PALYNOSTRATIGRAPHY, PALEOECOLOGY AND PALEOCLIMATOLOGY OF TERTIARY MOLASSE BASINS AND THE PERI-ADRIATIC DEPRESSION IN ALBANIA AND PALEOGEOGRAPHIC IMPLICATIONS

The Albanides are part of the Alpine orogenic system that encompasses the Dinaride-Hellenide mountain belt in the Balkan Peninsula and have evolved as a result of the oblique collision between Adria and Eurasia during the latest Mesozoic-Cenozoic. The External domain of the Albanides includes Paleogene and younger lithostratigraphic units of, from east to west, the Krasta-Çukali, Kruja, Ionian, and Peri-Adriatic Depression (foredeep) that are all affected by pre-Pliocene contractional deformation, manifested in west-directed folds, reverse to thrust and strike-slip faults. The Internal domain to the east consists mainly of Paleozoic-Mesozoic basement units, locally overlain by Paleogene-Quaternary molasse basins and alluvial depocenters. Pliocene and younger extensional normal faults and transtensional, dextral strike-slip fault zones are common in the Internal domain and played a significant role in the development of a series of basins and sub-basins as graben and half-graben systems, which are interspersed with local horst structures. In this study, we have examined the palynostratigraphy of the Peri-Adriatic Depression (PAD) in the External domain and several major inter-mountain basins in the Internal domain, and have identified paleoclimatic and paleoenvironmental changes using dinocysts, spores and pollen assemblages.

The PAD deposits consist mainly of conglomerate and mudstone rocks interbedded with sandstone, siltstone and lithothamnium limestone. Sandstone layers consistently become finer-grained from east to west. Gypsum horizons are abundant in the Messinian. Pliocene deposits consist of an argillaceous facies tapering out eastward and a conglomeratic facies pinching out westward. We have identified five dinoflagellate cysts zones and six spore and pollen assemblages in the Langhian to Pliocene strata in the PAD. Calibration is provided by planktonic foraminiferal biozones.

The Tertiary inter-mountain basins we have examined include the Korça basin in southern Albania, Librazhdi and Burreli basins in central Albania, and the shallow Erseka, Pogradeci, Tropoja, Kukesi and Peshkopia basins in eastern to northern Albania. The Korça basin includes basal conglomerates at the bottom overlying the ophiolitic ultramafic rocks, and coal and coral formations. The middle Oligocene-middle Miocene molasse section higher up starts with sandstone deposits intercalated with clay horizons. There are five dinoflagellate cysts zones within the middle Oligocene and Langhian strata. Tertiary deposits in the Librazhdi basin are made mainly of red-coloured, massive conglomerate and coarse sandstone locally grading upwards into siltstone. The spore-pollen assemblage is represented by only one Pliocene sample. The Burreli basin strata are made of massive conglomerate and coarse sandstone, and contain a Messinian–Pliocene sporo-pollen assemblage. The molasse deposits in the shallow Erseka basin lie transgressively on the Oligocene rocks and are made of sandstone, siltstone with sand pebbles, and argillite that contains rich, coal-bearing horizons. The sporo-pollen also occurs in the Pliocene strata. The molasse deposits of the Pogradeci basin lie transgressively on a Triassic limestone and include sandstone-siltstone units with commercially exploited coal-bearing horizons. The sporo-pollen assemblage belongs to the Pliocene. The molasse deposits in the Peshkopia basin onlap the Paleozoic rocks of the Korabi zone and contain a sporo-pollen assemblage in the Pliocene strata. The molasse deposits in the Kukesi basin in northeastern Albania onlap the Mesozoic deposits of the Mirdita zone and include conglomerate-sandstone units with a Pliocene sporo-pollen assemblage. The molasse deposits in the northernmost Tropoja basin also onlap the Mesozoic rock units of the Mirdita zone and contain conglomerate-siltstone sequences with a Pliocene sporo-pollen assemblage.

We have recorded a high diversity of dinoflagellate species in the Oligocene strata of the Korça basin, although its Miocene and Pliocene strata are lacking any dinoflagellate. Dinocysts are common in the Serravallian rock record of the Peri-Adriatic Depression, indicating warm temperatures and marine conditions during the middle Miocene. We observe a major change from cysts-rich palynomorphs in the Serravallian to pollen-rich palynomorphs the Messinian strata of the PAD. The majority of dinoflagellate cysts also disappear in this time frame, and their limited diversity suggests an open shallow marine environment during the late Miocene. The observed enrichment of grass plants in the Pliocene record indicates a temperate climate. The poor presence of dinoflagellate in the lower Pliocene is an indication of shallow marine conditions, whereas a rich dinoflagellate assemblage higher in the Pliocene sequence is an indication of a deeper marine basin in the beginning of the Quaternary. We interpret these palinostratigraphic, paleocological and paleoclimatological data from the Tertiary inter-mountain molasse basins and the Peri-Adriatic Depression within the framework of the Cenozoic geodynamic evolution of the Albanides and the Balkan Peninsula.