PETROGRAPHY OF LACUSTRINE DOLOMITES IN SİVRİHİSAR NEOGENE BASIN AND INTERPRETATION OF THEIR DEPOSITIONAL ENVIRONMENT USING STABLE ISOTOPES (d180;d13C)

The most common lithologies comprising the lacustrine deposits in the Sivrihisar Neogene (Upper Miocene-Pliocene) basin are dolomite, dolomite-bearing claystones, and gypsum. The scanning electron microscope (SEM) study of has revealed, microcrystalline dolomite (dolomicrite) different petrographical types such as euhedral, spheroidal, and sub-spheroidal. Stable d18O and d13C isotopes of above-mentioned dolomite types classify into 3 groups. 1) 818O between -1 and +4 %o; d13C between -4 and +0.5 %o; 2) d18O between 6 and -1 %o; d13C between -3 and -1 %o; 3) d18O between -5 and +2 %o;d 1 3C between -1.5 and 0.0 %o. Petrographically different dolomite types and difference in their stable isotopes values may reflect the effect of climatological and hydrodynamic conditions in the Neogene lake-basin which controls the variation in temperature, salinity, and biological activity. Dolomites were formed in a lake environment where the water balance and salinity changes continuously Alkaline dolomite lake was transformed into ephemeral lake which has resulted in the deposition of magnesite and strontianite at the upper limit of evaporation. Salinity was extremely decreased when fresh water inflowed into the lake area or rise in groundwater level, that is supported by lighter d18O values. The local swamps, which has developed at these stages, provided the suitable conditions for the formation of sepiolites and dolomite-bearing sepiolites. The different petrographic types of dolomite crystals and their stable isotope values reflect the continuously changes temperature, salinity, and depth of the lake area The environmental conditions ranging from hipersaline to hyposaline indicate that Sivrihisar Neogene dolomites had been formed in a schizohaline environment as recorded in the geological literature.

Keywords:

