Naslov
Synsedimentary tectonics and organic production - the controlling factors of prograding bioclastic clinoforms and rudist biostromes from the Uppermost Albian to Middle Cenomanian of Southern Istria, Croatia

Autori
Tišljar, Josip ; Vlahović, Igor ; Velić, Ivo ; Matičec, Dubravko

Izvornik
Globale und regionale Steuerungsprozesse biogener Sedimentation, Göttingen, 08.12 -10.12.1996.

Vrsta, podvrsta
Ostale vrste radova, ostalo

Godina
1988

Ključne riječi
Adriatic Carbonate platform; Shallow-water arbonates; Upper Albian; Lower Cenomanian

Sažetak
Jurassic and Cretaceous carbonates of the NW part of the Adriatic Carbonate Platform in the region of Istria are predominantly characterised by low-energy peritidal to lagoon depositional systems. However, during the Late Albian, and Early to Middle Cenomanian in the Istrian part of the Adriatic Carbonate Platform, a specific depositional system was established, characterised by a lateral and vertical succession from peritidal, foreshore and shoreface environments to subtidal sand bars, with prograding clinoforms and rudistid biostromes. Rapid changes of depositional systems during the latest Albian and Early Cenomanian in Southern Istria represent the consequences of the interaction of two main controlling factors: synsedimentary tectonics and extensive organic production. The Lower part of the Upper Albian deposits is represented by thin-bedded pelletal wackestones/packstones with common current ripples alternating with mudstones, LLH stromatolites and peritidal breccias (Facies unit 1: thin-bedded peritidal pelletal and stromatolitic limestones). As a result of synsedimentary tectonics during the latest Albian, large-scale open folds were formed, which caused a gradual deepening of the sedimentary environments and changes of environmental conditions. As a consequence, limestones of Facies Unit 2 were deposited (well-bedded foreshore - shoreface packstones/grainstones showing synsedimentary slumps and slides). The deeper parts of depressions, below fair-weather wave base, were characterised by amalgamated carbonate tempestites (Facies unit 3: shoreface to offshore storm-generated limestones of Early Cenomanian age). The apical parts of the folds and the upper parts of their slopes represented ideal habitats for rudists, which produced extensive colonies that were subsequently destroyed by higher-energy conditions. A considerable amount of rudist debris was reworked by strong waves and currents, which together with fine-grained peloids and orbitolina tests was redeposited as scattered bodies (Facies unit 4: massive off-shore - shoreface carbonate sand bars of Early Cenomanian age). Extensive production of bioclastic detritus and its intense reworking led to the progradation of the material towards the deeper parts of depressions, resulting in formation of the clinoform bodies (Facies unit 5: prograding clinoforms composed of rudist debris of Early to Middle Cenomanian age). These clinoforms were gently inclined (10 to 15 degrees in average), downlapping towards the South-East. Each clinoform is characterised by a fining-upward sequence, but their general succession represents a coarsening and shallowing-upward sequence.This progradational trend finally caused the reestablishment of shallow-water deposition, as evidenced by widespread rudist biostromes composed of numerous radiolitid specimens in primary growth position (Facies unit 6: rudist biostromes of Early to Middle Cenomanian age). These are overlain by peritidal deposits of Facies unit 7 (high-energy rudist coquinas with ostreid coquina storm-tide deposits of Middle Cenomanian age).

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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