THE SPONGE FAUNA OF LAKE BAIKAL IN THE LATE PLIOCENE (ACCORDING TO STUDIES OF CORE SAMPLES FROM DEEP BOREHOLE BDP-96-1)

Abstract

Spicules have been investigated in Late Pliocene core samples from the borehole BDP-96-1. The samples have been dated paleomagnetically. A total of 42 spicule types have been discovered, of which 15 are found in modern Baikal sponges and 27 are not. Analysis of the range of species and quantitative indices of the spicules in bottom sediments has revealed three stages of sponge-fauna development: 3.1-2.9, 2.9-2.5, and 2.5-2.1 Ma BP. The sponge fauna of the first stage is indicative of warm-water conditions. Most of thermophilic and fossil species disappeared from the second stage, which points to a dramatic cooling. At the third stage, regeneration of the sponge fauna began. However, it did not reach the efflorescence of the first stage. The results are in agreement with the palynological and diatom analysis of the core samples from the investigated depth range.