Naslov
Tertiary extension in eastern Adriatic Realm ("Adriatic Basin")

Autori
Marjanac, Tihomir ; Ćosović, Vlasta

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
The Mediterranean Basins: Tertiary Extension within the Alpine Orogen, International Workshop / - Cergy-Pontoise, 1996

Skup
International Workshop on Geodynamics of the Mediterranean Basins: Tertiary Extension Within the Alpine Orogen

Mjesto i datum
Cergy-Pontoise, Francuska, 1996

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Nije recenziran

Ključne riječi
basins; flysch; molasse; geotectonics; basins

Sažetak
Eastern Adriatic/External Dinaric realm is known for its "classic" carbonate suite of Late Triassic-Lutetian span. From Lutetian until Pleistocene, clastics have been deposited, although their age has been attributed differently by various authors. Herein, we present a synthesis of the present stage of knowledge on Tertiary-early Pleistocene deposits of Eastern Adriatic offshore and coastal region (which is locally extended some 100 km inland), based on the most recent data available. The first major break in sedimentation since the Late Triassic was caused by Laramian orogenic phase which uplifted Dinarides, except for Venetian- and Friuli Basins in northernmost Adriatic region (sensu lato), and southern Adriatic offshore which apparently did not suffer a change in deepmarine sedimentation. In most of the studied areas more-or-less thick bauxite accumulations overlie karstified upper Cretaceous platform carbonates. Renewed deposition, which first occurred in paralic facies, is due to regional eustatic (?) sea-level rise, and locally commenced in Late Paleocene, but most commonly in earliest Eocene ("Cuisian"). Being extremely shallow in origin, these deposits record numerous high-frequency sea-level oscillations, where the depositional environment was closer to the open sea (eg. in Central Dalmatia). Platform carbonates represented by Foraminiferal Limestones were deposited from "Cuisian" until Late Lutetian, exceptionally Late Bartonian (in Istria). Also their deposition was locally affected by sea-level changes, although less obvious. During that period of time shallow marine conditions have been established all over the Adriatic region, except for the Venetian- and Friuli Basins, SW Slovenia, and Southern Dalmatian offshore where basinal depositional regime continued since the Late Cretaceous. The first post-Laramian deepening is evidenced by Transitional Beds which include Globigerina Marls in their upper part. This event started during Early-Late Lutetian in Istria (already during "Cuisian" in SW Slovenia), Late Lutetian elsewhere, and the facies is characterized by upward increasing share of planktonic foraminifers and glauconite. This deepening is usually interpreted as caused by tectonic disintegration of Adriatic carbonate platform. However, the thickness variations and the reduction of some foraminiferal biozones was interpreted as a consequence of an orogenic phase (Istrian-Dalmatian phase ; Šikić, 1968), which is recently reinterpreted in terms of a sea-level fall (Marjanac & al., in press). Deepmarine clastics of turbiditic origin in Adriatic realm are usually referred to as Flysch and interpreted as syn-orogenic deposits. The older part of turbidite succession is dominated by deposition of megaturbidites and is interpreted as syn-rift in origin (Marjanac, 1991). Except for the above mentioned basins with continuous clastic deposition since Cretaceous, deposition of Flysch started diachronously along the Adriatic region, thus it is oldest (Paleocene) in Vipava valley (SW Slovenia), Middle -Late "Cuisian" age in Istria, Late Lutetian in Ravni Kotari, Bartonian in Dalmatia and of Bartonian/Priabonian age on Central Dalmatian islands. The youngest Flysch is of Pliocene age in Venetian Basin, Late Eocene age in Istria and SW Slovenia, whereas its age was recently revised in Ravni Kotari (Marjanac & al., submitted) and Central Dalmatia (Marjanac, 1993) where it lasts until the Late Miocene. Flysch is overlain by coarsegrained Promina Beds which are usually referred to as molasse of the External Dinarides, and crop-out only in eastern Adriatic coastal area. Its age was commonly attributed to Eocene-Oligocene span, but our new data indicate Miocene-Pliocene age in Ravni Kotari (Marjanac & al., submitted), whereas in Central Dalmatia Promina-conglomerates occur in Bartonian and Oligocene-Miocene (Marjanac, 1993). The Promina Beds were deposited in a range from deepmarine to paralic and alluvial environments, and show distinct response to sea-level changes. The above stratigraphic successions indicate that sea-level changes have strongly influenced deposition in eastern Adriatic realm. Although there is no consensus as of the causes of deepening events (tectonic vs. eustatic), it is possible to recognize two major deepening phases of the Adriatic carbonate platform. The first one occurred diachronously in Early Eocene, but with no evidence of syn-depositional tectonics, and we favour the eustatic cause. The second deepening phase (also diachronous) precedes deposition of Flysch, and was preferably caused by tectonic disintegration of the platform (primary extension). The evidence are slight angular unconformity of Flysch and underlying Transitional Beds, and variations in thickness of the Globigerina Marls. This tectonic event(s) has caused opening of half-graben basins with isolated depocentres where megaturbidites were deposited from ponded flows (Marjanac, 1991). Promina Beds depocentre in Ravni Kotari was shifted eastwards compared to that of the underlying Flysch, as a response to opening of half-graben basin with steeper NE margin (secondary extension) and high subsidence rate which caused accumulation of ca. 2000 m thick clastics. In the Central Dalmatia, however, no such rifting has been observed, but there is evidence of synsedimentary compressional events. The final phase in basin evolution was deposition in Miocene-Pliocene paralic and alluvial basins, which are only patchily preserved, whereas the final deformation (compression) of the coastal Dinarides occurred much later than previously thought, namely not before the late Pliocene.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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