Imperial College London

ProfessorSanjeevGupta

Faculty of EngineeringDepartment of Earth Science & Engineering

Professor of Earth Science
 
 
 
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Contact

 

+44 (0)20 7594 6527s.gupta

 
 
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Location

 

Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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104 results found

HolmAlwmark S, Kinch KM, Hansen MD, Shahrzad S, Svennevig K, Abbey WJ, Anderson RB, Calef FJ, Gupta S, Hauber E, Horgan BHN, Kah LC, Knade J, Miklusicak NB, Stack KM, Sun VZ, Tarnas JD, QuantinNataf Cet al., 2021, Stratigraphic relationships in Jezero crater, Mars: constraints on the timing of fluvial‐lacustrine activity from orbital observations, Journal of Geophysical Research: Planets, Vol: 126, Pages: 1-31, ISSN: 2169-9097

On February 18, 2021 NASA's Perseverance rover landed in Jezero crater, located at the northwestern edge of the Isidis basin on Mars. The uppermost surface of the present-day crater floor is dominated by a distinct geologic assemblage previously referred to as the dark-toned floor. It consists of a smooth, dark-toned unit overlying and variably covering light-toned, roughly eroded deposits showing evidence of discrete layers. In this study, we investigated the stratigraphic relations between materials that comprise this assemblage, the main western delta deposit, as well as isolated mesas located east of the main delta body that potentially represent delta remnants. A more detailed classification and differentiation of crater floor units in Jezero and determination of their relative ages is vital for the understanding of the geologic evolution of the crater system, and determination of the potential timeline and environments of habitability. We have investigated unit contacts using topographic profiles and DEMs as well as the distribution of small craters and fractures on the youngest portions of the crater floor. Our results indicate that at least some of the deltaic deposition in Jezero postdates emplacement of the uppermost surface of the crater floor assemblage. The inferred age of the floor assemblage can therefore help to constrain the timing of the Jezero fluviolacustrine system, wherein at least some lake activity postdates the age of the uppermost crater floor. We present hypotheses that can be tested by Perseverance and can be used to advance our knowledge of the geologic evolution of the area.

Journal article

Kumar Joshi S, Gupta S, Sinha R, Logan Densmore A, Prakash Rai S, Shekhar S, Mason PJ, Dijk WMVet al., 2021, Strongly heterogeneous patterns of groundwater depletion in Northwestern India, Journal of Hydrology, Vol: 598, Pages: 1-17, ISSN: 0022-1694

Northwestern India has been identified as a significant hotspot of groundwater depletion, with major implications for groundwater sustainability caused by excessive abstraction. We know relatively little about the detailed spatial and temporal changes in groundwater storage in this region, nor do we understand the interplay of factors controlling these changes. Groundwater managers and policymakers in India require such information to monitor groundwater development and make strategic decisions for the sustainable management of groundwater. Here, we characterise high-resolution spatio-temporal variability in groundwater levels and storage change across northwestern India through analysis of in situ measurements of historical groundwater level data. We note a slow gain in groundwater storage of + 0.58 ± 0.35 km3 for the pre-monsoon and + 0.40 ± 0.35 km3 for the post-monsoon period between 1974 and 2001. However, from 2002 to 2010, groundwater storage was rapidly depleted by −32.30 ± 0.34 km3 in the pre-monsoon and −24.42 ± 0.34 km3 in the post-monsoon period. Importantly, we observe marked spatial heterogeneity in groundwater levels and storage change and distinct hotspots of groundwater depletion with lateral length scales of tens of kilometers. Spatial variability in groundwater abstraction partially explains the depletion pattern, but we also find that the sedimentological heterogeneity of the aquifer system correlates broadly with long-term patterns of groundwater-level change. This correlation, along with the spatial agreement between groundwater level change and water quality, provides a framework for anticipating future depletion patterns and guiding groundwater monitoring and domain-specific management strategies.

Journal article

Davis JM, Grindrod PM, Banham SG, Warner NH, Conway SJ, Boazman SJ, Gupta Set al., 2021, A record of syn-tectonic sedimentation revealed by perched alluvial fan deposits in Valles Marineris, Mars, Geology, ISSN: 0091-7613

On Mars, basins formed by tectonic processes are rare and mostly have unconstrained subsidence histories. One method for understanding this record of subsidence is through associated alluvial fans, which are sourced from uplifted areas and accumulate in downthrown basins. The source, morphology, and superposition of fan deposits can be used to reconstruct fault kinematics, the relative timing of accommodation space formation, and, in turn, the influence tectonic processes had on Martian fan formation. Here we use high-resolution orbital data sets to characterize sediment fan deposits associated with syn-tectonic sedimentation in two regions of the Valles Marineris canyons: Coprates Chasma and Juventae Chasma. These deposits comprise sediment fans on the current canyon floor and low-gradient surfaces perched several kilometers above the canyon floor. We interpret the low-gradient surfaces as remnant sediment fan deposits, which originally formed at the former canyon floor and have since been offset due to normal faulting. The preservation of vertically offset generations of sediment fan deposits supports a progressive, basinward migration of fault activity into the original hanging wall or repeat activity along a fault zone. Each episode of faulting was followed by a basinward shift in drainages, which led to fault-scarp degradation and formation of a new generation of fans. Multiple episodes of syn-tectonic sedimentation occurred during the evolution of the basins, with fluvial activity sporadically active. Our results demonstrate, for the first time on Mars, that depositional cyclicity was linked to tectonic deformation, possibly representative of regional processes throughout Valles Marineris.

