The Barmer Basin is a poorly understood rift basin in Rajasthan, northwest India. Exposures in the Sarnoo Hills, situated along the central eastern rift margin of the Barmer Basin, reveal a sedimentary succession that accumulated prior to the main Barmer Basin rift event, and a rift-oblique fault network that displays unusual geometries and characteristics. Here, we present a comprehensive study of Lower Cretaceous sedimentology on the basin margin, along with a detailed investigation of riftoblique faults that are exposed nowhere else in the region and provide critical insights into Barmer Basin evolution. Lower Cretaceous sediments were deposited within a rapidly subsiding alluvial plain fluvial system. Subsequent to deposition, the evolving Sarnoo Hills fault network was affected by structural inheritance during an early, previously unrecognised, rift-oblique extensional event attributed to transtension between India and Madagascar, and formed a juvenile fault network within the immediate rift-margin footwall. Ghaggar-Hakra Formation deposition may have been triggered by early rifting which tectonically destabilised the Marwar Craton prior to the main northeast-southwest Barmer Basin rift event. The identification of early rifting in the Barmer Basin demonstrates that regional extension and the associated rift systems were established throughout northwest India prior to the main phase of Deccan eruptions. Inheritance of early oblique fault systems within the evolving Barmer Basin provides a robust explanation for poorly understood structural complications interpreted in the subsurface throughout the rift. Critically, the presence of syn-rift sedimentary successions within older oblique rift systems obscured beneath the present-day Barmer Basin has significant implications for hydrocarbon exploration. INTRODUCTIONDespite being a significant structure within the West Indian Rift System (Fig. 1a), and an important hydrocarbon province (Dolson et al., 2015), the structural geology and evolution of the Barmer Basin rift remains relatively poorly understood. The current understanding of rift evolution is based predominantly upon subsurface data sets, where an abundance of complex structures and rift-oblique faults are variably imaged on seismic data throughout the rift (Bladon et al., 2015; Fig. 1b). However, the origin of these structures remains elusive, and limited exposure of the structure and stratigraphy of the rift at outcrop has restricted outcrop-based studies. This work characterises a rift-oblique fault network that is apparent nowhere else in the region, and is exposed on the eastern rift margin of the Barmer Basin, in the Sarnoo Hills. Detailed sedimentological and structural analyses are used to clarify the origin of similar rift-oblique faults imaged in the Barmer Basin subsurface, and subsequently to place the findings within the wider context of northwest India. Sediments were deposited in a maturing fluvial system within a rapidly subsiding continental alluvial plain environment. The expos...

Fluvial strata of the Lower Cretaceous Ghaggar‐Hakra Formation are exposed in fault blocks on the central‐eastern margin of the Barmer Basin, Rajasthan. The sedimentology of these outcrops are described from 114 logs (thicknesses up to 100 m) and 53 two‐dimensional correlation panels. The formation comprises three distinct channel belt sandstone packages defined as the Darjaniyon‐ki Dhani, Sarnoo and Nosar sandstones separated by thick siltstone‐dominated floodplain successions. The sediments were deposited in a sub‐tropical, low sinuosity fluvial system that matures into a highly sinuous fluvial system. The Nosar Sandstone, the youngest of the three packages, exhibits a significant increase in energy and erosive power compared to those underlying it. This distinct change in fluvial style is interpreted as being rejuvenation due to an actively developing rift network forming accommodation space, rather than climatic controls acting on part of the depositional system. Consequently, the Ghaggar‐Hakra Formation at outcrop represents Lower Cretaceous syn‐rift deposition within the Barmer Basin with active localized fault movement from Nosar Sandstone times onward. These findings provide sedimentological evidence in support of pre‐Palaeogene northwest–southeast extension in the Barmer Basin. Moreover, they imply Cretaceous extension took place widely along the northern extremity of the West Indian Rift System consistent with plate tectonic models of the break‐up of Gondwana and evolution of the Indian Ocean. Outcrops of Lower Cretaceous strata are patchy across India and Pakistan. This study provides valuable material which, when combined with the available published data, facilitates a re‐evaluation of Lower Cretaceous palaeogeography for the north‐west Indian Plate. The reconstruction demonstrates a complex fluvial system, where the sediments are preserved sporadically as early syn‐rift strata. The findings imply a high preservation potential for early Cretaceous fluvial successions within rifted fault blocks near Saraswati and Aishwarya of the Barmer Basin beneath the Palaeogene fill that likely have significant potential for further hydrocarbon exploration.

