New Age of Fishes initiated by the Cretaceous?Paleogene mass extinction

Ray-finned fishes (Actinopterygii) comprise nearly half of all modern vertebrate diversity, and are an ecologically and numerically dominant megafauna in most aquatic environments. Crown teleost fishes diversified relatively recently, during the Late Cretaceous and early Paleogene, although the exact timing and cause of their radiation and rise to ecological dominance is poorly constrained. Here we use microfossil teeth and shark dermal scales (ichthyoliths) preserved in deep-sea sediments to study the changes in the pelagic fish community in the latest Cretaceous and early Paleogene. We find that the Cretaceous−Paleogene (K/Pg) extinction event marked a profound change in the structure of ichthyolith communities around the globe: Whereas shark denticles outnumber ray-finned fish teeth in Cretaceous deep-sea sediments around the world, there is a dramatic increase in the proportion of ray-finned fish teeth to shark denticles in the Paleocene. There is also an increase in size and numerical abundance of ray-finned fish teeth at the boundary. These changes are sustained through at least the first 24 million years of the Cenozoic. This new fish community structure began at the K/Pg mass extinction, suggesting the extinction event played an important role in initiating the modern “age of fishes.”Ray-finned fishes are a dominant and exceptionally diverse member of modern pelagic ecosystems; however, both the fossil record and molecular clocks suggest that the vast majority of living ray-finned fishes developed only recently, during the last 100 million years (1–3). It has been proposed that the explosion in actinoptygerian diversity in the Late Mesozoic and Early Cenozoic represents a new “age of fishes” in contrast to the initial diversification of fish clades in the Devonian (2, 3). However, the mechanisms and timing of this Mesozoic−Cenozoic radiation and rise to dominance by ray-finned fishes are not well constrained in current molecular phylogenies or from the relatively sparse fossil record. While the Cretaceous−Paleogene (K/Pg) mass extinction occurred ∼66 million years ago (Ma), in the middle of this radiation, there is little clear phylogenetic evidence linking any changes in fish diversity directly to this event (1), although a recent phylogenetic study on pelagic fish families suggested that open ocean fishes radiated during the early Paleogene following the extinction (4).The K/Pg extinction had a dramatic effect on open ocean marine ecosystems (5–7), although the severity of the extinction varied around the globe (7–9). Major groups at both the base and top of the food web were decimated (5, 6, 10). While the traditional model of mass extinction due to primary productivity collapse (11) has been generally discredited due to the continued productivity of select consumer groups (12, 13), it is likely that upheaval among primary producers reverberated up the food web to cause extinctions at higher trophic levels. In the open ocean, calcifying plankton such as foraminifera and calcareous nannofossils suffered >90% species-level extinctions (9, 14). These changes in the structure of the base of the food web likely helped to cause the extinctions of pelagic consumers such as ammonites and marine reptiles (10). The trophic link between the plankton and large consumers in pelagic ecosystems is small pelagic fish, which would be expected to be similarly decimated by changes in food web structure. However, recent work has shown that while there was a collapse of small pelagic fish production in the Tethys Sea, in the Pacific Ocean, these midlevel consumers maintained Cretaceous-like or higher levels of production in the earliest Danian (15).Changes in abundance do not tell the whole story of how pelagic fishes responded to the extinction event. Indeed, despite dramatic levels of extinction, a few species of planktonic foraminifera thrived in the postextinction oceans, reaching abundances in the ∼500,000 y following the event that far exceed those of typical high-diversity Cretaceous assemblages (7). This foraminifer response shows that taxonomic diversity and biological production can be decoupled in postdisaster ecosystems like those of the earliest Danian. Fishes are highly diverse and occupy a range of ecological niches, from the smallest plankton feeders through predatory sharks. This means that different groups could exhibit differential responses to the extinction (16). Work on well-preserved body fossils has found that there was a selective extinction of shallow marine predatory fishes at the K/Pg extinction, and a radiation during the early Cenozoic (17, 18). Additionally, a low level of extinction (<33%) of sharks and rays has been inferred across the event (19, 20). However, the magnitude of pelagic fish extinction is poorly known, although a relatively modest ∼12% extinction has been documented for fish tooth morphotypes between the Late Cretaceous and the early Paleocene (21).Here we use ichthyoliths, the isolated teeth and dermal scales (denticles) of sharks and ray-finned fishes found in deep-sea sediments, to investigate the response of sharks and fishes to the K/Pg extinction. Calcium phosphate ichthyoliths are found in nearly all marine sediments, even red clays (22), where other microfossils have been dissolved by corrosive bottom water conditions. Therefore, ichthyoliths are relatively unaffected by the preservation biases typically found in other microfossil groups. Teeth and denticles are reasonably common, with 10s to 100s found in a few grams of sediment, allowing studies of the fish community rather than isolated individuals. The abundance of ichthyoliths also allows for high-temporal resolution sampling similar to other microfossils. The well-resolved ichthyolith records stand in sharp contrast to those for the comparatively rare body fossil record, and can provide a complimentary analysis of abrupt biotic events such as mass extinctions or transient climate changes. In addition, the abundance, assemblage, and morphological composition of ichthyoliths record the productivity and biodiversity of the pelagic fish community.We investigate how the pelagic fish community responded to the K/Pg extinction at six deep-sea sites in the Pacific, Atlantic, and Tethys Oceans. We use ichthyolith community metrics, including the relative abundance of microfossils from sharks and ray-finned fishes, and the size structure of the tooth assemblage to assess the changes in the pelagic fish community across the K/Pg mass extinction around the world. This represents, to our knowledge, the first geographically comprehensive, high-resolution study of pelagic marine vertebrate communities across the extinction.     

