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Hydrocarbon-related fluid migration and processes of carbonate diagenesis – Pobiti Kamani area (Eocene, Varna, NE Bulgaria)

Researcher: Drs. Eva De Boever, Geodynamics and Geofluids Research Group, Biogeology Research Group, KULeuven
Promotor: Prof. Dr. Rudy Swennen, Geodynamics and Geofluids Research Group, KULeuven
Co-promotor: Prof. Dr. Philippe Muchez, Geodynamics and Geofluids Research Group, KULeuven
Funding: IWT

 

Keywords:
cold seep; authigenic carbonate, morphology, spatial distribution, fluid migration, fault-related, Eocene

 

Research abstract:
The manifestation of paleo-hydrocarbon seepage is exceptionally well preserved and exposed in the Lower Eocene sandy Dikilitash Formation in the Pobiti Kamani area (Varna, Bulgaria). Several outcrops are scattered over an area of about 40km² at the eastern side of the Moesian Platform. They reveal a large diversity in carbonate-cemented sandstone structures, consisting of chimney structures of variable dimensions with a local vertical continuity of up to 8m and interfering with horizontal cemented sandstone beds, ‘pisoid’-like structures and different carbonate-cemented vein types. Several outcrops are furthermore spatially related to regionally important NNE-NNW trending normal faults. The study of this paleoseep system can yield unique information about (i) the process of hydrocarbon-migration related carbonate diagenesis, (ii) the evolution of fluid sources, fluid discharge and fluid migration paths through time and space and (iii) their relation with the specific sedimentological and geodynamic setting. Several outcrops in the central part of the area are studied in detail, i.e. the Beloslav Quarry, the Central Group, the Slunchevo North and South outcrop and several parallel fault outcrops near the village of Beloslav.

 

 

edb_fig01

Figure 1: Cluster of tubular concretions in the Central group outcrop.

Research problem
 

Cold seep systems where hydrocarbon-bearing fluids migrate upward to the seafloor, are widely known and described in different settings (Hovland et al., 1987; Jensen et al., 1992; Sakai et al., 1992; Suess et al., 1999; Campbell et al., 2002; Peckmann et al., 2001; Mazzini et al., 2004; Orphan et al., 2004; Dupré et al., 2007 ). Locations of ebullition of hydrocarbon-related fluids draw the interest of the international scientific community since they mark sites where geological, (micro)biological and hydrological processes closely interact at different scales. Furthermore the emission of reduced carbon compounds into the hydrosphere might have a considerable impact on the (global) carbon cycle (Judd et al., 1997; Greinert et al., 2006).

The formation of diverse carbonate-cemented structures is a well-known (near-seafloor) phenomenon in these settings. Their spatial distribution, morphological characteristics, mineralogy and relation with their host rocks and other seep products provide a record of the fluids involved, the nature of shallow subsurface fluid pathways and the modes, the duration and possible episodicity of fluid migration.

In addition to active seep systems, the preserved products of fluid migration in paleo-seep systems allow to assess in more detail the complexity of and controlling factors on shallow subsurface fluid migration and processes of carbonate diagenesis in 4 dimensions; i.e. their variation in space and time (Aiello et al., 2001; Schwartz et al., 2003; Clari et al., 2004; Han et al., 2004; Nyman et al., subm.).

The “Pobiti Kamani” area (Varna, NE Bulgaria) consists of a well-exposed paleo-seep system, confined to Upper Ypresian sandy shelf sediments of the Dikilitash Formation (Nachev et al., 1986; Nachev and Nachev, 2001). Outcrops are scattered in a NS-elongated, ±40km² area between the villages of Banovo and Avren and offer a unique possibility to study these processes in detail. Most prominent are calcite-cemented tubular concretions of various morphologies which can reach heights of 10m. Depleted δ13C values indicate a hydrocarbon-derived carbon source (De Boever et al., 2006). Other carbonate-cemented structures are horizontal, cemented stratal horizons of variable lateral extent and small, spherical concretions.

 

 

 

 

 

Figure 2: (A) Geodynamic framework. Square west of Varna indicates the position of the study area (modified after Georgiev, 2001; Dimitrov, 2002). (B) Simplified geological map (modified arfter Chishitev et al., 1992; Nachev and Nachev, 2001)

edb_fig02

Research objectives


The main research objective is to understand the controlling factors on hydrocarbon-bearing fluid migration and processes of related carbonate diagenesis at different stages in the evolution of the seep-system and this in relation to its sedimentological and geodynamic framework. More specific this includes,

(1) The reconstruction of the formation and diagenesis of diverse carbonate-cemented structures, the controlling factors on their 3D-distribution and their position within the paleo-seep system.
(2) The process of carbonate cementation in relation to the influx of hydrocarbon-related fluids.
(3) The role of fault zones in the migration of hydrocarbon-related fluids.

