Research Article| November 01, 2007 Drainage reorganization during breakup of Pangea revealed by in-situ Pb isotopic analysis of detrital K-feldspar S. Tyrrell; S. Tyrrell 1UCD School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland Search for other works by this author on: GSW Google Scholar P.D.W. Haughton; P.D.W. Haughton 1UCD School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland Search for other works by this author on: GSW Google Scholar J.S. Daly J.S. Daly 1UCD School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland Search for other works by this author on: GSW Google Scholar Author and Article Information S. Tyrrell 1UCD School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland P.D.W. Haughton 1UCD School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland J.S. Daly 1UCD School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland Publisher: Geological Society of America Received: 07 Feb 2007 Revision Received: 15 Jun 2007 Accepted: 21 Jun 2007 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 The Geological Society of America, Inc. Geology (2007) 35 (11): 971–974. https://doi.org/10.1130/G4123A.1 Article history Received: 07 Feb 2007 Revision Received: 15 Jun 2007 Accepted: 21 Jun 2007 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation S. Tyrrell, P.D.W. Haughton, J.S. Daly; Drainage reorganization during breakup of Pangea revealed by in-situ Pb isotopic analysis of detrital K-feldspar. Geology 2007;; 35 (11): 971–974. doi: https://doi.org/10.1130/G4123A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Pb isotopes in detrital K-feldspar grains provide a powerful provenance tracer for feldspathic sandstones. Common Pb isotopic compositions show broad (hundred-kilometer scale) regional variation, and this signature can survive weathering, transport, and diagenesis. The feldspar Pb signature can be measured rapidly using laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS), and careful targeting can avoid inclusions and altered regions within grains. Here, we combine a new Pb domain map for the circum–North Atlantic with detrital K-feldspar Pb isotopic data from Triassic and Jurassic sandstones from basins on the Irish Atlantic margin. The Pb isotopic compositions reveal otherwise cryptic feldspar populations that constrain the evolving drainage pattern. Triassic sandstones originated from distant Archean and Paleoproterozoic rocks, probably in Green-land, Labrador, and the Rockall Bank to the NW, implying long (>500 km) transport across a nascent rift system. Later, Jurassic sandstones had a composite Paleo- and Mesoproterozoic source in more proximal sources to the north (<150 km away). No recognizable feldspar was recycled from Triassic into Jurassic sandstones, and the change in provenance is consistent with distributed, low-relief Triassic extension in a wide rift, followed by narrower Jurassic rifting with more localized fault-controlled sediment sources and sinks. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Pb isotopic data from K-feldspars in Middle Triassic (Anisian) sandstones in the Wessex Basin, onshore SW UK, and the East Irish Sea Basin, some 350 km to the north, show that the same grain populations are present. This indicates that the drainage system (the ‘Budleighensis’ river) feeding these basins originated from the same source/s, most probably the remnant Variscan uplands to the south. Fluvial and aeolian sandstones have the same provenance, suggesting that if water- and wind-driven sands were originally derived from different sources, this has been obscured through reworking prior to final deposition. Significant recycling of feldspar from arkosic sandstones in earlier sedimentary basins can be ruled out. The provenance data agree with previous depositional models, indicating transport distances in excess of 400 km, with a drainage pattern that linked separate basins. This supports the idea that the regional fluvial system was driven by topography and episodic flooding events of sufficient magnitude to overcome evaporation and infiltration over hundreds of kilometres. Importantly, this drainage system appears to have been isolated and independent from those operating contemporaneously to the NW of the Irish and Scottish massifs, where the remnant Variscan uplands apparently exerted no influence on drainage or sand supply.
Palaeodrainage models for the mixed fluvial‐aeolian systems, which supplied detritus to Triassic basins on and offshore Britain and Ireland are well established. Basins such as those across Northern Ireland are not as well understood. Provenance studies of Triassic sandstones in the Slyne Basin offshore western Ireland and in basins west of Shetland have indicated that sediment supply was through a southward flowing fluvial system. Similar work on Triassic sandstones in the Wessex and East Irish Sea basins on and offshore Britain identified source rocks to the south supporting models, which evoke the northward flowing “Budleighensis” river system. The basins across Northern Ireland are potentially situated along the drainage divide between these two large‐scale drainage systems. K‐feldspar Pb‐isotopic analysis, apatite U–Pb geochronology and trace element geochemistry identify the Hebridean Platform, and the Scottish and Irish massifs to the north and west, respectively, and the remnant Variscan Uplands to the far south of the basins as source areas. The proportion of the northern‐ and southern‐derived detritus fluctuates several times over the sampled intervals, suggesting the dominance of drainage systems supplying sand to the basins “switched” intermittently over time. This may be due to abnormally heavy rains periodically powering the Budleighensis river system farther north or perhaps localised subsidence temporarily disconnecting Triassic basins on and offshore Britain and Ireland. The Triassic basins in Northern Ireland acted as either a major drainage divide between southern and northern river systems or as a regional sink for sediment preventing further expansion of either system.
