NATURE OF THE DISTRIBUTION OF RARE EARTH ELEMENTS IN MESOZOIC SEDIMENTARY ROCKS OF THE LOWER AMUR REGION

Аннотация

The article presents original data on the contents of rare earth elements (REE) and characterizes their distribution in Mesozoic sedimentary rocks of the Lower Amur region. The author compares various parameters of the studied rocks with similar parameters in the standards of the same rocks. The stratigraphic divisions made on the M-54-I sheet of the 1:200,000 scale State Geological Map belong to the Amur (or Chayatyn) subzone (SFPZ) of the West Sikhote-Alin Structural-Formation Zone (SFZ). Among them, the Zhorminsky (K1 zm) strata, Silasinsky (K 1-2 sl) and Utitsky (K2 ut K2) formations are distinguished. The stratons are composed of sandstones and siltstones in different ratios. They also contain conglomerates, tuffs of different composition, and andesites.

The REE content in siltstones is higher than in sandstones. Higher concentrations of elements were found in the studied rocks relative to the rocks of the Caucasian Folded System (CC). Compared to the aleuropes of the Russian platform, the sandstones of Priamurye  subzone have less REE content, and the siltstones have more. Compared to PAAS (post-Archean Australian shale), the REE content is less. Chondrite normalized REE contents. The trend of the charts is negative. The same behavior of elements is characteristic of the distribution spectra in the studied sandstones, siltstones, RAAS, aleuropesstones of the Russian platform, and rocks of the Caucasian SS. In most of the rocks presented, the LRSE/TRSE is higher than 8, this indicates that the sedimentation basin of detrital material has a predominantly acidic composition.

There is a significant negative europium anomaly – from 0.34 to 0.71 in sandstones, and from 0.47 to 0.75 in siltstones. It also indicates the acidic rocks erosion. Consequently, a set of parameters determines the rocks acidic composition in the demolition areas.