Seismic stratigraphy, buried beach ridges and contourite drifts: the Late Quaternary history of the closed Lago Cardiel basin, Argentina (49°S)

The results of a seismic stratigraphic analysis of a closed lake basin, Lago Cardiel, in southernmost South America are reported. Very few high-resolution, continental records spanning the Late Quaternary have been obtained from this region. Seismic sequence stratigraphic analysis allows a reconstruction of lake level variations. Two major hiatuses of unknown age occurred during the early evolution of the basin with the deposition of an alluvial fan in a restricted area in the intervening time period. Following the development of a relatively shallow lake during the late Pleistocene and a short desiccation pulse around 11 220 ¹⁴C yr BP, a transgression of over 135 m occurred at the beginning of the Holocene. The transgression was associated with the formation of beach ridges preserved in the lake stratigraphy on the floor of the modern Lago Cardiel at four different elevations. The preservation of largely unreworked beach ridges indicates a stepwise rise in the lake level. There is no seismic evidence of a major lowering of the lake below modern level during the entire Holocene. Deposition since the mid-Holocene is marked by strong lateral differences in sediment accumulation with a depocentre slightly to the north of the basin midpoint and a pronounced mounded distribution. Seismic reflection geometries, as well as sedimentological characteristics indicate a lacustrine contourite drift covering an area of 80–100 km². As Lago Cardiel is under the influence of westerly winds, these most likely drove lake circulation. The identification of drowned beach ridges and of contourite drifts illustrates that high-resolution seismic stratigraphy is not only a powerful tool in reconstructing past lake level elevations for closed lake basins, but it can also provide information about the rate of lake level changes and the presence and strength of lake currents.     

Numerical experiments on the onset of convective instability in the Earth's mantle

Summary. A simplified model of convection in the mantle is used to investigate the transient effect of cooling a fluid layer from above, The model, representing the mantle overlain by the lithosphere, consists of a two-dimensional fluid layer overlain by a solid conducting lid. The initial temperature of both layers is the same, with the top surface of the lid kept at 0°C throughout. We observe the onset of small-scale flow in the model. In the absence of internal heating the behaviour of the system is controlled by the Rayleigh number, R , and the ratio of the thicknesses of the two layers, a . The onset time of convection as defined by reference to conduction temperature profiles is related simply to a boundary layer critical Rayleigh number. The mean temperature profiles for the convection model are also compared with the observed depth—age relation for oceanic lithosphere and the results are used to estimate the viscosity of the mantle.     

Preparing for climate change in Washington State

Climate change is expected to bring potentially significant changes to Washington State’s natural, institutional, cultural, and economic landscape. Addressing climate change impacts will require a sustained commitment to integrating climate information into the day-to-day governance and management of infrastructure, programs, and services that may be affected by climate change. This paper discusses fundamental concepts for planning for climate change and identifies options for adapting to the climate impacts evaluated in the Washington Climate Change Impacts Assessment. Additionally, the paper highlights potential avenues for increasing flexibility in the policies and regulations used to govern human and natural systems in Washington.     

A chemical and thermodynamic model of oil generation in hydrocarbon source rocks

Thermodynamic calculations and Gibbs free energy minimization computer experiments strongly support the hypothesis that kerogen maturation and oil generation are inevitable consequences of oxidation/reduction disproportionation reactions caused by prograde metamorphism of hydrocarbon source rocks with increasing depth of burial.These experiments indicate that oxygen and hydrogen are conserved in the process.Accordingly, if water is stable and present in the source rock at temperatures ?25 but ?100 °C along a typical US Gulf Coast geotherm, immature (reduced) kerogen with a given atomic hydrogen to carbon ratio (H/C) melts incongruently with increasing temperature and depth of burial to produce a metastable equilibrium phase assemblage consisting of naphthenic/biomarker-rich crude oil, a type-II/III kerogen with an atomic hydrogen/carbon ratio (H/C) of ∼1, and water. Hence, this incongruent melting process promotes diagenetic reaction of detritus in the source rock to form authigenic mineral assemblages.However, in the water-absent region of the system CHO (which is extensive), any water initially present or subsequently entering the source rock is consumed by reaction with the most mature kerogen with the lowest H/C it encounters to form CO₂ gas and a new kerogen with higher H/C and O/C, both of which are in metastable equilibrium with one another.This hydrolytic disproportionation process progressively increases both the concentration of the solute in the aqueous phase, and the oil generation potential of the source rock; i.e., the new kerogen can then produce more crude oil.Petroleum is generated with increasing temperature and depth of burial of hydrocarbon source rocks in which water is not stable in the system CHO by a series of irreversible disproportionation reactions in which kerogens with higher (H/C)s melt incongruently to produce metastable equilibrium assemblages consisting of crude oil, CO₂ gas, and a more mature (oxidized) kerogen with a lower H/C which in turn melts incongruently with further burial to produce more crude oil, CO₂ gas, and a kerogen with a lower H/C and so forth.The petroleum generated in the process progresses from heavy naphthenic crude oils at low temperatures to mature petroleum at ∼150 °C. For example, the results of Computer Experiment 27 (see below) indicate that the overall incongruent melting reaction in the water-absent region of the system C-H-O at 150 °C and a depth of ∼4.3 km of an immature type-II/III kerogen with a bulk composition represented by C₂₉₂H₂₈₈O_12(c) to produce a mature (oxidized) kerogen represented by C₁₂₈H₆₈O_7(c), together with a typical crude oil with an average metastable equilibrium composition corresponding to C_8.8H_16.9 (C_8.8H_16.9(l)) and CO₂ gas (CO_2(g)) can be described by writing

