Tephra record from the Sea of Marmara for the last 70 ka and its paleoceanographic implications
Abstract
Sea of Marmara (SoM) is a gateway between the Mediterraean and Black seas, and a tectonically active basin located on a transform plate boundary. Tephra record in the SoM is therefore very important for dating palaeoceanographic, paleoclimatic and tectonic events. We report three tephra units in cores from the SoM extending back to ca 70 ka BP and including an upper marine and a lower lacustrine units separated by a 12 ka (uncalib.) boundary. The uppermost tephra unit is up to 8 mm thick layer in the marine unit. It is heterogenous phonolitic with high total alkali content of 12.4-15.7 wt % and K2O/Na2O of 0.9 to 1.2. The middle and lower tephra layers occur in the lacustrine unit in ca 29 m-long Core MD-01-2430. The middle tephra (MT-1) is a 70 mm-thick homogeneously rhyolitic layer. The lower tephra (MT-2) is 140 mm thick and has a phonolitic-trachytic composition with CaO content of 1.7-1.9 wt % and bimodal K2O/Na2O of 1.0-1.4. Using their geochemical composition and stratigraphic analysis, we assign the tephra units, from top to bottom, to Vesuvius AP2 Pumice, Santorini Cape Riva and Campanian Ignimbrite, which have been previously dated at 3.5 ka BP, 21.95 ka BP, and 39.3 ka BP (all calender ka). The continuous sedimentary record in the Core MD-01-2430 covering the last ca 70 ka indicates that the SoM was lacustrine, disconnected from the Mediterraean Sea during MIS4, MIS3 and most of MIS2. This implies that the sill depth of the Çanakkale Strait (Dardanelles) was shallower than the present-day -65 m sill depth during MIS3 and MIS4. Figure 1: Morphotectonic map of the Sea of Marmara showing location of the studied cores (red stars).
Figure 2: Geochemical biplots of tephra glass composition. a) Total alkali silica diagram b) FeO versus total alkalies for allocating cryptotephras from core MNTKS34 and ML01 to the AP2 tephra from Vesuvius. c) FeO versus CaO for correlating tephra MT1 with the Y-2 tephra from Santorini. d) SiO2 versus CaO for discriminating the MT2 tephra (Campanian Ignimbrite).- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMPP13B1887C
- Keywords:
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- 1145 GEOCHRONOLOGY Tephrochronology;
- 4900 PALEOCEANOGRAPHY;
- 1065 GEOCHEMISTRY Major and trace element geochemistry;
- 1641 GLOBAL CHANGE Sea level change