Benthic anoxia, intermittent photic zone euxinia and elevated productivity during deposition of the Lower Permian, post-glacial fossiliferous black shales of the Paraná Basin, Brazil

Accepted Manuscript Benthic anoxia, intermittent photic zone euxinia and elevated productivity during deposition of the Lower Permian, post-glacial fossiliferous black shales of the Paraná Basin, Brazil

Lucas D. Mouro, Michał Rakociński, Leszek Marynowski, Agnieszka Pisarzowska, Sabiela Musabelliu, Michał Zatoń, Marcelo A. Carvalho, Antonio C.S. Fernandes, Breno L. Waichel PII: DOI: Reference:

S0921-8181(17)30356-9 doi:10.1016/j.gloplacha.2017.09.017 GLOBAL 2651

To appear in:

Global and Planetary Change

Received date: Revised date: Accepted date:

3 July 2017 13 September 2017 26 September 2017

Please cite this article as: Lucas D. Mouro, Michał Rakociński, Leszek Marynowski, Agnieszka Pisarzowska, Sabiela Musabelliu, Michał Zatoń, Marcelo A. Carvalho, Antonio C.S. Fernandes, Breno L. Waichel , Benthic anoxia, intermittent photic zone euxinia and elevated productivity during deposition of the Lower Permian, post-glacial fossiliferous black shales of the Paraná Basin, Brazil. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Global(2017), doi:10.1016/j.gloplacha.2017.09.017

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ACCEPTED MANUSCRIPT Benthic anoxia, intermittent photic zone euxinia and elevated productivity during deposition of the Lower Permian, post-glacial fossiliferous black shales of the Paraná Basin, Brazil Lucas D. Mouroa,b, Michał Rakocińskic, Leszek Marynowskic, Agnieszka Pisarzowskad, Sabiela Musabelliuc, Michał Zatońc*, Marcelo A. Carvalhoe, Antonio C. S. Fernandese

Programa de Pós-Graduação em Geologia, Instituto de Geociências, Universidade Federal

do Rio de Janeiro, 21941-901, Rio de Janeiro, Brazil.

Departamento de Geociências, Universidade Federal de Santa Catarina, PFRH-PB 240,

88040-970, Florianópolis, Santa Catarina, Brazil.

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b

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a

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& Breno L. Waichelb

Faculty of Earth Sciences, University of Silesia, Będzińska 60, 41-200 Sosnowiec, Poland.

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Institute of Geological Sciences, Polish Academy of Sciences, Senacka 1, 31-002 Kraków,

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Poland.

Departamento de Geologia e Paleontologia, Museu Nacional, Universidade Federal do Rio

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de Janeiro, 20940-040, Rio de Janeiro, Brazil.

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*Correspondin author: e-mail: [email protected]

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Key words: Palaeoenvironments; black shales; euxinia; anoxia; geochemistry; South America.

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ACCEPTED MANUSCRIPT Abstract: Here, the Lower Permian, post-glacial fossiliferous Lontras black shales from the Paraná Basin (southern Brazil) are studied using integrated palynological, geochemical and petrographic methods for the first time in order to decipher the prevalent palaeoenvironmental conditions during their sedimentation. These black shales were deposited in a restricted marine environment. Inorganic geochemical data (U/Th ratios, authigenic uranium, molybdenum), organic geochemical data (total organic carbon, biomarkers) and framboid pyrite size distributions point to predominantly anoxic/euxinic bottom-water conditions.

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Moreover, the presence of aryl isoprenoids and maleimide biomarkers indicates that euxinia in the water column was intermittently present in the photic zone. The onset of anoxic

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conditions was caused by elevated productivity in the basin, which was related to

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deglaciation, marine transgression and the increased delivery of terrestrial nutrients. The presence of a positive organic carbon isotope excursion indicates that the black shale

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deposition resulted from increased productivity and the expansion of anoxic and nitrogen- and phosphate-enriched waters into the shallow photic zone. The high values of δ15N (exceeding 9‰) may be related to the deglaciation-driven sea-level rise and advection of denitrified water

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mass from the Panthalassic Ocean to the intracratonic Paraná Basin. Prolonged periods of seafloor anoxia/euxinia excluded potential scavengers and bioturbators, thus enhancing the

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preservation of numerous fossil taxa, including fish, sponges, insects and their larval cases, and conodont apparatuses. The intermittent photic zone euxinia may also have contributed to

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the mass mortality of fish populations, the fossils of which are very well-preserved in these

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black shales.

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1. Introduction

The transgressive black shales referred to as the Lontras Shale was deposited in the Brazilian Paraná Basin during the Early Permian and are currently well-known for its abundant and well-preserved fossil contents. Although the first discovery of the Lontras Shale and its preserved fossils was made by Euzebio de Oliveira in 1908 (Oliveira, 1930), these

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deposits only began to yield a large number of marine and terrestrial fossils in 1997, when a new exposure was discovered that was named Campáleo (Hamel, 2005; Mouro et al., 2014).

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Since then, the palaeontological history of the Lontras Shale (at Campáleo, the only site that is

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now preserved and protected) is known around the world due to the diversity of its taxa and the quality of its fossil preservation; thus, it has been referred to as an important Upper

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Palaeozoic Lagerstätte by many scientists (Scomazzon et al., 2013; Ianuzzi et al., 2014; Ricetti et al., 2014a; Mouro et al., 2016). Additionally, the presence of conodonts and palynomorphs makes it an important reference section for the intercorrelation of Lower

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Permian marine and terrestrial deposits (Ianuzzi et al., 2014). Despite the presence of various fossil groups, such as poriferans (see Mouro et al., 2014;

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Mouro & Fernandes, 2012, 2014), actinopterygian fishes (see Malabarba, 1988, Richter, 1991; Hamel, 2005), chondrichtyes (see Pauliv et al., 2014), brachiopods (see Carvalho et al.,

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1942), insects (see Pinto and Sedor, 2000; Martins Neto et al., 2001; Mouro et al., 2016; Ricetti et al., 2016), crustaceans (see Adami-Rodrigues et al., 2012; Kallen et al., 2014), and conodonts (Scomazzon et al., 2013; Wilner et al., 2014, 2016), as well as annelids,

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ammonoids, foraminifers, coprolites, fossilized wood and cuticles (see: Lopes, 2016; Ricetti et al., 2011, 2014; Mouro, 2010; Urban et al., 2012; Gnaedinger et al., 2012), the most unique

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fossils are those that are exquisitely preserved. Such fossils comprise actinopterygian fishes that are preserved as articulated skeletons within phosphatic nodules (Hamel, 2005) and articulated hexactinellid and demospongid sponges (Mouro et al., 2014; Mouro and Fernandes, 2012, 2014). However, within these fossil assemblages, the insects and conodonts represent the most remarkable paleontological discoveries that have currently been made in the Lontras Shale. The well-preserved insects are usually compressed and pyritized or are preserved as carbonaceous compressions exhibiting venation details. These fossils are very diverse and represent such groups as Blattodea, Grylloblattida, Homoptera, Ephemeroptera, Hemiptera, Coleoptera, Mecoptera, Diaphanopteroidea, Orthoptera, and Eoblattida (see Pinto & Sedor, 2000; Ricetti, 2012; Ricetti et al., 2014b, 2016; Lopes, 2016). Moreover, the oldest 3

ACCEPTED MANUSCRIPT known caddisfly larval cases are found in these deposits and can thus be used to shed a light on the evolution and palaeoecology of the first Trichoptera (Mouro et al., 2016). The conodont elements recovered at Campáleo, which are represented by Gondolella sp. and Mesogondolella sp., show spectacular taphonomical preservation, as their apparatuses are found in anatomical arrangements and are parallel to the bedding plane (Scomazzon et al., 2013). Importantly, all of these fossils were preserved during a deglaciation-driven transgressive event. Thus, the black, fossiliferous Lontras Shale deposits offer a unique

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insight into the post-glacial Early Permian palaeoenvironment. However, the conditions that prevailed during the deposition of the black shales and the burial of their autochthonous and

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allochthonous biotic components are unknown.

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Here, we present the first detailed palaeoenvironmental study of the Lontras black shale deposits in the Lower Permian Paraná Basin of Brazil using a multi-proxy approach. By

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incorporating integrated palynological, geochemical and petrographic methods, we show that these post-glacial black shales were deposited in an oxygen-deficient marine environment characterized by elevated productivity. The results presented here should serve as a

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palaeoenvironmental background for any future studies related to these fossiliferous deposits.

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2. Geological setting

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The South American Paraná Basin (Ordovician – Cretaceous) is an enormous intracratonic volcanic-sedimentary ramp basin that covers an area of almost 1.600.000 km2 within presentday Brazil, Argentina, Uruguay and Paraguay (Zalán et al., 1987; Milani and Ramos, 1998;

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Holz et al., 2008). During the Late Carboniferous–Early Permian, the landscape of the Paraná Basin area contained multilobed glacial fronts that formed fjord-like incised valleys opening

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towards a shallow epicontinental sea (see Santos, 1987; Buatois et al., 2010). Despite the fact that the origin of the basin is still unclear, its evolution is related to the tectonic stabilization that occurred following the Brazilian Cycle (Almeida and Hasui, 1984). In Brazil, Milani (1997) subdivided the Paraná Basin into six second-order supersequences. Here, we focus on the Gondwana I supersequence, which comprises the Carboniferous to Triassic interval and is defined by the transgressive-regressive sedimentary succession of the Palaeozoic Sea (Milani et al., 2007). In the Gondwana I supersequence, the passage from the Late Palaeozoic Ice Age to the Permian Greenhouse in the Paraná Basin is recorded in the Itararé and Guatá groups, the thicknesses of which exceed 2.050 m (Vesely and Assine, 2006; Holz et al., 2010).

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ACCEPTED MANUSCRIPT The Late Palaeozoic Itararé Group comprises the most extensive lithological record of Gondwana glaciation in the world (Rocha-Campos et al., 2008). Based on surface data, this group was previously subdivided into three formations (i.e., Campo do Tenente, Mafra and Rio do Sul) by Schneider et al. (1974). Later, based on the analysis of drill cores, França and Potter (1998) subdivided this group into another three formations (i.e., Lagoa Azul, Campo Mourão and Taciba). Both series of subdivisions are correlated and differ only in the position of the Lontras Member (Castro, 2004; Weinschütz and Castro, 2004, 2005, 2006). Four

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sedimentary sequences recording three basin-wide maximum transgression events were recognized in the Itararé Group by Weinschütz and Castro (2004), where the second

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maximum transgression event is recorded at the base of the Lontras Shale in the Lontras

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Member.

