Four in one: a new crevasse-splay complex in the middle Miocene of central Poland

Abstract

This article focuses on a newly identified set of crevasse splays in the lignite-bearing Miocene of Poland. The sand bodies studied are situated within the First Mid-Polish Lignite Seam (MPLS-1) in the Tomisławice opencast mine, located near Konin in central Poland. The sand bodies form an alluvial complex of four superposed crevasse splays, separated by lignite layers, 0.1–0.8 m thick. They are considered to be overbank lateral splays, emplaced laterally by a fluvial channel, rather than its terminal splays. Their combined thickness reaches ~5 m, their length is <0.6 km and width <0.4 km, and their total area is ~0.1 km2. Nearly half of the sediments examined are subaerial deposits, while the rest are typical of crevasse-splay microdeltas, accumulated in a floodplain subaqueous environment. The sand bodies with local clay lenses are both underlain and overlain by, as well as interbedded with a range of lignite lithotypes, representing various sub-environments of a mid-Miocene mire (backswamp) realm. The estimated time span for the formation of the entire crevasse-splay complex, recording four short-term floods, is at least 48 kyr. The crevasse-splay complex is one of the best developed in lignite/coal successions worldwide. However, it poses a major technical obstacle to mining activity in the Konin Lignite Mine.