First-cycle sand supply and the evolution of the eastern Canadian continental margin: Insights from Pb isotopes in the Mesozoic Scotian Basin

Abstract

Provenance analysis provides a powerful means to understand, connect, and reconstruct source-to-sink systems and Earth surface processes, if reliable toolkits can be developed, refined, and applied. Deciphering sediment routing to the Scotian Basin, offshore eastern Canada, is marred by sedimentary recycling but is critical to understanding the evolution of the Canadian margin in response to the evolving Labrador rift. In this study, Pb isotopes in detrital K-feldspars were fingerprinted in 13 wells across the Scotian Basin to track first-cycle sand supply. Unlike previous approaches, which utilized less labile proxies such as zircon, detrital K-feldspars are unlikely to survive multiple sedimentary cycles. The Pb-isotopic data reveal a dynamic seesaw effect between hinterland sources across the Jurassic-Cretaceous boundary, reflecting the complex interplay between the northward propagation of uplift along the rising Labrador rift flank and the reactivation of fault systems in the lower drainage basin. Pb isotopes in K-feldspar record progressively increasing long-distance supply from eastern Labrador, as early as the Callovian in the central basin, alongside diminishing but persistent local sourcing from adjacent Appalachian terranes. Comparison with more resilient mineral proxies, notably zircon, appears to confirm recycling in the lower drainage basin and highlights the limitations of using a single mineral proxy in isolation. This case study serves as an example of the growing potential of multiproxy provenance toolkits not only to decipher sediment-routing corridors in paleodrainage systems, but to better define and connect the drivers, mechanisms, and spatial and temporal ranges of Earth surface processes and tectonic events.

Light fractions can also be heavy hitters: Comparison of detrital zircon U–Pb and detrital K‐feldspar Pb–Pb as provenance indicators—A case study from Cretaceous strata of southern Utah, USA

“…For sedimentary provenance studies, the most important control is the variable lithology, age and composition of associated basement rock serving as a sediment source. Sandstone provenance studies aim to investigate the relative influence of each factor on composition to interpret ancient drainage systems and can provide insights on a range of scales and types of controls, from climate to tectonics (Blowick et al, 2020; Garzanti et al, 2007). Palaeocurrent analysis provides complementary understanding of sediment dispersal patterns but does not directly trace to sediment source areas.…”

“…This chapter thus aims to expand the provenance applications of Pb‐in‐K‐feldspar by leveraging its detrital signal in combination with detrital zircon U–Pb geochronology, in application to the question of dominant transverse or axial sediment supply to the Kaiparowits basin during the Late Cretaceous. This is the first application of this direct, same‐sample double‐proxy approach in North America and allows for distinction between first cycle and recycled sediment source terrane signals (Barham et al, 2020; Blowick et al, 2020). The utility of Pb‐in‐K‐feldspar provides an additional proxy and test of hypothesized palaeo‐drainages in this basin, with important implications for foreland basin dynamics.…”

“…EAGE REAT WERSAN and JOHNSON Sandstone provenance studies aim to investigate the relative influence of each factor on composition to interpret ancient drainage systems and can provide insights on a range of scales and types of controls, from climate to tectonics (Blowick et al, 2020;. Palaeocurrent analysis provides complementary understanding of sediment dispersal patterns but does not directly trace to sediment source areas.…”

“…1.1 | Pb-in-K-feldspar Blowick et al (2020) define three characteristics of a system that can reliably address recycling: (1) It must be ubiquitous in the range of host-rock lithologies in the hinterland, (2) it must be unlikely to be recycled, and (3) it must retain a diagnostic signature of its source. Kfeldspars are commonly found in a wide variety of igneous and metamorphic rocks and are also a framework grain in most sandstones (Pettijohn et al, 2012).…”

“…detrital zircon U-Pb geochronology), the use of Pb-isotopes in detrital K-feldspar ('Pb-in-K-feldspar') is a single-grain technique that is currently underemployed by most basin analysts. The Pb-in-K-feldspar tool has been applied in a small number of sandstone provenance studies and has successfully matched grains to basement terranes from which they were derived (Barham et al, 2020;Blowick, 2017;Blowick et al, 2019Blowick et al, , 2020Gwiazda et al, 1996;Hemming et al, 1996;Hemming & Rasbury, 2000;Johnson et al, 2018;Tyrrell et al, 2007;Zhang et al, 2016). The potential advantages include the relative abundance of K-feldspar in clastic rocks, as well as the possibility that Pb-in-K-feldspar can be used to characterize important crustal boundaries with far fewer grains (typically less than 100, even as few as 10 per sample, depending on the complexity of the drainage catchment) due to their reflection of large volumes of the crust (Blowick, 2017;Pullen et al, 2014;Tyrrell et al, 2007;Tyrrell et al, 2012).…”