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Ferromanganese crusts in Jurassic limestones at Stankowa Skała, Pieniny Klippen Belt, Poland

Sidorczuk M., Nejbert K.

Volumina Jurassica

2006

Vol. 4, no. 1

66-68

Ferromanganese crusts (FMC) and nodules are known from the Jurassic limestones of the Pieniny Klippen Belt (Western Carpathians) as well as in the Alps, the Bethic Cordillera and Sicily, (e.g. Rojkovič et al. 2003, and papers citied therein). FMC and nodules at the Stankowa Skała near Nowy Targ, first described by Zydorowicz & Wierzbowski (1986), are developed in pelagic condensed limestones that belong to the Czorsztyn Limestone Formation (Birkenmajer 1977). The crusts appear on the uneven surface of non-nodular limestones, developed as limestones with thin-shelled Bositra bivalves. These rocks represent the stratigraphic interval from the uppermost(?) Bajocian to the Callovian (Sidorczuk 2005). The crusts are overlain by Oxfordian limestones rich in the planktonic foraminifer Globuligerina, containing Fe-Mn nodules and small fragments of calcite stromatolites rich in Mn, Fe and Ba oxides. The aim of this presentation is a mineralogical and petrographic description of the FMC occurring at Stankowa Skała and preliminary interpretation of their origin. Two crusts up to 2 cm thick were sampled (Fig. 1) for transmitted and reflected light microscopy, EPMA, and XRD analysis. The crusts from the Stankowa Skała revealed well preserved botryoidal textures, typical of numerous recent and fossil ferromanganese occurrences. The samples contain Fe, Mn, Ba hydrous oxides (rich in Ca, as well as Cu, Ni, and Co), calcite and minor amount of quartz. Large patches of Ce, Fe-carbonates, and small, euhedral crystals of different minerals including native gold were also determined. XRD data indicate that the main mass of the FMC is composed of fine-grained intergrowths of poorly crystallised 10 ? manganate (todorokite) and goethite. The crusts were cut by thin veins, filled by calcite or calcite-Mn, Ba oxide (hollandite) aggregates. Chemistry and petrology of the studied FMC correspond to hydrogenetic accumulation of the manganese minerals, deposited in the pelagic realm on seamounts with reduced supply of carbonate material. However, primary Fe, Mn, Ba hydrous oxides associations were strongly modified by later diagenetic and epigenetic processes. Manganese influx in these environments is commonly referred to hydrothermal activity on the ocean floor, being a visible manifestation of serpentinisation of mantle peridotites. During these processes large amount of Mn, Fe, Ca, Co, Ni, and Cu are released into the seawater, especially during periods of rapid sea-floor spreading. Widespread manganese mineralization at the interface between Callovian and Oxfordian strata in the Pieniny Klippen Belt basin, and also on all the passive continental margin of the European Tethys Ocean may be related to a period of extremely low deposition rate, presumably caused by a rapid sea-floor spreading in the western Tethys domain. Additionally, palaeomagnetic data from the Pieniny Klippen Belt indicating significant palaeolatitudinal shift during in the Callovian-Oxfordian time span (c.a. 1000 km) are in line with this hypothesis (Lewandowski et al. 2005, Lewandowski et al. 2006). The occurrence of FMC at Stankowa Skała correlates well with this geodynamic event.