Middle Miocene climate transition in the Tibetan Plateau: identification and significance

The Middle Miocene Climatic Optimum is known for abrupt events during the global cooling trend of the past 20 Ma. Its identification in the Tibetan Plateau can help explain the cause of the critical Middle Miocene climate transition in Central Asia. In this study, fine-grained mixed sediments widely distributed in the Miocene Qaidam Lake in the northern Tibetan Plateau were used as a sensitive indicator for palaeoclimate. Their geochemical characteristics were investigated, together with an analysis of 2600 m long successive gamma-ray logging data from the whole JS2 drillcore, to understand the mid-Miocene climate transition in the Tibetan Plateau. By comparing the gamma-ray curve of the mixed sediments with global temperature, the Middle Miocene Climatic Optimum event can be easily identified. Further, the detailed petrological features and geochemical data of lacustrine fine-grained mixed sediments from a 400 m drillcore show oxidizing, high-sedimentation rate and brackish-saline water conditions in a semi-arid climate during the Middle Miocene period, demonstrating a dryer climate in the Qaidam Basin than in the monsoon-sensitive regions in Central Asia. These fine-grained mixed sediments have recorded climate drying before 15.3 Ma that represents a climatic transition within the Middle Miocene Climatic Optimum; increasing carbonate-rich mixed sediments, decreasing algal limestone layers and decreasing lacustrine organic matter are indicators of this transition. Regional tectonic events include the retreat of the Paratethys from Central Asia at ∼15 Ma and the synchronous tectonic reorganization of the Altyn-Tagh fault system and the northeastern Tibetan Plateau. We find that global climate change is the primary factor affecting the overall characteristics and changes of the Neogene climate in the Qaidam Basin, including the occurrence of the Middle Miocene Climatic Optimum and the cooling and drying tendency, while the regional events are a secondary factor.

Grain-size and mineral composition of the upper layer of sediments of the Barents Sea

The paper presents data from grain size and mineralogical analyzes of surface bottom sediment samples obtained on several cruises of the R/V Akademik Mstislav Keldysh (2016–2018) from different parts of the Barents Sea. Pebble and gravel material is found in surface sediments in the form of impurities scattered throughout the sea. Such a chaotic distribution pattern is apparently associated with ice separation. Coarse material is most common in the Barents Sea off the coast of the Kola Peninsula, off the coast of Novaya Zemlya, Spitsbergen, where it accumulates due to coastal abrasion. In addition, a fraction >1 mm is widespread at depths where fine fractions are stirred and leached. The most common sediments in coastal shallow water are sands. Sands (0.1–1 mm) are widespread in the southern and southeastern regions of the sea, in the region of the Pechora polygon, the Kaninsky shallow water, the Kola Peninsula, and in the northwest, off the coast of Svalbard. With increasing depth, the sands are replaced by mixed sediments with a low admixture of pelite. Pelitic sediments are prevalent in the central part of the sea. Precipitation with a pelitic fraction (<0.01 mm) of more than 50% occupy about 70% of the Barents Sea. They are widespread in deep-sea hollows and trenches, as well as in the numerous fiords of the North Island of Novaya Zemlya and Franz Josef Land. Surface sediments have a predominantly terrigenous composition; only at the border with the Norwegian Sea the proportion of biogenic material increases. The mineral composition of sediments is dominated by quartz and feldspars, clay minerals are mainly represented by illite, smectite and kaolinite.

Remote sensing analysis of unnamed crater in Eastern Australia

Remote sensing (RS) can certainly provide deep insights about detecting the terrestrial structure of unknown origin. In this paper, we also detected impact crater of unknown origin in northeast Australia by RS techniques, specifically to enhance the credibility of scientific database on the possible impact craters in the continent of Australia. Following the RS procedures, a circular-shaped unnamed crater, hereafter the Winton crater, was detected with a diameter of approximately 130-km. Furthermore, the topographical parameter was obtained from RS data, which showed that the area, depth and volume of the crater are ~100-m2, ~130-m and ~99.8-m3, respectively. The geological data revealed that inside the crater, the outcrops are mainly consisted of sedimentary and low grade metamorphic rock, specifically included the mixed sediments and conglomerates, limestone and siltstone of the Craterous period. However, the exterior of the circular shaped in the southern part is consisted of unconsolidated deposits of the Tertiary period. The positive value of gravity anomaly for the major part of the crater is 3000 mGal and Bouguer gravity onshore grid has an anomaly of 900 mGal over the impact crater. It showed that the Winton crater could not be the due to any volcanic or karstic processes. On the other hand, a detailed field and petrology investigation should need to distinguish the origin of the crater of old and fossil travertine or an impact crater.

