Daria IVANOVA, Bogusław KOŁODZIEJ, Elena KOLEVA-REKALOVA & Ewa RONIEWICZ (2008) Oxfordian to Valanginian palaeoenvironmental evolution on the western Moesian Carbonate Platform: a case study from SW Bulgaria // Annales Societatis Geologorum Poloniae. Vol.78. no.2. P.65-90.

pdf: http://www.asgp.pl/2008/78_2/065-090.pdf (99 Mb)

Three sections (Rebro, Lyalintsi and Velinovo) of the Upper Jurassic-Lower Cretaceous carbonate sequences from the Lyubash unit (Srednogorie, Balkanides, SW Bulgaria) have been studied for elucidation of biostratigraphy and palaeoenvironmental evolution. Palaeontological studies of foraminifera, supplemented by studies of calcareous dinoflagellate cysts and corals, enabled the determination of the Oxfordian-Valanginian age of the analysed sequences. They were deposited on the Dragoman Block (western part of the Moesian Platform), and during Mid-Late Cretaceous included to the Srednogorie. A possible Middle to Late Callovian age of the lowermost part (overlying the Bajocian-Lower Bathonian Polaten Formation) of the studied sections assumed till now has not been confirmed by the present studies. Eleven facies have been distinguished and attributed to depositional environments. Marine sedimentation on a homoclinal ramp started in the Oxfordian and till the Early Kimmeridgian - in all three sections - was dominated by fine-grained peloidal-bioclastic wackestones to grainstones. Since the Late Kimmeridgian, when a rimmed platform established, facies pattern underwent differentiation into (i) the inner platform (lagoon and tidal flat facies) - only in Velinovo, (ii) reef and peri-reef facies/bioclastic shoals - mainly in Lyalintsi, and (iii) platform slope - mainly in Rebro. Sedimentation generally displays a shallowing-upward trend. Two stages in evolution of the rimmed platform are postulated. The mobile stage lasting till the Tithonian/Berriasian boundary was followed by a more stable stage in the Berriasian to Valanginian time. Reefs are developed mainly as coral-microbial biostromes, lower coral bioherms or coral thickets, in the environment of moderate energy and sedimentation. They contain highly diversified corals (72 species). Micro- bialites contributed to the reef framework, but they never dominated. Locally, microencrusters and cement crusts formed important part of reefal framework. During the mobile stage of the platform evolution a relative sea-level rise interrupted reef development, as evidenced by intercalations of limestones with Saccocoma. During the second stage high carbonate production and/or regressive eustatic events, not balanced by subsidence, decreased accommodation space, limiting reef growth and enhancing carbonate export to distal parts of the platform.

Ewa RONIEWICZ (2008) Kimmeridgian-Valanginian reef corals from the Moesian Platform from Bulgaria // Annales Societatis Geologorum Poloniae. Vol.78. no.2. P.91-134.

pdf: http://www.asgp.pl/2008/78_2/091-134.pdf (184 Mb !!!)

The coral fauna of the Late Kimmeridgian-Valanginian interval from the Slivnitsa Formation, Lyubash monocline, western part of the Moesian Platform, is presented. Coralliferous interbeds from a continuous, over 350 m thick sequence of well-bedded platform limestones, cropping out near the village of Lyalintsi, yielded 72 species (29 determined in open nomenclature) classified into 50 genera and 23 families belonging to the orders Scleractinia and Hexantiniaria. The following genera and/or species are described as new: Epistreptum communeformae gen. et sp.n., Lyubasha gracilis gen. et sp.n., Oedalmiopsis cretacea gen. et sp.n., Siderastreites lyalintsensis gen. et sp.n., Latomeandra obliqua sp.n., and Microphyllia elevata sp.n.; a new family Solenocoeniidae is erected. The fauna shows a mixed Late Jurassic/Early Cretaceous character, with Jurassic taxa pre- vailing over Cretaceous taxa. Epithecate phaceloid (pseudocolonial), lamellar, and ramose (colonial) growth forms dominate over massive (hemispherical) and solitary corals. Rich microencrusting organisms are associated. The predominantly pelmicritic sediment of thrombolite macrofabric, and the character of the fauna show that the palaeoenvironment was situated below wave base. The stratigraphical distribution of the Cretaceous coral taxa is conformable with the micropalaeontological (foraminifera, calcareous dinocysts, diploporids) stratigraphical zonation established in the Slivnitsa Formation.