A third superchron during the Early Paleozoic

Abstract

Research on geomagnetic reversal chronology has established the existence of two superchrons, one during the Cretaceous and the other (Kiaman) during the Late Paleozoic. Over the past few years, we have performed several magnetostratigraphic studies on Early Paleozoic (Cambrian and Ordovician) sedimentary sequences from Siberia. Our results show high magnetic reversal frequencies during the Middle Cambrian. In contrast, several records show the occurrence of a ~20 Myr long reversed polarity interval in the Lower and Middle Ordovician, suggesting the presence of a third superchron. We propose to give the name of "Moyero"to this new superchron; this name is attributed to the Siberian section which first yielded a complete record of this reversed polarity interval. Brief overview of the studied sections and evidences for a primary magnetostratigraphic signal The main sedimentary sections that we investigated (Moyero, Kulumbe, Khorbusuonka) are located in the northern part of the Siberian platform (Figure 1). They were all deposited in a shallow water environment, and principally consist of argillaceous reddish,

Simulating 2 Ga of geodynamo history

“…Global paleomagnetic observations indicate that the geodynamo has been active over at least the past 3.5 Ga [ Usui et al , ; Biggin et al , ] and possibly even 4.2 Ga [ Tarduno et al , ]. The paleomagnetic record includes hundreds of polarity reversals [ Lowrie and Kent , ], at least 3 and possibly 12 superchrons (periods where the field lingered in a single polarity for tens of million years) [ Pavlov and Gallet , ; Driscoll and Evans , ] and hundreds of paleointensity measurements [ Tauxe and Yamazaki , ; Biggin et al , ]. Suspiciously absent are significant long‐term trends in paleointensity that are expected from the thermal evolution of the core, nucleation of the inner core, changes in mantle convection associated with supercontinental cycles, and superchron episodicity.…”

Variations in geomagnetic reversal frequency during the Earth's middle age

“…For older periods of the Phanerozoic, magnetostratigraphic data obtained from biostratigraphically well‐dated sedimentary sections are less abundant and have provided so far only fragments of the entire geomagnetic polarity reversal history. Nevertheless, the available data show that the geomagnetic reversal frequency has significantly varied over time, from a zero value during long periods without any reversal (the so‐called superchrons) to periods characterized by frequent reversals, such as during the Middle Cambrian, the Middle Jurassic and during the Miocene (see, e.g., Pavlov and Gallet [2005, Figure 9] or Algeo [1996] and Opdyke and Channell [1996]). At present, three superchrons, each one lasting several tens of Myr, were detected during the Phanerozoic, one during the Early Paleozoic [e.g., Gallet and Pavlov , 1996; Pavlov and Gallet , 1998], another at the end of the Paleozoic and the most recent during the Cretaceous [e.g., Opdyke and Channell , 1996].…”

Geomagnetic reversal rates following Palaeozoic superchrons have a fast restart mechanism

“…Proposed end-Kiaman GPTS has both long chrons of 2–3.5 Myr duration1112 or numerous briefer chrons13. The data sets immediately before the Kiaman and Moyero superchrons (mid-Carboniferous and late-Cambrian–early Ordovician respectively) are less extensive1415. In the 2012 GPTS timescale for the Permian, Carboniferous and Ordovician, while the faunal ranges are scaled and converted into a composite position-scale using CONOP1617, the polarity chrons are qualitatively attached to the biozonal scale, at the last stage, after the biozones are scaled to Myrs (Fig.…”