A DATABASE FOR THE MATUYAMA-BRUNHES MAGNETIC REVERSAL

We present a paleomagnetic database, designated MBD97, comprising sedi mentary and lava data for the Matuyama-Brunhes reversal transition fie ld. Using criteria regarding suitability of the rock samples, measurem ent methods and temporal resolution of the data, we consider 62 differ ent studies of the Matuyama-Brunhes reversal; of these, only 11 satisf y our selection criteria: four lava sites, one loess site, three shall ow-marine sedimentary sites, and three deep-ocean sedimentary sites. W e discuss our reasons for accepting or disguarding each candidate data set. We investigate the distribution of transitional virtual geomagne tic poles (VGPs); they fall along American and Asian-Australian longit udes. The spatial and temporal complexity of the data indicate that th e transitional field was almost certainly nonaxisymmetric and nondipol ar. The directional transition of the Matuyama-Brunhes reversal took s imilar to 300-5000 years, during which time the surface intensity fell to similar to 10-20% of its pre-and post-transitional value. We do no t find any systematic bias due to site distribution or inclination sha llowing, although the errors in the data do vary over the duration of the reversal. MBD97 is a small database, but it has a fairly good geog raphic distribution and is suitable for studies of the Matuyama-Brunhe s transition, nonetheless, it is clear that further analysis of transi tions will benefit from a continued program of data collection and ana lysis. The data in MBD97 are listed. (C) 1997 Elsevier Science B.V.