Early diagenetic greigite as an indicator of paleosalinity changes in the middle Miocene Paratethys Sea of central Europe

Abstract

The Miocene epicontinental Paratethys Sea of central Eurasia has experienced multiple restriction and reconnection events to the open ocean. Magnetostratigraphy is an important dating tool to better understand the temporal and spatial paleoenvironmental variations associated with these changes. Magnetostratigraphy in the Paratethys domain, however, is complicated by the presence of greigite (Fe3S4). Here we report rock magnetic and X‐ray fluorescence data of the Tisa section (Romania) which was previously magnetostratigraphically dated at the middle Miocene (base at 12.8 Ma and top at 12.2 Ma). This section comprises the Badenian Sarmatian Extinction Event (BSEE), which is marked by a major salinity change from marine to brackish environments, related to the opening of the connection between the Central and the Eastern Paratethys basins. In the marine Badenian sediments below the BSEE, the pyritization process is shown to be complete because of abundant sulfate supply. In the brackish Sarmatian deposits, four intervals with early diagenetic greigite are observed, and linked to insufficient sulfate in the water column. These four greigite intervals appear to correspond to maxima in the ∼100 kyr eccentricity cycle. We propose that increased fresh water from the Eastern Paratethys basin during eccentricity maxima restricted the sulfate availability in the Tisa area, leading to a reduced HS− production and enhanced greigite preservation. The early diagenetic formation of greigite enables a quasi syn‐depositional recording of the paleomagnetic field, which allows reliable paleomagnetic dating in this section. Our results further suggest greigite as a potential indicator for salinity changes during marine/brackish transitions.

Late Miocene megalake regressions in Eurasia

“…Magnetostratigraphy can provide age dating for rock successions if the established polarity pattern of studied sections can be correlated to the reversal pattern of the Geomagnetic Polarity Time Scale 24 (GPTS). This approach has proven successful with Paratethys sediments, when adequate demagnetization techniques are applied to deal with the generally high concentration of iron sulphides in anoxic sediments, and particularly with the magnetic mineral greigite 55 , 56 .…”

Greigite as an Indicator for Salinity and Sedimentation Rate Change: Evidence From the Yangtze River Delta, China

“…Ferrimagnetic greigite (Fe 3 S 4 ) is commonly regarded as a precursor to pyrite (FeS 2 ), or a product of pyrite oxidation, in sedimentary environments (Cornwell & Morse, 1987; Roberts et al., 2011; Wilkin & Barnes, 1996). Due to its distinct magnetic properties, it has been widely found in lacustrine (Fu et al., 2015; Li et al., 2019; Qiang et al., 2018; Reynolds et al., 1999; Snowball & Thompson, 1988; Tudryn et al., 2010) and marine deposits (Blanchet et al., 2009; Chang et al., 2014; Duan et al., 2020; Fu et al., 2008; Liu et al., 2017, 2018; Oda & Torii, 2004) using magnetic measurement techniques. It is generally agreed that reaction between carbon (C), sulfur (S) and iron (Fe) drives the formation of greigite and pyrite, and a surplus of reactive iron oxides to H 2 S favors the occurrence of greigite (Roberts, 2015).…”

“…It is generally agreed that reaction between carbon (C), sulfur (S) and iron (Fe) drives the formation of greigite and pyrite, and a surplus of reactive iron oxides to H 2 S favors the occurrence of greigite (Roberts, 2015). C‐S‐Fe geochemistry reflects interactions between multiple factors such as organic matter content/lability, sedimentation rate and salinity (Chang et al., 2014; Fu et al., 2008; Liu et al., 2017), which are modulated by environmental processes such as climate and sea‐level change (Blanchet et al., 2009; Chang et al., 2014; Li et al., 2019; Liu et al., 2017; Qiang et al., 2018; Reynolds et al., 1999; Wang et al., 2014). For example, flood events in Holocene stratigraphy have been offered as an explanation for greigite occurrence in the Santa Barbara Basin, USA, as more terrigenous sediments, versus limited organic carbon input during flood events, favors the dominance of iron oxide over H 2 S (Blanchet et al., 2009).…”

“…For example, flood events in Holocene stratigraphy have been offered as an explanation for greigite occurrence in the Santa Barbara Basin, USA, as more terrigenous sediments, versus limited organic carbon input during flood events, favors the dominance of iron oxide over H 2 S (Blanchet et al., 2009). In the mid Miocene Paratethys Sea of central Europe, the occurrence of greigite is interpreted as the result of salinity change associated with sea‐level variations, with fresher conditions limiting sulphate supply and H 2 S production (Liu et al., 2017).…”

The mid-Langhian flooding in the eastern Central Paratethys: integrated stratigraphic data from the Transylvanian Basin and SE Carpathian Foredeep

“…Outflow of nutrient-rich brackish water from Eastern Paratethys (similar to present day Black Sea outflow and temporary nannoplankton blooms in the Marmara Sea) may be related to the temporarily blooms of the opportunistic Streptochilus foraminifera just below the flooding boundary in the studied areas of the East Carpathian Foredeep and Transylvanian Basin (Beldean et al 2010(Beldean et al , 2013. The temporary low oxic setting and anoxic levels in the Campiniţa and Brebu sections might be related to the low-density brackish outflow plume of Black Sea water (Liu et al 2017;Palcu et al 2019). The suggestion by Beldean et al (2010) that the Streptochilus blooms might have a similar age range as the blooms in the Atlantic and Indian Oceans (~ 19-17 Ma) is erroneous.…”