Papers by Prabhat C Neupane
The Depositional Record, 2019
The late Neogene vegetation change of C 4 plants replacing C 3 plants is widely documented across... more 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.
Geological Journal , 2017
The Ethiopian Plateau, situated on the Western Escarpment of the East African Rift System, consti... more The Ethiopian Plateau, situated on the Western Escarpment of the East African Rift System, constitutes a part of a large igneous province that has experienced extensive flood basalt volca-nism around 30 Ma related to the outpouring of the Afar mantle plume. This non-orogenic plateau with long-wavelength dynamic topography has been deeply incised by the Blue Nile River and its numerous tributaries. The plateau represents an excellent natural laboratory to study the interplay between bedrock river incision and uplift. Our analysis of a total of 202 convex upward and double-concave tributary longitudinal profiles reveals 244 knickpoints, the majority of which are not associated with lithologic boundaries or faults. The normalized steepness indices (k sn) of these profiles vary in upstream versus downstream from knickpoints indicating variable uplift within the plateau. Our investigation of integrating mantle seismic P-wave velocity anomaly with k sn and knickpoints suggests ongoing incision of the plateau surface in response to Afar plume related mantle dynamics. Tributary reaches with higher k sn generally lie above the areas with negative velocity anomaly, thus hotter (than normal) mantle that are likely undergoing more uplift. Therefore, this study suggests that the transient landscape incision of the Ethiopian Plateau is largely controlled by the ongoing uplift of the plateau, indicating that the plateau physiography is dynamic, not stable.
Thesis Chapters by Prabhat C Neupane
The Ethiopian Plateau is one of the few tectonically-active regions on Earth that is
situated in ... more The Ethiopian Plateau is one of the few tectonically-active regions on Earth that is
situated in continental rift zones. About 1.6 km deep gorge of the Nile was carved by the Blue
Nile River on the Ethiopian Plateau, as the plateau has been experiencing continuous uplift and
exhumation in the Cenozoic. Here, we used quantitative analysis of longitudinal rive-profile
forms and parameters (knickpoint and normalized steepness-index ksn) of the Blue Nile
tributaries to tease out regional tectonic signals.
244 knickpoints were examined in the tributaries, majority (>80%) of which are
unassociated with lithology or geological structures. Knickpoint distribution throughout the
plateau reveals three incision phases. The novel approach of correlation of ksn with mantle
tomography suggests that higher and lower ksn values occur above low-velocity and highvelocity zones, respectively, indicating that thermal upwelling beneath the plateau linked to Afar
mantle plume largely controls the uplift thus incision of the plateau.
Key words: Ethiopian Plateau; tectonic geomorphology; exhumation; stream profile analysis;
knickpoint; mantle tomography.
Conference Presentations by Prabhat C Neupane
The Arun River is one of the largest rivers across the Himalaya front. Its deep valley is flanked... more The Arun River is one of the largest rivers across the Himalaya front. Its deep valley is flanked by the >8 km peak of Mt. Everest and its ridge-to-valley relief reaches 6 km. Although its evolution can provide key insights concerning tectonic, climatic and erosional interactions, thermochronologic constraints along its course are scarce and limited to the Ama Drime Massif. This study combines (U-Th)/He and 40Ar/39Ar thermochronology, fluvial geomorphic analysis and thermo-kinematic modeling to decipher the pattern of uplift and exhumation along the Arun river. Three thermochronometers display a pattern of decreasing valley bottom cooling ages to the north. Total fusion 40Ar/39Ar muscovite ages decrease from 16 Ma near the Main Boundary Thrust to 6 Ma north of the Himalaya topographic front. Zircon (U-Th)/He ages decrease from 6 Ma south of the topographic front to 2 Ma and Apatite (U-Th)/He decrease from 3 to 0.8 Ma. The cooling ages north of the topographic front are older than along the Marsyandi river in central Nepal and the inferred exhumation rate is lower. No significant discontinuity in ages is observed across the topographic front. This limits the permissible duration and magnitude of out-of-sequence thrusting. 40Ar/39Ar ages undisturbed by Tertiary resetting are limited to valley bottom samples in the vicinity of the topographic front. At the same distance from the Main Frontal Thrust (MFT),
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Papers by Prabhat C Neupane
Thesis Chapters by Prabhat C Neupane
situated in continental rift zones. About 1.6 km deep gorge of the Nile was carved by the Blue
Nile River on the Ethiopian Plateau, as the plateau has been experiencing continuous uplift and
exhumation in the Cenozoic. Here, we used quantitative analysis of longitudinal rive-profile
forms and parameters (knickpoint and normalized steepness-index ksn) of the Blue Nile
tributaries to tease out regional tectonic signals.
244 knickpoints were examined in the tributaries, majority (>80%) of which are
unassociated with lithology or geological structures. Knickpoint distribution throughout the
plateau reveals three incision phases. The novel approach of correlation of ksn with mantle
tomography suggests that higher and lower ksn values occur above low-velocity and highvelocity zones, respectively, indicating that thermal upwelling beneath the plateau linked to Afar
mantle plume largely controls the uplift thus incision of the plateau.
Key words: Ethiopian Plateau; tectonic geomorphology; exhumation; stream profile analysis;
knickpoint; mantle tomography.
Conference Presentations by Prabhat C Neupane
situated in continental rift zones. About 1.6 km deep gorge of the Nile was carved by the Blue
Nile River on the Ethiopian Plateau, as the plateau has been experiencing continuous uplift and
exhumation in the Cenozoic. Here, we used quantitative analysis of longitudinal rive-profile
forms and parameters (knickpoint and normalized steepness-index ksn) of the Blue Nile
tributaries to tease out regional tectonic signals.
244 knickpoints were examined in the tributaries, majority (>80%) of which are
unassociated with lithology or geological structures. Knickpoint distribution throughout the
plateau reveals three incision phases. The novel approach of correlation of ksn with mantle
tomography suggests that higher and lower ksn values occur above low-velocity and highvelocity zones, respectively, indicating that thermal upwelling beneath the plateau linked to Afar
mantle plume largely controls the uplift thus incision of the plateau.
Key words: Ethiopian Plateau; tectonic geomorphology; exhumation; stream profile analysis;
knickpoint; mantle tomography.