Elsevier

Precambrian Research

Volume 363, 1 September 2021, 106327
Precambrian Research

Precambrian paleosols on the Great Unconformity of the East European Craton: An 800 million year record of Baltica’s climatic conditions

https://doi.org/10.1016/j.precamres.2021.106327Get rights and content

Highlights

  • Weathering on East European Craton.

  • Mature and well preserved Precambrian paleosol altered by low degree of diagenesis.

  • Studied profiles represent weathering sequences from early to advance stages, on a variety of parent materials and ages.

  • Paleosols are analogous to Recent weathering in warm and humid (tropical) climate.

  • Unique set of Meso and Neoproterozoic paleosols on the crystalline basement of the East European Craton.

  • Exceptionally low compaction and low diagenetic alteration.

  • Evidence of microbial life on land with U-Pb dating of pedogenic carbonate at 655 ± 45 Ma.

  • Lateritic type weathering indicative of hot and humid tropical climate dominating on Baltica in Meso- and Neoproterozoic.

Abstract

Meso- and Neoproterozoic paleosols, collected from different areas of the East European Craton: Belarus, Estonia, Lithuania, and Ukraine, offer a chance to examine continental weathering sequences from early to advanced stages of weathering on a variety of different parent materials such as gneisses, granites, gabbros and amphibolites. They were studied using quantitative XRD of the bulk rock, XRD and Mössbauer of the clay fractions, microscopic, geochemical, carbonate stable isotopes and carbonate U-Pb geochronology methods. These paleosol profiles are on average 10 m thick, reddish coloured, and many of them are characterized by a well-developed and well-defined alteration sequence with uppermost horizons approaching the lateritic stage, as indicated by the Chemical Index of Alteration values reaching 90. The dominant type of weathering leads towards kaolinite and a Fe-oxide/hydroxide mineral assemblage through a smectitic intermediate stage. In the paleosol profiles developed on mafic parent materials, dioctahedral smectite is the first weathering product at the base, it dominates in the middle-upper horizons and it later becomes unstable and alters into kaolinite; whereas in paleosols developed on felsic parent materials kaolinite forms already at the initial stage of weathering, as a result of Na-plagioclase dissolution. Kaolinite content in the uppermost horizons reaches 34 wt% in the best developed profile, and Fe-minerals (hematite and goethite) show a clear increasing trend towards the top, reaching 12 wt%. It is likely that uppermost kaolinite-dominated horizons, which are lacking in some profiles, have been eroded. Such paleosol composition and ferric composition of smectites indicate oxidative weathering and are interpreted to represent a warm and humid climate, which seems to have prevailed on the EEC over the Meso- and Neoproterozoic, except well-documented glacial periods. The δ13C signatures of the pedogenic carbonates document microbial processes in the paleosols, which is also indicated by the elevated U/Th values in their top layers. One paleosol was dated with in situ pedogenic calcite U-Pb geochronology at 655 ± 45 Ma (2σ), confirming the estimate based on its stratigraphic position. The Proterozoic paleosol profiles, and dioctahedral smectite in particular, remained unaltered for over 900 Ma until the Paleozoic, when they were affected by low-temperature (<110 °C) diagenesis, evidenced by the presence of K-Ar dated illite–smectite and aluminoceladonite. The maximum and the most common degree of the dioctahedral smectite illitization is 26% S; the %S zonation indicates that the illitizing fluids invaded paleosols from the overlying sediments.

Introduction

Paleosols, which record the interaction of rocks with the atmosphere and hydrosphere, offer a unique opportunity for studying past climates. Precambrian paleosols are known from many continents, but they are often thin (<50 cm) and developed on sediment (e.g. Ediacara Member paleosols in Australia; Retallack, 2012) or their mineralogical and geochemical composition is affected by various post-weathering processes (e.g. Beukes et al., 2002, MacFarlane and Holland, 1991, Mitchell and Sheldon, 2009, Mitchell and Sheldon, 2010, Wiggering and Beukes, 1990) and thus they are of limited use in climatic reconstructions. The East European Craton (EEC), has preserved exceptionally well-developed paleosol profiles of Meso- and Neoproterozoic age. Up to tens of meters thick paleosol was described previously under the Ediacaran sediments on the crystalline basement in Estonia (Kuuspalu et al., 1971, Vanamb and Kirs, 1990, Liivamägi et al., 2014, Liivamägi et al., 2015, Vircava et al., 2015, Driese et al., 2018). Although kaolinite-dominated lateritic paleosol in Estonia is mature and well preserved/unmetamorphosed, its mineralogical composition is affected by diagenesis, with smectite-rich middle sections having been replaced with illite and illite–smectite with 15–25% of expandable layers (Liivamägi et al., 2015). The Ediacaran paleosols, developed on the Ediacaran flood basalts in Volyn, Ukraine, and covered by the Ediacaran sediments, also show high maturity and preservation, but much lower degree of Paleozoic diagenesis, with 60–90% of smectite in the mixed layer illite–smectite (Liivamägi et al., 2018). In Belarus and Russia, paleosols containing kaolinite and smectite occur under sedimentary cover ranging from the upper Ediacaran to Mezoproterozoic (Vendian and Riphean in Russian nomenclature: Eroshev-Shak et al., 1969, Nesterenko et al., 1969, Makhnach and Levykh, 1973, Levykh, 1999). These reports document that the EEC holds a very unique set of well-preserved/unmetamorphosed Precambrian paleosols and that locally these paleosols are affected by a very low degree of diagenesis, which is also evident from the map of conodont alteration index in the Ordovician rocks (Nehring-Lefeld et al., 1997), deposited a few hundred meters above the crystalline basement. The low degree of diagenesis on the craton has been confirmed by a recent multi-method study of its Proterozoic sedimentary cover (Derkowski et al., 2021).

