Distribution,stratigraphic position and age of ash layer “L”, in the Panama Basin region |
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| Authors: | Dragoslav Ninkovich NJ Shackleton |
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| Institution: | CLIMAP, Lamont-Doherty Geological Observatory of Columbia University, Palisades, N.Y. USA;CLIMAP, International Corresponding Member, Sub-department of Quaternary Research, University of Cambridge, Cambridge Great Britain |
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| Abstract: | Deep-sea sediments in the Panama Basin-Carnegie Ridge area contain biogenic material, detrital carbonate, mineral clay and volcanic ash layers. Ash layer “L” of Bowles et al. (1973) is correlated mineralogically and by the physical property of glass shards through sixteen cores. Isopachs and grain-size analyses of the ash layer indicate that it originated in Colombia or Ecuador, and was carried by easterly winds. The distribution of the ash and of mica percentage in the ash form a W-shaped pattern opening towards the west. This suggests that two branches of the Cromwell current, one moving along the equator and one along 3°S, had a significant influence on the distribution of the ash.CaCO3 content has been measured down thirteen cores and oxygen isotope content of benthonic Foraminifera obtained in two. Two cores penetrate theStylatractus universus extinction datum. Ash “L” fell 230,000 years ago during the cold substage 7b of isotope stage 7. Deposition rates vary between 2.5 and 6 cm/1000 yr and show no relationship with bottom topography or proximity to land. |
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