Event and sequence stratigraphy of the Maastrichtian and Danian in Bulgaria

The events (physical, geochemical, biological – in the modern sense of the event stratigraphy) in the Maastrichtian and Danian in Bulgaria recently have been a subject of several publications. The main part of them is concentrated on the impact event at the Cretaceous/Tertiary (K/T) boundary and its consequences.
   After the discovery of the K/T boundary clay bed near Bjala (Stoykova, Ivanov, 1992), many authors had explored this locality and represented new data about the iridium anomaly in Bjala sections (Preisinger et aI., 1993a, b; Rogl et aI., 1996). Biological events and biostratigraphy across the K/T boundary in these sections are studied and discussed by Ivanov, Stoykova (1994), Stoykova, Ivanov (1995), Cтoйкoвa, Иванов (1996). The K/T boundary is located in the flysh section near Emona as well (Sinnyovsky, Stoykova, 1995). Later on, Синьовски (1999) reported an iridium anomaly at the K/T boundary in a clay bed, situated in-between shallow-water carbonate sediments in Mezdra region (NW Bulgaria).
   Many articles (or parts of articles) have been devoted to the problem of mass extinction and biological changes among the different fossil groups: calcareous nannoplankton – Preisinger et aI. (1993a, b) Ivanov, Stoykova (1994,1995), Ragl et aI.(1996), Cтoйкoвa, Иванов (1996);  planktonic foraminifera – Ragl et aI. (1996), Adatte ,et aI. (2002); benthic foraminifera – Вълчев (2001); macroinvertebrates – Ivanov Stoykova (1994), Stoykova, Ivanov (1995), Cтoйкoвa, Иванов (1996); Mileva-Ilieva (1998, 2000). There are two comprehensive studies on the K/T boundary in Bulgaria recently published – Стойкова и др. (2000), Adatte et aI. (2002). These papers summarize all data, that had been obtained from the different studies (stratigraphical, sedimentological, paleontological, mineralogical, geochemical, isotope), as well as newly acquired data andinterpretations.
   The value of other types of event-markers in the Maastrichtian – Danian interval is still poorly examined. Until now, Синьовски (1999) documented slumps, tephra-markers (beds containing volcanic ash) and biological events (colonization and immigration of fauna) in Maastrichtian-Danian of Mezdra region. Unfortunately
these event-markers are discerned in a restricted area and it's difficult to estimate their reliability for correlation.
   The first attempts for sequence stratigraphy subdivision of the Maastrichtian-Danian interval are made in the last few years. Синьовски (1999) divided two sequence units in this interval in Mezdra region. Вангелов (2000) separated two units in the Maastrichtian and one in the Maastrichtian-Danian in the East Balkan, Central Balkan-Fore Balkan and East Moesian Platform.
   The formulation of the present study is based of the choice of maximum informative for our purpose objects (sections). Therefore we discarded several well known to the geological community sections. We used only sections, which meet the following requirements: a) to have relatively continuous sedimentation across the  Maastrichtian-Danian, including the K/T border; b) to display different facial and bathymetrical zones in the basin. Three types of sections/environments can be distinguished: shallow-water, hemipelagic and deep-water.
The main goals of the study are: 1) to summarize all available data on the K/T boundary studies in Bulgaria, as well as to reveal some newly obtained data for correlation of the event-markers in the  Maastrichtian-Danian interval; 2) to produce a sequence stratigraphy subdivision and correlation of the third-order units in the interval.