Lithological Record Research Articles

Production and abundance of macro-aggregate bed clasts from moderately consolidated cohesive beds and their implications for sediment management

ABSTRACT Flume-based research has demonstrated that large (> 1mm), high-water-content mud aggregates can be eroded from cohesive beds and transported in bedload. Studies have also documented these types of mud clasts preserved in the lithologic record. However, questions pertaining to the abundance of muddy bed aggregates and the physical properties that result in their production remain largely unaddressed. New flume experiments were conducted on materials from numerous locations of sediment management projects across the United States. Image analysis of eroded sediment particles demonstrated that macro-aggregated (> 250 μm) mud clasts were commonly produced in moderately consolidated sediment beds (1.2–1.5 g/cm3) with water content above the plastic limit. These macro-aggregates commonly account for more than 20% of the total eroded sediment mass. Physical properties commonly associated with cohesive behavior were evaluated for correlation to bed aggregate production and size. Clay content of the sediment bed was shown to have the greatest correlation to both macro-aggregate size and abundance.

Upper Ordovician carbon isotope chemostratigraphy and a high-resolution assessment of the Hirnantian Stage in the Baltic Sea subsurface

ABSTRACT Based on a new deep drilling on southern Gotland (Sweden), this study is the first to document the carbon isotope chemostratigraphy of the Upper Ordovician through lowermost Silurian sedimentary record from the central parts of the Baltic Sea subsurface. The lithological record of the Stora Sutarve core has similarities with adjacent successions in both the Viki core in the East Baltic area and the Borenshult core in the Swedish mainland. The core includes the Kahula (including 13 bentonites in the “Kinnekulle K-bentonite complex”), Hirmuse(?), Rägavere, Paekna, Jonstorp, Loka, Motala and Kallholn formations. Several of the internationally recognized upper Ordovician δ13C excursions have been identified in the core, including the Guttenberg Isotope Carbon Excursion (GICE), Moe excursion, Hirnantian Isotope Carbon Excursion (HICE), and an undefined early Silurian carbon isotope excursion, presumably the Early Aeronian Carbon Isotope Excursion (EACIE). We particularly address the microstratigraphy of the Hirnantian Stage and the finer details of the HICE, which is not fully complete and entirely confined to the 2.09-m-thick Loka Formation. This formation yields abundant, but low-richness brachiopod faunas characteristic of the Hirnantian Stage and is, based on erosional-depositional surfaces and facies, interpreted as reflecting interglacial warming and eustatic transgression related to ice-sheet contraction in Gondwana. Based on very dense carbon isotope sampling we identify four clusters of δ13C values that aid to define significant changes in the preserved record of the HICE and which may facilitate global correlation of the succession and the herein interpreted sea-level record.

Astronomical pacing of third-order sea-level sequences during the middle miocene in the northern south China sea

The Miocene Hanjiang Formation of the Pearl River Mouth Basin (PRMB) forms one of the most productive hydrocarbon reservoirs in China. Sparse biostratigraphic age control and limited dating hinder a thorough understanding of sea-level change and its sedimentary expression through this formation. To establish the relationship between third-order sea-level changes, their expression in the lithological record and astronomical forcing, a sequence stratigraphic and cyclostratigraphic analysis has been conducted through the Hanjiang Formation in the LF14 borehole. One second-order sequence and six third-order sequences are recognized based on gamma ray (GR) data, vertical lithofacies changes and sedimentary stacking patterns. Time series analysis of the GR data and subsequent interpretation allows recognition of approximately eighteen 405 kyr long eccentricity cycles. Based on this cyclostratigraphy, we constructed a ∼7.22-Myr floating astronomical time scale (ATS) for the Hanjiang Formation. We anchored this timescale to globally significant biostratigraphic events preserved in the basin to build an absolute ATS spanning 17.423 ± 0.4 to 10.221 ± 0.4 Ma. A prominent ∼1.2-Myr periodicity is identified in the amplitude modulation (AM) envelope curves of ∼41-kyr obliquity cycles preserved in the record. This ∼1.2-Myr periodicity shows good agreement with our sequence stratigraphic analysis and global eustatic curves. Our results suggest that ∼1.2-Myr obliquity AM was the main driver of third-order sea-level change and sequence development in the PRMB. Combined application of cyclostratigraphic and sequence stratigraphic analysis (utilizing INPEFA and wavelet transform methods) are demonstrated to be useful for understanding the drivers and subdivisions of third-order sequence evolution on a regional scale.