(A)     

Solar coronal heating by high-frequency dispersive Alfvén waves

It is shown that high-frequency dispersive kinetic Alfvén waves can cause significant electron heating in the solar corona. The heating is produced by collisionless electron Landau dissipation of the parallel electron current associated with high-frequency dispersive kinetic Alfvén waves, which have a parallel electric field.     

Using Diurnal Temperature Signals to Infer Vertical Groundwater‐Surface Water Exchange

Heat is a powerful tracer to quantify fluid exchange between surface water and groundwater. Temperature time series can be used to estimate pore water fluid flux, and techniques can be employed to extend these estimates to produce detailed plan‐view flux maps. Key advantages of heat tracing include cost‐effective sensors and ease of data collection and interpretation, without the need for expensive and time‐consuming laboratory analyses or induced tracers. While the collection of temperature data in saturated sediments is relatively straightforward, several factors influence the reliability of flux estimates that are based on time series analysis (diurnal signals) of recorded temperatures. Sensor resolution and deployment are particularly important in obtaining robust flux estimates in upwelling conditions. Also, processing temperature time series data involves a sequence of complex steps, including filtering temperature signals, selection of appropriate thermal parameters, and selection of the optimal analytical solution for modeling. This review provides a synthesis of heat tracing using diurnal temperature oscillations, including details on optimal sensor selection and deployment, data processing, model parameterization, and an overview of computing tools available. Recent advances in diurnal temperature methods also provide the opportunity to determine local saturated thermal diffusivity, which can improve the accuracy of fluid flux modeling and sensor spacing, which is related to streambed scour and deposition. These parameters can also be used to determine the reliability of flux estimates from the use of heat as a tracer.     

黏声介质平面波有限差分叠前深度偏移及在莺歌海盆地的应用

莺琼盆地诸探区中存在底劈现象,深层气源产生的气体沿底劈产生的裂隙通道向上漫溢.漫溢过程中,一是充填在遇到的砂体中形成气藏;二是弥漫在上溢通道中,使得通道中的纵波速度发生变化,进而纵波波阻抗差异变小,反射变弱.另外,通道中气体的存在,会加强地层的吸收衰减,使得地震波振幅变弱、高频成分损失导致同相轴分辨率降低.利用OBC数据进行多波地震勘探和利用黏声介质的叠前深度偏移都是改善模糊区成像质量的重要方法技术.为此,本文提出用黏声介质平面波有限差分法叠前深度偏移成像方法改善气体充填区域的成像质量.黏声介质成像目的是补偿地震波的吸收衰减;平面波偏移成像目的是适应海上单炮数量巨大,提高波动方程叠前深度偏移成像的效率;有限差分法叠前偏移的目的是适应该区浅层气分布局域性极强、Q值的空间变化大的情况.在莺歌海某探区的实际数据上的黏声介质平面波有限差分叠前深度偏移试验证明,本方法是改善模糊区成像质量的较为有效的途径.     

塔里木盆地塔北露头区的古岩溶发育模式

目前塔里木盆地海相碳酸盐岩的油气勘探已进入高峰期,为弥补钻井岩心资料不足,进一步认识井下岩溶发育规律及发育模式特征,开展塔北露头区奥陶系风化壳古岩溶缝洞系统发育特征及发育模式研究。研究表明,岩溶发育主要受控于岩性因素和不整合面,主要发育层位为一间房组地层;主要岩溶作用期为吐木休克组／一间房组沉积间断岩溶期。为井下岩溶缝洞系统的认识及岩溶地质模型的建立提供了重要理论依据。