Academic literature on the topic 'Lacustrine sedimentary drifts'

Abstract. Borisoglebsk Upland is considered an example of a secondary upland plain in the marginal zone of the last Middle Pleistocene glaciation. Moraine hills and kames were reworked by glaciofluvial processes and incised by small fluvial forms later. Its postglacial surface drift cover is regularly defined as an undivided complex of mantle loams of dominantly subaerial origin with characteristic cryogenic features and remnants of paleosols. However, some previous studies suggest that lake sedimentation played an important role in the postglacial history of the Borisoglebsk Upland. This paper presents results of a detailed investigation of postglacial sedimentary cover of the eastern part of the Borisoglebsk Upland aimed to reconstruct the co-evolution of surface deposits, soil cover and geomorphic landscapes since degradation of the last Middle Pleistocene glaciation about 150 ka (MIS-6). The study is essentially based on a comprehensive lithological, pedological and geocryological description of postglacial deposits in cores (hand or machine-driven) and open sections, systematic sampling for grain size analysis and selective sampling for 14C absolute dating and monoliths structural examination. The results indicate that most of the surface drifts in this feature consists of stratified lacustrine deposits. Their Late Pleistocene age is stratigraphically confined by the underlying paleosols and incorporated peats of the Mikulino interglacial age (MIS-5) and several organic-rich layers within the lake sequence 14C dated to the Middle Valdai interstadial (MIS-3). Overlying mantle loams and colluvial deposits with cryogenic features and low organic matter content those facially substitute lacustrine sediments were attributed to the Late Valdai stadial (MIS-2). After the Mid-Holocene stabilization, relatively thin colluvial cover identified by the increased amount of organic matter also deposited. We conclude that lacustrine sedimentation is the primary Late Pleistocene agent that transformed the initial glacial topography and most characteristic type of lithodynamics of the eastern Borisoglebsk Upland.

The basins of the South Atlantic passive margins are filled with early rifting stage lacustrine sediments (Barremian, 129–125 Ma), transitional lacustrine and marine sediments (Aptian, 125–113 Ma), and drift stage marine sediments since early Cretaceous (Albian, 113 Ma). The South Atlantic margins can be divided into three segments by the Rio Grande Fracture Zone and the Ascension Fracture Zone according to variations in the basin evolution history and configuration style. The lacustrine shale and marine shale source rocks are developed in the rift stage and drift (post-rift) stage in the South Atlantic passive margins, respectively. The southern segment of the margins is dominated by the lacustrine sedimentary filling in the rifted stage overlain by a thin marine sag system as a regional seal, where the hydrocarbons are mainly accumulated in the structural-stratigraphic lacustrine reservoirs formed in the rift stage. The middle segment developed salty rift-sag-type basins with rift and sag systems and with salt deposited in the transitional intercontinental rift stage, where the lacustrine shale in the lower part of the rifted lacustrine sequence and the marine shale in the lower part of the sag sequence formed in the marine post-rift stage are high-quality source rocks. This segment in the middle is mainly dominated by pre-salt lacustrine carbonate and post-salt marine turbidite plays. The northern segment is characterized by sag-type basins with a narrowly and locally distributed rifted lacustrine system and its overlying widely distributed thick marine sag systems. Gravity-flow (mostly turbidite) marine sandstones as good reservoirs were extensively developed in the sag stage due to the narrow shelf and steep slope. The post-rift marine shales in the lower part of the sag sequence are the main source rocks in the northern segment and the hydrocarbons generated from these source rocks directly migrated to and accumulated in the deep marine turbidite sandstones in the same sag sequence formed in the drift stage. From southern segment to northern segment, source rocks and hydrocarbon accumulations tend to occur in the stratigraphically higher formations. The hydrocarbon accumulations in the southern segment are mainly distributed in the rifted lacustrine sequence while that in the northern segment primarily occur in the post-rift marine sequence.