Formation lithology predictions based on measurement while drilling (MWD) using gradient boosting algorithms

Many subsurface engineering applications require petrophysical and geomechanical properties as inputs for estimating the recoverable hydrocarbon volume and the reservoir deformation and properties' change during the life cycle of the production. Well log data plays a key role in estimating these reservoir properties, including volumes of minerals, Young's Modulus, and Poisson's Ratio. A conventional workflow using a multi-mineral petrophysical inversion model based on core-log integration requires an a priori rock-fluid model; therefore, it is often unavailable in reservoirs of complex minerals, such as carbonate or unconventional fields. In addition, most unconventional wells do not acquire Logging While Drilling (LWD) and/or wireline logs due to economic constraints or borehole instability reasons. Available measurements for these wells are typically Measurement While Drilling (MWD) Gamma Ray (GRMA) logs along with drilling dynamics measurements including Surface Weight-On-Bit (SWOB), Rate Of Penetration (ROP), Torque (TQA), Revolutions Per Minute (RPM), and the differential pressure. Thus, in this study, we demonstrate a machine learning approach, which does not require an a priori model, to predict formation lithologies based on conventional MWD and wireline well logs.We applied the Extreme Gradient Boosting Regression (XGBR) method to simultaneously predict the weight fractions of 5 minerals: QFM (Quartz-Feldspar-Mica), carbonate, clays, pyrite, and siderite from drilling dynamics measurements. The XGBR algorithm was tested with datasets from four adjacent wells in the Volve Field, located in the North Sea. A total of 10,575 data points were used to train and validate the model. The trained model was then applied to the blind test dataset of 10,446 data points from the same field. Lithology predictions from the trained model yield excellent results of weight concentrations with Root-Mean-Square Errors (RMSE) of 6.01 and 7.44% for training and test datasets, respectively. The prediction results agree with the lithology obtained from the Elemental Capture Spectroscopy (ECS) data as well as the dominant lithology record from rock cuttings. With the developed model, lithologic information and sonic logs of the formation could be predicted with MWD data, which could ultimately help optimize real-time drilling and completion operations in the field.

Total organic carbon variability of lower Jurassic successions in the Mandawa Basin, SE Tanzania

Over many decades, an understanding of total organic carbon (TOC) variability in various sedimentary basins has been constrained by the availability of suitable samples for geochemical analysis. Many attempts rely on selected sidewall core or cuttings samples, which do not provide a continuous lithological record of the succession. As a result, TOC variability as a response to facies evolution is often underestimated. An advancement in TOC evaluation from well logging techniques often has permitted a continuous analysis of source rock intervals, while eliminating issues associated with obtaining discrete physical samples. Geochemical and wireline geophysical logs investigation here aimed at constraining TOC variability and depositional conditions prevailing during the early Jurassic in the Tanzanian Mandawa Basin (Mbuo, Nondwa and Mihambia Formations), which to date are poorly documented. TOC was deduced from both well cuttings samples and wire log data. Depositional conditions were defined via the use of spectral Gamma-Ray (Th/U, U) logging and lithofacies data. Sediment composition and TOC from cuttings were compared to illustrate how organic matter distribution is influenced by changes in sediment type. Complex mineral composition of heterolithic facies dominated log-response, complicated log interpretation, and thus limited the effectiveness of well logging techniques to predict TOC. Cuttings data reveal three organic-rich intervals, i) at the transition of Upper Mbuo to basal Nondwa Formation with the highest TOC of 3.5 (wt%), ii) in the Nondwa Formation with a TOC of 2 (wt%), and iii) in the Mihambia Formation with a TOC of 2.8 (wt%). An inverse linear relationship between Th/U and TOC signifies relatively shallow deposition in a well-mixed water column under oxic conditions. Intervals with higher TOC imply organic matter preservation under suboxic conditions upon two marine incursions in the Mihambia and Nondwa Formations, whereas a limnic environment prevailed at the Upper Mbuo to Nondwa transition. Inverse trends in TOC versus clastic components, a positive linear relationship between TOC and carbonates, and higher amount of clastics (>57 wt%) in the Mbuo and Mihambia Formations suggest a dominantly clastic sedimentary system with relatively stable carbonate and organic matter input in proximity to the source area. We, therefore, argue that the organic rich intervals observed in the Upper Mbuo, Nondwa and Mihambia Formations were deposited during periods of higher organic productivity driven by a rise in eustatic sea level, and coincide with a decline in terrigenous input from the hinterland.

