Biomagnetostratigraphy of the Vikinghogda Formation, Svalbard (Arctic Norway), and the geomagnetic polarity timescale for the Lower Triassic

Abstract

A biomagnetostratigraphy for the Lower Triassic is constructed, using the ammonoid biostratigraphy from Arctic Boreal successions. Combined thermal and alternating fi eld demagnetization determines the Triassic magnetic fi eld polarity in 86% of specimens, with 36% showing linear trajectory line fi ts and the remainder showing great-circle trends toward the characteristic magnetization. Mean pole directions for the Deltadalen (λ = 50°, ϕ = 159°, dp/dm = 3.9°/5.1°), Lusitaniadalen (λ = 56°, ϕ = 163°, dp/dm = 4.4°/5.4°), and Vendomdalen (λ = 57°, ϕ = 143°, dp/dm = 4.4°/5.4°) members fall close to the European Lower Triassic apparent polar wander path. Mean directions for two of these membermeans pass the reversal test. The remanence is predominantly carried by magnetite. The polarity stratigraphy, when integrated with the ammonoid and meager conodont data, is similar to that determined from successions in the Sverdrup Basin (Canada). The Permian-Triassic boundary post-dates a pronounced palynofl oral turnover and predates a short duration reverse magnetozone (LT1n.1r). In the correlated Shangsi section (in South China), LT1n.1r occurs after the fi rst appearance datum (FAD) of H. parvus, but in the Arctic is within the Otoceras boreale Zone. The late Griesbachian to early Smithian is mostly reverse polarity, with three normal-polarity intervals, overlain by mid and late Smithian normal polarity. The Spathian contains four reverse-polarity intervals, the oldest one within the early Spathian with the remainder in the late Spathian. The transition into the Anisian is within the uppermost reverse magnetozone, a feature documented in other sections of this age. The polarity pattern is correlated to other marine sections, indicating the robustness of the biomagnetostratigraphic composite and its utility in calibrating Lower Triassic time.

Latest Permian to Middle Triassic cyclo-magnetostratigraphy from the Central European Basin, Germany: Implications for the geomagnetic polarity timescale

“…Kozur, 1999;Geluk, 2005), which in the Polish nomenclature (Kozur, 1999;Bachmann and Kozur, 2004) and magnetostratigraphy (on the left) with biostratigraphically calibrated magnetic records from the Boreal (Hounslow et al, 2006) and Tethyan realms (Li and Wang, 1989;Muttoni et al, 1996;Scholger et al, 2000), in which the biostratigraphy of the Southern Alps sections is taken from Farabegoli and Perri (1998). 1 age of 252.6 Ma for the PTB (Mundil et al, 2004) was used to anchor the Buntsandstein cyclostratigraphy (estimated ages are shown in italics within the Buntsandstein column), 2 radioisotopic age from (Ovtcharova et al, 2006), 3 radioisotopic age from (Lehrmann et al, 2006).…”

The origin and significance of pedogenic dolomite from the Upper Permian of the South Urals of Russia

“…The stratigraphy in the left column is the international stratigraphy; right column is the local Russian stratigraphy. Arrowed E indicates position of mass extinction horizon, from the global composite magnetostratigraphic correlation of Hounslow et al (2008). Above this, the Stage V calcrete units form lenses of reddened clay within the carbonate layers, which are 16 cm long and 8 cm high and pinch in and out through the bed.…”

“…The line graph on the far left shows percentage of the pedogenic dolomitic palaeosols across the basin for the specific chron. Arrowed E indicates position of mass extinction horizon, from the global composite magnetostratigraphic correlation of Hounslow et al (2008). to local basin conditions, but may relate to larger-scale climatic trends.…”

Occurrence and significance of phytanyl arenes across the Permian-Triassic boundary interval

“…Mørk et al (1999) originally placed the PTB at the base of the Vikinghøgda Formation while, more recently, Hounslow et al (2008) shifted the boundary 12 m above, based on magnetostratigraphic data, whereas Nakrem et al (2008) placed the PTB in-between on the basis of conodonts. The sediments are slightly more mature than the other sections, with MPI-1 values ranging from 0.46-0.69 (R c 0.68-0.82%; Nabbefeld et al, 2010a).…”