The Distal and Local Volcanic Ash in the Late Pleistocene Sediments Of

geosciences

Article The Distal and Local Volcanic Ash in the Late Pleistocene Sediments of the Termination I Interval at the Reykjanes Ridge, North Atlantic, Based on the Study of the Core AMK-340

Alexander Matul 1,* , Irina F. Gablina 2, Tatyana A. Khusid 1, Natalya V. Libina 1 and Antonina I. Mikhailova 2

1 Shirshov Institute of Oceanology, Russian Academy of Sciences, 117997 Moscow, Russia 2 Geological Institute, Russian Academy of Sciences, 119107 Moscow, Russia * Correspondence: [email protected]

Received: 18 June 2019; Accepted: 29 August 2019; Published: 30 August 2019

Abstract: We made the geochemical analysis of the volcanic material from the sediment core AMK-340 (the Russian research vessel “Akademik Mstislav Keldysh” station 340), the central zone of the Reykjanes Ridge. Two ash-bearing sediment units within the interval of the Termination I can be detected. They correlate with the Ash Zone I in the North Atlantic Late Quaternary sediments having an age of 12,170–12,840 years within the Younger Dryas cold chronozone and 13,600–14,540 years within the Bølling–Allerød warm chronozone. The ash of the Younger Dryas unit is presented mostly by the mafic and persilicic material originated from the Icelandic volcanoes. One sediment sample from this unit contained Vedde Ash material. The ash of the Bølling–Allerød unit is presented mostly by the mafic shards which are related to the basalts of the rift zone on the Reykjanes Ridge, having presumably local origin. Possible detection of Vedde Ash could help to specify the timing of the previously reconstructed paleoceanographic changes for the Termination I in the point of the study: significant warming in the area might have occurred as early as 300 years before the end of the conventional Younger Dryas cold chronozone.

Keywords: tephra in marine sediments; Ash Zone I in North Atlantic; tephrochronology of Termination I

1. Introduction Tephrochronology is a widely used tool for dating and correlating the marine and terrestrial sediment sequences, especially within the Quaternary [1]. Recent detailed mineralogical and geochemical studies of volcanic material revealed a high-resolution Late Pleistocene and Holocene chronostratigraphy for the North Atlantic [2–4]. Icelandic volcanoes are the major source of the ash in the marine sediments of the Nordic Seas and North Atlantic [5]. Extensive studies of the Icelandic soil, lake, and shelf sediments documented >150 tephra layers within the late glacial and Holocene time [6]. Thornalley et al. [7] detected numerous ash-bearing marine sediment layers south of Iceland within the last deglacial and Holocene time. Such data help to refine the regional and local sediment stratigraphy and synchronize the paleoclimatic archives between the distal oceanic and land regions. Numerous studies of the Late Pleistocene tephra layers in the North Atlantic domain exhibited a complicated mineral/geochemical composition of the ash material accumulated in the marine sediments during the Termination I between approximately 18 and 11 ka (e.g., [8–10]). Different processes influence the deposition of the specific ash layers: single eruption or closely-timed chain of eruptions in one locality,

Geosciences 2019, 9, 379; doi:10.3390/geosciences9090379 www.mdpi.com/journal/geosciences Geosciences 2019, 9, 379 2 of 18 Geosciences 2019, 9, 379 2 of 18 eruptionsdispersal in by one the locality, atmospheric dispersal and by oceanic the atmosphe flows, icebergric and andoceanic sea-ice flows, rafting, iceberg and and reworking sea-ice rafting, by the andbottom reworking currents by and the bioturbationbottom currents [11]. and bioturbation [11]. OurOur study’s study’s aim aim is is to get additional information onon thethe occurrenceoccurrence and and composition composition of of the the tephra tephra in inthe the North North Atlantic Atlantic sediments sediments at the at transitionthe transition from from the last the glacial last glacial period period to the Holocene.to the Holocene. The position The positionof the sediment of the sediment core AMK-340 core AMK-340 (the Russian (the research Russian vessel research “Akademik vessel “Akademik Mstislav Keldysh” Mstislav station Keldysh” 340) stationis in the 340) central is in zonethe central of the Reykjaneszone of the Ridge Reykjanes with a Ridge local sourcewith a oflocal the source eruptive of material.the eruptive Therefore, material. we Therefore,tried to recognize we tried the to di ffrecognizeerent sources the ofdifferent the volcanic sources ash, of local the or volcanic distal ones. ash, Geochemical local or distal analysis ones. of Geochemicalthe volcanic shardsanalysis using of the scanning volcanic electron shards using microscopy scanning will electron help to revealmicroscopy the specific, will help well-known to reveal thetephra specific, layers well-known like Vedde Ashtephra which layers can like be aVedde good markerAsh which for acan refinement be a good of marker the core for stratigraphy a refinement and ofchronology the core stratigraphy of the local and paleoceanographic chronology of the changes. local paleoceanographic changes.

2.2. Materials Materials and and Methods Methods TheThe sediment sediment core core AMK-340 AMK-340 was was obtained obtained during during the the 4th 4th cruise cruise of of the the Russian Russian research research vessel vessel “Akademik“Akademik Mstislav Keldysh” [[12]12] inin thethe centralcentral partpart ofof the the Reykjanes Reykjanes Ridge, Ridge, North North Atlantic Atlantic south south of ofIceland Iceland (Figure (Figure1): 1): 58 58°30.6´◦30.60 N, N, 31 31°31.2´◦31.20 W, W, water water depth depth of of 1689 1689 m, m, core core length length 387 387 cm. cm.

FigureFigure 1. 1. TheThe geographic geographic position position ofof the the sediment sediment core core AMK-340 AMK-340 (the (the Russian Russian research research vessel vessel “Akademik“Akademik MstislavMstislav Keldysh” Keldysh” station 340).station Source of the340). map isSource (https: //topex.ucsd.eduof the /marine_topomap is / (https://topex.ucsd.edu/marine_jpg_images/topo4.jpg). topo/jpg_images/topo4.jpg).

FigureFigure 2 presents some general litho- and biostratigraphic and chronological data on the core AMK-340.AMK-340. More More data data are are presented presented in in [13–15]. [13–15]. The The core core unit unit of of 0–307 0–307 cm cm is is composed composed of of the the white white pelitic calcareous to weakly calcareous (foraminiferal-coccolith) oozes with a CaCO content from pelitic calcareous to weakly calcareous (foraminiferal-coccolith) oozes with a CaCO3 content3 from 10– 25%10–25% to 40–50%. to 40–50%. In the In thelower lower core core unit unit of 307–387 of 307–387 cm, cm, the the sediment sediment color color becomes becomes mainly mainly grey grey with with thinthin alternations ofof greenish-grey, greenish-grey, yellowish-grey, yellowish-grey, and and dark, dark, almost almost black, black, bands. bands. This unit This is enrichedunit is in the diatoms (sometimes up to 10–30%). The CaCO content varies there between 5.5% and 20% [12]. enriched in the diatoms (sometimes up to 10–30%). 3The CaCO3 content varies there between 5.5% andA visual 20% [12]. lithological A visual description lithological of description the core exhibited of the core no signsexhibited of the no volcanic signs of material. the volcanic material. The linear interpolation between four AMS 14C-datings [13] (Figure 2) helped to develop an age model of the core AMK-340, taking into account litho- and biostratigraphy [14,15].

Geosciences 2019, 9, 379 3 of 18

Figure 2. Lithostratigraphy of the AMK-340. Lithological description (a): number 1 is pelitic Figure 2. Lithostratigraphy of the AMK-340. Lithological description (a): number 1 is pelitic calcareous calcareous oozes with a CaCO3 content of >40–50%, number 2 is pelitic weakly calcareous muds with oozes with a CaCO3 content of >40–50%, number 2 is pelitic weakly calcareous muds with a CaCO3 a CaCO3 content of 10–25%, and number 3 is silty-pelitic muds with a CaCO3 content between 5.5% content of 10–25%, and number 3 is silty-pelitic muds with a CaCO3 content between 5.5% and 20% and 20% and an admixture of biogenic SiO2 of up to 10–30% [12]. The green-colored graph (b) is a and an admixture of biogenic SiO2 of up to 10–30% [12]. The green-colored graph (b) is a distribution ofdistribution the radiolarian of the species radiolarianLithelius species spiralis Litheliusgroup spiralis as a marker group of as the a marker temperate of the (non-glacial) temperate conditions(non-glacial) in theconditions North Atlantic in the North [13]. TheAtlantic blue-colored [13]. The graphblue-colored (c) is a distributiongraph (c) is a of distribution the polar planktic of the polar foraminiferal planktic speciesforaminiferalNeogloboquadrina species Neogloboquadrina pachyderma sinistral pachyderma [13 ]sinistral as a glacial [13] as marker. a glacial The marker. dark-blue The dark-blue line (d) isline a distribution(d) is a distribution of the mineral of the grainsmineral in grai thens sediment in the sediment fraction of fraction>100 µ mof [>10013] as μm a marker [13] as ofa marker the ice-rafted of the material.ice-rafted Pinkmaterial. bars arePink the bars samples are the where samples the ash where material the ash was material analyzed. was Black analyzed. dotted Black arrows dotted with 14 captionsarrows with show captions positions show of positions the AMS of (Accelerator the AMS (Accelerator Mass Spectrometry) Mass Spectrometry)14C-dates. VioletC-dates. rectangle Violet indicatesrectangle theindicates Younger the Dryas Younger unit. Dryas unit.

