Paleogene-Neogene Boundary Research Articles

Multiple origins of freshwater invasion and parental care reflecting ancient vicariances in the bivalve family Cyrenidae (Mollusca)

Habitat transitions in living organisms are key innovations often coupled with species diversification after their successful adaptation to new environment. The Cyrenidae is among the most well-known heterodont bivalve groups that have successfully invaded freshwater systems from brackish water environments and display diverse lineage-specific developmental modes. Phylogenetic and molecular clock-based divergence time analyses using 12 complete mitochondrial genome sequences suggest that Cyrenidae species independently colonized freshwater habitats during three distinct spatial and geological periods: one from the American continents approximately in the Early Jurassic and the two others from Australasian/East Asian continents in the Early/Middle Cretaceous and the Paleogene-Neogene boundary, respectively. This study provides significant insight into the temporal and spatial patterns of multiple freshwater invasions, aligning with ancient vicariance events inferred from different geological timelines of plate tectonics. Additionally, mitogenome phylogeny confirms the earlier hypothesis of the repeated parallel evolution of parental care system within this bivalve group.

Geochemical investigation of the mixed Máriahalom vertebrate fauna at the Paleogene–Neogene boundary in the Central Paratethys: environmental conditions and age constrain

The fossil vertebrate fauna of Máriahalom contains remains from a wide range of ecologies including terrestrial and aquatic mammals, crocodiles, sharks, and rays among others. All these were found mixed in mollusc-rich, shallow water, coastal deposits. The aim of the study is to trace the origin of the fossils using their rare earth element (REE) content and their respective ecology with stable oxygen isotopic compositions. In addition, marine vertebrates and calcareous marine fossils were analysed for their Sr isotope composition to provide a new age estimate for the locality. The REE content and their distribution in the fossils indicate similar early diagenetic environments and possible contemporaneous fossilization for the entire vertebrate assemblage. Reworked fossils of significantly different age can be excluded. The enamel/enameloid-derived phosphate oxygen isotope composition of selected fossil taxa fit well with previously inferred habitats that include marine, brackish, and terrestrial environments. Notably, the stem-pinniped Potamotherium valletoni is best interpreted as freshwater dweller instead of marine, consistent with the sedimentology of other occurrences. Our novel 87Sr/86Sr data suggest an Aquitanian age (21.4 ± 0.5 Ma) for the Máriahalom site that is younger than the previously proposed Late Oligocene age based on biostratigraphy (MP28–30 European Mammal Paleogene Reference Levels). An Aquitanian age raises the possibility that the index fossil taxon, the anthracothere mammal Microbunodon minimum, may have vanished earlier in Western Europe than in the Central Paratethys region.

Cenozoic mountain building in eastern China and its correlation with reorganization of the Asian climate regime

Abstract The Cenozoic Asian climate system experienced a transformation from a zonal pattern to a monsoon-dominant pattern around the Paleogene-Neogene boundary. A series of dynamic mechanisms, such as uplift of the Tibetan Plateau, retreat of the Paratethys Sea, expansion of the South China Sea, and decreasing atmospheric CO2 content, has been suggested to be responsible for the transformation of the Asian climate pattern. However, the role of topographic growth in eastern China has been rarely considered. As the natural divides of geography, climate, and biology, the two most distinct sets of topographic relief in eastern China, the Qinling and Taihang Mountains, play an important role in shaping the Asian climate pattern. We report low-temperature thermochronology data from the Qinling and Taihang Mountains and use age-elevation relationships and thermal history modeling to show that both mountain ranges experienced a phase of rapid exhumation during the late Oligocene and early Miocene. The building of the Qinling and Taihang Mountains around the Oligocene-Miocene boundary temporally and spatially coincided with the reorganization of the Cenozoic Asian climate regime, suggesting that the mountain building in eastern China acted as a possible driving mechanism for the alleged reorganization of the Cenozoic Asian climate regime.

