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Sediment lithology, lithofacies relationships, palynological and diatom analysis indicate that two drill cores extracted from ancient valleys of the Juminda Peninsula, north Estonia, represent a previously undetected interglacial sedimentary sequence sandwiched between the Middle and Late Pleistocene glacigenic deposits. Four different coloured major lithofacies associations (units), representing two glacigenic cycles, and deposits with the Late Saalian pollen assemblages zone (LS1), the uppermost Eemian (E9), and Early Weichselian pollen zone (EW) were distinguished at the section. The bottommost depositional unit consists of brownish coloured clay, diamicton and gravel beds. The second depositional unit, correlative to the Eemian Interglacial, consists of a black organic-rich palaeosoil and stratified sand. A thick grey coloured bed of massive and partly stratified Weichselian diamicton, sand, clay and silt comprises the third unit, and the fourth, the topmost depositional unit, consists of yel...

This paper reviews both the current and previous studies of the Baltic Yoldia stage along with their alternative interpretations of the results and events. Focus is placed on the Tallinn area in northern Estonia. On the basis of palaeogeographical and diatom-stratigraphical studies, the changes in the palaeoenvironment, during the transition from late glacial to early Holocene (Preboreal) conditions, are described. The Tondi and Sojamae mires at altitudes just around the Yoldia level of the area (ca. 40 m a.s.l.) show only very slight influence of the brackish Yoldia Sea in their supralittoral to littoral environment. The two sites at lower altitudes with a Yoldia water-depth of approx. 40 m at Pirita and approx. 60 m at Harku, register pronounced brackish water conditions in their diatom assemblages, characteristic of the littoral to sublittoral environment of the Yoldia Sea. The litho- and biostratigraphical data cannot confirm a transgressive nature of the Baltic during the brackish Yoldia stage, but are rather suggesting a regressive development of shoreline. According to the present study the diatom composition of the Yoldia sediments was dependent on the depositional environment, and the abundance of saline water diatoms increased with water depth. The influx of older, redeposited, marine diatoms was here of minor importance.

Twenty one superficial sediment samples from areas of high and moderate eutrophication in the Gulf of Riga were studied with respect to siliceous microfossils, mainly diatoms.

The information obtained from a 21 m thick open-pit section of silty-clayey sediments in the Arumetsa bedrock valley, southwestern Estonia, revealed that lacustrine to glaciolacustrine sedimentation at the site started prior to 151 ka ago and lasted to about the end of marine isotope stage 6 (MIS6) at 130 ka. Further down from the 151 ka age-level to the bottom of the buried valley there are ca 60 m of lacustrine fine-grained sediments, the age of which remains still unclear. The Late Saalian sediments at Arumetsa are discordantly overlain by Middle Weichselian clay, silt and sand, deposited between ca 44 and 37 ka ago. As testified by optically stimulated luminescence (OSL) ages, and pollen and diatom record, the Middle Weichselian fine-grained sediments contain redeposited Holsteinian but no Eemian pollen, and have not been fully bleached during deposition. Chronological, microfossil and sedimentological data show two hiatuses in the Arumetsa section. The first hiatus has left no sedimentary evidence for the period between ca 130 ka and 44 ka ago (MIS5 to older half of MIS3). The younger hiatus from ca 37 to 22 ka occurs between the Middle Weichselian lacustrine silt and the Late Weichselian till layer on top of the section.