Sedimentary and tectonic evolution of Lake Ohrid (Macedonia/Albania)

L ake O hrid, located on the B alkan P eninsula within the D inaride– A lbanide– H ellenide mountain belt, is a tectonically active graben within the S outh B alkan E xtensional R egime ( SBER ). Interpretation of multichannel seismic cross sections and bathymetric data reveals that L ake O hrid formed during two main phases of deformation: (1) a transtensional phase which opened a pull‐apart basin, and (2) an extensional phase which led to the present geometry of L ake O hrid. After the initial opening, a symmetrical graben formed during the L ate M iocene, bounded by major normal faults on each side in a pull‐apart type basin. The early‐stage geometry of the basin has a typical rhomboidal shape restricted by two sets of major normal faults. Thick undisturbed sediments are present today at the site where the acoustic basement is deepest, illustrating that L ake O hrid is a potential target for drilling a long and continuous sediment core for studying environmental changes within the M editerranean region. Neotectonic activity since the P liocene takes place along the roughly N–S‐striking E astern and W estern M ajor B oundary N ormal F aults that are partly exposed at the present lake floor. The tectono‐sedimentary structure of the basin is divided into three main seismic units overlying the acoustic basement associated with fluvial deposits and lacustrine sediments. A seismic facies analysis reveals a prominent cyclic pattern of high‐ and low‐amplitude reflectors. We correlate this facies cyclicity with vegetation changes within the surrounding area that are associated with glacial/interglacial cycles. A clear correlation is possible back to ca . 450 kyrs. Extrapolation of average sedimentation rates for the above mentioned period results in age estimate of ca . 2 Myrs for the oldest sediments in L ake O hrid.