Journal article

Arosio R, Collier JS, Hawes J, Gupta S, Sperry Jet al., 2021, New perspectives on the English Channel megaflood hypothesis: High-resolution multibeam and seabed camera imaging of submarine landforms in the Northern Palaeovalley, Geomorphology, Vol: 382, Pages: 1-15, ISSN: 0169-555X

A network of large, bedrock-incised valleys is preserved on the seabed of the English Channel. Based on analysis of a 30 × 30 m bathymetric grid, the morphology of the valleys was interpreted to be a consequence of erosion by catastrophic flood processes from overspill of a large proglacial lake in the Southern North Sea. The significance of the “megaflood features” has since been recognized by the UK Government with the designation of their protected status in one of three Marine Protected Areas (MPAs) within the palaeovalley in the central English Channel. Here, we analyse recent multibeam bathymetry data (2 × 2 m DEM) from these MPAs, together with backscatter and high-definition seabed camera imagery. The new data allow us to ground truth and refine the earlier interpretation and recognize previously undiscovered finer features. Streamlined valley margins, streamlined islands and metres-deep scours eroded into the valley floor are described at higher detail, while new subtle features on the valley floor such as kilometre-long, sub-parallel inner channels and streamlined bedrock ridges are identified for the first time. These features are consistent with a high energy erosion origin. We also identify isolated large boulders (>1 m length) on flat seabed on the flanks of the palaeovalley, which are consistent with deposition from megaflood processes, although wave action during transgression/regression cannot be ruled out. Our new results enable more robust morphological evidence to support the influence of catastrophic flooding on bedrock valley incision in the English Channel.

Journal article

Banham SG, Gupta S, Rubin DM, Edgett KS, Barnes R, Van Beek J, Watkins JA, Edgar LA, Fedo CM, Williams RM, Stack KM, Grotzinger JP, Lewis K, Ewing RC, Day M, Vasavada ARet al., 2021, A Rock Record of Complex Aeolian Bedforms in a Hesperian Desert Landscape: The Stimson Formation as Exposed in the Murray Buttes, Gale Crater, Mars, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 126, ISSN: 2169-9097

Journal article

Fraeman AA, Edgar LA, Rampe EB, Thompson LM, Frydenvang J, Fedo CM, Catalano JG, Dietrich WE, Gabriel TSJ, Vasavada AR, Grotzinger JP, L'Haridon J, Mangold N, Sun VZ, House CH, Bryk AB, Hardgrove C, Czarnecki S, Stack KM, Morris RV, Arvidson RE, Banham SG, Bennett KA, Bridges JC, Edwards CS, Fischer WW, Fox VK, Gupta S, Horgan BHN, Jacob SR, Johnson JR, Johnson SS, Rubin DM, Salvatore MR, Schwenzer SP, Siebach KL, Stein NT, Turner SMR, Wellington DF, Wiens RC, Williams AJ, David G, Wong GMet al., 2020, Evidence for a diagenetic origin of vera rubin ridge, gale crater, Mars: summary and synthesis of curiosity's exploration campaign, Journal of Geophysical Research: Planets, Vol: 125, Pages: 1-34, ISSN: 2169-9097

This paper provides an overview of the Curiosity rover's exploration at Vera Rubin ridge (VRR) and summarizes the science results. VRR is a distinct geomorphic feature on lower Aeolis Mons (informally known as Mount Sharp) that was identified in orbital data based on its distinct texture, topographic expression, and association with a hematite spectral signature. Curiosity conducted extensive remote sensing observations, acquired data on dozens of contact science targets, and drilled three outcrop samples from the ridge, as well as one outcrop sample immediately below the ridge. Our observations indicate that strata composing VRR were deposited in a predominantly lacustrine setting and are part of the Murray formation. The rocks within the ridge are chemically in family with underlying Murray formation strata. Red hematite is dispersed throughout much of the VRR bedrock, and this is the source of the orbital spectral detection. Gray hematite is also present in isolated, gray-colored patches concentrated toward the upper elevations of VRR, and these gray patches also contain small, dark Fe-rich nodules. We propose that VRR formed when diagenetic event(s) preferentially hardened rocks, which were subsequently eroded into a ridge by wind. Diagenesis also led to enhanced crystallization and/or cementation that deepened the ferric-related spectral absorptions on the ridge, which helped make them readily distinguishable from orbit. Results add to existing evidence of protracted aqueous environments at Gale crater and give new insight into how diagenesis shaped Mars' rock record.

