Preliminary Cruise Results

1. Fault geometry. 

The North Branch of the NAF accounts for most of the current plate motion and is associated with all three main basins in the Marmara Sea. Its trace is tightly constrained by available data. However, wide disagreements remain about the subsurface geometry and kinematics of this master fault, about the locations and roles of second-order faults, and about the timing of basin growth. Many of these issues can be addressed with the high-resolution data of TAMAM.

 TAMAM data reveal a reverse component and compressional folding along the NAF in Tekirdağ basin, but also that this shortening is coupled with extensional structures from sediment collapse higher on the southern flank of the basin.  Deeper penetration previous MTA profiles show that below the shortening structure at the toe of the collapse, the NAF has a normal component and serves as the transtensional border fault of the basin.  Thus we reconcile shallow and deeper observations and provide higher resolution images of the structure.
 

        

Northern branch of the NAF across the 800-m deep Kumburgaz Basin. The progressive tilting as seen south of fault is characteristic of Marmara Sea basins, as is slumping seen on north side. If the NAF dips north and has a thrust component, then fault at depth would be closer to Istanbul and pose a greater risk. Acoustically transparent zone may be due to sedimentation, gas or both

2. Steady-State Tectonics.

Another fundamental issue in the Marmara Sea is the stability or evolution of the tectonic regime.  Some authors favor a major recent shift from strike-slip and extensional basin growth to a new purely strike-slip phase on a new plate-motion parallel strand of the fault. Such a major tectonic transition would alter depositional patterns, but the proposed young age (200 ka) implies that developments might be subtle. Testing this hypothesis, therefore, requires a compromise between high-resolution imaging of shallow young strata sufficient penetration to place them within the context of more deeply buried older deformed strata. The TAMAM data are expected to resolve subtle changes during the late Quaternary and thus test regime stability over many of the structures along the Marmara segment of the NAF.


TAMAM imaging in the eastern Cinarcik basin shows ponding of turbidite sediments related to changes in sea level.  The deeper “bathyl sequence boundary” may mark the same transition at the end of the previous glacial stage over 100,000 y earlier.  This suggests continued tilting and extensional basin growth over the last 130,000 years.

3. Sequence Boundaries and Paleo-Deltas. 

Turbidite sedimentation, from underwater avalanche flows, layer the bottoms of basins in the Marmara Sea. Changes in sealevel can cause large changes in the amount of turbidites and the area of the sea floor they cover.  This can produce angular unconformities in the sedimentary layers. Our high-resolution profiles reveal a series of these unconformities, which we name “bathyal sequence boundaries” such as the one shown above.

The seismic data also reveal a stack of at least four lowstand delta complexes.  These are shallow-water deltas formed when sealevel was low during glacial times.  The deltas were preserved because they were on the downdropped side of a major fault and were covered by sediments. We are using the lowstand deltas and the bathyal sequence boundaries as time markers to map out the ages of sediments in the Marmara Sea.

1. Gravity Collapse. 

Finally, TAMAM profiles show that rapid subsidence and tilting in the Marmara Trough are responsible for widespread and gravitational collapse, as seen in previous profiles above and also in ones below. Extensional and contractional structures at the heads and toes of gravitational collapses can be misleading if not interpreted correctly. Gravity collapse features are common along many of the steep basin margins in the Marmara Sea.  Collapse of sediments along the sides of the rapidly subsiding basins may be an important source for the sediments filling the basins.

Rhythmic growth folding with 1 km-wavelength. Colored horizons are the same as the lowstand delta tops shown earlier. These interpreted horizons are inferred to date from the latter half of the Pleistocene. High-resolution multibeam bathymetry images the folds as trending north and northeast. They may be secondary contractional folds related to a transverse ridge/anticline, or they may be growing above blind normal faults related to gravitational collapse. Anomalous high amplitudes at the crests of many of the anticlines are likely due to gas.

Seismic section across Western Ridge, transverse ridge separating the Tekirdag and Central Basins. (see map). The profile shows folding of strata above a blind thrust.  In addition there is  extensional failure of shallow sediments (arrow) behind a thrust.