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.

The global paleointensity database for 65-200 Ma was analyzed using a modified suite of paleointensity quality criteria (Q PI ) such that the likely reliability of measurements is assessed objectively and as consistently as possible across the diverse data set. This interval was chosen because of dramatic extremes of geomagnetic polarity reversal frequency ranging from greater than 10 reversals per million years in the Jurassic hyperactivity period (155-171 Ma) to effectively zero during the Cretaceous Normal Superchron (CNS; 84-126 Ma). Various attempts to establish a relationship between the strength of Earth's magnetic field and the reversal frequency have been made by previous studies, but no consensus has yet been reached primarily because of large uncertainties in paleointensity estimates and sensitivity of these estimates to data selection approaches. It is critical to overcome this problem because the evolution of the dipole moment is a first order constraint on the behavior of the geodynamo. Here we show that conventional statistical tests and Bayesian changepoint modeling consistently indicate the strongest median/average virtual dipole moment during the CNS. In addition, the CNS and Jurassic hyperactivity period are characterized by the highest and lowest percentage of virtual dipole moments exceeding the overall median for the 65-to 200-Ma interval, respectively. These observations suggest that the superchron dynamo was able to generate stronger fields than the dynamo operating in the frequently reversing regime. While the precise mechanism remains unclear, our results are compatible with the hypothesis that field strength and reversal rate variation are controlled by changes in core-mantle boundary thermochemical conditions.

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13The Sveconorwegian orogeny in SW Baltica comprised a series of geographically and 14 tectonically discrete events between 1140 and 920 Ma. Thrusting and high-grade 15 metamorphism at 1140-1080 Ma in central parts of the orogen were followed by arc 16 magmatism and ultra-high-temperature metamorphism at 1060-920 Ma in the westernmost 17 part of the orogen. In the eastern part of the orogen, crustal thickening and high-pressure 18 metamorphism took place at 1050 in one terrane and at 980 Ma in another. These discrete 19 tectonothermal events are incompatible with an evolution resulting from collision with 20 another major, continental landmass, and better explained as accretion and re-amalgamation 21 of fragmented and attenuated crustal blocks of the SW Baltica margin behind an evolving 22 continental-margin arc. In contrast, the coeval, along-strike Grenvillian orogeny is typically

A key mechanism responsible for a systematic bias in the global geomagnetic paleointensity database.