Journal article

Stack KM, Williams NR, Calef F, Sun VZ, Williford KH, Farley KA, Eide S, Flannery D, Hughes C, Jacob SR, Kah LC, Meyen F, Molina A, Nataf CQ, Rice M, Russell P, Scheller E, Seeger CH, Abbey WJ, Adler JB, Amundsen H, Anderson RB, Angel SM, Arana G, Atkins J, Barrington M, Berger T, Borden R, Boring B, Brown A, Carrier BL, Conrad P, Dypvik H, Fagents SA, Gallegos ZE, Garczynski B, Golder K, Gomez F, Goreva Y, Gupta S, Hamran S-E, Hicks T, Hinterman ED, Horgan BN, Hurowitz J, Johnson JR, Lasue J, Kronyak RE, Liu Y, Madariaga JM, Mangold N, McClean J, Miklusicak N, Nunes D, Rojas C, Runyon K, Schmitz N, Scudder N, Shaver E, SooHoo J, Spaulding R, Stanish E, Tamppari LK, Tice MM, Turenne N, Willis PA, Aileen Yingst Ret al., 2020, Photogeologic Map of the Perseverance Rover Field Site in Jezero Crater Constructed by the Mars 2020 Science Team, SPACE SCIENCE REVIEWS, Vol: 216, ISSN: 0038-6308

Journal article

Edgett KS, Banham SG, Bennett KA, Edgar LA, Edwards CS, Fairén AG, Fedo CM, Fey DM, Garvin JB, Grotzinger JP, Gupta S, Henderson MJ, House CH, Mangold N, McLennan SM, Newsom HE, Rowland SK, Siebach KL, Thompson L, VanBommel SJ, Wiens RC, Williams RME, Yingst RAet al., 2020, Extraformational sediment recycling on Mars, Geosphere, Vol: 16, ISSN: 1553-040X

Extraformational sediment recycling (old sedimentary rock to new sedimentary rock) is a fundamental aspect of Earth’s geological record; tectonism exposes sedimentary rock, whereupon it is weathered and eroded to form new sediment that later becomes lithified. On Mars, tectonism has been minor, but two decades of orbiter instrument–based studies show that some sedimentary rocks previously buried to depths of kilometers have been exposed, by erosion, at the surface. Four locations in Gale crater, explored using the National Aeronautics and Space Administration’s Curiosity rover, exhibit sedimentary lithoclasts in sedimentary rock: At Marias Pass, they are mudstone fragments in sandstone derived from strata below an erosional unconformity; at Bimbe, they are pebble-sized sandstone and, possibly, laminated, intraclast-bearing, chemical (calcium sulfate) sediment fragments in conglomerates; at Cooperstown, they are pebble-sized fragments of sandstone within coarse sandstone; at Dingo Gap, they are cobble-sized, stratified sandstone fragments in conglomerate derived from an immediately underlying sandstone. Mars orbiter images show lithified sediment fans at the termini of canyons that incise sedimentary rock in Gale crater; these, too, consist of recycled, extraformational sediment. The recycled sediments in Gale crater are compositionally immature, indicating the dominance of physical weathering processes during the second known cycle. The observations at Marias Pass indicate that sediment eroded and removed from craters such as Gale crater during the Martian Hesperian Period could have been recycled to form new rock elsewhere. Our results permit prediction that lithified deltaic sediments at the Perseverance (landing in 2021) and Rosalind Franklin (landing in 2023) rover field sites could contain extraformational recycled sediment.

Journal article

Sembhi H, Wooster M, Zhang T, Sharma S, Singh N, Agarwal S, Boesch H, Gupta S, Misra A, Tripathi SN, Mor S, Khaiwal Ret al., 2020, Post-monsoon air quality degradation across Northern India: assessing the impact of policy-related shifts in timing and amount of crop residue burnt, Environmental Research Letters, Vol: 15, Pages: 1-13, ISSN: 1748-9326

The past decade has seen episodes of increasingly severe air pollution across much of the highly populated Indo-Gangetic Plain (IGP), particularly during the post-monsoon season when crop residue burning (CRB) is most prevalent. Recent studies have suggested that a major, possibly dominant contributor to this air quality decline is that northwest (NW) Indian rice residue burning has shifted later into the post-monsoon season, as an unintended consequence of a 2009 groundwater preservation policy that delayed the sowing of irrigated rice paddy. Here we combine air quality modelling of fine particulate matter (PM2.5) over IGP cities, with meteorology, fire and smoke emissions data to directly test this hypothesis. Our analysis of satellite-derived agricultural fires shows that an approximate 10 d shift in the timing of NW India post-monsoon residue burning occurred since the introduction of the 2009 groundwater preservation policy. For the air quality crisis of 2016, we found that NW Indian CRB timing shifts made a small contribution to worsening air quality (3% over Delhi) during the post-monsoon season. However, if the same agricultural fires were further delayed, air quality in the CRB source region (i.e. Ludhiana) and for Delhi could have deteriorated by 30% and 4.4%, respectively. Simulations for other years highlight strong inter-annual variabilities in the impact of these timing shifts, with the magnitude and even direction of PM2.5 concentration changes strongly dependent on specific meteorological conditions. Overall we find post-monsoon IGP air quality to be far more sensitive to meteorology and the amount of residue burned in the fields of NW India than to the timing shifts in residue burning. Our study calls for immediate actions to provide farmers affordable and sustainable alternatives to residue burning to hasten its effective prohibition, which is paramount to reducing the intensity of post-monsoon IGP air pollution episodes.