TheCalibration linear interpolation of the 14C-datings between in fourthe calendar AMS 14C-datings age data [was13] (Figuremade in2) the helped CALIB to develop 7.1.0 computer an age modelsoftware of theusing core the AMK-340, MARINE13 taking calibration into account scale litho-with andthe standard biostratigraphy reservoir [14 correction,15]. of 405 years and Calibrationits regional of deviation the 14C-datings of 85 ± in 79 the years calendar [16]. age The data core was spans made the in thetime CALIB interval 7.1.0 of computer the last softwareapproximately using the14,500 MARINE13 years or calibrationthe Termination scale with I an thed Holocene. standard reservoirWe assign correction the core ofunit 405 of years 315–340 and itscm regional the Younger deviation Dryas of 85interval79 years based, [16 ].in The addition core spans to the the radiocarbon time interval dating, of the laston approximatelythe litho- and ± biostratigraphic information [13,15]. As in many other northern North Atlantic sediment cores, an abundance peak of the polar planktic foraminiferal species Neogloboquadrina pachyderma sinistral (left-

Geosciences 2019, 9, 379 4 of 18

14,500 years or the Termination I and Holocene. We assign the core unit of 315–340 cm the Younger Dryas interval based, in addition to the radiocarbon dating, on the litho- and biostratigraphic information [13,15]. As in many other northern North Atlantic sediment cores, an abundance peak of the polar planktic foraminiferal species Neogloboquadrina pachyderma sinistral (left-coiled shells) of up to >99% together with an occurrence of the Heinrich 0 layer (maximum of ice-rafted material accumulation—see a mineral grains distribution in Figure2) marks the Younger Dryas cooling event. In the same unit, the radiolarian species Amphimelissa setosa, which is now typical for the cold-water environments of the Nordic Seas and the Arctic, has a very noticeable increase in abundance; overall, the radiolarian assemblages were subarctic there. Rich benthic foraminiferal microfauna, including the specific bioproductivity-indicating species, appeared in the core just above this unit. A possible detection of Vedde Ash with the age of 12,170 years [3,17,18] in the sample 323–325 cm (see Discussion Section) allows us to make a more accurate age model of the sediment core AMK-340 for the time interval of the Termination I (sharp warming with the climatic fluctuations between the Last Glacial Maximum and Holocene). From new calculations regarding possible Vedde Ash detection, the lower time limit of the core AMK-340 could be 14,540 years B.P. The core units of 323–340 and 355–378 cm could have the presumable age of 12,170–12,840 and 13,600–14,540 years, respectively. During the micropaleontological analysis of the core AMK-340 sediments under the stereomicroscope (foraminiferal study of the sediment fraction of >100 µm) and transmitted light microscope (radiolarian study of the sediment fraction of >50 µm) (Figure3), we could recognize a remarkable admixture of the eruptive shards in the two core units (Figure1), 323–340 cm (four samples: 323–325, 328–330, 334–336, and 338–340 cm) and 355–378 cm (four samples: 355–357, 360–368, 370–372, and 376–378 cm). In all these samples, the content of the eruptive material was >10–15% from the whole number of grains in the sediment fraction >100 µm. Volcanic shards in other samples of the core within the interval of 0–323 cm were absent or occasional. From these samples, eruptive shards in the fraction >100 µm were picked out for the subsequent studies of their chemical composition. All in all, data on 16 shards in the natural state, 24 shards from the core unit of 323–340 cm, and 16 shards from the core unit of 355–378 cm in the polished thin sections are presented (Table1). Two instruments examined the chemical composition of the shards. The first one is a scanning electron microscope CamScan MV2300 with the energy dispersive analysis system (EDS) INCA at the Geological Institute of the Russian Academy of Sciences, Moscow, Russia, (gold-sprayed shards in the natural state). The selected locality of measurements was 1 µm, and the voltage was 20 kV. The microanalyzer was equipped with a mylar input window of 0.5 µm in caliber which allowed to analyze light elements including oxygen and carbon. The reference samples for the quantitative analysis were obtained from the standard mineral collection provided by Oxford Instruments. From this collection, an analytical program tried to find a number of reference samples which were chemically close to the analyzed samples. The analytical accuracy was as high as 0.15%. Further, the scanning electron microscope VEGA3 TESCAN with EDS (Electron Dispersive Spectrometry) X-Max was used at the Institute of Oceanology of the Russian Academy of Sciences, Moscow, Russia (carbon-sprayed shards in the polished thin sections). The diameter of the electron beam was 1 µm, and the accelerating voltage was 20 kV. The concentrations of elements were detected using a correction on the absorption and dispersion of the X-rays with the help of the INCA standard software. The analytical accuracy was as high as 0.2%. Table S1 presents the normalized (along with some raw) data of the measurements. Geosciences 2019, 9, 379 5 of 18 Geosciences 2019, 9, 379 5 of 18

FigureFigure 3. MicrophotographsMicrophotographs of thethe sedimentsedimentsamples samples of of the the core core AMK-340. AMK-340. Left Left panel panel present present photos photos of ofthe the sediment sediment fraction fraction>0.1 >0.1 mm mm under under the the stereomicroscope: stereomicroscope: (a a)) core core sample sample of of 323–325323–325 cm,cm, (bb)) sample sample ofof 328–330 cm, c (c) )sample sample of of 338–340 338–340 cm. cm. Right Right panel panel present present photographs photographs of of the the sediment fraction >0.05>0.05 mm mm under under the the transmitted transmitted light light microscope: microscope: d) core (d) sample core sample of 323–325 of 323–325 cm, e) cm,sample (e) of sample 328-330 of cm,328–330 f) sample cm, ( fof) sample 338–340 of cm. 338–340 The regular cm. The microphotographs regular microphotographs of the sediment of the sedimentfractions were fractions obtained were withobtained the stereomicroscope with the stereomicroscope Zeiss Stemi Zeiss 508 Stemi equipped 508 equipped with the with camera the camera AxioCam AxioCam Icc5 (left Icc5 panel), (left panel), and theand transmitted the transmitted light lightmicroscope microscope used was used the was Ze theiss Axio Zeiss Lab.A1 Axio Lab.A1 powered powered by the byCanon the CanonEOS 1100D EOS camera1100D camera (right panel). (right panel).

TwoTable instruments 1. The number examined of shards the and chemical measurements composition in the studiedof the shards. samples The of the first core one AMK-340. is a scanning electron microscope CamScan MV2300 withShards the inenergy Polished dispersiveMeasurements analysis systemMeasurements (EDS) INCA in at the Core Sample, cm Shards in Total Geological Institute of the Russian AcademyThin of Sections Sciences, Moscow,in Total Russia, (gold-spraPolished Thinyed Sectionsshards in the natural323–325 state). The selected 9 locality of measurements 3 was 1 μm, 23 and the voltage was 12 20 kV. The microanalyzer328–330 was equipped 9 with a mylar input 5 window of 0.5 20μm in caliber which 14 allowed to analyze334–336 light elements including 13 oxygen and carb 7on. The reference 23 samples for the 13 quantitative 338–340 9 9 29 29 analysis were obtained from the standard mineral collection provided by Oxford Instruments. From thisCore collection, Unit 323–340 an analytical 40 program tried to 24find a number of 95 reference samples66 which were chemically355–357 close to the analyzed 3 samples. The analytical 3 accuracy was 8 as high as 0.15%. 8 Further, the 360–368 5 5 15 15 scanning370–372 electron microscope 3 VEGA3 TESCAN with 3 EDS (Electron 10Dispersive Spectrometry) 10 X-Max was used376–378 at the Institute of Oceanology 5 of the Russian 5 Academy of Sciences, 13 Moscow, Russia 13 (carbon- sprayedCore Unit shards 355–378 in the polished 16 thin sections). The 16 diameter of the electron 46 beam was 1 46 μm, and the accelerating voltage was 20 kV. The concentrations of elements were detected using a correction on In Total 56 40 141 112 the absorption and dispersion of the X-rays with the help of the INCA standard software. The analytical accuracy was as high as 0.2%. Table S1 presents the normalized (along with some raw) data of the measurements.

