Browsing by Subject "WESTERN NEWFOUNDLAND"

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  • Klein, R.; Salminen, Johanna; Mertanen, S. (2015)
    We present a new Late Neoproterozoic paleomagnetic pole for Baltica from an inclined 272 m deep oriented sedimentary drill core in Hailuoto, Western Finland. The depositional age of the Hailuoto sediments is poorly constrained at 570-600 Ma. Three components of magnetization were isolated with thermal and alternating field (AF) demagnetization treatments. The ChRM (characteristic remanence magnetization) component is a high coercivity/unblocking temperature dual polarity component that passes a reversal test. The combined observed ChRM component of the Hailuoto sediments (D = 334.2 degrees; I = 44.4 degrees; alpha(95) = 7 2; k = 16.5) yields a paleomagnetic pole of Plat = 48.7 degrees N and Plon = 241.1 degrees E with A95 = 8.1 degrees. The inclination corrected direction (f = 0.6) of D = 334.4 degrees; I = 57.7 degrees; alpha(95) = 5.8 degrees; k = 25.2 yields a paleomagnetic pole of Plat = 60.5 degrees N and Plon = 247.9 degrees E with A95 = 7.6 degrees. As it is a dual-polarity ChRM carried by both magnetite and hematite, with no resemblance to younger events, we interpret it as a primary component. A paleolatitude for Hailuoto of 383 was calculated from the ChRM. Two secondary components were identified. The first is a low coercivity/blocking temperature component with a remanent magnetization of D = 239.0 degrees; I = 67.3 degrees; alpha(95) = 8.7 degrees (N = 13 samples), which we interpret as drilling-induced remanent magnetization (DIRM). The second secondary component has a remanent magnetization of D = 49.4 degrees; I = 34.9 degrees; alpha(95) = 8.6 degrees (N = 5 samples) and is commonly seen in Fennoscandian formations. The ChRM Hailuoto pole adds to the scattered Ediacaran paleomagnetic data of Baltica and indicate large distances between other late Neoproterozoic and early Cambrian paleomagnetic poles. We present reconstructions of Baltica and Laurentia between 616 and 550 Ma which move Baltica from high latitudes (615 Ma), over the polar region, to low latitudes (550 Ma), and Laurentia from low latitudes (615 Ma) to a polar position (570 Ma) and back to an equatorial position (550 Ma). A low to mid latitude position of Baltica determined by the Hailuoto paleomagnetic pole, and the lack of glaciogenic sediments determined in an earlier study of Hailuoto sediments indicate a warm deposition environment. (C) 2015 Elsevier B.V. All rights reserved.
  • Kröger, Björn; Penny, Amelia (2020)
    During the late Cambrian–Early Ordovician interval the predominant non-microbial reef builders were sponges or sponge-like metazoans. The lithological and faunal composition of Cambro-Ordovician sponge-dominated reefs have previously been analyzed and reviewed. Here we take the relationship between reef aggregation pattern at reef to seascape scale into account, and look for changes during the Early–Middle Ordovician interval, in which metazoans became dominant reef builders. In a comparison of sponge-rich reefs from eight sites of the Laurentia paleocontinent three different seascape level reef growth patterns can be distinguished: (1) mosaic mode of reef growth, where reefs form a complex spatial mosaic dependent on hard substrate; (2) episodic mode, where patch reefs grew exclusively in distinct unconformity bounded horizons within non-reefal lithological units that have a much larger thickness; and (3) belt-and-bank mode, where reefs and reef complexes grew vertically and laterally as dispersed patches largely independent from truncation surfaces. The distinct modes of growth likely represent specific reef forming paleocommunities, because they differ in content and abundance of skeletal metazoan framebuilders, bioturbation intensity of non-skeletal reef sediment matrix, and in association of reef growth with underlying hard substrate. We suggest, based on a review of Laurentian reef occurrences, that the mosaic mode dominated in Early Ordovician strata and that the dominance shifted toward the belt and bank mode from Middle Ordovician strata onward.
  • Kroger, Bjorn; Finnegan, Seth; Franeck, Franziska; Hopkins, Melanie J. (2017)