The Lontras Member (which is the uppermost unit of the Campo Mourão Formation)

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is almost 40 m thick and comprises a series of thin, varved shales containing dropstones that are overlain by ichnofossiliferous siltstones and fossiliferous black shales (i.e., the Lontras Shale) with abundant concretions and shaley rhythmites at its top (Hamel, 2005). The

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presence of dropstone-rich varved shales at its base provides evidence that deglaciation processes occurred during the deposition of the Itararé Group (Ricetti et al., 2016), while the

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Lontras Shale records its maximum transgression. Based on the previous dating of the Rio do Sul Formation to the Early Permian (Sakmarian–Artinskian, 294–275 Ma) presented by Petri

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and Souza (1993) and Dino and Rösler (2001), Holz et al. (2010) dated this formation to the Asselian–Sakmarian (299–284 Ma). This latter age is supported by palynological data (Souza, 2005) pointing to the Protohaploxypinus goraiensis Subzone of the Vittatina costabiliz

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Interval Zone (Asselian-Sakmarian). However, the results of the Rb-Sr dating of the Lontras Shale yielded an Artinskian age (287 ± 10 Ma), which supports the age defined by the

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international stratigraphic distribution of the conodont Mesogondolella found in the Lontras Shale (Scomazzon et al., 2016). If this result can be corroborated by other chronological methods, then the Itararé Group is probably younger than previously thought.

Figure 1 near here

The Campáleo outcrop (UTM 22J 0.618.473, 7.106.243) is located along road BR-280 in the city of Mafra, which is located to the north of the state of Santa Catarina in southern Brazil (Fig. 1). This site comprises the first 10 m of the Lontras Member, which contains a 1m-thick silty bioturbated argillite bed (i.e., the Glossifungites suite, Balistieri and Netto, 2002) 5

ACCEPTED MANUSCRIPT at its base and is overlain by a fossiliferous, 1.10-m-thick black shale layer (i.e., the Lontras Shale), followed by a non-fossiliferous, 7-m-thick shelly rhythmite layer (Fig. 2). Based on its pyrite concentration, rock fractures and fossil content, the Lontras Shale can be informally divided into four levels, including sublevels (Weinschütz, 2010). Based on the quantitative and qualitative features of the fossils that have been recovered in the Lontras Shale and are exposed at the Campáleo outcrop, this site has been identified as an important CarboniferousPermian Fossil-Lagerstätte (Scomazzon et al., 2013; Iannuzzi et al., 2014; Ricetti et al., 2014;

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Mouro et al. 2016; Ricetti et al., 2016).

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Figure 2 near here

3. Material and methods

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The samples studied here were collected from a 1.1-m-thick section of fossiliferous black shales (i.e., the Lontras Shale). Before this section was sampled, it was subjected to a detailed investigation of its fossil content and the occurrence of potential changes in its

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lithology. A total of 11 samples were collected (Fig. 2) and subjected to the same methods and analytical techniques in order to retrieve a detailed picture of the palaeoenvironmental

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conditions that were present during the sedimentation of the black shale. These methods include palynofacies analysis, total organic carbon and total sulphur determination, inorganic

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geochemical analysis (of major, minor and trace elements), organic geochemical analysis (of biomarkers), stable isotopic analysis of organic carbon and nitrogen, and framboid pyrite

Palynofacies analysis

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3.1.

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diameter analysis.

Palynofacies analysis is a well-known general analytical method that can be applied to retrieve information about depositional environments and source area conditions. Despite the existence of many published kerogen classification systems, given the objectives of the current project, we used the definitions of Tyson (1995) and Mendonça Filho et al. (2012), who recognized three main groups of kerogen, namely, palynomorphs, phytoclasts and amorphous organic matter (AOM). Palynomorphs are organic-walled microfossils that are useful for the description of palaeoenvironments and palaeoclimate; they can be subdivided into terrestrial (i.e., spores and pollen grains) and aquatic microfossils (e.g., marine prasinophyte algae and acritarchs, as well 6

ACCEPTED MANUSCRIPT as freshwater Botryococcus and Pediastrum, see Mendonça Filho et al., 2011). Phytoclasts are small-sized (i.e., clay- or fine-sand-sized) particles derived from higher plants or fungi (Bostick, 1971). They are primarily subdivided into opaque or non-opaque categories and can provide reliable information about their distance from the source area and thus the transportation of particles. Similar to the other kerogen components is AOM, which is defined as a series of organic, structureless particles that are derived from phytoplankton, bacteria, higher plant resins and macrophyte tissues (Mendonça Filho et al., 2011). AOM is an

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important qualitative feature that can be used for palaeoenvironmental interpretations. For marine palaeoenvironments, the qualitative features and abundances of these kerogen groups

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are directly related to sea-level variations and can be linked to a sequence stratigraphic

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context (Blondel et al., 1993; Tyson, 1993, 1995; Hashimoto, 1995; Tyson, 1996; Oboh and Yepes, 1996; Oboh-Ikuenobe et al., 1997; Bombardiere and Gorin, 2000; Oboh-Ikuenobe et

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al., 2005; Carvalho et al., 2006).

For the palynofacies analysis performed in this study, the samples were prepared using the non-oxidative standard preparation procedures of Tyson (1995) and Mendonça Filho et al.

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(2012). All mineral constituents were dissolved using hydrochloric acid (HCl – 32%) and cold hydrofluoric acid (HF – 40%) before undergoing separation. The remaining organic matter

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was then washed in distilled water, sieved (through a 10-mm mesh) and mounted on slides. These samples were prepared at the Palynology Laboratory Marleni Marques Toigo, Federal

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University of Rio Grande do Sul; the obtained material was stored at the Geochemistry Laboratory of the Federal University of Santa Catarina, Brazil.

Total organic carbon (TOC) and total sulphur (TS) determinations

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3.2.

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The abundances of total carbon (TC) and total inorganic carbon (TIC) were measured using an Eltra CS-500 IR-analyser with a TIC module. The contents of TC and TIC were measured using an infrared cell detector of CO2 gas, which was evolved by combustion under an oxygen atmosphere for TC and was obtained from its reaction with 10% hydrochloric acid for TIC. In all samples, TIC = 0. Therefore, the TOC values that were obtained were equal to the values of the measured TC. Calibrations were performed based on the analyses of Eltra standards.

3.3.

Inorganic geochemistry

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ACCEPTED MANUSCRIPT To decipher the detrital input to the basin, we used a series of lithogenic element ratios, such as Zr/Rb, Zr/Al, Si/Al, K/Al, Al/(Al+Fe+Mn) and Ti/Al, which can also be represented as Al2O3/TiO2 (e.g., Dypvik and Harris, 2001; Pujol et al., 2006; Riquier et al., 2006; Tribovillard et al., 2006; Calvert and Pedersen, 2007; Ver Straten et al., 2011; Racki et al., 2012). Samples were normalized using the post-Archean average shale (PAAS) compositions of Taylor and McLennan (1985); see also Tribovillard et al. (2012). To decipher bottom redox conditions, we used several indicators that are based on trace

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metal concentrations, such as U/Th, V/Cr, V/V+Ni, and Ni/Co (see e.g., Jones and Manning, 1994; Wignall, 1994; Rimmer, 2004; Rimmer et al., 2004, Racka et al., 2010; Śliwiński et al.,

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2010; Marynowski et al., 2012; Wójcik-Tabol, 2015). In fact, U/Th ratios are considered to be

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more reliable indicators of redox conditions than those involving other trace metals, such as V/V+Ni, V/Cr or Ni/Co (see e.g., Jones and Manning, 1994; Szczepanik et al., 2007; Zatoń et

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al., 2009; Racka et al., 2010; Marynowski et al., 2012; Rakociński et al., 2016). This is because the latter ratios often reflect extremely different redox conditions, ranging from euxinic/anoxic to oxic, respectively (see e.g., Racka et al., 2010; Rakociński et al., 2016 and

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references therein).

Molybdenum is an another very useful redox-sensitive trace element that is commonly

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used in palaeoenvironmental reconstructions (see e.g., Zheng et al., 2000; McManus et al., 2006; Algeo and Tribovillard, 2009; Tribovillard et al., 2006, 2012; Zhou et al., 2012) and

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was also analysed in the present study. In oxic environments, Mo occurs in seawater as the stable and largely unreactive molybdate oxyanion (MoO42-); under anoxic-euxinic conditions, molybdate converts to (MoOxS2-(4-x), x= 0 to 3) thiomolybdate (see e.g.,

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McManus et al., 2006; Algeo and Tribovillard, 2009 and references therein). Based on their observations of modern oxygen-depleted marine systems, such as the Black Sea, the Cariaco

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and Orca basins and the eastern tropical Pacific, as well as the differences observed in the covariations of uranium and molybdenum, Algeo and Tribovillard (2009) provided useful tools with which to reveal aspects of the watermass compositions and environmental dynamics of ancient palaeoceanographic systems (see also Tribovillard et al., 2012). In this study, TOC and Corg/P ratios were also used as productivity proxies (Schmitz et al., 1997; Brumsack, 2006; Tribovillard et al., 2006; Algeo and Ingall, 2007; Calvert and Pedersen, 2007). In environments with at least short-term oxygenated bottom waters, P that is initially sorbed onto Fe-oxyhydroxides may be fixed in authigenic carbonate fluorapatite phases while Ca2+ and F− diffuse into the sediment (Algeo and Ingall, 2007).

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ACCEPTED MANUSCRIPT The collected samples were powdered and analysed at the Bureau Veritas Acme Labs Canada Ltd. The concentrations of major, minor and trace elements were analysed using inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS) methods (e.g., Racki et al., 2012). The reliability of the analytical results was monitored based on the analyses of several international standard reference materials and duplicate analyses of several samples. The precision and accuracy of the results were better than ±0.05% (mostly ±0.01%) for the major elements and generally

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better than ±1 ppm for the trace elements (see Electronic Supplementary Material ESM Table 1-2). Major and minor oxide concentration data are given in weight percentages (wt.%) and

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Identification and quantification of biomarkers

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3.4.

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trace elements are given in parts per million (ppm).

Biomarkers (molecular fossils) are commonly used as indicators of depositional conditions in ancient sedimentary basins (e.g., Grice et al., 1996a, 2005; Schwark and

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Frimmel, 2004; Rohrssen et al., 2012; Smolarek et al., 2017b). In this study, aliphatic (nalkanes, steranes and hopanes), aromatic (aryl isoprenoids and alkylated PAHs) and polar

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(maleimides) organic compounds were used.

