Alexey Krylov - Academia.edu (original) (raw)

Papers by Alexey Krylov

In the past few years sampling of deepwater seabed gained an increasingly important role in study... more In the past few years sampling of deepwater seabed gained an increasingly important role in studying geological structure of the Arctic Ocean. A common concept of virtually uninterrupted pelagic drape in the Amerasia Basin and exclusively ice-rafted nature of all clastic components that occur in bottom sediments was challenged by recent discoveries of bedrock exposures in the sea floor, while correlation of results of analytical study of bottom samples collected by the Russian expeditions in 2000, 2005 and 2007 with bathymetric environments at respective sites suggested that certain dredged and cored coarse rock fragments appeared meaningful for bedrock characterization if even the source subpelagic outcrop was not positively documented. The first results of age determinations of detrital zircons that were extracted from coarse fragments of lithic sedimentary rocks resting on the seabed and in the immediate sub-bottom, as well as of zircons from fragments of magmatic/metamorphic rocks and of zircon grains separated directly from sub-pelagic unlithified sediments are in agreement with published interpretations of the Lomonosov Ridge bedrock as composed of Mesozoic terrigenous sequences; the presence of an older Neoproterozoic(?) -Early-Middle Paleozoic basement is also possible. The Mendeleev Rise bedrock, too, is believed to mainly consist of Paleozoic-Early(?) Mesozoic sedimentary superstructure that may locally rest on the Earliest Paleozoic or even older units. Basaltic rocks likely to originate from the High Arctic Large Igneous Province (HALIP) has not so far been found among the collected fragments but limited loose zircon grains probably derived from broadly contemporaneous magmatic products were recorded in sub-pelagic sediment along with dropstones of variably metamorphosed Precambrian mafic and granitoid rocks.

The Amundsen Basin is a part of the Eurasian Basin located between the Gakkel and Lomonosov ridge... more The Amundsen Basin is a part of the Eurasian Basin located between the Gakkel and Lomonosov ridges. It was formed due to ocean floor spreading during Cenozoic. Because of the difficult accessibility, the Amundsen Basin is poor studied by geological and geophysical methods. The results of ACEX (IODP-302) drilling on the Lomonosov Ridge became certain breakthrough in understanding of its geology.

Oceanology, 2008

... The St. Anna Trough is the larg-est of them. It is located in the northwestern part of the Ka... more ... The St. Anna Trough is the larg-est of them. It is located in the northwestern part of the Kara Sea and is limited by Frantz Josef Land, the Cen-tral Kara Rise, and the northern island of the Novaya Zemlya Archipelago (Fig. ... Anna Trough (Kara Sea) ...

Geo-Marine Letters, 2010

Detailed lithological, biogeochemical and molecular biological analyses of core sediments collect... more Detailed lithological, biogeochemical and molecular biological analyses of core sediments collected in 2002-2006 from the vicinity of the Malenky mud volcano, Lake Baikal, reveal considerable spatial variations in pore water chemical composition, with total concentrations of dissolved salts varying from 0.1 to 1.8‰. Values of methane δ 13 С in the sediments suggest a biogenic origin (δ 13 С min . −61.3‰, δ 13 С max. −72.9‰). Rates of sulphate reduction varied from 0.001 to 0.7 nmol cm −3 day −1 , of autotrophic methanogenesis from 0.01 to 2.98 nmol CH 4 cm −3 day −1 , and of anaerobic oxidation of methane from 0 to 12.3 nmol cm −3 day −1 . These results indicate that methanogenic processes dominate in gas hydrate-bearing sediments of Lake Baikal. Based on clone libraries of 16S rRNA genes amplified with Bacteria-and Archaea-specific primers, investigation of microbial diversity in gas hydrate-bearing sediments revealed bacterial 16S rRNA clones classified as Deltaproteobacteria, Gammaproteobacteria, Chloroflexi and OP11. Archaeal clone sequences are related to the Crenarchaeota and Euryarchaeota. Baikal sequences of Archaea form a distinct cluster occupying an intermediate position between the marine groups ANME-2 and ANME-3 of anaerobic methanotrophs. T. I. Zemskaya (*) : T. V. Pogodaeva : O. V. Shubenkova :

