TURONIAN MARKER FORAMINIFERA ASSOCIATIONS FROM THE SOUTHERN PART OF THE EASTERN CARPATHIANS: DAMBOVITA VALLEY-INTORSURA BUZAULUI AREA
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Abstract:
Within the Turonian deposits of the area beteen Dambovitza Valley and the upper part of the Buzau Valley the foraminiferal fauna is represented by two very distinct assemblages. One of them mainly consists of planctonic foraminifera - up to 90 % (Whiteinella, Helvetoglobotruncana, Dicarinella, Marginotruncana, Hedbergella, Praeglobotruncana, Schackoina). The remaining 10 % belong to benthic (agglutinated and calcareous ) foraminifera. The other association consists totally of small and primitive agglutinated taxa with siliceous wall cement and a long stratigraphic range. The corresponding biozones show also a relatively large range (Bulbobaculites problematicus, Uvigerinammina jankoi ): from the Upper Cenomanian to the Lower Senonian. The comparative study of these two micropaleontological assemblages allows a correlation between the standard (areal) biozone established on planktonic foraminifera and the local agglutinated deep water assemblages.Keywords:
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Cenomanian
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Abstract Bąk, K. and Bąk M. 2013. Foraminiferal and radiolarian biostratigraphy of the youngest (Late Albian through Late Cenomanian) sediments of the Tatra massif, Central Western Carpathians. Acta Geologica Polonica, 63 (2), 223-237. Warszawa. The foraminiferal and radiolarian biostratigraphy of selected sections of the Zabijak Formation, the youngest sediments of the Tatra massif (Central Western Carpathians), have been studied. Benthic foraminifers, mainly agglutinated species, occur abundantly and continuously throughout the studied succession, while planktic foraminifers are generally sparse. Five planktic and two benthic foraminiferal zones have been recognized. The marly part of the Zabijak Formation comprises the Pseudothalmanninella ticinensis (Upper Albian) through the Rotalipora cushmani (Upper Cenomanian) planktic foraminiferal zones, and the Haplophragmoides nonioninoides and Bulbobaculites problematicus benthic foraminiferal zones. The radiolarians were recognized exclusively in the Lower Cenomanian part of the formation.
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Cenomanian
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Cenomanian
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The assemblage of foraminifera in turbidite beds in Middle Triassic basinal deposits straddling the Anisian/Ladinian boundary interval was studied in 224 thin sections. The fauna consists mainly of shallow-water inhabitants, associated with calcareous hyaline foraminifera ( Lagenina ) of open marine environment. Due to a well established biostratigraphy in the studied interval, the first and last appearance of some shallow water, benthic foraminifera can be assigned to the Mid Triassic ammonoid stratigraphy. The species Meandrospira dinarica Kochansky-Devide & Pantic and Arenovidalina chialingchiagensis Ho are limited to the Reitzi ammonoid zone. The species Variostoma alta Kristan and Hoyenella gr. sinensis both do not superate the Curionii zone in age in the studied succession. The biostratigraphic most important event occurs at the base of the Gredleri zone, with the appearance of the family Involutinidae Butschli, represented by the genera Lamelliconus and Aulotortus . The faunal composition is similar to those of neighbouring paleoprovinces, but generally a lower faunistical diversification compared to foraminiferal assemblages in the Anisian or Carnian is observed.
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A biostratigraphic zonation of the Cenomanian–Coniacian rocks of the Guerrero–Morelos basin (southern Mexico) is proposed. The stratigraphic distribution of 70 species of calcareous algae and benthic and planktonic foraminifers is used to characterize four Zones that in ascending order are: Pseudorhapydionina dubia TRZ (Total Range Zone); Whiteinella archaeocretacea IRZ (Interval Range Zone); Helvetoglobotruncana helvetica TRZ, and Marginotruncana sigali IRZ. The top of P. dubia (upper Cenomanian) is marked at the last appearance of the marker fossil, which closely corresponds to the last appearance of most miliolid benthic foraminifers. Over most of the area, the transition from shallow–marine limestones up into pelagic facies occurs within the W. archaeocretacea Zone (uppermost Cenomanian–lowermost Turonian). A characteristic of this zone is the scarcity of both benthic and planktonic foraminifers, including the zonal marker. Most large benthic foraminifers disappear in the lower part of this zone. The changes observed within the W. archaeocretacea Zone reflect the successive stages of the platform drowning. The H. helvetica (lower–middle Turonian) is characterized by the presence the nominal taxon, dicarinellids, praeglobotruncanids, whitenelids and hedbergelids. This zone is recognized in the Mexcala Formation and represents deposition in fully pelagic conditions. Toward the central and eastern part of the area in shallow–open marine facies (Cuautla Formation), this zone is represented by an assemblage characterized by hippuritids, echinoids (crinoids and roveacrinids), gymnocodiacean and udoteacean algae and scarce planktonic foraminifers. The Marginotruncana sigali (upper Turonian–Coniacian) was defined with the last appearance of H. helvetica, whilst its top was difficult to recognize. Toward the central and eastern part of the area, this zone is represented in shallow–open marine facies (Cuautla Formation) by an assemblage dominated by the hippuritid Vaccinites gosaviensis, solitary corals, gymnocodiacean algae, calcisphaerulids and very scarce planktonic foraminifers. The Cenomanian–Turonian boundary lies in the lower part of the Cuautla Formation. The appearance of hippuritid mollusks and the diversification of whiteinellids can be used to mark this boundary.
Cenomanian
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The aim of this study is to compare the assemblages of foraminifera and calcareous nannoplankton from the Middle Miocene sediments from SE Poland and western Ukraine. Detailed investigations revealed a high degree of similarity of foraminiferal assemblages of the Pecten/Spirialis beds of Poland and the Kosiv Formation of Ukraine. Assemblages from both areas are characterized by numerous arenaceous species of foraminifera (Hyperammina granulosa, Ammodiscus miocenicus, Haplophragmoides indentatus, H. laminatus), radiolarians, pteropods and index planktic species Velapertina indigena. High degrees of similarity also display assemblages from the Krakowiec beds (Poland) and the Dashava Formation (Ukraine). The lower parts of both subdivisions are characterized by the presence of Anomalinoides dividens. Saccammina sarmatica, Bolivina sarmatica, Brizalina nisporenica, and Porosononion granosum occur in the upper parts. Chloropycean Halicoryne morelleti is a characteristic element of the assemblages.
The calcareous nannoplankton assemblages contain almost identical species. The deposits lying above the evaporites (which belong to the NN6 zone) are included into the NN6, undivided NN6-NN7, and NN7 zones. The gradual impoverishment of the species of the upper part of NN6 and the lower part of NN7 zones is observed. The assemblages of the Krakowiec beds and the upper part of the Kosiv and Dashava formations are of low species diversity and are mainly restricted to a few species with high abundance. The assemblage is composed of placoliths (Coccolithus and Reticulofenestra species), high number of the reworked nannofossils and damaged elements.
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