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3.4.1. Extraction, fractionation and derivatisation All eleven shale samples were extracted at conditions of 60°C and 150 bars using a DCM/methanol mixture (5:1, v:v) using a Dionex ASE 350 accelerated solvent extractor; 9-

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phenylindene was then added as an internal standard. The obtained extracts were separated into three fractions (i.e., aliphatic, aromatic and polar fractions) using modified column

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chromatography according to Bastow et al. (2007). Silica gel was activated at 120°C for 24 h and then put into Pasteur pipettes. The following eluents were used for the collection of these fractions: n-pentane (aliphatic), n-pentane and DCM (7:3 - aromatic), and DCM and methanol (1:1 - polar). An aliquot of the polar fraction was then again fractionated through the silica gel using acetone. These acetone fractions were evaporated, dissolved in super-dehydrated DCM and derivatised using MTBSTFA (N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide) to obtain the maleimide tertiary-butyl-dimethylsilyl compounds. Then, fractions were heated at 50°C for 1 h and run directly after derivatisation. A blank sample was analysed using the same procedure. Tracers of n-tert-butyl fatty acids and n-alkanols were detected.

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ACCEPTED MANUSCRIPT 3.4.2. Gas chromatography – mass spectrometry (GC-MS) GC-MS analyses were carried out using an Agilent Technologies 7890A gas chromatograph coupled with an Agilent 5975C Network mass spectrometer with a Triple-Axis Detector. A J&W DB5-MS (60 m x 0.25 mm x 0.25 m) capillary column coated with a 5% phenyl, 95% methylsiloxane phase was used. The GC was programmed to increase after 1 min from 50°C to 120°C at 20°C/min, to then increase to 280°C at 3°C/min, and to maintain

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this final temperature for 80 min. Mass spectra were recorded from 45–550 Da (0–40 min) and 50–700 Da (after 40 min). The MS was operated in the electron impact mode (with an ionization energy of 70 eV). Helium (6.0 Grade) was used as the carrier gas. An Agilent

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Technologies Enhanced ChemStation (G1701CA ver. C.00.00) and Wiley Registry of Mass

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Spectral Data (9th edition) software were used for the collection and processing of MS data.

Stable isotopes of organic carbon and nitrogen

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3.5.

The carbon and nitrogen isotopic compositions of organic matter have been widely used to detect biogeochemical cycling in depositional environments. The carbon isotopic

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compositions of organic matter are usually used as proxy indicators of palaeoproductivity, organic matter burial and atmospheric pCO2 levels (e.g., Popp et al, 1997). Nitrogen isotopic

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ratios can be used to determine changes in the marine N-cycle and are mainly used to

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determine the extent of biological N2-fixation and water column denitrification, as well as their relationships with palaeoredox conditions. The ratios of sedimentary organic carbon to nitrogen are frequently used to characterize sedimentary organic matter and to distinguish between organic matter of marine and terrestrial origins. Marine organic matter records lower

Meyers, 1994).

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values (4–10) than organic matter that is derived from higher vascular land plants (>20;

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Samples that were analysed for the carbon and nitrogen isotopic compositions of their bulk organic matter were prepared and analysed at the Institute of Geological Sciences, Polish Academy of Sciences (Poland). Samples were powdered and acidified with an excess of 10% HCl and were kept at 60°C for at least 8 h to remove inorganic carbonate material. Samples were then rinsed with ultrapure (>18 MΩ) deionized water to remove acid and were ovendried at 60°C. Sedimentary organic δ13C and δ15N values were analysed using a Thermo Flash EA 1112HT elemental analyser connected to a Thermo Delta V Advantage isotope ratio mass spectrometer in a Continuous Flow system. Isotopic values are reported in ‰ relative to the Vienna PeeDee Belemnite (VPDB) standard for carbon and the air N2 reference standard for

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ACCEPTED MANUSCRIPT nitrogen. The precision of δ13C analyses is better than ±0.33‰ and that of δ15N analyses is better than ±0.43‰. The percent concentrations of nitrogen were determined using a Vario MicroCUBE elemental analyser at the IGS PAS. Samples wrapped in tin capsules were combusted at 1150°C. The released gas (N2) was separated on a GC column and measured using a thermal conductivity detector. Percent amount values were normalized to a sulphanilic acid standard. The results of this measurement are reported in wt% and have a precision of better than

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Framboid pyrite diameter analysis

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3.6.

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±0.18%.

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The analysis of the size distribution of pyrite framboids is a useful method for inferring the redox conditions of modern marine environments, as was first shown by Wilkin et al. (1996). These authors showed that in an euxinic setting (in which there is no oxygen but

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free H2S is present), after achieving a critical size (ca. 6 µm or less), pyrite framboids rapidly sink to the seafloor, where they cease to grow. As a result, when they form in a euxinic

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setting, framboids accumulate as small-sized populations with a narrow size distribution that is characterized by a small standard deviation (Wilkin et al. 1996; see also Wilkin et al. 1997).

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In a dysoxic setting with a weakly oxygenated seafloor, pyrite framboids forming within surficial sediment can attain larger sizes due to the availability of local reactants. In effect, such framboid populations are generally larger and more variable in size (i.e., they have a

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larger standard deviation) (Wilkin et al. 1996). This method was quickly applied to the fossil record by Wignall and Newton (1998);

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currently, using the analyses of framboid pyrite size distributions to decipher redox conditions is a standard approach (e.g., Zhou and Jiang, 2009; Bond and Wignall, 2010; Wignall et al., 2010; Hammarlund et al., 2012; Marynowski et al., 2012; Tian et al., 2014; Huang et al., 2017; Smolarek et al., 2017a). Although the analysis of pyrite framboid size distribution is a useful method even when used alone (e.g., Wignall and Newton, 1998; Bond and Wignall, 2010; Wignall et al., 2010; Tian et al., 2014), it is even more effective and reliable when used together with other geochemical proxies. For the purposes of the current study, samples were cut perpendicular to the bedding plane. The polished small chips of samples were then inspected using the environmental scanning electron microscope (ESEM) housed at the Faculty of Earth Sciences in Sosnowiec, 11

ACCEPTED MANUSCRIPT Poland. The uncoated samples were observed under low vacuum conditions using backscattered imaging. To perform the pyrite framboid size distribution analysis, 100 specimens in each sample were measured (e.g., Wignall and Newton, 1998; Bond and Wignall, 2010; Wignall et al., 2010). The results are primarily shown in the form of standard box-andwhisker plots in which the minimum, maximum and mean sizes of the framboids, along with their median values, are indicated.

Palynofacies

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4. Results

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For each analysed sample, 373 to 375 kerogen components were counted and classified within the following kerogen groups: palynomorphs (spores, pollen grains, fungi,

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algae and acritarchs), phytoclasts (opaque – equidimensional, lath and corroded; non-opaque – non-biostructured degraded, non-opaque degraded biostructured and non-biostructured), and AOM with lower or absent fluorescence. In total, 4114 components were counted and

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classified (ESM Table 3). Of the three evaluated kerogen groups, AOM is predominant (with an average value of 74.4%), while the average phytoclast and palynomorph contents are

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22.8% and 2.8%, respectively. Despite the fact that the observed palynomorphs are diverse and include acritarchs (0.07%) and Portalites (0.09%), the most abundant palynomorphs are

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prasinophytes (Tasmanites: 0.62%), followed by spores (0.53%) and pollen grains (0.16%). The phytoclast components are predominantly opaque particles (14.7% in total; opaque equidimensional: 1.68%, opaque lath: 4.03% and opaque corroded: 8.91%), while non-opaque

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phytoclasts were present in average amounts (7.9% in total; non-opaque, non-degraded, biostructured: 0.06%, non-opaque, degraded, non-biostructured: 7.33%, and non-opaque,

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degraded, biostructured: 0.48%). Higher values were obtained using the Phytoclast Preservation Index (PPI) (average 8.28, sd 0.64), the opaque/non-opaque ratio (average 2.29, sd 1.30), and the lath-opaque/equidimensional-opaque ratio (average 3.91, sd 3.37). The fluctuations of particular components moving up the section are clearly visible (Fig. 3); this is discussed below in the context of the proximity to the source area.

Figure 3 near here

4.2.

TOC and TS determinations

12

ACCEPTED MANUSCRIPT The total organic carbon content in the investigated shales is high and ranges from 5.5 to 12.4% (Fig. 4, ESM Table 4). Samples collected from the middle part of the section (from 1C to 2B) contain TOC values that are less than 10%, whereas samples collected from the bottom and the top of the section record TOC values that are greater than 10% (Fig. 4, ESM Table 4). The values of total sulphur are greater than 1% and range from 1.2 to 4.5% (ESM Table 4). There is no any correlation between TS and TOC content, and most sulphur occurs in shales as iron sulphides. The extractable organic matter amount is generally similar for all

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samples; within the content of a particular fraction, the polar fraction is dominant (ESM Table

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4).

Inorganic geochemistry

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4.3.

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Figure 4 near here

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In the investigated sediments, the use of Si as a proxy of detrital input is somewhat

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problematic, because some silica is biogenic in origin (Racki et al., 2002; Pujol et al., 2006; Riqiuer et al., 2006; Turgeon and Brumsack, 2006; Calvert and Pedersen, 2007). This can be confirmed by the presence of numerous siliceous hexactinellid sponges (e.g., Mouro et al.,

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2014), which constitute at least a partial source of silica within the investigated sediments. However, Si exhibits a very weak correlation with Al (r = 0.15) but moderate to good

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correlations with other lithogenic elements, such as Th (r = 0.62) and Ti (r = 0.81). In these samples, Si recorded very low degrees of enrichment (with an average EFSi value of 1.12 and a maximum value of 1.28), which are close to the average values of shales. The Zr/Rb ratios measured in the Campáleo section ranged from 0.85 to 1.30 (Fig. 5, Table 1). The enrichment factor of Zr ranged from 0.88 to 1.26 (Table 2). In contrast, the measured Ti/Al ratios were low and ranged from 0.044 to 0.054, with an average EFTi value of 0.81; this reflected depletion compared to the post-Archean average shale values (cf. Taylor and McLennan, 1985). The measured Al/(Al+Fe+Mn) and K/Al ratios (Fig. 5, Table 1) were higher, ranging from 0.58 to 0.68 and 0.34 to 0.4, respectively, with an average EFK value of 1.22 (Table 2).