 

Methdology
 


Field observations and field mapping (sedimentological and geodynamic framework; spatial variability)


Grain size analysis (sedimentological framework)


Geostatistical data analysis (Dr. Marijke Huysmans, K.U.Leuven)


Integration of diverse petrographical (standard microscopy, fluorescence microscopy, cathodoluminescence, SEM-EDX) and geochemical techniques (XRD, EPMA, stable carbon-oxygen isotopes, radiogenic Sr-isotope analyses) and where possible microthermometry in the study of the diagenetic evolution of the diverse cemented structures and fault-related deformation structures.


Lipid biomarker analyses (in cooperation with V. Thiel, D. Birgel, J. Peckmann).


 

edb_fig03

Figure 3: Part of the exposed vertical statigraphic section at the Beloslav quarry where vertical tubular concretions can be seen to interact with cemented stratal horizons, characteristic of the host formation. Wall is about 20m high.

Research in cooperation with:

  • L. Dimitrov (IO-BAS, Varna, Bulgaria) www.io-bas.bg
  • D. Vangelov (St. Kliment Ohridski University, Sofia, Bulgaria) www.uni-sofia.bg/faculties/geo/index.html
  • RCMG (UGent, Ghent, Belgium) www.rcmg.ugent.be
  • B. Cavallazzi (University of Bologna, Bologna, Italy)  www.geomin.unibo.it/paleo/Geomicrobiology.html
  • V. Thiel (Geobiologie Lab, Universität Göttingen, Göttingen, Germany)  www.geobiologie.uni-goettingen.de/index_e.shtml
  • D. Birgel, J. Peckmann (MARUM, Bremen, Germany) www.marum.de
Publications

 

De Boever, E., Huysmans, M., Swennen, R., Muchez, Ph., Dimitrov, L., in prep. The build-up of tubular concretions and controlling factors on their spatial distribution – a field-based study, Pobiti Kamani area (Varna, Bulgaria).
De Boever, E., Swennen, R., Dimitrov, L., 2006. Lower Eocene carbonate cemented chimneys (Varna, NE Bulgaria): formation mechanisms and the (a)biological mediation of chimney growth? Sedimentary Geology, 185(3-4), 159-173.
De Boever, E., Swennen, R., Dimitrov, L., 2006. Lower Eocene carbonate cemented “chimney” structures (Varna, Bulgaria). – Control of seepage rates on their formation and geochemical signature. Journal of Geochemical Exploration, 89, 78-82.
References

 

