巴黎盆地下侏罗统的岩石磁学研究及其意义

ROCK-MAGNETIC STUDY OF THE LOWER JURASSIC SEDIMENTARY ROCKS FROM PARIS BASIN AND ITS IMPLICATIONS

通过下佛罗统磁性地层学研究,获得了一些能记录岩石形成时的地磁场的样品,根据常规的古地磁方法,等温剩磁和热退磁实验,说明这些岩石的主要载磁矿物为磁铁矿.磁滞回线参数的测量表明多数载磁矿物磁铁矿为假单磁畴,少量样品则可能为假单磁畴与多磁畴的混合物.通过与北美古生代重磁化岩石的磁滞回线参数比值对比,说明重磁化与非重磁化岩五磁滞回线参数比值的分布趋势有明显差别,这一差别可能用于判定岩石的重磁化和非重磁化性质.

Rock magnetic study was carried out on the lower Jurassic sedimentary rocksfrom the Paris basin. Hysteresis properties of several rock chips (up to l8mgl weremeasured on the Micr0mag 29O0' The rati0 0f saturation remanence to saturati0nmagnetizati0n (Jrs/Jr), and remanent coercivity to bulk coercivitY (Hc,/H) indcatesthat m0st 0f them are predondnantly pseudosingle domain (PSD) magnetite grain' Sev-en out 0f twenty five sample fall in multi-domain field of the Day et al- plot, whichare characteristized by a more uwispy' loops with higher values of H,/Hc and lowerMrs/M' We prefer that the c0mposite PSD and multidomain magnetites are the princi-pal magnetic phases which carried respectively the ChRM and sec0ndary lowertemperature magnetizati0n in these normal and reversal samples' The hysteresis experi-ments als0 indicate the important paramagnetic mineral (e'g' pyrite) influence at highfields' These results als0 supp0rt the small PSD grain magnetites carried the primarymagnCtization' All our results fall in the trend for the SD and MD ndalng, which isdislocated to the trend of N0rth American remagnetization limestones' Our results isconsistent with the prop0sision of the 'fingerprinting' criteria which could bu used toexplore the primary nature of the remanent magnetization-