13

ACCEPTED MANUSCRIPT Table 1 and Figure 5 near here

Generally, low U/Th values (<0.75) are indicative of oxic conditions, while values ranging between 0.75 and 1.25 are typical of dysoxic conditions. Higher U/Th values (>1.25) are indicative of anoxic bottom-water conditions (e.g., Jones and Manning, 1994; Szczepanik et al., 2007; Racka et al., 2010; Marynowski et al., 2012; Rakociński et al., 2016). Here, the measured U/Th ratios range from 1.10 to 2.06 (Table 1) and generally exceed 1.25, which is

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indicative of oxygen-depleted waters. The high U/Th ratios (>1.25) observed in almost all samples are thus indicative of anoxia in bottom waters. Only two samples (1C and 1D)

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collected from the lower part of the section record values that are typical of dysoxic

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environments (Fig. 6). The most severely oxygen-depleted conditions are observed in the lowermost and uppermost parts of the investigated section. The presence of authigenic

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uranium (ranging from 9.23 to 18.87) confirms the presence of an oxygen-depleted, even euxinic bottom-water environment (see e.g., Wignall, 1994; Jones and Manning, 1994; Racka et al., 2010). Measured molybdenum concentrations range from 3.4 to 11.8 ppm (see ESM

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Table 1) and record enrichment ranging from 4.28 to 15.78, with an average EFMo value of 9.74 (Table 2). Additional signs of oxygen depletion include the elevated concentrations of

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other redox-sensitive elements, such as Cr, V, Zn, Pb, and Ni (see Francois, 1988; Wignall, 1994; Motzer and Engineers, 2005; Brumsack, 2006; Tribovillard et al., 2006; Calvert and

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Pedersen, 2007), which are expressed by their moderate to high EF values (Table 2). Moreover, this can be confirmed by the observed depletion in Mn, which records an average

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EFMn value of 0.38 (Table 2).

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Table 2 near here

Zinc and lead in the Campáleo section record very high degrees of enrichment (with an average EFZn value of 68.19 and an average EFPb value of 38.97; Table 2); in contrast, Cu is depleted (with an average EFCu value of 0.67), except in the uppermost part of the section, where its slight enrichment is observed (ranging from 1.25 to 2.18; Table 2). A similar trend can be observed in the measured Cd contents, which record elevated values in the upper part of the section (ESM Fig. 1).

Figure 6 near here

14

ACCEPTED MANUSCRIPT 4.4.

Occurrence and concentrations of organic compounds

The aliphatic fraction is characterized by the minor predominance of low-molecular weight n-alkanes that dominantly comprise n-C17 and n-C19 (ESM Table 4). High-molecular weight n-alkanes are present in comparable, slightly lower concentrations, except for sample 2A, in which the ratio of short- to long-chain n-alkanes is much higher than that in other

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samples (ESM Table 4). All of the shales contain predominantly odd over even highmolecular weight n-alkanes, which is manifested by their values of CPI and (especially)

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CPI(25-31) that are higher than 1 (ESM Table 4). Pristane and phytane, which are isoprenoids that are commonly present in sedimentary organic matter (OM), are the most abundant

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compounds in this fraction; their concentrations are three to seven times higher than those of n-C17 and n-C18. Although the values of Pr/Ph are higher than 1 and are even higher than 2 in

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most samples, no correlation is observed between Pr/Ph ratios and TOC values. Steranes and hopanes, which are biomarkers of eukaryotic and prokaryotic origin, are present in all samples. Within the hopanes, C30 17α21β(H)-hopane is the dominant compound; in the case of

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homohopanes, their abundance gradually decreases from C31 to C35. The values of C31 S/(S+R) range from 0.49 to 0.59; in contrast, the values of the 30M/(M+H) ratio in all samples are

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very similar and reach a maximum of approximately 0.3 (ESM Table 4). The regular sterane

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percentages are shown in ESM Table 4. The C27 sterane occurs in all samples as the dominant compound, with the exception of two samples where C29 steranes are dominant. C30 steranes occur in all samples in consistently relatively small abundances. The sterane to hopane ratios in these samples are diverse (ESM Table 5). In samples

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1C and 1D, they are less than 1; in the remaining samples, their values are greater than 1; in sample 3C, they are even higher than 2 (ESM Table 5). Although there is a quite good

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correlation between Ster/Hop ratios and TOC values (R2 = 0.76; ESM Fig. 3), there is no correlation between Ster/Hop ratios and Pr/Ph ratios. The observed distributions of polycyclic aromatic compounds and their alkyl derivatives are typical of sedimentary OM, as they record the prevalence of naphthalenes, phenanthrenes, dibenzothiophenes and their methyl-, dimethyl- and trimethyl-derivatives. Between alkylnaphthalenes, the 4-isopropyl-1,6-dimethylnaphthalene (cadalene) conifer biomarker was identified. Other conifer biomarkers in the investigated samples are represented by low concentrations (less than 0.4 g/g TOC) of 5,6,7,8-tetrahydrocadalene,

15

ACCEPTED MANUSCRIPT simonellite and retene (for mass spectra, see Simoneit and Mazurek, 1982). Perylene was identified in all samples; its concentrations range from 0.06 to 0.42 g/g TOC. Aryl isoprenoids were found in variable but generally low concentrations in all samples except for samples 1C and 1D, where these compounds are below detection limits (ESM Table 5; Fig. 4). In samples collected from the upper part of the section (3C, 3D, 4A), in addition to the aryl isoprenoids, diaryl compounds and the diagenetic products of

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isorenieratane (Grice et al., 1996b; Koopmans et al., 1996; Grice et al., 1997) were also detected. However, isorenieratane is not present in the analysed samples. One of the most abundant compounds in the aromatic fraction is alkylbiphenyl, which was tentatively

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identified as 3,4,5,5’-tetramethyl, 2’-ethyl biphenyl (see Racka et al., 2010; ESM Table 5). Its

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concentration correlates well with that of aryl isoprenoids (R2 = 0.88; ESM Fig. 3), thus suggesting that they have the same origin (as products of isorenieratane transformation), as

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well as with an unknown trimethylphenanthrene isomer (R2 = 0.82; Racka et al., 2010), which is another compound that is abundant in the aromatic fraction (ESM Table 5). A positive correlation between C19 biphenyl and aryl isoprenoids was recently identified in the Cambrian

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sedimentary rocks of the Georgia Basin (Australia), thus denoting photic zone euxinia (Pagès et al., 2016; Pagès and Schmid, 2016; see also Nabbefeld et al., 2010). Triaromatic steroids and benzohopanes are also important constituents of the aromatic

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g/g TOC, respectively.

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fraction; the sums of their concentrations reach maximum values of 23.4 g/g TOC and 1.5

Methyl, ethyl maleimide is the major polar compound in the polar fraction.

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Additionally, maleimides are represented by methyl, methyl maleimide, which is the secondmost important peak, as well as other maleimide compounds, between which methyl, isobutyl maleimides were clearly identified in all samples except for 1C, 1D and 2A (Fig. 4,

4.5.

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ESM Table 5).

Stable isotopic compositions of organic carbon and nitrogen

13

The δ C values of organic carbon were measured at 11 points throughout the section (Fig. 7, Table 3). Organic carbon isotopic values range from -27.1 to -27.7‰ in the base of the black shale facies (samples 1A and 1B). Above the base, the δ13C values increase to -25.9‰. After this excursion, the organic carbon isotopic values settle into a steady equilibrium state with a mean δ13C value of −26.5‰ (± 0.26‰).

16

ACCEPTED MANUSCRIPT Figure 7 near here Nitrogen isotopes were measured at the same sample locations as δ13C (Fig. 7, Table 3). Their values in the Lontras Shales are generally high. The base of the black shale records very high values ranging from +14.8 to +17.4‰ (samples 1A and 1B). The horizon lying 3-4 cm above sample 1B is marked by a rapid excursion to lighter δ15N values of +10.5‰. Then, the δ15N values settle to relatively uniform values, with a mean value of +9.2‰ (± 0.55‰)

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measured at the top of the section.

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Table 3 near here

The ratio of organic carbon to nitrogen (C/N) measured in the studied section exhibits

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its lower value of 23 in the base of the black shale facies, which is followed by an excursion of approximately 8 to its maximum value of 31 (Fig. 7, Table 3). Above this excursion, the values of C/N decrease to approximately 26. The measured δ13C and C/N values exhibit good

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correlation (r = 0.82, p = 0.002). The highest C/N value corresponds to the most positive δ13C value (Fig. 7). The values of δ15N and C/N exhibit negative covariation (r = -0.46, p = 0.16).

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The strong covariance between TOC and TN of r = 0.97 (p < 0.001) suggests that this

4.6.

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nitrogen has an organic origin (ESM Fig. 2).

Populations of pyrite framboids

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In all of the analysed samples, pyrite framboids were abundant; thus, it was possible to measure 100 specimens in each sample. Generally, the sizes of framboids in all inspected

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samples range from 2.14 to 25.4 µm. However, larger framboids (>10 µm) are significantly less common than small framboids, and the largest framboids (>15 µm) only recorded single occurrences in two samples (Fig. 8). Small-sized framboids dominate the size populations, which is clearly shown in the box-and-whisker plots and selected histograms (Fig. 8). Except for two samples (3C and 3D), which record mean values of 6.16 and 6.12 µm, respectively, all samples are characterized by mean framboid diameters that are less than 6 µm (5.07 – 5.76 µm). The narrow size distributions of the framboid populations are well-supported by their small standard deviation values (sd), which are all less than 2, except in sample 3C (sd = 2.81) (Fig. 8). Pyrite crystals were also encountered in all samples. No distinct trends in framboid pyrite size distribution are evident moving up the section, but some small changes in redox 17

ACCEPTED MANUSCRIPT conditions may have occurred during sedimentation. This may be indicated by the presence of intervals recording increasing sizes of pyrite framboids (1D, 3B-3D, Fig. 8).

Figure 8 near here

5. Discussion Organic matter maturation

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5.1.

According to the distribution of organic compounds, the thermal maturation of OM

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falls on the low range, just below the oil window. The values of the homohopane parameter

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[22S/(22S+22R)] are close to its equilibrium values (ESM Table 4), while the values of the moretane to hopane ratio 30M/(M+H) are still relatively high, thus indicating the rather low

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thermal changes of OM below the oil window (Peters et al., 2005). Moreover, the dominance of odd over even high-molecular weight n-alkanes is typical of the lower range of OM maturation. The same trend is observed in the case of the C29 20S/(20S+20R) regular sterane

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isomerization parameter. Because the equilibrium value of this parameter is ca. 0.55 (Peters et al., 2005), its lower values measured in our samples denote the low thermal transformation of

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OM (ESM Table 4). However, the investigated samples contain no ββ-hopanes, hopenes, sterenes or diasterenes, which are compounds that are characteristic of immature OM (e.g.,

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Peters et al., 2005; Marynowski et al., 2007). Based on all of these data, we can conclude that the degree of OM maturity corresponds to vitrinite reflectance values of ca. 0.5 - 0.55%,

Organic matter and detritic input to the basin

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5.2.

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which fall below the oil window (Peters et al., 2005).

