南海盆地新近纪浮游有孔虫带、气候、生物生产力爆炸事件和沉降速度的转换时限

依据浮游有孔虫带的研究,南海北部浅海区LH-19-4-1井和南海北部陆坡区ODP1148站更新世的N22带,晚上新世的N21带和N20带,早上新世的N19—N18带,中新世的N17带至N4带,和晚渐新世的N3带(N3带=P22带)的地层相当,可以对比。如生物多样性在时间上的变化所示,南海北部浅海区,从晚渐新世的N3带末期至更新世N22带经历了五次降温事件(C1—C5)。C1,晚渐新世N3带末期(23.20~23.40Ma),可能相当于Mi-1事件;C2,早中新世早期N4带中晚期(22.50~21.80Ma),它与Mi-1a事件相当,C2降温事件在陆坡区也有反应;C3,早中新世晚期N7带早中期(17.15~17.10Ma),可能相当Mi-1b事件;C4,中中新世中期N10带晚期(14.65~14.60Ma),可能与Mi-3事件相当;C5发生于早更新世N22带早期。14.60Ma是C4事件结束的时限、是本区古环境长时间尺度变化的时限,也是南海盆地在新近纪期间的沉降速度由慢速转入快速的时限。它还可能是青藏高原在中中新世中期开始由慢速隆升转入中速隆升变化的时限。本区从晚渐新世末期至更新世早期的环境为中-外浅海环境,在此期间,共有五次生物生产力爆炸事件(BEE1—BEE5)。BEE1和BEE2发生在早中新世早期N4带,23.2~21.5Ma期间;BEE3发生在早上新世N18—N19交界处,4.80Ma;BEE4发生在晚上新世晚期N21带,3.10~1.80Ma期间;BEE5发生在早更新世初期,1.60Ma。爆炸事件期间的生物生产力高出非爆炸事件期间平均生产力5~11倍,为原生油气藏提供了丰富的物源,给探寻原生油气田提供了重要的信息。     

Early Pliocene Paleoceanography of the Vityaz Fracture Zone, Central Indian Ridge

Planktic foraminifera from the calcareous substrate of a ferromanganese crust in the Vityaz Fracture Zone （VFZ）, Central Indian Ridge were studied to reconstruct the early Pliocene paleoceanography of this region. Eleven species of planktic foraminifera were encountered, among them Globorotalia menardii, Neogloboquadrina dutertrei, Globigerina bulloides and Globigerinoides tuber are prominent. Predominance of N. dutertrei in the top 3 cm of the carbonate substrate is attributed to an influx of fresh water which eventually triggered their productivity by increasing the nutrient level. The presence of G. bulloides and G. menardii in significant proportions in deeper layers suggests the prevalence of open ocean upwelling. The bulk chemical compositions of the substrate at different depth intervals indicates higher enrichment of trace metals in the upper sections which could have been supplied through oceanic water by the chemical weathering of terrestrial matter during the peak of Pliocene Asian monsoon. Thus, it is concluded that during the early Pliocene the biogenic components of the substrate were distinctly contributed by both upwelling and productivity triggered by an influx of fresh water originating from the intensification of the Asian monsoon during the early Pliocene Period.     

Neogene–Quaternary Mammalian Paleobiogeography of the Indian Subcontinent: An appraisal

A biostratigraphic evaluation of the Indian subcontinent Neogene–Quaternary mammal genera at 1 Ma intervals reveals a strong correlation between faunal turnovers (first and last appearances and immigrations), diversity and major tectonic and climate-induced sea level and vegetation changes at 23–22, 20–18, 17–16, 15–14, 11–10, 9–8, 3–2 and 1–0 Ma. The Early Miocene collision of Afro-Arabian and Eurasian Plates, followed by the Middle Miocene Climate Optima and the presence of evergreen rainforests, most likely facilitated the dispersals into and out of the subcontinent from the west along the coast and included African proboscideans, primates, creodonts, thryonomyid rodents and Asian chalicotheres, rhinos, suids, anthracotheres, carnivores and muroid rodents. The Late Miocene and Early Pleistocene cooler and drier conditions, the spread of grasslands and sea level drops may have influenced the exchange of African monkeys, Eurasian carnivores, bovids, equids, camelid, and South Asian suids, leporids and murids. Immigrations from the east (East and SE Asia) occurred mostly during the Miocene and involved primarily small mammals.     

Palynology: A useful tool in understanding palaeoclimatic changes through the Pliocene-Pleistocene from the deep offshore Niger Delta,Nigeria

Recent global ecological problems have necessitated more research into past environments so that accurate comparisons between past and present climatic conditions can be established and projections made for the future. In order to achieve this, palynological data from Well-C from the deep offshore (> 200 m) Niger Delta region were employed in an attempt to reconstruct the Late Pliocene-Pleistocene palaeoclimate. Four informal palynofloral assemblage zones (PAZ) I–IV are defined and correlated with four major cycles of alternating dry and wet climatic conditions. Within the major cycles, savanna and montane pollen assemblages became dominant in the late-Pliocene and mid-Pleistocene, while mangroves, brackishwater swamp, freshwater swamp and lowland rainforest prevailed during the early- and late-Pleistocene. The palaeoclimate of the late Pliocene and mid-Pleistocene was relatively colder and drier, with alternating relatively warmer and wetter conditions in the early and late Pleistocene, respectively. The pollen data from Well-C showed periods of climatic change during Late Pliocene-Pleistocene times, while the periods of climatic change revealed by pollen data from Lake Tilla, NE Nigeria, during Holocene times ranged from ∼2.0 to ∼3.8 Ka. Therefore, the cyclicity of climate change during Upper Pliocene-Pleistocene time is far greater than that of Holocene times. Our palaeo-climatic reconstruction conflicts with those that indicate predominantly dry climatic conditions in the Niger Delta region during the Pliocene-Pleistocene. The reconstructed palaeoclimate in this study can help to compare the past climatic conditions to that of the present and perhaps serve as a basis for studies of future climatic change.     

