D. Bi et al., COSMIC NICKEL-IRON ALLOY SPHERULES FROM PLEISTOCENE SEDIMENTS, ALBERTA, CANADA, Geochimica et cosmochimica acta, 57(16), 1993, pp. 4129-4136
A large number of Ni-Fe alloy spherules, containing from 27.63% up to
approximately 100% Ni by weight, have been found in Pleistocene sedime
nts in Alberta, Canada. Most spherules are Ni-Fe metals; a few have ir
on oxide rims, and some have iron-rich dendrites in the main metal pha
se, The concentrations of Ni and Fe in the alloys and X-ray powder dif
fraction data reveal the dominant mineral phase to be taenite (gamma-F
e). The spherules appear to be similar in composition, morphology, and
size to Ni-Fe cores of cosmic spherules found in deep-sea sediments a
nd polar ice. We suggest that the Ni-Fe alloy spherules represent the
ejected Ni-Fe cores of cosmic spherules. A four-stage model, which inv
olves ablation, oxidation, core protrusion, and core ejection, is prop
osed to explain the formation of such spherules. It is estimated that
the accretion rate of cosmic Fe spherules to Earth was approximately 8
.9 X 10(6) tonnes/yr in the Pleistocene.