Calcareous nannofossil biostratigraphy of the External Dinarides flysch (Vrčić‐Staravasa Pag Island, Croatia): A key to an Eocene tectono‐stratigraphic and paleoenvironmental interpretation

Abstract

It is largely accepted that in the Dinaric shallow foredeep basin, the onset of Cenozoic synorogenic sedimentation is diachronous along strike and shows orogenparallel southward younging, creating a large uncertainty in the age of the Dalmatian flysch. Calcareous nannofossil biostratigraphy was studied to investigate a turbiditic succession exposed in Pag Island (Croatia) with the main purpose of constraining its age, which is still a matter of debate. The age assignment for the turbiditic deposition bears important implications for better understanding of the geodynamic and paleoenvironmental evolution of the External Dinarides.We logged a well-exposed sedimentary section in the south-western limb of the Pag anticline and performed calcareous nannofossil quantitative analyses revealing a high species diversity and abundant assemblage. The age diagnostic species indicate CNE14-CNE15 biozones, suggesting that flysch deposition occurred in the Lutetian-Bartonian. This age can be further restricted to the CNE14 (42.37-40.51 Ma) by means of the lowest occurrence of Reticulofenestra reticulata and the highest occurrence of Sphenolithus furcatolithoides. Vertical facies variation and paleoecological indications suggest an increase in paleobathymetric depth during deposition. Our data support a post-Lutetian age of folding and thrusting for the Pag Island region and suggest a relatively short time span during the middle-late Eocene period for the main contractional stage in this sector of the External Dinarides. This result has important implications for the evolution of the Dinaride foreland basin system in Cenozoic times. K E Y W O R D S calcareous nannofossils, Dalmatian flysch, Eocene, External Dinarides, Pag anticline

Deformation Sequence and Paleofluids in Carbonate Buckle Folds Under Transpression (Pag Anticline, External Dinarides, Croatia)

“…Deposition of the foraminiferal limestones marked the onset of the foreland basin stage in the region, in Ypresian times (Babić et al., 1993; Pamić et al., 1998; Persico et al., 2019; Piccoli & Proto Decima, 1969). In the foreland basin stage, the burial of Cretaceous limestones reached at least 600 m (Sokač et al., 1976) due to the deposition of the Lutetian‐Bartonian Dalmatian flysch, providing the necessary sedimentary load for development of bedding‐parallel stylolites, that formed in the studied Upper Cretaceous carbonate succession (Figure 12b).…”

“…in Cretaceous limestones and foraminiferal limestones, respectively, and continuing nucleation of axial parallel tectonic stylolites as suggested by mutual crosscutting relationships (Figure 12), indicate the switch between σ 2 and σ 3 stress axes, possibly triggered by the onset of folding and later by amplification of the Pag anticline (Figure 13b; Marshak, 1988; Macedo & Marshak, 1999; Tavani et al., 2015). Increasing the vertical load by sedimentation of the proximal turbidites in a tectonically controlled basin may have favored buckle folding of the multilayer and the switch from a contractional (vertical σ 3 ) to a strike‐slip stress field configuration (vertical σ 2 ; Babić & Zupanič, 2008; Persico et al., 2019). The strike of V 2 veins indicates that the direction of σ 1 during the folding stage was still from N40°E to N50°E, while the direction of σ 3 was parallel to the axis of the Pag anticline, that is, a strike‐slip stress field configuration.…”

“…This long‐lasting erosional phase is testified by a regional stratigraphic gap spanning from Coniacian‐Santonian to Ypresian times (Jelaska et al., 1994; Korbar, 2009; Mittempergher et al., 2019). Sedimentation resumed in the Lutetian and Bartonian with the deposition of the ramp‐carbonates regionally known as foraminiferal limestones (Figure 2e), passing upward to the transitional beds (Globigerina marls) (Figure 2f) and the predominantly shallow marine clastic succession of the Dalmatian flysch (Figure 2g; Persico et al., 2019). The Eocene‐Oligocene Velebit breccia outcrop just NW of the Paški zaljev and unconformably cover the folded cretaceous substrate (Figure 2h).…”

Post-collisional mantle delamination in the Dinarides implied from staircases of Oligo-Miocene uplifted marine terraces

“…Such a barrier on the lithospheric scale would rather favor orogen-parallel over orogen- perpendicular mantle flow patterns. Continued shortening, crustal thickening, and foreland flexure in the External Dinarides led to the deposition of Eocene–Oligocene syntectonic deposits 27 – 31 , subdivided into the proximal coarse-grained molasse (Promina Beds) 27 – 30 and the fine-grained distal “flysch” deposits 31 . The most important geological processes shaping the Dinarides are summarized in Fig.…”

Post‑collisional mantle delamination in the Dinarides implied from staircases of Oligo‑Miocene uplifted marine terraces

“…Such a barrier on the lithospheric scale would rather favor orogen-parallel over orogen-perpendicular mantle flow patterns. Continued shortening, crustal thickening, and foreland flexure in the External Dinarides led to the deposition of Eocene-Oligocene syntectonic deposits [27][28][29][30][31] , subdivided into the proximal coarse-grained molasse (Promina Beds) [27][28][29][30] and the fine-grained distal "flysch" deposits 31 . The most important geological processes shaping the Dinarides are summarized in Fig.…”