Journal article

Balme MR, Gupta S, Davis JM, Fawdon P, Grindrod PM, Bridges JC, Sefton-Nash E, Williams RMEet al., 2020, Aram Dorsum: An Extensive Mid-Noachian Age Fluvial Depositional System in Arabia Terra, Mars, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 125, ISSN: 2169-9097

Journal article

Edgar LA, Fedo CM, Gupta S, Banham SG, Fraeman AA, Grotzinger JP, Stack KM, Stein NT, Bennett KA, Rivera-Hernandez F, Sun VZ, Edgett KS, Rubin DM, House C, Van Beek Jet al., 2020, A Lacustrine Paleoenvironment Recorded at Vera Rubin Ridge, Gale Crater: Overview of the Sedimentology and Stratigraphy Observed by the Mars Science Laboratory Curiosity Rover, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 125, ISSN: 2169-9097

Journal article

Rivera-Hernandez F, Sumner DY, Mangold N, Banham SG, Edgett KS, Fedo CM, Gupta S, Gwizd S, Heydari E, Maurice S, Nachon M, Newsom H, Schieber J, Stack-Morgan K, Stein N, Wiens RCet al., 2020, Grain Size Variations in the Murray Formation: Stratigraphic Evidence for Changing Depositional Environments in Gale Crater, Mars, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 125, ISSN: 2169-9097

Journal article

Stack KM, Grotzinger JP, Lamb MP, Gupta S, Rubin DM, Kah LC, Edgar LA, Fey DM, Hurowitz JA, McBride M, Rivera-Hernández F, Sumner DY, Van Beek JK, Williams RME, Aileen Yingst Ret al., 2019, Evidence for plunging river plume deposits in the Pahrump Hills member of the Murray formation, Gale crater, Mars, Sedimentology, Vol: 65, Pages: 1768-1802, ISSN: 0037-0746

Recent robotic missions to Mars have offered new insights into the extent, diversity and habitability of the Martian sedimentary rock record. Since the Curiosity rover landed in Gale crater in August 2012, the Mars Science Laboratory Science Team has explored the origins and habitability of ancient fluvial, deltaic, lacustrine and aeolian deposits preserved within the crater. This study describes the sedimentology of a ca 13 m thick succession named the Pahrump Hills member of the Murray formation, the first thick fine‐grained deposit discovered in situ on Mars. This work evaluates the depositional processes responsible for its formation and reconstructs its palaeoenvironmental setting. The Pahrump Hills succession can be sub‐divided into four distinct sedimentary facies: (i) thinly laminated mudstone; (ii) low‐angle cross‐stratified mudstone; (iii) cross‐stratified sandstone; and (iv) thickly laminated mudstone–sandstone. The very fine grain size of the mudstone facies and abundant millimetre‐scale and sub‐millimetre‐scale laminations exhibiting quasi‐uniform thickness throughout the Pahrump Hills succession are most consistent with lacustrine deposition. Low‐angle geometric discordances in the mudstone facies are interpreted as ‘scour and drape’ structures and suggest the action of currents, such as those associated with hyperpycnal river‐generated plumes plunging into a lake. Observation of an overall upward coarsening in grain size and thickening of laminae throughout the Pahrump Hills succession is consistent with deposition from basinward progradation of a fluvial‐deltaic system derived from the northern crater rim into the Gale crater lake. Palaeohydraulic modelling constrains the salinity of the ancient lake in Gale crater: assuming river sediment concentrations typical of floods on Earth, plunging river plumes and sedimentary structures like those observed at Pahrump Hills would have required lake densities near freshwater to form. The dep

Journal article

Davis JM, Gupta S, Balme M, Grindrod PM, Fawdon P, Dickeson ZI, Williams RMEet al., 2019, A diverse array of fluvial depositional systems in arabia terra: Evidence for mid‐noachian to early hesperian rivers on Mars, Journal of Geophysical Research: Planets, Vol: 124, Pages: 1913-1934, ISSN: 2169-9097

Branching to sinuous ridges systems, 100s of kilometers in length and comprising layered strata, are present across much of Arabia Terra, Mars. These ridges are interpreted as depositional fluvial channels, now preserved as inverted topography. Here we use high resolution image and topographic datasets to investigate the morphology of these depositional systems and show key examples of their relationships to associated fluvial landforms. The inverted channel systems likely comprise indurated conglomerate, sandstone, and mudstone bodies, which form a multi‐storey channel stratigraphy. The channel systems intersect local basins and indurated sedimentary mounds, that we interpret as paleolake deposits. Some inverted channels are located within erosional valley networks, which have regional and local catchments. Inverted channels are typically found in downslope sections of valley networks, sometimes at the margins of basins, and numerous different transition morphologies are observed. These relationships indicate a complex history of erosion and deposition, possibly controlled by changes in water or sediment flux, or base level variation. Other inverted channel systems have no clear preserved catchment; likely lost due to regional resurfacing of upland areas. Sediment may have been transported through Arabia Terra towards the dichotomy and stored in local and regional‐scale basins. Regional stratigraphic relations suggest these systems were active between the mid‐Noachian and early Hesperian. The morphology of these systems is supportive of an early Mars climate which was characterized by prolonged precipitation and runoff.

