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Orthophragmines are a group of discoidal, lenticular or stellate ‘orbitoidal’ larger benthic foraminifera that thrived in shallow-marine environments in low-to-middle latitudes during the late Paleocene and Eocene. They consist of two phylogenetically independent families with similar morphology, such as Discocyclinidae (with two Tethyan genera—Discocyclina and Nemkovella) and Orbitoclypeidae (with three genera—Orbitoclypeus, Asterocyclina and Hexagonocyclina in the Tethys) distinguishable by the different microspheric juvenarium of the microspheric (B) forms. Sixty-one species of orthophragmines are herein described and illustrated based on material from various Tethyan localities in Europe, North Africa, Turkey, the Arabian Peninsula, the Indian Subcontinent and SE Asia. Thirty-two species of Discocyclina, six species of Nemkovella, thirteen species of Orbitoclypeus, nine species of Asterocyclina and one species of Hexagonocyclina are included. Some species include chrono-subspecies, established by applying the principles of embryonic and nepionic acceleration in the megalospheric (A) forms, primarily expressed by the increase in the size of the deuteroconch, morphological modifications forming various embryonic configurations through the phylogeny, and the increase in the number of adauxiliary chamberlets that arise from the embryonic apparatus. This study is mainly based on investigating oriented sections of many free specimens, and some random rock thin sections where obtaining free tests of orthophragmines was not possible. The Atlas is designed as a laboratory handbook for micropaleontology students and a guidebook to assist professionals with the easy identification of orthophragmines in thin sections.
Orthophragmines are a group of discoidal, lenticular or stellate ‘orbitoidal’ larger benthic foraminifera that thrived in shallow-marine environments in low-to-middle latitudes during the late Paleocene and Eocene. They consist of two phylogenetically independent families with similar morphology, such as Discocyclinidae (with two Tethyan genera—Discocyclina and Nemkovella) and Orbitoclypeidae (with three genera—Orbitoclypeus, Asterocyclina and Hexagonocyclina in the Tethys) distinguishable by the different microspheric juvenarium of the microspheric (B) forms. Sixty-one species of orthophragmines are herein described and illustrated based on material from various Tethyan localities in Europe, North Africa, Turkey, the Arabian Peninsula, the Indian Subcontinent and SE Asia. Thirty-two species of Discocyclina, six species of Nemkovella, thirteen species of Orbitoclypeus, nine species of Asterocyclina and one species of Hexagonocyclina are included. Some species include chrono-subspecies, established by applying the principles of embryonic and nepionic acceleration in the megalospheric (A) forms, primarily expressed by the increase in the size of the deuteroconch, morphological modifications forming various embryonic configurations through the phylogeny, and the increase in the number of adauxiliary chamberlets that arise from the embryonic apparatus. This study is mainly based on investigating oriented sections of many free specimens, and some random rock thin sections where obtaining free tests of orthophragmines was not possible. The Atlas is designed as a laboratory handbook for micropaleontology students and a guidebook to assist professionals with the easy identification of orthophragmines in thin sections.
The Central Pontides of N Turkey represents a mobile orogenic belt of the southern Eurasian margin that experienced several phases of exhumation associated with the consumption of different branches of the Neo-Tethys Ocean and the amalgamation of continental domains. Our new low-temperature thermochronology data help to constrain the timing of these episodes, providing new insights into associated geodynamic processes. In particular, our data suggest that exhumation occurred at (1)~110 to 90 Ma, most likely during tectonic accretion and exhumation of metamorphic rocks from the subduction zone; (2) from~60 to 40 Ma, during the collision of the Kirşehir and Anatolide-Tauride microcontinental domains with the Eurasian margin; (3) from~40 to 25 Ma, either during the early stages of the Arabia-Eurasia collision (soft collision) when the Arabian passive margin reached the trench, implying 70 to 530 km of subduction of the Arabian passive margin, or during a phase of trench advance predating hard collision at 20 Ma; and (4)~11 Ma to the present, during transpression associated with the westward motion of Anatolia. Our findings document the punctuated nature of fault-related exhumation, with episodes of fast cooling followed by periods of slow cooling or subsidence, the role of inverted normal faults in controlling the Paleogene exhumation pattern, and of the North Anatolian Fault in dictating the most recent pattern of exhumation.
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