Unusually Well Preserved Casts of Halite Crystals: a Case from the Upper Frasnian of Northern Lithuania

Sedimentary Geology 308 (2014) 44–52

Contents lists available at ScienceDirect

Sedimentary Geology

journal homepage: www.elsevier.com/locate/sedgeo

Unusually well preserved casts of halite crystals: A case from the Upper Frasnian of northern Lithuania

Tomasz Rychliński a,⁎, Piotr Jaglarz a, Alfred Uchman a,JuliusVainoriusb a Institute of Geological Sciences, Jagiellonian University, Oleandry 2a, 30-063 Kraków, Poland b Šiauliai Aušros Museum, Vilniaus St. 74, LT-76283 Šiauliai, Lithuania article info abstract

Article history: Upper Frasnian carbonate-siliciclastics of the Stipinai Formation (northern Lithuania) comprise a bed of calcare- Received 28 February 2014 ous silty arenite with casts of halite crystals, including hopper crystals. Unusually well-preserved casts occur on Received in revised form 14 May 2014 the lower surface of the bed, while poorly-preserved casts are present on the upper bedding surface. The casts Accepted 18 May 2014 originated as the result of the dissolution of halite crystals which grew in the sediment. The dissolution took Available online 23 May 2014 place during early stages of diagenesis, when host sediment was soft. Unstable cavities after crystal dissolution ﬁ Editor: B. Jones were lled by overlying sediment forming their casts. The collapsing sediment form sink-hole deformation structures which disturb wave–ripple cross lamination from the upper part of the bed. Dewatering pipe structures are Keywords: also present. The casts and accompanying sink-hole and dewatering pipes are classiﬁed as the postdepositional Deformation structures deformation structures caused by haloturbation. Halite casts © 2014 Elsevier B.V. All rights reserved. Haloturbation Evaporites Main Devonian Field Stipinai Formation

1. Introduction complete obliteration of primary sedimentary features. Such processes are termed haloturbations (Smith, 1971; Mazzullo et al., 1991). Gener- Crystals of highly soluble evaporitic minerals, such as halite, are spo- ally, the halite crystal casts, even if recognized properly, remain not radically preserved in clastic or calcareous sediments because of their well explained. Pseudomorphs originate by chemical substitution or allow preservation potential. Their pseudomorphs, ﬁlled with calcite, teration, but the formation of crystal casts can be caused by a more com- dolomite or silica are more common (e.g., Staples, 1950; Handford and plex combination of chemical and physical processes, a scenario which Moore, 1976; Álvaro et al., 2000; Gandin et al., 2005; Martill et al., can shed a light on sedimentary and diagenetic environmental changes. 2007; Leitner et al., 2013), while casts of crystals are relatively rare. Unusually well preserved casts of hopper cubic halite crystals, men- The casts of halite crystals have been described among others from tioned earlier by Khabakov (1962) and Sorokin (1978), occur in the the Cambrian Aretomy Formation of the Canadian Rocky Mountains carbonate-siliciclastic Upper Devonian (Frasnian) sediments of north- (Demicco and Hardie, 1994), the Silurian Wills Creek Formation of ern Lithuania. Their high-quality preservation and the presence of ac- the central Appalachians (Demicco and Hardie, 1994), the Lower companying intrastratal deformation structures, analysed in sections Triassic Moenkopi Formation of the Little Colorado River valley, U.S.A. perpendicular and parallel to the bedding surfaces, allow a precise (McKee, 1954), the Upper Triassic of the Lorraine region (Plaziat and reconstruction of the mechanism of crystal cast formation and clearly Desprairies, 1969), and the Oligocene of the Southern Pyrenees (De deﬁnes early diagenetic environmental changes. The mechanism Raaf, 1964). Casts or pseudomorphs of halite crystals are unequivocal seems to be not unique and limited to the studied case, because it refers indicators of evaporitic conditions in a sedimentary environment, but to common phenomena, which are not stratigraphically or geographi- they are usually poorly preserved in host sediments because of the cally restricted. Therefore, the interpretation can be successfully applied high solubility of halite. Growth and dissolution of halite or other evap- to other geological formations, deposited in a hypersaline environment orates during early diagenesis resulted in the disturbance or even under hot and arid climatic conditions.