AbstractAn 18-m-high coastal bluff at Togiak Bay (northwestern Bristol Bay, southwestern Alaska) exposes marine, lacustrine, fluvial, glacial, volcanic, and organic deposits that record the ∼50,000-year-long transition from the peak of the last interglaciation to the early Wisconsin glaciation. The base of the section is dominated by stratified sand and silt extending up to 4.3 m above sea level; marine diatoms are present, and pollen assemblages are characterized by relatively high percentages of Picea, Alnus, and Betula and low percentages of Poaceae and Cyperaceae. The marine sediment was probably deposited during the peak of marine oxygen-isotope stage (OIS) 5e. An infrared stimulated luminescence (IRSL) age of 151,000±13,000 yr from near the base of the exposure is permissive of this correlation. The marine sand and silt are overlain by 0.8 m of peaty silt with diatoms that record a transition from marine to lacustrine conditions. During this interval, Poaceae and Cyperaceae dominate the pollen assemblages, and Picea and shrubs are nearly absent, suggesting that herb tundra occupied the landscape. This interval probably encompasses OIS 5d on the basis of the herb tundra and an IRSL age of 119,000±10,000 yr from 60 cm below the marine/lacustrine transition. The organic mud is overlain by 3.1 m of stratified sand and organic silt that apparently record shallowing of the lake; reappearance of spruce and shrubs (=OIS 5c?); and subsequent deepening of the lake (=OIS 5b?); followed by aggradation of a floodplain (=OIS 5a?), which was dry at the time basaltic lava buried the site. Thermoluminescence analyses on lava-baked sediment indicate that the eruption occurred 70,000±10,000 yr ago. Sometime thereafter, but prior to 53,600 14C yr B.P. an outlet of the Ahklun Mountains ice cap advanced over the site and deposited ∼7 m of bouldery ice-contact drift. The sedimentary sequence contains at least four tephra beds. Major- and trace-element chemistry provide a basis for correlating two of the tephras with tephra beds at nearby sites. The tephras, luminescence ages, and correlations with marine isotope stages provide the geochronological control to place the Togiak Bay section into a global context. The site serves as an important new reference section for late Pleistocene paleoenvironmental change in eastern Beringia.

A 210 m section of Late Triassic Fleming Fjord Formation (the Malmros Klint Member and the lowermost 80m of the overlying Carlsberg Fjord beds of the Ørsted Dal Member) in the Tait Bjerg area of the Jameson Land Basin, East Greenland, was sampled for paleomagnetic study and measured for cycle stratigraphie analysis. Paleomagnetic samples were also taken from the underlying Gipsdalen Formation in the Gipsdalen area. A high stability characteristic magnetization carried by hematite was successfully isolated in 63 sampling levels in the Fleming Fjord Formation and 9 sampling sites in the Gipsdalen Formation using progressive thermal demagnetization. The mean characteristic directions for the Herning Fjord and the Gipsdalen Formations may be be biased by sedimentary inclination error but are consistent with a northward drift of East Greenland of about 10° from the arid (ca. 25° N) to semihumid (ca. 35° N) paleoclimatic belts in the Middle to Late Triassic. Seven normal and reversed polarity intervals are clearly delineated in the Fleming Fjord Formation section. A preferred correlation of the magnetostratigraphy to a cyclostratigraphically calibrated reference polarity sequence recently derived from drill cores in the Newark Basin of eastern North America suggests that the sampled interval represents about a 3.5 m.y. interval of the late Norian. The Malmros Klint Member and the overlying Carlsberg Fjord beds have composite sedimentary cycles that vary in thickness from 25 m to about 1 m and seem to match Milankovitch orbital climatic cyclicity with periods of ~400ky, ~100ky, ~40ky, and ~20ky. The composition and thickness ratio of the cycles suggest that the measured section of the Malmros Klint Member and the Carlsberg Fjord beds represents lacustrine accumulation over about 4 m.y., a duration consistent with the magnetostratigraphic correlations.

Vertical water transport plays an important role in the development and maintenance of lakes in arid zones. However, previous study of this phenomenon has focused mainly on the effects of regional precipitation, rather than effects of groundwater recharge, on arid-zone environmental change. We selected a sedimentary profile from a seasonal lake basin located in the hinterland of the Badain Jaran Desert, northwestern China, to assess the Holocene environmental evolution of this region and its response to climate change. Our results show that peat deposition from 11 to 10 ka indicates humidification after Younger Dryas (YD) event; the lake sediment and lower EM2 and lower principal component analysis (PCA)-1 scores indicate relative more humid environment from 10 to 7.8 ka; the lake sediment and higher EM2 and higher PCA-1 scores indicate most humid environment from 7.8 to 5.8 ka; the transition from lacustrine facies to limnetic facies and increasing salinity indicate drying trend from 5.8 to 2.5 ka; the aeolian sand sediment and lowest EM2 and lowest PCA-1 scores indicate driest environment from 2.5 to 0.8 ka; and lacustrine facies and finest grain size indicate relative humid environment during the ‘Little Ice Age’ period. The environment was relative humid in early Holocene, most Humid in mid-Holocene, and dry in mid-late Holocene. The moisture pattern in the hinterland of the Badain Jaran Desert was synchronous with that in the northeastern of Tibetan Plateau, which implies that the groundwater recharge lake was dominated by the intensity of groundwater recharge from monsoon margin area, especially the northeastern of Tibetan Plateau. As a record from groundwater recharge lake without runoff, our study provides the groundwater output quantity record from northeastern of Tibetan Plateau and would benefit the environment change research and regional water resources allocation around the Tibetan Plateau.

