Climate change impacts on U.S. Coastal and Marine Ecosystems

Increases in concentrations of greenhouse gases projected for the 21st century are expected to lead to increased mean global air and ocean temperatures. The National Assessment of Potential Consequences of Climate Variability and Change (NAST 2001) was based on a series of regional and sector assessments. This paper is a summary of the coastal and marine resources sector review of potential impacts on shorelines, estuaries, coastal wetlands, coral reefs, and ocean margin ecosystems. The assessment considered the impacts of several key drivers of climate change: sea level change; alterations in precipitation patterns and subsequent delivery of freshwater, nutrients, and sediment; increased ocean temperature; alterations in circulation patterns; changes in frequency and intensity of coastal storms; and increased levels of atmospheric CO₂. Increasing rates of sea-level rise and intensity and frequency of coastal storms and hurricanes over the next decades will increase threats to shorelines, wetlands, and coastal development. Estuarine productivity will change in response to alteration in the timing and amount of freshwater, nutrients, and sediment delivery. Higher water temperatures and changes in freshwater delivery will alter estuarine stratification, residence time, and eutrophication. Increased ocean temperatures are expected to increase coral bleaching and higher CO₂ levels may reduce coral calcification, making it more difficult for corals to recover from other disturbances, and inhibiting poleward shifts. Ocean warming is expected to cause poleward shifts in the ranges of many other organisms, including commercial species, and these shifts may have secondary effects on their predators and prey. Although these potential impacts of climate change and variability will vary from system to system, it is important to recognize that they will be superimposed upon, and in many cases intensify, other ecosystem stresses (pollution, harvesting, habitat destruction, invasive species, land and resource use, extreme natural events), which may lead to more significant consequences.     

Famennian microbial reef facies, Napier and Oscar Ranges, Canning Basin, western Australia

Following the Frasnian–Famennian mass extinction, which eliminated most skeletal reef-building fauna, the early Famennian reefs of the Canning Basin were constructed primarily by reef-framework microbial communities. In the Napier and Oscar Ranges, the Famennian reef complexes had high-energy, reef-flat depositional environments on a reef-rimmed platform that transitioned into low-energy, deep-water reefs growing in excess of 50 m below sea level. High-energy, reef-flat depositional environments contain doming fenestral stromatolites that grade into porous thrombolites and are associated with coarse-grained sandstones and grainstones. The reef-margin subfacies contains mounds of microdigitate thrombolites, which are more delicate than the reef-flat thrombolites and locally contain abundant red algae, Girvanella, renalcids and sediment-filled tubes. Within the thrombolites, the red algae are in upright growth positions, suggesting that the thrombolites are largely composed of carbonate that precipitated in situ. Reefal-slope environments are dominated by Wetheredella and Rothpletzella with locally abundant Girvanella, renalcids and Uralinella. In reefal-slope strata, delicate fans and microdigitate stromatolites of Wetheredella and Rothpletzella are often oriented horizontal or diagonal to bedding and are interpreted as syndepositionally toppled over. Most mesoscale microbial community structures contain several species of microbial fossils, and no single microbial species appears to have controlled the morphology of the community structure. Therefore, the depositional environment must have determined the distribution and morphology of the stromatolites, thrombolites and other microbial community structures. The adaptability of microbial communities to various reef environments allowed them to fill ecological niches opportunistically after the Frasnian–Famennian mass extinction.     

江苏煤层气资源分析

简要地归纳了江苏省煤层气的成矿地质环境，分析了成煤区地质构造特征、煤层及围岩储层的物性特征，在此基础上，对主要地区煤层气资源进行了估算。     

岩层离距图法研究沉积岩断裂发育史——以松辽盆地敖古拉断裂为例

利用断裂活动过程中留下的各种地质标记研究断裂发育史是比较困难的 ,已有的研究方法主要可归纳出七种 ,都存在局限性。岩层离距图法是以地震剖面为基础 ,将穿过断裂的各剖面上的标志层投影到沿断裂走向的铅垂面上 ,得到多组标志层的垂向断距数据 ,然后用下部各标志层的断距减去最上部标志层的断距 ,并作多轮次计算 ,直到最后的断距差近似为零或仅剩一个非零标志层。每一轮次计算代表一个活动期次 ,如果出现负值 ,则表示有构造反转。对松辽盆地敖古拉断裂作了实例计算 ,结果为该断裂发育经历了三个正断活动期和一个逆断活动期 ,与盆地区域性活动有些差别。岩层离距图法比起其他已有方法 ,可靠程度大大提高     

