Magnetic polarity stratigraphy of the Neogene Siwalik Group at Khutia Khola, far western Nepal

Ojha, T. P.; Butler, Robert F.; Quade, Jay; DeCelles, Peter G.; Richards, David R.; Upreti, B. N.

doi:10.1130/0016-7606(2000)112<424:mpsotn>2.0.co;2

Cited by 84 publications

(66 citation statements)

References 31 publications

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“…This significant climatic change is consistent with the expansion of C 4 biomass (Saylor et al, 2009). Climate transition observed at 7.2 Ma in the Zhada region is in good agreement with climate changes elsewhere in the Himalaya (Flynn and Jacobs, 1982;France-Lanord and Derry, 1994;Quade et al, 1995;Garzione et al, 2000;Ojha et al, 2000;Wang et al, 2006). As shown in Figure 5, the Kü bler index value shows considerable fluctuations, though it has a large value overall in the period, indicating fluctuations between warm/humid and warm/arid conditions, consistent with the results of Dettman et al (2001) and Kempf et al (2009).…”

Section: Paleoclimatic Evolution In the Zhada Areasupporting

confidence: 86%

Clay Mineralogy of the Zhada Sediments: Evidence for Climatic and Tectonic Evolution Since ~9 Ma in Zhada, Southwestern Tibet

Hong

Wang

Zeng

et al. 2012

Clays and clay miner.

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The clay mineralogy of the Zhada sediments was investigated, using X-ray diffraction and scanning electron microscopy, to obtain a better understanding of climatic change and uplift of the Himalayas in the Zhada region of Tibet. The sediments of Zhada basin in the late Miocene to Pliocene consist of lacustrine and fluvial deposits >800 m thick and can be subdivided into five clay assemblage zones based on their clay-mineral composition. The upward zonation is as follows: (1) smectite-kaolinite;(2) illite-chlorite; (3) chlorite-illite-kaolinite; (4) illite-chlorite; and (5) smectite, illite, and kaolinite. The ratio of chlorite + illite to kaolinite + smectite (Ch+I/K+S) and the Kü bler index indicate a warm and humid climate from 9.5 to 8.4 Ma, a cold and dry climate from 8.4 to 7.2 Ma, a warm and seasonal arid climate from 7.2 to 4.5 Ma, a cool and humid climate from 4.5 to 3.6 Ma, and a warm and seasonally humid climate from 3.6 to 3.0 Ma. Intense fluctuations in the Kü bler index and in the quantities of evaporite minerals dolomite, aragonite, and gypsum, during the period 7.2À4.5 Ma suggest strong climatic fluctuations between humid and seasonally humid conditions in the Zhada basin. Rapid uplift around the Zhada basin occurred at 8.4 and 3.6 Ma, with sharp subsidence at 7.2 and 4.5 Ma. Evolution of the climate at Zhada showed a different model from that of global climate change, and tectonics-led climate change was the major contributor to climate evolution in the area.

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Section: Paleoclimatic Evolution In the Zhada Areasupporting

confidence: 86%

Clay Mineralogy of the Zhada Sediments: Evidence for Climatic and Tectonic Evolution Since ~9 Ma in Zhada, Southwestern Tibet

Hong

Wang

Zeng

et al. 2012

Clays and clay miner.

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“…The paleomagnetic inclination of the Neogene Siwalik Group red beds can provide additional information about the a factor of fine‐grained hematite particles typically found in red beds. The average inclination of the Siwalik Group is ∼20° [ Butler , 1992; Ojha et al , 2000; Gautam and Fujiwara , 2000], whereas the expected paleomagnetic inclination for the Siwalik locality of 28°N 80°E is 45° at 10 Ma based on Besse and Courtillot 's [1991] reference pole for the Indian plate. This indicates a 25° inclination error for the Siwalik Group red beds.…”

Section: Discussionmentioning

confidence: 99%

“… Tauxe and Kent [1984] showed that modern fluvial hematite‐bearing deposits from the River Soan in Pakistan suffer ∼25° inclination shallowing. Although depositional error may be removed by postdepositional realignment of magnetic particles in magnetite‐bearing sediments [ Verosub , 1977], the 20°–30° anomalously shallow inclinations of the Neogene Siwalik group red beds [ Butler , 1992; Roesler and Appel , 1998; Gautam and Fujiwara , 2000; Ojha et al , 2000] suggests that either postdepositional realignment may not be important for hematite‐bearing sediments or that compaction has shallowed their inclination. Compaction‐induced inclination shallowing has been observed in laboratory compaction experiments of fine‐grained, magnetite‐bearing sediments [ Anson and Kodama , 1987; Deamer and Kodama , 1990; Kodama and Sun , 1992; Sun and Kodama , 1992].…”

