Gümüşhane ve Bayburt yörelerindeki üst jura-alt kretase karbonat istiflerinin stratigrafik, paleocoğrafik ve mikropaleontolojik incelenmesi

Abstract

ÖZET Bu çalışma, Doğu Gümüşhane ve Bayburt yörelerindeki Üst Jura -Alt Kretase platform tipi karbonat istiflerinin (Ber- diga formasyonu) stratigraf ik, paleocograf ik ve mikropale- ontolojik incelemesi ile ilgilidir. Litostratigraf ik incelemeler sonucu, ortak mikraf asiyes ve litolojik özellikleri ile tanımlanan 9 litofasiyes ayırdedilmiştir. Her litofasiyesin mikrofosil içeriği liste lenmiş ve çökelme ortamı yorumlanarak, yanal ve düşey yönde ki- ilişkileri ortaya konmuştur. Bentik foraminif erlere dayalı olarak, dördü (A, D, E, F) yeni olmak üzere aşağıdaki yerel biyozonlar ayırdedilmiştir; A. Archaeosepta basiliensis ara zonu (Kalloviyen - Alt Oksfordiyen) B. Alveosepta jaccardi menzil zonu (Üst Oksfordiyen - Alt Kimmericiyen) C. Fosilsiz ara zon (Üst Kimmericiyen - Berriyasiyen) D. Pseudotextulariella salevensis menzil- zonu ( Valan jiniyen) Dİ. Barkerina barkerensis menzil altzonu (üst Valanjiniyen) E. Pseudotextulariella keciensis menzil zonu (Alt Hotriviyen) F. Cuneolina hensoni/ Evert icyclammina hedbergi ortak menzil zonu (üst Hotriviyen - Alt Barremiyen?) İnceleme alanındaki karbonat platformunun evrimi Kallo viyen? transgresyonu ile başlar, yerel uyumsuzluk ve sürek sizlikler içeren gelişim yaklaşık Alt Kretase sonunda, bölge ölçeğinde etkili olan bir aşınma dönemi ile son bulur. Mikropaleontolo jik incelemeler sonucu çok sayıda bentik foraminifer türleri tanımlanmış ve resimlenmiştir. Mayncina, Pseudotextulariella, Cuneolina ve Everticyclammina cinsleri ne ait 4 yeni tür tanımlanmıştır. Bugüne kadar cins teşhisi tartışmalı olan Conicospirillina basiliensis MOHLER türü, Archaeosepta WERNLI cinsine yerleştirilmiştir. Labyrinthina WEYNSCHENK ve Lituosepta ÇATI cinsleri arasındaki ilişkilere yeniden değinilmiştir. Ayrıca, çoğunluğu dasycladacea guru buna ait olmak üzere başlıca alg cins ve türleri resimlene rek, stratigrafik dağılımları verilmiştir. vı