Aiello, I.W., Garrison, R.E., Moore, J.C., Kastner, M. Stakes, D.S., 2001. Anatomy and origin of carbonate structures in a Miocene cold-seep field. Geology, 29(12), 1111-1114.
Campbell, K.A., Farmer, J.D., Des Marais, D., 2002. Ancient hydrocarbon seeps from the Mesozoic convergent margin of California: carbonate geochemistry, fluids and palaeoenvironments. Geofluids, 2, 63-94.
Chechistev, G., Milanova, V., Popov, N. Kojumdgieva, E. 1992. Geological map of Bulgaria. Sheet Varna and Resort Zlatni Pjasaci. Sofia, Committee mineral and energy resources. Deparment of geological prospecting and geological mapping.
Clari, P., Cavagna, S., Martire, L., Hunziker, J., 2004. A Miocene mud volcano and its plumbing system : A chaotic complex revisited (Monferrato, NW Italy). Journal of Sedimentary Research, 75, 662-676.
Dimitrov, L., 2002. Contribution to atmospheric methane by natural seepages on the Bulgarian continental shelf. Continental Shelf Research, 22, 2429-2442.
Dupre, S., Woodside, J., Foucher, J.P., de Lange, G., Mascle, J., Boetius, A., Mastalerz, V., Stadnitskaia, A., Ondreas, H., Huguen, C., Harmegnies, F.O., Gontharet, S., Loncke, L., Deville, E., Niemann, H., Omoregie, E., Roy, K.O.L., Fiala-Medioni, A., Dahlmann, A., Caprais, J.C., Prinzhofer, A., Sibuet, M., Pierre, C. Damste, J.S.S., 2007. Seafloor geological studies above active gas chimneys off Egypt (Central nile deep sea fan). Deep-Sea Research Part I - Oceanographic Research Papers, 54(7), 1146-1172.
Georgiev, G., Dabovski, C. Stanisheva-Vassileva, G. 2001. East Srednogorie-Balkan Rift Zone, in: P. A. Ziegler, W. Cavazza, A. H. F. Robertson and S. Crasquin-Soleau (Eds.), Peri-Tethys Memoir 6: Peri-Tethyan Rift/Wrench Basins and Passive Margins. Mém. Mus. natn. Hist. nat., Paris, pp. 259-293.
Greinert, J., Artemov, Y., Egorov, V., De Batist, M., McGinnis, D., 2006. 1300-m-high rising bubbles from mud volcanoes at 2800m in the Black Sea: Hydroacoustic characteristics and temporal variability. Earth and Planetary Science Letters, 244(1-2), 1-15.
Han, X., Suess, E., Sahling, H. Wallmann, K., 2004. Fluid venting activity on the Costa Rica margin: new results from authigenic carbonates. Int J Earth Sci, 93, 596-611.
Hovland, M., Talbot, M.R., Qvale, H., Olaussen, S. Aasberg, L., 1987. Methane-related carbonate cements in pockmarks of the North-Sea. Journal of Sedimentary Petrology, 57(5), 881-892.
Jensen, P., Aagaard, I., Burke, J., R.A., Dando, P.R., Jorgensen, N.O., Kuijpers, A., Laier, T., O'Hara, S.C.M. Schmaljohann, R., 1992. 'Bubbling reefs' in the Kattegat: submarine landscapes of carbonate-cemented rocks support a diverse ecosystem at methane seeps. Marine Ecology Progress Series, 83, 103-112.
Judd, A., Davies, G., Wilson, J., homes, R., Baron, G., Bryden, I., 1997. Contributions to atmospheric methane by natural seepages on the UK continental shelf. Marine Geology, 137(1), 165-189.
Mazzini, A., Ivanov, M.K., Parnell, J., Stadnitskaia, A., Cronin, B.T., Poludetkina, E., Mazurenko, L. van Weering, T.C.E., 2004. Methane-related authigenic carbonates from the Black Sea: geochemical characterisation and relation to seeping fluids. Marine Geology, 212(1-4), 153-181.
Nachev, I.K., Mandev, P.D. Zhelev, S.K., 1986. "Pobitite kamani" - algal bioherms. Review of the Bulgarian Geological Society, 47(3), 1-12.
Nachev, I.K., Nachev, I., 2001. “Pobitite Kamani”.  Sofia, pp.110 (in Bulgarian, extended English summary).
Nyman, S., Nelson, C.S., Campbell, K.A., Schellenberg, F., Pearson, M.J., Kamp, P.J.J., Browne, G.H. and King, P.R., submitted. Tubular carbonate concretions as hydrocarbon migration pathways? Examples from North Island, New Zealand.
Orphan, V.J., Ussler III, W., Naehr, T.H., House, C.H., Hinrichs, K.-U. Paull, C.K., 2004. Geological, geochemical and microbiological heterogeneity of the seafloor around methane vents in the Eel River Basin, offshore California. Chemical Geology, 205, 265-289.
Peckmann, J., Reimer, A., Luth, U., Hansen, B.T., Heinicke, C., Hoefs, J. Reinter, J., 2001. Methane-derived carbonates and authigenic pyrite from the northwestern Black Sea. Marine Geology, 177, 129-150.
Sakai, H., Gamo, T., Ogawa, Y. Boulegue, J., 1992. Stable isotopic-ratios and origins of the carbonates associated with cold seepage at the eastern Nankai Through. Earth and Planetary Science Letters, 109(3-4), 391-404.
Schwartz, H., Sample, J., Weberling, K.D., Minisini, D. Moore, J.C., 2003. An ancient linked fluid migration system: cold-seep deposits and sandstone intrusions in the Panoche Hills, California, USA. Geo-Marine Letters, 23, 340-350.
Suess, E., Torres, M.E., Bohrmann, G., Collier, R.W., Greinert, J., Linke, P., Rehder, G., Trehu, A., Wallmann, K., Winckler, G. Zuleger, E., 1999. Gas hydrate destabilization: enhanced dewatering, benthic material turnover and large methane plumes at the Cascadia convergent margin. Earth and Planetary Science Letters, 170, 1-15.
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