Geosciences 2019, 9, 379 6 of 18 Geosciences 2019, 9, 379 6 of 18

3. Results Results 3.1. Morphological Types of the Eruptive Material in the Studied Sediment Samples 3.1. Morphological Types of the Eruptive Material in the Studied Sediment Samples Angular fragments of the pumiceous basalts and basaltic andesites were black and sometimes Angular fragments of the pumiceous basalts and basaltic andesites were black and sometimes greenish, aphanitic (microlithic) and porous, with cavities ﬁlled with the light volcanic ash and greenish, aphanitic (microlithic) and porous, with cavities filled with the light volcanic ash and sometimes with the fragmented diatom frustules (Figure4). sometimes with the fragmented diatom frustules (Figure 4).

Figure 4. Scanning electron microphotographs of the ba basaltsalt and andesitic basalt ash shards from the core unit of 323–340 cm: a) vesicular black basalt glass with a SiO2 content of 49.10–57.15% in the core unit of 323–340 cm: (a) vesicular black basalt glass with a SiO2 content of 49.10–57.15% in the sample of 323–325 cm, b) massive black semi-transparent glass with a SiO2 content of 49.45% in the sample of 323–325 cm, (b) massive black semi-transparent glass with a SiO2 content of 49.45% in the sample of 323–325 cm, c) vesicular black shard (SiO2 content of 50.22%) with cavities filled with the sample of 323–325 cm, (c) vesicular black shard (SiO2 content of 50.22%) with cavities ﬁlled with the andesitic (SiO2 content of 55.79%) and persilicic (SiO2 content of 63.89–65.97%) dust in the sample of andesitic (SiO2 content of 55.79%) and persilicic (SiO2 content of 63.89–65.97%) dust in the sample of 323–325 cm, d) highly vesicular dark-green semi-transparent andesitic basalt glass with a SiO2 content 323–325 cm, (d) highly vesicular dark-green semi-transparent andesitic basalt glass with a SiO2 content of 52.52% in the sample of 334–336 cm. Yellow-outlin Yellow-outlineded rectangles show pointspoints ofof measurements.measurements.

Angular transparenttransparent/subtransparent/subtransparent fragments fragments of of the the persilicic persilicic glass glass were were olive olive and bottle-green,and bottle- green,elongate elongate (columnar) (columnar) with roughwith rough scratching scratching on the on surface the surface parallel parallel to the to elongationthe elongation or havingor having an anirregular irregular shape, shape, and and aphanitic aphanitic (Figure (Figure5). 5).

Geosciences 2019, 9, 379 7 of 18

Figure 5. 5. ScanningScanning electron electron microphotographs microphotographs of ofthe the persilicic persilicic ash ashshards shards from from the core the coreunit of unit 323– of

340323–340 cm: cm:a) angular (a) angular dense dense greenish greenish transparent transparent glass glass with with a median a median content content of of SiO SiO2 2ofof 76.37% 76.37% in in the sample of 323–325 cm, (bb)) rectangular rectangular light light semi-transparent semi-transparent dens densee foliated foliated shard shard with a SiO2 content of 75.57–76.88% in the sample ofof 328–3330328–3330 cm,cm, (cc)) and d (d) )general general view view and and fragment, fragment, respectively, respectively, of vesicular, greenish, semi-transparent glassglass (SiO(SiO22 content of 70.38%) in the sample of 334–336 cm, with layered andesitic insertions (SiO 2 contentcontent of of 55.90%) and titanomagnetite crystals and fragments of diatom frustules. Yellow-outlined rectanglesrectangles show points of measurements.

Pisolites were identified identiﬁed as rounded/semi-rounded rounded/semi-rounded grains and fragmentary grains, light (almost white), massive, and occasionally porous and were composed of persilicic and andesitic ash with inclusions of the fragmented diatom frustules, titanomagnetite, andand quartzquartz (Figure(Figure6 6b–d).b–d).

Geosciences 2019, 9, 379 8 of 18

Figure 6. Scanning electron microphotogr microphotographsaphs of the andesitic ash shards and pisolites from the core unit of 323–340 cm: a) rounded fine-pored black heterogeneous andesitic shard with a SiO2 content of unit of 323–340 cm: (a) rounded ﬁne-pored black heterogeneous andesitic shard with a SiO2 content 53.30–53.66%of 53.30–53.66% in the in thesample sample of 323–325 of 323–325 cm; cm;inclusions inclusions are the are sheet-like the sheet-like fragments fragments with witha higher a higher SiO2 content of 55.50–56.05% and small ilmenite crystals; b) light pisolite which is composed of the SiO2 content of 55.50–56.05% and small ilmenite crystals; (b) light pisolite which is composed of the andesitic basalt ash dust with a SiO2 content of 62.03–65.98% in the sample of 323–325 cm; inclusions andesitic basalt ash dust with a SiO2 content of 62.03–65.98% in the sample of 323–325 cm; inclusions are small titanomagnetite crystals; (cc)) unconsolidated unconsolidated grain grain of of light light color color which which is is composed of the andesitic basaltbasalt ash ash dust dust in the in sample the sample of 328–330 of cm;328–330 inclusions cm; areinclusions small ilmenite are small and titanomagnetite ilmenite and titanomagnetitecrystals; (d) white crystals; pisolite d which) white is pisolite composed which of theis composed diatom frustules of the diatom fragments frustules and volcanic fragments dust and in volcanicthe sample dust of in 328–330 the sample cm. Yellow-outlined of 328–330 cm. Yellow-out rectangleslined show rectangles points of measurements. show points of measurements.

Pisolites werewere foundfound as as semi-rounded semi-rounded/non-rounded/non-rounded grains, grains, black, black, and and composed composed of the of andesiticthe andesitic and andmafic mafic ash with ash inclusionswith inclusions of the fragmentedof the fragmented diatom frustules,diatom frustules, quartz, and quartz, pyroxene and(Figures pyroxene6 and (Figures7a,b,d). 6 and 7Besides,а–b,d). mostly rounded, transparent, colorless or sometimes rose or yellow-brown (ferruginized) quartzBesides, was found. mostly rounded, transparent, colorless or sometimes rose or yellow-brown (ferruginized)What are thequartz pisolites was found. in our samples? WhatPart of are the the ash pisolites material in consistsour samples? of the rounded and semi-rounded aggregates of the very thin, usuallyPart slightly of the ash cemented material ash consists particles of the of arounded size of and50 µ semi-roundedm having the variousaggregates components of the very with thin, a ≤ usuallysometimes slightly substantial cemented admixture ash particles of the of fragmented a size of ≤50 diatom μm having frustules, the various sponge spicules,components and with other a sometimesmicrofossils. substantialWe refer to admixture them as pisolites of the or fragmented ash shatters. diatom They are frustules, aggregates sponge of thin spicules, volcanic and ash. other They microfossils.can form during We therefer penetration to them as ofpisolites raindrops or ash within shatters. ash clouds They are and aggregates during the of vapor thin condensationvolcanic ash. They can form during the penetration of raindrops within ash clouds and during the vapor condensation on the ash particles in the eruptive clouds [19–22]. According to the classification of the

Geosciences 2019, 9, 379 9 of 18

onGeosciences the ash particles 2019, 9, 379 in the eruptive clouds [19–22]. According to the classiﬁcation of the volcaniclastic9 of 18 material in [23], particles <0.1 mm are ﬁne-grained ash dust. This material appears at andesite volcanicvolcaniclastic eruptions, material and thein [23], area particles of its dispersal <0.1 mm is are unlimited. fine-grained It can ash be dust. contaminated This material with appears terrestrial at particlesandesite (e.g., volcanic minerals, eruptions, fresh-water and the diatoms) area of its during dispersal the eolianis unlimited. transport It can and be with contaminated marine particles with (e.g.,terrestrial microfossils) particles during (e.g., theminerals, sedimentation fresh-water in diat the ocean.oms) during the eolian transport and with marine particlesWe recognized (e.g., microfossils) two types during of pisolites the sedimentation in our samples: in the (1) ocean. semi-rounded, black, dense, sometimes We recognized two types of pisolites in our samples: 1) semi-rounded, black, dense, sometimes pumiceous aggregates of the mixed composition and (2) rounded, white, loose aggregates of the pumiceous aggregates of the mixed composition and 2) rounded, white, loose aggregates of the intermediate composition (Figures6 and7). intermediate composition (Figures 6 and 7).

