Ichnology of the Middle Jurassic hiatus concretions from Poland: implications for their formation, exhumation, and palae
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ORIGINAL PAPER
Ichnology of the Middle Jurassic hiatus concretions from Poland: implications for their formation, exhumation, and palaeoenvironment Grzegorz Sadlok 1
&
Michał Zatoń 1
Received: 14 May 2019 / Revised: 2 August 2019 / Accepted: 19 November 2019 # Senckenberg Gesellschaft für Naturforschung and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In the present study, the Middle Jurassic exhumed carbonate concretions (the so-called hiatus concretions) from the Polish Jura (southern Poland) were studied ichnologically (precursor burrows and their tiering and bioerosion patterns) in order to decipher the palaeoenvironmental conditions leading to their formation and exhumation. The ichnological approach to the concretionary bodies used in this study yielded information on the scale of seafloor erosion and its relative timing compared to the burrowinfilling phase. The bioerosion patterns also provided information on proximal-distal trends and the frequency and strength of currents in the environment below storm wave base, a setting recorded in the monotonous, concretion-bearing siliciclastic sections which is studied here. The significance of the stratigraphic sequence is also briefly discussed based on the horizons containing the hiatus concretions. Keywords Hiatus concretions . Ichnology . Bioerosion pattern . Middle Jurassic . Poland
Introduction All concretionary bodies, regardless of their composition, form within host sediment (e.g. Coleman 1993; Chan et al. 2004). The position of the redox boundary, the concentration of organic matter within sediment, and the metabolic activity of microbes are all key drivers affecting the growth and mineralogy of concretions (Coleman 1993). This also applies to the so-called hiatus concretions, first described by Voigt (1968) and subsequently reported by many authors from deposits of various ages (e.g. Kaźmierczak 1974; Baird 1976, 1981; Wilson 1985; Hesselbo and Palmer 1992; Brett 1995; Brett et al. 2008; Zatoń et al. 2011; Wilson et al. 2012). According to Voigt (1968), such concretions underwent a complex burial-exhumation process following their formation. The activity of burrowers can modify the redox boundary position, organic content, and microbial activity within sediment and thus may affect the formation processes of concretions * Grzegorz Sadlok [email protected] 1
Faculty of Earth Sciences, University of Silesia in Katowice, 41-200 Sosnowiec, Poland
controlled by water geochemistry. Burrows introduce heterogeneity within sediment, as the infilling sediment often differs, e.g. in texture from the host bed (see Braithwaite and Talbot 1972; Bromley 1990; Papaspyrou et al. 2005; Kinoshita et al. 2007; Uchman 2009). This heterogeneity affects cementation paths and therefore affects the growth of the concretions (e.g. Bromley 1967; Gunatilaka et al. 1987; Pemberton and Gingras 2005; Gingras et al. 2012). In some cases, after concretions nucleated and became cemented, their host sediment must have been removed due to erosion during sed
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