Mid‐Miocene initiation of E‐W extension and recoupling of the Himalaya

The Tibetan plateau is host to numerous ~N‐S striking graben that have accommodated E‐W directed extension. The development of these structures has been interpreted to reflect a variety of different geological processes including plateau collapse, oroclinal bending or mid‐to‐lower crustal flow. New ⁴⁰Ar/³⁹Ar thermochronology and quartz c‐axis data from the Thakkhola graben of west‐central Nepal show that E‐W extension was ongoing at least locally by the early Miocene (ca. 17 Ma). Our new, and previously published chronologic information on the initiation of graben across the orogen shows that they typically developed immediately after cessation of the South Tibetan detachment system, a structural network that facilitated differential southward movement of the upper and middle crust. We interpret this fundamental switch in orogen kinematics to reflect recoupling of the middle and upper Himalayan crust such that the subsequent widespread flow of the mid‐to‐lower crust out of the system to the east forced brittle accommodation in the upper crust.     

Thrombolite fabrics and origins: Influences of diverse microbial and metazoan processes on Cambrian thrombolite variability in the Great Basin,California and Nevada

Thrombolites are a common component of carbonate buildups throughout the Phanerozoic. Although they are usually described as microbialites with an internally clotted texture, a wide range of thrombolite textures have been observed and attributed to diverse processes, leading to difficulty interpreting thrombolites as a group. Interpreting thrombolitic textures in terms of ancient ecosystems requires understanding of diverse processes, specifically those due to microbial growth and metazoan activity. Many of these processes are reflected in thrombolites in the Cambrian Carrara, Bonanza King, Highland Peak and Nopah formations, Great Basin, California, USA; they comprise eight thrombolite classes based on variable arrangements and combinations of depositional and diagenetic components. Four thrombolite classes (hemispherical microdigitate, bushy, coalescent columnar and massive fenestrated) contain distinct mesoscale microbial growth structures that can be distinguished from surrounding detrital sediments and diagenetic features. By contrast, mottled thrombolites have mesostructures that dominantly reflect post‐depositional processes, including bioturbation. Mottled thrombolites are not bioturbated stromatolites, but rather formed from disruption of an originally clotted growth structure. Three thrombolite classes (arborescent digitate, amoeboid and massive) contain more cryptic textures. All eight of the thrombolite classes in this study formed in similar Cambrian depositional environments (marine passive margin). Overall, this suite of thrombolites demonstrates that thrombolites are diverse, in both internal fabrics and origin, and that clotted and patchy microbialite fabrics form from a range of processes. The diversity of textures and their origins demonstrate that thrombolites should not be used to interpret a particular ecological, evolutionary or environmental shift without first identifying the microbial growth structure and distinguishing it from other depositional, post‐depositional and diagenetic components. Furthermore, thrombolites are fundamentally different from stromatolites and dendrolites in which the laminae and dendroids reflect a primary growth structure, because clotted textures in thrombolites do not always reflect a primary microbial growth structure.     

Cloud Forest Conservation in the Central Highlands of Guatemala Hinges on Soil Conservation and Intensifying Food Production

Soil erosion threatens long-term soil fertility and food production in Q’eqchi’ communities native to the Sierra Yalijux and Sierra Sacranix mountain ranges in the central highlands of Guatemala. Environmental factors such as steep topography, erodible soils, and intense precipitation events, combined with land subdivision and reduced fallow periods as a consequence of population growth, contribute to severe erosion and strain soil resources. The preservation of the region's cloud forests hinges on enhancing production of staple crops through agricultural intensification while maintaining soil fertility through implementation of soil conservation measures.