Post-remagnetisation vertical axis rotation and tilting of the Murihiku Terrane (North Island, New Zealand)

<p>We collected palaeomagnetic sample sets from Murihiku Terrane, North Island to constrain its palaeolatitude during the Late Triassic–Jurassic. The majority of the sample host rocks were remagnetised. However, a few samples show a magnetic signal that possibly recorded a primary remanent magnetisation. These samples preliminarily indicate that Murihiku Terrane was located at c. 63°S during the Early Jurassic. The remagnetised samples reveal significant post-remagnetisation tectonic rotation and tilting of the host rocks. We estimated an 83 ± 5 Ma timing of remagnetisation by plotting the palaeolatitude data on the apparent polar wander path of northern Zealandia. Samples from southernmost sites have lower inclination, which we interpret as reflecting eastward post-remagnetisation tilt of this region by 20°. In addition, declination data indicate large-scale post-remagnetisation rotation of Port Waikato and Awakino Gorge areas. This study contributes to the ongoing debate on the age and tectonic origin of oroclines in New Zealand basement.</p

Cycladophora davisiana の古海洋学的意義 : 北太平洋亜寒帯に設置されたセディメント・トラップからの考察

第5回放散虫研究集会論文集A time-series sediment trap was deployed at 3,200m in the Bering Sea (StationAB) during August 1990 to August 1993.The trap samples were studied for seasonal fluxes of radiolarians. The seasonal flux patterns of total polycystine radiolarians showed maxima during spring or summer whereas fluxes of C.ycladophora davisiana davisiana Ehrenberg increased during fall. Morley and Hays (1983) interpreted that high % C d. davisiana values in the Sea of Okhotsk were related to their dwelling depth and characteristic oceanographic conditions in the subsurface layer. Our sediment trap data provide a new insight into the arguments proposed by Morley and Hays. Morley and Hays (1983) suggested that the spring radiolarian production was inhibited by the sea ice cover in the Sea of Okhotsk. However C d. davisiana should not be significantly affected by that because of the observed main fluxes of this species in the fall. Therefore, the high percent of C. d. davisiana seen in the core tops in the Sea of Okhotsk, as well as high latitude oceans during the glacial intervals, are considered to be due to seasonal sea ice cover Stylochlamydium venustum (Bailey) is one of the dominant radiolarian species in the Bering Sea.Although tentative for a definite seasonality, the possible spring fiux increase of this taxon might explain why % S. vemtstttm decreased during the glacials. Downcore change of % S. venttstum shows an opposite trend of what ％ C. d. davisiana does in the Bering Sea (Blueford, 1983.), suggesting that the spring increase of S. venustum could have been restricted by sea ice cover and/or melt water during the glacials

Locations, ages, sea surface temperature calculations with standard deviation, and paleolatitude values for sites used to calculate meridional temperature profiles for time slices in the Early (55–48 Ma) and Middle Eocene (45–39 Ma).

<p>Published paleolatitudes refer to values published by the original authors. Values in column paleolatitude.org and error are calculated using methods presented in this paper.</p><p>Locations, ages, sea surface temperature calculations with standard deviation, and paleolatitude values for sites used to calculate meridional temperature profiles for time slices in the Early (55–48 Ma) and Middle Eocene (45–39 Ma).</p

Plate reconstruction at 50 Ma, around the moment of the Early Eocene Climate Optimum, with the sites used for sea surface temperature estimates in Figs 1 and 5.

<p>Reconstruction made in <i>GPlates</i> from Seton and colleagues [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126946#pone.0126946.ref014" target="_blank">14</a>], with modifications as indicated in the main text, placed in the paleomagnetic reference frame of Torsvik and colleagues [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126946#pone.0126946.ref020" target="_blank">20</a>]. Absolute paleolongitude of the global plate motion chain is unconstrained, and irrelevant for paleoclimate reconstructions. Meridians are spaced with 30 degree intervals. Italic numbers 1–14 indicate the reconstructed locations of the sites used for a case study on Eocene meridional temperature, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126946#pone.0126946.g005" target="_blank">Fig 5</a>, and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126946#pone.0126946.t002" target="_blank">Table 2</a>.</p

A Paleolatitude Calculator for Paleoclimate Studies - Fig 1

<p>(A) Example of a plate circuit. The motion of India versus Eurasia cannot be directly constrained since these plates are bounded by a destructive plate boundary (trench). Relative motions between these plates can be reconstructed by restoring the opening history of the North Atlantic ocean between Eurasia and North America, the Central Atlantic Ocean between Africa and North America, and the Indian Ocean between India and Africa. With the relative positions of all these plates known through time, a paleomagnetic pole of one of these plates can be used to constrain all of these plates relative to the geodynamo. (B) schematic outline of plate and mantle motions and reference frames. Plates move relative to the mantle (plate tectonics), and plates and mantle together can undergo phases of motion relative to the liquid outer core (true polar wander). Both processes lead to motion of a rock record relative to the Earth’s spin axis, and hence both influence the angle of insolation that is relevant for paleoclimate study. Mantle reference frames <i>A-C</i> (see text for explanation of these frames) can only reconstruct plate motion relative to the mantle, but cannot reconstruct true polar wander. These frames are therefore used for analysis of geodynamics, but should not be used for paleoclimate studies. Instead, a paleomagnetic reference frame should be used. On geological timescales, the geodynamo coincides with the Earth’s spin axis. The orientation of the paleomagnetic field in a rock can be used to restore a rock record into its original paleolatitude relative to the spin axis.</p

Latitudinal sea surface temperature (SST) gradients for the early- (orange) and middle (blue) Eocene (modified from Bijl and colleagues [2]).

<p>See text for full derivation of data. TEX₈₆-derived SSTs (squares) were recalibrated to TEX₈₆-H following Kim and colleagues [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126946#pone.0126946.ref094" target="_blank">94</a>]. (A) with paleolatitudes as published by Bijl and colleagues [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126946#pone.0126946.ref002" target="_blank">2</a>] and references therein, (B) with paleolatitudes and error bars using the paleolatitude calculator provided with this paper (<a href="http://www.paleolatitude.org" target="_blank">www.paleolatitude.org</a>), in the default reference frame of Torsvik et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126946#pone.0126946.ref020" target="_blank">20</a>]. (C) comparison of paleolatitudes of the same paleotemperature data using paleomagnetic reference frames of Torsvik et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126946#pone.0126946.ref020" target="_blank">20</a>], Besse and Courtillot [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126946#pone.0126946.ref018" target="_blank">18</a>] and Kent and Irving [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126946#pone.0126946.ref034" target="_blank">34</a>]. For data, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126946#pone.0126946.t002" target="_blank">Table 2</a>, for present-day locations see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126946#pone.0126946.g002" target="_blank">Fig 2</a>, for reconstructed locations at 50 Ma see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126946#pone.0126946.g004" target="_blank">Fig 4</a>.</p