Marine Tephra Layers Research Articles

Revisiting the occurrence and distribution of Indian Ocean Tephra: Quaternary marine Toba ash inventory

The Toba Caldera on Sumatra, Indonesia is the host of the Young Toba eruption (∼74 ka), globally one of the largest and most recognized eruptions during the Quaternary and regionally concentrated in the eastern Indian Ocean. Three older deposits (Middle, and Old Toba Tuff as well as Haranggaol Dacite Tuff) are also attributed to Toba caldera, with their eruption products distributed over the Indian Ocean.We present the Quaternary marine tephra record from an array of 14 sites and 28 holes from deep ocean drilling programs, complementing earlier work on distal to ultra-distal Indian Ocean sediment cores and terrestrial distribution data of Toba deposits. A unique set of major and trace element glass-shard compositions on 115 primary ash layers together with glass shard morphologies, core pictures and statistical analysis support geochemical fingerprinting between marine tephra layers and known deposits from Toba and five so far unidentified medium to large eruptions assigned to northern Sumatra. Additionally, zircon crystallization ages have been determined for the Haranggaol Dacite Tuff resulting in a new maximum eruption age of 1.42 ± 0.034 Ma.Tephra volumes and magma masses for the (co-ignimbrite) fallout are estimated based on the compiled marine tephra distribution that are complemented by published proximal ignimbrite volumes. For YTT the resulting tephra and DRE volumes of 5600 km3 and 3600 km3, respectively, are in between the previous estimates. For MTT (253 km3 DRE), ODT (1550 km3 DRE), HDT (129 km3 DRE), and the five additionally identified eruptions from Northern-Sumatran volcanoes, new magma volumes have been determined. Overall, the Indian Ocean tephra record reveals in one large eruption every 200 kyr in the Quaternary that is derived from northern Sumatra. Plain language summaryThe Toba Caldera on Sumatra, Indonesia, is a famous spot for volcanism since it is the host of one of the largest and most recognized eruptions on the world, the ∼74 ka Young Toba supereruption. It produced widespread volcanic particles (volcanic ash) that were distributed around the globe by winds, but most deposits are concentrated in the eastern Indian Ocean. Next to the Young Toba Tuff (YTT), three older deposits from probably similar large eruptions are known from this caldera that are also found as ash layers in the Indian Ocean.We investigated this marine tephra record, including 28 locations from the three phases of the deep ocean drilling program (DSDP, ODP, IODP), and created a unique set of glass-shard trace element (LA-ICP-MS) compositions that complements our major element (EMP) data on 115 primary ash layers. Comparing these compositions between the different marine locations and to known terrestrial deposits of the Toba eruptions is done by geochemical fingerprinting where the characteristic chemical “fingerprint” of marine ash layers is correlated between oceanic and to on-land deposits to find out from which eruption it originated. Glass shard morphologies, core pictures and statistical analysis complement this approach to support the correlations to four known tephras from Toba (Young, Middle, and Old Toba Tuff, as well as Haranggaol Dacite Tuff) and five so far unidentified eruptions from Northern Sumatra.The distribution of all tephras in the Indian Ocean allows to estimate erupted volumes by mapping out the occurrence and thicknesses of the tephras on the seafloor using drill cores. The resulting magma volumes amount to, for example, between 3600 km3 and 129 km3 magma for Young, Middle, and Old Toba Tuff as well as the Haranggaol Dacitic Tuff. Together with the five additionally identified (northern)Sumatra eruptions, these results indicate that one large eruption has happened every 200 kyr in northern Sumatra over the last 2.4 Ma.

Advances in New Zealand's Tephrochronostratigraphy Using Marine Drill Sites: The Neogene

