Recent research suggests that major meteorite impact events into a Late Hesperian/Early Amazonian ocean likely produced a mega‐tsunami that would have resurfaced coastal areas in northwestern Arabia ...Terra. The orientations of the associated lobate deposits, a conspicuous type of landforms called Thumbprint Terrain, suggests that if an impact event triggered the mega‐tsunami, the most likely location of the source crater is within the northern plains regions situated north of Arabia Terra. This study focuses on the identification of impact craters that impacted into the ocean and are likely to have produced the tsunami. We selected 10 complex impact craters, based on their diameters, location, and geomorphic characteristics. Of those, the Late Hesperian ~120‐km‐diameter Lomonosov crater exhibits a unique topographic plan view asymmetry (compared to other similar‐sized and similar‐aged craters in the northern plains such as Micoud, Korolev, and Milankovic). We attribute its broad and shallow rim, in part, to an impact into a shallow ocean as well as its subsequent erosion from the collapsing transient water cavity. The likely marine formation of the Lomonosov crater, and the apparent agreement in its age with that of the Thumbprint Terrain unit (~3 Ga), strongly suggests that it was the source crater of the tsunami. These results have implications for the stability of a late northern ocean on Mars.
Key Points
Unusual morphometric characteristics of Lomonosov crater in comparison to the other northern complex craters
Lomonosov crater was probably due to the presence of a shallow ocean of liquid water at the time of the impact
Agreement of the Lomonosov age with that of the Thumbprint Terrain unit (~3 Ga) suggests that it was the source crater of the tsunami
SUMMARY
The continental Lomonosov Ridge spans across the Arctic Ocean and was the subject of a geophysical study in 2016 with two seismic reflection lines crossing the ridge in proximity to the North ...Pole, one of which continues across the continent–ocean transition zone into the Amundsen Basin. One seismic station and 15 sonobuoys were deployed along these two lines to record seismic wide-angle reflections and refractions for development of a crustal-scale velocity model. Its viability is checked using gravity data from the experiment which are also used to interpolate crustal structure in areas with poor seismic constraints. On the line extending into the Amundsen Basin, continental crust composed of two layers with velocities of 6.0 and 6.5 km s–1 is encountered beneath the Lomonosov Ridge where the Moho depth is 21 km based on gravity modelling. The crust is overlain by a 1-km-thick layer with velocities of 4.7 km s–1 coinciding with a zone of positive magnetic anomalies of up to 180 nT. This layer is interpreted to include extrusive volcanic rocks related to the Cretaceous High Arctic Large Igneous Province (HALIP). Within the Amundsen Basin, three distinct crustal domains can be distinguished. Closest to the ridge is a 40-km-wide zone with a crustal thickness around 5 km interpreted as thinned continental crust. Five distinctive faulted basement blocks display high-amplitude reflections along their crests with velocities of 4.6 km s–1, representing the continuation of the magmatic rocks further upslope. Brozena et al. (2003) interpreted magnetic Chron C25 to be located in this zone but our data are not consistent with this being a seafloor spreading anomaly. In the adjacent crustal domain, heading basinward, the basement flattens and two layers with velocities of 5.2 and 6.8 km s–1 can be distinguished, where the upper and lower layer have a thickness of 1.5 and 2.0 km, respectively. The upper layer is interpreted as exhumed and highly serpentinized mantle while the lower layer may be less serpentinized mantle with some gabbroic intrusions. This may explain the high-amplitude reflections within the overlying sediments that are interpreted as sill intrusions. Continuing basinward, the last crustal domain represents 4-to 5-km-thick oceanic crust with a variable basement relief and velocities of 4.8 and 6.5 km s–1 at the top of oceanic layers 2 and 3, respectively. It is within this zone that the first true seafloor spreading anomaly Chron C24 is observed, which argues for a similar breakup age in the Eurasia Basin as in the Northeast Atlantic. On the other profile crossing the Lomonosov Ridge, a 60-km-wide intrusion into the lower crust is observed where velocities are increased to 6.9 km s–1. Gravity modelling supports the interpretation of magmatic underplating beneath the intrusion. Seismic data in this region show that the crust is overlain by a 2-km-thick series of high-amplitude reflections with a velocity of 4.8 km s–1 in a 30-km-wide zone where strong magnetic anomalies (>800 nT) are observed, suggesting a composition of basalt flows. This part of the Lomonosov Ridge appears therefore to have a HALIP-related magmatic overprint at all crustal levels.
