Evidence for photic‐zone euxinia in the Early Albian Santana Formation (Araripe Basin, NE Brazil)

Abstract

Organic matter from two black shale units in the Santana Formation, Araripe Basin, NE Brazil, has been studied to investigate the palaeoenvironmental conditions prevailing during formation of this famous fossil lagerstätte. Optical and organic geochemical analyses indicate a predominantly autochthonous source with very limited terrestrial input. Molecular fossils of green sulphur bacteria show that the water column was stratified with euxinic conditions reaching up into the photic zone. Thus, mass‐mortality events of fish may be explained by intrusion of sulphide‐containing waters. The low quantity of material derived from land plants in this interior marine setting is interpreted to reflect a consequence of enhanced marine productivity, resulting in dilution of the continental signal. Different depositional scenarios are proposed to explain our findings including (1) coastal erosion and nutrient leaching during a transgressive event, (2) intrusion of euxinic waters during an early Albian OAE or (3) an estuarine circulation pattern associated with thermohaline stratification.

No evidence for anoxia during the Valanginian carbon isotope event—An organic-geochemical study from the Vocontian Basin, SE France

“…These compounds are considered to be indicative for a stratified water column and the establishment of euxinic waters reaching the photic zone (Summons and Powell, 1986;Grice et al, 1996;Kenig et al, 2004;Schwark and Frimmel, 2004;Heimhofer et al, 2008). Isorenieratene derivatives are ubiquitous compounds in many mid-Cretaceous black shales deposited during OAEs and have been reported from the Cenomanian-Turonian OAE2 (Sinninghe Damsté and Köster, 1998;Kuypers et al, 2002) as well as from the ConiacianSantonian OAE3 (Wagner et al, 2004).…”

The taphonomic fate of isorenieratene in Lower Jurassic shales—controlled by iron?

“…Diagenetic products of isorenieratene and also their stable carbon isotopic signals are commonly used for tracking photic zone anoxia through the Phanerozoic (e.g., Blumenberg, Heunisch, Lückge, Scheeder, & Wiese, ; Grice et al., ; Hays, Beatty, Henderson, Love, & Summons, ; Heimhofer et al., ; Marynowski, Filipiak, & Pisarzowska, ; Marynowski et al., ; Sinninghe Damsté & Köster, ; Summons & Powell, ). Anoxic conditions with potential photic zone anoxia have probably also been widespread during the Proterozoic (e.g., Canfield, ; Planavsky et al., ; Poulton & Canfield, ; Poulton, Fralick, & Canfield, ; Scott et al., ).…”

Testing the ancient marine redox record from oxygenic photosynthesis to photic zone euxina

“…The stratigraphic change in the relative supply of terrigenous organic matter , which is supported by the HI, molecular, and petrographic results, may have been driven by effects related to rising sea level (Hesselbo, 2008;Suan et al, 2011).…”

“…Aromatic C40 Carotenoid* Locality References Holocene 1 Black Sea Holocene 1, 2 Amvrakikos Gulf (Greece) Holocene 1, 4 Kyllaren Fjord Pliocene 1 Eastern Mediterranean Sapropels (ODP) Messinian 1 Vena del Gesso Basin (Italy) Messinian 1, 2 Gebellina Marl (Sicily) (Schaeffer et al, 1995) Oligocene 1 Menilite Formation (Poland) (Wagner et al, 2004) Late Turonian 1 Canje Formation (British Guyana) OAE-2 1, 2 North Atlantic (DSDP & ODP) OAE-1b 1 Santana Formation (Brazil) (Heimhofer et al, 2008) OAE-1a 1 Venetian Alps (Italy) (van Breugel et al, 2007) Late Jurassic 1 Kimmeridge Clay (UK) Late Jurassic 1, 2 Calcaires en Plaquettes (France) ; Van Kaam-Peters and Sinninghe Damsté, 1997) Middle Callovian 1 Oxford Clay (UK) Toarcian 1, 2 Northern Europe (Allgäu; Schistes Cartons; Posidionia) Toarcian OAE 1, 2, 4 Hawsker Bottoms; Cleveland Basin UK; MRM rock extract (French et al, 2014) Middle Sinemurian to Middle Hettangian 1 Frick Swiss Jura (Schwab and Spangenberg, 2007) Early Carboniferous 1, 3 Exshaw Formation (Canada) Upper Famennian 1, 3 Holy Cross Mountains (Poland) (Racka et al, 2010) Frasnian/Famennian 1, 3 Holy Cross Mountains (Poland) (Joachimski et al, 2001) Frasnain 1, 3 Duvernay Fm (Canada) Hartgers et al, 1993;) Early-Mid Frasnian transition 1, 3 Holy Cross Mountains (Poland) (Marynowski et al, 2008) Middle Devonian; Givetian 1, 3 Keg River Formation (Canada) (Behrens et al, 1998) Late Ordovician-Early Silurian 1, 3 Batra Formation (Jordon) (Armstrong et al, 2009) Late Ordovician 1, 3 Boas Oil Shale (Canada) Caradocian 1 Decorah Formation (USA) (Pancost et al, 1998) Middle Ordovician 1, 3 Womble Shale (USA) Late Cambrian …”