The Himalayan-sourced Ganges-Brahmaputra river system and the deep-sea Bengal Fan represent Earth’s largest sediment-dispersal system. Here we present detrital zircon U-Pb provenance data from Miocene to middle Pleistocene Bengal Fan turbidites, and evaluate the influence of allogenic forcing vs. autogenic processes on signal propagation from the Himalaya to the deep sea. Our data record the strong tectonic and climatic forcing characteristic of the Himalayan system: after up to 2500 km of river transport, and >1400 km of transport by turbidity currents, the U-Pb record faithfully represents Himalayan sources. Moreover, specific U-Pb populations record Miocene integration of the Brahmaputra drainage with the Asian plate, as well as the rapid Plio-Pleistocene incision through, and exhumation of, the eastern Himalayan syntaxis. The record is, however, biased towards glacial periods when rivers were extended across the shelf in response to climate-forced sea-level fall, and discharged directly to slope canyons. Finally, only part of the record represents a Ganges or Brahmaputra provenance end-member, and most samples represent mixing from the two systems. Mixing or the lack thereof likely represents the fingerprint of autogenic delta-plain avulsions, which result in the two rivers delivering sediment separately to a shelf-margin canyon or merging together as they do today.

Morphological characteristics in river systems, including channel dimensions and river gradients, scale to drainage basin area, which provides the means for such elements to be predicted, measured and modeled. Moreover, recent studies interpret downstream changes in channel morphological and sedimentary characteristics to be the product of changing flow hydraulics as rivers transit from the normal flow to the backwater reach and approach the coastal ocean. This paper quantifies how large modern rivers undergo morphological and sedimentary transformations in response to normal flow to backwater transition. Morphologies adapting to such backwater hydraulic conditions is a potential for further investigation. With applications in modeling of modern river systems, this also provides the means for paleoenvironment reconstructions based on changing morphological characteristics since such quantitative framework is grounded by similar depositional processes. Building on previous studies, we construct river-long profiles, estimate backwater lengths, measure the ratio between channel-belt and channel widths (B_ChB/B_Ch), and measure the ratio between sand-rich to mud-dominated environments of deposition (S/M ratio) in five large modern river systems. We use results from >55,000 measurements of morphological and lithological characteristics from ~3,850 valley cross-sections over ~5,500 river kilometers to show that: (a) channel gradients decrease by ~30-50% as the channel goes through the normal flow to backwater transition, whereas (b) B_ChB/B_Ch decreases by >~60% and (c) S/M ratios decrease by ~35-90% within the upper backwater reach. These values further decrease in the lower backwater reach and approach unity (B_ChB/B_Ch = 1; S/M = 0) as the gradient reaches zero (sea level). Such systematic transformations in morphologic and sedimentary characteristics indicate they are both inherent and predictable, and can be used to interpret normal flow vs. backwater hydraulics in ancient fluvial deposits.

Continental-scale recycling of detrital zircon (DZ) grains and associated sediment across North American is not well understood. We trace a through line following the DZ proxy for the detritus originally sourced from Grenville and Appalachian orogens. This paper lays out an antecedent framework for one of the greatest sedimentation episodes of the Phanerozoic: the initial dispersal of Appalachian- and Grenville-age DZ grains to the western passive margin of Laurentia and the subsequent paleodrainage reorganization and sediment remobilization back to the east. The DZ U-Pb signature of the Appalachian-Ouachita orogenic system is dominated by Grenville (ca. 1250–950 Ma) and Appalachian (ca. 500–275 Ma) age groups and dominates the Phanerozoic record of North America. This study juxtaposes Pennsylvanian to modern DZ U-Pb data from across North America and demonstrates a persistent Appalachian signature, including a recycled Appalachian signature across Western North America. Lower Pennsylvanian deposits proximal to the Appalachian orogen are 50%–75% Appalachian- and Grenville-age DZ grains, representing the key component in the primary Appalachian signature. It remains unclear how the Appalachian signal was propagated to the west, but the Appalachian DZ signature was clearly present across the late Paleozoic passive margin of Laurentia and thus antecedent to potential DZ recycling throughout the Mesozoic and Cenozoic Eras. Triassic DZ samples document transcontinental fluvial systems that reached the western Laurentian margin, but subsequent Jurassic-Cretaceous samples indicate drainage reversal due to the rise of the Mesozoic Western Cordillera. A persistent Appalachian signature exists in these western-sourced, eastward-flowing systems—a phenomenon that continues to the present: samples are frequently composed of >40% Appalachian- and Grenville-age DZ. However, none of these systems are interpreted to be sourced by primary Appalachian or Grenville terranes, suggesting a recycled Appalachian signature. The persistent Appalachian signature, originally sourced by the linking of two orogenic terranes, continues to dominate the Phanerozoic record of much of North America to this day.

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Stable isotope, trace element, and cathodoluminescence analyses were performed on gastropods and matrix from rock cores of the Middle to Upper McMurray Formation (Lower Cretaceous/Aptian, Northwestern Alberta, Canada) to characterize the extent to which pristine material remained from which depositional environmental conditions could be estimated. Aragonitic gastropod shells retain their original depositional chemistry, and along with other closely associated authigenic carbonate components, indicate that the Middle to Upper McMurray Formation was deposited in a freshwater environment that was part of a continent-scale river system.