AbstractThree volcanic arcs have been the source of New Zealand's volcanic activity since the Neogene: Northland arc, Coromandel Volcanic Zone (CVZ) and Taupō Volcanic Zone (TVZ). The eruption chronology for the Quaternary, sourced by the TVZ, is well studied and established, whereas the volcanic evolution of the precursor arc systems, like the CVZ (central activity c. 18 to 2 Ma), is poorly known due to limited accessibility to, or identification of, onshore volcanic deposits and their sources. Here, we investigate the marine tephra record of the Neogene, mostly sourced by the CVZ, of cores from IODP Exp. 375 (Sites U1520 and U1526), ODP Leg 181 (Sites 1123, 1124 and 1125), IODP Leg 329 (Site U1371) and DSDP Leg 90 (Site 594) offshore of New Zealand. In total, we identify 306 primary tephra layers in the marine sediments. Multi‐approach age models (e.g. biostratigraphy, zircon ages) are used in combination with geochemical fingerprinting (major and trace element compositions) and the stratigraphic context of each marine tephra layer to establish 168 tie‐lines between marine tephra layers from different holes and sites. Following this approach, we identify 208 explosive volcanic events in the Neogene between c. 17.5 and 2.6 Ma. This is the first comprehensive study of New Zealand's Neogene explosive volcanism established from tephrochronostratigraphic studies, which reveals continuous volcanic activity between c. 12 and 2.6 Ma with an abrupt compositional change at c. 4.5 Ma, potentially associated with the transition from CVZ to TVZ.

The cenozoic marine tephra record in Indian Ocean deep drill sites

Provenance studies of widely distributed tephra deposits are important to deduce systematic changes in the source, size, distribution, and temporal variation of regional explosive volcanism. Long-term deep ocean drilling sedimentary records are particularly useful for these kind of studies. In this study, we establish a robust tephrochronostratigraphy for 235 primary marine tephra layers collected during International Ocean Discovery Program Expeditions 353, 354, and 362, complemented by older drill cores from Deep Sea Drilling Program and Ocean Drilling Program Legs 22, 119, 120, 121, and 183. We infer at least two major phases of highly explosive arc volcanism during the Early Miocene to Pleistocene, as well as three episodes related to explosive ocean island volcanism located in the Kerguelen plateau, the Broken Ridge, and close to Réunion reaching back to the Paleogene.Twenty-two widespread arc-derived tephra layers from individual eruptions can be correlated by geochemical fingerprinting between multiple holes. These provide nine Quaternary and 13 Neogene temporal tie points in the sedimentary sequence including four new UPb zircon ages. Provenance analysis of the marine tephra layers, which is based on glass composition, assign eleven of these layers to a Toba-like source, ranging from 24 Ma to 75 ka, with the youngest correlative being Young Toba Tuff. Based on distribution pattern, thickness decay, and compositional evidence another eleven tephra layers can be assigned to a northern Sumatran Arc or to an Andaman Arc provenance. First-order minimum eruptive volume estimates for the Neogene tephra layers imply eruptive magnitudes ranging from M = 6.5 to M = 7.5, proving a continuous history of large explosive eruptions from the Sumatran/Andaman Arc since the Neogene, as previously known from the Quaternary. Plain language summaryKnowing the origin of large volcanic eruptions is important to deduce systematic changes in the source, size, distribution, and changes of regional explosive volcanism. In this study we use widely dispersed marine volcanic deposits in the Indian Ocean, so-called marine tephra layers, to reconstruct the history of a) Sumatran highly explosive eruptions over the last 24 Ma, and b) ocean island volcanism frequently observed in the Indian Ocean. The marine deposits are often the only evidence of major eruptions in the past because respective volcanic edifices and terrestrial deposits are often destroyed by subsequent eruptions, eroded or overlain by younger deposits. Deep ocean drilling provides the unique possibility to overcome these problems by recovering long, tephra-bearing marine sediment sequences in the drill cores. We present the results for 235 primary marine tephra layers that have been collected during eight deep drilling campaigns in the Indian Ocean. Twenty-two widespread connections of arc-derived tephra layers are established by comparing distinctive geochemical fingerprints of the tephras between multiple locations. These provide nine Quaternary and 13 Neogene temporal tie points in the sedimentary sequence. The origin of these marine tephra layers is determined based on the unique glass compositions of individual volcanoes and eruptions, assigning 11 of these layers to a Toba-Caldera-like source ranging from 24 Ma to 75 ka, with the youngest correlative being the iconic Young Toba Tuff. Another eleven tephra layers can be assigned to a northern Sumatran Arc or to an Andaman Arc provenance.Our record demonstrates a continuous history of large explosive eruptions from the Sumatran/Andaman Arc since the Neogene. We additionally infer (1) at least two major phases of highly explosive arc volcanism from the Sumatra-Andamen volcanic chain during Early Miocene to Pleistocene times, and (2) three episodes related to explosive ocean island volcanism found in the Kerguelen plateau, the Broken Ridge, and close to Réunion.

