Multiple co-seismic soft sediment deformation structures reveal abrupt changes in sedimentation in Lower Pleistocene lacustrine deposits of the Denizli Basin (Western Türkiye)

Soft sediment deformation structures (SSDSs) form as a consequence of paroxysmal events and act as indicators of significant environmental and depositional changes within a sedimentary basin. SSDSs in the Lower Pleistocene lacustrine succession of the Denizli Basin reflect a marked shift in local sedimentation, driven by the tectonically induced creation of accommodation space during basin development. The presence of these structures indicates a period of intense tectonic activity accompanied by seismic events. The SSDSs formed in a distal lacustrine environment, immediately above sub-lacustrine avalanche deposits, and are observed as sandy to marly layers, ranging from a few decimetres to 3 m thick and confined by undeformed beds. Based on the typology and development mechanisms of the SSDSs, the tectonic setting of the basin, the sedimentological characteristics of the successions, the recurrence of these deformations at different stratigraphic levels and their similarity to SSDSs in other settings, these structures are interpreted as earthquake-induced deformation features. In this context, the SSDSs were formed by repeated tectonic pulses that triggered seismicity during the activity of the fault system bounding the Denizli Basin to the SW, represented today by the Babadağ Fault. The SSDSs developed over a period from 1.72 to 1.7 Ma, corresponding to the recovery of the Denizli lacustrine phase following a sudden palaeoenvironmental perturbation between 1.9 and 1.8 Ma, which was marked by alluvial fan progradation and biotic turnover. This evolution provides the first documented co-seismic records within the Denizli Basin during the Early Pleistocene and highlights a significant change in the configuration of the basin.