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.
Abstract. While a large cryosphere may be a necessary boundary condition for millennial-scale events to persist, a growing body of evidence from previous interglacial periods suggests that high-magnitude climate events are possible during low-cryosphere climate states. However, the full spectrum of variability, and the antecedent conditions under which such variability can occur, have not been fully described. As a result, the mechanisms generating high-magnitude climate variability during low-cryosphere boundary conditions remain unclear. In this study, high-resolution climate records from Deep Sea Drilling Project (DSDP) site 610 are used to portray the North Atlantic climate's progression through low ice, boundary conditions of Marine Isotope Stage (MIS) 11c into the glacial inception. We show that this period is marked by two climate events displaying rapid shifts in both deep overflow and surface climate. The reorganization between Polar Water and Atlantic Water at subpolar latitudes appears to accompany changes in the flow of deep water emanating from the Nordic Seas, regardless of magnitude or boundary conditions. Further, during both intermediate and low ice boundary conditions, we find that a reduction in deep water precedes surface hydrographic change. The existence of surface and deep-ocean events, with similar magnitudes, abruptness, and surface–deep phasing, advances our mechanistic understanding of, and elucidates antecedent conditions that can lead to, high-magnitude climate instability.
Sediment delivery and supply are explicitly controlled by variations in broad-scale processes such as climate, tectonics and eustasy. These in turn influence fluvial processes and hinterland evolution. A bespoke multi-proxy approach (integrating apatite and zircon U-Pb geochronology, trace elements in apatite, and Pb-in-K-feldspar provenance tools) coupled with outcrop investigation is used to constrain the temporal trends in sediment delivery to channel sandstones of the fluvio-estuarine mid-Viséan Mullaghmore Sandstone Formation, Ireland. Provenance data indicate unique detrital signatures for all sampled horizons, indicating the fluctuating nature of sediment supply to this medium-sized basin. Tectonism and/or abrupt relative sea-level fall likely caused fluvial rejuvenation, resulting in local basement sourcing of the initial fill. Older and more distal sources, such as the Nagssugtoqidian Belt of East Greenland, become more prominent in stratigraphically younger channel sandstones suggesting catchment expansion. Paleoproterozoic to Mesoproterozoic sources are most dominant, yet the detrital grain cargo varies in each channel sandstone. Proximal sources such as the Donegal Batholith and Dalradian Supergroup are variable and appear to switch on and off. These signal shifts are likely the result of channel migration and paleoclimatic fluctuation. A monsoonal climate and large-scale wildfire events (evidenced by fusain) likely contributed to modify plant cover, intensify erosion, and increase run-off and sediment delivery rates from specific areas of the hinterland.
To assess provenance data and derive basin infill models with a higher level of certainty it is vital to understand how minerals used in sedimentary provenance behave in the sedimentary system. A multi-proxy approach helps ensure rigour in how provenance data are interpreted. U–Pb geochronology of refractory zircon and relatively less stable apatite, and Pb isotopic analysis of labile K-feldspar are employed in this study to reassess the provenance of Triassic sandstones in the Slyne Basin, offshore western Ireland. This approach aims at reducing the potential bias in each method, producing a complementary dataset. U–Pb zircon and apatite geochronology yields Archean–Paleoproterozoic ages, Caledonian ages and previously unrecognized Permo-Triassic ages. Pb isotopic analysis of K-feldspar does not identify the Permo-Triassic as a source. The detection of Permo-Triassic-aged detritus may suggest that volcanism was more widespread than previously recognized. These results support the hypothesis of a Triassic drainage divide between the basins offshore western Ireland and those onshore Britain and in the Irish Sea. Sand supply was dominantly from the north, with significant input from the flanks of the basin, and previously unrecorded sources, such as Permian-aged rocks, playing an important role. The provenance signal is consistent and homogenized throughout the sampled sequence indicating that the drainage system was long-lived. Supplementary material: Details of laboratory and sample preparation, data tables and summary pie charts for each sample are available at https://doi.org/10.6084/m9.figshare.c.4571096
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