Journal article

Durcan JA, Thomas DSG, Gupta S, Pawar V, Singh RN, Petrie CAet al., 2019, Holocene landscape dynamics in the Ghaggar-Hakra palaeochannel region at the northern edge of the Thar Desert, northwest India, Quaternary International, Vol: 501, Pages: 317-327, ISSN: 1040-6182

Precession-forced change in insolation has driven de-intensification of the Asian Monsoon systems during the Holocene. Set against this backdrop of a weakening monsoon, Indus Civilisation populations occupied a number of urban settlements on the Ghaggar-Hakra plains during the mid-Holocene from 4.5 ka until they were abandoned by around 3.9 ka. Regional climatic variability has long been cited as a potential factor in the transformation of Indus society, however there remain substantial gaps in the chronological framework for regional climatic and environmental change at the northern margin of the Thar Desert. This makes establishing a link between climate, environment and society challenging. This paper presents 24 optically stimulated luminescence ages from a mixture of 11 fluvial and aeolian sedimentological sites on the Ghaggar-Hakra floodplain/interfluve, an area which was apparently densely populated during the Indus urban phase and subsequently. These ages identify fluvial deposition which mostly pre-dates 5 ka, although fluvial deposits are detected in the Ghaggar palaeochannel at 3.8 ka and 3.0 ka, post-dating the decline of urbanism. Aeolian accumulation phases occur around 9 ka, 6.5 ka, 2.8 ka and 1.7 ka. There is no clear link to a 4.2 ka abrupt climate event, nor is there a simple switch between dominant fluvial deposition and aeolian accumulation, and instead the OSL ages reported present a view of a highly dynamic geomorphic system during the Holocene. The decline of Indus urbanism was not spatially or temporally instantaneous, and this paper suggests that the same can be said for the geomorphic response of the northern Thar to regional climate change.

Journal article

Balme MR, Curtis-Rouse MC, Banham S, Barnes D, Barnes R, Bauer A, Bedford CC, Bridges JC, Butcher FEG, Caballo-Perucha P, Caldwell A, Coates AJ, Cousins C, Davis JM, Dequaire J, Edwards P, Fawdon P, Furuya K, Gadd M, Get P, Griffiths A, Grindrod PM, Gun M, Gupta S, Hansen R, Harris JK, Hicks LJ, Holt J, Huber B, Huntly C, Hutchinson I, Jackson L, Kay S, Kyberd S, Lerman HN, McHug M, McMahon WJ, Muller J-P, Ortner T, Osinski G, Paar G, Preston LJ, Schwenze SP, Stabbins R, Tao Y, Traxler C, Turner S, Tyler L, Venn S, Walker H, Wilcox T, Wright J, Yeomans Bet al., 2019, The 2016 UK Space Agency Mars Utah Rover Field Investigation (MURFI), PLANETARY AND SPACE SCIENCE, Vol: 165, Pages: 31-56, ISSN: 0032-0633

Journal article

García-Moreno D, Gupta S, Collier JS, Oggioni F, Vanneste K, Trentesaux A, Verbeeck K, Versteeg W, Jomard H, Camelbeeck T, De Batist Met al., 2019, Middle–Late Pleistocene landscape evolution of the Dover Strait inferred from buried and submerged erosional landforms, Quaternary Science Reviews, Vol: 203, Pages: 209-232, ISSN: 0277-3791

Prominent landforms, either buried or preserved at the seafloor, provide important constraints on the processes that led to the opening and present-day configuration of the Dover Strait. Here, we extend previous investigations on two distinct landform features, the Fosse Dangeard and Lobourg Channel, to better understand the poly-phase history of their formation and inferences for the opening and Pleistocene evolution of the Dover Strait. The Fosse Dangeard consist of several interconnected palaeo-depressions. Their morphology and spatial distribution are interpreted to be the result of plunge-pool erosion generated at the base of north-eastward retreating waterfalls. Their infills comprise internal erosional surfaces that provide evidence for the occurrence of several erosional episodes following their initial incision. The Lobourg Channel comprises various sets of erosional features, attesting to the occurrence of several phases of intense fluvial and/or flood erosion. The last one of these carved a prominent inner channel, which truncates the uppermost infill of the Fosse Dangeard. The morphology of the Lobourg inner channel and the erosional features associated with its incision strongly resemble landforms found in megaflood-eroded terrains, indicating that this valley was likely eroded by one or several megafloods. Our study therefore corroborates the existence of waterfalls in the Dover Strait at least once during the Pleistocene Epoch. It also provides evidence of the occurrence of multiple episodes of fluvial and flood erosion, including megafloods. Finally, this study allows us to establish a relative chronology of the erosional/depositional episodes that resulted in the present-day morphology of this region.

Journal article

Peter F, Gupta S, Davis J, Warner N, Adler J, Balme M, Bell III J, Grindrod P, Sefton-Nash Eet al., 2018, The Hypanis Valles delta: The last highstand of a sea on early Mars?, Earth and Planetary Science Letters, Vol: 500, Pages: 225-241, ISSN: 0012-821X

