Author	Brinkhuis, H.
Year	1992a
Journal	PhD thesis, Utrecht University, the Netherlands.PhD thesis, Utrecht University, the Netherlands.
Title	Late Eocene to early Oligocene dinoflagellate cysts from central and northeast Italy

Abstract Brinkhuis, H. 1992. Late Eocene to early Oligocene dinoflagellate cysts from central and northeast Italy. PhD thesis, Utrecht University, the Netherlands. ABSTRACT This thesis decribes the results of palynological investigations aimed at the integration of the dinoflagellate cyst record in the stratigraphic and paleoenvironmental analysis of Late Eocene and Early Oligocene deposits in the Mediterranean region. Chapter II concentrates on three sections straddling the pelagic Eocene/Oligocene (E/O) transition sequence in central Italy, viz. the Contessa Highway, Massignano (recently proposed as the E/O boundary-stratotype) and Monte Cagnero sections. Eight dinoflagellate cyst (DC) zones are defined enabling the establishment of a high-resolution Late Eocene to Early Oligocene dinoflagellate cyst biostratigraphy. The zones are calibrated against magnetostratigraphy and zonal schemes based on other microfossils. The invasion of the Mediterranean area by several higher-latitude dinoflagellate taxa marks the proposed E/O boundary, as characterized by the last occurrence of the Hantkeninidae (planktonic foraminifera) and calibrated against a level just above the youngest normal magnetic polarity excursion within Chron C13R. Dinoflagellate cyst events across the E/O boundary allow the recognition of warmer and cooler intervals, as well as sea-level fluctuations. The data indicate that Late Eocene warm conditions and a sea level highstand is followed by short-term cooler conditions and a lowstand around the presumed E/O boundary horizon. Following a short-term warmer interval and a highstand during the earliest Oligocene, a "second" cool and lowstand episode occurred. This second cool interval was more pronounced and it was of longer duration than the one at the presumed E/O junction. It also corresponds to the globally recognized cooling event reported from the base of Chron C13N. Chapter III demonstrates that marginal-marine Late Eocene through Early Oligocene dinoflagellate cyst successions from the Priabonian type-section at Priabona and the reference-section at Bressana (NE Italy) allow the recognition of the DC zones defined in the deeper marine E/O succession of central Italy. Successive shifts in the quantitative composition of the dinoflagellate cyst assemblages in the sections are interpreted in terms of changes in relative sea-level and sequence stratigraphy. These sea-level fluctuations can be correlated to third order "Vail" cycles TA4. 1 through TA4.4 of the Exxon chart. Also at Priabona and Bressana the dinoflagellate record enables the deduction of temperature change. The suite of inferred temperature and sea level-changes and their timing correlate wel] to previously established results obtained from the central Italian sections, further strengthening correlations. Similar to the results from central Italy, it is demonstrated that relatively cool intervals correlate with periods of sea level lowering. This suggests that glacio-eustacy best explains the Late Eocene to Early Oligocene sea-level fluctuations. In chapter IV chronostratigraphic implications of the new biostratigraphic information are discussed in relation to the status of the Priabonian Stage and the position of the E/O boundary. Dinoflagellate zonation of the E/O transition interval in the Mediterranean area now provides the possibility of selecting a biostratigraphically diagnosed upper boundary for the Priabonian Stage. The most suitable boundary-stratotype remains the top of the "Bryozoan limestone" in the type-section at Priabona. This level can be inter-regionally traced in different sedimentary settings by means of dinoflagellate cyst studies (last occurrence of Areosphaeridium diktyoplokus) and sequence stratigraphic analysis (onset third-order cycle TA4.4). There is every indication that this boundary can be reasonably correlated with the base of the Rupelian Stage as recognized in its type-area in Belgium. However, such a boundary concept is not in harmony with the newly proposed E/O boundary- stratotype in central Italy. At Priabona the position of the time-equivalent level is well below the "Bryozoan limestone". Acceptance of this level as the top of the Priabonian would create a new Priabonian/Rupelian boundary problem at the very time the old uncertainties and controversies on the mutual delimitation of these stages are becoming resolved. Since only stage boundaries should serve to define chronostratigraphic units of higher rank, a concluding recommendation to the IUGS Commission on Stratigraphy emphasizes temporization of formal decision-making with respect to the status of the Massignano section.