In this contribution, we investigate 15 weathering profiles/paleosols, developed on the crystalline basement of the EEC in Belarus, Estonia, Lithuania, and Ukraine (Fig. 1). These paleosols offer a chance to examine continental weathering and alteration sequences from early stages of weathering to completely weathered paleosols on a variety of different parent materials during the Meso- to Neoproterozoic. An overview including the parent material, age constraints, mineralogy and geochemistry of all studied paleosol profiles is presented in Table 1. The top surface of the EEC crystalline basement (EEC “Great Unconformity”) is very old. The youngest eroded rocks under the sedimentary cover are 1.5–1.3 Ga old Rapakivi granites (Fig. 1a in Paszkowski et al., 2019). The paleosol ages on this surface are constrained by the ages of overlying sediments (Table 1).

Section snippets

Geological setting and age constraints

The EEC paleosols are developed on different rocks including granitoids, gneiss, amphibolite, and gabbro (Table 1). In the central part of the craton, in the Volyn-Orsha Graben (Fig. 1), the weathered crystalline basement is covered by the continental clastic sediments of different units (called “svita” in the Russian stratigraphic scheme) of the Mesoproterozoic (Riphean in Russian literature), of not well-constrained age: Bortnikov (locally at the bottom; <1350 Ma according to Kruchek et al.,

Macroscopic characteristics

15 weathering profiles were available for this study (Fig. 1): 2 from Estonia (Metspere F261, Kiiu), 5 from Lithuania, (Glukelis 348, Sirvintos 1, Vilkiskiai 68, Tverecius 336, and Šaškai 2), 6 from Belarus (Slonim 3, Slonim 14, Slonim 5, Slonim 18, Pinsk 26, and Lida 43) and 2 from Ukraine (Vyshcheolchedayiv and 1679). 6 were sampled by the authors from core materials, 1 (Vyshcheolchedayiv) from an abandoned quarry, 1 (Metspere) was provided by Kalle Kirsimäe, and 7 (the Belarus profiles,

Whole-rock mineralogy

Whole-rock mineral compositions based on the bulk rock XRD are given in Supplementary Table 1, where the paleosol profiles developed on mafic and felsic rocks are listed separately. The bulk rock XRD patterns for the most complete profiles of both types are presented in Fig. 3.

The assemblage of major minerals typical of magmatic/metamorphic rocks includes quartz, K-feldspars (both orthoclase and microcline), Ca-plagioclases in mafic rocks (gabbro and amphibolite) and some felsic rocks, and

Diagenetic overprint

EEC paleosol profiles investigated in this study have been affected by Paleozoic diagenesis, evidenced to occur over the entire area of the western EEC by the K-Ar dates of clay fractions containing illite–smectite and aluminoceladonite (Liivamägi et al., 2018, Środoń et al., 2002, Derkowski et al., 2021). The presence of aluminoceladonite is indicated by both XRD analysis and SEM observations (Fig. 3, Fig. 5), and illite–smectite by XRD (Fig. 3). Well-constrained ages of paleosols diagenetic

Conclusions

  • 1.

    Paleosols of the East European Craton, ranging in age from ca. 1350 to ca. 550 Ma, all represent the same type of kaolinite + hematite weathering under a hot and humid climate, preserving - due to variable erosion - different portions of the weathering profile (Fig. 10). Such a climate must have prevailed on the EEC in these times, with the exception of well-documented glaciation periods (e.g. Chumakov, 2003, Paszkowski et al., 2018).

  • 2.

    Dioctahedral clays: smectite and kaolinite are the main

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

Many thanks to the Republican Unitary Enterprise Belarusian Scientific Geological Survey Institute and Oksana Kuzmenkova, Alla Laptsevich, and Sergei Mankevich personally for providing access to the core material, core descriptions, and the Minsk collection of Nikolay Levykh. Jurga Lazauskiene and Jaunutis Bitinias of the Lithuanian Geological Survey are thanked for providing access to the core material and core descriptions. Kalle Kirsimäe provided the Metspere sample set from Estonia. We

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