FigureFigure 7. Scanning7. Scanning electron electron microphotographs microphotographs of the basaltsbasalts and and pisolites pisolites of of the the andesitic andesitic and and mafic mafic compositioncomposition on on the the polished polished thin thin sections sections from fromthe the corecore unitunit ofof 323–340323–340 cm: a ()a )Irregularly Irregularly elongated elongated non-rounded black grain composed of mainly andesitic (SiO2 content of 52.39–58.97%) and sometimes non-rounded black grain composed of mainly andesitic (SiO2 content of 52.39–58.97%) and sometimes persilicic (SiO2 content of 64.94%) dust in the sample of 328–330 cm. Inclusions are more massive persilicic (SiO2 content of 64.94%) dust in the sample of 328–330 cm. Inclusions are more massive mafic shards, quartz, and microfossil fragments. b) Semi-rounded black shard composed of andesitic mafic shards, quartz, and microfossil fragments. (b) Semi-rounded black shard composed of andesitic ash dust with a mean SiO2 content of 57.5% in the sample of 328–330 cm. Inclusions are occasionally ash dust with a mean SiO2 content of 57.5% in the sample of 328–330 cm. Inclusions are occasionally more massive basalt shards with a SiO2 content of 49.22%. c) Microlithic basalt glass with a mean SiO2 more massive basalt shards with a SiO content of 49.22%. (c) Microlithic basalt glass with a mean content of 50.31% in the sample of 328–3302 cm. Microlites are intermediate/mafic plagioclase. d) Semi- SiO2 content of 50.31% in the sample of 328–330 cm. Microlites are intermediate/mafic plagioclase. rounded black shard composed of andesitic ash dust with a SiO2 content of 54.83% in the sample of (d) Semi-rounded black shard composed of andesitic ash dust with a SiO2 content of 54.83% in the 338–340 cm. Inclusions are occasionally larger basalt fragments with a mean SiO2 content of 50.52% sample of 338–340 cm. Inclusions are occasionally larger basalt fragments with a mean SiO content of and some possible Fe oxides. Yellow-outlined rectangles show points of measurements. 2 50.52% and some possible Fe oxides. Yellow-outlined rectangles show points of measurements.

3.2.3.2. Distribution Distribution of of the the Eruptive Eruptive Material Materialin in thethe StudiedStudied Sediment Samples Samples

3.2.1.3.2.1. The The Core Core Unit Unit of of 323–340 323–340 cm cm with with anan AgeAge ofof 12,170–12,840 Years Years Here,Here, we we found found abundant abundant ash ash particles particles andand pisolites,pisolites, together with with foraminiferal foraminiferal shells, shells, from from 0.1–0.5 to 2–2.5 mm, sometimes up to 6.5 mm in size; the regular size of the ash shards is between 0.2 0.1–0.5 to 2–2.5 mm, sometimes up to 6.5 mm in size; the regular size of the ash shards is between 0.2 and 0.5 mm (Figure 3). Black fragments (basalts, andesitic-basalts, and pisolites of the intermediate and 0.5 mm (Figure3). Black fragments (basalts, andesitic-basalts, and pisolites of the intermediate and mafic composition) prevail in the upper and lower parts of the unit in the samples of 323–325 and maﬁc composition) prevail in the upper and lower parts of the unit in the samples of 323–325

Geosciences 2019, 9, 379 10 of 18 and 334–336 cm, respectively, with a content of 30–40% of the whole sediment fraction (Figure3). The largestGeosciences fragments 2019, 9, 379 of >1–5 mm in size are typical for the upper part of the unit. 10 of 18 The content and size of the black eruptive fragments decrease sharply in the sample of 328–330 cm; and 334–336 cm, respectively, with a content of 30–40% of the whole sediment fraction (Figure 3). The they comprisedlargest fragments 5–10% of >1–5 of the mm sediment in size are fraction, typical for and the theirupper sizepart wasof the typically unit. <0.5–1 mm. In this sample, theThe light content pisolites and size of 0.25–0.5of the black mm eruptive in size, fragments composed decrease of persilicic sharply and in andesiticthe sample ash of 328–330 with quartz, prevailed,cm; they reaching comprised 50–70% 5–10% of of the the sediment sediment fraction. fraction, and their size was typically <0.5–1 mm. In this Thesample, content the light of pisolites the volcanic of 0.25–0.5 particles mm in in size, the composed lowermost of persilicic part of and the andesitic unit, sample ash with 338–340 quartz, cm, decreasedprevailed, signiﬁcantly reaching to50–70% 8–10% of ofthe the sediment sediment fraction. fraction. They are present mostly in the form of black volcanic glassThe content with an of admixture the volcanic of particles the olive-green in the lowermost ash, white part pisolites of the ofunit, the sample persilicic 338–340 composition, cm, quartz,decreased and rare significantly fragments to of 8–10% the pyroxene of the sediment and plagioclase. fraction. They The are size present of the particlesmostly in rarelythe form exceeded of black volcanic glass with an admixture of the olive-green ash, white pisolites of the persilicic 1 mm, with a maximum of up to 2.5 mm. composition, quartz, and rare fragments of the pyroxene and plagioclase. The size of the particles 3.2.2.rarely The Core exceeded Unit 1 of mm, 355–378 with a cm maximum with an of Age up to of 2.5 13,600–14,540 mm. Years The3.2.2. eruptive The Core material Unit of 355–378 is present cm with in the an formAge of of 13,600–14,540 sharply angular, Years mainly pumiceous, black basalt fragmentsThe with eruptive white material ash dust is in present the cavities, in the form the semi-transparentof sharply angular, bottle-green, mainly pumiceous, sometimes black basalt yellowish, maﬁcfragments glass particles, with quartz,white ash feldspar, dust andin the sporadic cavities semi-rounded, the semi-transparent white pisolites bottle-green, composed sometimes of persilicic and andesiticyellowish, ash mafic dust glass (Figure particles,8). In thequartz, analyzed feldspar, sediment and sporadic fraction, semi-rounded fragments of thewhite eruptive pisolites rocks and mineralscomposed are of persilicic larger compared and andesitic to theash dust biogenic (Figure particles, 8). In the beinganalyzed 0.5–1 sediment mm, fraction, occasionally fragments 2–4 mm, in size.of Thethe eruptive eruptive rocks material and minerals within the are unit larger is distributedcompared to irregularly the biogenic with particles, the highest being amounts0.5–1 mm, of up to 20–25%occasionally of the sediment2–4 mm, in fraction size. The in eruptive the middle material (sample within 360–362 the unit cm)is distributed and lower irregularly (sample with 376–378 the cm) parts;highest its content amounts in other of up samples to 20–25% stands of the at sediment 5–10%. fraction in the middle (sample 360–362 cm) and lower (sample 376–378 cm) parts; its content in other samples stands at 5–10%.

FigureFigure 8. Scanning 8. Scanning electron electron microphotographs microphotographs ofof the er eruptiveuptive shards shards on on the the polished polished thin thin sections sections from the core unit of 355–378 cm: a) andesitic basalt shard with a SiO2 content of 52.60% in the sample from the core unit of 355–378 cm: (a) andesitic basalt shard with a SiO2 content of 52.60% in the sample of 355–357 cm, b) microlithic andesitic basalt glass shard with a SiO2 content of 51.68% in the sample of 355–357 cm, (b) microlithic andesitic basalt glass shard with a SiO content of 51.68% in the sample of 366-368 cm, inclusions are intermediate/mafic crystals of plagioclase,2 c) persilicic pisolite with a of 366-368 cm, inclusions are intermediate/maﬁc crystals of plagioclase, (c) persilicic pisolite with SiO2 content of 79.1% in the sample of 370–372 cm, inclusions show some crystals of plagioclase, d)

a SiOdark-grey2 content ofandesitic 79.1% pisolite in the samplewith a ofSiO 370–3722 content cm, of inclusions53.38–56.96% show in the some sample crystals of 376-378 of plagioclase, cm, (d) dark-greyinclusions andesiticare light-grey pisolite basalt with fragments a SiO (SiO2 content2 content of of 53.38–56.96% 50.42–51.81%). in the sample of 376–378 cm, inclusions are light-grey basalt fragments (SiO2 content of 50.42–51.81%). Geosciences 2019, 9, 379 11 of 18

3.3. Chemical Composition of the Volcanic Material in the Studied Samples

3.3.1. The Core Unit of 323–340 cm with an Age of 12,170–12,840 Years

Sample 323–325 cm

Basalt fragments, which prevail here, have a typical content of SiO2 of 49.05–51.67%, a degraded concentration of K2O of 0–0.91%, and a high TiO2 amount of 1.49–5.43%. The TiO2 content drops down to 0.68% in some grains with the highest SiO2 concentration. The glass composition on the surface of one shard can vary in some cases from basaltic, with a SiO2 content of 49.10%, to andesitic, with a SiO2 content of 57.15% (Figure4a). Cavities of the black pumiceous basalt fragments are filled in many cases with volcanic ash dust of the different compositions, from the andesitic one, with a SiO2 content of 55.79%, to the persilicic one, with a SiO2 content of 63.89–65.97% (Figure4c). Rhyolites (volcanic persilicic shards) were less numerous than the basaltic fragments. We analyzed the chemical composition of one grain (Figure5a) where the SiO 2 and K2O contents were high, up to 76.37% and 3.92%, respectively. TiO2 was absent. Pisolites, which were present here mostly in the form of a white, rounded, loose intermediate variety (Figures6 and7), were composed of the ash dust with a SiO 2 content from 53.30–53.66% to 58.18% with occasional inclusions of titanomagnetite. Black pisolites had fragments of the mixed mafic (SiO2 content of 42.08–50.76%) to persilicic (SiO2 content of 65.49% on average) composition.

Sample 328–330 cm Most of the volcanic material was present in the form of pisolites, predominantly of the intermediate-persilicic composition (Figure6c,d) similar to those in the sample 323–325 cm. Ash dust in pisolites had a SiO2 content of 62.03–65.98%. Inclusions in pisolites were small crystals of titanomagnetite and ilmenite and diatom frustules (Figure6d). We also found pisolites of the mixed composition with the andesitic (SiO2 content of 58.97%) and persilicic (SiO2 content of 64.94%) ash dust, larger andesitic basalt particles (mean SiO2 content of 52.39%), occasional quartz inclusions, and a high admixture of the microfossil fragments (mostly diatoms) (Figure7a). Most black pisolites consisted of the intermediate ash dust with a mean SiO 2 content of 57.5% and occasional larger basalt particles (Figure7b) with a SiO 2 content of 49.22%. Furthermore, there was sporadic mafic with a SiO2 content of 52.04%, intermediate with a SiO2 content of 61.22%, and persilicic ash shards, the latter with a high concentration of SiO2 and K2O, of 75.11% on average and up to 4.88%, respectively. Some mafic shards were microlithic (Figure7c) and consisted of the basalt glass with a mean SiO2 content of 50.31% and thin mafic plagioclase microliths.

Sample 334–336 cm The eruptive material consisted predominantly of the ash shards of the maﬁc (Figure3d) with a SiO2 content of 50–51%, persilicic with a SiO2 content of 70.49–75.26% and K2O up to 3.39%, and mixed (Figure4c,d) composition. Less often, the andesitic basalt shards with a SiO 2 content of 52.78% occurred. The persilicic shards are notable here for their elongated shape, presence of the lengthwise scratching, and dense texture. Basalt shards had an irregular shape and were pumiceous (Figures4 and5 ). Shards of the mixed composition were close to the persilicic ones in shape; on their transverse shear surfaces, we could see many small round cavities (bubbles) ﬁlled with the fragmented diatom frustules (Figure5c,d). Some pisolites consisted of thin andesitic ash dust with a SiO2 content of 59.94%, and abundant diatom fragments were found.

Sample 338–340 cm

Basalt shards with a SiO2 content of 50.17–51.01%, a low K2O content of <1%, and a high TiO2 concentration of up to 4.44% prevailed in the sample. Andesitic basalt shards with a SiO2 content of GeosciencesGeosciences2019 2019, 9,, 3799, 379 12 of12 18 of 18

53.46% and sharply angular transparent persilicic glass shards with a SiO2 content of 71.45–71.84%

53.46%were andless numerous. sharply angular The latter transparent had a relatively persilicic high glass К2О shardscontentwith of 3.31–3.48%. a SiO2 content of 71.45–71.84% were lessSporadic numerous. black, The semi-rounded latter had a relativelygrains of the high isom K2Oetric content or oval of 3.31–3.48%.form of pisolites consisted of andesiticSporadic ash black, dust semi-roundedwith a SiO2 content grains of of 52.56–56.30% the isometric and or ovaloccasionally form of pisolitesmore massive consisted basalt of andesiticshards (Figure 7d) with a mean SiO2 content of 50.52%. ash dust with a SiO2 content of 52.56–56.30% and occasionally more massive basalt shards (Figure7d) with a mean SiO2 content of 50.52%. 3.3.1. The Core Unit of 355–378 cm with an Age of 13,600–14,540 Years (Figure 8). 3.3.2. TheWe Core analyzed Unit 16 of eruptive 355–378 grains cm with in the an Agepolished of 13,600–14,540 thin sections Yearsfrom four (Figure samples8) at 355–357, 360– 368,We 370–372, analyzed and 16 eruptive376–378 cm. grains Most in theof them polished were thin andesitic sections basalt from fourshards samples (Figure at 8 355–357,а) with a 360–368, SiO2 content of 52.5%; they occurred in all samples of this core unit. The sample 355–357 cm also contained 370–372, and 376–378 cm. Most of them were andesitic basalt shards (Figure8a) with a SiO 2 content of andesitic volcanic shards with a SiO2 content of 53.26 %, microlithic basalt shards with a mean SiO2 52.5%; they occurred in all samples of this core unit. The sample 355–357 cm also contained andesitic content of 51.68% from three analyses, and intermediate-mafic plagioclase crystals (Figure 7b). In the volcanic shards with a SiO2 content of 53.26 %, microlithic basalt shards with a mean SiO2 content of sample of 370–372 cm, we found persilicic glass shards with a SiO2 content of 66.90–67.65% and a 51.68% from three analyses, and intermediate-maﬁc plagioclase crystals (Figure7b). In the sample very high К2О concentration of up to 7.93% and persilicic pisolite (Figure 8c) with a SiO2 content of of 370–372 cm, we found persilicic glass shards with a SiO2 content of 66.90–67.65% and a very high 79.1% and with intruded plagioclase. The sample 376–378 cm had andesitic pisolites with a SiO2 K2O concentration of up to 7.93% and persilicic pisolite (Figure8c) with a SiO 2 content of 79.1% and content of 53.38–56.96 % or a mean of 55.17% with intruded basalt (SiO2 content of 50.42–51.81% or with intruded plagioclase. The sample 376–378 cm had andesitic pisolites with a SiO content of 51.12% on average) and titanomagnetite fragments (Figure 8d) and basalt shards with SiO2 2 content 53.38–56.96%of 45.88%. or a mean of 55.17% with intruded basalt (SiO2 content of 50.42–51.81% or 51.12% on average) and titanomagnetite fragments (Figure8d) and basalt shards with SiO 2 content of 45.88%. 4. Discussion 4. Discussion The diagram of SiO2 versus К2О in Figure 9 shows that most analyzed volcanic grains from the coreThe unit diagram of 323–340 of SiO cm2 matchversus the K2 ashO in material Figure9 from shows the that Icelandic most volcano analyzed eruptions. volcanic grains from the core unit of 323–340 cm match the ash material from the Icelandic volcano eruptions.

FigureFigure 9. 9.Position Position of of the the eruptive eruptive shards shards fromfrom thethe ash-bearingash-bearing core core unit unit of of 323–340 323–340 cm cm in inthe the binary binary SiO2/К2О system according to [24]. GIN (Geological Institute) samples present data on the shards in SiO2/K2O system according to [24]. GIN (Geological Institute) samples present data on the shards in the naturalnatural state. SIO SIO (Shirshov (Shirshov In Institutestitute of of Oceanology) Oceanology) samples samples show show data data on on the the shards shards in inthe the polishedpolished thin thin sections. sections. Areas Areas of of the the volcanic volcanic materialmaterial from different diﬀerent sources sources are are according according to to [25,26]. [25,26 ].

Geosciences 2019, 9, 379 13 of 18

The sample of 323–325 cm contains basalt shards and pisolites enriched in TiO2 and occasional The sample of 323–325 cm contains basalt shards and pisolites enriched in TiO2 and occasional rhyolites with an elevated K2O and high FeO concentrations. The bi-plots in Figure 10 present the rhyolites with an elevated К2О and high FeO concentrations. The bi-plots in Figure 10 present the composition of the presumable Vedde Ash material in the sample of 323–325 cm in comparison with composition of the presumable Vedde Ash material in the sample of 323–325 cm in comparison with well-known published data. Such ash composition is typical for Vedde Ash whose age in the Greenland well-known published data. Such ash composition is typical for Vedde Ash whose age in the ice-core chronology appears to be 12,170 57 years [3,17,18]. A source of the eruptive material for Greenland ice-core chronology appears to± be 12,170 ± 57 years [3,17,18]. A source of the eruptive Vedde Ash could be the Katla volcano in Southern Iceland [8,27]. Besides, we found some intermediate material for Vedde Ash could be the Katla volcano in Southern Iceland [8,27]. Besides, we found some ash shards, also as dust in pisolites, with a low K2O content, but their origin is unclear. intermediate ash shards, also as dust in pisolites, with a low К2О content, but their origin is unclear.

