Abstract
The oceanic magnetic anomaly record contains low amplitude, short wavelength anomalies (‘tiny wiggles’ or ‘cryptochrons’) of uncertain source. A magnetostratigraphic investigation of their origin has been carried out in a 40 m long core (the Massicore) drilled through the Early Oligocene grey-green Scaglia cinerea marlstone and multi-hued Scaglia variegata limestone in the Marches region of northern Italy. The Massicore contains a complete magnetostratigraphy that matches the geomagnetic polarity sequence from chron C16n to chron C12r. It contains no additional short polarity chrons that might account for ‘tiny wiggles’. The marine magnetic record has several of these events within the chron sequence C13r/C13n/C12r. These chrons fall in the 22 m thick Scaglia cinerea part of the Massicore. This formation has a simple magnetic mineralogy dominated by magnetite and is suitable for paleointensity investigations. Magnetic susceptibility is rather uniform within the formation and is determined by paramagnetic minerals. The intensities of natural (NRM), anhysteretic (ARM) and isothermal (IRM) remanent magnetizations vary coherently with depth. Power spectra of the ARM, IRM and NRM variations show significant activity close to the 413 ka period of the Earth's orbital elements. ARM and IRM intensities are proportional except in two stratigraphic intervals. The ratio of NRM intensity to ARM intensity, used as a proxy for relative variation of paleomagnetic field intensity, fluctuates systematically. Its minimum values lie close to the reported positions of cryptochrons in the marine record. The Massicore results favour the interpretation that ‘tiny wiggles’ represent paleointensity variations of the geomagnetic field rather than unresolved short polarity chrons.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call