“Excess Ar” by laboratory alteration of biotite

AbstractMany biotite phenocrysts from marine tephra layers have substoichiometric potassium concentrations and alkali occupation <<2.0 atoms per formula unit. Diagenetic alteration is an expected effect of exposure of fresh magmatic minerals to interstitial water and brine intrusions after the deposition and burial of sediments. To test the effect of diagenetic alteration on potassium-argon ages, we irradiated and step heated untreated Fish Canyon biotite (t = 28.2 Ma) and several aliquots leached to various extents in strong and weak acids. Laboratory alteration caused loss of K, age spectrum discordance, high step ages and total gas ages, Ar release at lower furnace temperature, higher Cl/K and Ca/K, and a slight decrease in 36Ar concentration. Potassium loss was always higher than 40Ar* loss. Electron microprobe element maps document that acids preferentially penetrated in phyllosilicate interlayers, removing K (and Na). Because Ar* is removed to a lesser extent than K, we propose that natural 40K decay partly implants radiogenic Ar* into the tetrahedral-octahedral-tetrahedral (T-O-T) phyllosilicate layer, where Ar is shielded from interlayer leaching. The recoiled 39Ar, which was produced by irradiation after the leaching, also partitioned between T-O-T and the interlayer; age spectrum discordance was probably enhanced by the heterogeneous partition of 39Ar and 40Ar* in leached samples.

Tephra layers in the marine environment: a review of properties and emplacement processes

Abstract This review focuses on the recognition of volcanic ash occurrences in marine sediment cores and on using their appearance and properties to deduce their origin. Widespread marine tephra layers are important marker horizons for both volcanological as well as general geological investigations. We describe ash detection by visual inspection and logging of sediment cores. Ash layer structure and texture, particle morphologies and lithological compositions of primary volcanic deposits are summarized and processes modifying them are discussed, both natural processes acting on and in the seafloor, i.e. erosion and bioturbation, and anthropogenic modifications during drilling/coring and core preparation. We discuss primary emplacement processes of marine fall and flow tephra deposits derived from either subaerial or submarine sources in order to identify distinguishing properties. We also elaborate on processes generating secondary, resedimented volcaniclastic layers such as submarine landslides and shelf erosion as well as fluvial input and ice-rafting, and how they can be distinguished from primary volcaniclastic deposits, which is essential in tephrostratigraphy. Finally, methods of tephra correlation between cores and on-land deposits/volcanoes are illustrated because they allow us to extend the 1D information from single cores to 3D distribution and facies changes of tephras and to bridge the land–sea gap.

Detection and Characterisation of Eemian Marine Tephra Layers within the Sapropel S5 Sediments of the Aegean and Levantine Seas

The Eemian was the last interglacial period (~130 to 115 ka BP) to precede the current interglacial. In Eastern Mediterranean marine sediments, it is marked by a well-developed and organic-rich “sapropel” layer (S5), which is thought to reflect an intensification and northward migration of the African monsoon rain belt over orbital timescales. However, despite the importance of these sediments, very little proxy-independent stratigraphic information is available to enable rigorous correlation of these sediments across the region. This paper presents the first detailed study of visible and non-visible (cryptotephra) layers found within these sediments at three marine coring sites: ODP Site 967B (Levantine Basin), KL51 (South East of Crete) and LC21 (Southern Aegean Sea). Major element analyses of the glass component were used to distinguish four distinct tephra events of Santorini (e.g., Vourvoulos eruption) and possible Anatolian provenance occurring during the formation of S5. Interpolation of core chronologies provides provisional eruption ages for the uppermost tephra (unknown Santorini, 121.8 ± 2.9 ka) and lowermost tephra (Anatolia or Kos/Yali/Nisyros, 126.4 ± 2.9 ka). These newly characterised tephra deposits have also been set into the regional tephrostratigraphy to illustrate the potential to precisely synchronise marine proxy records with their terrestrial counterparts, and also contribute to the establishment of a more detailed volcanic history of the Eastern Mediterranean.