Lower Cretaceous (Aptian-Albian) sandstones of the Ghaggar-Hakra Formation in the Barmer Basin of northwest Rajasthan, India, have a complex depositional history which is confusing given they are quartzose arenites. The heavy mineral grains are very well-rounded, and the assemblage is dominated by zircon and rutile grains suggesting that the sediments have been recycled multiple times, whilst the presence of staurolite indicates a metapelite provenance component. Petrographical analysis suggests that extreme diagenesis cannot account for the quartzose arenite composition, despite Early Cretaceous soil formation and at least two periods of subsequent telogenetic modification. An alternative explanation to extreme chemical weathering in the provenance area is that the Ghaggar-Hakra sandstones are multi-cycle sediments derived, at least in part, from the quartzose arenites of the Cambrian Jodhpur Group. This analysis suggests that variations in detrital mineralogy across the Western India Rift System and Indus Basins are the result of transcontinental fluvial transport systems sourcing sediment from specific basement highs (Nagar Parker High, Devikot High, Deodar Ridge and Aravalli Mountain Range) mixed with varying proportions of sediment derived from sandstones of the Jodhpur Group. Consequently, we suggest that Cretaceous fluvial systems were controlled by the local palaeogeographies within the failed rifts of the Barmer and Cambay Basins and that both basins formed barriers to sediment transport from the Aravalli Mountain Range across the northwest Indian plate and into surrounding basins. EAGE BEAUMONT et al. Highlights • Ghaggar-Hakra Formation sandstones are compositionally quartzose arenites. • Weathering and diagenesis cannot account for the quartzose arenite composition. • Alternative explanation is that Ghaggar-Hakra sandstones are multicycle sediments. • Most likely from the quartzose arenites of the Cambrian Jodhpur Group.

<p>Microplastic contamination of river sediments has been found to be pervasive at the global scale however, the physical controls governing the storage, remobilization and pathways of transfer in fluvial sediments remain largely unknown. This is particularly so in sand bed rivers where the migration of bedforms has the potential to both store and release any microplastics contained within the sediment bed.  Without detailed experiments to model the movement of microplastics through, and storage within, sand bedforms it is impossible to understand what the environmental legacy of our excessive plastic pollution will be.</p><p>We report a series of mobile-bed laboratory flume experiments designed to explicitly quantify the relationship between sand bed surface development and microplastic flux characteristics. Experiments were performed within a glass sided, flow recirculating flume of rectangular cross section (8m x 0.5m x 0.5m). A uniform sand bed (D<sub>50</sub> of 450μm) was seeded with either PVC pellets (d=1.4g/cm<sup>3</sup>), Nylon pellets (d= 1.2 g/cm<sup>3</sup>), Polycarbonate fragments (d=1.2 g/cm<sup>3</sup>), Acetal beads (d = 1.4g/cm<sup>3</sup>) or Nylon fibres (d = 1.15g/cm<sup>3</sup>). Plastics were mixed into the sediment bed at either 0.1% or 0.5% concentration by mass and sediment beds were exposed to a flow rate of either 0.6 or 0.8 ms<sup>-1</sup>. Experiments were run until equilibrium conditions were attained as measured by bedform migration rate. During each experiment aerial photographs were taken every 2.5 minutes and videos shot through both the side walls and from top down to track bedform migration and plastic flux. Transported sediment and plastics were captured at the downstream end of the flume in a sediment trap to allow fluxes to be calculated. At the end of each run photographs were taken of the drained bed surface with photogrammetry then used to model the 3D bed surfaces.</p><p>Controls on microplastic flux as a result of bed evolution is discussed in terms of both flow rate flow rate and microplastic type.  </p>