A Transitional Mammalian Carnivore Community from the Paleogene–Neogene Boundary in Northern Kenya

ABSTRACT The Paleogene–Neogene boundary is an important transitional time for the evolution of African fauna. Many taxa that evolved endemically in the Paleogene begin to wane in diversity, while new taxa, many of which will become exemplars of the modern African fauna, immigrate from Eurasia via newly opened terrestrial connections. The Paleogene–Neogene boundary is documented in the fossil record at Nakwai, in northern Kenya. Here we describe the mammalian carnivore fauna, which includes the earliest carnivoran records in Africa, and an interesting mix of Paleogene and Neogene hyaenodont taxa. The carnivoran fauna includes Jinomrefu lakwanza, gen. et sp. nov., the earliest barbourofelid in Africa, which has a transitional sabertooth morphology. An analysis of ecomorphological change in African mammalian carnivores across this boundary shows that hyaenodonts become more disparate in body size and more hypercarnivorous as they are displaced by invading carnivorans. This provides another test case for possible competition between carnivorans and hyaenodonts, a group that goes extinct in Africa and globally during the Neogene. http://zoobank.org/urn:lsid:zoobank.org:pub:D803E9DB-B2F1-497D-B796-57BED91BC744

On the Paleogene-Neogene boundary and age of the Alkun Formation in the North Caucasus and Ciscaucasia

The problems related to age of the lower part of the Caucasian regional stage (Alkun Formation) and Paleogene-Neogene boundary in the North Caucasus and Ciscaucasia are discussed with analysis and generalization of the data on nannoplankton and dinocyst assemblages from Alkun sediments in their different areas. The new data obtained from the section of the Alkun Formation in the stratotypical area of the Caucasian regional stage (valley of the Kuban River middle reaches, Karamurzinskii village), including finds of the index species Triquetrorhabdulus carinatus and typical species of the zonal nannoplankton assemblage, confirm the belonging of Alkun sediments to Zone NN1. The composition and peculiar features of the Karamurzinskii nannoflora and dinocyst assemblages indicate their Neogene age. It is established that the Alkun sediments in the Kuban, North Ossetia, and Belorechensk areas are characterized by similar nannoplankton and dinocyst assemblages, which implies their synchronism in these localities. The dinocyst assemblages from the Alkun Formation exhibit significant similarity with their counterparts from the uppermost part of the “lower Krosno Subformation” and lower part of the “upper Menilite Subformation” of the Ukrainian Carpathians and from lower layers of the “Chernobaevka Formation” of the northern Black Sea region. The analysis of available data reveals that the Paleogene-Neogene boundary in the North Caucasus and Ciscaucasia corresponds to a narrow interval spanning from the upper layers of the Batalpasha Formation and its analogs to the lower layers of the Alkun Formation. Thus, it is shown that the Caucasian regional stage belongs practically in its entire volume, probably except for its basal layers, the age of which needs to be specified, to the lower Miocene. New data on hydrology and bionomy of the basin, vegetation, and climate of the Alkunian time are also considered.

On the estimated age of recent fauna in different latitudinal zones (by the example of brachiopods)

Maximum period of existence of endemic genera in the temperately warm-water (subtropical) and temperately cold-water (low boreal and subantarctic) faunal belts is revealed on the base of latest data on the composition of brachiopod fauna of recent seas and oceans and most full data on the paleontological finds of recent brachiopod genera. Most of the subtropical endemics inhabit southern hemisphere; one of them is Bouchardia, which is known beginning with the Late Cretaceous (Maastrichtian), that brings together southern subtropical faunal belt with the tropical zone and suggests that subtropical waters could serve as a refuge for representatives of ancient warm-water faunas during large geological and hydrological reconstructions at the Mesozoic-Cenozoic boundary. Most of the younger endemics of low boreal and subantarctic faunal belts appeared at the Paleogene-Neogene boundary, during the period of formation of modern contrast climate on the Earth that was caused by the formation of Antarctic Circumpolar Current. The appearance of recent species and genera in the Holocene was influenced by last considerable postglacial reconstruction of climate.

