Porosity Development Controlled by Deep-Burial Diagenetic Process in Lacustrine Sandstones Deposited in a Back-Arc Basin (Makó Trough, Pannonian Basin, Hungary)

Figure 6

SEM-BSE images, photomicrographs, and CL image showing diagenetic components.(a) Fine-grained sandstones are characterized by concavo-convex grain contacts. Calcite (Cal1) crystals exhibit a faint crosspattern that resembles coccolith morphology. Large mottles of calcite (Cal3) include replacive and cement phases. Microcrystalline quartz cement occurs on quartz grains, well Mcs1, 4060 m, Endrőd Fm. (b) Ankerite cement crystals on dolomite grain. Replacive calcite (Cal3) includes the small remnants of detrital K-feldspar, well M7, 4103 m, Szolnok Fm. (c) Sandstones of the Szolnok Formation are characterized by linear grain contacts. Diagenetic minerals consist of replacive and cement calcite (Cal3), albite and kaolinite, well M7, 3410 m, Szolnok Fm. (d) CL image of the field of view shown in (c). Detrital K-feldspar of pale blue luminescent includes nonluminescent diagenetic albite. Detrital albite of greenish blue fluorescent color (empty arrow) is present among kaolinite. Postcompactional calcite (Cal3) exhibits dull red luminescent color (filled arrows), well M7, 3410 m, Szolnok Fm. (e) Vuggy porosity (blue resin) includes secondary intragranular pores, which are typical in calcite (stained pink) and K-feldspar (stained yellow) and secondary, dissolution-enlarged intergranular pores, which are characterized between framework grains. Kaolinite occurs next to K-feldspar, well K1, 3020 m, Algyő Fm. (f) Quartz with straight crystal face indicates authigenic overgrowth cement precipitation. Postcompactional calcite (Cal3) engulfs quartz cement, well K1, 3036 m, Algyő Fm. Abbreviations: Ab: albite; Ank: ankerite; Cal: calcite; Dol: dolomite; KFs: K-feldspar; Kln: kaolinite; Ms: muscovite; Qz: quartz; Qz au: authigenic quartz. (a)–(c) SEM-BSE images. (d) Cathodoluminescent image. (e, f) Plane polarized light.

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