Chukchi Borderland Composite Tectono-Sedimentary Element, Arctic Ocean

Cores from Northwind Ridge, a high-standing continental fragment in the Chukchi borderland of the oceanic Amerasia basin, Arctic Ocean, contain representatives of every Phanerozoic system except the Silurian and Devonian systems. Cambrian and Ordovician shallow-water marine carbonates in Northwind Ridge are similar to basement rocks beneath the Sverdrup basin of the Canadian Arctic Archipelago. Upper Mississippian(?) to Permian shelf carbonate and spicularite and Triassic turbidite and shelf lutite resemble coeval strata in the Sverdrup basin and the western Arctic Alaska basin (Hanna trough). These resemblances indicate that Triassic and older strata in southern Northwind Ridge were attached to both Arctic Canada and Arctic Alaska prior to the rifting that created the Amerasia basin. Late Jurassic marine lutite in Northwind Ridge was structurally isolated from coeval strata in the Sverdrup and Arctic Alaska basins by rift shoulders and grabens, and is interpreted to be a riftogenic deposit. This lutite may be the oldest deposit in the Canada basin. A cap of late Cenomanian or Turonian rhyodacite air-fall ash that lacks terrigenous material shows that Northwind Ridge was structurally isolated from the adjacent continental margins by earliest Late Cretaceous time. Closing Amerasia basin by conjoining sea-floor magnetic anomalies beneath the Canada basin or by uniting the pre-Jurassic strata of Northwind Ridge with kindred sections in the Sverdrup basin and Hanna trough yield similar tectonic reconstructions. Together with the orientation and age of rift-margin structures, these data suggest that (1) prior to opening of the Amerasia basin, both northern Alaska and the continental ridges of the Chukchi borderland were part of North America, (2) the extension that created the Amerasia basin formed rift-margin grabens beginning in Early Jurassic time and new oceanic crust probably beginning in Late Jurassic or early Neocomian time. Reconstruction of the Amerasia basin on the basis of the stratigraphy of Northwind Ridge and sea-floor magnetic anomalies in the Canada basin accounts in a general way for the major crustal elements of the Amerasia basin, including the highstanding ridges of the Chukchi borderland, and supports S. W. Carey9s hypothesis that the Amerasia basin is the product of anticlockwise rotational rifting of Arctic Alaska from North America.

Geologic mapping and petroleum exploration in northern Alaska and seismic surveys offshore suggest that 2 pulses of rifting created the Canada basin. Mississippian to Triassic miogeoclinal rocks in northern Alaska, derived from a now-displaced northerly source land, correlate with similar strata in the Canadian Arctic Islands. Underlying Ordovician and Silurian argillite and graywacke may correlate with the clastic succession in Heezen trough of the Arctic Islands. Closing Canada basin about a Mackenzie delta pole would rejoin these correlative rocks and recreate a unified pre-Jurassic Arctic paleogeography. Rifting began in earliest Jurassic time, creating a west-northwest-trending trough beneath the Beaufort Shelf and probably the southern Canada basin. The main rifting pulse, however, began in late Neocomian time, and the main post-rift progradational sedimentary prism off Alaska is Aptian or Albian and younger. Apparently both late Neocomian and Laramide rifting thinned the crust beneath North Chukchi basin. Marked basinward thickening of Cretaceous strata records the earlier event, and extensional faulting and basinward thickening of Tertiary strata record the later one. The high-standing, north-trending ridges and troughs of the Chukchi borderland, which trend into the North Chukchi basin from the north, may represent localized Laramide(?) crustal extension subparallel to that which created the Laramide(?) and Cenozoic Makarov and Eurasia basins of the Arctic Ocean. This model requires crustal shortening between the Chukchi borderland and Canada basin and transform faults north and south of the borderland. North of our seismic lines, the southern transform may be buried by Tertiary sediment of the North Chukchi basin. End_of_Article - Last_Page 259------------

