A pre-Messinian Rise in Mediterranean Sea Surface Salinity Evidenced by Clumped Isotopes of Cements and Skeletal Fragments in a Shallow-Water Carbonate Ramp (Novaglie Formation, Southern Italy)
Abstract
The Messinian Salinity Crisis (MSC) is the most dramatic event impacting the Mediterranean in the Cenozoic, leading to a near complete dry-up of the basin, precipitation of a thick evaporitic cap, and alteration of regional and global climate patterns. The probable cause of the MSC is a combination of eustatic fall and tectonic closure of the Mediterranean sill, however, the exact mechanism leading to the event remains elusive. Here we show that by combining careful cement stratigraphy with carbonate clumped isotope paleo-thermometer, we can extract both a diagenetic history and a paleo-salinity record from shallow-water carbonate ramp deposits that spans the Messinian period. The Novaglie Formation (Southern Italy) is an ideal target as it has not been structurally loaded, never been deeply buried and still contain preserved aragonitic textures. Petrography reveals early marine botryoidal cements are often preserved as aragonite but sometimes transformed into calcite. Circumgranular aragonitic cements are also visible, especially surrounding preserved vermitids and serpulids. Other organisms include barnacles, corals, bivalve fragments, encrusting algae and foraminifers. Many of the original textures of the reef appear recrystallized. FTIR analysis confirms the presence of aragonite in the well-preserved botryoidal cements and some of the fossils, whilst the recrystallized textures are all calcite. Clumped isotope thermometry confirms that the recrystallized textures are meteoric in origin. The preserved aragonite material show formation temperatures at around 15ºC for most seafloor cements, and up to 25ºC for preserved calcitic barnacles. The reconstructed δ18O seawater shows a steady increase in values from the early to the late Messinian. When converted into salinity units, this indicates a progressive near doubling of salinities in the course of the Messinian, and thus that the onset of the salinity crisis has roots several million years before the event.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP52A..06J
- Keywords:
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- 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCESDE: 1051 Sedimentary geochemistry;
- GEOCHEMISTRYDE: 3675 Sedimentary petrology;
- MINERALOGY AND PETROLOGYDE: 4863 Sedimentation;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL