Steady-state Quaternary Basin Formation Along the North Anatolian Fault System in Marmara Sea, Turkey
Abstract
Continental transforms such as the San Andreas, Caribbean-bounding, and North Anatolian can be distributed across tens or hundreds of km. For tectonic regimes measured in a few million years or less, fault strand and basin evolution can be divided into four models: 1: Steady-State; 2: Coherently Variable; 3: See-Saw (episodic); 4: progressive abandonment and activation. The Coherently Variable model allows long-term slip rate increases or decreases across the whole transform while maintaining constant ratios between fault strands. The North Anatolian Fault system (NAF) splits into three major branches at the longitude of Istanbul. Right-lateral plate motion has driven formation of transtensional basins across releasing double bends or stepovers in fault strands, with thrust-related folding more locally associated with restraining geometries. Basin subsidence resulted in Marmara Sea, which hosts the Northern and Central branches of the NAF. Slip has been about 2 cm/yr during Holocene and present time, with most of this slip interpreted to be along the northern branch, the Main Marmara Fault. Several authors favor a major shift at ~200 ka from transtensional basin growth to a new purely transcurrent phase on the Main Marmara fault. Others favor a steady-state pull-apart model for the last few million years. We produced the first quantitative stratigraphic age model back to 500 ka for the basins of Marmara Sea. This model is based on high-resolution seismic reflection imaging of stacked subsiding and tilting low-stand shelf-edge deltas. We correlated this stratigraphy to several of the Marmara Sea basins. There is continual growth and tilting in the basins with no evidence of a change in pattern or rate for at least the last 500 ka. We could not correlate reflections to a basin along the Holocene-active Central Branch of the NAF in southernmost Marmara Sea. Instead, we counted erosional unconformities and matched them to the global sea level curve. Progressive tilt in this basin is still active, and affects the inferred ~500 ka horizon as well as the several times thicker section below it. Progressive tilting of strata in the Cinarcik basin, located offshore Istanbul along the Main Marmara fault, extends below the ~500 ka horizon. The North Imrali basin, located midway between the Cinarcik and Southern basins, exhibits progressive tilting that affects the entire section above basment, with the ~500 ka section being half way down. It seems a reasonable hypothesis that tilting and subsidence of most Marmara Sea basins has been continuous since 1 Ma or longer. Since we do not have an age model for the tilting strata beneath the ~500 ka horizon, older deformation in Marmara Sea could be Steady-State or Coherently Variable.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.T33G2500S
- Keywords:
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- 3025 MARINE GEOLOGY AND GEOPHYSICS / Marine seismics;
- 8010 STRUCTURAL GEOLOGY / Fractures and faults;
- 8106 TECTONOPHYSICS / Continental margins: transform;
- 8169 TECTONOPHYSICS / Sedimentary basin processes