Meso–Cenozoic evolution of the southwestern Chukchi Borderland, Arctic Ocean

The Chukchi Borderland is a large bathymetric high that extends from the Alaskan Chukchi Shelf into the Amerasia Basin of the Arctic Ocean. Widely interpreted to be underlain by continental crust, the Chukchi Borderland has played a pivotal role in plate reconstructions of the Arctic, despite the fact that its geologic nature, origin and evolution are largely unknown. We present new lithologic descriptions, along with U-Pb, 40Ar/39Ar, and apatite fission track analyses, for rocks dredged from the Chukchi Borderland. These new results provide constraints on the Chukchi Borderland9s crustal architecture, Paleozoic evolution, and pre-Cretaceous paleogeographic position prior to the formation of the Amerasia Basin. Based on the location and nature of dredged rocks, the Chukchi Borderland comprises at least two distinct terranes, juxtaposed by the proposed Chukchi Borderland fault zone. Early Paleozoic units recovered from Northwind Ridge in the eastern Chukchi Borderland consist of low-grade metasedimentary rocks with a Laurentian detrital zircon signature that is statistically indistinguishable from that of Cambrian age units of the Franklinian passive margin exposed on Ellesmere Island in the Canadian Arctic Archipelago. In contrast, high-grade gneisses and amphibolites dredged from the Chukchi Plateau in the central Chukchi Borderland yield U-Pb and 40Ar/39Ar ages that suggest an affinity with rock units of the Pearya terrane of Arctic Canada. U-Pb and 40Ar/39Ar ages reveal a Paleozoic tectonic history beginning in Early Cambrian to Early Ordovician time with subduction/arc-related high-T metamorphism. Intrusive relationships indicate that Late Ordovician to Silurian orthogneisses intruded the high-T units within an arc setting. Devonian exhumation of these high-grade units is recorded by U-Pb dating of sphene and 40Ar/39Ar thermochronology of micas and potassium feldspar. The exhumation of the high-grade rocks was coeval with the deposition of coarse-grained sediments bearing detrital zircon compositions similar to Silurian foreland basin sediments deposited in Pearya, as well as with greenschist facies metamorphism of metasedimentary rocks dredged from Northwind Ridge. The new data suggest paleogeographic restoration of the Chukchi Borderland to a position adjacent to Ellesmere and Axel Heiberg islands prior to Amerasia Basin rifting. This pre-rift position supports and refines the widely cited rotational models for opening of the Canada Basin.

Fifty new heat flow measurements from the Chukchi Borderland (CBL) and adjacent regions of the central Arctic Ocean are reported, where heat flow measurements have been very limited. The average heat flow of the CBL (65 mW/m2) is significantly higher than that of the entire Amerasia Basin (53 mW/m2). In the CBL, the heat flow of the Chukchi Plateau (CP), Northwind Basin (NWB), and Northwind Ridge (NWR) are 64 mW/m2, 69 mW/m2, and 60 mW/m2, respectively. With the aid of nearby seismic profiles, the elevated regional heat flow in the CP and NWR was attributed to the enhanced radiogenic heating of the thick crust (25–29 km), while the most prominent heat flow in the relatively thin crust of the NWB is likely due to the residual heat of a major tectonic extension event. Further numerical heat conduction modeling suggests that the initial rifting of the Amerasia Basin during the Jurassic–Early Cretaceous could not induce such high heat flow in the NWB. Together with recent interpretations of seismic profiles, the elevated heat flow in the NWB could be explained by the residual heat of the Late Cretaceous–early Cenozoic extension. This extension event was contemporaneous with the seafloor spreading in the Makarov Basin and had also been associated with the onset of seafloor spreading in the Eurasia Basin.

Synthesis of seismic velocity, potential field, and geological data from Canada Basin and its surrounding continental margins suggests that a northeast‐trending structural fabric has influenced the origin, evolution, and current tectonics of the basin. This structural fabric has a crustal origin, based on the persistence of these trends in upward continuation of total magnetic intensity data and vertical derivative analysis of free‐air gravity data. Three subparallel northeast‐trending features are described. Northwind Escarpment, bounding the east side of the Chukchi Borderland, extends ∼600 km and separates continental crust of Northwind Ridge from high‐velocity transitional crust in Canada Basin. A second, shorter northeast‐trending zone extends ∼300 km in northern Canada Basin and separates inferred continental crust of Sever Spur from magmatically intruded crust of the High Arctic Large Igneous Province. A third northeast‐trending feature, here called the Alaska‐Prince Patrick magnetic lineament (APPL) is inferred from magnetic data and its larger regional geologic setting. Analysis of these three features suggests strike slip or transtensional deformation played a role in the opening of Canada Basin. These features can be explained by initial Jurassic‐Early Cretaceous strike slip deformation (phase 1) followed in the Early Cretaceous (∼134 to ∼124 Ma) by rotation of Arctic Alaska with seafloor spreading orthogonal to the fossil spreading axis preserved in the central Canada Basin (phase 2). In this model, the Chukchi Borderland is part of Arctic Alaska.