One of the most contentious hypotheses in the geological history of Mars is whether the northern lowlands ever contained an oceanic water body. Arguably, the best evidence for an ocean comes from the presence of sedimentary fans around Mars' dichotomy boundary, which separates the northern lowlands from the southern highlands. Here we describe the palaeogeomorphology of the Hypanis Valles sediment fan, the largest sediment fan complex reported on Mars (area >970 km2). This has an extensive catchment () incorporating Hypanis and Nanedi Valles, that we show was active during the late-Noachian/early-Hesperian period (∼3.7 Ga). The fan comprises a series of lobe-shaped sediment bodies, connected by multiple bifurcating flat-topped ridges. We interpret the latter as former fluvial channel belts now preserved in inverted relief. Meter-scale-thick, sub-horizontal layers that are continuous over tens of kilometres are visible in scarps and the inverted channel margins. The inverted channel branches and lobes are observed to occur up to at least 140 km from the outlet of Hypanis Valles and descend ∼500 m in elevation. The progressive basinward advance of the channellobe transition records deposition and avulsion at the margin of a retreating standing body of water, assuming the elevation of the northern plains basin floor is stable. We interpret the Hypanis sediment fan to represent an ancient delta as opposed to a fluvial fan system. At its location at the dichotomy boundary, the Hypanis Valles fan system is topographically open to Chryse Planitia – an extensive plain that opens in turn into the larger northern lowlands basin. We conclude that the observed progradation of fan bodies was due to basinward shoreline retreat of an ancient body of water which extended across at least Chryse Planitia. Given the open topography, it is plausible that the Hypanis fan system records the existence, last highstand, and retreat of a large sea in Chryse Planitia and perh

Journal article

Davis JM, Grindrod PM, Fawdon P, Williams RME, Gupta S, Balme Met al., 2018, Episodic and declining fluvial processes in southwest Melas Chasma, Valles Marineris, Mars, Journal of Geophysical Research: Planets, Vol: 123, Pages: 2527-2549, ISSN: 2169-9097

There is abundant evidence for aqueous processes on Noachian terrains across Mars; however, key questions remain about whether these processes continued into the Hesperian as the martian climate became less temperate. One region with an extensive Hesperian sedimentary record is Valles Marineris. We use high‐resolution image and topographic data sets to investigate the fluvial systems in the southwest Melas basin, Valles Marineris, Mars. Fluvial landforms in the basin exist across a wide area, and some are preserved as inverted channels. The stratigraphy of the basin is complex: Fluvial landforms are preserved as planview geomorphic features and are also interbedded with layered deposits in the basin. The fluvial morphologies are consistent with formation by precipitation‐driven runoff. Fluvial processes in the basin were episodic, suggesting multiple wet and dry periods. During dry periods, mantling material accumulated, and significant volumes of sediment were eroded, inverting fluvial channels. During wet periods, inverted channels and mantling material infilling valleys were incised by further fluvial erosion. These trends for episodic fluvial processes are similarly reflected in the central depression of the southwest Melas basin, previously described as a paleolake. Ultimately, fluvial processes in the basin gradually shut down, becoming geographically restricted, and then ceased entirely. We show that branching valley networks are also present on the plateaus above Melas and Ius Chasma, which converge on the heads of tributary canyons. These suggest that precipitation‐driven runoff processes also extended onto the plateaus of Valles Marineris.

Journal article

Barnes R, Gupta S, Traxler C, Ortner T, Bauer A, Hesina G, Paar G, Huber B, Juhart K, Fritz L, Nauschnegg B, Muller J-P, Tao Yet al., 2018, Geological Analysis of Martian Rover-Derived Digital Outcrop Models Using the 3-D Visualization Tool, Planetary Robotics 3-D ViewerPRo3D, EARTH AND SPACE SCIENCE, Vol: 5, Pages: 285-307, ISSN: 2333-5084

Journal article

Eigenbrode JL, Summons RE, Steele A, Freissinet C, Millan M, Navarro-González R, Sutter B, McAdam AC, Franze H, Glavin D, Archer PD, Mahaffy P, Conrad PG, Hurowitz JA, Grotzinger JP, Gupta S, Ming D, Sumner DY, Szopa C, Malespin C, Buch A, Coll Pet al., 2018, Organic matter preserved in 3-billion-year-old mudstones at Gale crater, Mars, Science, Vol: 360, Pages: 1096-1101, ISSN: 0036-8075

Establishing the presence and state of organic matter, including its possible biosignatures, in martian materials has been an elusive quest, despite limited reports of the existence of organic matter on Mars. We report the in situ detection of organic matter preserved in lacustrine mudstones at the base of the ~3.5-billion-year-old Murray formation at Pahrump Hills, Gale crater, by the Sample Analysis at Mars instrument suite onboard the Curiosity rover. Diverse pyrolysis products, including thiophenic, aromatic, and aliphatic compounds released at high temperatures (500° to 820°C), were directly detected by evolved gas analysis. Thiophenes were also observed by gas chromatography–mass spectrometry. Their presence suggests that sulfurization aided organic matter preservation. At least 50 nanomoles of organic carbon persists, probably as macromolecules containing 5% carbon as organic sulfur molecules.

Journal article

Bristow TF, Rampe EB, Achilles CN, Blake DF, Chipera SJ, Craig P, Crisp JA, Des Marais DJ, Downs RT, Gellert R, Grotzinger JP, Gupta S, Hazen RM, Horgan B, Hogancamp JV, Mangold N, Mahaffy PR, McAdam AC, Ming DW, Morookian JM, Morris RV, Morrison SM, Treiman AH, Vaniman DT, Vasavada AR, Yen ASet al., 2018, Clay mineral diversity and abundance in sedimentary rocks of Gale crater, Mars., Science Advances, Vol: 4

Clay minerals provide indicators of the evolution of aqueous conditions and possible habitats for life on ancient Mars. Analyses by the Mars Science Laboratory rover Curiosity show that ~3.5-billion year (Ga) fluvio-lacustrine mudstones in Gale crater contain up to ~28 weight % (wt %) clay minerals. We demonstrate that the species of clay minerals deduced from x-ray diffraction and evolved gas analysis show a strong paleoenvironmental dependency. While perennial lake mudstones are characterized by Fe-saponite, we find that stratigraphic intervals associated with episodic lake drying contain Al-rich, Fe3+-bearing dioctahedral smectite, with minor (3 wt %) quantities of ferripyrophyllite, interpreted as wind-blown detritus, found in candidate aeolian deposits. Our results suggest that dioctahedral smectite formed via near-surface chemical weathering driven by fluctuations in lake level and atmospheric infiltration, a process leading to the redistribution of nutrients and potentially influencing the cycling of gases that help regulate climate.

