The paper presents new data from a comparative analysis of sedimentary rocks from the Mendeleev Rise (seamount Shamshura), presumably of Triassic age, with sandstones of Aptian age, obtained during underwater sampling of the Alpha-Mendeleev Rise during expeditions in 2012, 2014 and 2016. The geochemical characteristics of the rocks are very similar, and, as a rule, data from samples of different ages form common fields on different diagrams. The petrographic investigations have established that the sandstones of presumably Late Triassic age, as well as the sandstones of Chukotka and Wrangel Island, are dominated by fragments of shale and acid effusives. The Aptian samples are dominated by fragments of mafic rocks. Also, sharp differences are observed in the nature of the age spectra of detrital zircon populations, indicating fundamentally different feeding provinces for the Triassic and Cretaceous sandstones of the Alpha-Mendeleev Rise. Samples from the Shamshura seamount are characterized by populations similar to populations from Triassic rocks of Chukotka and Wrangel Island, indicating the presence of Triassic rocks in this part of the Mendeleev Rise.