Individual Project VU University Amsterdam, University of Utrecht, The Netherlands

Basins connectivity and gateways controlling sedimentary architecture during final stages of orogenic build-up

Project financed by the Netherlands Research Centre for Integrated Solid Earth Science

Investigators:drs. Marten ter Borgh (Amsterdam), dr. Liviu Matenco (Amsterdam), dr. Wout Krijgsman (Utrecht), prof. Stefan Schmid (Basel), dr. Daniel Garcia-Castellanos (Barcelona), dr. Dimitrios Sokoutis (Amsterdam), dr. Fred Beekman (Amsterdam)

Entrance of the Danube in the South Carpathians Gateway (Bazna, Romanian-Serbian border)

Objectives of the project: The mechanisms controlling orogenic shortening and collision govern the evolution of the coeval sedimentary infill and the subsequent exhumation of foreland and back-arc basins. Mountain building processes lead to exhumation of orogenic cores during and after gradual shortening by nappe stacking. As a result, large basins become fragmented and reduced in size during active subduction, collision and resulting uplift with particular and sometimes endemic evolution (e.g., Meijer and Krijgsman, 2005). Ongoing subsidence after the onset of collision may locally preserve the syn-orogenic basins, but these will be ultimately filled and the sediment depocenters shifted elsewhere (e.g., Leever, 2007).
Such processes often lead to isolation of sub-basins either in the foreland or in the hinterland of collisional orogens. These are characterised by a gradual transition towards brackish to fresh water sediments with endemic faunas, with short-lived connections to the main marine realm. The parameters controlling connectivity amongst late orogenic semi-isolated basins and with open marine environments are mainly function of (1) the interplay between uplift and subsidence creating/filling the accommodation space and building sediment source areas; (2) inherited tectonic pathways across mountain chains (i.e. gateways); (3) climate and sea-level variations and (4) local hydrological balance.

a) Conceptual definition of connectivity and gateways in the Danube basin system; b) The extent of Mediterranean and Paratethys during the Messinian Salinity Crisis (Popov et al., 2006)

Goals:

• Quantify different types of connectivity influencing budgets/pathways of sedimentary fluxes including mechanisms of depocenters shifts across basins and their impact on the evolution of geomorphic landforms, in particular during and after orogenic shortening;
• Derive the controls of gateways evolution between semi-enclosed basins and their impact on rapid flooding and basin-fill events;
• Analyse the controls of major sea-level changes in large seas into the evolution of adjacent (semi-) enclosed basins connected through gateways;
• Study the tectonic controls of post-orogenic deformation on sediment fluxes between semi-enclosed basins and towards the active sink;
• Develop and models for stability and evolution of gateways at different elevations and between individual sea-levels.

The Pannonian-Carpathians region is the ideal region to study point wise the general/global interest in inter-basins processes. This is given by advanced knowledge on the tectonic/structural evolution, paleogeography, absolute time scales, endemic environments and the multiple gateways connecting successively various basins at different time scales (e.g., Vasiliev et al., 2004; Matenco et al., 2007).

Deliverables:

• Comparative analysis of the temporal evolution of gateways between basins during and after mountain building processes;
• Quantitative analysis of patterns of basin infill in time and space, from the Source - by successively filling up orogenic basins - to the presently active Sink;
• Comparative analysis between long-term basin processes and short-lived basin connectivity events, prone for major natural hazards;
• Quantitative understanding of the impact of former and ongoing orogenic activity at crustal-lithospheric scales on the evolution of basin gateways;

Details: The connectivity between basins has been inferred mainly by biostratigraphic events; a phenomenological and quantitative link is still missing. By contrast with open marine environments, sedimentological base-level variations in isolated basins are controlled by a higher number of parameters, among which connectivity features are essential: evolution of local sea-levels, basin overspill (function of run-off precipitation), uplift and fluvial incision of the connecting gateways, drainage capture or (tectonic) migration of drainage divides, gradual filling patterns and transition towards continental environments.
All these features are yet poorly understood; a quantitative understanding of the main controls on basin connectivity along basin gateways is still missing because this is normally too complex to be studied in one isolated project. However, an opportunity is uniquely provided by the current research stage of the ISES Pannonian Carpathians and by the multidisciplinary collaboration of 21 (associated) partners in 14 countries in the TopoEurope SourceSink programme. The potential paleogeographic consequences of the connectivity changes are addressed for instance by several ongoing ISES projects which provide direct support to this proposal in a) detailed age control on the Paratethys sedimentation (with their endemic faunas), allowing the correlation to global climate and sea level curves and enhancing the tectonic signals; b) detailed control on rates of change by magnetostratigraphic and radioisotopic dating; c) studying paleoenvironmental changes and quantifying the hydrological budgets/salinity variations.

Concept of basin connectivity, gateways and depocenters shift compared with preliminary numerical modelling (Bartol, 2008).