Figure 10. Bi-plots of major oxidesoxides inin thethe ashashmaterial material from from the the core core AMK-340 AMK-340 sample sample of of 323–325 323–325 cm cm in incomparison comparison to to the the published published data. data. Black-outlined Black-outlined red red circles circlesare are thethe geochemicalgeochemical measurementsmeasurements of the solid shards in the samplesample of 323–325323–325 cm.cm. Pink circles are the geochemical measurements of the pisolites in the sample of 323–325 cm. Blue Blue circles circles ar aree data of the Vedde Ash from the lake Kråkenes in western Norway, green circlescircles areare datadata fromfrom thethe lakelake LochLoch AshikAshik inin Scotland,Scotland, andand black-outlinedblack-outlined yellow squares are data from thethe GreenlandGreenland NGRIPNGRIP iceice corecore [[9].9].

Mangerud et et al. al. [28] [28 and] and Kvamme Kvamme et al. et [8] al. summarized [8] summarized findings ﬁndings of Vedde of VeddeAsh, starting Ash, startingas early as the early 1940s, as the within 1940s, the withinYounger the Dryas Younger chronozone Dryas chronozonesediments in sediments the North inAtlantic, the North Nordic Atlantic, Seas, andNordic surrounding Seas, and surroundingEuropean continental European areas. continental Bond et areas. al. [29] Bond and et Thornalley al. [29] and et Thornalley al. [7], as Kvamme et al. [7], aset al.Kvamme [8] before, et al. demonstrated [8] before, demonstrated a complicated a geochemi complicatedcal composition geochemical of composition the ash beds of in the the ash Ash beds Zone in I.the Vedde Ash ZoneAsh cannot I. Vedde be Asha simple cannot synonym be a simple of the synonym Ash Zone of I. theMoreover, Ash Zone Lane I. Moreover, et al. [9] and Lane Tomlinson et al. [9] etand al. Tomlinson[10] concluded et al. that [10 ]the concluded Icelandic that eruptions the Icelandic could have eruptions produced could ash have material produced comparable ash material to the Veddecomparable Ash tobefore, the Vedde within Ash and before, after within the Younger and after Dryas the Younger chronozone. Dryas Therefore, chronozone. they Therefore, claimed they an appropriateclaimed an appropriate stratigraphic/chronologi stratigraphic/chronologicalcal control to controlprove a to Vedde-like prove a Vedde-like ash occurrence ash occurrence within the within late Youngerthe late Younger Dryas time Dryas interval. time interval.As we presented As we presented in the Materials in the Materials and Methods and MethodsSection and Section in Figure and in2, theFigure core2, theAMK-340 core AMK-340 sample sample of 323–325 of 323–325 cm, where cm, where the possible the possible Vedde Vedde Ash Ash is isdetected, detected, is is from from thethe Younger DryasDryas unit. unit. However, However, we we are are aware aware that that this this sample sample does does not contain not contain pure Veddepure Vedde Ash shards Ash shardsbut mixed but eruptivemixed eruptive material material originated originated from possible from distalpossible airfall, distal local airfall, sources local within sources the within Reykjanes the ReykjanesRidge rift zone,Ridge iceberg rift zone, and iceberg sea-ice rafting,and sea-ice reworking rafting, during reworking the sedimentation during the sedimentation and bioturbation. and bioturbation.Unfortunately, Unfortunately, we are not able we to are quantify not able an to exact quan proportiontify an exact of theproportion airfall material. of the airfall An admixture material. Anof the admixture local eruptive of the shards local must eruptive take place. shards Ice-rafting must take inﬂuenced place. theIce-raft ash accumulationing influenced in the area.ash accumulationRuddiman and in Glover the area. [30] describedRuddiman a rhyoliticand Glover ash [30] bed indescribed the pre-Holocene a rhyolitic sediments ash bed inin the the North pre- AtlanticHolocene which sediments can be in referred the North to as Atlantic the regional which Ash can Zone be referred I. As the to authors as the suggested,regional Ash this Zone ash bed I. As must the authorsbe mostly suggested, ice-rafted. this Kvamme ash bed et al.must [20] be and mostly Gibbs etice-rafted. al. supposed Kvamme rather et fast al. Late [20] Pleistocene and Gibbs sea-ice et al. supposedrafting in therather North fast Atlantic Late Pleistocene ranging from sea-ice a few rafting years in to the a few North decades, Atlantic and ranging this is notfrom critical a few for years the totime a few assignment decades, ofand the this core is AMK-340not critical sample for the of time 323–325 assignment cm. According of the core to studiesAMK-340 of Ruddimansample of 323– and 325Glover cm. [According30], the bioturbation to studies canof Ruddiman mix the ash and through Glover the [30], sediment the bioturbation thickness can of dozens mix the of ash centimeters through the sediment thickness of dozens of centimeters at pelagic sedimentation rates of 2.4–6.7 cm×10−3 years. In the core AMK-340, the thickness of the ash-bearing sediments from two core units is 40 cm within the time interval of approximately 12,100–14,500 years B.P. The average sedimentation rate

Geosciences 2019, 9, 379 14 of 18

3 at pelagic sedimentation rates of 2.4–6.7 cm 10− years. In the core AMK-340, the thickness of Geosciences 2019, 9, 379 × 14 of 18 the ash-bearing sediments from two core units is 40 cm within the time interval of approximately 12,100–14,500 years B.P. The average sedimentation rate there is approximately 17 cm 10 3 years or there is approximately 17 cm × 10−3 years or much higher compared to that mentioned× by Ruddiman− much higher compared to that mentioned by Ruddiman and Glover [30]. We can expect a lower than and Glover [30]. We can expect a lower than dozens of centimeters sediment mixing depth at the dozens of centimeters sediment mixing depth at the bioturbation within the Younger Dryas, especially bioturbation within the Younger Dryas, especially if a high activity of the benthic organisms during if a high activity of the benthic organisms during the cold paleoclimatic environments is not assumed, the cold paleoclimatic environments is not assumed, because the faunal activity (benthic because the faunal activity (benthic foraminiferas) in the core point started to increase after the Younger foraminiferas) in the core point started to increase after the Younger Dryas [13]. Studies of the modern Dryas [13]. Studies of the modern sediment mixed depth at the bioturbation in the deep-sea Temperate sediment mixed depth at the bioturbation in the deep-sea Temperate North Atlantic and Subarctic North Atlantic and Subarctic Nordic Seas exhibited values as high as 3.9 and 6–7 cm [31]. Therefore, Nordic Seas exhibited values as high as 3.9 and 6–7 cm [31]. Therefore, we accept possible bottom we accept possible bottom reworking of the ash-bearing sediments. However, based on the litho- and reworking of the ash-bearing sediments. However, based on the litho- and biostratigraphic biostratigraphic information together with the radiocarbon datings, we suppose that the ice-rafting information together with the radiocarbon datings, we suppose that the ice-rafting and sediment and sediment reworking cannot mask/dispose of the occurrence of the Younger Dryas unit in the reworking cannot mask/dispose of the occurrence of the Younger Dryas unit in the core AMK-340. If core AMK-340. If so, eruptive material from the sample of 323–325 cm can partially have a Vedde so, eruptive material from the sample of 323–325 cm can partially have a Vedde Ash origin. Ash origin. The possible Vedde Ash occurrence in the sediment sample of 323–325 cm allows to re-estimate The possible Vedde Ash occurrence in the sediment sample of 323–325 cm allows to re-estimate the timing of the paleoenvironmental changes during the Younger Dryas chronozone (Glacial Stadial the timing of the paleoenvironmental changes during the Younger Dryas chronozone (Glacial Stadial 1 1 in Rasmussen et al. [18]) for the core АМК-340 [13]. Figure 11 presented the age-depth plot for the in Rasmussen et al. [18]) for the core AMK-340 [13]. Figure 11 presented the age-depth plot for the core core AMK-340 based on the radiocarbon datings and corrected the possible Vedde Ash detection with AMK-340 based on the radiocarbon datings and corrected the possible Vedde Ash detection with age age of 12,170 years [32]. Matul et al. [13] assigned the pre-Holocene warming at the Reykjanes Ridge of 12,170 years [32]. Matul et al. [13] assigned the pre-Holocene warming at the Reykjanes Ridge in the in the North Atlantic within the Younger Dryas cold chronozone to the time interval of 12,500–12,200 North Atlantic within the Younger Dryas cold chronozone to the time interval of 12,500–12,200 years B.P. years B.P. or significantly earlier than the beginning of the Holocene (11,700 years B.P.). Now, we can or signiﬁcantly earlier than the beginning of the Holocene (11,700 years B.P.). Now, we can assume that assume that this change occurred 12,200–12,000 years B.P., which was at least 300 years before the this change occurred 12,200–12,000 years B.P., which was at least 300 years before the Holocene start. Holocene start.

