Latitude Dependence of Geomagnetic Paleosecular Variation and its Relation to the Frequency of Magnetic Reversals: Observations From the Cretaceous and Jurassic

Abstract

Nearly three decades ago paleomagnetists suggested that there existed a clear link between latitude dependence of geomagnetic paleosecular variation (PSV) and reversal frequency. Here we compare the latitude behavior of PSV for the Cretaceous Normal Superchron (CNS, 84–126 Ma, stable normal polarity) and the preceding Early Cretaceous‐Jurassic interval (pre‐CNS, 126–198 Ma, average reversal rate of ~4.6 Myr−1). We find that the CNS was characterized by a strong increase in the angular dispersion of virtual geomagnetic poles (VGPs) with latitude, which is consistent with the results of earlier studies, whereas the VGP dispersion for the pre‐CNS period was nearly invariant with latitude. However, the PSV behavior for the last 5 or 10 million years (average reversal frequency of ~4.4–4.8 Myr−1) shows that the latitude invariance of VGP scatter cannot be considered as a characteristic feature of a frequently reversing field and that a strong increase in VGP dispersion with latitude was not restricted to the long periods of stable polarity. We discuss models describing the latitude dependence of PSV and show that their parameters are not reliable proxies for reversal frequency and should not be used to make inferences about the geomagnetic field stability. During the pre‐CNS interval, the geodynamo may have operated in a regime characterized by a high degree of equatorial symmetry. In contrast, more asymmetric geodynamos suggested for 0–10 Ma and the CNS were evidently capable of producing a very wide range of reversal frequencies.

Rare palaeomagnetic evidence of long-term mantle control of the geodynamo and possible role of the NAD field in the reversal process

“…et al (2008) and quite recentlyDoubrovine et al (2019). However controversial, when considered along with the results of this study, we argue thatMcFadden et al's …”

Analysis of an Updated Paleointensity Database (QPI‐PINT) for 65–200 Ma: Implications for the Long‐Term History of Dipole Moment Through the Mesozoic

“…This criterion, which was not included in the original suite proposed by Biggin and Paterson (), requires that a VDM is associated with a well‐defined paleomagnetic direction, calculated as mean of a minimum of five individual samples directions with attendant Fisher () precision parameter k ≥ 50. These minimal threshold values for the number of samples and within‐site precision are commonly used in paleomagnetic studies of secular variation for discriminating the site‐mean directions that can be reasonably deemed to be reliable (e.g., Johnson et al, ; Biggin et al, ; Cromwell et al, ; Doubrovine et al, ). If only a 95% cone of confidence ( α 95 ) was provided, k was calculated using the equation: where N is the number of samples used to calculate the site‐mean direction.…”

Analysis of geomagnetic secular variation for the last 1.5 Ma recorded by volcanic rocks of the Trans Mexican Volcanic Belt: new data from Sierra de Chichinautzin, Mexico

“…Mean directions and VGPs were calculated at each site with Fisher statistics (Fisher, 1953) and summarized in Table 2 with their α95-confidence circle and Fisher precision parameter (k) parameters. A constant VGP latitude of 45º was used as a cutoff to discriminate the transitional values (Tauxe et al, 2003;Johnson et al, 2008;Doubrovine et al, 2019).…”

“…During the last years, different compilations of directional data from different latitudes around the world, including Mexico were performed (e.g. Johnson, et al, 2008;Opdyke, et al, 2015;Cromwell, et al, 2018, Doubrovine, et al, 2019. The objective is to assembly the record of the PSV at different intervals of time at different latitudes, showing the dependence of the dispersion of the VGP scatter with the latitude.…”

“…Latitude dependence of the VGP's for the last 5 Ma (Johnson, et al, 2008 andOpdyke, et al, 2015) and for the last 10 Ma (Cromwell, et al 2018). Modified from, Doubrovine, et al (2019).…”