Stratigraphy of the Oligocene-Miocene boundary sediments in the Nezhinsky brown coal field (Primorye) and the problem of the Paleogene-Neogene boundary in the region

The geological characteristics of the productive coaliferous sequence and the overlying strata (the Nezhino Sequence) at the Nezhinsky brown coal field are provided with detailed geological and paleobotanical data on the Nezhino Sequence (operating quarry), which is proposed as its type section. Based on the analysis of the macro- and microfloral assemblages, the transitional Late Oligocene-early Miocene age is inferred for these sediments. The floras from both the sequences demonstrate no principal differences, being moderately thermophilic in composition, although the Nezhino flora is more thermophilic. The coaliferous and Nezhino sequences are assumed to be separated by a stratigraphic hiatus. It is shown that they are similar to the Oligocene-Miocene boundary sections in the adjacent regions. The Nezhino Sequence (lower Miocene) most likely corresponds to the upper Aquitanian-Burdigalian interval in the Standard stratigraphic scale. The Paleogene-Neogene boundary in the Primorye region is proposed to be placed at the top of the Pavlovka Horizon. In the Nezhino brown coal field, it coincides with the upper boundary of the coaliferous sequence.

Bivalve fauna succession in the north Pacific during the Paleogene-Neogene transition

Cluster analysis was used to compare species composition of marine and brackish water bivalves in the Cenozoic deposits of the Russian Far East, Hokkaido, and California. Bivalvia species composition allows us to divide these deposits into two groups of clusters. The first group includes both extant and extinct species, while the second one is largely composed of extinct species. The drastic change in the bivalve species composition suggests that the base of the Uinin Horizon in the northern Sakhalin, Kuluven Horizon in the western Kamchatka, Tsubetsu Formation in eastern Hokkaido, and, possibly, the central part of the provincial Vaqueros Formation in California correspond to the Paleogene-Neogene boundary. The change in species composition was accompanied by the taxonomical diversity changes. At a higher level, the equitability of species richness among families significantly decreased.

Mammalian biochronology of the Paleogene-Neogene boundary at Aktau Mountain, eastern Kazakhstan

At Aktau Mountain in the Ili depression of eastern Kazakstan, fossil mammals that encompass the Paleogene-Neogene boundary occur at three stratigraphic levels. The lowest level is in the lower Kyzylbulak Formation and produces Brontotheriidae and the hyracodontidArdynia and is tentatively assigned a late Eocene (Ergilian) age. The lower part of the overlying Aktau Formation produces fossils of the giant rhinocerosParaceratherium and is tentatively assigned a late Oligocene (Tabenbulukian) age. The upper part of the Aktau Formation yields a fossil mammal assemblage that includesGomphotherium,Stephanocemas, Brachypotherium andLagomeryx. It is clearly of Miocene age, probably late early Miocene (late Burdigalian), a correlative of European Reference Level MN 5 and the late Shanwangian of China. The Paleogene-Neogene boundary at Aktau Mountain thus is in the Aktau Formation.

Continental and marine paleoenvironments reflected by west Pacific clay sedimentation

Various stratigraphic and paleoenvironmental results arise from mineralogical, geochemical and micromorpho logical investigations on Late Cretaceous and Cenozoic sediments recovered by the Deep Sea Drilling Project in the West Pacific: Stratigraphic correlations. The deep pelagic red clays deposited on either side of the Shatsky Rise contain a variety of clay minerals, which point to the importance of eolian detrital supply and allow rough stratigraphic correlations. Climate and paleocirculation. Neogene sediments of the Lord Howe Rise area reflect closely the relationship between the evolution of the Antarctic ice sheet and related aridification stages, and the atmospheric and oceanic circulation pattern since 14 my. Regional and global tectonics. The post-Eocene deposits around New Zealand express a sequence of tectonic events and of relaxation stages, associated with changes in the circulation regime. Along the inner wall of the Japan Trench, clay mineral successions document the existence of an outer continental landmass until the late Oligocene, its collapse associated with volcanism close to the Paleogene-Neogene boundary, and an increased detrital influence from Japan since the early-middle Miocene. Volcanism, diagenesis and detrital supply. The Aptian to Maastrichtian sediments in the Mariana Basin document a complex sequence of geochemical and geodynamical events: proximal volcanism and local supply from subaerial archipelagoes; early marine diagenesis during lithospheric subsidence and plate migration; and finally the occurrence and evolution of terrigenous input from distant sources distributed by marine currents.