Figure 11. CorrectedCorrected age-depth age-depth plot plot for for the the Termination Termination I I interval interval of of the the core AMK-340 (red (red line) according to the occurrence of Vedde Ash in the sample of 323–325 cm (black-outlined red red square). square). Black squaressquares andand black black captions captions on on the the plot plot show show the the radiocarbon radiocarbon datings datings converted converted to calendar to calendar dates (seedates also (see Figure also Figure2). 2).

In thethe corecore unitunit of of 328–335 328–335 cm cm with with the the corrected corrected age age estimate estimate of approximately of approximately 12,700–12,900 12,700–12,900 years, years,the ash the is presentash is present mainly mainly in the form in the of form andesitic of an pisolitesdesitic pisolites with the with admixture the admixture of basalts of and basalts rhyolites. and rhyolites.Most of them Most suit of the them material suit fromthe material the Icelandic from volcanoes. the Icelandic However, volcanoes. some basaltHowever, fragments some with basalt an fragmentselevated K 2withO in an the elevated andesitic К pisolites2О in the can andesitic be related pisolites to the Jancan Mayenbe related volcanoes to the (FigureJan Mayen9). A volcanoes common (Figureoccurrence 9). A of common the marine occurrence microfossil of the (diatom) marine fragments microfossi insidel (diatom) pisolites fragments and ash inside shard pisolites cavities mayand ashsuggest shard that cavities the marine may transportationsuggest that the and marine sedimentation transportation could have and inﬂuencedsedimentation an accumulation could have influencedof the volcanic an accumulation material to a of large the volcanic degree in material the area toof a large study. degree However, in the we area cannot of study. be sure However, of the we cannot be sure of the Jan Mayen origin of the above-mentioned andesitic pisolites because Abbot and Davies [3] noted that it is rare to find the Jan Mayen volcanic deposits in the distal areas. The ash in the core unit of 355–378 cm with an age of 13,600–14,540 years differs from that in the core unit of 323–340 cm with an age of 12,170–12,840 years.

Geosciences 2019, 9, 379 15 of 18

Jan Mayen origin of the above-mentioned andesitic pisolites because Abbot and Davies [3] noted that it isGeosciences rare to find2019, the9, 379 Jan Mayen volcanic deposits in the distal areas. 15 of 18 The ash in the core unit of 355–378 cm with an age of 13,600–14,540 years differs from that in the core unitIn ofthe 323–340 samples cm of with 355–368 an age cm ofand 12,170–12,840 376–378 cm years.with an age of 13,600–14,100 and 14,540 years, respectively,In the samples we can of see 355–368 a dominance cm and of 376–378 the basalt cm and with andesitic an age basalt of 13,600–14,100 shards with a and SiO2 14,540 content years, of respectively,52.32–53.13%, we FeO can seecontent a dominance of 9.71–11.13%, of the MgO basalt content and andesitic of 6.31–8.69%, basalt and shards К2О withcontent a SiO of <1%.2 content In of 52.32–53.13%,terms of the geochemical FeO content composition, of 9.71–11.13%, they are MgO close content to the oftholeiitic 6.31–8.69%, basalts and and K basalt2O content glass in of the<1%. In termsrift zone of theof the geochemical Reykjanes composition,Ridge [12] (Figure they 12 are) but close differ to the from tholeiitic them in basalts terms andof a basalt higher glass SiO2 in concentration. The SiO2 content is 49.76% and 50.56% on average in the tholeiitic basalts and the basalt the rift zone of the Reykjanes Ridge [12] (Figure 12) but differ from them in terms of a higher SiO2 shards of the Reykjanes Ridge, respectively. The ash in the core unit of 355–378 cm may be mainly concentration. The SiO2 content is 49.76% and 50.56% on average in the tholeiitic basalts and the basalt the local eruptive material originated from the volcanism and tectonics in the Reykjanes Ridge rift shards of the Reykjanes Ridge, respectively. The ash in the core unit of 355–378 cm may be mainly the zone [12] and may have transformed under the influence of the acidic hydrothermal fluids during local eruptive material originated from the volcanism and tectonics in the Reykjanes Ridge rift zone [12] sedimentation. and may have transformed under the influence of the acidic hydrothermal fluids during sedimentation.

FigureFigure 12. 12.Position Position of of the the eruptive eruptive shards shards fromfrom thethe ash-bearingash-bearing core core unit unit of of 355–378 355–378 cm cm in in the the binary binary

SiOSiO2/K22/КO2О system system according according to to [24 [24].]. All Alldata data onon ourour samplessamples are are from from the the polished polished thin thin sections. sections. Areas Areas of theof the volcanic volcanic material material from from di differentﬀerent sources sources are are according according toto [[25,26].25,26].

OtherOther ash ash materials materials in in the the core core unit unit of of 355–378355–378 cmcm areare (1) mafic mafic shards shards with with a adecreased decreased SiO SiO2 2 contentcontent of 45.88%of 45.88% in thein the lowermost lowermost sample sample of of 376–378 376–378 cm cm and and (2) (2) persilicic persilicic glass glass with with a a SiO SiO22content content of 2 67.65%of 67.65% and aand high a high K2O К concentrationО concentration in in the the sample sample of of370–372 370–372 cm; the the sources sources of of both both are are unclear. unclear. Persilicic pisolites in the sample of 370–372 cm and mafic pisolites with a SiO2 content of 51.12% in Persilicic pisolites in the sample of 370–372 cm and mafic pisolites with a SiO2 content of 51.12% in the samplethe sample of 376–378 of 376–378 cm can cm have can have a possible a possible origin origin from from the Icelandicthe Icelandic volcanoes, volcanoes, but but the the source source of of the the andesitic pisolites with a SiO2 content of 55.17% in the sample of 376–378 cm is not defined and andesitic pisolites with a SiO2 content of 55.17% in the sample of 376–378 cm is not defined and could could be more distal. be more distal.

Geosciences 2019, 9, 379 16 of 18

5. Conclusions Two sediment units of the core AMK-340, Reykjanes Ridge, North Atlantic, contain a significant amount of volcanic ash. They can be related to the Ash Zone I in the North Atlantic Late Quaternary sediments. Accumulation of the ash-bearing sediments in the studied core samples occurred within the time intervals of 12,170–12,840 and 13,600–14,540 years B.P. or the Younger Dryas cold chronozone and Bølling–Allerød warm chronozone, respectively. The ash in the core AMK-340 within the Younger Dryas unit is present mostly in the form mafic and persilicic material originated from the Icelandic volcanoes, and ice-rafted to the point of the study. In one sediment sample, we could detect shards of possible bimodal Vedde Ash. If it was accepted that the core sample of 323–325 cm contains Vedde Ash, the age model of the core AMK-340 and timing of the previously reconstructed paleoceanographic changes for the Termination I time interval can be specified. However, in any case, significant warming in the area could have occurred as early as 300 years before the end of the conventional Younger Dryas cold chronozone. The ash in the core AMK-340 within the Bølling–Allerød unit is present mostly in the form of mafic shards which are close to the basalts and basalt glass of the rift zone in the Reykjanes Ridge, i.e., have presumably a local origin. In some samples of both units, we found aggregated pisolites of andesitic ash dust with inclusions of persilicic/mafic particles and fragments of marine diatom frustules. The origin of these pisolites is unclear.