Glass shard K-Ar dating of the Chalupas caldera major eruption: Main Pleistocene stratigraphic marker of the Ecuadorian volcanic arc

Abstract New K-Ar ages obtained on juvenile pumice glass shards indicate that the Chalupas ignimbrite, one of the main Pleistocene tephra markers of the Ecuadorian arc, was emplaced at 216 ± 5 ka. Morphology and major and trace element contents of the glass shards are similar to those of ash layers from deep-sea cores and allow correlation between continental deposits and marine tephra layers. Based on biostratigraphy and δ18O data, the age models of these cores support our K-Ar age. Fine ashes from the Chalupas eruption column have been found about 1000 km away from the source caldera, and the estimated deposit volume of both ignimbrite and co-ignimbrite deposits ranges from 200 to 265 km3. This suggests that the Chalupas event could have been strong enough to reach the stratosphere and inject large amount of SO2 in both hemispheres, possibly impacting global temperatures. In addition, the age of the Chalupas ignimbrite obtained here could provide a new radiometric constraint for the age of isotope stage 7 recorded in orbitally-tuned δ18O deep-sea cores. This study highlights the relevance of K-Ar dating applied to small glass shards from massive ignimbrite deposits, and the potential that it represents to improve risk assessments in volcanic zones where dating crystals is not possible. Finally, detailed tephrochronology of deep-sea cores and correlation between marine ash-layers and continental volcanic deposits constitute a strong tool to investigate the eruptive history of an active volcanic arc whose proximal products have been eroded or deeply buried by younger deposit sequences.

Miocene to Holocene Marine Tephrostratigraphy Offshore Northern Central America and Southern Mexico: Pulsed Activity of Known Volcanic Complexes

AbstractWe studied the tephra inventory of 14 deep sea drill sites of three Deep Sea Drilling Project and Ocean Drilling Program legs drilled offshore Guatemala and El Salvador (Legs 67, 84, and 138) and one leg offshore Mexico (Leg 66). Marine tephra layers reach back from the Miocene to the Holocene. We identified 223 primary ash beds and correlated these between the drill sites, with regions along the volcanic arcs, and to specific eruptions known from land. In total, 24 correlations were established between marine tephra layers and to well‐known Quaternary eruptions from El Salvador and Guatemala. Additional 25 tephra layers were correlated between marine sites. Another 108 single ash layers have been assigned to source areas on land resulting in a total of 157 single eruptive events. Tephra layer correlations to independently dated terrestrial deposits provide new time markers and help to improve or confirm age models of the respective drill sites. Applying the respective sedimentation rates derived from the age models, we calculated ages for all marine ash beds. Hence, we also obtained new age estimates for eight known but so far undated large terrestrial eruptions. Furthermore, this enables us to study the temporal evolution of explosive eruptions along the arc, and we discovered five pulses of increased activity: (1) a pulse during the Quaternary, (2) a Pliocene pulse between 6 and 3 Ma, (3) a Late Miocene pulse between 10 and 7 Ma, (4) a Middle Miocene pulse between 17 and 11 Ma, and (5) an Early Miocene pulse (ca. >21 Ma).

One Million Years tephra record at IODP Sites U1436 and U1437: Insights into explosive volcanism from the Japan and Izu arcs

AbstractThe 1 Myr tephra records of IODP (International Ocean Discovery Program) Holes U1436A and U1437B in the Izu‐Bonin fore‐ and reararc were investigated in order to assess provenance and eruptive volumes, respectively. In total, 304 tephra samples were examined and 260 primary tephra layers were identified. Tephra provenance was determined by means of major and trace element compositions of glass shards and distinguished between Japan and Izu‐Bonin arc origin of the tephra layers. A total of 33 marine tephra compositions were correlated to the Japan arc and 227 to the Izu arc. Twenty marine tephra layers were correlated between the two drilling sites. Additionally, we defined eleven correlations of marine tephra deposits to major widespread Japanese eruptions; from the 1.05 Ma Shishimuta‐Pink Tephra to the 30 ka Aira‐Tn Tephra, both from Kyushu Island. These eruptions provide independent time markers within the sediment record and six correlations were used to date tephra layers from Japan in Hole U1436A to establish an alternative age model for this hole. Furthermore, the minimum distal tephra volumes of all detected events were calculated, which enabled the comparison of the tephra volumes that derived from the Japan and the Izu‐Bonin arcs. For some of the major Japanese eruptions these are the first volume estimations that also include distal deposits. All of the Japanese tephras derived from events with eruption magnitude Mv ≥ 5.6 and three of the investigated eruptions reach magnitudes Mv ≥ 7. Volcanic events of the Izu‐Bonin arc have mostly eruption magnitudes Mv ≤ 5.