Fire has been an important component of ecosystems on a range of spatial and temporal scales. Fire can affect vegetation distribution, the carbon cycle, and climate. The relationship between climate ...and fire is complex, in large part because of a key role of vegetation type. Here, we evaluate regional scale fire–climate relationships during a past global warming event, the Paleocene–Eocene Thermal Maximum (PETM), in order to understand how vegetation influenced the links between climate and fire occurrence in the Arctic region. To document concurrent changes in climate, vegetation, and fire occurrence, we evaluated biomarkers, including polycyclic aromatic hydrocarbons (PAHs), terpenoids, and alkanes, from the PETM interval at a marine depositional site (IODP site 302, the Lomonosov Ridge) in the Arctic Ocean.
Biomarker, fossil, and isotope evidence from site 302 indicates that terrestrial vegetation changed during the PETM. The abundance of the C29n-alkanes, pollen, and the ratio of leaf-wax n-alkanes relative to diterpenoids all indicate that proportional contributions from angiosperm vegetation increased relative to that from gymnosperms. These changes accompanied increased moisture transport to the Arctic and higher temperatures, as recorded by previously published proxy records. We find that PAH abundances were elevated relative to total plant biomarkers throughout the PETM, and suggest that fire occurrence increased relative to plant productivity. The fact that fire frequency or prevalence may have increased during wetter Arctic conditions suggests that changes in fire occurrence were not a simple function of aridity, as is commonly conceived. Instead, we suggest that the climate-driven ecological shift to angiosperm-dominated vegetation was what led to increased fire occurrence. Potential increases in terrestrial plant biomass that arose from warm, wet, and high CO2 conditions were possibly attenuated by biomass burning associated with compositional changes in the plant community.
•Increased PAH abundances relative to plant biomarkers suggests increased fire.•Angiosperms increased relative to gymnosperms based on pollen and plant biomarkers.•Wetter and hotter conditions preceded increased angiosperms and greater fire.•During the PETM in the Arctic, climate-driven changes in ecology increased fire.•Fire may have attenuated the effects of increases in plant biomass on carbon cycle.
Establishing a solid chronological framework for Arctic marine sediments is a critical first step towards glacial and palaeoceanographic reconstructions. However, this has historically been more ...challenging than elsewhere in the world, and often results in core chronologies and subsequent paleoenvironmental reconstructions being questioned and overturned. Optically stimulated luminescence (OSL) dating provided important constraints on late Quaternary ages for central Arctic marine sediments, and has considerable potential to underpin chronologies in other parts of the Arctic Ocean. This study applies OSL and infrared stimulated luminescence (IRSL) geochronology to multi-grain quartz and feldspar samples from a sediment core collected from the Lomonosov Ridge off the Siberian shelf during the 2014 SWERUS-C3 Expedition. Testing and advancing the proposed chronology of late Quaternary sediments in this part of the Arctic is essential to better constrain the timing of ice sheet growth on the Siberian Arctic shelf and subsequent ice shelf development in the Arctic Ocean. The results of luminescence dating support a pre-Eemian age for extensive ice grounding and scouring of the southern Lomonosov Ridge. Furthermore, we combine the OSL ages with data from rock magnetic measurements and propose an age-depth model for cores in this region. As in other areas in the Arctic, magnetic grain size/mineralogy profiles resemble the global oxygen isotope curve and may have the potential to be a dating tool. This can be tested and further refined in future studies that obtain longer sedimentary archives. Our results also indicate that changes in the inclination of the natural remanent magnetisation do not reflect geomagnetic field variation in the investigated sediment cores.
