Diagenetically and environmentally controlled changes across the K/T transition at Koshak, Mangyshlak (Kazakstan)

The Koshak section located on the northeastern margin of the Tethyan ocean reveals a distinctive oxygen and carbon isotope pattern from surface and bottom water dwellers. Trends in δ¹⁸O are similar in bulk samples as well as planktonic and benthic foraminifera. Concentration of selected trace elements from bulk carbonate indicate enriched Na, Fe, Ba, Mn and depleted Sr contents compared with average concentrations in recent pelagic carbonates. The ⁸⁷Sr/⁸⁶Sr ratios at Koshak are comparatively low to values reported from other K/T sections. Carbon and oxygen isotope records show no drastic changes at the K/T boundary. Throughout the section benthics show more positive δ¹³C values than planktonic and bulk samples. We assume that the surface water carbon record is imprinted by an admixture of fresh water which was possibly reduced during the early Danian zone Pla. This input of fresh water may be related to a major climatic change (warming?) during the terminal Maastrichtian possibly associated with intensified volcanic activity (Deccan traps). Carbon isotopes show similar values to other high latitude sites in Denmark (Nye Klov) and the southern Indian Ocean (ODP Site 738) with only minor depletion of -0.5‰ across the K/T boundary. Geochemical analyses from Koshak section record changes which have to be attributed to postdepositional processes on the external platform and in basinal environments. Changes in trace element concentrations and δ¹⁸O are related to dissolution-precipitation processes. However, these processes did not affect the primary δ¹³C and Sr isotope patterns.