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Alkaline lakes are significant for exploring the evolution of life, reconstructions of environments, and exploration and exploitation of energy resources; however, despite modern alkaline lakes being widely distributed on Earth, deep-time (pre-Neogene) examples are scarce, in general, compared with other types of saline lake deposits (e.g., chloride and sulfate salts). This raises the question as to whether this scarcity is due to their extreme formation conditions or because they have yet to be discovered, owing to the difficulty in identification of these deep-time lakes. This paper addresses this question by analyzing the distribution and formation mechanisms of modern alkaline lakes in order to interpret the past based on the present. These results indicate that alkaline lakes can be identified from the presence of alkali minerals, such as trona and nahcolite, and heavy N isotopes (>10‰) caused by NH 3 volatilization. Modern alkaline lakes can be classified into two main types, including those in tectonically active and inland arid zones. Their formation mechanisms are controlled by multiple factors, such as a (semi-)closed basin geography, (semi-)arid climate that favors high degrees of evaporation, and the presence of strongly alkaline fluids that are rich in HCO 3 − and CO 3 2−. The formation mechanisms of discovered deep-time alkaline lakes are similar to those of modern examples. The δ13C, and δ18O of carbonates, Mg/Ca, chemical index of alteration, and chemical index of weathering indicate that deep-time alkaline lakes were also generally deposited in (semi-)closed basins with a (semi-)arid climate, which were conducive to strong evaporation and concentration of saline waters. Furthermore, chemical weathering and hydrolysis of silicate minerals, volcanic–hydrothermal activity and circulation of basinal brines, and microbially mediated processes also produced alkaline fluids rich in HCO 3 − and CO 3 2− necessary for the formation of ancient alkaline lakes. Alkaline lakes should be widespread throughout geological history, but may be poorly preserved in old stratigraphic sequences or difficultly in identification because of their limited outcrop and depth. Future studies of evaporite mineralogy and the N isotope geochemistry of ancient saline lacustrine basins are necessary to further our understanding of their identification and formation mechanisms. Such studies should also investigate the favorable development zones, characteristics of organic matter accumulation, astrobiology, etc. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an extensive review of the process of ghost-rock karstification and highlights its role in the formation of cave systems. The process integrates chemical weathering and mechanical erosion and extends a number of existing theories pertaining to continental landscape development. It is a two stage process that differs in many respects from the traditional single-stage process of karstification by total removal. The first stage is characterised by chemical dissolution and removal of the soluble species. It requires low hydrodynamic energy and creates a ghost-rock feature filled with residual alterite. The second stage is characterised by mechanical erosion of the undissolved particles. It requires high hydrodynamic energy and it is only then that open galleries are created. The transition from the first stage to the second is driven by the amount of energy within the thermodynamic system. The process is illustrated by detailed field observations and the results of the laboratory analyses of samples taken from the karstotype area around Soignies in southern Belgium. Thereafter, a series of case studies provide a synthesis of field observations and laboratory analyses from across western Europe. These studies come from geologically distinct parts of Belgium, France, Italy, and the United Kingdom. The process of ghost-rock karstification challenges a number of axioms associated with the process of karstification by total removal. On the basis of the evidence presented it is argued that it is no longer acceptable to use karst morphologies as a basis with which to infer specific karstogenetic processes and it is no longer necessary for a karst system to relate to base level as ghost-rock karstification proceeds along transmissive pathways in the rock. There is also some evidence to suggest that ghost-rock karstification may be superseded by karstification by total removal, and vice versa, according to the amount of energy within the thermodynamic system. The proposed chemical weathering and subsequent mechanical erosion of limestone suggest that the development of karst terrain is related far more closely to the geomorphological development of aluminosilicate and siliceous terrains than is generally supposed. It is now necessary to reconsider the origin of many karst systems in light of the outlined process of ghost-rock karstification. [Copyright &y& Elsevier]

