A Late Cretaceous‐Eocene Geomagnetic Polarity Timescale (MQSD20) That Steadies Spreading Rates on Multiple Mid‐Ocean Ridge Flanks

Abstract

Magnetic anomalies over mid‐ocean ridge flanks record the history of geomagnetic field reversals, and the width of magnetized crustal blocks can be combined with absolute dates to generate a Geomagnetic Polarity Timescale (GPTS). We update here the current GPTS for the Late Cretaceous‐Eocene (chrons C33–C13, ~84–33 Ma) by extending to several spreading centers the analysis that originally assumed smoothly varying spreading rates in the South Atlantic. We assembled magnetic anomaly tracks from the southern Pacific (23 ship tracks), the northern Pacific (35), the southern Atlantic (45), and the Indian Ocean (51). Tracks were projected onto plate tectonic flow lines, and distances to magnetic polarity block boundaries were estimated by fitting measured magnetic anomalies with a Monte Carlo algorithm that iteratively changed block model distances and anomaly skewness angles. Distance data from each track were then assembled in summary sets of block model distances over 13 ridge flank regions. We obtained a final MQSD20 GPTS with another Monte Carlo algorithm that iteratively perturbed ages of polarity chron boundaries to minimize the variability of spreading rates over all ridge flanks and fit an up‐to‐date set of radioisotopic dates. The MQSD20 GPTS highlights a major plate motion change at 50–45 Ma, when spreading rates decreased in the Indian Ocean as India collided with Eurasia while spreading rates increased in the South Atlantic and Northern Pacific and the Hawaii‐Emperor seamount chain changed its orientation.

High resolution reconstructions of the Southwest Indian Ridge, 52 Ma to present: implications for the breakup and absolute motion of the Africa plate

“…The extreme values for spreading rates that are estimated from stage angular velocities that depend on the C17n.1 rotations for all three plate pairs are also another likely artefact (Section 4.5), which we attribute to a likely error in the GTS20 reversal age estimate for C17n. Alternative spreading rates that we derived using reversal ages from GTS12 (Ogg 2012) and MQSD20 (Malinverno et al 2020) exhibited ≈50 per cent less variation for stages whose young or old limits included C17n.1, thereby supporting our contention. Notably, the GTS20 ages for C15 through C19 are all from Westerhold et al's (2014) astronomically tuned age sequence.…”

“…Although other features of the three stage spreading histories are likely to be artefacts of errors in the GTS20 reversal timescale, we found that alternative spreading rate histories that we estimated with the GTS12 timescale (Ogg 2012) or more recent MQSD20 timescale (Malinverno et al 2020) were not sufficiently different to alter any of our interpretations. The primary features in the stage spreading histories, including the rapid rate slowdown and recovery from 42-37 Ma (Fig.…”

One and a Half Million Yearlong Aridity During the Middle Eocene in North‐West China Linked to a Global Cooling Episode

“…We note that recent two geomagnetic polarity time scales that include reassignment of the Eocene chron boundaries (Boulila et al., 2018; Malinverno et al., 2020) slightly differ from each other and the GPTS from Gradstein et al. (2012) that was used by Li et al.…”

“…We note that recent two geomagnetic polarity time scales that include reassignment of the Eocene chron boundaries (Boulila et al, 2018;Malinverno et al, 2020) (Gradstein et al, 2012). Red dots indicate samples measured additionally to the number of samples recorded in Li et al (2018).…”

A Physical Explanation for the Formation of Auroras

“…The geomagnetic field direction or polarity is reversed depending on whether the mantle rotates relative to the core fast or slow, which is called the geomagnetic field reversal. In the geological history of the Earth, the geomagnetic field has been inverted many times [19]. Geomagnetic inversion was recorded in sediments distributed parallel on both sides of the mid-ocean ridge [20] [21].…”