information that can be retrieved from the 91 Siwaliks are considerable compared to other sequences of comparable age. 92 In the following, we discuss the geological and geographic setting for the major 93 fossil-producing regions of the Indian Subcontinent. We sketch the history of exploration 94 by early workers in the Indian Subcontinent. We touch on major features of the terrestrial 95 deposits and age determination, and then turn to our current assessments of faunas and 96 paleohabitats of the Miocene. 97 98 2. Major Fossil-Producing Sequences and History of Exploration 99 Early fossil collecting involved a gradual realization that fossil resources across the 100 northern part of the Indian Subcontinent are considerable. Cautley and Falconer (1835) 101 reported vertebrates from the “Sivalik” Hills of northern India (Figure 1, area 6); fossils 102 noted by them and by other early workers (e.g., Pentland, 1828) came to light from field 103 campaigns under the direction of British officers. Vickary (1846) recorded the richness of 104 fossil beds from the Bugti area of Baluchistan. This work was not systematic, but 5 105 stimulated later study, for example by Pilgrim (1908) and Cooper (1924 and earlier), and 106 much later by Raza and Meyer (1984). Welcomme et al. (2001) documented the 107 Oligocene age of the oldest Bugti beds, discovering great faunal diversity there, and 108 Antoine et al. (2013) reviewed the Miocene biostratigraphy of the Bugti area (Figure 1, 109 area 4). Lindsay et al. (2005) concentrated on the Zinda Pir Dome deposits (area 3), 110 finding similar assemblages and adding several superposed early Miocene microfaunas. 111 While earlier collecting tended to mix together fossils by collecting area, regardless of 112 stratigraphy, these recent studies maintained stratigraphic control to record the succession 113 of assemblages. 114 Working widely throughout the northern Indian Subcontinent in Neogene age 115 strata, Pilgrim (1910, 1913) distinguished and named successive fossiliferous sequences. 116 He recognized a series of both strata and faunas in the Potwar Plateau of present-day 117 Pakistan and the foothills of northern India. Rocks of the Potwar Plateau from late early 118 Miocene to early Pliocene came to be designated formally as formations, the Kamlial, 119 Chinji, Nagri, Dhok Pathan, and Tatrot formations. Pilgrim (1910) also noted the older 120 early Miocene Murree Formation, adjacent to the northern margin of the Potwar. The type 121 area of the late Pliocene Pinjor Formation lies to the east in India. Prior to the 1970s, the 122 ages of these units were not known, and the faunal content was not only poorly 123 documented, but confounded with fossils from other parts of the subcontinent. 124 Potwar Plateau formations are stratified, dominantly fluvial sediments. They 125 represent mainly floodplain silts and sands, with lesser components of clays, gravels, and 126 ponded sediments.

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