Doklady Earth Sciences, 2011

Studies in the Amundsen Basin have revealed six seismostratigraphic complexes (SSCs) in this regi... more Studies in the Amundsen Basin have revealed six seismostratigraphic complexes (SSCs) in this region. The horizons bounding these complexes were dated by identifying the linear magnetic anomalies. The recognized SSCs are correlated with the seismostratigraphic and lithostratigraphic units of Lomonosov Ridge. Based on these correlations, the lithological composition of SSCs in the Amundsen Basin is suggested. The formation of SSC2 is supposed to be due to the diagenetic processes associated with the conversion of opal A to opal CT. It is found that, generally, the rate of sedimentation in the Amundsen Basin has consis tently decreased since the beginning of its formation. However, in the Hattian time, the global regression resulted in a sharp increase in the rate of sedimentation in the basin. Arguments in favor of the duration of the Middle Cenozoic sedimentary hiatus on Lomonosov Ridge reduced to 16.3 Ma are presented. It is supposed that the decrease in the intensity of oceanic crustal accretion in the Eurasian Basin, which is identified by the slowdown in the rate of its opening in the interval from 46 to 20-23 Ma might have resulted in a gradual decline in the sea level of the Arctic Ocean isolated from the World Ocean. This fact probably accounts for Lomonosov Ridge having remained dominated by subaerial conditions over the period from 36.7 to 20.4 Ma ago.

The Arctic Coring Expedition (ACEX) penetrated over 400 m of Cenozoic sediments from the central ... more The Arctic Coring Expedition (ACEX) penetrated over 400 m of Cenozoic sediments from the central part of the Lomonosov Ridge in the Arctic Ocean. The pervasive occurrence of dropstones and sand lenses in the Neogene ACEX sediments, which clearly are of terrigeneous origin, must have been brought to this mid-oceanic location by sea-ice and icebergs. Critical to understanding the paleoclimate history of the Arctic is a reconstruction of the magnitude and timing of the occurrence of perennial sea-ice. Unambiguously determining whether or not the sea-ice was seasonal or perennial is a challenging undertaking. One approach to addressing this challenge is to determine the source areas of the mineral assemblages that were deposited at the ACEX drill site. To establish the source areas for the terrigeneous material, the mineralogical composition of the upper 300 m of drilled sequence was investigated. Heavy and clay mineral associations indicate a major and consistent shift in provenance that occurs across a boundary at ca. 156 meters below seafloor. This boundary defines a change in source region from the Barents-Kara-western Laptev Sea, identified by the presence of common clinopyroxene and smectite below 156 m, to the eastern Laptev-East Siberian seas above 156 m, identified by common hornblende (amphibole) and illite. Bccause of the geographic distance, sea-ice originating from the eastern Laptev-East Siberian seas source region would have survived at least one summer melt cycle in order to reach the ACEX drill site, based on modern sea-ice trajectories and velocities. This shift in mineral assemblages, and thus source areas, is interpreted to represent the onset of a perennial sea-ice cover in the Arctic Ocean, which occurred at about 13 Ma, indicating a coeval cooling in the Arctic and Antarctic regions.

ABSTRACT This study focuses on the determination of potential source areas for the terrigenous ma... more ABSTRACT This study focuses on the determination of potential source areas for the terrigenous material derived from Eurasia and North America to reconstruct the glacial/interglacial variability and sedimentary processes in the Amerasian Basin of the Arctic Ocean during late Quaternary times. The research is based on marine sediment core PS72/340-5 recovered during the ARK-XXIII/3 (2008) Expedition of RV "Polarstern" at the eastern flank of the Mendeleev Ridge in the Chukchi Abyssal Plain (Stein et al., 2010). Stratigraphical framework for cores is constrained using paleomagnetic parameters (relative paleointensity, inclination) and foraminiferal data (abundances, stable isotope composition), calibrated by radiocarbon ages in the uppermost part of the core. Additional age control is provided by correlation with other dated cores from the Mendeleev Ridge (e.g. HLY0503-8JPC, Adler et al., 2009). Bulk mineral composition and petrography of rock clasts were utilized to distinguish sediment source areas. Factor analysis was used to determine, whether the composition of our complex mineralogical data set is composed of a limited number of contributing factors (or source areas). In order to distinguish between different agents of particle transportation such as icebergs, sea ice and currents, we study the grain-size distribution of the sediments. Trends in mineralogical composition were compared to the grain-size distribution in order to attribute the provenance changes to different transportation mechanisms in variable sedimentary environments. Based on comparison with the numerous studies of mineral compositions of surface samples from the Arctic Ocean, we can distinguish two major sources of incoming terrigenous material: East Siberian Sea (ESS) versus Canadian Arctic Archipelago (CAA). Mineralogical differences in cores are associated with distribution of gravel and finer fractions in sediments. Mineral composition of intervals with high contents of finer fractions is dominated by clay minerals from ESS, thus, indicating sea-ice transport. Sediment material supplied from CAA is characterized by high contents of coarse fraction > 0.5 mm which is indicative of iceberg transport. We discuss the timing of ice-rafted events based on our age model.

