Testing the synchronicity of Pleistocene biostratigraphic events in the central Arctic – Do we have a consistent biostratigraphic framework?

<p>Harsh environmental and taphonomic conditions in the central Arctic Ocean make age-modelling for Quaternary palaeoclimate reconstructions challenging. Pleistocene age models in the Arctic have relied heavily on cyclostratigraphy using lithologic variability tied to relatively poorly calibrated foraminifera biostratigraphic events. Recently, the identification of <em>Pseudoemiliania lacunosa</em> in a sediment core from the Lomonosov Ridge, a coccolithophore that went extinct during marine isotope stage (MIS) 12 (478-424 ka), has been used to delineate glacial-interglacial units back to MIS 14 (~500 ka BP). Here we present a comparative study on how this nannofossil biostratigraphy fits with existing foraminifer biohorizons that are recognised in central Arctic Ocean sediments. A new core from the Alpha Ridge is presented, together with its lithologic variability and down-core compositional changes in planktonic and benthic foraminifera. The core exhibits an interval dominated by <em>Turborotalita egelida</em>, a planktonic foraminifer that is increasingly being adopted as a marker for MIS11 in sediment cores from the Amerasian Basin of the Arctic Ocean. We show that the new age-constraints provided by calcareous nannofossils are difficult to reconcile with the proposed MIS 11 age for the <em>T. egelida</em> horizon. Instead, the emerging litho- and coccolith biostratigraphy implies that Amerasian Basin sediments predating MIS5 are older than the egelida-based age models suggest, i.e. that the <em>T. egelida</em> Zone is older than MIS11. These results expose uncertainties regarding the age determination of glacial-interglacial cycles in the Amerasian basin and point out that future work is required to reconcile the micro- and nannofossil biostratigraphy of the Amerasian and Eurasian basin.</p>

Origin of the coarse-grained (> 1 cm) clasts from the Mendeleev Ridge area (Central Arctic Ocean)

The morphometric and petrographic characteristics of the coarse-grained clasts (> 1 cm) sampled from the sediments of the Amerasian Basin, Central Arctic Ocean, were studied. Most of the clasts are represented by dolomites (46,4%), sandstones (22,8%) and limestones (19,8%); the amount of other rocks fragments (chert, shale, igneous) is about 10%. A variety of lithological types were identified among the studied rock fragments. Limestones and dolomitic limestones often contain fragments of fauna. The majority of clasts is poorly rounded and characterized by a wide variety of shapes. More than half of the studied clasts have a size of 1-2 cm, a quarter - 2-3 cm, and larger clasts only occur in insignificant amounts. Geophysical surveys across the sampling sites showed a lack of bedrock outcrops, so the studied coarse-grained clasts are not of local origin. It is concluded that they were predominantly delivered from the Canadian Arctic Archipelago (likely from the platform area, e.g., Victoria Island), mainly due to iceberg rafting during deglaciation periods. The maximum possible contribution of the clasts from the Siberian sources is less than 23%. Distribution of the coarse-grained clasts argues for the existence of a quite stable ice drift path in the past, which is similar to the modern Beaufort Gyre.

Postcollisional granitoids and aptian-albian extension in tectonic evolution of Chukotka mesozoides, Northeast Russia

New U–Pb SIMS zircon datings from granitoid plutons and dikes of Western Chukotka together with earlier obtained data confirm that postcollisional granitoid magmatism and dike intrusion occurred in Aptian–Albian (117–105 m.y.) and fix change of tectonic regime from collision to extension in tectonic evolution of Chukotka Mesozoides. These events may be related to continuing expansion of Amerasian basin since Jurassic and forma- tion in Aptian—Albian time of both oceanic Makarov, Podvodnikov basins and Anakhurgen, Nutesyn and Kameshkov basins in continental framework of Eastern Arctic. Synchronism of tectonic events of extension and spreading in the Canada Basin and collisional events, deformations and reorganization of structural style and sedimentary environment in the South-Anyui suture is noted. This may be regarded as confirmation of rotation hypothesis of Amerasian Basin formation.

