Orbitally paced phosphogenesis in Mediterranean shallow marine carbonates during the middle Miocene Monterey event

Abstract

During the Oligo‐Miocene, major phases of phosphogenesis occurred in the Earth's oceans. However, most phosphate deposits represent condensed or allochthonous hemipelagic deposits, formed by complex physical and chemical enrichment processes, limiting their applicability for the study regarding the temporal pacing of Miocene phosphogenesis. The Oligo‐Miocene Decontra section located on the Maiella Platform (central Apennines, Italy) is a widely continuous carbonate succession deposited in a mostly middle to outer neritic setting. Of particular interest are the well‐winnowed grain to packstones of the middle Miocene Bryozoan Limestone, where occurrences of authigenic phosphate grains coincide with the prominent carbon isotope excursion of the Monterey event. This unique setting allows the analysis of orbital forcing on phosphogenesis, within a bio, chemo, and cyclostratigraphically constrained age‐model. LA‐ICP‐MS analyses revealed a significant enrichment of uranium in the studied authigenic phosphates compared to the surrounding carbonates, allowing natural gamma‐radiation (GR) to be used as a qualitative proxy for autochthonous phosphate content. Time series analyses indicate a strong 405 kyr eccentricity forcing of GR in the Bryozoan Limestone. These results link maxima in the GR record and thus phosphate content to orbitally paced increases in the burial of organic carbon, particularly during the carbon isotope maxima of the Monterey event. Thus, phosphogenesis during the middle Miocene in the Mediterranean was controlled by the 405 kyr eccentricity and its influence on large‐scale paleoproductivity patterns. Rare earth element data were used as a tool to reconstruct the formation conditions of the investigated phosphates, indicating generally oxic formation conditions, which are consistent with microbially mediated phosphogenesis.

Sedimentary response to current and nutrient regime rearrangement in the Eastern Mediterranean Realm during the early to middle Miocene (southwestern Cyprus)

“…Phosphogenesis became prevalent in the southern central Mediterranean and parts of the northern Mediterranean during the early Miocene (Auer et al, 2016;Föllmi et al, 2007), parallel to the phosphogenesis observed in Cyprus. The Miocene phosphatisation is a departure from a long term trend where intensive phosphogenesis in the Mediterranean Tethys had, for the most part, halted as of the late Eocene (Soudry et al, 2006) due to change in circulation patterns.…”

“…However, in the eastern Mediterranean, dramatic change in the oceanographic conditions likely also played a role and might have been the reason for apparent fewer reefs in the middle Miocene and their absence in Cyprus. (Kiessling, 2001;Kiessling and Flügel, 2002), Mediterranean phosphate accumulation (Auer et al, 2017(Auer et al, , 2016Föllmi et al, 2015Föllmi et al, , 2007, regional climate patterns (Böhme et al, 2008;John et al, 2003;Schneck et al, 2010), connectivity of the Mediterranean to the Indian Ocean (IO) following (Bialik et al, 2019), initiation of sapropels (Shipboard Scientific Party, 1978;Taylforth et al, 2014), mass accumulation rate (MAR) of CaCO3 in the Levant Basin (Torfstein and Steinberg, 2020), global phosphate accumulation patterns (Föllmi, 1995;Föllmi et al, 1994), high latitude climate patterns (AIS = Antarctic Ice Sheet; Flower and Kennett, 1994;Groeneveld et al, 2017), bulk rock carbon isotope record from the TZ section and benthic foraminifera carbon and oxygen isotopes from the North Atlantic (Cramer et al, 2009). Sea level curve from Miller et al (2020).…”

“…Through the Miocene fundamental shifts in phosphogenesis patterns (Auer et al, 2016;Föllmi et al, 2015), sedimentation patterns (Torfstein and Steinberg, 2020) and structure of shallow-water calcifying communities (Bosellini and Perrin, 2008;Pomar and Hallock, 2007) occurred. Modelling work suggests that the direct effects of the change in connectivity were the reversal of zonal circulation in the upper water column and reduced turnover of the lower water column (de la Vara, 2015;de la Vara et al, 2013;de la Vara and Meijer, 2016), which might have reduced ventilation.…”

A LA-ICP-MS analysis of rare earth elements on phosphatic grains of the Ediacaran Doushantuo phosphorite at Weng'an, South China: implication for depositional conditions and diagenetic processes

“…Additionally, REE can be important proxies for the reconstruction of the depositional and diagenetic history of phosphate rocks (e.g. Jiang et al 2007; Joosu et al 2015; Alibert, 2016; Auer et al 2016; Xin et al 2016).…”