ALBERT

Description: Highlights • Five Pleistocene and Holocene explosive eruptions of Mt. Erciyes dated. • Holocene Dikkartın and Perikartın pumices chemically equal Mediterranean S1 tephra. • Karagüllü dome eruption identified as the source of a Black Sea cryptotephra. • Eastward dispersal of Dikkartın fall-out consistent with probabilistic modeling. • Southerly S1 tephra occurrence suggests low altitude ash dispersal from Mt. Ericyes. Abstract Deposition of early Holocene Eastern Mediterranean S1 tephra and a Black Sea cryptotephra coincides with cultural transitions in the Fertile Crescent termed the Neolithic Revolution as well as sapropel formation during climate variability of the African humid period, classifying them as paramount regional marker horizons for archaeology as well as paleoclimatology. Their correlations with specific eruptions of the Mt. Erciyes stratovolcanic complex (Central Anatolia) remained inconclusive though. Here, we use zircon double-dating by (U–Th)/He and U–Th disequilibrium methods, major and trace element tephra glass geochemistry, and probabilistic modeling of tephra dispersal in an attempt to characterize all major late Quaternary proximal tephras of Mt. Erciyes, and to correlate them with distal deposits. Furthermore, we discuss contrasting proximal and distal tephra dispersal. Three nearly-coeval rhyolitic satellite domes (Dikkartın, Perikartın, and Karagüllü) erupted at Mt. Erciyes in the early Holocene, and their dome extrusions were all preceded by explosive phases producing pyroclastic material that formed tephra fall and pyroclastic flow deposits. The new eruption age of 9.03 ± 0.55 ka (1σ uncertainty here and elsewhere) for proximal Dikkartın pumice is consistent with 14C-based S1 tephra chronologies in distal locations averaging 8.92 ± 0.03 cal ka BP. Perikartın pyroclastic flow deposits predate S1 tephra by ca. 0.8 ka according to a pair of published 14C ages, and stratigraphically overlie Karagüllü fall-out, here dated to 8.2 ± 1.8 ka. Previously undated proximal tephras of Mt. Erciyes erupted in the Late (85.2 ± 4.9 ka) and Middle Pleistocene (154.5 ± 5.3 ka). S1 tephra glass is chemically similar to that of Dikkartın fall-out, but also indistinguishable from that of Perikartın fall-out. Karagüllü pumice is characterized by a distinct glass chemical composition, which correlates with that of unnamed cryptotephra reported for the southeastern Black Sea instead, where these results call for a re-evaluation of existing age models. Maximum lithic clast size isopleths for proximal Dikkartın fall-out indicate eastward dispersal of a 20 ± 5 km high eruption plume by stratospheric winds, in agreement with results of probabilistic tephra dispersal modeling. This azimuth contrasts with the known distribution of S1 tephra at distal locations that are all south of Mt. Erciyes. Significant tephra occurrences at up to 1300 km distance and orthogonal to prevalent stratospheric wind directions either result from very atypical wind conditions (probability ≪10 %), or are caused by tephra transport by prevailing low altitude winds. Two scenarios are proposed for low altitude transport: eolian reworking of primary fall-out (more likely from the more widespread Dikkartın deposits), or co-ignimbrite ash cloud dispersal (more likely from the Perikartın eruption which predominantly produced pyroclastic flows). Because S1 tephra is chemically indistinguishable from both Dikkartın and Perikartın by major and trace element glass compositions, its exact source and dispersal mechanism remain ambiguous, although existing 14C ages for Perikartın predating those for S1 tephra favor Dikkartın as its source.

Description: The climactic Los Chocoyos (LCY) eruption from Atitlán caldera (Guatemala) is a key chronostratigraphic marker for the Quaternary period given the extensive distribution of its deposits that reached both the Pacific and Atlantic Oceans. Despite LCY tephra being an important marker horizon, a radioisotopic age for this eruption has remained elusive. Using zircon (U–Th)/He geochronology, we present the first radioisotopically determined eruption age for the LCY of 75 ± 2 ka. Additionally, the youngest zircon crystallization 238U–230Th rim ages in their respective samples constrain eruption age maxima for two other tephra units that erupted from Atitlán caldera, W-Fall (130 +16/−14 ka) and I-Fall eruptions (56 +8.2/−7.7 ka), which under- and overlie LCY tephra, respectively. Moreover, rim and interior zircon dating and glass chemistry suggest that before eruption silicic magma was stored for 〉80 kyr, with magma accumulation peaking within ca. 35 kyr before the LCY eruption during which the system may have developed into a vertically zoned magma chamber. Based on an updated distribution of LCY pyroclastic deposits, a new conservatively estimated volume of ~1220 ± 150 km3 is obtained (volcanic explosivity index VEI 〉 8), which confirms the LCY eruption as the first-ever recognized supereruption in Central America.