Pliocene Scelidotheriinae (Xenarthra,Tardigrada) from the Pampean region of Argentina: Morphology,chronology, and comments on the diversity of the subfamily

Scelidotheriinae (Mammalia, Pilosa) is a xenarthran mylodontid clade recorded in much of South America from the middle Miocene to the early Holocene. However, studies of their Neogene representatives are still scarce compared to their Quaternary representatives. The main goal of this contribution is to report new remains of Proscelidodon rothi (Ameghino, 1908) found in the basal levels of the El Polvorín Formation (Pliocene), cropping out near the city of Olavarría (Buenos Aires Province, Argentina). On the basis of the faunistic association, these deposits were assigned to the late Pliocene. The new materials include a skull, a mandible, and a calcaneal fragment (Xen-121), which enhance the characterization of this taxon, and allow more precise comparisons with other Neogene and Quaternary Scelidotheriinae. This new record extends the biochron and geographic distribution of the species, until now recorded in the latest Pliocene (Marplatan Stage/Age, Vorohuean Subage) of Olavarría.     

Reconsidering locomotor habits and life style of the Balearic insular giant rodent Hypnomys Bate, 1918 from the allometry of the limb long bones

The genus Hypnomys Bate, 1918 includes some endemic Neogene chronospecies from Mallorca and Menorca, evolved in insularity conditions from the Lower Pliocene to the human arrival at the archipelago. The study of the allometric proportions (functional length and sagittal diameter) of the limbs’ long bones of Hypnomys eliomyoides Agusti, 1980 (Lower Pleistocene of Menorca), Hypnomys sp. (Pleistocene of Menorca), Hypnomys onicensis (Reumer, 1994) (Upper Pliocene-Lower Pleistocene of Mallorca) and Hypnomys morpheus Bate, 1918 (Upper Pleistocene of Mallorca) only indicates small differences with the garden dormouse (Eliomys quercinus Linnaeus, 1776) and other mainland rodents and insectivores. The study about the locomotion type by means of Similarity Matrix of Bou indicates that 1) Hypnomys spp. presents the greater similarities with the arboreal, jumping and gliding species; 2) the jumping and digging life style of Hypnomys spp. are more developed (25%) than in E. quercinus; 3) the walking locomotion of Hypnomys spp. is only a 7% greater than in E. quercinus; and 4) the degree of similarity with the gliding locomotion of Hypnomys sp. is greater (17%) than in E. quercinus. Some of this data indicates that Hypnomys spp. was better adapted to the arboreal life than E. quercinus, due to the relationship between the jumping and gliding capacities with the arboreal locomotion. The greater similarity of Hypnomys spp. with the walking locomotion does not necessarily involve more terrestrial habits. Our interpretation contrasts with earlier conclusions of Hypnomys life style (Hypnomys cf. onicensis and Hypnomys morpheus) where the terrestrial locomotion was overestimated in front of the arboreal locomotion. The locomotion type of Hypnomys would be related with the presence of important forest masses on the Balearic Islands during the Neogene, a different degree of environmental stress from that of the mainland ecosystems and a probable expansion of the ecological niche occupied by these species.     

The endemic molluscs of the Late Miocene Lake Pannon: their origin, evolution, and family-level taxonomy

Long-lived lakes are often sites of spectacular endemic radiations. During the Oligocene to recent history of the Paratethys, large, long-lived (more than a million years) lakes with endemic faunas formed three times, in three different basins: the first in the Pannonian basin, the second in the Euxinian (Black Sea) basin, and the third in the Caspian basin. Because the Euxinian lake inherited much of the fauna of Lake Pannon, the three lakes together hosted two endemic radiations of molluscs. The most long-lived lake in the region was Lake Pannon, which persisted approximately seven million years from the late Middle Miocene to the Early Pliocene. Lake Pannon was formed by isolation from the sea. Changes in hydrological regime and/or water chemistry in addition to the relative lowstand which accompanied (or caused) the isolation almost completely exterminated the restricted marine fauna of the basin. A few highly euryhaline and marginal marine cardiids, dreissenids, and hydrobiids survived this environmental change. As in other fossil and extant long-lived lakes, the originally low-diversity fauna radiated into a high number of related endemic species (‘species flocks’) and genera in the expanding and ecologically vacated lake. Many originally freshwater taxa (unionids, sphaeriids, viviparids, valvatids, melanopsids, lymnaeids, planorbids) entered the lake as well, and some of them also gave rise to endemic clades. Evolution in both relict and freshwater immigrant groups led to the appearance of highly unusual shell shapes. Many lineages exhibit gradual morphological changes over one to several million years. More than 900 endemic mollusc species have been described from Lake Pannon, although this number includes junior synonyms, invalid species names, and highly similar chronospecies. Applying a conservative taxonomy, all these species belong to four bivalve and eight gastropod families. The high degree of endemism, however, is reflected by proposals of some authors to establish as many as five new families based on Lake Pannon endemics.