STRATIGRAPHY, PALEOGEOGRAPHY AND MICROPALEONTOLOGY OF UPPER JURASSIC - LOWER CRETACEOUS CARBONATE SEQUENCES OF GÜMÜŞHANE - BAYBURT REGION (EASTERN PONTIDS, NE TURKEY) ABSTRACT Upper Jurassic - Lower Cretaceous carbonate sequences (Berdiga formation) is divided into nine lithofacies on the basis of their microfacies and lithological characteristics. * In the eastern Gümüşhane area, from the base to top, the following lithofacies are distinguished: Lithofacies la. Sandy oosparitic, onkoidal biointrasparitic and dolomitic limestones, containing mainly Protopeneroplis striata, Archaeosepta basil iensis, Trocholinâ, Everticyc- lammina, Nautiloculina, Permocalculus, Acicularia, Arabi- codium, Thaumatoporella, gastropoda and remains öf pelecy- poda and echiriodermata. Lithofacies II. Oncoidal micrite, micrite and biomicrite, containing Alveosepta jaccardi, Pseudocyclammina, Rectocyc- lammina, Mesoendothyra izumiana, Mesoendothyra croatica, Parurgonina caelinensis, Pfenderella, Thaumatoporella, Favreina and ostrocoda. This litofacies includes a spilitic- diabasic lavas and tuffs in the middle part. Lithofacies Ilia. Sandy conglomerate at the base, laminated pelsparites, biomicrites and dolomites interbedded with sandstone in the middle and upper parts. This lithofacies contains Mayncina gediki n. sp., Pseudocyclammina cf. maynci, Ammobaculites, Clypeina sp., Actinoporella podolica, Favreina, and remains of ostrocoda and gastropoda. Lithofacies Illb. Massive dolomite, laminated and clayey dolomites; barren of fossils. Lithofacies IV. Dolomitic limestones at the base and bio- pel-intrasparitic limestones with abundant benthic forami- nifera and algae in the upper part. * ? Lithofacies Va.'Cherty biomicritic limestones with Proto- globigerina, sponge, bryozoa and remains of echinodermata. This lithofacies makes up the upper most stratigraphic level of Berdiga formation in the eastern Gümüşhane area. VllLithofacies Vb. Sandy biopelsparites with remains of echinodermata and red algae. This lithofacies makes up the upper most stratigraphic level of Berdiga formation in the west Bayburt area. In the eastern Bayburt area, the litofacies development is as follows (from the base to the top): Lithofacies la. Sandy oosparites and biointrasparites with benthic foraminifera and algae. Lithofacies lb. Pelmicrosparites with ooid, biomicrites with calcitized radiolaria, calcareous sponge spicules and ammo nites in the lower and middle parts, and pinkish nodular limestone with abundant ammonites in the top. Lithofacies Ic. Biosparite with extraclast at the base, oo- bio-intrasparites and reefal limestones with colonial corals in the middle and upper parts. This lithofacies contains mainly Labyrinthina mirabilis, Archaeosepta basiliensis, Protopeneroplis striata, Nautiloculina circularis, Salpingo- porella cf. pygmaea, Cayeuxia, Arabicodium, Tubiphytes. This sequence is overlain b^ biomicrites which are interbedded with sandstones and marls. The biomicrites contain radiolaria and tintinnids. A local biozonation using benthic foraminifera is proposed in the Upper Jurassic - Lower Cretaceous carbonate platform of the eastern Pontids: -Archaeosepta basiliensis interval zone (Callovo-Oxfordian) -Alveosepta jaccardi range zone (Upper Oxfordian - Lower Kimmeridgian) -Unfossilif erous interval zone (Upper Kimmeridgian Berriasian) -Pseudotextulariella salevensis range zone (Valanginian) -Barkerina barkerensis range subzone (Upper Valanginian) -Pseudotextulariella keciensis range zone (Lower Hauterivian) -Cuneolina hensoni/Everticyclanunina hedbergi concurrent range zone. Evolution of carbonate platform of the eastern Pontids begins with Callovian<?) transgression which developped app roximately from the east to the west. Inter-to supratidal conditions were dominant during Callovo-Oxfordian. After this period, the paleogeographic development differs locally: a) In the eastern Gümüşhane - western Bayburt area: Depositional environment is transformed into a subtidal one (protected lagoon) during the Upper Oxfordian - Lower VlllKimmeridgian. After Lower Kimmeridgian, in some places, an erosive phase (subaerial) affected the sedimentation. Upper Kimmeridgian - Berriasian indicate a regressive period. This sedimentary platform area was covered by a shallow and agitated sea as a result of the Valanginian transgression. After Hauterivian, a rapid subsidance occured in the eastern Gümüşhane area, while a regressive sequence was developping in the western Bayburt area. b) In the eastern Bayburt area: An open sea facies is developped in the Upper Oxfordian - Lower Kimmeridgian. After Lower Kimmeridgian, a threshold - reef facies has developped, due to a relative sea-level fall. In the Upper Tithonian - Lower Cretaceous, an open and deep marine conditions was dominant. In the western Bayburt and Gümüşhane area, evolution of the carbonate platform completed at the end of the Lower Cretaceous, as a result of subaerial exposure. On the other- hand, in the eastern Bayburt area, an olistrostroma! facies was developped during the middle part of the Cretaceous time. A number of Upper Jurassic - Lower Cretaceous sections have been investigated mainly for benthic foraminif era. The stratigraphical distribution of about 40 species, belonging to suborders Textulariina and Involutinina, is shown in the range charts. The most species are founded for the first time in the eastern Pontids. Four new species (Mayncina gediki n. sp., Evert icy clammina cylindrica n. sp., Cuneolina altmeri n. sp., Pseudotextulariella keciensis n. sp.) are described and figured. Relations between genera Lituosepta CATI and Labyrinthina WEYNSCHENK are reviewed. Conicospiril- lina basiliensis MOHLER, whose generic position is ques tionable, has been assigned to genus Archaeosepta WERNLI. Algae genera are also figured. Finally, benthic foraminif era associations which are founded in the investigated area, are compared with those of tethys platforms. IX