The Eocene–Oligocene transition in the C-isotope record of the carbonate successions in the Central Mediterranean

Abstract

The Eocene-Oligocene transition marks a fundamental step in the evolution of the modern climate. This climate change and the consequent major oceanic reorganisation affected the global carbon cycle, whose dynamics across this crucial interval are far from being clearly understood. In this work, the upper Eocene to lower Oligocene δ 13 C Carb and δ 13 C TOC records of a shallow-water and a hemipelagic carbonate settings within the Central Mediterranean area have been studied and discussed. The shallow-water carbon isotope signal has been analysed in the northern portion of the Apula Platform, cropping out in the Majella Mountain, Central Apennines (Santo Spirito Formation). A coeval Umbria-Marche basinal succession has been investigated in the Massignano section (Conero area, Central Italy). The purposes of this work are: to discriminate between the global and the local (Mediterranean) signature of C-isotope record during the Oi-1 event, to correlate the regional C-isotope signal with the global record, and to evaluate the carbon cycle dynamics across the greenhouse-icehouse transition through the integration of complementary records (shallow-water vs pelagic settings, δ 13 C Carb vs δ 13 C TOC). The upper Eocene carbon isotope record of the analysed successions matches with the global signal. The overall trend shows a decrease of the δ 13 C Carb and a contemporary increase of the δ 13 C TOC. The decoupling of the two curves is consistent with a reduced fractionation effect by primary producers that characterised the interval between the Middle Eocene Climatic Optimum and the onset of the Oi-1 event. However, regional factors superimposed the global signal. In fact, the upper Eocene basinal δ 13 C TOC record is marked by short-term negative spikes, which possibly represent times of higher productivity triggered by the westward subtropical Eocene Neotethys current entering from the Arabian-Eurasian gateway. On the contrary, the shallow-water record does not display these short-term productivity pulses. A change in the carbonate factory is only recorded at the Eocene-Oligocene transition, marked by a reduction of the larger benthic foraminifera and the spread of seagrass and corals. Moreover, in the shallow-water record of the Santo Spirito Formation, no major carbon isotope shift related to the Oi-1 event is recorded due to the presence of extensive slumps that disrupt the bedding. These slumps are the main evidence of the sea-level drop that occurred concomitantly with the onset of the Antarctica ice-sheet, which caused the deepening of the storm wave base and increased the instability over the entire ramp.

The Tethyan and Tyrrhenian margin record of the Central Apennines: a guide with insights from stratigraphy, tectonics, and hydrogeology

“…Over the Mesozoic platform top, the succession is thin and discontinuous, while it is thicker and more continuous northward, over the platform margin and slope (Vecsei et al, 1998). Overall, the "Santo Spirito fm" consists of breccias with lithoclasts, biodetrital calcareous turbidites, and pelagic limestone deposited in an outer ramp to basin environment (Vecsei et al, 1998;Raffi et al, 2016;Cornacchia et al, 2018). Foraminifera grainstone shoal deposited on the top of the Mesozoic platform ("Alveolina Limestone" of Bally, 1954).…”

“…Slumps at the Eocene-Oligocene boundary were recognised in several other sections of the "Santo Spirito fm" (Raffi et al, 2016). Cornacchia et al (2018) interpreted these slumps as the physical expression of the major greenhouseicehouse transition that occurred at the Eocene-Oligocene boundary (Zachos et al, 2001;Coxall & Pearson, 2007) when an ~80 m sea-level fall (Miller et al, 2009;Houben et al, 2012) led to the deepening of the storm-weather wave-base. Furthermore, storms could have been more frequent and intense due to the onset of the icehouse climate, which triggered a global ocean reorganisation and the intensification of latitudinal thermal gradients and winds (Coxall & Pearson, 2007).…”

The potential of carbonate ramps to record C-isotope shifts: insights from the upper Miocene of the Central Mediterranean area

“…Unlike the Latium‐Abruzzi and the southern portion of the Apula platforms, no Palaeogene long‐lasting hiatus is recorded within the Majella succession, where the Palaeogene succession is represented by the Danian–Rupelian Santo Spirito Formation (Fig. 4; Vecsei et al 1998; Raffi et al 2016; Cornacchia et al 2018b). An Oligocene unconformity marks the boundary between the Santo Spirito Formation and the overlying Bolognano Formation, which identifies the upper Oligocene–upper Miocene homoclinal carbonate ramp (Figs 2B, 3A, B, 4).…”

Latest Priabonian larger benthic foraminiferal assemblages at the demise of theSoğucak Carbonate Platform (Thrace Basin and Black Sea shelf, NW Turkey): implications for the shallow marine biostratigraphy

“…The late Eocene-Oligocene transition corresponds to a major biotic turnover (Pomerol and Premoli-Silva, 1986). In the Tethys, the record of this global event in the carbonate platforms, however, faces difficulties because of the rareness of outcrops encompassing the Eocene-Oligocene transition (Adams et al, 1986;Cornacchia et al, 2018). The biotic events in this interval are not well recorded in Turkey due to the absence of continuous sections encompassing the latest Priabonian and lowest Oligocene, although taxonomic and biostratigraphic information from separate localities are available.…”