2. Geological setting ⁎ Corresponding author. E-mail addresses: [email protected] (T. Rychliński), [email protected] (P. Jaglarz), [email protected] (A. Uchman), [email protected] The Upper Devonian of northern Lithuania (Fig. 1) belongs to the (J. Vainorius). western part of the so-called Main Devonian Field of the East European

In northern Lithuania, the Upper Devonian is characterized by intercalated carbonate, sulphate and argillaceous-marly facies (Vodzinskas and Kadūnas, 1969). In the study area (Petrašiūnai Quarry, Pakruojis District), Upper Devonian (Upper Frasnian) rocks belonging to the Stipinai Formation crop out (Paškevičius, 1997). Silty dolostones, calcareous siltstones and green dolomitic marlstones form the lower part of the section, which contains the casts of halite preserved in one bed of ﬁne-grained siliciclastic sediments. The upper part of the section is built of metasomatic cavernous dolostones comprising marine skeletal fossils, including tetracorals, brachiopods and gastropods (Sorokin, 1978; Paškevičius, 1997). In the study area, Devonian rocks are covered by Quaternary tills and sands, which are a few metres thick.

3. Materials and methods

A detailed measured proﬁle was done for the lower part of the study section (Fig. 3). Well-preserved casts of cubic halite crystals were found in situ only on the lower surface of one bed of calcareous silty arenite Fig. 1. The location of the studied area. in the lower part of the Stipinai Formation (Fig. 3) (GPS coordinates: E023°54.344′, N55°59.586′; ±3 m). The bed is about 2 cm thick. It was sampled for laboratory studies. Most of the samples with the best Platform (Vodzinskas and Kadūnas, 1969). The Main Devonian Field preserved casts were collected ex situ on the near slag heap of the is an area of the largest Devonian outcrops and subcrops in Europe. It Petrašiūnai Quarry (E023°54.333′, N55°59.616′; ±3 m). Halite cast encompasses northern Lithuania, Latvia, southern Estonia, and adjacent morphology and their arrangement within the bed as well as accom- parts of Russia and the Baltic Sea. This area belongs to the Baltic Syneclise panying sedimentary structures were determined from numerous (Paškevičius, 1997; Bełka and Narkiewicz, 2008). The Devonian succes- polished slabs. A dozen of thin sections through the casts oriented sion comprises a part of the Palaeozoic cover of the East European perpendicular to the bedding was analysed by means of an optical mi- Platform. The Lower and Middle Devonian succession of the Main croscope under the 20–200× magniﬁcations. Petrographic analyses of Devonian Field is built of continental siliciclastics intercalated by rock fragments and thin sections were made also by means of the scan- shallow-marine sediments (Ziegler, 1988; Bełka and Narkiewicz, ning electron microscope (SEM). Selected thin sections were stained 2008). The Upper Devonian consists of alluvial siliciclastics and shallow with alizarin red-S and potassium ferricyanide in order to distinguish marine carbonate (dolomite) and evaporitic facies (Paškevičius, 1997; calcite from dolomite and ferroan from non-ferroan carbonate minerals. Bełka and Narkiewicz, 2008, with references therein; Fig. 2). The illustrated specimens are hosted in the Institute of Geological

Fig. 2. Palaeogeographic–palaeotectonic sketch of north-eastern Europe during Late Devonian times with marked location of the study area. After Ziegler (1988),modiﬁed. Download English Version: https://daneshyari.com/en/article/4689429

Download Persian Version:

https://daneshyari.com/article/4689429

Daneshyari.com