Abstract: Forested hillslopes form a special geoecosystem, an environment of geomorphic processes that depend strongly on forest ecology, including the growth and decay of trees, changes in structure, disturbances and other fluctuations. Hence, the following various functions of trees are reviewed here: their role in both biomechanical and biochemical weathering, as well as their importance for the hillslope geomorphic subsystem and for transport of soil material via tree uprooting and root growth. Special attention is paid to tree uprooting, a process considered the most efficient and most frequent biogeomorphological indicator of bio-physical activity within forest in complex terrain. Trees have varied implications for soil formation in different environments (boreal to tropical forests) and altitudes. In this paper an attempt has been made to emphasize how trees not only modulate geomorphic processes, but also how they act as a direct or indirect agent of microrelief formation, the most striking example of which being widespread and long-lasting pit-and-mound microtopography. Based on the analyzed literature it seems that some problems attributed to forest ecology can have a fundamental effect on forested hillslope dynamics, a relationship which points to the need for its integration and interpretation within the field of geomorphology. The biology of individual trees has a key influence on the development of e.g. rock faces, weathering front migration and changes in the soil biomantle within upper and lower forest belts. Additionally, forms and sediments depend largely on the horizontal and vertical extent, volume and structure of root systems, as well as on active processes taking place in the root zone and rhizosphere. Furthermore, although trees to a large extent stabilize slope surfaces, their presence can also have a dual effect on slope stability due to tree uprooting, a process which in some circumstances can trigger mass movements (e.g. debris avalanches). So far, several attempts at quantifying the influence of trees on slopes have been made via the use of mathematical equations, enabling researchers to calculate: 1) the root plate volume of uprooted trees, 2) the amount of soil displacement due to tree root growth, and 3) rates of erosion, sedimentation and soil creep. In light of the reviewed literature, the most urgent issue appears to be the need for a thorough study of the interactions and feedbacks occurring between trees and geomorphic systems (e.g. soil mixing and biotransport by trees) in different climate zones, altitudes and time frames, especially in terms of the development of forest ecosystems during the Holocene. [Copyright &y& Elsevier]

From the latest Cretaceous (late Campanian to Maastrichtian, ~75–66 Ma) to the earliest Paleogene, fluctuations in greenhouse climate, inferred primarily from marine sediments, have been linked to volcanism, the Chicxulub asteroid impact, and the Cretaceous-Paleogene (K-Pg) mass extinction. In this paper, we summarize terrestrial climate records in mid-latitude East Asia during the latest Cretaceous and across the K-Pg boundary, based on a multi-proxy approach from the geochronologically well-constrained Sifangtai and Mingshui formations (SMF), accessed by scientific drilling of the Songliao Basin in northeastern China. Evolution of sedimentary environments is characterized by five depositional units of fluvial-deltaic-lacustrine facies. Development of four types of paleosols, including Inceptisols, Aridisols, Vertisols and Alfisols, is interpreted to primarily reflect climatic changes. Correlations among sedimentary facies, paleosol features, illite chemistry index, chemical index of alteration, as well as stable and clumped isotopes of pedogenic carbonates and clay minerals of the SMF validate their reliability for paleoclimate reconstruction, and indicate significant fluctuations in terrestrial climate and sedimentary environment. During global warming intervals possibly triggered by volcanism (e.g. ~69.5–68.5 Ma), the Songliao Basin experienced a warmer and wetter climate with stronger terrestrial chemical weathering and more monsoon-derived moisture sourced from the Pacific. In contrast, during global cooling intervals (e.g. ~70.5–69.5 Ma and ~ 68.5–66.5 Ma), the SMF record a cooler and drier climate with less intensive chemical weathering and more westerlies-derived moisture. Across the K-Pg boundary, dramatic changes in land temperatures and hydroclimate correspond to the latest Maastrichtian warming episode (~66.4–66.1 Ma), the transient cooling preceding the K-Pg boundary (~66.1–66.0 Ma), and the earliest Paleogene warming interval (~66.0–65.7 Ma). Temporal correlation of weathering index changes with the Deccan Traps volcanism suggests that volcanism and subsequent intensified weathering played a major role for climatic changes across the K-Pg boundary. The integrated records of sedimentological and geochemical datasets from the Songliao Basin robustly demonstrate that the terrestrial climate of mid-latitude East Asia responded strongly to greenhouse climate changes and to the catastrophic geological events from the latest Cretaceous to the earliest Paleogene. [ABSTRACT FROM AUTHOR]