The Chukchi Edges project was designed to establish the relationship betweenthe Chukchi Shelf and Borderland and indirectly test theories of opening forthe Canada Basin. During this cruise, ~5300 km of 2D multi-channel seismicprofiles and other geophysical measurements (swath bathymetry, gravity, magnetics, sonobuoy refraction seismic) were collected from the RV Marcus G. Langseth across the transition between the Chukchi Shelf and ChukchiBorderland. These profiles reveal extended basins separated by faulted high-standingblocks. Basin stratigraphy can be subdivided on the basis of gross stratalgeometry, reflection terminations and inferred unconformities. The wedge-shapedsynrift sequences terminate against the basement highs and/or major faults, burying the basement topography. The inferred postrift seismic units are morenearly tabular, but thicken locally due to compaction of underlying synriftsediments. Reflection character is dominated by alternating high and low amplitudecontinuous reflectors which may be consistent with pelagic or turbiditesediments. Chaotic units are also observed, which may indicate mass-flowdeposits. The truncated sediments over the basement highs of the Chukchi Shelf, Chukchi Plateau and Northwind Ridge suggest major erosion due both to glacialplanation and earlier erosional events perhaps associated with basement upliftprior to or during rifting and extension. It is believed that the bulk of the synrift sediments are Mesozoic in age. Certainly Cenozoic sediments are also preserved in these basins, but theposition of the boundary is uncertain. Locally, continuous reflectors areobserved underlying the rift basin fill. These older units, of very uncertainage, would, if sampled, provide constraint on the history and affinities of theChukchi Borderland. In addition to the extensional basins, a number of small symmetric basinsare observed on the flanks of the Chukchi Plateau. These basins may betranstensional and argue for a 2nd phase of tectonism, which overprinted theobvious extensional fabric of the Borderland. This is supported by theobservation of uplifted postrift sediments on the flanks of some of theintermedial basement highs. Understanding the timing, distribution and extentof these two phases of tectonism, relative to the known history of N-Sextension on the Chukchi shelf and the apparent orthogonal extension observedon the Beaufort Shelf will further constrain the unknown history of the CanadaBasin.

The Chukchi Borderland, a prominent bathymetric feature within the Arctic Ocean, has been interpreted as a fragment of an undeformed continental platform sequence rifted from the passive margin of Arctic Canada. Dredges collected for the U.S. Extended Continental Shelf project aboard the icebreaker U.S. Coast Guard Cutter Healy (cruise number HLY0905) recovered hundreds of kilograms of broken crystalline basement lithologies consisting of mylonitically deformed biotite-bearing amphibolite, garnet-bearing feldspathic gneiss, and augen-bearing orthogneiss from the Chukchi Border land. Metamorphic zircon within the amphibolite and associated leucogranitic seams within these rocks yielded U-Pb zircon ages between ca. 480 and 530 Ma. Garnet-bearing feldspathic gneisses contain variably discordant Mesoproterozoic zircon, ca. 600 Ma igneous zircon, and ca. 485–505 Ma metamorphic overgrowths. While we interpret these gneisses as deformed and metamorphosed granitoids, they could, instead, have a very immature sedimentary protolith. The youngest rocks sampled were K-feldspar augen orthogneisses that yield ca. 430 Ma zircon crystallization ages. Whole-rock geochemistry and Sr-Nd isotopic data indicate that the orthogneisses are I-type calc-alkaline granitoids. All of the basement rocks including the orthogneisses are variably metamorphosed and mylonitized. Collectively, the U-Pb age, geochemistry, and fabric of the dredged Chukchi Borderland basement samples indicate that they represent Neoproterozoic–Ordovician orogenic crust and Silurian arc batholithic rocks. This geologic origin is inconsistent with the Neoproterozoic to early Paleozoic passive margin history of western Arctic Canada to which the Chukchi Borderland has been previously correlated. We alternatively propose that the basement of the Chukchi Borderland is related to the peri-Laurentian composite terranes of Pearya and western Svalbard that have similar geologic histories.

Recent rapid sea ice reduction in the Pacific sector of the Arctic Ocean is potentially associated with inflow of Pacific-origin water via the Bering Strait. For the first time, we detected remarkable subsurface warming around the Chukchi Borderland in the Arctic Ocean over the recent two decades (i.e., the early 21st century). A statistically significant decadal trend of 16.6 ± 10.6 MJ m− 2 year− 1 in the subsurface ocean heat content during 1999–2020 was captured by shipboard hydrographic data, and associated with the transport of Pacific Summer Water from Barrow Canyon northwest of the Alaskan coast, where similar warming appeared. Satellite-derived geostrophic ocean velocity indicated that the northwestward ocean current flowing from Barrow Canyon to the Chukchi Borderland became faster in the late 2010s, in association with southeastward shift of the Beaufort Gyre, circulating clockwise around the Canada Basin. Therefore, we suggest that warming of the Pacific Summer Water passing over the Chukchi shelf and intensification of the northwestward ocean current along the shelf–basin boundary both acted to enhance the heat transport and contributed to the positive trend in downstream subsurface ocean heat content. Our findings fill important gaps in the understanding of ocean heat distribution/transport, which is a key factor for sea ice freezing/melting, in the central Arctic.