ГЕОДИНАМІКА

Purpose. The objective of this study is the investigation of the Silurian-Lower Devonian (Lochkovian) carbonate-clay sedimentary complex of the southwestern slope of the East-European platform. Its formation was the result of a single cycle of geodynamic and sedimentary events in the lithological record of the southern continental margin of Baltica. Methodology. The study is based on well-logs correlation, lithological and geochemical investigations of core samples, and petrographic thin sections analysis. The obtained results were used to establish patterns of changes in the material composition of the studied strata in time and space in order to determine the basin development dynamics of the continental margin of the Eastern European platform southwestern slope in the Silurian-Early Devonian. Results. It is established that the formation of the carbonate-clay sequence represents a single sedimentary cycle and was the result of a complex of geodynamic, depositional and paleoclimatic events that took place on the Baltica southern continental margin. The Silurian period was characterized by intensive development of benthic organisms and reef structure formation in the proximal part of the basin and clay-carbonate muds enriched with dispersed organic matter in its distal part. In the Early Devonian, carbonate biogenic sedimentation continued throughout the basin. The carbonate maximum content (80–98%) proves the existence of the reef constructions in the basin sedimentary record. Lower values of carbonate content are characteristic of marls (40–55%) and biodetritic limestones (56–75%), which make up the main part of the Silurian sequence. There are no reef constructions in the section of the Lochkovian stage of Devonian, and the calcium carbonate content in the rocks varies from 45 to 83%. The content of CaCO3 in mudstones and calcareous mudstones of the Silurian varies from 5 to 15%. Originality. The applied complex of lithological, geochemical, geological-geophysical and paleogeographic investigations allowed studying the sedimentary basin dynamics in the Silurian-Early Devonian with the assessment of the possibility of participation of these strata in oil and gas hydrocarbons generation. Practical significance. The obtained results show that the carbonate-clay complex of sedimentary rocks of the Silurian and Lower Devonian (Lochkovian) of the studied region can be considered as a separate petroleum system, including source rocks, reservoir rocks and possible conventional and unconventional oil and gas accumulations.

Holocene Environmental Dynamics of the Lago Cochrane/Pueyrredón Valley, Central West Patagonia (47°S)

Deglaciation modeling of the Patagonian Ice Field since the Last Glacial Maximum has been a topic of intensive research in Central West Patagonia (44°–49°S). However, the chronology of deglaciation onset, acceleration, and the subsequent thinning and recession of the different ice lobes as well as the timing and extension of large proglacial systems are still a matter of discussion. The maximum eastward extension the Lago Cochrane/Pueyrredón ice lobe was around ∼20,000–27,000 cal yrs BP; its associated proglacial lake drained toward the Pacific between 12,600 and 8,000 cal yrs BP. This study presents the first two pollen and charcoal records from the Lago Cochrane/Pueyrredón valley, spanning the last 11,650 cal yrs BP. The Laguna Maldonado record spans between 11,650 and 8,500 cal yrs BP, while the Laguna Anónima record the last 8,500 cal yrs BP, thereby overlapping chronologically. The lithological record of Laguna Maldonado shows that organic sedimentation began at the onset of the Holocene (11,650 cal yrs BP), once the site was free of glacio-lacustrine influence. Between 11,650 and 10,500 cal yrs BP, an open Nothofagus forest developed associated with high fire occurrence/frequency, followed by a transitional phase to a closer forest associated with a shift from low to high fire activity up to 9,400 cal yrs BP. Between 9,400 and 8,500 cal yrs BP, the Laguna Maldonado record suggests the development of an open forest or probably scattered patches of forest of variable size in a steppe matrix, probably related to geomorphological and paraglacial dynamics as well as climatic forcings, while the Laguna Anónima record indicates the development of a closed Nothofagus forest and high to low fire occurrence/frequency from 8,200 to 3,800 cal yrs BP. Since 3,800 cal yrs BP, a highly dynamic open forest or forest patches scattered in a grass/shrub–grass steppe matrix occurred around Laguna Anónima associated with high fire occurrence/frequency synchronous with an important increase in the presence of hunter-gatherers during the last 3,000 years. The results from the Lago Cochrane/Pueyrredón valley are integrated and discussed at the regional scale alongside other records from Central West Patagonia.

