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

Aoife Blowick,Shane Tyrrell,Yuanyuan Zhang,David J.W Piper,Georgia Pe-Piper

doi:10.1130/b35419.1

Abstract

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.

Highlights

Applications of provenance analysis extend far beyond determining the transitional or final source of a sediment
The Scotian Basin, offshore Nova Scotia (Fig. 1), presents the ideal laboratory in which to demonstrate the potential of Pb-isotopic fingerprinting of K-feldspar as part of a multiproxy approach to better estimate the abundance of recycled material in detrital archives and unravel the tectonic evolution of the southeastern Canadian margin
Comparisons between detrital K-feldspar Pb isotopes and zircon, monazite, and muscovite geochronology indicate a progressive decrease in the abundance of recycled grains delivered to the Scotian Basin from the mid-Jurassic to Early Cretaceous, which is interpreted to reflect the continued reworking and ultimate removal of much of the Carboniferous sedimentary cover on horsts in the lower drainage basin

Summary

INTRODUCTION

Applications of provenance analysis extend far beyond determining the transitional or final source of a sediment. The Scotian Basin, offshore Nova Scotia (Fig. 1), presents the ideal laboratory in which to demonstrate the potential of Pb-isotopic fingerprinting of K-feldspar as part of a multiproxy approach to better estimate the abundance of recycled material in detrital archives and unravel the tectonic evolution of the southeastern Canadian margin. We used Pb-isotopic fingerprinting of K-feldspar to track first-cycle sources to the Scotian Basin during the mid-Jurassic to Early Cretaceous. In order to facilitate comparison with potential hinterland sources, Pb-isotopic analysis of K-feldspars from granites in the South Mountain Batholith in the Meguma terrane (Fig. 1), the Permian German Bank pluton, offshore Nova Scotia, and Early Cretaceous volcanic rocks sampled in the Mallard M-45 well (North Atlantic, south of St. John’s) were analyzed.

RESULTS

B Hatton

CONCLUSIONS