Stockwork Molybdenum Deposits in the Western Cordillera of North America

Molybdenum extraction from the western Cordillera of North America in the last half century has grown primarily by increased production from porphyry-type deposits. The Climax mine alone has contributed approximately half the total world production in past years. Response to industrial demand, aside from by-product molybdenum, has resulted in development of five mines of the Climax-type in the last half decade, and at least one similar major ore body will begin operation by 1975. The six producing stockwork deposits accounted for approximately 71 percent of free world molybdenum production in 1969.The stockwork deposits contain 0.2-0.5 percent molybdenite, distributed throughout or near contacts of associated siliceous intrusives. With the exception of the Climax deposit where tin, tungsten and pyrite are recovered, stockwork ores produce only molybdenum. Simple, composite, or multiple intrusions, dikes and breccia pipes localize these ores. Compositionally igneous phases vary from granodiorite to granite, whereas textures may be porphyritic, aplitic, or inequigranular.Hydrothermal alteration is primarily marked by K-feldspathization and silicification. Commonly, assemblages can be arranged in order of decreasing hydrogen metasomatism and include sericitic, argillic, propylitic and potassium silicate types. Oxidation products are often fixed at the surface and supergene enrichment is absent.Molybdenite in stockworks occurs in (a) veinlets associated with quartz, and lesser amounts of other sulfides, oxides and gangue; (b) fissure veins; (c) fine fractures containing molybdenite paint; (d) breccia filling; and more rarely (e) disseminated grains. Intrusion and mineralization commonly occur in the epizone of the crust. Temperatures of formation where reconstructed are less than 400 degrees C. Mineral and alteration assemblage zoning, while variable, are best displayed in ores associated with multiple intrusions. Paragenetically, molybdenum occurs early in a mineralizing stage in ores that are commonly near the center of igneous activity.The stockwork ores and some other classes of molybdenum deposits occur in igneoustectonic provinces, where intrusives are localized by crossing fractures, lineaments, or domes. These provinces, distributed in particular segments of the Cordillera, include (1) Alaska-Yukon, passing into (2) British Columbia-Washington, (3) (eastern) Oregon-Idaho-(western) Montana, (4) Colorado-New Mexico, (5) Nevada-southern California, and (6) Sonora-Sinaloa. To date the productive deposits are located in the southern Rocky Mountains (Urad-Henderson, Climax and Questa) and in the Interior Belt of British Columbia (Alice (B.C. Molybdenum), Endako and Boss Mountain).The geologic history of the productive provinces exhibits major sedimentational, igneous and tectonic differences. The western stockwork provinces occur in eugeosynclinal environments, whereas the eastern part of the Idaho belt and the southern Rocky Mountains area are old miogeosynclinal or shelf areas. Additionally, plutonic events associated with these deposits have different ages and reflect, in part, the geologic evolution of the western Cordillera. Correspondingly, the southern Rocky Mountain deposits were formed 30 to 23 m.y. ago, around the Paleogene-Neogene boundary, and are correlatable with a Mid-Tertiary phase of igneous activity in this and adjacent areas. Those deposits in British Columbia vary in age from 142 to 53 m.y., corresponding to an interval from Late Jurassic to Eocene. Apparent lack of a preferred depositional environment, together with preliminary sulfur and strontium isotope data, suggest that some fraction of the source materials is subcrustal.