Microbially Induced Sedimentary Structures in Clastic Deposits: Implication for the Prospection for Fossil Life on Mars.

Abundant and well-preserved fossil microbenthos occurs in siliciclastic deposits of all Earth ages, from the early Archean to today. Studies in modern settings show how microbenthos responds to sediment dynamics by baffling and trapping, binding, biostabilization, and growth. Results of this microbial-sediment interaction are microbially induced sedimentary structures (MISS). Successful prospection for rich MISS occurrences in the terrestrial lithological record requires unraveling genesis and taphonomy of MISS, both of which are defined only by a narrow range of specific conditions. These conditions have to coincide with high detectability which is a function of outcrop quality, bedding character, and rock type. Assertions on biogenicity of MISS morphologies must be based on the presence of microbially induced sedimentary textures (MIST), which are MISS-internal textures comprising replacement minerals arranged into microscopic biological morphologies, ancient carbonaceous matter, trace fossils, and geochemical signals. MISS serve as possible templates for the decryption of ancient life-processes on Mars. This article closes with a perspective on selected deposits and ancient environments in Meridiani Planum, Gale Crater, and Jezero Crater, Mars, regarding their potential for MISS occurrences. The earlier hypothesis of structures on Mars as potentially being MISS is revised.

The stratigraphy of latest Devonian and earliest Carboniferous rocks in Ireland

Thick successions of latest Devonian and early Carboniferous siliciclastic rocks of fluviatile and shallow marine origin are well exposed in numerous coastal sections in the south of Ireland. Correlations based on palynostratigraphy demonstrate that an overall northward transgression, in detail consisting of several fluctuations of relative sea level, resulted in the replacement of fluvial coastal plain environments by shallow marine conditions. The most conspicuous lithological record of transgression occurred at or close to the base of the Carboniferous, when a regionally distributed mudstone deposited in a shallow sea, replaced the generally sandy strata that had prevailed in the latest Devonian. There is no evidence for very large glacioeustatic changes of sea level related to the coeval western Gondwanan glaciation. Of the three horizons for a new GSSP for the base of the Carboniferous currently under review, the base of the Protognathodus kuehni Zone/basal Siphonodella sulcata Zone and coastal plant extinction is the most easily applied in Ireland and can be identified using palynology and corresponds to an easily recognised, extensively developed lithological change in the south of the country.

Lower Cretaceous Provenance and Sedimentary Deposition in the Eastern Carpathians: Inferences for the Evolution of the Subducted Oceanic Domain and its European Passive Continental Margin

AbstractReconstructing orogenic systems made up dominantly by sediments accreted in trenches is challenging because of the incomplete lithological record of the subducted oceanic domain and its attached passive continental margin thrusted by collisional processes. In this respect, the remarkable ~600 km long continuity of sediments exposed in the Eastern Carpathian thin‐skinned thrust and fold belt and the availability of quantitative reconstructions for adjacent continental units provide excellent conditions for a paleogeographical study by provenance and sedimentological techniques constraining sediment routing and depositional systems. These sediments were deposited in the Ceahlău‐Severin branch of the Alpine Tethys Ocean and over its European passive continental margin. We report sedimentological, paleomagnetic, petrographic, and detrital zircon U‐Pb data of Lower Cretaceous sediments from several thin‐skinned tectonic units presumably deposited in the Moldavides domain of the Eastern Carpathians. Sedimentological observations in the innermost studied unit demonstrate that deposition took place in a deepwater basin floor sheets to sandy turbidite system. Detrital zircon age data demonstrate sourcing from internal Carpathian basement units. The sediment routing changes in more external units, where black shales basin floor sheets to sandy mud turbidites were sourced from an external, European continental area. Although some degree of mixing between sources located on both margins of the ocean occurred, constraining a relatively narrow width of the deep oceanic basin, these results demonstrate that the internal‐most studied unit was deposited near an Early Cretaceous accretionary wedge, located on the opposite internal side relative to the passive continental margin domain of other Moldavides units.