The results of palaeogeographic reconstructions (e.g., Limarino & Spalletti, 2006; Rocha-Campos et al., 2008; Spalletti et al., 2010) indicate that the Parana Basin constituted a semi-enclosed, intracratonic basin. The distribution of phytoclasts and the higher values of their ratios and the PPI index indicate that a distal palaeoenvironmental setting existed during the deposition of the black shales, in which the source area varied with distance. The qualitative and quantitative characteristics (Tyson, 1993, 1995; Mendonça Filho, 1999; Mendonça Filho et al., 2011) of the three identified kerogen groups within the studied section define the palaeoenvironment of the Lontras black shale deposits as a restricted (i.e., exhibiting a limited connection to other basins) marine (suboxic-anoxic) environment (Fig. 3). 18

ACCEPTED MANUSCRIPT The inference of such restricted conditions in this basin is also supported by the high contents of TOC (5.5 to 12.4%) and TS (1.2 to 4.5%) measured in all samples (ESM Table 4). The TS content is almost entirely correlated with pyrite, because organic sulphur compounds are rare and occur in very low concentrations in these samples. Moving from samples 1A to 3D, two system tracts alternating each other (i.e., a transgressive system tract, TST, and a high system tract, HST) can be distinguished. This environment, which is defined as a distal suboxic-anoxic shelf, denotes a deep basin or

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stratified shelf sea that is characterized not only by high contents of AOM and lower abundances of palynomorphs (comprising a few bissacate pollen grains and spores but

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dominantly prasinophycean algae) but also by abundant alginites. In the basal sample 1A, the

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very high abundances of AOM (87.7%) and TOC (12.4%) are probably related to the final moments of a TST (i.e., a maximum transgressive phase). Here, phytoclasts and

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palynomorphs are also present, but in conspicuously lower quantities. In samples 1B and 1C, increases in phytoclast abundances (ESM Table 3) reflect the first phase of the HST. At the base of this HST interval, the presence of acritarchs and an increase in the supply of

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terrigenous material are recorded; this transition is confirmed by the presence of Portalites, higher percentages of pollen grains and the occurrence of conifer biomarkers.

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Moving from samples 1D to 3B, the values of AOM increase up to 90% in sample 3A, which is accompanied by the low abundance of phytoclasts (ESM Table 3), thus reflecting the

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maximum transgression that occurred during the following TST. Despite the decrease in phytoclasts, the values of non-opaque particles increase from samples 1D to 2B. The presence of this type of phytoclast is related to lower surface exposition or completely reduced

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transport, e.g., by turbiditic currents. The higher abundances of non-opaque particles support the inference of the transgressive moment, which reduced the distance to the source area. In

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addition to its higher AOM and TOC contents, sample 3B is characterized by the presence of conodonts, articulated autochthonous hexactinellid sponges and well-preserved caddisfly larval cases, which represent a calm, deeper and subtidal palaeoenvironment (Mouro et al., 2016). Later, in samples 3C and 3D, the values of AOM begin to decrease, which is accompanied by the increase of phytoclasts, especially opaque particles. This indicates that another change to HST, recording more terrestrial contributions and the presence of acritarchs and Portalites, is recorded in sample 3C. The repetition of this scenario allows us to suggest that the acritarchs contained in the Lontras Shale had a lower salinity tolerance. However, in this case, the TOC content remained at a constant level of approximately 11.5%. At the end of the analysed sequence (sample 4A), lower values of AOM (51%) than phytoclasts (49%) are 19

ACCEPTED MANUSCRIPT recorded. This indicates the establishment of a new environment, corresponding to a proximal suboxic-anoxic shelf, as indicated by the high degree of AOM preservation (reflecting reducing conditions in the basin) and moderate to high phytoclast contents (reflecting proximity to the source area) (Tyson, 1993). In sublevel 4A, an HST can be established based on the presence of Portalites and acritarchs. The interpretations of the contents of mixed, marine and terrestrial organic matter in the Lontras Shale are also supported by those derived from the observed biomarker

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compositions. The CPI(25-31) values close to 2 and the occurrence of cadalene and other conifer biomarkers in all samples indicate the input of terrestrial OM to the kerogen. Moreover,

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perylene, which is a wood-degrading fungi biomarker of terrestrial origin (Grice et al., 2009;

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Marynowski et al., 2013), was also found. However, the dominance of short chain n-alkanes and C27 steranes, as well as the presence of C30 steranes, is characteristic of marine OM

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(Moldowan, 1984; Moldowan et al., 1990; Peters et al., 2005). It is thus very difficult to assess the quantitative relationship between terrestrial and marine OM based only on the analysis of biomarkers. However, the generally low concentrations of terrestrial compounds

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observed in all samples suggest that the input of OM from land was rather minor. This supports the palynofacies data presented above, which record the definitive dominance of

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marine OM within the AOM and marine palynomorphs. The highest Zr/Rb values occur in the lowermost sample 1A and correspond to the

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highest values of Ti/Al and Zr/Al, thus indicating the higher supply of coarse clastics to the basin. In fact, the value of Ti/Al is slightly lower than that of the post-Archean average shale (with an average EFTi value of 0.81), while the value of Zr/Al is close to that of the post-

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Archean average shale (with EFZr ranging from 0.88 to 1.26 and an average EFZr value of 0.98; see Table 2), with its maximum enrichment recorded in the lowermost sample 1A.

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Therefore, it is clear that the supply of coarse clastics was limited during the deposition of the investigated shales in this part of the Paraná Basin, which is supported by the changes observed in the Zr/Rb and Zr/Al ratios beginning from sample 1C and moving up the section. The higher amounts of coarse clastic supply at the base of the section compared to the low amounts of land-derived phytoclasts and palynomorphs may indicate that the source area of the latter components was located far from the basin or that the post-glacial vegetation cover surrounding the basin was limited. More distinct is the increased supply of the clay fraction to the basin, which is expressed by the higher values (>0.6) of Al/(Al+Fe+Mn) (cf. Bellanca et al., 1996; Racki et al., 2002; Dias and Barriga, 2006) and K/Al (cf. Turgeon and Brumsack, 2006) that are especially intensive in the lower and middle parts of the investigated section 20

ACCEPTED MANUSCRIPT (Fig. 5). However, the values of EFK are not too high and reflect only minor enrichments (ranging from 1.1 to 1.29; Table 2). According to Akul'shina (1976), Al2O3/TiO2 values of less than 20 are indicative of humid climates, those greater than 30 are indicative of arid climates, and those ranging from 20 to 30 reflect semi-arid or semi-humid climates (for details, see Kiipli et al., 2012). The Al2O3/TiO2 values measured in the black shales (i.e., whole-rock samples), which range from 20.83 to 26.02 (Table 1; with an average Al2O3/TiO2 value of 23.36), could thus be indicative

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of semi-humid conditions. These values indicate that gradual climatic change occurred from arid cold glacial climate to warm humid climate in the Parana Basin during the Cisuralian

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epoch. This can be confirmed by the fact that the basin is underlain by Permian glacio-marine

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sediments containing numerous dropstones and overlain by the coal-bearing Rio Bonito Formation (Artinskian-Kungurian age; see e.g., Guerra-Sommer et al., 1995; Kalkreuth et al.,

Palaeo-oxygenation of the basin

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5.3.

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2006, 2010; Goldberg and Humayun, 2010; Boardman et al., 2012).

5.3.1. Redox conditions on the sea bottom

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Changes in the bottom redox conditions during the sedimentation of the Lontras black shales are very well supported by their TOC values, biomarker compositions, and U/Th

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ratios. Good correlations have been observed between Ster/Hop ratios and TOC contents (Fig. 4, ESM Fig. 3). Because steranes mainly originate from (micro)algae, which are primary producers in sedimentary basins, whereas hopanes are indicators of the bacterial reworking of

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primary OM (e.g., Connan et al., 1986), we can conclude that in our samples, Ster/Hop ratios increase with increasing anoxia. In other words, steranes are preferentially preserved under

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restricted conditions on the seafloor and during early diagenesis, while hopane biomarkers increase under conditions containing increased amounts of oxygen. Anoxic conditions are less favourable to heterotrophic bacteria activity, which results in the better preservation of steranes. Therefore, the interval of the section between samples 1C and 2B was clearly enriched in oxygen during OM deposition, while the bottom-water redox conditions recorded in the lowermost (samples 1A and 1B) and uppermost (samples 3A to 4A) parts of the section were oxygen-depleted. The same pattern is observed in the case of U/Th ratios, which indicate benthic anoxia during the deposition of the lowermost samples 1A and 1B, after which the redox conditions briefly improved to dysoxic (1C and 1D) and then again became truly anoxic in the 21

ACCEPTED MANUSCRIPT interval moving up the section from sample 2B. However, afterwards, the benthic conditions became even worse, as evidence of severe anoxia is established in the upper part of the section (Fig. 6). Such conditions can also be confirmed based on the distribution of authigenic uranium, which reaches values that are typical of euxinic bottom-water conditions in the upper part of the section (Uauth>15, e.g., Wignall, 1994), as well as TOC contents. The observed correlation between the U/Th and Ster/Hop ratios is also quite good (R2 = 0.6). In restricted, silled basins, such as the modern Black Sea, in which deep watermasses

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have prolonged renewal times (ranging from ~400 to 2000 years), the molybdenum concentrations in the water column below the chemocline decrease sharply, reaching aqueous

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Mo/U values that are only ~0.04 that of seawater, which in turn produces deep-water

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sediments that are depleted in Moauth relative to Uauth (see Algeo and Lyons, 2006; Algeo et al., 2007; Algeo and Tribovillard, 2009). Our samples collected from the Campáleo section have

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Moauth/Uauth values (ESM Fig. 4) that are similar to those occurring below water depths of ~200 - 400 m in the Black Sea (cf. Algeo and Tribovillard, 2009: Fig. 3C). This indicates that the investigated sediments were formed in the restricted Paraná Basin, which was then an

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intracratonic Palaeozoic basin that was most likely similar to the anoxic Black Sea and featured a slow renewal time of its deep watermass. Our MoEF vs. UEF values are similar to

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those of the Late Devonian Woodford shale of the Delaware Basin in Texas (see Fig. 8C in Algeo and Tribovillard, 2009). Although the surface waters of individual basins were

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probably in contact in the Late Devonian Seaway of the North American Craton, the circulation of deep waters in many silled basins remained restricted (Algeo and Tribovillard, 2009).