克拉苏构造带古近系盐下白垩系裂缝性低孔砂岩储层特征及控制因素

克拉苏构造带古近系盐下白垩系巴什基奇克组砂岩储层发育宽缓湖盆三角洲沉积,以中—中细粒岩屑长石砂岩为主,储集空间类型主要为粒间溶孔—溶蚀扩大孔、粒内溶孔、微孔隙和裂缝,物性特征表现为特低孔低渗—特低渗,总体表现为裂缝性低孔砂岩储层。提出克拉苏构造带古近系盐下白垩系发育受应力控制的特殊储层类型,揭示其形成的关键因素:宽缓湖盆沉积、物源充分,三角洲前缘砂体叠置连片的沉积背景;长期浅埋,晚期快速深埋的成岩演化过程;侧向挤压为主的构造应力。明确古近系盐下白垩系储层受断背斜应力中和面控制,具有垂向分层特征。     

Direct and indirect effects of biological factors on extinction risk in fossil bivalves

Biological factors, such as abundance and body size, may contribute directly to extinction risk and indirectly through their influence on other biological characteristics, such as geographic range size. Paleontological data can be used to explicitly test many of these hypothesized relationships, and general patterns revealed through analysis of the fossil record can help refine predictive models of extinction risk developed for extant species. Here, I use structural equation modeling to tease apart the contributions of three canonical predictors of extinction--abundance, body size, and geographic range size--to the duration of bivalve species in the early Cenozoic marine fossil record of the eastern United States. I find that geographic range size has a strong direct effect on extinction risk and that an apparent direct effect of abundance can be explained entirely by its covariation with geographic range. The influence of geographic range on extinction risk is manifest across three ecologically disparate bivalve clades. Body size also has strong direct effects on extinction risk but operates in opposing directions in different clades, and thus, it seems to be decoupled from extinction risk in bivalves as a whole. Although abundance does not directly predict extinction risk, I reveal weak indirect effects of both abundance and body size through their positive influence on geographic range size. Multivariate models that account for the pervasive covariation between biological factors and extinction are necessary for assessing causality in evolutionary processes and making informed predictions in applied conservation efforts.     

End-Cretaceous marine mass extinction not caused by productivity collapse

An asteroid impact at the end of the Cretaceous caused mass extinction, but extinction mechanisms are not well-understood. The collapse of sea surface to sea floor carbon isotope gradients has been interpreted as reflecting a global collapse of primary productivity (Strangelove Ocean) or export productivity (Living Ocean), which caused mass extinction higher in the marine food chain. Phytoplankton-dependent benthic foraminifera on the deep-sea floor, however, did not suffer significant extinction, suggesting that export productivity persisted at a level sufficient to support their populations. We compare benthic foraminiferal records with benthic and bulk stable carbon isotope records from the Pacific, Southeast Atlantic, and Southern Oceans. We conclude that end-Cretaceous decrease in export productivity was moderate, regional, and insufficient to explain marine mass extinction. A transient episode of surface ocean acidification may have been the main cause of extinction of calcifying plankton and ammonites, and recovery of productivity may have been as fast in the oceans as on land.     

Cenozoic climate change influences mammalian evolutionary dynamics

Global climate change is having profound impacts on the natural world. However, climate influence on faunal dynamics at macroevolutionary scales remains poorly understood. In this paper we investigate the influence of climate over deep time on the diversity patterns of Cenozoic North American mammals. We use factor analysis to identify temporally correlated assemblages of taxa, or major evolutionary faunas that we can then study in relation to climatic change over the past 65 million years. These taxa can be grouped into six consecutive faunal associations that show some correspondence with the qualitative mammalian chronofaunas of previous workers. We also show that the diversity pattern of most of these chronofaunas can be correlated with the stacked deep-sea benthic foraminiferal oxygen isotope (δ(18)O) curve, which strongly suggests climatic forcing of faunal dynamics over a large macroevolutionary timescale. This study demonstrates the profound influence of climate on the diversity patterns of North American terrestrial mammals over the Cenozoic.     

柯克亚凝析气田古近系碳酸盐岩气藏类型再认识及其意义

柯克亚凝析气田位于塔里木盆地西南坳陷柯克亚构造带上,以往按构造气藏模式对该含油气层系进行评价部署,评价井失利后对该气藏类型一直认识不清。通过综合分析该地区卡拉塔尔组优质储层的控制因素、地层水特征、地层压力、生产动态等资料,认为该气藏类型属于岩性型,油气流体分布受储层物性所控制,明确了下步在研究区构造低部位寻找岩性型气藏的有利方向。     

塔北隆起英买力地区古近系膏盐岩层卡层方法研究

盐下地层变化较大,导致盐底卡层失误较多。通过已钻井盐层卡层实例的统计分析发现,软泥岩的相对低钻时、岩屑呈团块状,硬泥岩的高钻时、岩屑呈片状且具切屑面；一定厚度的高钻时硬泥岩、井漏或气测显示或大段砂层的出现是盐层钻完的标志；通过控制揭开盐下膏泥岩段高钻时泥岩的厚度以确定中途完钻井深。