Morphometric Characteristics of the Aziana Valley Basin

The present study aims at examining quantitatively the morphometric characteristics of Iziana Valley basin that is located in the northern part of Iraq; particularly in south of Erbil Governorate. This basin is considered one of the small sub-basins where its valleys run on formations of the Triple and Quadrant Ages, which are represented by the Bay Hassan formations, and the sediments and mixed sediments of the cliffs, respectively. The area of ​​the Iziana basin amounts to (36.39 km2) whereas the percentage of its rotation reaches (0.17); a low percentage, which indicates that the basin diverges from the circular to the rectangular shape. The value of the elongation ratio of the basin reaches (0.38) while the terrain ratio of the basin is (0.03), a low percentage that entails the weakness of its erosion processes and the small volume of the carried and transported sediments. As for the relative topography of the basin, it was (1.08), which is also a low value. It indicates a relatively large area of ​​the basin and the impressive strides that it has made in its erosion cycle. The total river levels of the basin reach (5) ranks, and their numbers vary from one rank to another. Moreover, the total length of the drainage networks in the basin reached (187.4 km), and the prevailing drainage patterns in the basin are the tree and parallel patterns. The researcher has adopted spatial, formal, topographical, and river net-work properties for the purpose of first determining the shape of the basin, the stage of its erosion, its secondary basins, and its terrestrial features that have been developed as a result of the contrast between the erosion and sedimentation processes.

The relationship between source supply and mixed deposition of siliciclastic and carbonate: First to second member of the Shahejie Formation, Paleogene, Bohai Sea area, China

There are various types of mixed siliciclastic-carbonate sediments developed in the Bohai Sea area during the period of the first to second member of the Shahejie Formation (E2s1-2) of the Paleocene. We have concluded that the period of E2s1-2 was very suitable for the development of carbonate minerals and organisms because of the stable tectonic background, the weak siliciclastic influence of large source systems outside the basin, and the high salinity of the water. There were many local uplifts inside the basin during E2s1-2, and the source area, supply direction, and quantity of the local provenance varied greatly. We summarized that the mixed sediments generally developed in the intermittent and stagnant periods of the source supply, or on the flank or distal end of the source supply direction due to the absence of direct interference of terrigenous clasts. To a large extent, the formation of different types of mixed deposits is controlled by the different spatiotemporal relationship with siliciclastic supply. The background of strong source supply led to the formation of large-scale mixed deposits that were mainly composed of terrigenous clasts. Mixed deposits are mainly composed of organisms and carbonate with relatively large depositional thickness formed on the flank of source supply in the steep slope area. On the flank of source supply in the gentle slope belt, thinner mixed deposits with terrigenous clasts mainly formed and thin-layer carbonate clastic-dominated deposits formed on abandoned deltas. On the uplift of the buried hill far away from the provenance, thick mixed deposits mainly composed of bioclastic were formed whereas fine-grained mixed deposits formed under the low-energy argillaceous background.

Lacustrine mixed siliciclastic-carbonate sedimentary rocks in Paleogene Funing Formation of the Subei Basin, eastern China: characteristics and origin

The study of sedimentary characteristics and genetic mechanism of the mixed siliciclastic-carbonate sediments (MSCSs) is not only the focus of sedimentary geology, but also the important issue in petroleum exploration and development. We discover the lacustrine MSCSs, both the interstratified siliciclastic-carbonate sediments and the textural mixture of siliciclastic and carbonate materials (s-MSCSs) in the second member of Paleogene Funing Formation (E1f2) in Gaoyou and Jinhu sags, Subei Basin, eastern China. We use core, mud-log and thin section data to clarify the E1f2 s-MSCSs into 5 types, and we also use geochemical data of the E1f2 mudstone including XRD whole rock, XRD clay and trace elements to quantitatively analyze lake paleosalinity. The E1f2 s-MSCSs mainly consist of siliciclasts, ooids, intraclasts and mud, could be siliciclasts-dominated, allochems-dominated or without dominant component. We analyze that mixed sediments occur under either traction flow or gravity flow. The s-MSCSs of traction flow origin develop small-scale wavy cross-bedding and consist of siliciclasts and ooids of similar size; the s-MSCSs of gravity flow origin develop massive

Limitations of Predicting Substrate Classes on a Sedimentary Complex but Morphologically Simple Seabed