•The timing of ice sheet growth on the Siberian Arctic shelf during the Late Pleistocene is not well constrained.•Quartz luminescence dating supports a pre-Eemian age for ice grounding on the Lomonosov Ridge.•Changes in inclination of natural remanent magnetisation do not reflect geomagnetic field variation in the studied sediments.
A negative carbon isotope excursion recorded in terrestrial and marine archives reflects massive carbon emissions into the exogenic carbon reservoir during the Paleocene-Eocene Thermal Maximum. Yet, ...discrepancies in carbon isotope excursion estimates from different sample types lead to substantial uncertainties in the source, scale, and timing of carbon emissions. Here we show that membrane lipids of marine planktonic archaea reliably record both the carbon isotope excursion and surface ocean warming during the Paleocene-Eocene Thermal Maximum. Novel records of the isotopic composition of crenarchaeol constrain the global carbon isotope excursion magnitude to -4.0 ± 0.4‰, consistent with emission of >3000 Pg C from methane hydrate dissociation or >4400 Pg C for scenarios involving emissions from geothermal heating or oxidation of sedimentary organic matter. A pre-onset excursion in the isotopic composition of crenarchaeol and ocean temperature highlights the susceptibility of the late Paleocene carbon cycle to perturbations and suggests that climate instability preceded the Paleocene-Eocene Thermal Maximum.
Mercury stable isotopic compositions were determined for marine sediments from eight locations in the Arctic Ocean Basin. Mass dependent fractionation (MDF) and mass independent fractionation (MIF) ...of Hg stable isotopes were recorded across a variety of depositional environments, water depths, and stratigraphic ages. δ202Hg (MDF) ranges from −2.34‰ to −0.78‰; Δ199Hg (MIF) from −0.18‰ to +0.12‰; and Δ201Hg (MIF) from −0.29‰ to +0.05‰ for the complete data set (n=33). Holocene sediments from the Chukchi Sea and Morris Jesup Rise record the most negative Δ199Hg values, while Pleistocene sediments from the Central Arctic Ocean record the most positive Δ199Hg values. The most negative δ202Hg values are recorded in Pleistocene sediments. Eocene sediments (Lomonosov Ridge) show some overlap in their Hg isotopic compositions with Quaternary sediments, with a sample of the Arctic Ocean PETM (56Ma) most closely matching the average Hg isotopic composition of Holocene Arctic marine sediments. Collectively, these data support a terrestrially-dominated Hg source input for Arctic Ocean sediment through time, although other sources, as well as influences of sea ice, atmospheric mercury depletion events (AMDEs), and anthropogenic Hg (in core top samples) on Hg isotopic signatures must also be considered.
Arctic lithosphere — A review Pease, V.; Drachev, S.; Stephenson, R. ...
Tectonophysics,
07/2014, Letnik:
628
Journal Article
Recenzirano
This article reviews the characteristics of Arctic lithosphere and the principal tectonic events which have shaped it. The current state-of-knowledge associated with the crust, crustal-scale ...discontinuities, and their ages, as well as knowledge of the lithosphere as a whole from geophysical data, permits the division of Arctic lithosphere into discrete domains.
Arctic continental lithosphere is diverse in age, composition, and structure. It has been affected by at least two periods of thermal overprinting associated with large volumes of magmatism, once in the Permo-Triassic and again in the Aptian. In addition, it was attenuated as the result of at least five phases of rifting (in the late Devonian–early Carboniferous, Permo-Triassic, Jurassic, Early Cretaceous, and Late Cretaceous–Cenozoic).