Section: Introductionmentioning

confidence: 99%

Paleomagnetism and magnetic anisotropy of Cretaceous red beds from the Tarim basin, northwest China: Evidence for a rock magnetic cause of anomalously shallow paleomagnetic inclinations from central Asia

et al. 2003

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[1] Anomalously shallow paleomagnetic inclinations from Tarim basin red beds have suggested more than 1000 km of northward translation of the Tarim block since the Cretaceous. This is in conflict with geologic observations that indicate only a few hundred kilometers of crustal shortening north of the Tarim basin. To determine whether a rock magnetic effect could be the cause of the shallow inclinations, samples were collected from the Cretaceous Kapusaliang Group red beds. Both thermal and chemical demagnetization were employed to isolate the characteristic remanence (ChRM). The ChRMs pass the reversals test, as well as a local fold test. The anisotropy of magnetic susceptibility of the ChRM-bearing particles was isolated by chemical demagnetization and had an oblate fabric with minimum axes perpendicular to bedding and foliations of $1.035. A 10-20% remanent anisotropy was obtained by comparing the saturation isothermal remanent magnetization for subsamples drilled parallel and perpendicular to bedding planes. The correlation of AMS and remanent anisotropy parameters yielded a value for the individual particle magnetic susceptibility anisotropy between 1.05 and 1.62. A particle anisotropy of 1.0638 allowed the best fit between corrected data and theoretical correction curves. An inclination correction corrected the mean Kapusaliang direction from D = 16.3°, I = 29.0°, a 95 = 7.4°to D = 14.1°, I = 61.5°, a 95 = 6.4°. The inclination correction reduced the paleomagnetically predicted latitudinal offset from more than 1000 km to less than the mean direction's 95% confidence limits, suggesting that paleomagnetic inclination shallowing is the cause of low inclinations recorded by the red beds from the Tarim basin.

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“…The Lower Siwalik consists of interbedded fine to medium grained, grey sandstone and variegated or grey mudstone ( Figure 2) deposited in fluvial and floodplain environments (Gautam and Rösler, 1999;Ulak, 2009). The medium to coarse grained, 'salt and pepper' sandstones, which are often multistory in nature and intercalated with mudstones ( Figure 2), indicate braided river deposition in the Middle Siwalik (Gautam and Rösler, 1999;Nakayama and Ulak, 1999;Ojha et al, 2000;Ulak, 2009). Conversely, the Upper Siwalik consists of bedded pebble and cobble conglomerates intercalated with loosely packed sandstone and claystone layers that are interpreted to represent alluvial fan environments deposited closer to the mountain belt (Gautam and Rosler, 1999;Ojha et al, 2000;Ulak, 2009).…”

Section: Geology Of the Study Areamentioning

confidence: 99%

“…The medium to coarse grained, 'salt and pepper' sandstones, which are often multistory in nature and intercalated with mudstones ( Figure 2), indicate braided river deposition in the Middle Siwalik (Gautam and Rösler, 1999;Nakayama and Ulak, 1999;Ojha et al, 2000;Ulak, 2009). Conversely, the Upper Siwalik consists of bedded pebble and cobble conglomerates intercalated with loosely packed sandstone and claystone layers that are interpreted to represent alluvial fan environments deposited closer to the mountain belt (Gautam and Rosler, 1999;Ojha et al, 2000;Ulak, 2009). Several palaeomagnetic studies were conducted in the Nepalese Siwalik to reveal high-resolution ages of the Siwalik succession ( Figure 3).…”

Section: Geology Of the Study Areamentioning

confidence: 99%

Neogene vegetation shift in the Nepalese Siwalik, Himalayas: A compound‐specific isotopic study of lipid biomarkers

Neupane

Gani

et al. 2019

The Depositional Record

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The late Neogene vegetation change of C 4 plants replacing C 3 plants is widely documented across the world. This vegetation shift has been particularly well-documented in the Himalayan foreland based on δ 13 C isotopic data from palaeosol carbonates and bulk organic matter in the Siwalik sedimentary rocks of Pakistan, India and Nepal, showing asynchronous expansion of C 4 plants between 8 and ~5 Ma, 9 and 6 Ma, and around 7 Ma, respectively. In this study, compound-specific isotopic analysis of lipid biomarkers extracted from shale and palaeosols in the palaeomagnetically age-constrained Nepalese Siwalik is utilized to better understand this vegetation shift. This is the first comprehensive lipid biomarker study in the Nepalese Siwalik, with new isotopic results from the previously undocumented Karnali River section. The δ 13 C n-alkane (C 27-31 ) results from the Surai Khola section suggest C 3 plants were dominant between 12 and 8.5 Ma. A stepwise expansion of C 4 plants that started gradually at 8.5 Ma escalated rapidly after 5.4 Ma, so that by 5.2 Ma C 4 vegetation dominated the landscape. This dramatic ecological shift at the Miocene-Pliocene boundary was likely linked with an intriguing tectonic-climate coupling in the Himalayan-Tibetan region, prompting wetter summers and drier winters that drove C 4 grass expansion.However, in the Karnali River section, the data show no clear sign of C 4 plant expansion until 5.2 Ma (youngest sample age). In the two study locations separated laterally by ~200 km along tectonic-strike, this different trend of vegetation change likely indicates local controls like river-catchment influence. However, it is possible that, similar to the Surai Khola section, C 4 plants dominated after 5.2 Ma in the Karnali River section. This study also suggests that the past vegetation makeup of an area is better reconstructed using isotopic signatures of molecular markers than of bulk organic matter or pedogenic nodules.

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Magnetic polarity stratigraphy of the Neogene Siwalik Group at Khutia Khola, far western Nepal

Cited by 84 publications

References 31 publications

Clay Mineralogy of the Zhada Sediments: Evidence for Climatic and Tectonic Evolution Since ~9 Ma in Zhada, Southwestern Tibet

Clay Mineralogy of the Zhada Sediments: Evidence for Climatic and Tectonic Evolution Since ~9 Ma in Zhada, Southwestern Tibet

Paleomagnetism and magnetic anisotropy of Cretaceous red beds from the Tarim basin, northwest China: Evidence for a rock magnetic cause of anomalously shallow paleomagnetic inclinations from central Asia

Neogene vegetation shift in the Nepalese Siwalik, Himalayas: A compound‐specific isotopic study of lipid biomarkers

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