The ocean floor, its species and habitats are under pressure from various human activities. Marine spatial planning and nature conservation aim to address these threats but require sufficiently detailed and accurate maps of the distribution of seabed substrates and habitats. Benthic habitat mapping has markedly evolved as a discipline over the last decade, but important challenges remain. To test the adequacy of current data products and classification approaches, we carried out a comparative study based on a common dataset of multibeam echosounder bathymetry and backscatter data, supplemented with groundtruth observations. The task was to predict the spatial distribution of five substrate classes (coarse sediments, mixed sediments, mud, sand, and rock) in a highly heterogeneous area of the south-western continental shelf of the United Kingdom. Five different supervised classification methods were employed, and their accuracy estimated with a set of samples that were withheld. We found that all methods achieved overall accuracies of around 50%. Errors of commission and omission were acceptable for rocky substrates, but high for all sediment types. We predominantly attribute the low map accuracy regardless of mapping approach to inadequacies of the selected classification system, which is required to fit gradually changing substrate types into a rigid scheme, low discriminatory power of the available predictors, and high spatial complexity of the site relative to the positioning accuracy of the groundtruth equipment. Some of these issues might be alleviated by creating an ensemble map that aggregates the individual outputs into one map showing the modal substrate class and its associated confidence or by adopting a quantitative approach that models the spatial distribution of sediment fractions. We conclude that further incremental improvements to the collection, processing and analysis of remote sensing and sample data are required to improve map accuracy. To assess the progress in benthic habitat mapping we propose the creation of benchmark datasets.

Tomorrow’s mundane is today’s extraordinary: A case study of a plastered installation during Neolithization

For reconstructing past human ways of life we study mundane remains, but in order to detect special worldviews and behaviors we endeavor to observe the extraordinary embedded in those remains. There are many ways to define the ‘extraordinary’. Here we center on early occurrences of phenomena that later become mundane, rendering them ‘extraordinary’ through being rare compared to later frequent appearances. This study explores such extraordinary phenomena with relation to the processes of Neolithization in the Southern Levant, focusing on a round plastered installation (Feature 6) that was unearthed in the Late Natufian village of Nahal Ein Gev II (ca. 12,000 calBP). To investigate the feature’s function, we conducted a micro-geoarcheological analysis of the walls and fill to understand its use and formation processes, using Fourier-transform infrared (FTIR) spectroscopy and micromorphology. Our results show that the walls were not exposed to elevated temperatures and that the interior of the installation was filled with mixed sediments. We therefore rule out the use of the feature as a cooking installation or a kiln. The interior mixed assemblage indicates secondary infilling after the feature was no longer in use for its initial purpose, thus challenging the identification of its original function. To date, there are no parallels for such lime and clay plastered installations in the Natufian culture. Yet, this type of feature becomes increasingly common with the advance of Neolithization where such features served as storage installations, integral to the farming way of life. We conclude that Feature 6 in NEG II is ‘extraordinary’ in the context of the Late Natufian, heralding the development of clay lined storage installations. We argue that this example of ‘extraordinary’ within the long process of Neolithization in the Near East helps to illuminate the gradual process of cultural innovation in which new features appear at first as extraordinary phenomena which later will become mundane.

Sedimentary characteristics and genetic mechanisms of high-quality reservoirs in a mixed siliciclastic-carbonate system in the Qinhuangdao area, Bohai Sea, China

Mixed siliciclastic-carbonate sediments occur broadly in modern and ancient systems. Studies on mixing processes began in shallow shelf environments; however, the genetic model of marine mixed sediments is difficult to apply to continental rift basins due to the complex palaeogeographic environment. We identified three mixing types in the first and second members of the Palaeogene Shahejie Formation (E2s1–2) in the Qinhuangdao area of the Bohai Sea: (1) mixed fan delta, (2) retrogradation mixed sheet, and (3) mixed sheet without siliciclastic influx. Tectonic stability, arid climate, and saline lakes are prerequisite conditions for the development of mixed sediments, whereas the palaeogeomorphologic unit should be the critical factor. We also concluded that the primary sedimentary material contains near-source coarse terrestrial debris, and the advantageous lithologic facies producing biological components are the foundation for high-quality mixed reservoirs, which are characterized by thick layers and favorable porosities and permeabilities. The micritic coatings and early dolomitization against the background of a saline lake environment favored the preservation of primary pores, whereas the leaching by atmospheric water and organic acid erosion during thermal evolution of the source rock created many secondary pores. In addition, hydrocarbon charging protected the reservoir space from carbonate cementation.