Older phases of consolidation are associated with continental lithosphere and occurred through a series of continent–continent collisions in the Paleozoic. Jurassic and Cretaceous extensional phases are related to the dismembering of Pangea and Eurasia, and were concentrated in the Norway-Greenland and Canadian-Alaskan Arctic regions. Large areas of submarine, hyperextended continental (?) lithosphere developed in parts of the Amerasia Basin. After continental breakup and the accretion of new oceanic lithosphere, the Eurasia and Canada basins were formed.
•We present a review of Arctic lithosphere.•Arctic lithosphere is characterized using geophysical and geological data.•Arctic lithosphere is divided into discrete domains of specific ages.•Finally, we present a map summarizing the age of Arctic lithosphere.
High Arctic new seismic data, collected by Russian Federation from 2011 to 2014, and additional geological and geophysical information, are used to interpret the basement and sedimentary structure of ...central and eastern Eurasia Basin, the Gakkel Ridge, and their transition into the Laptev Sea. We find that significant changes in basement topography occur in Nansen Basin at C20 (43.43Ma) and in the Amundsen basins at C21 (45.7Ma), and in both basins at C13 (33Ma). A long seismic profile, that documents for the first time the structure of conjugate flanks and their margins in the central-eastern Eurasia Basin, confirms that oceanic accretion was asymmetric, with 10% less crust developed in the Amundsen Basin since continental break-up. In the eastern Amundsen Basin, we observe mid-ocean ridge uplift since C13 (33Ma). We identify four distinct sedimentary packages in the Eurasia Basin: Early to Mid Eocene (c. 56 to 45.7Ma), Mid Eocene to Early Oligocene (45.7 to 33.2Ma), Early Oligocene to Early Miocene (33.2 to 19.7) and Early Miocene to Present (19.7 to 0Ma); they are linked to the oceanic lithosphere age determined from magnetic data.
The deepest part of the Gakkel Ridge (5215m), situated close to the easternmost part of this mid ocean ridge, is imaged for the first time by seismic data that reveals volcanic constructions within the older axial ridges and on the flanks. Gakkel Ridge's asymmetric flanks with shallow, regularly-spaced, and rugged structure, typical to ultra-slow spreading ridges, imply periodicity of tectonic phases. The Khatanga-Lomonosov Fault between Lomonosov Ridge and the Laptev Sea region, is identified on few seismic profiles; kinematic models predict that it may have been active only for a maximum of 10myr after continental break-up.
Display omitted
•Asymmetric spreading in the eastern Eurasia Basin•East Gakkel Ridge tectono-magmatic segmentation•Strike-slip and transtension north of Laptev Sea since Eocene
Acoustic and detailed swath bathymetry data revealed a systematic picture of submarine landslides on the Siberian part of Lomonosov Ridge. Whereas numerous studies on mass movement exist along the ...margin of the Arctic Ocean less is known from central Arctic. A regional survey comprising swath bathymetry, sediment echo sounder and multichannel seismic profiling was performed on the southeastern Lomonosov Ridge. The data provide constraints on the present-day morphology of the Siberian part of Lomonosov Ridge, between 81°–84°N and 140°–146°E. We mapped twelve crescent-shaped escarpments located on both flanks on the crest of Lomonosov Ridge. The escarpments are 2.1 to 10.2 km wide, 1.7 to 8.2 km long and 125 to 851 m high from which 58 to 207 m are occupied by crescent-shaped headscarps. Subbottom data show chaotic reflections within most of the escarpment areas. The unit is overlain by ~110–340 m of semi-coherent parallel reflections. At its bottom the chaotic reflections are limited by a partly eroded high-amplitude reflection sequence that is inclined with <1° basinwards. We find the escarpments to be remnants of submarine landslide events that mobilized 0.09 to 7.58 km3 of sediments between mid Pliocene and mid Miocene. The relatively small amounts of mobilized sediments seem to be typical for the Lomonosov Ridge. The epoch corresponds to the ongoing subsidence of the Lomonosov Ridge below sea level. During that time deposition and the load of sediments changed. We suggest that changes in sediment type preconditioned, and co-occurring earthquakes finally triggered the submarine landslides.
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