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The sediments investigated here are enriched in Cr (with an average EFCr value of 2.62; Table 2). Although they could have been derived from igneous rocks (Motzer and

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Engineers, 2005), the high Cr contents of these samples (ranging from 109.47 to 369.47 ppm) are most likely the result of an anoxic environment, which can be confirmed by the presence of the good correlations of Cr with TOC and TS (r = 0.73 and r = 0.82, respectively). The observed Cr concentrations in the black shales range from 20 to 3000 ppm (Motzer and Engineers, 2005). The studied Lontras Shale section is also enriched in vanadium and nickel (with an average EFV value of 3.12 and an average EFNi2 value of 2.91). Sediments that form in anoxic environments are commonly enriched in lead (e.g., Francois, 1988; Racka et al., 2010). Although acidic igneous rocks are enriched in Pb, it mainly occurs in K-feldspars and micas (Francois, 1988 and references therein). In the investigated sediments, Pb records a high degree of enrichment (with an average EFPb value of 38.97) and exhibits moderate 22

ACCEPTED MANUSCRIPT correlations with TOC and TS (r = 0.55 and r = 0.5, respectively). Similar enrichment is observed in other anoxic black shales, such as the Tournaisian Sunbury shale from the Central Appalachian Basin (Rimmer, 2004) and the Famennian Annulata black shale in Ściegnia in the Holy Cross Mountains (Racka et al., 2010). The investigated sediments are depleted in Mn (with EFMn values ranging from 0.24 to 0.49), which is also indicative of anoxic conditions, as Mn is very mobile in reduced sediments (see Tribovillard et al., 2006). In contrast, trace elements such as Cd and Zn suffer a dramatic decrease in solubility in the euxinic waters of

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some modern restricted basins (i.e., the Framvaren Fjord and Black Sea) and are trapped in sediments as sulphides (Jacobs et al., 1985; Brumsack, 2006). This is confirmed by the strong

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correlations of Cd and Zn with TS (in which r = 0.93 for both of these elements) observed in

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the investigated section (ESM Fig. 1). It is well known that sediments that form in highproductivity and/or anoxic bottom waters record high Corg/P ratios (that are generally >50 and

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are greater than ~150:1 in permanently anoxic environments, e.g., the Black Sea or Framvaern Fjord), while lower values of Corg/P ratios are indicative of oxic-suboxic conditions (Algeo and Ingall, 2007). Here, the high Corg/P ratios observed (Fig. 6, Table 1) in the sediments of

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the Campáleo section may be indicative of a generally high-productivity and anoxic regime during sedimentation. In fact, the very high TOC contents observed in all of the analysed

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samples (ranging from 5.53 to 12.42% TOC), as well as the presence of a rich phytoplankton assemblage and the occurrence of AOM, are the best indicators of a high-productivity regime

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under oxygen-depleted conditions.

The distribution of framboid pyrite sizes is also indicative of an oxygen-depleted palaeoenvironment during the deposition of the Lontras shales. Based on the framboid size

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distribution criteria of Bond and Wignall (2010: Table 1; see also Huang et al., 2017), the majority of the analysed samples exhibit pyrite framboid populations that are characteristic of

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euxinic/anoxic environments. According to these authors, euxinic conditions (i.e., persistently sulphidic conditions in the lower water column) are characterized by abundant, small (with a mean size of 3-5 µm) framboids with a narrow size range (i.e., a small standard deviation), while pyrite framboids that are characteristic of anoxic conditions (i.e., in which no oxygen is present in bottom waters for long periods of time) are characterized by their abundance, small sizes (with a mean size of 4-6 µm) and the presence of a few, larger framboids. Recently, Tian et el. (2014), using Lower Triassic samples collected from South China, united the characteristics of framboids produced under the euxinic and anoxic conditions of Bond and Wignall (2010) and provided broader criteria for euxinic conditions (i.e., mean values of <6.5 µm, a standard deviation of <2.5, and abundant or minor authigenic pyrite). 23

ACCEPTED MANUSCRIPT Size distributions of pyrite framboids that are similar to that obtained in the present study have been detected in modern Black Sea sediments by Wilkin et al. (1996) as well as in many Permian-Triassic sections (e.g., Wignall et al., 2010; Tian et al., 2014; Huang et al., 2017). This framboid size distribution is characteristic of all but one sample (3C) which, although characterized by dominantly small-sized framboids (<6 µm), has a larger standard deviation and contains much larger specimens (>20 µm). However, these large framboids are very rare in this sample (Fig. 8) and should be regarded as outliers in the present study,

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especially given that the dominant framboid population consists of specimens with diameters that are less than 6 µm (Fig. 8). Authigenic pyrite crystals also occur in all of the investigated

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samples. Moreover, in the investigated section, four separate pyrite-rich levels were found.

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Such pyrite crystals have also been found in Lower Triassic samples containing abundant, small-sized pyrite framboids that formed under euxinic conditions by Tian et al. (2014).

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However, interpreting palaeo-oxygenation conditions based on the pyrite framboid size distribution derived from a few centimetre-thick rock samples must be undertaken with caution, because we must consider that a time-averaged population (e.g., Bond and Wignall,

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2010) may preserve signals of changing redox conditions within a given palaeoenvironment. Indeed, although the domination of small-sized framboids with a narrow size distribution

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characterized by a small standard deviation points to euxinic/anoxic conditions in bottom waters, the presence of large framboids (as in sample 1D and those beginning in 3B to 3D and

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culminating in 3C) may indicate the brief onset of slightly oxygenated (dysoxic) conditions in the water column above the seafloor. The presence of authigenic pyrite crystals associated with tiny framboids may also point to the transient, periodic oxygenation of bottom waters,

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which is clearly indicated by the presence of some representative benthic fauna (e.g., sponges, bivalves, gastropods, brachiopods) in the investigated deposits. It is worth mentioning that

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recent studies (Mills et al., 2014) have proposed that sponges can tolerate very low oxygen contents (i.e., 0.5% – 4% of present atmospheric levels). Thus, it is possible that Early Permian sponges, which are common and sometimes very well-preserved in the Lontras Shale (Mouro et al., 2014), could either have appeared during a brief interval in which water was oxygenated or were able to cope in oxygen-deficient bottom waters. Such short periods of oxygenation during generally euxinic/anoxic bottom-water conditions in a restricted basin, which can be detected even during worldwide anoxic events, have also been described in other Palaeozoic basins (e.g., Marynowski et al., 2012; Rakociński et al., 2016), thus denoting that these the seemingly monotonous black shales may record complex depositional histories. 24

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5.3.2. Intermittent photic zone euxinia

The compounds present in the Lontras shales that are characteristic of photic zone euxinia (PZE) are aryl isoprenoids (AI), which are the diagenetic products of the transformation of isorenieratane (i.e., a green sulphur bacteria biomarker) (Summons and Powell, 1987; Koopmans et al., 1996a). Although these compounds can also be produced by

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the degradation of -carotene (Koopmans et al., 1996b), when they occur together with the products of di- and tri-aromatic isorenieratane transformations (for a detailed description, see

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Koopmans et al., 1996a; Grice et al., 1996b; Clifford et al., 1998), their origin seems to be

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strictly connected with the degradation of isorenieratane. The second characteristic of AI formed from isorenieratane is their heavy 13C values (Koopmans et al., 1996b); however,

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samples must contain high concentrations of these compounds in order for them to be detected during carbon isotopic measurements. Aryl isoprenoids were detected in all samples except for 1C, 1D and 3A, but their concentrations were rather small, ranging from 0.2 to 1.7

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g/g TOC (Fig. 4, ESM Table 5). The identification of di- and triaromatic compounds with 21, 22 and 26 carbon atoms in their molecules as well as 3,4,5,5’-tetramethyl, 2’-ethyl

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biphenyl (as the main compound in the fraction), which all are diagenetic products of

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isorenieratane degradation, thus confirm the occurrence of PZE. Pagès et al. (2016) and Pagès and Schmid (2016) also observed that the correlation between alkylbiphenyl compounds and aryl isoprenoids represented evidence of photic zone euxinia. However, they identified C19

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biphenyl (which is also present in aryl isoprenoid-rich samples; see Racka et al., 2010), while in our samples, C18 biphenyl is present as the major component. There is no correlation between AI and TOC or the Ster/Hop ratio. The main reason for this is the difference in the

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sources of AI and steranes, as well as the generation periods of the individual compounds in the water column. The low AI concentrations and lack of isorenieratane recorded in relatively low-maturity samples (ESM Fig. 5) suggest that intermittent photic zone euxinia conditions occurred within the generally oxic water column that is rich in nutrients and features high productivity. Moreover, on the plot of Pr/Ph vs. aryl isoprenoids ratio (AIR) most of the samples is located in the episodic rather than persistent PZE field with oxidation episodes (ESM Fig. 6; see Schwark and Frimmel, 2004 and Melendez et al., 2013a). The elevated production of microorganisms causes dysoxic (samples 1C to 2B) to anoxic (samples 1A and 3A to 4A) bottom-water conditions below the photic zone. Although anoxia (or even euxinia)

25

ACCEPTED MANUSCRIPT on the seafloor below the photic zone was continuous, euxinic conditions in the photic zone of the water column were rare and interrupted. This explains the high TOC contents and Ster/Hop ratios but the low AI concentrations and lack of correlation between these proxies. Another important group of compounds confirming that euxinic conditions existed in the water column during the deposition of the Lontras shales is the 1H-pyrrole-2,5-diones (maleimides). The key compounds of Me,i-Bu maleimides and Me,n-Pr maleimide, which originate from bacteriochlorophyll-related pigments and denote PZE (Pancost et al., 2002;

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Naeher et al., 2013; Naeher and Grice, 2015) were identified in all samples, except for samples 1C to 2A.

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The values of the Me,i-Bu/Me,Et ratio are relatively small (Fig. 4, ESM Table 5) and

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correspond to values measured in the Givetian/Frasnian deposits of the Canning Basin in Western Australia (see Naeher and Grice, 2015). Both low values of aryl isoprenoids and low

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values of the Me,i-Bu/Me,Et ratio indicate the intermittent occurrence of PZE during the deposition of the Early Permian Lontras black shales.

Stable isotopes of organic carbon and nitrogen

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5.4.