Journal article

Banham S, Gupta S, Rubin D, Watkins J, Sumner D, Edgett K, Grotzinger J, Lewis K, Edgar L, Stack-Morgan K, Barnes R, Bell III J, Day M, Ewing R, Lapotre M, Stein N, Rivera-Hernandez F, Vasavada Aet al., 2018, Ancient Martian aeolian processes and palaeomorphologyreconstructed from the Stimson formation on the lowerslope of Aeolis Mons, Gale crater, Mars, Sedimentology, Vol: 65, Pages: 993-1042, ISSN: 0037-0746

Reconstruction of the palaeoenvironmental context of Martian sedimentary rocks is central to studies of ancient Martian habitability and regional palaeoclimate history. This paper reports the analysis of a distinct aeolian deposit preserved in Gale crater, Mars, and evaluates its palaeomorphology, the processes responsible for its deposition, and its implications for Gale crater geological history and regional palaeoclimate. Whilst exploring the sedimentary succession cropping out on the northern flank of Aeolis Mons, Gale crater, the Mars Science Laboratory rover Curiosity encountered a decametre‐thick sandstone succession, named the Stimson formation, unconformably overlying lacustrine deposits of the Murray formation. The sandstone contains sand grains characterized by high roundness and sphericity, and cross‐bedding on the order of 1 m in thickness, separated by sub‐horizontal bounding surfaces traceable for tens of metres across outcrops. The cross‐beds are composed of uniform thickness cross‐laminations interpreted as wind‐ripple strata. Cross‐sets are separated by sub‐horizontal bounding surfaces traceable for tens of metres across outcrops that are interpreted as dune migration surfaces. Grain characteristics and presence of wind‐ripple strata indicate deposition of the Stimson formation by aeolian processes. The absence of features characteristic of damp or wet aeolian sediment accumulation indicate deposition in a dry aeolian system. Reconstruction of the palaeogeomorphology suggests that the Stimson dune field was composed largely of simple sinuous crescentic dunes with a height of ca 10 m, and wavelengths of ca 150 m, with local development of complex dunes. Analysis of cross‐strata dip azimuths indicates that the general dune migration direction and hence net sediment transport was towards the north‐east. The juxtaposition of a dry aeolian system unconformably above the lacustrine Murray formation represents starkly contrasting palaeoenvironmental and p

Journal article

Grindrod PM, Warner NH, Hobley DEJ, Schwartz C, Gupta Set al., 2018, Stepped fans and facies-equivalent phyllosilicates in Coprates Catena, Mars, Icarus, Vol: 307, Pages: 260-280, ISSN: 0019-1035

Journal article

Stein N, Grotzinger JP, Schieber J, Mangold N, Hallet B, Newsom H, Stack KM, Berger JA, Thompson L, Siebach KL, Cousin A, Le Mouelic S, Minitti M, Sumner DY, Fedo C, House CH, Gupta S, Vasavada AR, Gellert R, Wiens RC, Frydenvang J, Forni O, Meslin PY, Payre V, Dehouck Eet al., 2018, Desiccation cracks provide evidence of lake drying on Mars,Sutton Island member, Murray formation, Gale Crater, Geology, Vol: 46, Pages: 515-518, ISSN: 0091-7613

Mars Science Laboratory (MSL) Curiosity rover data are used to describe the morphology of desiccation cracks observed in ancient lacustrine strata at Gale crater, Mars, and to interpret their paleoenvironmental setting. The desiccation cracks indicate subaerial exposure of lacustrine facies in the Sutton Island member of the Murray formation. In association with ripple cross-stratification and possible eolian cross-bedding, these facies indicate a transition from longer-lived perennial lakes recorded by older strata to younger lakes characterized by intermittent exposure. The transition from perennial to episodically exposed lacustrine environments provides evidence for local to regional climate change that can help constrain Mars climate models.

