Mineralogy, Geochemistry, and Genesis of Sepiolite and Palygorskite in Neogene Lacustrine Sediments, Eskişehir Province, West Central Anatolia, Turkey

Abstract

Sepiolite and palygorskite are common as layers and nodules in the Neogene lacustrine sediments of the Eskişehir area. This study aims to determine their mineralogical and geochemical characteristics, plus the distribution of these economically important sepiolite and palygorskite deposits within the lacustrine environment. Using these data the research goes on to discuss the environmental conditions for their formation. Sepiolite and palygorskite layers are associated with dolomite, marlstone, and argillaceous limestone. The sepiolite nodules (meerschaum), which are former magnesite gravels, are observed in the Upper Miocene reddish-brown fluvial deposits derived from the ophiolite and its fractureinfills at the northern margin of the basin. Sepiolite and palygorskite are only sparsely associated with dolomite and accessory magnesite, quartz, feldspar, and amphibole. Sepiolite and palygorskite fibers formed as oriented platy fan, interwoven, and knitted aggregates in the absence of dolomite indicated precipitation from supersaturated solution. Sepiolite and palygorskite fibers edging dolomite crystals postdate dolomite and formed through precipitation in a vadose environment under semi-arid to arid climatic conditions. High values of Mg+Fe+Ni and enrichment of light rare earth elements (LREE) relative to middle rare earth elements (MREE) and heavy rare earth elements (HREE), Sr content, depletion of Rb+Ba and K, and negligible negative Eu anomalies all reflect the derivation from the Paleozoic metamorphic and Upper Cretaceous ophiolitic rocks. Locally, Upper Miocene to Lower Pliocene volcanic, volcanoclastic, and fluvio-lacustrine sedimentary rocks supplied the required Si, Mg, Al, and Fe for precipitation of Al-sepiolite and Mg-palygorskite with average structural formulae of Si11.91Al0.09O30Mg6.60Al0.78Fe0.13 (OH)4Na0.12K0.06(OH2)4·nH2O and Si7.74Al0.26O20Mg2.52Al1.13Fe0.38(OH)2(OH2)4Na0.32K0.14 Ca0.12·nH2O, respectively. In contrast to the layered sepiolites, the absence of Al and high Ni content in sepiolite nodules suggest formation through replacement of magnesite gravels at shallow burial in an alkal ine environment. The calculated meerschaum sepiol ite chemical formula i s: Si12.02O30Mg7.87Fe0.01(OH)4Na0.13K0.03(OH2)4·nH2O.

Dolomite dissolution: An alternative diagenetic pathway for the formation of palygorskite clay

“…Palygorskite, with an ideal composition of (Mg, Al) 2 Si 4 O 10 (OH)Á4(H 2 O), is a magnesiumrich monoclinic and orthorhombic clay mineral with a characteristic fibrous habit (Weaver & Beck, 1977;Singer, 1979Singer, , 1984Singer, , 2002Galan, 1996;Galan & Carretero, 1999;Guggenheim & Krekeler, 2011;Murray et al, 2011). Palygorskite is observed in a wide variety of sedimentary deposits worldwide (Isphording, 1973;Callen, 1977Callen, , 1984Weaver & Beck, 1977;Torres-Ruiz et al, 1994;Akbulut & Kadir, 2003), with the largest deposits located within the Middle Tertiary sediments of China, Senegal, Spain, Turkey, Ukraine and the south-eastern United States (Krekeler, 2004;Garcia-Romero et al, 2007;Murray et al, 2011;Yeniyol, 2012Yeniyol, , 2014Kadir et al, 2016Kadir et al, , 2017. The mineral also serves as an important constituent in soils in arid to semi-arid environments (Singer & Norrish, 1974;Singer, 1984Singer, , 2002.…”

Sepiolite as an efficient adsorbent for ethylene gas

“…In the Sivrihisar region, the 200-500 m-thick Miocene-Pliocene volcaniclastic succession unconformably overlies the Palaeozoic metamorphic basement rocks, Mesozoic clastic rocks, carbonates, serpentinites and Eocene granitoids (Fig. 1) (Yeniyol, 1992(Yeniyol, , 2012Ece & Çoban, 1994;Karakaş & Varol, 1994;Kadir et al, 2016). The Miocene-Pliocene succession consists of conglomerate, limestone, dolomite, clayey dolomite, sepiolite, gypsum, magnesite and pyroclastics.…”

Searching for biosignatures in sedimentary rocks from early Earth and Mars

“…1). For example, terrestrial primary or diagenetic clay minerals such as sepiolite, palygorskite and saponite that typically occur in association with dolomite in lacustrine deposits can preserve up to 3% of organic compounds and produce root and gastropod casts 249,250 . These clay minerals are even suggested to nucleate on organic polymers 251,252 .…”

“…These clay minerals are even suggested to nucleate on organic polymers 251,252 . Abundant and thick, organic-rich, brown-to-black precipitates are found basinward, indicating anoxic, yet, shallow, conditions, such as mudflats 250,253 .…”