The Evolution of the Silver Hills Volcanic Center, and Revised 40Ar/39Ar Geochronology of Montserrat, Lesser Antilles, With Implications for Island Arc Volcanism

AbstractStudying the older volcanic centers on Montserrat, Centre Hills and Silver Hills, may reveal how volcanic activity can change over long time periods (≥1 Myr), and whether the recent activity at the Soufrière Hills is typical of volcanism throughout Montserrat's history. Here we present the first detailed mapping of the Silver Hills, the oldest and arguably least studied volcanic center on Montserrat. Volcanism at the Silver Hills was dominated by episodic andesite lava dome growth and collapse, produced Vulcanian style eruptions, and experienced periodic sector collapse events, similar to the style of volcanic activity that has been documented for the Centre Hills and Soufrière Hills. We also present an updated geochronology of volcanism on Montserrat, by revising existing ages and obtaining new 40Ar/39Ar dates and paleomagnetic ages from marine tephra layers. We show that the centers of the Silver, Centre, and Soufrière Hills were active during at least ∼2.17–1.03 Ma, ∼1.14–0.38 Ma, and ∼0.45 Ma to present, respectively. Combined with timings of volcanism on Basse‐Terre, Guadeloupe, these ages suggest that ∼0.5–1 Ma is a common lifespan for volcanic centers in the Lesser Antilles. These new dates identify a previously unrecognized overlap in activity between the different volcanic centers, which appears to be a common phenomenon in island arcs. We also identify an older stage of Soufrière Hills activity ∼450–290 ka characterized by the eruption of hornblende‐orthopyroxene‐phyric lavas, demonstrating that the petrology of the Soufrière Hills eruptive products has changed at least twice throughout the volcano's development.

Tephrostratigraphy and Provenance From IODP Expedition 352, Izu‐Bonin Arc: Tracing Tephra Sources and Volumes From the Oligocene to Recent

AbstractProvenance studies of widely distributed tephras, integrated within a well‐defined temporal framework, are important to deduce systematic changes in the source, scale, distribution, and changes in regional explosive volcanism. Here, we establish a robust tephrochronostratigraphy for a total of 157 marine tephra layers collected during IODP Expedition 352. We infer at least three major phases of highly explosive volcanism during Oligocene to Pleistocene time. Provenance analysis based on glass composition assigns 56 of the tephras to a Japan source, including correlations with 12 major and widespread tephra layers resulting from individual eruptions in Kyushu, Central Japan, and North Japan between 115 ka and 3.5 Ma. The remaining 101 tephras are assigned to four source regions along the Izu‐Bonin arc. One, exclusively assigned to the Oligocene age, is proximal to the Bonin Ridge islands; two reflect eruptions within the volcanic front and back‐arc of the central Izu‐Bonin arc, and a fourth region corresponds to the Northern Izu‐Bonin arc source. First‐order volume estimates imply eruptive magnitudes ranging from 6.3 to 7.6 for Japan‐related eruptions and between 5.5 and 6.5 for IBM eruptions. Our results suggest tephras between 30 and 22 Ma reflect a subtly different Izu‐Bonin chemical signature compared to the recent arc. After a ∼9 Ma gap in eruption, tephra supply from the Izu‐Bonin arc predominated from 15 to 5 Ma, and finally a subequal mixture of tephra sources from the (palaeo)Honshu and Izu‐Bonin arcs occured within the last ∼5 Ma.

Late Cenozoic tephrostratigraphy offshore the southern Central American Volcanic Arc: 2. Implications for magma production rates and subduction erosion

AbstractPacific drill sites offshore Central America provide the unique opportunity to study the evolution of large explosive volcanism and the geotectonic evolution of the continental margin back into the Neogene. The temporal distribution of tephra layers established by tephrochonostratigraphy in Part 1 indicates a nearly continuous highly explosive eruption record for the Costa Rican and the Nicaraguan volcanic arc within the last 8 Myr. The widely distributed marine tephra layers comprise the major fraction of the respective erupted tephra volumes and masses thus providing insights into regional and temporal variations of large‐magnitude explosive eruptions along the southern Central American Volcanic Arc (CAVA). We observe three pulses of enhanced explosive volcanism between 0 and 1 Ma at the Cordillera Central, between 1 and 2 Ma at the Guanacaste and at >3 Ma at the Western Nicaragua segments. Averaged over the long‐term the minimum erupted magma flux (per unit arc length) is ∼0.017 g/ms. Tephra ages, constrained by Ar‐Ar dating and by correlation with dated terrestrial tephras, yield time‐variable accumulation rates of the intercalated pelagic sediments with four prominent phases of peak sedimentation rates that relate to tectonic processes of subduction erosion. The peak rate at >2.3 Ma near Osa particularly relates to initial Cocos Ridge subduction which began at 2.91 ± 0.23 Ma as inferred by the 1.5 Myr delayed appearance of the OIB geochemical signal in tephras from Barva volcano at 1.42 Ma. Subsequent tectonic re‐arrangements probably involved crustal extension on the Guanacaste segment that favored the 2–1 Ma period of unusually massive rhyolite production.