Supplementary Materials: The following are available online at http://www.mdpi.com/2076-3263/9/9/379/s1, Table S1: Major oxides (weight %) in the analyzed ash shards from the sediment fraction of >100 µm in samples of the core AMK-340. Author Contributions: Conceptualization, A.M.; methodology, I.F.G.; investigation, I.F.G., T.A.K., A.I.M.; writing—original draft preparation, A.M., I.F.G.; writing—review and editing, A.M., I.F.G.; visualization, N.V.L. Funding: Funds for this research were acquired from the Ministry of Education and Science of the Russian Federation, Project No. 0149-2019-0007 for the Shirshov Institute of Oceanology, and additional funding was obtained from Project No. 0135-2019-0050 for the Geological Institute (IFG and AIM). Acknowledgments: We thank two anonymous reviewers for the constructive criticism and valuable suggestions which helped to improve our paper significantly. The authors are grateful to N.V.Gorkova, V.V. Mikheev, A.G. Boev, G.Kh. Kazarina, and A.V. Tikhonova for their valuable consultations and technical support. Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

References

1. Lowe, D.J. Tephrochronology and its application: A review. Quat. Geochronol. 2011, 6, 423. [CrossRef] 2. Turney, S.M.; Lowe, J.J.; Davies, S.M.; Hall, V.A.; Lowe, D.J.; Wastegård, S.; Hoek, V.Z.; Alloway, B.V. Tephrochronology of Last Termination sequences in Europe: A protocol for improved analytical precision and robust correlation procedures (a joint SCOTAV-INTIMATE proposal). J. Quat. Sci. 2004, 21, 335–345. [CrossRef] 3. Abbott, P.M.; Davies, S.M. Volcanism and the Greenland ice-cores: The tephra record. Earth-Sci. Rev. 2012, 115, 173–191. [CrossRef] 4. Bourne, A.J.; Cook, E.; Abbot, P.M.; Seierstad, I.K.; Steﬀensen, J.P.; Fischer, H.; Schnupback, S.; Davies, S.M. A tephra lattice for Greenland and a reconstruction of volcanic events spanning 25–45 ka b2k. Quat. Sci. Rev. 2015, 118, 122–141. [CrossRef] 5. Thordarson, T.; Höskuldsson, A. Postglacial volcanism in Iceland. Jökull 2008, 58, 198–228. 6. Gudmundsdóttir, E.R.; Larsen, G.; Björck, S.; Ingólfsson, Ó.; Striberger, J. A new high-resolution Holocene tephra stratigraphy in eastern Iceland: Improving the Icelandic and North Atlantic tephrochronology. Quat. Sci. Rev. 2016, 150, 234–249. [CrossRef] 7. Thornalley, D.J.R.; McCave, I.N.; Elderﬁeld, H. Tephra in deglacial ocean sediments south of Iceland: Stratigraphy, geochemistry and oceanic reservoir ages. J. Quat. Sci. 2011, 26, 190–198. [CrossRef] Geosciences 2019, 9, 379 17 of 18

8. Kvamme, T.; Mangerud, J.; Furnes, H.; Ruddiman, W.F. Geochemistry of Pleistocene ash zones in cores from the North Atlantic. Nor. Geol. Tidsskr. 1989, 69, 251–272. 9. Lane, C.; Blockley, S.; Mangerud, J.; Smith, V.; Lohne, S.; Tomlinson, E.; Matthews, I.; Lotter, A. Was the 12.1 ka Icelandic Vedde Ash one of a kind? Quat. Sci. Rev. 2012, 33, 87–99. [CrossRef] 10. Tomlinson, E.L.; Thordarson, T.; Lane, C.S.; Smith, V.C.; Manning, C.J.; Müller, W.; Menzies, M.A. Petrogenesis of the Sólheimar ignimbrite (Katla, Iceland): Implications for tephrostratigraphy. Geochim. Cosmochim. Acta 2012, 86, 318–337. [CrossRef] 11. Griggs, A.J.; Davies, S.M.; Abbott, P.M.; Rasmussen, T.L.; Palmer, A.P. Optimising the use of marine tephrochronology in the North Atlantic: A detailed investigation of the Faroe Marine Ash Zones II, III and IV. Quat. Sci. Rev. 2014, 106, 122–139. [CrossRef] 12. Lisitzin, A.P.; Zonenshain, L.P. Rift Zone of the Reykjanes Ridge: Tectonics, Magmatism, Conditions of Sedimentation; Nauka Press: Moscow, Russia, 1990; p. 239. (In Russian) 13. Matul, A.; Barash, M.S.; Khusid, T.A.; Behera, B.; Tiwari, M. Paleoenvironment Variability during Termination I at the Reykjanes Ridge, North Atlantic. Geosciences 2018, 8, 375. [CrossRef] 14. Matul, A. Late Quaternary paleoceanology of the North Atlantic based on radiolaria analysis data. Oceanology 1994, 34, 550–555. 15. Matul, A. On the problem of paleoceanological evolution of the Reykjanes ridge region (North Atlantic) during the last deglaciation based on a study of radiolaria. Oceanology 1994, 34, 806–814. 16. Stuiver, M.; Reimer, P.J.; Reimer, R.W. CALIB 7.1 [WWW program], 2018. Available online: http://calib.org (accessed on 1 July 2019). 17. Mortensen, A.K.; Bigler, M.; Grönvold, K.; Steffensen, J.P.; Johnsen, S.J. Volcanic ash layers from the Last Glacial Termination in the NGRIP ice core. J. Quat. Sci. 2005, 20, 209–219. [CrossRef] 18. Rasmussen, S.O.; Bigler, M.; Blockley, S.P.; Blunier, T.; Buchardt, S.L.; Clausen, H.B.; Cvijanovic, I.; Dahl-Jensen, D.; Johnsen, S.J.; Fischer, H.; et al. A stratigraphic framework for abrupt climatic changes during the Last Glacial period based on three synchronized Greenland ice-core records: refining and extending the INTIMATE event stratigraphy. Quat. Sci. Rev. 2014, 106, 14–28. [CrossRef] 19. Lyakhovich, V.V. On pisolitic tufa on the Siberian platform. Dokl. AN SSSR 1956, 110, 137–139. (In Russian) 20. Moore, J.Y.; Peck, D.L. Accretionary lapilli in volcanic rocks of the Western Continental United States. J. Geol. 1962, 70, 182–194. [CrossRef] 21. Kotova, L.N. Ash lapilli from Devonian volcanogenic-sedimentary series of Tarbagai Ridge. Lithol. Miner. Resour. 1966, 2, 58–64. (In Russian) 22. Shcherbakova, M.N. Ash rain in volcanogenic sediments of near-Balkhash (Kazakhstan). Lithol. Miner. Resour. 1972, 1, 155–160. (In Russian) 23. Dzozenidze, G.S.; Markhinin, E.K. Volcanoclastic products and problem of their evolution. In Problems of the Volcanogenic-sedimentary Lithogenesis; Nauka Press: Moscow, Russia, 1974; pp. 4–12. (In Russian) 24. Le Maitre, R.W.; Bateman, P.; Dudek, A.; Keller, J.; Lameyre, J.; Le Bas, M.J.; Sabine, P.A.; Schmid, R.; Sorensen, H.; Streickeisen, A.; et al. A Classification of Igneous Rocks and Glossary of Terms; Blackwell Scientific Publications: Oxford, UK, 1989; p. 193. 25. Mutschler, F.E.; Rougon, D.J.; Lavin, O.P.; Hughes, R.D. PETROS—A Data Bank of Major Element Chemical Analyses of Igneous Rocks for Research and Teaching (version 6.1); NOAA, National Geophysical and Solar-Terrestrial Data Center: Boulder, CO, USA, 1981. 26. Wallrabe-Adams, H.J.; Lackschewitz, K.S. Chemical composition, distribution, and origin of silicic volcanic ash layers in the Greenland – Iceland – Norwegian Sea: explosive volcanism from 10 to 300 ka as recorded in deep-sea sediments. Mar. Geol. 2003, 193, 273–293. [CrossRef] 27. Lacasse, C.; Sigurdsson, H.; Johanntson, H.; Paterne, M.; Carey, S. Source of Ash Zone 1 in North Atlantic. Bull. Volcan. 1995, 57, 18–32. [CrossRef] 28. Mangerud, J.; Lie, S.E.; Furnes, H.; Kristiansen, I.L.; Lømo, L. A Younger Dryas Ash Bed in western Norway, and its possible correlations with tephra in cores from the Norwegian Sea and the North Atlantic. Quat. Res. 1984, 21, 85–104. [CrossRef] 29. Bond, G.C.; Mandeville, C.; Hoffmann, S. Were rhyolitic glasses in the Vedde ash and in the North Atlantic’s Ash Zone 1 produced by the same volcanic eruption? Quat. Sci. Rev. 2001, 20, 1189–1199. [CrossRef] 30. Ruddiman, W.F.; Glover, L.K. Vertical mixing of ice-rafted volcanic ash in north Atlantic sediments. Geol. Soc. Am. Bull. 1972, 83, 2817–2836. [CrossRef] Geosciences 2019, 9, 379 18 of 18

31. Teal, L.R.; Bulling, M.T.; Parker, E.R.; Solan, M. Global patterns of bioturbation intensity and mixed depth of marine soft sediments. Aquat. Biol. 2008, 2, 207–218. [CrossRef] 32. Soltwedel, T.; Hasemann, C.; Vedenin, A.; Bergmann, M.; Taylor, J.; Krauß, F. Bioturbation rates in the deep Fram Strait: Results from in situ experiments at the arctic LTER observatory HAUSGARTEN. J. Exper. Mar. Biol. Ecol. 2019, 511, 1–9. [CrossRef]

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).