Distribution of crustal types in Canada Basin, Arctic Ocean

Changes in sediment source areas to the Amerasia Basin, Arctic Ocean, over the past 5.5 million years based on radiogenic isotopes (Sr, Nd, Pb) of detritus from ferromanganese crusts

The Canada Basin, 1,600 km long and 650 to 1,050 km wide, is an extensive area of moderately deep water lying in the Amerasia sector of the Arctic Ocean (Fig. 1 and Plate 1). Unlike many other ocean basins, it is poorly understood. The tectonic processes that formed it are thought to have played an important role in the structural development and configuration of Alaska and the northeastern USSR, and in the development of the large hydrocarbon resources that have been discovered around the margins of the basin. The borders of the Canada Basin are North America on the east and south and a complex of submarine ridges and plateaus on the north and west that may have diverse origins. The submarine ridge features include the Northwind Ridge and Chukchi Cap of the Chukchi Borderland on the southwest, and the Mendeleev and Alpha Ridges on the northwest and north respectively. Much of the basin has an extensive continental rise that slopes westward from the Canadian Arctic Islands toward the deep Canada Abyssal Plain. This abyssal plain, which underlies the western Canada Basin, is its deepest part. The Mendeleev Abyssal Plain (Fig. 1) lies to the west of the northern part of the Canada Abyssal Plain and is separated from it by a scarp 300 m to more than 500 m high. This scarp and the Northwind Escarpment (the east face of Northwind Ridge) together form the west boundary of the Canada Abyssal Plain; and their continuity may have

Abstract. It is expected that coastal erosion, upwelling, and increased river runoff from Arctic warming will increase the concentration of suspended particles in the Arctic Ocean. Here we analyze in situ transmissometer and fluorometer data from the summers of 2003 through 2008 and bottle-derived particulate organic carbon (POC) and total suspended solids (TSS) measurements sampled in the summers of 2006 and 2007 from the Canada Basin and surrounding shelves. We divided our study area into five regions to account for the significant spatial variability and found that the highest attenuation, POC and TSS values were observed along the Beaufort shelf and the lowest values were located along the eastern shelf of the Canada Basin. We then explored the correlation of POC and TSS with beam attenuation coefficients to assess the viability of estimating POC concentrations from archived transmissometer data. POC (but not TSS) and attenuation were well-correlated over the Northwind Ridge, in the Canada Basin interior, and along the eastern shelf of the Canada Basin. Neither TSS nor POC were well-correlated with attenuation along the entire Beaufort shelf. An interannual comparison of the attenuation and fluorescence data was done. We found no evidence of increasing attenuation from the summers of 2003 through 2008 and, although not statistically significant, it even appeared that attenuation decreased over time in the upper 25 m of the Northwind Ridge and in the 25–100 m layer (that includes the chlorophyll maximum) of the eastern Beaufort shelf and within the Canada Basin. In the Canada Basin interior, the subsurface chlorophyll maximum deepened at a rate of 3.2 m per year from an average of 45 m in 2003 to 61 m in 2008, an example of how changes to the Arctic climate are impacting its ecology.

Abstract. Knowledge on past variability of sedimentary organic carbon in the Arctic Ocean is important to assess natural carbon cycling and transport processes related to global climate changes. However, the late Pleistocene oceanographic history of the Arctic is still poorly understood. In the present study we show sedimentary records of total organic carbon (TOC), CaCO3, benthic foraminiferal δ18O and the coarse grain size fraction from a piston core recovered from the northern Northwind Ridge in the far western Arctic Ocean, a region potentially sensitively responding to past variability in surface current regimes and sedimentary processes such as coastal erosion. An age model based on oxygen stratigraphy, radiocarbon dating and lithological constraints suggests that the piston core records paleoenvironmental changes of the last 155 kyr. TOC shows orbital-scale increases and decreases that can be respectively correlated to the waxing and waning of large ice sheets dominating the Eurasian Arctic, suggesting advection of fine suspended matter derived from glacial erosion to the Northwind Ridge by eastward flowing intermediate water and/or surface water and sea ice during cold episodes of the last two glacial-interglacial cycles. At millennial scales, increases in TOC might correlate to a suite of Dansgaard-Oeschger Stadials between 120 and 45 ka before present (BP) indicating a possible response to abrupt northern hemispheric temperature changes. Between 70 and 45 ka BP, closures and openings of the Bering Strait could have additionally influenced TOC variability. CaCO3 content tends to anti-correlate with TOC on both orbital and millennial time scales, which we interpret in terms of enhanced sediment advection from the carbonate-rich Canadian Arctic via an extended Beaufort Gyre during warm periods of the last two glacial-interglacial cycles and increased organic carbon advection from the Siberian Arctic during cold periods when the Beaufort Gyre contracted. We propose that this pattern may be related to orbital- and millennial-scale variations of dominant atmospheric surface pressure systems expressed in mode shifts of the Arctic Oscillation.

Multibeam bathymetric and sediment profiler evidence for ice grounding on the Chukchi Borderland, Arctic Ocean