U-Pb and oxygen isotope characteristics of Timanian- and Caledonian-age detrital zircons from the Brooks Range, Arctic Alaska, USA

The Devonian connection between the Brooks Range of Alaska, USA, with the continental margin of Arctic Canada and its subsequent Jurassic–Cretaceous counterclockwise rotation to form the Amerasian Basin, is a highly debated topic in Arctic tectonics. This resource-rich region was assembled from terranes that formed part of Laurentia or Baltica, or were juvenile oceanic arcs in the early Paleozoic that were brought together during Caledonian Orogenesis and the subsequent collision that formed Pangea (Uralide Orogeny). Elements of these orogens, as well as older ones, are predicted to occur in the Brooks Range of Arctic Alaska. This study presents the first combined zircon U-Pb and oxygen data from six Brooks Range metasedimentary units with assumed Neoproterozoic to Devonian ages. Three distinct detrital zircon patterns are identified in these units: (1) those with Neoproterozoic maximum depositional ages characteristic of the Timanide Orogen of northern Baltica and adjacent parts of Siberia, (2) an almost unimodal Siluro–Ordovician (443.5 ± 2.3 Ma) detrital zircon population consistent with the oceanic Apoon arc believed to have existed off shore of northern Laurentia and to have accreted to the North Slope subterrane during the Caledonian event, and (3) those with Middle Devonian maximum depositional ages consistent with post-accretion extension during the final (Scandian) phase of Caledonian Orogenesis. Oxygen isotopes from the same zircons reveal minor to significant crustal contamination with approximately two thirds (n = 255/405) having δ18O values >5.9‰ (above the mantle field of 5.3 ± 0.6‰). Pattern 1 units exhibit a progressive increase in δ18O values throughout the Proterozoic (5.99 to 9.29‰) indicative of increasing crustal growth and Timanide age zircons yield average δ18O values of 7.18 ± 0.64‰ (n = 26) suggestive of more crustal influence than Caledonian age zircons, possibly reflecting northern Baltica signatures. The unimodal population in Pattern 2 yields average δ18O values of 5.49 ± 0.66‰ (n = 17) and 6.02 ± 0.27‰ (n = 23) prior to and during, respectively, the main Caledonian event and suggest derivation from Devonian juvenile arc sources possibly representing the initiation of the collision between Laurentia and Baltica. Similar to Pattern 1, the δ18O values associated with Pattern 3 show a progressive increase in δ18O values throughout the Proterozoic (5.00 to 9.39‰). However, Pattern 3 also exhibits a distinct juvenile fingerprint (6.13 ± 0.24‰, n = 51) during the main Caledonian event and a slight increase to 7.12 ± 1‰ (n = 7) in post-Caledonian zircons possibly suggest correlating with a post-accretion phase in which proximally sourced zircon-bearing detritus was deposited in extension-related basins marking the joining of Laurentia and Baltica.

Decorrelation scales for Arctic Ocean hydrography – Part I: Amerasian Basin

Any use of observational data for data assimilation requires adequate information of their representativeness in space and time. This is particularly important for sparse, non-synoptic data, which comprise the bulk of oceanic in situ observations in the Arctic. To quantify spatial and temporal scales of temperature and salinity variations, we estimate the autocorrelation function and associated decorrelation scales for the Amerasian Basin of the Arctic Ocean. For this purpose, we compile historical measurements from 1980 to 2015. Assuming spatial and temporal homogeneity of the decorrelation scale in the basin interior (abyssal plain area), we calculate autocorrelations as a function of spatial distance and temporal lag. The examination of the functional form of autocorrelation in each depth range reveals that the autocorrelation is well described by a Gaussian function in space and time. We derive decorrelation scales of 150–200 km in space and 100–300 days in time. These scales are directly applicable to quantify the representation error, which is essential for use of ocean in situ measurements in data assimilation. We also describe how the estimated autocorrelation function and decorrelation scale should be applied for cost function calculation in a data assimilation system.