Composition and properties of the iron hydroxides-cemented lenses in Estonian sandstone of Middle Devonian age

Abstract

The formation of hematite and goethite concretions in different sedimentary rocks including sandstones is an important diagenetic process in the geologic history of the Earth. Its interpretation can also contribute to understanding the diagenetic history of Martian iron hydroxide concretions.A case study of iron-rich concretions from Estonian Middle Devonian sandstones exposed in ancient river valleys in southeastern Estonia was carried out based on the results of mineralogical, petrographical, geochemical, petrophysical and magnetic analyses. It was found that the high Fe 2 O 3 (total) content (25.0−39.5%), high magnetic susceptibility, bulk and grain density, very low porosity, corrosion and fracturing of the quartz grains of the platy iron concretions are in contrast with properties of the Devonian host sandstones. However the ferrous iron content (measured as FeO) of iron-rich concretions was as low as in the other Devonian rocks, suggesting an oxidizing environment and arid climate during the cementation by iron-hydroxides. The fracturing of quartz grains cemented by iron hydroxides could take place at near-surface conditions including vadose and phreatic zones in arid climate with high evaporation rates. Such climatic conditions have been reported for the Baltic region during Devonian, Upper Permian and Triassic times.We have found that goethite is prevalent in the cement, replacing clay and carbonate minerals. We assume that this iron-rich cement is originated from the mobilization of iron in host sandstones by groundwater, associated with tectonic activity at the end of the Middle Devonian, evidenced by fracturing in Devonian outcrops and caves. Although this mobilization could occur under reducing conditions, precipitation of goethite and hematite for the cementation could take place in oxidizing environment along bedding planes close to the surface during short sedimentation breaks. Another possible time for the formation of iron concretions could be Permian, under the condition of both arid climate and tectonic activity. A. Shogenova et al. 112 Stud. Geophys. Geod., 53 (2009) K e y wo r d s : Middle Devonian, iron hydroxides, sandstone, hematite and goethite concretions, chemical composition, mineralogy, magnetic susceptibility, density, porosity

Linkage of diagenesis to depositional environments and stratigraphy in the northern part of the Baltic basin

“…9A-C), are morphologically similar in loose and dolomite-cemented rocks (Kleesment 2009). Clear corrosion features have been recorded in iron-oxide cemented sandstones of the Burtnieki Fm (Shogenova et al 2009) and in the matrix-supported sandstones of the Pärnu and Leivu Fms (Tamme 1964), and also in Cambrian sandstones (Pirrus 2002).…”

“…Interbeds of medium-grained sandstones occur in the Rezekne, Pärnu, Burtnieki and Gauja Fms, those of siltstones in the Kernave and Aruküla Fms. Besides dolomitecemented rocks, also gypsum, late diagenetic calcite (Kleesment & Shogenova 2005) and Fe-hydroxidecemented (Shogenova et al 2009) interlayers are found.…”

Structural and palynomorph evidence for Early Palaeogene‐Neogene conglomerate series in Peninsular Malaysia: Implication for basin development and tectonic history

“…The presence of haematite along with iron cement in Chenderoh conglomeratic series which is composed of authigenic goethite and associative magnetite (Figure 14a–f) implies a diagenetic process of iron oxyhydroxide in a near‐surface oxidizing environment (Shogenova et al, 2009). It is believed to originate from the transformation of iron‐rich kaolinite of a shale unit, which releases goethite and haematite (Langmuir, 1971; Rozenson et al, 1982).…”

Remobilization of HFSE, Y, and REE during Diagenetic Alteration of Heavy Minerals in Sandstones from the Chvalčov Site, Flysch Belt of the Outer Western Carpathians, Czech Republic

“…Therefore, it is often not possible to assess their original size and shape. The dissolution of grain margins is indicated by teeth-or saw-shaped grain outlines as well as deep embayments fulfilled by calcite cement (Figure 2a-d) [28][29][30]. In addition, the dissolution processes operated also along cracks in mineral grains (Figure 2a,b), which is indicated by complexly shaped fractures with unmatching walls (contrary to fractures with matching walls), which originated due to the mechanical opening of a fracture without significant dissolution of the host mineral [31,32].…”