Naslov
Lias to Malm evolution of the northeastern part of the Adriatic-Dinaric carbonate platform

Autori
Bucković, Damir ; Cvetko Tešović, Blanka

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

Izvornik
23nd IAS Meeting of Sedimentology, Coimbra, September 15-17, 2004 : Abstracts book / Pena dos Reis, Rui ; Callapez, Pedro ; Dinis, Pedro - Coimbra : International Association of Sedimentologists (IAS), 2004

Skup
23nd IAS Meeting of Sedimentology

Mjesto i datum
Coimbra, Portugal, 15.09.2004. - 17.09.2004

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
Lias; Malm; carbonate successions; Adriatic-Dinaric carbonate platform

Sažetak
The 465 m thick, succession of the Jurassic carbonates at Mt. Žumberak (Sošice locality) shows the evolution of the marginal NE part of the Adriatic-Dinaric carbonate platform. Four facies units have been distinguished showing progressive deepening (Gušić & Babić, 1970). The lowest facies unit (125 m thick), Lower-Middle Lias limestones with coarsening-upward cycles, directly overlies the Upper Triassic Hauptdolomite. The cycles contain mudstone or pelletal wackestone as the lower cycle members and peloidal-bioclastic wackestone/packstone to grainstone or ooid grainstone as the upper cycle members. Among the typical shallow-water nonskeletal carbonate particles (pellets, peloids, intraclasts and ooids) skeletal particles contain various molluscan bioclasts and rare Palaeodasycladus mediterraneus (Pia), Amijiella amiji (Henson), Lituosepta recoarensis Cati and Orbitopsella praecursor (Gümbel). Within the next facies unit (20 m thick) of pelletal-bioclastic wackestones, shallow-water particles are rare ; instead, tiny echinoderm fragments predominate, with sporadic radiolarians as well as sponge spicules. The age of that facies unit is the Late Lias. The pelagic trend increasingly continues into the overlying facies unit (ca. 300 m thick), where two parts can be distinguished. The lower part consists of pelletal-bioclastic wackestones to packstones that contain "filaments" (pelagic bivalves), globigerinid foraminifera and rare Lower Dogger benthic foraminifer Mesoendothyra croatica Gušić. This part of succession is interrupted with a 80 m thick package of poorly sorted breccia. The breccia contains Liassic shallow-water and Lower Dogger deeper-water fragments with "filaments" and globigerinids up to 0.5 m in size. In the upper part of this facies unit, pelletal-bioclastic wackestones to packstones are frequently intercalated with graded bioclastic-intraclastic grainstone/rudstones. From the underlying wackestones to packstones these 0.2-0.5 m thick intercalations are always terminated by a sharp and uneven erosional surface. They contain poorly sorted, coarse-grained, and angular to suboval, echinoderm fragments and micritic intraclasts with "filaments" and globigerinids. Elongated fragments are always oriented parallel to the bedding. These intercalations contain Protopeneroplis striata Weynschenk, Nautiloculina oolithica Mohler, Pseudocyclammina lituus (Yokoyama), Trocholina alpina (Leupold) and Trocholina elongata (Leupold). According to this microfossil assemblage, the upper part of this facies unit belongs to the Upper Dogger-Lower Malm. The uppermost facies unit (20 m thick) consists of pelletal--skeletal wackestones to wackestone/packestones. In carbonate mud there are frequent Calpionella alpina Lorenz and Calpionella elliptica Cadisch. Sporadically, saccocomas, radiolarians, sponge spicules and even aptichi are also present. Such microfossil content indicates the Upper Malm, i.e. a Tithonian to Berriasian age (Babić, 1973). Regarding the succession of mentioned facies units, it can be seen, that, starting from the Late Middle Lias, the marginal part of the Adriatic-Dinaric carbonate platform has been transformed into a deeper-water environment, i.e. a basin area spread over the sunken part of the platform. The thick package of the Lower Dogger breccia indicates that this was probably caused by block faulting, sometimes rather "brisk", when already lithified deposits were broken. These tectonically produced differences in the sea-bottom depth triggered gravity flows along the platform slope that produced coarse-grained intercalations at the bottom of the slope (toe-of-slope). Concerning the disappearance of these intercalations in the uppermost facies unit, it can be supposed that block-faulting at the platform margin continued, causing the platform-basin boundary to gradually shift its position toward the platform interior. According to Babić (1976), during the Jurassic this shifting of platform-basin boundary was toward southwest and amounted approximately 25 km.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

POVEZANOST RADA