We have studied the magnetic properties of wet and dry late Pleistocene Lake Lisan sediments and the Holocene Dead Sea sediments. Our initial prediction was that the properties of both would be quite similar, because they have similar source and lake conditions, unless diagenetic change had occurred. Rock magnetic and paleomagnetic experiments revealed three stages of magnetization acquisition. Our findings suggest two magnetic carriers in the Holocene Dead Sea and wet Lisan sediments: titanomagnetite and greigite. The titanomagnetite grains are detrital and carry a detrital remanent magnetization (DRM), whereas the greigite is diagenetic in origin and carries a chemical remanent magnetization (CRM) that dominates the total natural remanent magnetization (NRM) of Holocene Dead Sea and wet Lisan sediments. The magnetization of dry Lisan sediments is a DRM and resides in multidomain (MD) grains. We propose that magnetic properties of the Lisan Formation and Holocene Dead Sea sediments can be explained by a model that incorporates dissolution, precipitation, and alteration of magnetic carriers. At the time of deposition, titanomagnetite grains of varying size were deposited in Lake Lisan and the Holocene Dead Sea, recording the geomagnetic field via a primary DRM. Sedimentation was followed by partial or complete dissolution of titanomagnetite in anoxic lake bottom conditions. As the kinetics of dissolution depends upon surface area, the single-domain (SD) grains dissolved faster, leaving only the larger pseudo-single domain (PSD) and MD grains. Titanomagnetite dissolution occurred simultaneously with precipitation of greigite in anoxic, sulfate-reducing conditions probably related to bacterial degradation of organic matter. This process added a secondary CRM that overwhelmed the DRM and the primary geomagnetic record. Later, when the level of Lake Lisan dropped, these sediments were exposed to air. At this time, the greigite was oxidized, removing the CRM from the system and leaving only the original detrital PSD and MD titanomagnetite grains as the dominant DRM carriers. Presently, wet Lisan sediments have not been completely altered and therefore contain secondary greigite preserved by the original formation water that carries a secondary CRM. Thus, the magnetization in the Holocene Dead Sea and the wet Lisan magnetic record cannot be considered as an accurate, reliable geomagnetic record, while magnetization of dry Lisan sediments is a primary DRM.

Observations of intraclast breccia layers in the Dead Sea basin, formerly termed “mixed layers,” provide an exceptionally long and detailed record of past earthquakes and define a frontier of paleoseismic research. Multiple studies of these seismites have advanced our understanding of the earthquake history of the Dead Sea and of the processes that form the intraclast breccias. In this paper, we describe a systematic study of intraclast breccia layers in laminated sequences. The relationship of intraclast breccia layers to intraformational fault scarps has motivated the investigation of these seismites. Geophysical evidence shows that the faults extend into the subsurface, supporting their potential association with strong earthquakes. We define field criteria for the recognition of intraclast breccias, focusing on features diagnostic of a seismic origin. The field criteria stem from our understanding of the mechanisms of breccia formation, which include ground acceleration, shearing, liquefaction, water escape, fluidization, and resuspension of the originally laminated mud. Comparison between a dated record of breccia layer and the record of historical earthquakes provides an independent test for a seismic origin. The historical dating is significantly more precise and accurate than the radiocarbon dating of breccia layers. Yet, assuming that the lamination of the sediments shows an annual cycle, the precision of counting laminae may approach the precision of the historical record. A similar accuracy is then expected for the intervals between earthquakes. We review our work based on counting laminae representing the historical period, mutually corroborating the seismic origin and the annual lamination. The correlation of documented historical earthquakes with individual breccia layers provides quantitative estimates for the threshold of ground motion for breccia formation in terms of earthquake magnitude and epicentral distance. The investigation of breccia layers and the associated historical earthquakes has underscored cases in which a breccia layer represents a pair of earthquakes. We consider the resolution of individual events in records of breccia layers. A thick breccia layer can account for multiple events, biasing the paleoseismic record. The resolution of an interseismic time interval is no better than the ratio between the thickness of a breccia layer and the rate of sedimentation. We use revised age data for the Lisan Formation and reassess temporal clustering of earthquakes during the late Pleistocene. The variation of recurrence interval corroborates significant clustering. During periods of clustered earthquakes, of order of 1000–5000 yr, the interseismic interval becomes short, and the resolution diminishes, so the peak rate of recurrence may be underestimated. Recurrence intervals inferred from the Dead Sea record of Holocene breccia layers do not feature the extreme variation encountered in the late Pleistocene record. Yet the Holocene record shows marked transitions between periods, each with relatively uniform recurrence interval. Two of the transitions are contemporaneous with transitions in the recurrence intervals of the Anatolian faults, implying broad-scale elastic coupling.