Alkalic marine tephra layers at ODP Site 1241 - Major explosive eruptions from an oceanic volcano in a pre-shield stage?

We report a series of fourteen marine tephra layers that are the products of large explosive eruptions of Subplinian to Plinian intensities and magnitudes (VEI >4) from Cocos Island, Costa Rica. Cocos Island is a volcanic island in the eastern Central Pacific Ocean ~500km offshore Costa Rica, and is situated on the northwestern flank of the aseismic Cocos Ridge. Geochemical fingerprinting of Pleistocene (~2.4–1.4Ma) marine tephra layers from Ocean Drilling Project (ODP) Leg 202 Site 1241 using major and trace element compositions of volcanic glass shards demonstrates unequivocally their origin from Cocos Island rather than the Galápagos Archipelago or the Central American Volcanic Arc (CAVA). Cocos Island and the adjacent seamounts of the Cocos Island Province have alkalic compositions and formed on young (≤3Ma) oceanic crust from an extinct spreading ridge bounded by a transform fault against the older and thicker crust of the aseismic Cocos Ridge. Cocos Island has six times the average volume of the adjacent seamounts although all appear to have formed during the 3–1.4Ma time period. Cocos Island lies closest to the transform fault and we explain its excessive growth by melts rising from garnet-bearing mantle being deflected from the thick Cocos Ridge lithosphere toward the thinner lithosphere on the other side of the transform, thus enlarging the melt catchment area for Cocos Island compared to the seamounts farther away from the transform. This special setting favored growth above sea level and subaerial explosive eruptions even though the absence of appropriate compositions suggests that the entirely alkalic Cocos Island (and seamounts) never evolved through the productive tholeiitic shield stage typical of other Pacific Ocean islands, possibly because melt production rates remained too small. Conditions of magma generation and ascent resembled Hawaiian pre-shield volcanoes but persisted for much longer (<1m.y.) and formed evolved, trachytic magmas. Therefore Cocos Island may be a unique example for a volcanic ocean island that did not pass through the typical growth stages.

Japan's Volcanic History, Hidden Under the Sea

Scientists investigate marine tephra layers for clues to Japan's volcanic past.

Differential resilience of ancient sister lakes Ohrid and Prespa to environmental disturbances during the Late Pleistocene

Abstract. Ancient lakes, such as lakes Ohrid and Prespa on the Balkan Peninsula, have become model systems for studying the link between geological and biotic evolution. Recently, the scientific deep-drilling project Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) was initiated to better understand the environmental, climatic, and limnological evolution of the lake. It revealed that Lake Ohrid experienced a number of environmental disturbances during its ca. 2.0 million year long history. These are comprised of disturbances that lasted over longer periods of time (“press events”) such as glacial–interglacial cycles and Heinrich events, as well as sudden and short disturbances (“pulse events”) like the deposition of landslides, earthquakes, and volcanic ash depositions. The latter includes one of the most severe volcanic episodes during the Late Pleistocene: the eruption of the Campanian Ignimbrite (known as Y-5 marine tephra layer) from the Campi Flegrei caldera, dated to 39.6 ± 0.1 thousand years ago. The event is recorded by the deposition of a ca. 15 cm thick tephra layer in sediment cores of lakes Ohrid (DEEP-5045-1) and Prespa (Co1204). Coincidently, this pulse event is superimposed by the Heinrich H4 event, 40.4–38.4 thousand years ago. In the current paper, diatoms were used as proxies to compare the responses of these lakes to the Y-5 (pulse) and the H4 (press) disturbances. Based on stratigraphically constrained incremental sum of squares cluster (CONISS) and unconstrained Partitioning Around Medoids (PAM) analyses, we found little evidence that diatom community compositions in either lake responded to the H4 event. However, the Y-5 influx caused clear and rapid diatom community changes. After the initial response, community compositions in Lake Ohrid and, to a lesser extent, in Lake Prespa slowly returned to their quasi pre-disturbance state. Moreover, there is no evidence for disturbance-related extinction events. The combined evidence from these findings suggests that lakes Ohrid and Prespa likely did not experience regime shifts. It is therefore concluded that both lakes show resilience to environmental disturbance. However, it seems that Lake Ohrid is more resilient than Lake Prespa, as the recovery of diatom communities is more pronounced and its estimated recovery time is only ca. 1100 years vs. ca. 4000 years in Lake Prespa. The reasons for the differential responses remain largely unknown, but differences in geology, lake age, limnology, and intrinsic parameters of the diatom proxies may play an important role.

