Organic Geochemistry 64 (2013) 84–93 Contents lists available at ScienceDirect Organic Geochemistry journal homepage: www.elsevier.com/locate/orggeochem Biomarker evidence for intermittent photic zone euxinia in the Aptian–Albian organic sedimentary record from the Ionian Zone (Epirus, Greece) ⇑ Evi Tzortzaki a, , Vassilis Karakitsios a, Harilaos Tsikos b a Faculty of Geology and Geoenvironment, National and Kapodistrian University of Athens, Panepistimiopolis, 15784 Athens, Greece b Department of Geology, Rhodes University, Grahamstown 6140, South Africa article info abstract Article history: New biomarker evidence is presented that constrains the conditions of deposition and preservation of Received 30 April 2013 sediments rich in extractable organic matter from the Aptian–Albian sedimentary record of the Ionian Received in revised form 23 July 2013 Zone in NW Greece. Analyses were specifically carried out on total lipid extracts from 12 organic rich Accepted 25 August 2013 samples from the Vigla Shale Member, two of which represent the regional record for the early Albian Available online 5 September 2013 Paquier Event of OAE1b. In the aliphatic fractions, compound groups such as n-alkanes, isoprenoid alkanes, steroids, hopanoids and terpenoids were recognized, pointing to a mixed origin from algae and prokaryotes with an additional measurable contribution from terrigenous plant matter. These com- pounds suggest deposition of the primary organic sediments under conditions of decreased bottom water oxygen concentrations. Mass spectral evidence from the aromatic fractions of most samples reveal the variable presence of diagenetic and catagenetic derivatives of carotenoid pigments (including some with bound sulfur) that are characteristic of photoautotrophic sulfur bacteria. The presence of specific bio- markers originating from photosynthetic anaerobic microorganisms, similar to those in ancient and con- temporary euxinic basins such as the Black Sea, suggest that photic zone euxinic conditions were intermittently operative in the Aptian–Albian stages of the Ionian Basin, but were not exclusively char- acteristic of the black shale representing the Paquier Event itself. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction zone (Repeta, 1993; Sinninghe Damsté et al., 1993; Grice et al., 1996a). This is because green SB are restricted today to silled fjords The term ‘‘euxinic’’ traditionally describes an environment of and lakes with intense water stratification and anoxia (Repeta water column stagnation and limited circulation, or one where an- et al., 1989), conditions similar to those hypothesized for the oxic, anaerobic and sulfidic conditions are simultaneously present oceans during OAEs (Jenkyns, 1980; Overmann et al., 1992; Repeta, and thus conducive to the growth of photoautotrophic sulfur bac- 1993; van Gemerden and Mas, 1995; Sinninghe Damsté and teria (PSB) (Repeta, 1993). This group of prokaryotic microorgan- Köster, 1998). isms comprises strictly anaerobic, photosynthetic bacteria which The diagenetic transformations of specific carotenoid pigments require hydrogen sulfide and light for their development, such as from PSB, belonging to the broader group of the geosphere tet-ra- the green sulfur bacteria (green SB) of the family Chlorobiaceae ter-pen-oids, have been the subject of intensive research efforts to (Imhoff, 1995); and the purple sulfur bacteria (purple SB) of the identify traces of PSB in sediments deposited in ancient euxinic ba- family Chromatiaceae, which exhibit a comparable physiology sins (Repeta, 1993; Schaeffer et al., 1997). These include particu- and ecology as the green SB (Brocks and Schaeffer, 2008). The light larly the isorenieratene biosynthesized exclusively by brown and hydrogen sulfide dependencies of PSB shown by their modern strains of green SB (Liaaen-Jensen, 1978a,b; Imhoff, 1995), chloro- ecological data (Overmann et al., 1992; Repeta, 1993; van Gemer- bactene biosynthesized by green strains of green SB (Imhoff, 1995; den and Mas, 1995) and the assumption of a physiological unifor- Brocks and Schaeffer, 2008) and okenone biosynthesized by purple mitarianism for these bacteria, have permitted the detection of SB (Brocks and Schaeffer, 2008). From these, the fossilization po- their specific biomarkers in Phanerozoic sediments, particularly tential of the isorenieratene carbon skeleton is the one that has re- those recording oceanic anoxic events (OAEs), to be interpreted ceived the most attention (Schwark and Püttmann, 1990; Hartgers as indicative of a euxinic water layer extending up to the photic et al., 1994; Hoefs et al., 1995; Grice et al., 1996b; Koopmans et al., 1996a, 1997; Sinninghe Damsté and Koopmans, 1997). Sulfurization of isorenieratene during diagenesis results in ⇑ Corresponding author. Tel.: +30 6945224012. numerous sulfur-containing isorenieratene derivatives which can E-mail address: [email protected] (E. Tzortzaki). 