PALYNOLOGY AND CHEMOSTRATIGRAPHY OF MIDDLE TRIASSIC SUCCESSIONS IN NORTHERN SWITZERLAND (WEIACH, BENKEN, LEUGGERN) AND SOUTHERN GERMANY (WEIZEN, FREUDENSTADT)

New Anisian to Ladinian palynology, palynofacies and stable carbon isotope records are reported for the Middle Triassic from deep Swiss wells (Weiach, Benken, Leuggern), well B3/13 (Weizen, S-Germany) and the type area of the Freudenstadt Formation in southern Germany. A wide spectrum of moderately to well-preserved palynomorphs represent a high Middle Triassic plant diversity. Based on the distribution of diverse spore-pollen assemblages five Anisian Palynozones (A–E) and two Ladinian ones (F, G) are differentiated. Throughout these Palynozones the occurrence of spores and pollen, assigned to plant groups so far known only from the Palaeozoic, shed a new light on the evolution of plant assemblages during the Triassic. The comparison of Palynozones A–G with palynostratigraphic schemes from the central part of the Germanic Basin and from the Tethyan realm demonstrate the regional variability of marker species ranges – especially for the Anisian. n agreement with the lithological record, two prominent transgressive events (Lower Muschelkalk, Upper Muschelkalk) are indicated by increased abundances of marine particulate organic matter in palynofacies data. Marginal marine influence is documented at the base of the studied interval, comprising the Buntsandstein and the base of the Lower Muschelkalk. Carbonate carbon isotopes data show a negative shift at the boundary between lower and middle Muschelkalk. Coincidently, a prominent change in relative abundances of climate-sensitive plant groups (e.g. Triadispora spp. vs. Pteridophytes) indicate a change to relatively dryer climatic conditions during the middle Muschelkalk.

Cretaceous–Paleogene Boundary in the Sequences of the Northeastern Caucasus, Dagestan: Sedimentology, Geochemistry, and Biota

The results of integrated study of the Cretaceous/Paleogene transition in the northeastern Caucasus are reported. The lithological, geochemical and micropaleontological characteristics of the sediments from two sections (Okhli and Gubden, Mountainous Dagestan) accumulated in different parts of paleobasin are displayed. An analysis of nannofossil distribution at the Cretaceous/Paleogene transition allowed to define the stratigraphic position of the stage boundary and reveal the interval of sediments (1–2 m thick transitional zone) accumulated under stress conditions. The large-scale sea-level fall occurred at the onset of the Cretaceous/Paleogene boundary event is evidenced. It led to the erosion and redeposition of the Maastrichtian calcareous sediments. In Okhli section, the occurrence of palygorskite is detected in the clay mineral assemblage of the transitional zone. The local concentrations of coprolites (Decapoda?) and spherical nodules of different composition (more likely, concretions) are found in the clay layer onlapping the erosional surface at the top of Maastrichtian. There is no reliable evidence of the impact nature of these nodules. The lithological record at the Cretaceous/Paleogene transition of the studied sections is similar to those exposed in other areas of the NE Peri-Tethys (e.g., southern Turkmenistan and Mangyshlak Peninsula).

Climate cycles in the southern Levant and their global climatic connections

The history of Levant paleo-hydrology, which is expressed by the absolute water level record of the Dead Sea over the last 70 kyrs, has been shown to be closely coupled with global climate patterns, and specifically argued to be modulated by northern hemisphere climate systems. Here, this coupling is rigorously tested and the absolute lake level curve is compared with a variety of globally distributed climate archives and used to deconvolve the processes controlling regional climate and hydrology. Considering that different archives are based on different sampling resolutions, and hence might have inherently different recording sensitivities, each of the chosen archives was interpolated and then smoothed at varying temporal resolutions. The synthetic curves, ranging between temporal smoothing resolutions between 10 years and 15 kyrs were compared to the similarly processed lake level record over the last 60 kyrs. The best fit to the Dead Sea lake level was found to be with Antarctica temperatures and atmospheric CO2 levels. Greenland temperatures and proximal archives such as the Soreq Cave and the Dead Sea lithological record, all yielded weaker correlations to the lake level curve.An exception to the strong correlation between Levant climate and atmospheric CO2 concentrations, is observed during Marine Isotope Stage (MIS) 5e, at a time when the Dead Sea watershed was exposed to very weak Mediterranean westerly systems that imposed hyperarid conditions, and a superposition of southern derived systems that delivered short but intense precipitation to the region. At this time, Antarctic temperatures cross a temperature threshold beyond 1 °C above present. It is suggested that this exceptional warming phase induces a reorganization of global and regional climate systems influencing the Levant.These results have two important implications. The first is the understanding that global temperatures and atmospheric CO2 concentrations impose the first order control over Levant climate. The second, is that the Antarctic records can be used as synthetic lake level proxies, extending the absolute lake level curve to ca. 800 ka, compared with its current span of 70 kyrs. Considering the importance of the Dead Sea lake level curve as a regional paleo-climatic-hydrologic recorder, the new synthetic curve provides a prominent proxy of Levant hydro-climate history.

