Carbon and oxygen isotope record of Lower-Middle Jurassic belemnites and rocks from the Western Balkan Mts. (Bulgaria)

• Autorzy: Metodiev, L. , Koleva-Rekalova, E.
• Konferencja: International Congress on the Jurassic System (7 ; 06-18.09.2006 ; Kraków, Poland)
• Języki publikacji: EN

Abstrakty

EN

Methods This work is based on the study of 76 belemnites and bulk samples, collected from section Dobravitsa-1, located at 60 km to the north of Sofia. Elemental measurements were performed with an ICP-OES instrument (Perkin Elmer, Optima 3000), following microwave digestion (MLS Ethos 1600). Stable isotope data from belemnites (ä13Ccarb and ä18Ocarb) and rocks (ä13Corg) were collected by Finnigan Mat 251/252 and Finnigan Mat Delta E mass spectrometers. TC and TOC measurements were realized with a CS-200 Carbon/Sulfur Analyzer. Overview of results (Fig. 1) We have documented a negative ä13Corg excursion from a background of c. -25.74‰ of the Upper Pliensbachian to -28.63‰ in the base of the Lower Toarcian Tenuicostatum Zone. The ä13Corg record displayed upwards a shift to -25.43‰ in the Falciferum Zone, a fall to -27.41‰ in the Dispansum Zone and rise to -25.83‰ in the Pseudoradiosa Zone. Two smaller rises of ä13Corg were detected in the Aalenian. The ä13Ccarb and ä18Ocarb signatures provided coeval positive C isotope excursions and negative O isotope shifts localized in the Lower Toarcian. The samples produced the following values: Upper Pliensbachian (ä18O from -0.47 to -2.16‰, ä13C from +0.74 to +2.73‰); Toarcian (ä18O from -1.01 to -3.94‰, ä13C from -0.03 to +3.21‰); Aalenian and Lower Bajocian (ä18O from -1.0 to -2.86‰, ä13C from +0.02 to +1.47‰). The extreme values came from the base of the Tenuicostatum Zone, as well as from the Falciferum and Bifrons zones. The TOC contents is low, mostly <0.5 wt%, with maximum of 1.25 wt% in the Pseudoradiosa Zone. The S values range from 0.05 to 2.24 wt%. Both TOC and S show fluctuations that correlate with the isotope curves. The Mn values compose a flat temporal trend (range from 224 to 568 ppm) with an apparent rise to 1263 ppm in the Bifrons Zone. The TC values (varying from 2.72 to 9.97 wt%) are inferring short-term depositional changes. Summary Stable carbon and oxygen isotope data (ä13Corg, ä13Ccarb and ä18Ocarb) are used to appraise the pattern of their stratigraphic variations in an Upper Pliensbachian – Lower Bajocian succession of the Western Balkan Mts. (Bulgaria). A section, which is composed of alternating offshore ferruginous marls, shales and limestones, and divided into 15 ammonite zones (from the Spinatum Zone to the Discites Zone), has been sampled. Several coeval excursions were found to be superimposed on the O and C isotope trends that are pursued by concomitant variations of the organic-carbon (TOC), total-carbon (TC), S and Mn contents. The observed variations seem to be of both global and local significance. Some of them show a synchronicity with other similar events widely recorded in coeval strata in Europe (Jenkyns et al. 2002).

Słowa kluczowe

EN

carbon; oxygen; isotopes; TOC; Lower-Middle Jurassic; Bulgaria

• Czasopismo: Volumina Jurassica
• Rocznik: 2006
• Tom: Vol. 4, no. 1
• Strony: 188-190
• Opis fizyczny: Bibliogr. 1 poz.

Twórcy

autor

Metodiev, L.

autor

Koleva-Rekalova, E.

• Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str. Bl. 24, 1113 Sofia, Bulgaria,

Bibliografia

• Jenkyns H. C., Jones C. E., Grocke D. R., Hesselbo S. P. and Parkinson D. N. 2002. Chemostratigraphy of the Jurassic System: applications, limitations and implications for palaeooceanography. Journal Geological Society, 159: 351-378.