Controls on Sedimentation Style and Distribution during initiation of Large Igneous Provinces- Case studies from the North Atlantic and the Columbia River Basalt Provinces

Promoting the understanding of Large Igneous Provinces (LIPs) is very important as these catastrophic periods in earth’s history can yield information concerning the scale of volcanic hazards, palaeo-climate as well as... [ view full abstract ]

Promoting the understanding of Large Igneous Provinces (LIPs) is very important as these catastrophic periods in earth’s history can yield information concerning the scale of volcanic hazards, palaeo-climate as well as playing host to valuable resources. By studying the sediments interbedded with volcanics within two case studies; The Skye Lava Fields of the North Atlantic Igneous Province (NAIP) (Selandian, 61-59 Ma) and the Clearwater Embayment of the Columbia River Basalt Province (Miocene, 16-6 Ma), we postulate the causal mechanisms for different styles of sedimentation and volcanic emplacement during the initiation of LIPs.
The Skye Lava Fields belong to the North Atlantic Igneous Province (NAIP) and is one of a suite of early volcanic centres emplaced in the Selandian (61-59Ma) along the NW European continental margin prior to the rifting of the North Atlantic in the Eocene (~55Ma). The volcanic rocks were emplaced from axial fissures constrained within a tilted half graben basin structure. Fluvio-estuarine sand bodies are restricted to a maximum thickness of 1m and widths of <200m, lack dune scale bed forms, contain >20% tuffaceous component and are intercalated with carbonaceous mudstones. These sediments are intercalated with both primary and re-sedimented hyaloclastites which form para-sequences with thicknesses up to 25m. Extra-basinal sediment was largely prohibited from entering the basin due to the underlying tectonic fabric which only allowed the development of small catchments draining intra-basinal highs with low stream accumulation factors.
The Columbia River Basalt Province was emplaced during the mid-Miocene (~16.5Ma) within a back arc setting between the Rocky Mountains and the proto Cascades in the NW of the USA. During initiation of volcanism, fissure fed volcanics were erupted into deeply dissected palaeo-valleys which caused ponding of fluvial systems with large external, dendritic catchments (extending up to 1000km in reach) with largely granitic bedrock. This caused rapid aggradation of fluvio-lacustrine sedimentary bodies which intercalated with tabular basalt flows and pillow-hyaloclastite sequences. Sedimentary interbeds ranged from 1-40m in thickness, with fluvial channel belts commonly showing a multi-lateral, nested architecture with thicknesses ranging from 10-25m in height. Channel belt widths, thicknesses and composition (variation in basaltic lithic sand component) are controlled by a number of factors including, lava flow morphology, proximity to fluvial source and proximity to the volcanic source.
The contrasting volcanic and sedimentation style within these LIPs demonstrates the complexity in the volcanogenic and sedimentary processes within LIPs and the need for further work in these unique environments.