Magnetic properties of the Campanian Ignimbrite and the marine Y5 tephra layer

Abstract A set of magnetic measurements (hysteresis loops, thermomagnetic curves, magnetic susceptibility, anhysteretic and isothermal remanences) were performed for samples collected from stratigraphic layers (basal ash, L1, 2a and 2b) of the Campanian Ignimbrite (CI) and from its marine equivalent, the Y5 tephra layer. Day plots, Lowrie–Fuller tests and interparametric ratios demonstrate that the carrier of the remanence is low Ti-magnetite with grain size mostly characterized by pseudo-single-domain (PSD) grains. The magnetite content increases toward the top, particularly in the uppermost 2b layer which is also characterized by smaller grain size. The distribution of the magnetic content is different among the different layers and it may reflect a primary signature as well as post-depositional transformation such as zeolitization and/or maghemitization. The magnetic data confirm the correlation between the CI and the Y5 tephra layer and indicate that a unique eruption was responsible for their emplacement. First-order reversal curve (FORC) diagrams clearly display that the plinian basal ash can be considered the only true source for the marine tephra layer. The results demonstrate the potential of magnetic methods to characterize pyroclastic flow deposits and provide support for the identification and correlation of distal tephra.

The late MIS 5 Mediterranean tephra markers: a reappraisal from peninsular Italy terrestrial records

We present new tephrostratigraphic records from the late MIS 5 (ca 110–80 ka) terrestrial sediments from southern and central Italy. On the one hand, the central Italy record consists of an outcropping lacustrine sequence from the Sulmona intermountain basin that contains four trachytic–phonolitic tephra layers (POP3, POP2a, POP2b, POP1), all of which show a K-alkaline affinity that is typical for the Roman co-magmatic Province. The POP3 and POP1 layers were dated by 40Ar/39Ar method at 106.2 ± 1.3 ka (2σ) and 92.4 ± 4.6 ka (2σ), respectively. The sequence in southern Italy, on the other hand, is represented by post-Tyrrhenian coastal deposits of the Cilento area, Campania, which contain two trachytic layers (CIL2, CIL1) that show the same K-alkaline affinity. Based on their chemical compositions and radiometric ages, POP3 and POP1 are firmly correlated with the marine tephra layers X-5 (105 ± 2 ka) and C-22 (ca 90 ka), which, in turn, match tephras TM-25 and TM-23-11, respectively, in the lacustrine sequence of Lago Grande di Monticchio (southern Italy). Of note, the POP1 layer also matches the Adriatic Sea tephra PRAD 2517 that was previously correlated with the older X-5 layer. The tephra couplet POP2a and POP2b (ca 103 and 103.5 ka, extrapolated ages) are compatible with the TM-24b and TM-24-3 tephras in Monticchio, which match both the stratigraphic positions and the chemical compositions. In the Cilento area, as well as the already described X-6 layer (ca 108 ka) (CIL2), we recognise a new stratigraphic superimposed layer (CIL1) that matches the POP3/TM-25/C-27/X-5 Mediterranean marker(s). In summary, the data presented here provide new chemical and 40Ar/39Ar chronological constraints towards a robust late MIS 5 tephrostratigraphy of the central Mediterranean, although at the same time, they also reveal how the tephrostratigraphy itself might be flawed when dealing with tephra markers that are not adequately constrained and characterised.

