engleski

Wall texture of Oligocene normal perforate and some microperforate planktonic foraminifera

The Atlas of Oligocene planktonic foraminifera followed a similar concept of wall texture that was applied to Eocene planktonic foraminifera (Hemleben & Olsson, 2006). Detail analyses of wall texture in normal perforate and microperforate planktonic foraminifera was used to determine phylogenetic groups important for their classification. Special attention is paid to the pore diameter and concentration that determines development of specific type of wall texture during ontogeny. Spinose wall texture exhibits the widest range of pore concentrations and diameter whereas nonspinose wall texture is more uniform. Spinose wall textures The sacculifer-type, observed in the recent Globigerinoides sacculifer, is recognized in Oligocene genera Subbotina, Catapsydrax, Globorotaloides, and Globoturborotalita. These taxa is characterized by equally distributed pores and cancellate, symmetrical (honeycomb) wall structure. The ruber/sacculifer-type of wall texture is observed in some species of Globoturborotalita, Paragloborotalia, Subbotina, and also in the first member of Globigerinoides lineage, G. primordius. These taxa possess partly symmetrical, and partly asymmetrical cancellate structure of the test wall. Neogloboquadrina-type is developed in the adult stage of genus Paragloborotalia. Turborotalita-type of wall texture occurs in the modern Turborotalita quinqueloba, which evolves in Oligocene from species T. praequinqueloba. It is characterized by rather smooth primary wall on which a ruber/sacculifer arrangement is developed. The conglobatus-type wall texture occurs in the new genus Parapsydrax. Ciperoella-type is developed in the new genus Ciperoella, in species C. ciperoensis, C. angulisuturalis and C. anguliofficinalis. The bulloides-type of wall texture first appears in middle Eocene in the species G. officinalis. The Recent species Globigerina bulloides which evolved in the late Oligocene from G. archeobulloides Hemleben and Olsson n. sp., possesses wall texture where the pore pattern is irregular and the spine collars are connected with short and long irregular ridges. Quiltella/Beella-type of wall texture, observed in Eocene genera Clavigerinella and Pseudoglobigerinella, is characterized by dense pore pattern and narrow cancellate ridges which result in reticulate surface. In Oligocene this type of wall texture is observed in some species of Globigerinella and Quiltella. Nonspinose wall texture Globoquadrina–type wall texture has a geometrically oriented, high porosity test. The pores are evenly distributed and pustules of various morphologic types may develop in the interpore area. Several species of the genus Dentoglobigerina exhibit evidence of having possessed spines. Smooth wall is developed in Pseudohastigerina, whereas muricate wall is developed only in small Acarinina species (A. medizzai, A. colactea, A. echinata), which persisted from Eocene ; Wade & Hernitz Kucenjak, 2018. Microperforate wall texture Serial planktonic genera Chiloguembelina and Jenkinsina are characterized by biserial or triserial arrangement of chambers, and smooth to ornamented microperforate wall with pore size less than 1 μm in diameter. They possess an ototara-type wall (Pearson, 2018). Recently discovered Paleocene origin of Jenkinsina most probably confirms their relationship to the species Guembelitria cretacea (Premec Fucek et al., 2018).

planktonic foraminifera, wall texture

nije evidentirano