0146-6380/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.orggeochem.2013.08.013 E. Tzortzaki et al. / Organic Geochemistry 64 (2013) 84–93 85 be, and have been, subsequently recognized in sediments (Koop- studies have recently proved this to be otherwise (e.g. Sinninghe mans et al., 1996a,b; Kok et al., 2000). Diagenetic and catagenetic Damsté et al., 2001). Identification of isorenieratene derivatives isorenieratene derivatives have been found in organic carbon rich in sediments recording OAEs has hitherto provided crucial infor- sedimentary rocks from many different palaeoenvironmental set- mation about water column redox conditions during organic mat- tings, ranging from Precambrian to Cenozoic age (van Kaam-Peters ter accumulation; possible variations in PSB productivity; et al., 1995; Koopmans et al., 1996a; Bosch et al., 1998; Sinninghe chemocline shifts; and/or role of anoxia in the preservation of or- Damsté and Köster, 1998; Passier et al., 1999; Schouten et al., ganic matter (Demaison and Moore, 1980; Summons and Powell, 2000; Pedentchouk et al., 2004; Wagner et al., 2004; Bowden 1986; Pedersen and Calvert, 1990; Sinninghe Damsté et al., 1993; et al., 2006; Brocks and Schaeffer, 2008; Heimhofer et al., 2008). Koopmans et al., 1996a; Pancost et al., 2002; Kuypers et al., Stable carbon isotopes and molecular distribution patterns have 2002b; Kenig et al., 2004; Schwark and Frimmel, 2004). also been used to document the source of PSB biomarkers (Ost- The OAE1b spanning the Aptian/Albian boundary (113–109 Ma) roukhov et al., 1982; Summons and Powell, 1986, 1987; Schwark represents a protracted interval of oceanic dysoxia with multiple and Püttmann, 1990; Requejo et al., 1992; Hartgers et al., 1994). discrete black shales deposited in regions across Mexico, the North Green SB biomass, in particular, is known to be significantly more Atlantic Basin (western Tethys) and the Mediterranean (eastern enriched in 13C compared to the algal biomass (Sirevåg and Orm- Tethys; Arthur and Premoli Silva, 1982; Bréhéret et al., 1986; Pre- erod, 1970; Quandt et al., 1977; Summons and Powell, 1987; Sin- moli Silva et al., 1989; Bralower et al., 1993; Leckie et al., 2002; Tsi- ninghe Damsté et al., 1993; Hartgers et al., 1994; Koopmans kos et al., 2004). The OAE1b comprises major phenomena of et al., 1996a; Grice et al., 1996b; van der Meer et al., 1998; van transition in mid-Cretaceous tectonics, sea level, climate, lithofa- Breugel et al., 2005). cies and marine plankton populations (Leckie et al., 2002). A sea le- Although the development of photic zone euxinic conditions vel fall near the Aptian/Albian boundary separates uppermost was initially considered to be rare in the context of OAEs, several Aptian black shales (‘‘Jacob Event’’ in the Vocontian Basin, and Fig. 1. The zones of the northwestern Hellenides (modified after Karakitsios and Rigakis, 2007). 86 E. Tzortzaki et al. / Organic Geochemistry 64 (2013) 84–93 ‘‘113 Event’’ in Umbria–Marche Basin, central Italy) from lower Al- The base of the Vigla Limestone Formation (Figs. 2 and 3) repre- bian black shales (‘‘Paquier’’ and ‘‘Leenhardt’’ Events in the Vocon- sents the break up unconformity of the post-rift sequence in the Io- tian Basin, and the ‘‘Monte Nerone’’ and ‘‘Urbino’’ Events in the nian Basin which largely obscures the pre-existing syn-rift Apennines of central Italy). Erbacher et al. (1998) note a significant structures (Karakitsios, 1995). The Vigla Formation comprises a difference between the uppermost Aptian Jacob Event of the thick succession of thin layered (5–20 cm) sub-lithographic, pela- Vocontian Basin as an OAE driven by detrital input and the lower gic limestones (white to grey micritic packstone with abundant Albian Paquier and Leenhardt Events as OAEs driven by productiv- radiolaria), in rhythmic alternations with centimeter to decimeter ity and rising sea level. thick radiolarian chert beds containing rare shale intercalations. In this paper, we explore the Aptian–Albian biomarker record of The Vigla Shale Member in the upper part of the Formation, is organic rich horizons partly attributed to the Paquier Event of attributed to the Aptian–Cenomanian interval, and comprises mar- OAE1b from the Ionian Basin of NW Greece, following on from ly limestone and chert beds interbedded with marlstone beds rich an earlier inter-disciplinary study on the same strata carried out in organic matter, and dark greenish-grey shale (Karakitsios, 1992, by Tsikos et al. (2004). In this instance, we focus on assessing the 1995; Karakitsios and Koletti, 1992;