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5.4.1. Preservation of the original nitrogen and carbon isotopic compositions

The relationships between the TN and TOC contents of the studied samples and their

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correlations with their isotopic compositions were considered in order to evaluate the effects of diagenetic imprints on their original isotopic compositions. The preferential loss of 14N during early diagenesis, thermal maturation and

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(palaeo)weathering lead to the increase in the 15N values of the organic matter in black shales (e.g., Altabet and Francois, 1994; Williams et al., 1995; Marynowski et al., 2017) and

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produce negative correlations between 15N values and TN contents. The plot of 15N vs. TN shows no correlation in the analysed samples (r = 0.45, p = 0.17), thus indicating that the selective loss of 14N that occurred after burial is not significant. Increasing C/N ratios and decreasing TOC content may reflect thermal maturation after deposition (Bristow et al., 2009). The moderate negative correlation between the C/N ratios and TOC contents in the analysed samples (r = -0.71, p = 0.01) suggests that the organic matter records little thermal maturation. On the other hand, the poor linear correlation between 15N values and C/N ratios observed in the Lontras Shales (r = -0.46, p = 0.16) implies that the influence of maturation on 15N values is insignificant. Furthermore, the negative correlation between 15N and

26

ACCEPTED MANUSCRIPT δ13Corg values recorded in the studied section (r = -0.68, p = 0.02) suggests that hydrothermal alteration and/or metamorphic devolatilization did not overprint the original isotopic compositions (Pinti et al., 2009). The generally poor correlations observed in the analysed samples suggest that even though some post-depositional processes may have slightly changed the 15N and δ13Corg values of the analysed rock samples, their measured isotopic

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values basically represent their original compositions.

5.4.2. Productivity as inferred from stable isotopes of organic carbon and nitrogen

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In the lower part of the studied Lontras black shale succession, the 15N values are

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very high and range from +17.4 to 14.8‰ (samples 1A and 1B, Fig. 7). In our opinion, these highly positive 15N values suggest that denitrification occurred in the Paraná Basin.

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Denitrification mostly occurs in oxygen-deficient zones (with oxygen concentrations of <20 μM, Ganeshram et al., 2000; or <5 μM, Robinson et al., 2007) where nitrate, rather than oxygen, is utilized as the primary electron acceptor for the oxidation of organic matter.

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Nitrogen fixation produces organic matter that is highly depleted in 15N, while denitrification produces subsurface waters that are highly enriched in 15N. In the euphotic zone, 15N-enriched

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nitrate is assimilated by phytoplankton, resulting in the deposition of sedimentary organic

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matter with higher isotopic values (Altabet et al., 1999; Kienast et al., 2002). A similar but smaller effect is generated when nitrate is limited and this preference can no longer be accommodated. Therefore, positive 15N values may reflect a period when the stagnation and

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stratification of the ocean occurred, during which time organic nitrogen was exported to deep waters or sedimentary deposits, thus producing an oceanic nitrate pool recording the residual enrichment of 15N (Cline and Kaplan, 1975).

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Water-column denitrification in mid-water anoxic zones has been observed in modern regions of the ocean, such as the eastern tropical Pacific Ocean (i.e., the Peru Margin), the eastern tropical North Pacific Ocean and the Arabian Sea, where large settling fluxes of organic detritus in coastal upwelling areas near continental margins have led to the consumption of oxygen in subsurface waters (Brandes and Devol, 2002). These regions often record sedimentary 15N values ranging from 7–10‰ (locally >15‰, Brandes and Devol, 2002; Algeo et al., 2008). Horizontal advection is one mechanism that can transport denitrified water masses over distances of more than 1000 km to semi-enclosed marine basins (such as the Paraná Basin) while preserving their high δ15N signals (Brandes et al., 1998; 27

ACCEPTED MANUSCRIPT Ganeshram et al., 2000; Kienast et al., 2002). Taboada et al. (2016) proposed that a proto-rift system, coupled with a sea-level rise of at least 100 m, reinforced the trans-Gondwanan marine connection during the Asselian-Sakmarian. Thus, we cannot exclude the possibility that the very high 15N values in the Lower Permian Lontras black shale record the transfer of 15

N-rich water masses from the Panthalassa Ocean to the mid-continental region of the Paraná

Basin by the Carboniferous-Permian intracontinental rift system during transgression. The horizon located 4 cm above the base of the Lontras shales (1C sample) records a

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rapid excursion to lighter 15N values (10.5‰), which is gradually followed by lighter 15N

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values (~9‰, Fig. 7). The potential causes of this decline in sedimentary 15N could be 1) enhanced nitrogen fixation, 2) incomplete nitrate utilization, 3) the decline of water-mass

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denitrification, or 4) the increased flux of terrestrial plant material to the sedimentary environment (Saitoh et al., 2014). Microbial nitrogen fixation produces minor isotopic

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fractionation (0 to -2‰), and the 15N value of generated ammonium is similar to that of atmospheric N2 (~0‰). We can rule out incomplete nitrate utilization because the occurrence

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of enhanced redox-sensitive proxies (see above), such as high U/Th values (>1), high TOC concentrations, evidence of pyrite rain-out events (see Schoepfer et al., 2012; Knies et al., 2013), and undisturbed laminae, all indicate that oxygen-depleted conditions prevailed during

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the deposition of the Lontras black shale. Anoxia would have promoted the recycling of

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sedimentary phosphorus into the water column, further stimulating nitrate utilization (Knies et al., 2013). A decline in the denitrification of the water column is also unlikely to explain the observed decrease in the 15N values of the deposits studied here, as nitrate is generally a

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major oxidant in oceanic biogeochemical cycles under oxygen-depleted conditions (e.g., Codispoti and Christensen, 1985). Alternatively, a change in the balance between marine denitrification and nitrogen

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inputs from continental erosion likely caused the decline in δ15N values (Christensen et al., 1987). Palynofacies data and the presence of certain specific organic compounds in the studied section indicate the presence of marine and terrigenous organic matter, which is dominated by marine OM (see discussion above). This marine origin is not consistent with the obtained C/N values (22–31), which suggest the predominance of a terrestrial source (as terrestrial organic matter records C/N values of > 20, Meyers et al., 2006). However, similar C/N ratios have also been reported for marine OM deposited in areas of high productivity (Núñez-Useche et al., 2016). The C/N ratios obtained in this study agree well with those measured under eutrophic conditions. These high values could have resulted from the loss of 28

ACCEPTED MANUSCRIPT nitrogen during oxygen-stress periods linked to high productivity (e.g., Núñez-Useche et al., 2016). On the other hand, the higher δ13Corg values recorded above the base of the Lontras shale section could be attributed to changes in the sources of OM. The lower δ13Corg values measured in the samples collected from the basal part of the studied section indicate that they were primarily contributed from marine OM sources, while the samples recording higher δ13Corg values contain contributions from both marine and terrestrial OM (Nabbefeld et al., 2010). The palynological observations of plant–derived particles in these samples, as well as

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the concentrations of selected elements, indicate that the decrease in 15N is linked to the increase in the C/N ratios and δ13Corg values of the samples (samples 1C-1D, Fig. 7), which

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may be interpreted as evidence of an increase in the input of terrestrial OM. Some authors

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(Sephton et al., 2005; Meyers, 2006, Xie et al., 2007) have suggested that increased continental runoff would have delivered abundant nutrients to the basin (e.g., phosphate and

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iron) that would have first stimulated algal productivity, magnified the export of OM, and increased the mid-water oxygen demand. The combination of surface water dilution, which increased the salinity stratification of the upper water column and thereby discouraged mixing

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and mid-water ventilation, as well as magnified oxygen draw-down, would have intensified

Implications for fossil preservation

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5.5.

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and expanded the oxygen minimum zone.

Although it is known that anoxia retards decay rather than halts it (Allison, 1988a, b), anaerobic conditions can exclude potential scavengers and bioturbators (e.g., Allison and

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Briggs, 1993; Orr et al., 2003). The latter biological agents not only directly degrade organic matter but may also disrupt the anaerobic conditions and chemical gradients in the vicinity of

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buried organisms (Sagemann et al., 1999; Or et al., 2003). Thus, the strongly reducing conditions (anoxic/euxinic) caused by enhanced productivity, as well as the occurrence of episodic burial during the deposition of the black fossiliferous Lontras Shale, played crucial roles in the preservation of its fossil assemblage, the examples of which are presented on Fig. 9. This fossil preservation could also have been enhanced by cold water temperatures, which could have slowed down bacterial activity (Hamel, 2005). When interpreting the preservation of fish in the Lontras Shale, Hamel (2005) stated that these organisms might have been buried by episodic turbidity currents. Moreover, these turbidity flows could also have released H2S accumulated at the sea bottom, thus poisoning the fish populations living nearby within the oxygenated water column. 29

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Figure 9 near here

Although there is no evidence supporting the role of turbidity flows releasing H2S from bottom sediments, the presence of periodic poisonous waters can be confirmed using biomarker data, which indicate the occurrence of intermittent photic zone euxinia. Indeed, such episodic poisonous conditions in the water column very likely affected the local fish

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populations, thus leading to their mass mortality, accumulation on the anoxic sea-bottom and burial. The mass mortality events of fish caused by PZE have also been proposed by

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Heimhofer et al. (2008) within the famous Cretaceous Santana Formation in Brazil. Recently,

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it was also found (Melendez et al., 2013a, b) that PZE contributed significantly to the preservation of organisms within Upper Devonian Gogo Formation Lagerstätte concretions in

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Australia.

The episodic rapid burial by turbidity currents also affected fossils such as caddisfly larval cases. These delicate structures are either preserved intact or disarticulated,

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and it is possible that these larval cases originally formed in shallower waters and were transported to the deeper parts of the basin, where they were rapidly buried and preserved

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(Mouro et al., 2016). The intact hexactinellid sponges (Mouro et al., 2014) and conodont apparatuses (Scomazzon et al., 2013; Wilner et al., 2014, 2016) were likely buried in the

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deeper, more oxygen-deficient and calmer parts of the basin. Only under such conditions would sponge spicules and particular conodont elements closely associated with the seabottom still remain intact. The anoxic/euxinic conditions again occurring in the bottom waters

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would have enhanced their preservation by the simple exclusion of any scavenging animals.

6. Conclusions

1. The Early Permian Lontras black shales studied here were deposited in a restricted marine environment of the Paraná Basin recording two alternating system tracts: a transgressive system tract and a high system tract. 2. Organic matter present in the Lower Permian Lontras shale is of mixed, marine and terrestrial origins. However, the marine type is predominant, according to the results of palynofacies and biomarker analyses. 30

ACCEPTED MANUSCRIPT 3. Bottom-water conditions were predominantly anoxic/euxinic, as is evidenced by inorganic geochemical data (i.e., U/Th ratios and authigenic uranium and molybdenum concentrations) and organic geochemical data (i.e., TOC and steranes/hopanes ratios), as well as framboid pyrite size distributions. Euxinia in the water column was intermittently present in the photic zone, as is evidenced by the presence of specific biomarkers (i.e., aryl and diaryl isoprenoids and maleimides). 4. Anoxic sea-floor conditions were caused by enhanced productivity in the ocean related

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to deglaciation, marine transgression and the increased transport of nutrients from the land. The increase of productivity and the expansion of anoxic and nitrogen- and

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phosphate-enriched waters into the shallow photic zone may have resulted in a

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positive organic carbon isotope excursion.