Extraterrestrial dust, the marine lithologic record, and global biogeochemical cycles

Extraterrestrial dust, the marine lithologic record, and global biogeochemical cycles

Eemian and Vistulian (Weichselian) paleoenvironmental changes: A multi-proxy study of sediments and mammal remains from the Ławy paleolake (Eastern Poland)

The Eemian-Vistulian developmental history of the Ławy paleolake (Eastern Poland) has been studied by analysing records of micro- (pollen, Cladocera, Ostracoda), macrofossils (molluscs, mammal remains), the lithological record and radiocarbon dating from a 5.30 m sediment core. At Ławy, in the Paterebo stream valley, well-preserved mammal fossil remains accompanied by organic deposits have also been investigated. The results of the multi-proxy analyses suggest explicitly that the climate was the main driving force of the changes in terrestrial and aquatic ecosystems, and in the geomorphological processes in the catchment. However, we propose that the water level fluctuations were also an important factor in the modification of the aquatic assemblages. Pollen, cladocerans, molluscs and ostracods from Ławy indicate the existence of a small, shallow, well-vegetated paleolake during the warm Eemian climate optimum. In the final phase of the Eemian the lake was transformed into a mire. In the Early Vistulian, the variable hydrological conditions were the main driver force for the development of the study area. Finally the existence of the basin at Ławy was closely associated with periodic coexistence of limnic, telmatic and river environments.

A record of astronomically forced climate change in a late Ordovician (Sandbian) deep marine sequence, Ordos Basin, North China

The late Ordovician Pingliang Formation on the southwestern margin of the Ordos Basin, North China, consists of rhythmic alternations of shale, limestone, and siliceous beds. To explore the possible astronomical forcing preserved in this lithological record, continuous lithological rank and magnetic susceptibility (MS) stratigraphic series were obtained from a ~34m thick section of the Pingliang Formation at Guanzhuang. Power spectral analysis of the MS and rank series reveal 85.5cm to 124cm, 23cm to 38cm, and 15cm to 27cm thick sedimentary cycles that in ratio match that of late Ordovician short eccentricity, obliquity and precession astronomical cycles. The power spectrum of the MS time series, calibrated to interpreted short orbital eccentricity cycles, aligns with spectral peaks to astronomical parameters, including 95kyr short orbital eccentricity, 35.3kyr and 30.6kyr obliquity, and 19.6kyr and 16.3kyr precession cycles. The 15cm to 27cm thick limestone–shale couplets mainly represent precession cycles, and siliceous bed deposition may be related to both precession and obliquity forcing. We propose that precession-forced sea-level fluctuations mainly controlled production of lime mud in a shallow marine environment, and transport to the basin. Precession and obliquity controlled biogenic silica productivity, and temperature-dependent preservation of silica may have been influenced by obliquity forcing.

The Outwash Plain Of The Rospuda River Valley – A Record Of Depositional Environments

Abstract The Rospuda subglacial channel hosts not only deep ribbon lakes and the Rospuda River itself, but also an outwash plain. The paper deals with a lithofacies analysis of deposits from exposures within the Rospuda outwash plain. With the support of geomorphological and geological analyses, it has been found that the outwash plain formed along the Rospuda subglacial channel that was being exposed from under the ice cover. The lithological record of the Rospuda outwash plain shows a distinct division into a proximal and a distal zone. The deposits under study reveal a record of a break in basial sedimentation, when ice-wedge casts developed under conditions of periglacial climate. The development of the Rospuda outwash plain is linked with the ice-marginal zone of the Pomeranian phase, similarly to the Olecko-Rajgród outwash plain that is located to the west.

