Calcareous nannofossil assemblages of the Late Campanian- Early Maastrichtian form Gurpi Formation (Dezful embayment, SW Iran): Evidence of a climate cooling event

Abstract

A succession of Late Campanian- Early Maastrichtian is analyzed from Gurpi Formation with regard to the calcareous nannofossils. Correlation Matrix was applied for the first time to the entire nannofossil assemblage to reconstruct environmental conditions. A detailed quantitative calcareous nannofossil analyses is performed on samples in order to further investigate the climate events, and interpret changes of surface water temperature. The calcareous nannofossil assemblage is divided into 3 groups as cold, cool and warm water taxa. Although cold water taxa (<em>Ahmuellerella</em> <em>octoradiata</em> and <em>Gartnerago</em> <em>segmentatum</em>) are rare (less than 1%), cool (<em>Eiffellithus</em> <em>turriseiffelii</em>, <em>Prediscosphaera</em> <em>cretacea</em>, <em>Micula</em> <em>staurophora</em>, <em>Zeugrhabdotus</em> spp., <em>Arkhangelskiella</em> <em>cymbiformis</em>, <em>Biscutum</em> <em>constans</em>, <em>Tranolithus</em> <em>orionatus</em> and <em>Lucianorhabdus</em> <em>cayeuxii</em>) and warm (<em>Watznaueria</em> <em>barnesae</em>, <em>Uniplanarius</em> <em>trifidus</em>, <em>Uniplanarius</em> <em>sissinghii</em>, <em>Ceratolithoides</em> spp. and <em>Broinsonia</em> spp.) water taxa are more frequent. The number of warm water taxa is higher than the number of cool water taxa and a reverse trend can be observed between them. Concerning the temperature index (TI), four important trends of climate variability from warmer to cooler phases (two cooling phases and two warming phases) have been documented at the studied interval. According to the recorded data, two pronounced cooling event are observed at Late Campanian and Early Maastrichtian, respectively.