5. High values of 15N (>9‰) during the Early Permian were associated with a

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deglaciation-driven sea-level rise that was likely caused by the advection of a denitrified water mass from the Panthalassic Ocean to the intracratonic Paraná Basin. 6. Due to their exclusion of potential scavengers and bioturbators, long-lasting periods of

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anoxia/euxinia in bottom waters are considered to be the main factor responsible for the excellent preservation of many fossils, including fish, sponges, insects, caddisfly

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larval cases and conodont apparatuses. It is also likely that the intermittent occurrence

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of photic zone euxinia in the water column might have caused the mass mortality of fish populations, which are excellently preserved in these deposits.

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Acknowledgements

This work had the financial support of Programa de Formação em Recursos Humanos

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em Geologia da Petrobras (PFRH-PB 240) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). Inorganic geochemistry analyses has been financed by the National Science Centre in Poland (Grant nr 2014/15/B/ST10/03705 to M.R.). Paulo Alves Souza is specially acknowledged for letting us conduct the palynofacies analyses in the Marleni Marques Toigo Laboratory at the Federal University of Rio Grande do Sul. The article benefited from constructive reviews of two journal referees.

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ACCEPTED MANUSCRIPT Table and figure captions: Table 1. Geochemical data of samples collected from the Campáleo section: total organic carbon (TOC); total sulphur (TS); authigenic uranium, which was calculated as follows: Uauthig=Utotal−Th/3 (Wignall and Myers, 1988); and ratios of U/Th, Corg/P, Al/(Al+Fe+Mn), Fe/Mn, K/Al, Ti/Al, Zr/Al [x104], Zr/Rb, Al2O3/TiO2 and Si/Al.

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Table 2. Enrichment factors of selected major and trace elements. Avg. EF – Average

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enrichment factor.

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Table 3. Total organic carbon (TOC) and total nitrogen (TN) contents, C/N ratios, and carbon

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and nitrogen isotopic compositions of bulk organic matter.

Figure 1. A. Location of the Campáleo site within the Paraná Basin in Brazil. B. Detailed location of the Campáleo site (indicated by star) near Mafra in Santa Catarina State (source:

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Google Maps).

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Figure 2. Lithological section of the Lower Permian Lontras Shale (left) showing the studied 1.10-m-thick section of fossiliferous black shales (right) outcropping at the Campáleo site

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(modified from Mouro et al., 2016). 1A to 4A - samples analysed. The distribution of fossils and their symbols are adopted from Ricetti et al. (2016).

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Figure 3. Trends in the abundances of palynomorphs, phytoclasts and amorphic organic matter (AOM) contents throughout the Campáleo section. TST – transgressive system tract,

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HST – highstand system tract, AC – acritarchs, PT – Portalites.

Figure 4. Campáleo section, showing total organic carbon (TOC) and biomarker redox condition proxies, which indicate at least intermittent euxinic conditions in the basal and upper parts of the section.

Figure 5. Composite plot of the Campáleo section showing detrital input indicators, such as Al/(Al+Fe+Mn), K/Al, Ti/Al, Zr/Al, Zr/Rb and Al2O3/TiO2.

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ACCEPTED MANUSCRIPT Figure 6. Composite plot of the Campáleo section showing uranium/thorium ratios, concentrations of authigenic uranium and molybdenum, Corg/P ratios, and total organic carbon (TOC) contents. Authigenic uranium was calculated as follows: Uauthig=Utotal−Th/3 (Wignall and Myers, 1988).

Figure 7. Composite plot of the Campáleo section showing total organic carbon (TOC)

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contents along with C and N isotopic compositions and C/N ratios.

Figure 8. Pyrite framboid size data along the Campáleo section and histograms showing their

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median, mean – mean value, st.dev. – standard deviation.

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size distributions in selected samples. min – minimum value, max – maximum value, med –

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Figure 9. Selected fossils of the Lontras black shales. A. Hexactinellid sponge Microhemidiscia greinerti (CP.I 450, adapted from Mouro et al., 2014). B. Caddisfly (Trichoptera) larval cases (from Mouro et al., 2016). C. Blattodea insect Anthracoblattina

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mendesi (CP.I 2182, adapted from Ricetti et al., 2016). 4. D. Natural assemblage of conodont elements of Mesogondolella sp. (CP.E 7618a, adapted from Scomazzon et al., 2013). E-F.

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Actinopterygii fish Santosichthys mafrensis (CP.E 8150). Scale bars are 10 mm.

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ACCEPTED MANUSCRIPT Table 1. Geochemical data of samples collected from the Campáleo section: total organic carbon (TOC); total sulphur (TS); authigenic uranium, which was calculated as follows: Uauthig=Utotal−Th/3 (Wignall and Myers, 1988); and ratios of U/Th, Corg/P, Al/(Al+Fe+Mn), Fe/Mn, K/Al, Ti/Al, Zr/Al [x104], Zr/Rb, Al2O3/TiO2 and Si/Al.

Sample 4A 3D 3C 3B 3A 2B 2A 1D 1C 1B 1A

TOC

TS

[wt.%]

[wt.%]

11.36 11.59 11.13 11.61 11.89 8.56 7.13 5.53 7.18 11.89 12.42

4.54 3.98 3.67 2.62 2.73 1.73 1.96 1.72 1.24 1.71 1.49

Uauth [ppm] 18.87 18.80 16.90 17.47 16.07 12.80 12.07 9.23 10.80 13.80 13.57

Corg/P

Al/(Al+Fe+Mn)

Fe/Ti

K/Al

Ti/Al

Zr/Al*104

2.06 1.98 1.82 1.81 1.66 1.35 1.28 1.11 1.17 1.51 1.48

56.57 139.83 63.74 48.38 68.09 109.01 33.33 70.34 102.84 143.38 177.81

0.60 0.62 0.62 0.67 0.58 0.65 0.62 0.64 0.68 0.65 0.67

14.45 14.13 12.68 10.00 14.41 11.46 13.18 10.88 9.57 10.56 9.15

0.35 0.34 0.36 0.36 0.39 0.39 0.39 0.39 0.40 0.38 0.38

0.046 0.044 0.049 0.049 0.050 0.046 0.047 0.050 0.049 0.052 0.054

20.38 18.88 20.44 20.41 21.37 18.70 19.63 18.38 18.91 22.61 26.54

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T P

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U/Th

Zr/Rb

Al2O3/TiO2

Si/Al

0.97 0.95 0.98 1.01 0.97 0.85 0.91 0.87 0.88 1.09 1.30

24.79 26.02 23.20 23.11 22.70 24.61 24.02 22.50 23.27 21.93 20.83

2.96 2.99 3.19 3.20 3.18 3.15 3.26 3.75 3.38 3.56 3.66

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Table 2. Enrichments factors of selected major and trace elements. Abbreviation: Avg. EF – Average enrichments factor Sample 4A 3D 3C 3B 3A 2B 2A 1D 1C 1B 1A Avg. EF

Ba(EF) 2.59 1.15 3.88 5.58 1.20 1.49 1.43 0.82 0.80 0.85 0.86 1.88

Co(EF) 1.47 0.90 0.95 0.82 0.74 0.76 0.85 1.17 1.05 1.19 1.06 1.00

Sr(EF) 1.54 0.66 1.60 2.01 0.76 0.64 0.59 0.63 0.65 0.76 0.78 0.97

Th(EF) 1.00 1.03 1.08 1.08 1.15 1.09 1.12 1.10 1.12 1.13 1.16 1.10

U(EF) 9.71 9.63 9.22 9.25 9.00 6.90 6.78 5.77 6.18 8.06 8.13 8.06

V(EF) 4.56 5.05 3.69 3.57 3.22 2.79 2.71 2.24 2.19 2.20 2.13 3.12

Zr(EF) 0.97 0.90 0.97 0.97 1.02 0.89 0.94 0.88 0.90 1.08 1.26 0.98

Mo(EF) 15.78 10.30 12.70 7.37 6.10 4.28 4.77 8.53 8.50 13.42 15.41 9.74

Cu(EF) 2.18 1.32 1.25 0.74 0.45 0.25 0.13 0.17 0.09 0.24 0.57 0.67

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Pb(EF) 35.20 50.21 47.08 38.50 71.19 30.93 31.99 29.37 21.94 38.89 33.38 38.97

Zn(EF) 157.33 151.72 160.49 77.60 48.36 21.15 9.99 20.37 14.36 26.95 61.76 68.19

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Cr(EF) 3.24 4.44 3.18 3.17 3.19 1.88 1.93 1.35 1.50 2.46 2.51 2.62

P(EF) 3.85 1.57 3.45 4.61 3.47 1.42 3.95 1.52 1.27 1.68 1.44 2.57

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Si(EF) 1.01 1.02 1.09 1.09 1.08 1.07 1.11 1.28 1.15 1.21 1.24 1.12

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Ni(EF) 3.11 2.25 2.34 2.27 2.20 1.84 2.26 3.51 3.12 4.52 4.60 2.91

Ti(EF) 0.76 0.73 0.81 0.82 0.83 0.77 0.79 0.84 0.81 0.86 0.91 0.81

K(EF) 1.14 1.10 1.18 1.18 1.26 1.26 1.28 1.28 1.29 1.24 1.24 1.22

Fe(EF) 1.31 1.22 1.23 0.97 1.42 1.04 1.23 1.08 0.92 1.08 0.99 1.14

Mn(EF) 0.49 0.24 0.38 0.24 0.38 0.34 0.35 0.49 0.46 0.39 0.39 0.38

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Table 3. Total organic carbon (TOC) and total nitrogen (TN) contents, C/N ratios, and carbon

TN (%)

C/N

δ13C (‰)

δ15N (‰)

4A

11.36

0.43

26.42

-26.2

9.1

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11.59

0.46

25.20

-26.5

10.1

3C

11.13

0.44

25.30

-26.6

8.5

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11.61

0.43

27.00

-26.5

9.0

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11.89

0.54

22.02

-27.0

9.8

2B

8.56

0.32

26.75

8.8

2A

7.13

0.29

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-26.2

24.59

-26.6

9.4

1D

5.53

0.18

30.72

-25.9

10.1

1C

7.18

0.26

27.62

-26.5

10.5

1B

11.89

0.52

22.87

-27.7

14.8

1A

12.42

0.54

23.00

-27.1

17.4

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Integrated study of the Lower Permian black shales of the Paraná Basin, Brazil Benthic anoxia/euxinia present in the bottom waters Intermittent photic zone euxinia present in the water column The presence of denitrified waters and elevated productivity

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