A window into eastern Mediterranean productivity conditions over three
Pliocene precession-forced climate cycles
Abstract
Here, we explore the importance of export productivity versus anoxia in
the formation of sedimentary layers with enhanced total organic carbon
(TOC) content. We use geochemical, sedimentological and
micropaleontological records from two SW Sicily outcropping successions,
Lido Rosello (LR) and Punta di Maiata (PM), over three mid-Pliocene
precession-forced climate cycles (4.7 – 4.6 million years ago
[Ma]). Grey marls, deposited during precession minima, show enhanced
TOC in both records. We suggest that basin-wide, low-oxygenated
bottom-waters, resulting from freshwater-induced stratification during
precession minimum, was integral to preserving grey marl TOC.
Furthermore, prolonged eastern Mediterranean stratification may have
produced a deep chlorophyll maximum (DCM), leading to ‘shade-flora’
dominated productivity. The LR succession displays two unique laminated
layers containing enhanced TOC. These laminations do not occur at
specific times in the precession cycle or in time-equivalent PM samples.
They are likely to have been produced by an intermittent dysoxic/anoxic
pool at LR, caused by a local depression, which enhanced TOC
preservation. Consequently, the laminations provide a rare window into
‘true’ eastern Mediterranean productivity conditions during precession
maxima, as organic matter is typically poorly preserved during these
period due to enhanced ventilation. The laminated ‘windows’ indicate
that eastern Mediterranean export productivity may not have been
significantly lower during precession maxima compared to precession
minima, as previously thought. During these periods, productivity
conditions are likely to have been comparable to the modern eastern
Mediterranean, with a spring-bloom caused by enhanced winter/spring
deep-water mixing preceding a summer ‘shade-flora’ bloom caused by a
summer-stratification induced DCM.