Changes of Terrigenous Sediments in Zones of Contact With Basalts (Mouth of the California Gulf, Hole DSDP 474/474a)

The article presents the results of a study using a set of analytical methods of the mineral and chemical composition of sediments from the DSDP Hole 474/474A, 626 m deep, and their changes in contact zones with basalt sills. Jarosite, bassanite and anhydrite were formed in the sediments from these zones. In sediments located above the sill, the thickness of which is 6.73 m, the concentration of Mn and Mo decreased from a weak level of change to a strong one when approaching the roof of the sill. In sediments located above the sill with a thickness of 9.73 m, closer to its roof, the concentration of Mn and P decreased. In these sediments, the quantity of microelements, the content of which has changed, has become greater than in the sediments located above the 6.73 m thick sill. In sediments located between the 4 m thick pillow basalts and the 11.97 m thick massive basalt, a decrease in the concentration of Mo, Cd, and Sb occurred at the level of average intensity of change. Sills of different thicknesses from Hole 474/474A had a limited effect on the mineral and chemical composition of the enclosing sediments, in contrast to the significant influence of hot sills from Holes 478 and 481/481A (Guaymas Depression) on the composition of sediments.