Description: Knowledge of temporal patterns of past explosive eruptions is necessary to understand possible future eruptive behavior. However, volcanic records based on geological reconstructions remain incomplete. This inference is true not only for remote and sparsely populated areas like the Aleutian or Kurile-Kamchatka arcs, but also for Europe, where past large explosive events are continuously recognized in the geological record. Here we report the first age and geochemical data on the violent middle to late Pleistocene explosive eruptions from the Elbrus volcanic center (Greater Caucasus), which towers over the densely populated regions in southern Russia and Georgia. We attribute six disparate ash deposits found in the terrestrial and marine sediments along the SE European margin to the Elbrus volcanic center based on major and trace element compositions of individual shards of volcanic glass and radiogenic Sr-Nd-Pb isotope compositions of bulk tephra. We suggest that these deposits represent products of five different eruptions that were dispersed over distances of more than 150–560 km from their source. Three of four eruptions are dated at 522 ± 36, 258 ± 13, and 84.6 ± 7.4 ka by a combined zircon U–Th–Pb and (U–Th)/He approach. One sample revealed an overdispersed spectrum of single crystal (U–Th)/He dates with an average of 176 ± 40 ka. Zircon characteristics and statistical deconvolution of the geochronology data suggest that this sample contains zircon crystals from two different eruptions tentatively dated at 156.5 ± 7.7 ka and 222.8 ± 13 ka. These eruption ages represent the first recognition of a suite of large pumiceous eruptions from the Elbrus volcanic center postdating the previously known explosive activity, documented by ∼800 ka old welded tuffs. These data also provide the first geochemical and geochronological characterization of both proximal and distal Elbrus tephra glasses and contribute to the global tephra database, permitting the identification of Elbrus tephras in distal terrestrial and marine paleoenvironmental archives and hence their use as paleoclimate and archaeological markers. We consider the significance of the identified tephras for paleoenvironmental research and show their potential for tephrochronological studies in the East European Plain and adjacent areas.

Description: Highlights • Combined U-Pb and (U-Th)/He dating provides accurate eruption ages for the Gorelka tephra. • The largest marine transgression of the Eastern Paratethys in the Miocene was at ∼11.5 Ma. • VEI ∼7.4 eruption from a volcanic source in the Carpathians produced the Gorelka tephra. • Westerly winds transported the Gorelka tephra ∼1500 km ENE from the volcanic source. Volcanic ash layers (tephras) dispersed over large areas may offer important time markers in the geological record provided their age and geochemical fingerprint can be established. Accurately dated and geochemically characterized tephras are essential in correlation of temporally and spatially discontinuous geological records, which is key for paleoenvironmental, paleoclimatic, and paleogeographic reconstructions. Here we report geochronological and geochemical data for the Gorelka tephra (southwestern Russia) – a prominent tephra of uncertain age and origin that provides a key time marker for the largest marine transgression of the Eastern Paratethys Sea in the Miocene. Coupled U-Pb and (U-Th)/He dating of zircon crystals constrains the eruption age of the Gorelka tephra, and hence the age of the highest stand of Eastern Paratethys in the Miocene, to 11.5±0.5 Ma. Geochemical characteristics in combination with the new eruption age and tephra volume estimates suggest a magnitude ∼7.4 eruption from a volcanic source in the Transcarpathian region. The Gorelka tephra was transported ∼1,500 km ENE from its source by westerly winds, which were typical for the atmospheric circulation regime within the Ferrel cell in Central Europe during Sarmatian times. Based on the results presented here, the Gorelka tephra provides a reliable tie-point for paleoenvironmental and stratigraphic correlations across southeastern Europe.