GEOLOGICAL- AND CHEMICAL-PALEOOCEANOGRAPHIC ASPECTS OF SEDIMENTOGENESIS OF THE СARPATHIAN-BLACK SEA SEGMENT OF TETHYS OCEAN

This study represents a scientific synthesis of the results of authors’ investigations on the problem «Geological and chemical paleooceanography of Carpathian-Black Sea segment of the Tethys ocean». Examination of sedimentary processes, which took place within the ancient continental margin, allowed studying of the maim features of terrigenous, edaphogenic and biogenic sedimentation and identifying in the lithological record of Precambrian-Phanerozoic a series of anoxic events, with which a range of mineral resources is related in the region under study. Analysis of data on geological and geochemical nature of the present-day upwelling in the World Ocean and obtained results on the nature of the upwelling process in the Tethyan part of the Carpathian-Black Sea region in Mesozoic-Cenozoic allowed distinguishing among the existing sedimentary formations of marine (oceanic) range a separate genetic type – «upwelling formation», which is suggested to be introduced into the doctrine about the sedimentary deposits, and this new scientific direction in geological paleooceanography to distinguish under the term «upwelling geology» and consider it as an original part of the Earth sciences.

Multiple early Holocene climate oscillations at Silver Lake, New Jersey and their possible linkage with outburst floods

Episodic discharges from the Laurentide Ice Sheet are considered to be one of the major causes of climate oscillations during the glacial to interglacial transition. These outburst floods disrupted thermohaline circulation and might have caused cooling events in the North Atlantic region and beyond, including the Younger Dryas, Preboreal Oscillation, and 8.2-ka events. However, few terrestrial sedimentary records show regional climate changes directly linked to outburst floods during the early Holocene. Here we present lithologic and isotopic data from Silver Lake in northern New Jersey to document temperature and moisture changes during the early Holocene and to discuss possible linkage with outburst flooding events. The lithologic record shows multiple intervals with coupled decreases in carbonate and increases in organic matter during the early Holocene, suggesting lower lake levels and drier climate conditions. Simultaneous with these changes were decreases in carbonate δ18O values, likely reflecting a decrease in air temperature during these dry periods. The apparent correlation of these sedimentary events at Silver Lake with documented outburst floods from the melting ice sheet suggests a possible causal connection, implying that the climate in the Mid‐Atlantic region was extremely sensitive to perturbations of ocean circulation.

Late Holocene change in climate and atmospheric circulation inferred from geochemical records at Kepler Lake, south-central Alaska

Climate records during the last millennium are essential in placing recent anthropogenic-induced climate change into the context of natural climatic variability. However, detailed records are still sparse in Alaska, and these records would help elucidate climate patterns and possible forcing mechanisms. Here we present a multiple-proxy sedimentary record from Kepler Lake in south-central Alaska to reconstruct climatic and environmental changes over the last 800 years. Two short cores (85 and 101 cm long) from this groundwater-fed marl lake provide a detailed stable isotope and sediment lithological record with chronology based on four AMS 14C dates on terrestrial macrofossils and 210Pb analysis. The δ18O values of inorganic calcite (CaCO3) range from −17.0 to −15.7 ‰, with the highest values during the period of 1450–1850 AD, coeval with the well-documented Little Ice Age (LIA) cold interval in Alaska. The high δ18O values during the cold LIA are interpreted as reflecting shifts in atmospheric circulation. A weakening of the wintertime Aleutian low pressure system residing over the Gulf of Alaska during the LIA would have resulted in 18O-enriched winter precipitation as well as a colder and possibly drier winter climate in south-central Alaska. Also, elevated calcite contents of >80 % during the LIA reflect a lowering of lake level and/or enhanced seasonality (warmer summer and colder winter), as calcite precipitation in freshwater lakes is primarily a function of peak summer temperature and water depth. This interpretation is also supported by high δ13C values, likely reflecting high aquatic productivity or increased residence times of the lake water during lower lake levels. The lower lake levels and warmer summers would have increased evaporative enrichment in 18O, also contributing to the high δ18O values during the LIA. Our results indicate that changes in atmospheric circulation were an important component of climate change during the last millennium, exerting strong influence on regional climate in Alaska and the Arctic.