Selected natural laboratory: Following a complex orogenic evolution, the Tethys basin in the Alps-Carpathians-Dinarides realm started to divide since the Oligocene due to continued mountain build-up into several sub-basins (e.g., Schmid et al., 2008 and references therein). Miocene tectonic events in the Carpathians generated further fragmentation of the Paratethys, basins became gradually isolated during and after the Carpathians collision, sediments gradually filling the Vienna, Danube, Pannonian, Transylvania and Dacic basins in Miocene-Quaternary. At the same time, the sediments pathways were gradually shifted towards the presently active Black Sea sink. Major changes in the system did occur as a combined result of (1) climatic and oceanic conditions and (2) vertical tectonic motions leading to gateways activity between individual basins.
One relevant example is the closure of the gateways between Central and Eastern Paratethys during the late Middle Miocene, an initial large transgression being recorded at the entire intra-Carpathians scale. This is unlikely related to eustasy, transgression occurring in the already enclosed and endemic lake Pannonian, distal sequences recording maximum flooding surfaces are observed at high altitudes overlying directly pre-Miocene strata (Krezsek et al., 2008). The gradual Pannonian lake-level rise was potentially controlled by runoff precipitation, an important parameter in the case of tectonic lakes (Garcia-Castellanos, 2006). Basin widening can be controlled by the height of the gateways towards the Carpathians foreland, whose activity is recorded much later by Pannonian waters invading the foreland during the Upper(most) Miocene. During this basin widening, exhumation of Transylvania basin at ~9Ma is a result of Carpathians collision and the activity of another gateway (Apuseni) is recorded (Fig. 2). This is a key study area for a tectonic induced gateway, as the basin was disconnected from the cyclic nature of sea-level variations.

In the same system, another relevant area is the Dacic basin, which acted as a suspended lake in respect to the Black Sea with positive precipitation/evaporation balance and shifting sedimentation between basins in periods of sea-level drop such as the large MSC event, comparable in amplitudes with the Mediterranean (e.g., Leever, 2007). This MSC event apparently controls all related Paratethys basin by upstream gateways and connectivity events (Fig. 1a and 2). Quantification of these events and their sedimentary effects in the connected Paratethys basins is needed to derive a coherent scenario. For instance, the impact in stabilizing the gateway in the recent Danube Delta position and changing sediment fluxes towards the deep-water sedimentation presently observed is unknown. These changes are accompanied by large variations of both the far- and close-field tectonic-induced vertical and horizontal motions actively modifying physiography.

The yet not understood influences of these major tectonic and sea-level events onto the overall Paratethys environment therefore relate mostly to the evolution of connecting gateways and gradual basin infill, and require an integrated study.
In order to attain the project objectives, we will investigate in the field two of these major gateways presently exposed, while for the third a data compilation will be used. Combined with the past gateways analogues of Vienna and Danube basins by SourceSink partners (e.g., Kovac et al., 2006), these will provide key constrains for the physical modelling of late stage vertical movements (e.g., Sokoutis et al., 2005) and for the numerical modelling including at the scale of the entire system using existing tectonic, sedimentological, climate, bio- and magneto-stratigraphyc constraints (e.g., Cloetingh et al., 2006; Stoica et al., 2007 and references therein).

Innovative aspects:

• Analysis of connections between basins during orogenic build-up. A quantitative analysis of connectivity between basins at the scale of the entire system will provide predictive modelling of the main controlling parameters for opening and closing basin gateways.
• Linking different temporal and spatial scales. Gateways evolve at a rather restricted scale in time and space. A link with regional basin filling patterns and the interplay between exhumation and sedimentation in basins across mountain chain is required to understand sediment budgets. The predictive power is ensured by comparative analysis of sedimentation near an active/recent (103-105Ma) gateway (i.e. Danube Delta) with past analogues (105-106Ma);
• Linking deep to surface processes. Well quantified lithospheric structure, exhumation history and sediment flux in a recently active orogen (i.e., SE Carpathians) will be used to derive the sensitivity between strain rates and surface processes controlling gateways evolution.
• Impact on the major sea-level changes debates such as the Messinian Salinity Crisis (MSC) or the Upper Quaternary Noah flooding event. The comparable in size MSC event in Paratethys occurring in an endemic environment suggests a common triggering mechanism, but different than the local Mediterranean ones. Water exchanges during the Quaternary with the Black Sea such as the debated catastrophic re-flooding events (e.g. “Noah's flood”, Ryan et al., 2003) bring a significant societal relevance.

We aim to link field-based observations with process-oriented numerical and physical modelling. The project will combine observations in areas and time-scales with modelling to derive the relationship between long term basin evolution and short-lived connectivity events.

Cooperation:

Relevant references:

• Garcia-Castellanos, D., 2006, Long-term evolution of tectonic lakes: Climatic controls on the development of internally drained basins: Geological Society of America Special Paper, 398, 283-294.
• Leever, K.A., 2007. Foreland of the Romanian Carpathians: controls on late orogenic sedimentary basin evolution and Paratethys paleogeography. PhD Thesis, VU University Amsterdam, Amsterdam, 182 pp.
• Krézsek, C., Filipescu, S., Silye, L., Maţenco, L. and Doust, H., 2008. Miocene facies associations and sedimentary evolution of the Southern Transylvanian Basin (Romania): implications for hydrocarbon exploration. Marine and Petroleum Geology: submitted.
• Kovac, M. et al., 2006. Late Miocene to Early Pliocene sedimentary environments and climatic changes in the Alpine-Carpathian-Pannonian junction area: A case study from the Danube Basin northern margin (Slovakia). Palaeogeography, Palaeoclimatology, Palaeoecology, 238(1-4): 32-52.
• Matenco, L., Bertotti, G., Leever, K., Cloetingh, S., Schmid, S., Tărăpoancă, M., and Dinu, C., 2007, Large-scale deformation in a locked collisional boundary: Interplay between subsidence and uplift, intraplate stress, and inherited lithospheric structure in the late stage of the SE Carpathians evolution: Tectonics, 26, TC4011.
• Meijer, P.Th. and Krijgsman, W. (2005). A quantitative analysis of the desiccation and re-filling of the Mediterranean during the Messinian Salinity Crisis, Earth Planet. Sci. Lett., 240, 510-520.
• Ryan, W.B.F., Major, C.O., Lericolais, G. and Goldstein, S.L., 2003. Catastrophic flooding of the Black Sea. Annu. Rev. Earth Planet. Sci., 31: 525-554.