-,

PDF

___

Amiri-Garroussi, K., 1988, Eocene spheroidal dolomite from the western Sine Basin, Libya: Sedimentolo- gy, 35, 577-585. Anderson, T.F. ve Arthur, M.A., 1983, Stable isotopes of oxygen and carbon and their application to sedimentologic and paleoenvironmental prob- lems: Arthur, M.A.; Anderson, T.F.; Kaplan, I.R., Veizer, J. and Land, L.S., ed., Stable isotopes in Sedimentary Geology, Society of Economic Pa- leontologist and Mineralogist short course, 10, 1-151. Arakel, A.V., 1980, Genesis and dagenesis of Holocene evaporitic sediments in Hun and Leeman lagoons, Western Australia: Jour. Sed. Petrology, 50,1305- 1326.
Becker, R.H. and Clayton, R.N.. 1972, Carbon isotopic evidence for the origin of a banded iron-formation in Western Australia: Geochim. Cosmochim. Acta, 36, 577-596. Bellanca, A.; Calvo, J.P.; Censi, P.; Neri, R. and Pozo, M., 1992, Recognition of lake-level changes in Miocene lacustrine units, Madrid Basin, Spain. Evidence from facies analysis, isotope geochem- istry and clay mineralogy: Sedimentary Geolo- gy, 76, 135-153. ; Karakaş., Z.; Neri, R. and Varol, B., 1993, Sedi- mentology and isotope geochemistry of lacustrine dolomite-evaporite deposits and associated days (Neogene, Turkey): environmental implication: Miner. Petrogr. Acta, XXXVI, 245-264.
Cody, R.D. and Cody, A.M., 1988, Gypsum nuclea- tion and crystal morphology in analog saline terrestrial environments: J. Sediment. Petrol.,58, 247-255.
Cook, P.J., 1973, Supratidal environments and geochem- istry of some recent dolomite concretions, Queensland, Australia: J. Sediment. Petrol., 43, 998-1012.
Epstein, S.; Graf, D.L. and Degens. E.T., 1964, Oxygen isotope studies on the origin of dolomites: Craig, H.; Miller, S.L. and Wassenburg, G.J., ed., Isotop- ic and cosmic chemistry, North Holland Publ. Comp., Amsterdam, 169-180.
Folk, R.L. and Land, L.S., 1975, Mg/Ca ratio and salinity: Two controls over crystallization of dolomite: Am. Assoc. Petrol. Geol. Bull., 59, 60-68.
Gasse, F.; Fontes, J.C.; Plaziat, J.C.; Carbonel, P.; Kac- marska, I.; De Deckker, P.; SouIie-Marsche, I.; Callot, Y. and Dupeuble, P.A., 1987, Biological re- mains, geochemistry and stable isotopes for the reconstruction of environmental and hydrological changes in the Holocene lakes from North Saha- ra: Palaeogeogr., Palaeoclim., Palaeocol., 60, 1- 46.
Gonfiantini, R., 1986, Environmental isotopes in lake studies: Fritz, P. and Fontes, J.Ch., ed., Hand- book of Environmental Isotope Geochemistry, 2., Elsevier Sc. Publ., Amsterdam, 113-168.
Hardie, LA., 1987, Perspectives: Dolomitization: A critical view of some current vrews: J. Sediment. Petrolo- gy, 57, 166-183.
Hoefs, J., 1987, Stable isotope geochemistry: Springer- Verlag-Berlin, 241p.
Irion, G., 1970, Mineralogisch sediment petrographische und geochemische Untersuchungen am Tuz Gölü (Salzseen), Turkei: Doctora Thesis, Ruprecht Karl-Üniversitaet (Heidelberg), 68 p. (unpub- lished).
Karakaş., Z., and Varol, B., 1993, Sivrihisar-İlyaspaşa ci- varı sepiyolitlerinin elektron mikroskop incelemesi: A. Suat Erk Simpozyumu Bildirileri, (2-5 Eylül 1991)303-310.
Land, L.S., 1980, The isotopic and trace element geo- chemistry of dolomite: The state of the art: Zen- ger, D.H., Dunham, J.B. and Ethington, R.L., ed., Concept of models of dolomitization: Society* of Economic Paledntologist and Mineralogist Special Publication, 28,87-110.
Magee, J.W., 1991, Late Quaternary lacustrine, ground- water, aeolian and pedogenic gypsum in the Prungle lakes, Southeastern Australia: Palaeog- eogr., Palaeoclim., Palaeoecol., 84, 3-42. '
Masson, P.H., 1955, An occurrence of Gypsum in southwest Texas: J. Sediment. Petrology, 25, 72-77.
Müller, G., 1968, Occurrence and origine of salt umbrellas in the Tuz Gölü (Salt Lake) Turkey: Cont. Mineral and Petrol., 20, 295-297.
, 1970, High-magnesian calcrte and proto dolomite in the lake Balaton (Hungary) sediments: Nature, 226, 749-750.
and Irion, G., 1969, Subaerial cementation and subsequent dolomitization of lacustrine carbonate muds and sands from Paleo-Tuz Gölü Turkey: Sedimentology, 12, 193-204.
and Fischbeck, R., 1973, Possible natural mecha- nism for protodolomite formation: Nat. Phys. Sci., 242,139-141.
Peryt, T.M. and Magaritz, M., 1990, Genesis of evaporite- associated platform dolomites: case study of Main Dolomite (Zechstein, Upper Permian), Leba eleva- tion, northern Poland: Sedimentology, 37, 745- 761.
Rosen, M.R. and Warren, J.K., 1990, The origin and sig- nificance of groundwater-seepage gypsum from Bristol Dry lake, California, USA: Sedimentology, 37, 983-996.
Salomons, W. and Mook, W.G., 1986, Isotope geochem- istry of carbonates in the weathering zone: Fritz, P. and Fontes, J. Ch. ed., Handbook of Environ- mental Geochemistry, 2., Elsevier Sc. Publ. Am- sterdam, 239-269.
Talbot, M.R., 1990, A review of the palaeohydrological in- terpretation of carbon and oxygen isotopic ratios in primary lacustrine carbonates: Chem. Geol. (Isot. Geosci. Sect.) 80, 261 -279.
and Kelts, K., 1990, Paleolimnological signatures from carbon and oxygen isotopic ratios in carbo- nates from organic carbon-rich lacustrine sedi- ments: Katz, B.J. and Rosendahl, B.R., ed., La- custrine Exploration: Case Studies and Modern Analogues, Am. Assoc. Pet. Geql. Memoir, 50,99- 119.
Von Der Borch, C.C. and Jones, J.B., 1976, Spheru- lar modern dolomite from the Coorong area, South Australia: Sedimentology, 23, 587-591.
and Lock, D., 1979, Geological significance of Coorong dolomites: Sedimentology, 26, 813-824.
Warren, J.K., 1990, Sedimentology and mineralogy of dol- omitic Coorong lakes, South Australia: J. Sed. Petrol., 60, 843-858.
Weaver, C.E. and Beck, K.C., 1977, Miocene of the S.E. United States: A model for chemical sedimentation in a peri-marine environment: Sedimentary Geolo- gy, 17,1-234.

ISSN: 0026-4563
Yayın Aralığı: Yılda 3 Sayı
Başlangıç: 1950
Yayıncı: Cahit DÖNMEZ

Arşiv