In the past few years sampling of deepwater seabed gained an increasingly important role in study... more In the past few years sampling of deepwater seabed gained an increasingly important role in studying geological structure of the Arctic Ocean. A common concept of virtually uninterrupted pelagic drape in the Amerasia Basin and exclusively ice-rafted nature of all clastic components that occur in bottom sediments was challenged by recent discoveries of bedrock exposures in the sea floor, while correlation of results of analytical study of bottom samples collected by the Russian expeditions in 2000, 2005 and 2007 with bathymetric environments at respective sites suggested that certain dredged and cored coarse rock fragments appeared meaningful for bedrock characterization if even the source subpelagic outcrop was not positively documented. The first results of age determinations of detrital zircons that were extracted from coarse fragments of lithic sedimentary rocks resting on the seabed and in the immediate sub-bottom, as well as of zircons from fragments of magmatic/metamorphic rocks and of zircon grains separated directly from sub-pelagic unlithified sediments are in agreement with published interpretations of the Lomonosov Ridge bedrock as composed of Mesozoic terrigenous sequences; the presence of an older Neoproterozoic(?) -Early-Middle Paleozoic basement is also possible. The Mendeleev Rise bedrock, too, is believed to mainly consist of Paleozoic-Early(?) Mesozoic sedimentary superstructure that may locally rest on the Earliest Paleozoic or even older units. Basaltic rocks likely to originate from the High Arctic Large Igneous Province (HALIP) has not so far been found among the collected fragments but limited loose zircon grains probably derived from broadly contemporaneous magmatic products were recorded in sub-pelagic sediment along with dropstones of variably metamorphosed Precambrian mafic and granitoid rocks.

The Amundsen Basin is a part of the Eurasian Basin located between the Gakkel and Lomonosov ridge... more The Amundsen Basin is a part of the Eurasian Basin located between the Gakkel and Lomonosov ridges. It was formed due to ocean floor spreading during Cenozoic. Because of the difficult accessibility, the Amundsen Basin is poor studied by geological and geophysical methods. The results of ACEX (IODP-302) drilling on the Lomonosov Ridge became certain breakthrough in understanding of its geology.

Oceanology, 2008

... The St. Anna Trough is the larg-est of them. It is located in the northwestern part of the Ka... more ... The St. Anna Trough is the larg-est of them. It is located in the northwestern part of the Kara Sea and is limited by Frantz Josef Land, the Cen-tral Kara Rise, and the northern island of the Novaya Zemlya Archipelago (Fig. ... Anna Trough (Kara Sea) ...

Geo-Marine Letters, 2010

Detailed lithological, biogeochemical and molecular biological analyses of core sediments collect... more Detailed lithological, biogeochemical and molecular biological analyses of core sediments collected in 2002-2006 from the vicinity of the Malenky mud volcano, Lake Baikal, reveal considerable spatial variations in pore water chemical composition, with total concentrations of dissolved salts varying from 0.1 to 1.8‰. Values of methane δ 13 С in the sediments suggest a biogenic origin (δ 13 С min . −61.3‰, δ 13 С max. −72.9‰). Rates of sulphate reduction varied from 0.001 to 0.7 nmol cm −3 day −1 , of autotrophic methanogenesis from 0.01 to 2.98 nmol CH 4 cm −3 day −1 , and of anaerobic oxidation of methane from 0 to 12.3 nmol cm −3 day −1 . These results indicate that methanogenic processes dominate in gas hydrate-bearing sediments of Lake Baikal. Based on clone libraries of 16S rRNA genes amplified with Bacteria-and Archaea-specific primers, investigation of microbial diversity in gas hydrate-bearing sediments revealed bacterial 16S rRNA clones classified as Deltaproteobacteria, Gammaproteobacteria, Chloroflexi and OP11. Archaeal clone sequences are related to the Crenarchaeota and Euryarchaeota. Baikal sequences of Archaea form a distinct cluster occupying an intermediate position between the marine groups ANME-2 and ANME-3 of anaerobic methanotrophs. T. I. Zemskaya (*) : T. V. Pogodaeva : O. V. Shubenkova :

