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Berriasian peperites in the Ukrainian Carpathians – their biostratigraphical control and sedimentological significance
Michał Krobicki

Building: Muséum d'Histoire Naturelle de Genève
Room: Amphithéâtre
Date: 2018-12-05 04:40 PM – 05:00 PM
Last modified: 2018-12-01

Abstract


Peperites are special kind of volcano-sedimentary rocks where sharp-boundaries volcanic pieces (usually basaltic) occur within sedimentary deposits and were formed on the sea-floor as effect of submarine eruption and disintegration of magma/lavas intruding and mingling with unconsolidated, or at least poorly consolidated, wet sediment (e.g., Busby-Spera & White, 1987; Skilling et al., 2002; Chen et al., 2016). Volcano-sedimentary sequences, which occur in several tectonostratigraphic units in the Transcarpathian Ukraine (Pieniny Klippen Belt, Kamyanyi Potik, Porkulets units) (Lomize, 1968) sometimes have peperites as well.

In the first case, in the Veliky Kamenets active quarry (Pieniny Klippen Belt – PKB) a continuous section with Lower Jurassic (since Hettangian?) to lowermost Cretaceous (Berriasian) sedimentary succession occur (Fig. 1). Biostratigraphy of the Toarcian–Berriasian part of this section is very precise based on ammonites, dinoflagellates and calpionellids (Reháková et al., 2011). Basaltic rocks occur in the uppermost part and overlie creamy-white Calpionella limestones, and directly are covered by biodetritic limestones and synsedimentary breccia (the latter – so-called Walentowa Breccia Member of the Łysa Limestone Formation, according to the Polish and Slovakian part of the PKB; after Birkenmajer, 1977) which are dating by callpionellids as Middle and/or Upper Berriasian and Upper Berriasian, respectively. Importantly, in this breccia some clasts of basaltic rocks occur (Fig. 1) and by this fact they are Middle and/or Upper Berriasian in age as well. Additionally, on the contact between Calpionella limestones and basalts (sometimes developed as pillow basaltic lavas with interstitial limestones) peperites have been discovered recently. According to magnetostratigraphic study (Grabowski et al., this volume) magnetozones from M23r to M18n have been identified in studied section, and the Jurassic/Cretaceous boundary (Colomi/Alpina boundary) occurs in the middle of the M19n2n polarity zone. The newest our investigations are concentrating now on radiometric dating of these basaltic rocks, which geochemically have been earlier determined as intra-plate volcanism (Krobicki et al., 2008; Oszczypko et al., 2012). Integrated litho-, bio-, chemo- and magneto-stratigraphic studies realized in this section can be here supplemented by absolute age of submarine volcanic event as unique chance to calibration of J/K boundary age.

In the second case, the Kamyanyi Potik Unit (Nappe) is the most internal and structurally highest unit of the Fore-Marmarosh units (Krobicki et al., 2014; Hnylko et al., 2015 with literature). It forms the separate nappe and consists of the earliest Cretaceous Chyvchyn Formation (up to 1000 m in thickness), composed mainly by basic effusives, and the Kamyanyi Potik Formation (200 m in thickness) represented by dark, thin-bedded limestones, black shales, sandstones and conglomerates with volcanic material. The best places for study of this unit occur both on the Chyvchyn Mount (1766.1m a.s.l.) – the highest peak of the Chyvchyn Mountains, and in the Rakhiv city vicinity. First geological structure of the Chyvchyn Mountains was shown on  the  geological  map  published  by  Zapałowicz (1886) and Pazdro (1934), where

 

Figure 1: Schematic cross-section of the Veliky Kamenets quarry with sequence of Jurassic and lowermost Cretaceous rocks (after Krobicki et al., 2012; modified; lithostratigraphical names adopted from Birkenmajer, 1977). Explanations: 1-5 – Hettangian(?)-lowermost Bajocian: 1 – white-yellowish conglomerate and cherry shales; 2 – yellow sandstones; 3 – fine-grained sandstones and mudstones with coal; 4 – black shales with spherosiderites; 5 – mudstones with bivalve coquina; Bajocian: 6 – pink crinoidal limestones (Smolegowa and/or Krupianka Limestone Formation); uppermost Bajocian-Oxfordian: 7 – red nodular limestones of the Ammonitico Rosso-type facies (Niedzica Limestone Formation); Kimmeridgian: 8 – red thin-bedded radiolarites (Czajakowa Radiolarite Formation); Upper Kimmeridgian-Upper Tithonian: 9 – red nodular limestones of the Ammonitico Rosso-type facies (Czorsztyn Limestone Formation); 10-14 – Upper Tithonian-Berriasian: 10 – creamy and white Calpionella limestones (Dursztyn Limestone Formation); 11 – black basalts (including peperites); 12 – creamy biodetritic limestones (Harbatowa Limestone Member of the Łysa Limestone Formation); 13 – green tuffites; 14 – yellowish carbonate breccia (Walentowa Breccia Member of the Łysa Limestone Formation). Arrow indicates origin of basaltic clasts within Walentowa Breccia Member.

 

volcano-sedimentary deposits were attributed to the Triassic. Recently, our geological mapping work showed that this complex forms the tectonic klippe/cap which consists four small thrust slices (Hnylko et al., 2015) and biostratigraphical investigations (calpionellids) indicate their Berriasian age. Structurally the lowermost slice (i) (100-200 m in thickness) is developed as thin-bedded micritic Maiolica-type limestones with cherts which are intercalated by calcareous pyroclastic turbidites (similar to stratotype in the Kamyanyi Potik stream near Rakhiv). The second slice (ii) (250-300 m) is formed by hyaloclastic breccias/conglomerates (gravelstones) with volcano-tuffitic matrix and different size of blocks, pebbles and olistoliths of limestones (often with corals and other benthic fauna; formed even huge blocks over 5 m), which genetically represents submarine debris flows. The third slice (iii) (up to 30-40 m) is filled by classical peperites (limestones with irregular pieces of basaltic rocks). The last, fourth slice (iv) (200-250 m) crop out on the Chyvchyn peak and is represented by massive basaltic pillow lavas. In our interpretation the primary volcano-sedimentary sequence was beginning from basaltic pillow lava flows, then peperites, great debris flows with olistoliths and distal pyroclastic turbidities finally, intercalated by micritic, pelagic limestones (Maiolica-type). In this case peperites were transitional event between main submarine basaltic flooding and mingling with carbonate mud on the sea-floor.

In conclusion, in two analyzed cases (Veliky Kamenets quarry and Chyvchyn Mt) we have very unique consortium of volcanogenic rocks and limestones which occur together as sedimentary episode of submarine eruption of basaltic lavas on the unconsolidated wet carbonate mud. Such volcano-sedimentary structure is additional perfect proof for age of volcanic activity by dating of limestones, which are sometimes full both in macro-fossils (e.g., corals of the Štramberk-type limestones – shallow-water carbonates known as olistoliths and exotic pebbles in flysch deposits of the Outer Carpathians; e.g., Eliášová, 2008; Kołodziej, 2015 with literature cited therein) and micro-fossils (calpionellids) which are Berriasian in age (Iwańczuk et al., 2015).

 

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