The Late Palaeozoic – Mesozoic extensional basin complex of East Greenland contains a record of deposition during a period of Rhaetian – Early Bajocian thermal subsidence, the onset of rifting in the Late Bajocian, its growth during the Bathonian–Kimmeridgian, culmination of rifting in the Volgian – Early Ryazanian, and waning in the Late Ryazanian – Hauterivian. The area was centred over a palaeolatitude of about 45°N in the Rhaetian and drifted northwards to about 50°N in the Hauterivian. A major climate change from arid to humid subtropical conditions took place at the Norian–Rhaetian transition. Deposition was in addition governed by a long-term sea-level rise with highstands in the Toarcian–Aalenian, latest Callovian and Kimmeridgian, and lowstands in the latest Bajocian – earliest Bathonian, Middle Oxfordian and Volgian. The Rhaetian – Lower Bajocian succession is considered the upper part of a megasequence, termed J1, with its base in the upper Lower Triassic, whereas the Upper Bajocian – Hauterivian succession forms a complete, syn-rift megasequence, termed J2. The southern part of the basin complex in Jameson Land contains a relatively complete Rhaetian–Ryazanian succession and underwent only minor tilting during Middle Jurassic – earliest Cretaceous rifting. Rhaetian – Lower Jurassic deposits are absent north of Jameson Land and this region was fragmented into strongly tilted fault blocks during the protracted rift event. The syn-rift successions of the two areas accordingly show different long-term trends in sedimentary facies. In the southern area, the J2 syn-rift megasequence forms a symmetrical regressive–transgressive–regressive cycle, whereas the J2 megasequence in the northern area shows an asymmetrical, stepwise deepening trend. A total of eight tectonostratigraphic sequences are recognised in the Rhaetian–Hauterivian interval. They reflect major changes in basin configuration, drainage systems, sediment transport and distribution patterns, and in facies and depositional environments. The sequences are bounded by regional unconformities or flooding surfaces and have average durations in the order of 10 Ma. They are subdivided into conventional unconformity-bounded depositional sequences with durations ranging from tens of thousands of years, in the Milankovitch frequency band, up to several million years. Deposition was alluvial and lacustrine in the Rhaetian–Sinemurian, but almost exclusively marine during the Pliensbachian–Hauterivian time interval when a marine strait, up to 500 km wide and more than 2000 km long, developed between Greenland and Norway, connecting the Arctic Sea and the North Sea. Coal-bearing fluvial and paralic deposits occur, however, at the base of the onlapping Middle Jurassic succession in the central and northern part of the basin complex. The sedimentary development is similar to that in the Northern North Sea and on the Norwegian shelf, and East Greenland offers important onshore analogues for virtually all of the types of deeply buried Jurassic depositional systems of these areas and especially their hydrocarbon reservoirs.

Establishing robust environmental proxies at newly investigated terrestrial sedimentary archives is a challenge, because straightforward climate reconstructions can be hampered by the complex relationship between climate parameters and sediment composition, proxy preservation or (in)sufficient sample material. We present a minimally invasive hyperspectral bidirectional reflectance analysis on discrete samples in the wavelength range from 0.25 to 17 µm on 35 lacustrine sediment core samples from the Chew Bahir Basin, southern Ethiopia for climate proxy studies. We identified and used absorption bands at 2.2 μm (Al–OH), at 2.3 μm (Mg–OH), at 1.16 μm (analcime), and at 3.98 μm (calcite) for quantitative spectral analysis. The band depth ratios at 2.3/2.2 μm in the spectra correlate with variations in the potassium content of the sediment samples, which also reflect periods of increased Al-to-Mg substitution in clay minerals during drier climatic episodes. During these episodes of drier conditions, absorption bands diagnostic of the presence of analcime and calcite support this interpretation, with analcime indicating the driest conditions. These results could be compared to qualitative analysis of other characteristic spectral properties in the spectral range between 0.25 and 17 µm. The results of the hyperspectral measurements complement previous sedimentological and geochemical analyses, allowing us in particular to resolve more finely the processes of weathering in the catchment and low-temperature authigenic processes in the sediment. This enables us to better understand environmental changes in the habitat of early humans.