Doklady Earth Sciences, 2011

Studies in the Amundsen Basin have revealed six seismostratigraphic complexes (SSCs) in this regi... more Studies in the Amundsen Basin have revealed six seismostratigraphic complexes (SSCs) in this region. The horizons bounding these complexes were dated by identifying the linear magnetic anomalies. The recognized SSCs are correlated with the seismostratigraphic and lithostratigraphic units of Lomonosov Ridge. Based on these correlations, the lithological composition of SSCs in the Amundsen Basin is suggested. The formation of SSC2 is supposed to be due to the diagenetic processes associated with the conversion of opal A to opal CT. It is found that, generally, the rate of sedimentation in the Amundsen Basin has consis tently decreased since the beginning of its formation. However, in the Hattian time, the global regression resulted in a sharp increase in the rate of sedimentation in the basin. Arguments in favor of the duration of the Middle Cenozoic sedimentary hiatus on Lomonosov Ridge reduced to 16.3 Ma are presented. It is supposed that the decrease in the intensity of oceanic crustal accretion in the Eurasian Basin, which is identified by the slowdown in the rate of its opening in the interval from 46 to 20-23 Ma might have resulted in a gradual decline in the sea level of the Arctic Ocean isolated from the World Ocean. This fact probably accounts for Lomonosov Ridge having remained dominated by subaerial conditions over the period from 36.7 to 20.4 Ma ago.

The Arctic Coring Expedition (ACEX) penetrated over 400 m of Cenozoic sediments from the central ... more The Arctic Coring Expedition (ACEX) penetrated over 400 m of Cenozoic sediments from the central part of the Lomonosov Ridge in the Arctic Ocean. The pervasive occurrence of dropstones and sand lenses in the Neogene ACEX sediments, which clearly are of terrigeneous origin, must have been brought to this mid-oceanic location by sea-ice and icebergs. Critical to understanding the paleoclimate history of the Arctic is a reconstruction of the magnitude and timing of the occurrence of perennial sea-ice. Unambiguously determining whether or not the sea-ice was seasonal or perennial is a challenging undertaking. One approach to addressing this challenge is to determine the source areas of the mineral assemblages that were deposited at the ACEX drill site. To establish the source areas for the terrigeneous material, the mineralogical composition of the upper 300 m of drilled sequence was investigated. Heavy and clay mineral associations indicate a major and consistent shift in provenance that occurs across a boundary at ca. 156 meters below seafloor. This boundary defines a change in source region from the Barents-Kara-western Laptev Sea, identified by the presence of common clinopyroxene and smectite below 156 m, to the eastern Laptev-East Siberian seas above 156 m, identified by common hornblende (amphibole) and illite. Bccause of the geographic distance, sea-ice originating from the eastern Laptev-East Siberian seas source region would have survived at least one summer melt cycle in order to reach the ACEX drill site, based on modern sea-ice trajectories and velocities. This shift in mineral assemblages, and thus source areas, is interpreted to represent the onset of a perennial sea-ice cover in the Arctic Ocean, which occurred at about 13 Ma, indicating a coeval cooling in the Arctic and Antarctic regions.

ABSTRACT This study focuses on the determination of potential source areas for the terrigenous ma... more ABSTRACT This study focuses on the determination of potential source areas for the terrigenous material derived from Eurasia and North America to reconstruct the glacial/interglacial variability and sedimentary processes in the Amerasian Basin of the Arctic Ocean during late Quaternary times. The research is based on marine sediment core PS72/340-5 recovered during the ARK-XXIII/3 (2008) Expedition of RV "Polarstern" at the eastern flank of the Mendeleev Ridge in the Chukchi Abyssal Plain (Stein et al., 2010). Stratigraphical framework for cores is constrained using paleomagnetic parameters (relative paleointensity, inclination) and foraminiferal data (abundances, stable isotope composition), calibrated by radiocarbon ages in the uppermost part of the core. Additional age control is provided by correlation with other dated cores from the Mendeleev Ridge (e.g. HLY0503-8JPC, Adler et al., 2009). Bulk mineral composition and petrography of rock clasts were utilized to distinguish sediment source areas. Factor analysis was used to determine, whether the composition of our complex mineralogical data set is composed of a limited number of contributing factors (or source areas). In order to distinguish between different agents of particle transportation such as icebergs, sea ice and currents, we study the grain-size distribution of the sediments. Trends in mineralogical composition were compared to the grain-size distribution in order to attribute the provenance changes to different transportation mechanisms in variable sedimentary environments. Based on comparison with the numerous studies of mineral compositions of surface samples from the Arctic Ocean, we can distinguish two major sources of incoming terrigenous material: East Siberian Sea (ESS) versus Canadian Arctic Archipelago (CAA). Mineralogical differences in cores are associated with distribution of gravel and finer fractions in sediments. Mineral composition of intervals with high contents of finer fractions is dominated by clay minerals from ESS, thus, indicating sea-ice transport. Sediment material supplied from CAA is characterized by high contents of coarse fraction > 0.5 mm which is indicative of iceberg transport. We discuss the timing of ice-rafted events based on our age model.