Journal article

Joshi SK, Rai SP, Sinha R, Gupta S, Densmore AL, Rawat YS, Shekhar Set al., 2018, Tracing groundwater recharge sources in the northwestern Indian alluvial aquifer using water isotopes (δ18O, δ2H and 3H), Journal of Hydrology, Vol: 559, Pages: 835-847, ISSN: 0022-1694

Rapid groundwater depletion from the northwestern Indian aquifer system in the western Indo-Gangetic basin has raised serious concerns over the sustainability of groundwater and the livelihoods that depend on it. Sustainable management of this aquifer system requires that we understand the sources and rates of groundwater recharge, however, both these parameters are poorly constrained in this region. Here we analyse the isotopic (δ18O, δ2H and tritium) compositions of groundwater, precipitation, river and canal water to identify the recharge sources, zones of recharge, and groundwater flow in the Ghaggar River basin, which lies between the Himalayan-fed Yamuna and Sutlej River systems in northwestern India. Our results reveal that local precipitation is the main source of groundwater recharge. However, depleted δ18O and δ2H signatures at some sites indicate recharge from canal seepage and irrigation return flow. The spatial variability of δ18O, δ2H, d-excess, and tritium reflects limited lateral connectivity due to the heterogeneous and anisotropic nature of the aquifer system in the study area. The variation of tritium concentration with depth suggests that groundwater above c. 80 mbgl is generally modern water. In contrast, water from below c. 80 mbgl is a mixture of modern and old waters, and indicates longer residence time in comparison to groundwater above c. 80 mbgl. Isotopic signatures of δ18O, δ2H and tritium suggest significant vertical recharge down to a depth of 320 mbgl. The spatial and vertical variations of isotopic signature of groundwater reveal two distinct flow patterns in the aquifer system: (i) local flow (above c.80 mbgl) throughout the study area, and (ii) intermediate and regional flow (below c. 80 mbgl), where water recharges aquifers through large-scale lateral flow as well as vertical infiltration. The understanding of spatial and vertical recharge processes of groundwater in the study area pr

Journal article

Ewing RC, Lapotre MGA, Lewis KW, Day M, Stein N, Rubin DM, Sullivan R, Banham S, Lamb MP, Bridges NT, Gupta S, Fischer WWet al., 2017, Sedimentary processes of the Bagnold Dunes: Implications for the eolian rock record of Mars, Journal of Geophysical Research: Planets, Vol: 122, Pages: 2544-2573, ISSN: 2169-9097

The Mars Science Laboratory rover Curiosity visited two active wind-blown sand dunes within Gale crater, Mars, which provided the first ground-based opportunity to compare Martian and terrestrial eolian dune sedimentary processes and study a modern analog for the Martian eolian rock record. Orbital and rover images of these dunes reveal terrestrial-like and uniquely Martian processes. The presence of grainfall, grainflow, and impact ripples resembled terrestrial dunes. Impact ripples were present on all dune slopes and had a size and shape similar to their terrestrial counterpart. Grainfall and grainflow occurred on dune and large-ripple lee slopes. Lee slopes were ~29° where grainflows were present and ~33° where grainfall was present. These slopes are interpreted as the dynamic and static angles of repose, respectively. Grain size measured on an undisturbed impact ripple ranges between 50 μm and 350 μm with an intermediate axis mean size of 113 μm (median: 103 μm). Dissimilar to dune eolian processes on Earth, large, meter-scale ripples were present on all dune slopes. Large ripples had nearly symmetric to strongly asymmetric topographic profiles and heights ranging between 12 cm and 28 cm. The composite observations of the modern sedimentary processes highlight that the Martian eolian rock record is likely different from its terrestrial counterpart because of the large ripples, which are expected to engender a unique scale of cross stratification. More broadly, however, in the Bagnold Dune Field as on Earth, dune-field pattern dynamics and basin-scale boundary conditions will dictate the style and distribution of sedimentary processes.

Journal article

Gupta S, Singh A, Thomsen KJ, Sinha R, Buylaert JP, Carter A, Mark DF, Mason PJ, Densmore AL, Murray AS, Jain M, Paul Det al., 2017, Counter-intuitive influence of Himalayan river morphodynamics on Indus Civilisation urban settlements, Nature Communications, Vol: 8, Pages: 1-14, ISSN: 2041-1723

Urbanism in the Bronze-age Indus Civilisation (~4.6–3.9 thousand years before the present, ka) has been linked to water resources provided by large Himalayan river systems, although the largest concentrations of urban-scale Indus settlements are located far from extant Himalayan rivers. Here we analyse the sedimentary architecture, chronology and provenance of a major palaeochannel associated with many of these settlements. We show that the palaeochannel is a former course of the Sutlej River, the third largest of the present-day Himalayan rivers. Using optically stimulated luminescence dating of sand grains, we demonstrate that flow of the Sutlej in this course terminated considerably earlier than Indus occupation, with diversion to its present course complete shortly after ~8 ka. Indus urban settlements thus developed along an abandoned river valley rather than an active Himalayan river. Confinement of the Sutlej to its present incised course after ~8 ka likely reduced its propensity to re-route frequently thus enabling long-term stability for Indus settlements sited along the relict palaeochannel.

Journal article

Mark C, Chew D, Gupta S, 2017, Does slab-window opening cause uplift of the overriding plate? A case study from the Gulf of California, TECTONOPHYSICS, Vol: 719, Pages: 162-175, ISSN: 0040-1951

Journal article

Davies NS, Gibling MR, McMahon WJ, Slater BJ, Long DGF, Bashforth AR, Berry CM, Falcon-Lang HJ, Gupta S, Rygel MC, Wellman CHet al., 2017, Discussion on 'Tectonic and environmental controls on Palaeozoic fluvial environments: reassessing the impacts of early land plants on sedimentation' Journal of the Geological Society, London, JOURNAL OF THE GEOLOGICAL SOCIETY, Vol: 174, Pages: 947-950, ISSN: 0016-7649

Journal article

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