Tephra stratigraphy on the North Icelandic shelf: extending tephrochronology into marine sediments off North Iceland

Tephra stratigraphical and tephrochronological studies of marine core MD99‐2275 on the North Icelandic shelf have revealed 58 new tephra horizons within the last 7050 cal. a BP, bringing the total number of identified tephra layers to 76. So far, over 100 tephra layers have been identified in the entire core spanning the last 15 000 years. The majority of the newly identified tephra layers are basaltic in composition and originate from the most active volcanic systems in Iceland, namely Grímsvötn, Veidivötn‐Bárdarbunga and Katla. A total of 40 tephra layer land–sea correlations have been made within this time period, of which 16 represent absolutely dated tephra markers. In addition, two tephra marker series are revealed in the marine sediments and in the terrestrial tephra stratigraphy, located between c. 2300–2600 and between 5700–5900 years. For the last 15 000 years, 21 tephra markers have been recognized. The marine tephra layer frequency (TLF) reveals two peaks, within the last 2000 years, and between 5000 and 7000 years ago. It shows the same general characteristics as the terrestrial TLF curve in Iceland, which indicates that marine sediments can yield important information about volcanism in Iceland. This is useful in time segments in which terrestrial records are poor or non‐existent. The study contributes to a high‐resolution tephrochronological framework on the North Icelandic shelf, with core MD99‐2275 representing a potential stratotype section in the area, and for the northern North Atlantic–Nordic Seas region, as well as being an important contribution to the Lateglacial–early Holocene volcanic history of Iceland.

Deep-sea ash layers reveal evidence for large, late Pleistocene and Holocene explosive activity from Sumatra, Indonesia

Deep-sea tephra layers sampled from sediment cores collected within, and adjacent to the Sunda trench of offshore Sumatra reveal evidence for five previously undocumented, and apparently large (minimum volume >0.6–>6.3km3; volcanic explosivity index values of 4–5) explosive eruptions over the last ~31,000years, with a presumptive source of mainland Sumatra. Chemical analysis of glass shards and 14C age constraints are used to distinguish the five tephra layers, as well as a sixth that likely correlates with the Youngest Toba tuff (YTT). The tephra layers are labeled V-1 through V-6 relative to their north-to-south positioning along the Sunda trench. The three tephra layers taken from cores west of central Sumatra (V-3, V-4, V-5) are well-constrained by 14C age determinations, whereas less reliable sedimentation-rate estimates are available for the northern (V-1, V-2) and southern (V-6) tephra layers. Deposition of the northernmost tephra, layer V-1, was likely accompanied by seismicity as two chemically indistinguishable tephras are separated by 12cm of course-grained turbidite. Layer V-2 shows a strong chemical resemblance to the YTT and age estimates do not rule out the correlation. With the exception of a likely correlation with the YTT, no other correlations were made between the tephras analyzed in this study with the marine or terrestrial record from the published literature. The most frequent, widespread, and youngest marine tephra layers were found in the central region of the study area. Layers V-3, V-4, and V-5 were all deposited within the last 17 thousand years with minimum eruptive volumes of >0.6 to >5.2km3. A complex depositional sequence of layer V-6 is estimated at ~27.5ka, and may be associated with Late Pleistocene ignimbrite volcanism of southern Sumatra. The ages and suggested minimum volumes represented by the deep-sea tephra layers are consistent with an active volcanic arc, and demonstrate the need for further terrestrial studies.

Tephrostratigraphy and tephrochronology of lakes Ohrid and Prespa, Balkans

Abstract. Four cores from Balkans lakes Ohrid and Prespa were examined for recognition of tephra layers and cryptotephras, and the results presented along with the review of data from other two already published cores from Lake Ohrid. The six cores provide a previously unrealised tephrostratigraphic framework of the two lakes, and provide a new tephrostratigraphic profile (composite) for the Balkans, which spans from the end of the Middle Pleistocene to the AD 472. A total of 12 tephra layers and cryptotephras were recognised in the cores. One is of Middle Pleistocene age (131 ka) and correlated to the marine tephra layer P-11 from Pantelleria Island. Eight volcanic layers are Upper Pleistocene in age, and encompass the period between ca. 107 ka and ca. 31 ka. This interval contains some of the main regional volcanic markers of the central Mediterranean area, including X-6, X-5, Y-5 and Y-3 tephra layers. The other layers of this interval have been related to the marine tephra layers C20, Y-6 and C10, while one was for the first time recognised in distal areas and correlated to the Taurano eruption of probable Vesuvian origin. Three cryptotephras were of Holocene age. Two of which have been correlated to Mercato and AD 472 eruptions of Somma-Vesuvius, while the third has been correlated to the FL eruption from Mount Etna. These recognitions provide a link of the Ohrid and Prespa lacustrine successions to other archives of the central Mediterranean area, like south Adriatic, Ionian, and south Tyrrhenian seas, lakes of southern Italy (Lago Grande di Monticchio, Pantano di San Gregorio Magno and Lago di Pergusa) and Balkans (Lake Shkodra).