PROVENANCE OF TURBIDITE SANDS IN THE MARMARA SEA, TURKEY: A TOOL FOR SUBMARINE PALEOSEISMOLOGY

Paleoseismology studies asses seismic risk and fault motion along transform boundaries by dating earthquakes and characterizing drainages from the sedimentary record provided by trenching. To evaluate seismic risk and fault motion along the submerged regions of transform boundaries, we are developing techniques for paleoseismology by using high-resolution bathymetry, subbottom profiling (CHIRP), coring, sediment analyses (petrography, heavy mineral separation, SEM/EDX), and dating (short-lived radioisotopes and radiocarbon). The North Anatolia Fault Zone in the Marmara Sea, Turkey, is a good setting for paleoseismology because it has a historical record of earthquake activity that goes back 2000 years, and the fluvial systems that contribute sediment to the sea cross distinct lithologic terrains.

Turbidites recovered from the floor of Izmit Gulf (east and west of the Hersek promontory) were correlated to earthquakes that occurred in 181, 740, and 1509 years. The mineralogy of the sands related to the 181 yr event (east of Hersek) is dominantly mafic (basalts, diabase, metabasalts, metacarbonates). In contrast, the mineralogy of the younger events 740 and 1509 years (east and west of Hersek, respectively) is dominantly intermediate to felsic in composition (andesite, spillite, granodiorite, granite, and medium to high grade gneiss, schist, and amphibole). The mineral suites are derived from the southern shores of the Marmara Sea and their variability upcore and from east to west, suggests drainage changes that may be related to motion along the transform boundary.

Similar techniques can be applied to turbidites of passive continental margins adjacent to major ice sheets such as the Laurentide. In these settings, drainage changes would be the result of glaciation.