@georgeob1,
MAjor polar reversals have been given names by which we can detect them in magma and sedimentary rocks. (Remember that, because the plates are always moving, we have to conduct what are called palinspastic analyses wherein we correct the paleomagnetics with tectonics.
You are correct that there were many mag reversals but we actually measure the time operiods (in chrons) during which the normal or reversed magnetics prevail. Thus the sediments or cooling magma along ocean ridges record these chrons like stripes in a barcode line on a soda bottle.
Chron data gives each geological timespan in a system series or stage, a unique name and alphanumeric title(eg C3n[4n]) describes the time period of stratigraphy in the earliest Pliocene period. It conforms to a specific stratigraphic range of time/sediment.
The chron methiod is mostly important for cultural and paleo anthropological analyses where some geologist is called in on a archeo site to describe the geology. Usually, in the past, one could only describe a uniquely local geologic sequence. But with chron numbers, we can identify the actual time stratigraphic sequence that is unique to that time peweriod worldwide. It applies to sediments, marine sediments, magmas and metamorphics.
I use it in mineral resource evaluations where I may need to (for example), identify a really good deposit of cement rock that is low Magnesium. I can go do a lot of drilling, or I can, do an initial field survey and seek out rocks of a specific chron where, in a regional basin, shows that the limestones contain high Calcium and low magnesium. Saves some time in initial exploration.
The thing that concerns me is that, during the time period that the dipole dissapears and the mag field decays to almost zero, there is a period of time that, maybe less than a few hundred years, could be an environmental nightmare to folks who live in, say Denver or Santiago.
