1. Meeting of Young Geoscientists, 5th April 2013.
The results of sedimentological and gamma-ray logging of Upper Miocene lacustrine turbidites of the Transylvanian Basin
Lilla Tőkés Department of Physical and Applied Geology, Eötvös University, Budapest
István Róbert Bartha Institute of Geology, Babes-Bolyai University, Cluj Napoca, Romania

2. Aims
Krézsek et al (2010) have studied the sedimentology of the Upper Miocene sediments of the Transylvanian Basin, but an in-depth study is lacking from the Southwestern part of the basin
Study the relationship between natural gamma-ray radiation and facies
Paleoenvironmental reconstruction

3. 9,5 Ma
Magyar et al 1999
Krézsek 2011
Upper Miocene

4. Krézsek et al 2010 Micesasa Tau Seica Mare Daia Ocna Sibiului
Gusterita

5. Methods Detailed facies analysis Gamma-ray logging
Portable gamma-ray spectrometer
Scintillation Bismuth Germanate Oxide (BGO) detector of 20 cm3 volume

6. Test measurements
Ocna Sibiului (Vízakna)
Height
Dose rate

7. Test measurements 30 sec measuring time unsteady, too scattered
Ocna Sibiului (Vízakna)
30 sec measuring time unsteady, too scattered
60 sec measuring time
180 sec mesuring time correlates less with grain size
Hereafter: measuring distance 3 or 10 points/meter
Height
Dose rate

8. Gusterița (Szenterzsébet)
50 m clay, silty clay
Rarely very fine, fine grained sand beds are intercalated

9. Gusterița (Szenterzsébet)
Height
Gamma dose rate does not correlate with clay and silty clay variability – at macro scale
10 cm thick sand bed is evident on gamma graph
Interpretation:
Background sedimentation with occasional low-density turbidity currents
Overbank deposit or outer lobe
Dose rate

10. Daia (Dolmány) 4 5 1 2 4 3 3 2 1 6 5

11. Daia (Dolmány)

13. Interpretation: Gravelly and sandy high-density turbidity currents
Dolmány (Daia)
Interpretation:
Gravelly and sandy high-density turbidity currents
Channel erosion and fill – the finer part of the turbidity current was deposited on channel flanks
Complex channel: channel fills are eroded repeatedly
1,5 km away from Gusterita, about 50 m higher – what is their relationship?

14. Micasasa (Mikeszásza)SW NE NE

15. Micasasa
4 + TG 3B 3A 2 1

16. Micasasa (Mikeszásza)
Interpretation:
I. thin-bedded clay, sand alternation – levee deposit
II. erosion, 3 upward thinning cycles – channel
III. erosion, upward thinning cycle – channel
Channel-levee system
1,5x vertical exaggeration SW NE

17. Tau (Székástóhát) NW SE
2x vertical exaggeration

18. Tau (Székástóhát) NW SE

19. Channel-levee system:
Tau (Székástóhát)
2x vertical exaggeration NW SE
Interpretation
Clay and channel fill sand sequences alternating horizontally and vertically
Channel-levee system:
Some 10 meters away from a channel filled with sand, thin- bedded clay and sand is deposited
After filling, the channel moves away, clay is deposited
Later another channel arrives: thick sand, numerous erosion surfaces

20. Ocna Sibiului (Vízakna)

21. Ocna Sibiului (Vízakna)

22. Ocna Sibiului (Vízakna)

23. Ocna Sibiului (Vízakna)

24. Ocna Sibiului (Vízakna)

25. High-density sandy turbidity currents or sandy debris flows
Ocna Sibiului (Vízakna)
Interpretation:
High-density sandy turbidity currents or sandy debris flows
Thinning and fining upward cycles, lack of erosion
Mid-fan, lobe – the system gets filled, the centre of deposition migrates

26. Şeica Mare (Nagysejk)

27. High-density sandy turbidity currents or sandy debris flows
Şeica Mare (Nagysejk)
Interpretation:
High-density sandy turbidity currents or sandy debris flows
Lobe or channel on mid-fan

28. Conclusions
Gamma-ray and facies logs correlate
Small scale heterogeneity (on the order of 10 cm) can be roughly mapped with 10 cm measuring distance
In a homogene succession a different lithology with only 10 cm thickness alters the graph for 1 m
Rip-up clay clasts should not be overlooked
No significant difference in gamma-ray response for different composition of sand

29. Conclusions Paleoenvironment ?
Complex channel fill – Daia (Dolmány), Tau (Székéstóhát)
Channel-levee systems – Micasasa (Mikeszásza), Tau (Székástóhát) ?
Lobe – Ocna Sibiului (Vízakna), Seica Mare (Nagysejk) ?
Overbank or outer fan – Gusterita (Szenterzsébet)
Richards et al 1998

30. Thank you for your kind attention!
We are grateful to Dr. Orsolya Sztanó, Dr. Csaba Krézsek and Dr. Lóránd Silye for the supervision; to Dr. László Lenkey for his help in interpreting gamma-ray graphs
to Szabolcs Kövecsi for gamma-ray measuring
to Papp Simon Foundation and Koch Antal Geological Society for funding our work.
Thank you for your kind attention!