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Compositional variations and origin of glauconite-bearing sandstones (Macelj formation, NW Croatia)


Aljinović, Dunja; Jurak, Vladimir; Kompar, Dario
Compositional variations and origin of glauconite-bearing sandstones (Macelj formation, NW Croatia) // 22nd IAS Meeting of Sedimentology - Opatija 2003: Abstracts Book / Vlahović, Igor (ur.).
Zagreb: Institute of Geology Zagreb, 2003. (poster, nije recenziran, sažetak, znanstveni)


Naslov
Compositional variations and origin of glauconite-bearing sandstones (Macelj formation, NW Croatia)

Autori
Aljinović, Dunja ; Jurak, Vladimir ; Kompar, Dario

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
22nd IAS Meeting of Sedimentology - Opatija 2003: Abstracts Book / Vlahović, Igor - Zagreb : Institute of Geology Zagreb, 2003

Skup
22nd IAS Meeting of Sedimentology -Opatija 2003

Mjesto i datum
Opatija, Hrvatska, 17-19.09.2003

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
glauconite-bearing sandstones; Macelj sandstones; synsedimentary volcanism; shallow nearshore marine environment; Early Miocene; NW Croatia

Sažetak
In the NW part of Croatia a glauconite-bearing sandstones appeared as a main constituent of the Early Miocene (Egerian-Eggenburgian) Macelj formation.They represent specific type of sedimentation of the Paratethyan marine realm. Previous investigations claimed deposition of glauconite-bearing sandstones as strongly influenced by synsedimentary volcanism (Šimunić et al., 1995). In our investigation four lithotypes of Macelj sandstones have been distinguished in a vertical succession.These are lithotype D, C, B, and B/C.They represent shallow marine nearshore deposits, reflecting two shallowing upward cycles.Laboratory tests pointed out to the different physical properties of each lithotype.Their compositional variation was investigated to establish possible relation between composition, origin and mechanical behaviour, especialy expansiveness and durability.In optical and modal analysis criteria proposed by Zuffa (1985) and Dickinson (1985) has been applied. Well sorting of the medium grained sandstones provided reliable results. The sedimentation of the oldest deposits (lowermost part of Macelj formation) is represented by the dark green ripple cross-laminated glauconite rich sandstones of lithotype D.The large amount of glauconitic material is accumulated in a form of a very thin lamina or as a matrix in intergranular pores. Among the lithic component, fragments of volcanic rocks, glass and pumice dominate. Different sizes and shapes of those grains may suggest direct influence of the synsedimentary volcanism (ash-fall material), although sedimentary structures assume deposition in a shallow marine environment. Lithotype D occurred only in the southern part of Macelj Mt. Glauconitic material which appeared in the intergranular pores is explained as the primary matrix accumulated in rocks that transform diageneticaly to glauconite. (Glauconitic material air-fall material ejected directly into the basin. Although previous investigations interpreted direct ejection of volcanic materials into the basin (V2b , and V3 neovolcanic rocks sensu Zuffa, 1985), the compositional variations of lithotype C, B and B/C suggest rather erosion of the uplifted orogen and erosion of the volcanic rocks located in the source areas as their composition reflects derivation from volcanic and metamorphic sources. Lithotype C is represented by thin-bedded, mainly fine-grained, ripple-cross laminated or trough-cross bedded sandstones. In mineral composition of lithic graywackes/arenites of lithotype C, quartz is the main constituent while lithic fragments are less abundant. Among lithoclasts, fragments of volcanic rocks, cherts and extrabasinal carbonates are present. Feldspars grains are a minor component.Quartz-sericite and/or glauconitic matrix or calcite cement fills the intergranular pores.The main characteristic of lithotype B is massive structure due to intense bioturbation.The compositional variations related to the lithotype C is the dominance of lithic fragments (among which the metamorphic grains are the most abundant rock types) and decrease of glauconite content.The amount of metamorphic fragments exceeds the amount of volcanic particles.The topmost part of the vertical succession is composed of irregular or lensoid beds of the lithotype B/C.Modal analyses pointed out that lithic fragments are its main constituent, while the amount of glauconite is small. Clasts of metamorphic rock as well as of extrabasinal carbonates appear while the volcanic litoclasts disappear. According to criteria proposed by Zuffa (1985) lithotypes C, B and B/C do not display characteristics proposed for sandstones, whose material was derived from active volcanoes such as: discrete pyroclastic layers, appearance of shards and different grain size of pyroclasts related to other grain types.On the contrary, there is evidence of bedload transport (ripples and dunes) well sorting and similar shapes of volcanic and other lithoclasts. The large amount of volcanic lithoclasts could have been derived from the old, eroded volcanic suites or from the contemporaneous volcanic rocks located in the source area.Moreover, modal analyses link all three lithotypes (C, B, B/C) to the field of the reworked orogen or volcanic arcs (Dickinson, 1985). As sedimentary structures pointed out to the shallow see, the oceanic and trench realm (related to the magmatic arcs) as a possible depositonal environment can be excluded.The suture belts, back-arc thrusted belts or magmatic arcs are possible source provenance, while the deposition took place in a shallow nearshore marine environment.

Izvorni jezik
Engleski

Znanstvena područja
Geologija



POVEZANOST RADA


Projekt / tema
0195034

Ustanove
Rudarsko-geološko-naftni fakultet, Zagreb

Profili:

Avatar Url Vladimir Jurak (autor)

Avatar Url Dunja Aljinović (autor)

Citiraj ovu publikaciju

Aljinović, Dunja; Jurak, Vladimir; Kompar, Dario
Compositional variations and origin of glauconite-bearing sandstones (Macelj formation, NW Croatia) // 22nd IAS Meeting of Sedimentology - Opatija 2003: Abstracts Book / Vlahović, Igor (ur.).
Zagreb: Institute of Geology Zagreb, 2003. (poster, nije recenziran, sažetak, znanstveni)
Aljinović, D., Jurak, V. & Kompar, D. (2003) Compositional variations and origin of glauconite-bearing sandstones (Macelj formation, NW Croatia). U: Vlahović, I. (ur.)22nd IAS Meeting of Sedimentology - Opatija 2003: Abstracts Book.
@article{article, editor = {Vlahovi\'{c}, I.}, year = {2003}, pages = {5}, keywords = {glauconite-bearing sandstones, Macelj sandstones, synsedimentary volcanism, shallow nearshore marine environment, Early Miocene, NW Croatia}, title = {Compositional variations and origin of glauconite-bearing sandstones (Macelj formation, NW Croatia)}, keyword = {glauconite-bearing sandstones, Macelj sandstones, synsedimentary volcanism, shallow nearshore marine environment, Early Miocene, NW Croatia}, publisher = {Institute of Geology Zagreb}, publisherplace = {Opatija, Hrvatska} }