Miocene larger foraminiferal biostratigraphy in the mediterranean and the indo-pacific areas

Resumen

Larger benthic foraminifera (LBF) constitute an outstanding tool for biostratigraphic, palaeoecological and palaeobiogeographic studies because of their widespread geographical distribution, fast evolutionary changes, high susceptibility to environmental changes, and high abundance in the sedimentary successions. The PhD project dealt with Miocene LBF (alveolinoids, austrotrillinids, lepidocyclinids and nummulitids) newly recorded in the Mediterranean (southeastern Spain) and Indo-Pacific areas (Indonesia, northern Philippine sea, the Maldives and Ryukyu Islands). The new LBF record from the Sierra de Marmolance (Granada province, southeasrtern Spain) belongs to a 270-m thick continuous and in situ limestone succession of middle Miocene age (dated by the occurrence of Langhian–Serravallian planktonic foraminifera at the bottom of the succession). The LBF assemblage is represented by Austrotrillina brunni, Austrotrillina striata, Borelis inflata, Eulepidina formosoides, Eulepidina ex.interc dilatata et formosoides, Heterostegina assilinoides, Neorotalia viennoti, Nephrolepidina ex.interc. morgani et praemarginata, Nephrolepidina tournoueri, Nummulites fichteli, Nummulites kecskemetii, Nummulites vascus, Operculina complanata, Risananeiza crassaparies and Spiroclypeus sp. These species, up to now considered indicative of Rupelian–Chattian and Aquitanian–Burdigalian, extend their time ranges from the Rupelian to the early Serravallian. Since they are considered as Neogene biochronostratigraphic markers, this study highlights the need of a substantial revision of the Oligocene–Miocene SBZs. The new records of Austrotrillina from Ibi and Sierra de Marmolance (southeastern Spain), Indonesia (Mankalihat and Wailawi) and western Pacific (Kitadaito-jima and Kikai Seamount) allowed to assess their taxonomy according to the shell structure (tectum and a parakeriotheca with subsutural alcoves), biostratigraphy and palaeobiogeography. Austrotrillina eocaenica first appears in the middle–late Eocene of Iran. Two Rupelian descendants, A. brunni and A. striata, migrated from the western Tethys into the Indo-Pacific. Austrotrillina striata reached Indonesia and western Australia in the Chattian, then disappeared in the Langhian of Kita-daito-jima. Austrotrillina brunni first occurred in the Burdigalian of Indonesia and western Australia and disappeared in the early Serravallian of western and South Australia. Austrotrillina brunni and A. striata disappeared in the Serravallian westernmost Mediterranean (southeastern Spain). From the Burdigalian the exclusive occurrence of A. howchini in the Indo-Pacific areas is a possible result of the closing Tethyan Seaway, which differentiated the Mediterranean and Indo-Pacific bioprovinces. This species disappears in the latemost Langhian–early Serravallian of South Australia and in the Kikai Seamount. The palaeobiogeographical distribution of these species suggests an early Miocene active connection of Eastern Africa with the Central Indo–West Pacific. The new records (fossil and Recent) from the Maldives, Indonesia and Ryukyu Islands (Okinawa) were analysed to assess the taxonomic status of Flosculinella and Alveolinella species and to understand the alveolinoid phylogeny in the Indo-Pacific area. The latest Oligocene–middle Miocene Flosculinella globulosa, the early–middle Miocene F. reicheli, F. bontangensis, F. cucumoides, Alveolinella borneensis and the late Miocene–Recent A. quoyi are herein circumscribed in terms of shell length, diameter of the proloculus, whorl number of the first attic occurrence, and number of supplementary chamberlets in the attic floor per chamberlet in the main floor. The occurrence of the preseptal passage only and Y-shaped septula in Borelis schlumbergeri, Flosculinella and Alveolinella are characters of phylogenetic significance. Oligocene–early Miocene Borelis philippinensis is inferred as the common ancestor of these taxa. The diversification of Flosculinella and Alveolinella occurred in the Coral Triangle of southeast Asia during the early–middle Miocene. The northernmost occurrence of the Tortonian–Recent A. quoyi, widespread from Central to the Eastern Indo-Pacific areas, is in the Ryukyu Islands.