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

Metodiev L., Koleva-Rekalova E.

Volumina Jurassica

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2006

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Vol. 4, no. 1

188-190

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).

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High resolution microfossil, microfacies and palynofacies studies as the only method in recognition of the Jurassic and Cretaceous "black shales" in a strongly tectonised section of the Czorsztyn Succession, Pieniny Klippen Belt, Poland

Bąk K., Barski M., Bąk M.

Studia Geologica Polonica

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2005

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Vol. 124

171-198

EN

Combined stratigraphic studies based on foraminifers, radiolarians and palynomorphs together with microfacies and palynofacies characteristics allowed us to separate the Lower Turonian sediments corresponding to the Cenomanian/Turonian boundary event from the Lower-Middle Jurassic black facies in a strongly tectonised section of the Czorsztyn Succession in the Pieniny Klippen Belt, Poland. The studied section, located at Trawne creek, includes tectonised incompetent series of black marly facies and pink, cherry-red marls and marly limestones. The Cenomanian/Turonian boundary event deposits (ca. 0.5 m thick) belong to the upper part of the Altana Shale Bed of the Jaworki Formation with uncertain transition to the pelagic pink and cherry-red marly limestones and marls. Both facies represent the Helvetoglobotruncana helvetica planktonic foraminiferal Zone (Lower-Middle Turonian). The other black facies in the studied section include dark-grey marly shales with dark-grey calcareous mudstone (ca. 1.5 m of total thickness). These sediments most likely belong to the Skrzypny Shale Formation. This is documented by the filament-radiolarian microfacies, dinocyst and radiolarian stratigraphic data. An Early Bajocian age was determined only for one thin package of dark-grey shale. Other packages of black facies include long-ranging dinocyst taxa of Late Pliens- bachian-Early Bathonian age. Following the earlier stratigraphic data for the Skrzypny Shale Formation (Middle Aalenian-Lower Bajocian), based on ammonite fauna, it may be suggested that a part of these black facies might represent the underlying lithostratigraphic unit, the Krempachy Marl Formation, or its transition to the Skrzypny Shale Formation. Pelagic cherry-red marls and marly limestones which in most cases are in tectonic contact with the black facies are here also strongly tectonised. They represent different, non-continuous stratigraphic horizons of the Lower-Middle Turonian and the Lower Campanian.

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Utwory jury środkowej i ?dolnej w rejonie Księżpol-Lubaczów (SE Polska)

Moryc W.

Biuletyn Państwowego Instytutu Geologicznego

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2004

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nr 408

5-71

PL

Obszar Księżpol-Lubaczów w dolnej i środkowej jurze należał do północnego skłonu, wschodniego przedłużenia bruzdy środkowopolskiej. Opisane utwory środkowej i przypuszczalnej dolnej jury to osady klastyczne o maksymalnej miąższości rzeczywistej około 400 m. W ich najniższej części występuje cienka, około 20 m grubości seria ilasto- piaszczysta, zaliczona do dolnej jury. Środkową jurę reprezentują, od dołu, utwory piaskowcowe, którym przypisuje się wiek od aalenu do kujawu dolnego oraz leżące wyżej osady ilasto-mułowcowe, miejscami z wkładkami piaskowców, należące do kujawu środkowego i górnego, batonu oraz keloweju. W pracy przedstawiono również tektonikę i układ strukturalny badanych utworów oraz uwagi dotyczące paleogeografii. Ponadto określono związek tych osadów z podobnymi utworami występującymi na obszarach graniczących z rejonem badań.

EN

In the Early and Middle Jurassic, the area of Księżpol-Lubaczów constituted the northern margin of the eastern continuation of the Mid-Polish Trough. Middle and probably Lower Jurassic deposits consist of clastic rocks, approximately 400 metres thick. In its lowermost part, the thin (ca 20 m thick) clay-sandy series is considered to be of Early Jurassic age. The basal layer of the Middle Jurassic lithostratigraphic succession consists of sandstones, whose age was established as Aalenian-early Kuiavian. The upper layers of the succession are composed of clayey and muddy sediments with sandstone intercalations, representing the middle and upper Kuiavian, Bathonian and Callovian. The present study focuses on the Middle Jurassic deposits as well as the tectonic, structural and palaeogeographic problems of the area. Moreover, a comparison is made of the discussed sediments and stratigraphic index-fossils with those of the neighbouring regions.