Presented at the 1st IAAS Symposium, Bar Ilan University, Israel, 2004
New insights into the tectonic and sedimentry processes in the northeastern Levant
Ben-Avraham Z. (1), Hall J.K. (2), Schattner U. (1), Ben-Gai
Y. (3), Neev D. (2), Reshef M. (1)
1. Department of Geophysics and Planetary Sciences, Tel Aviv University, P.O.B.
39040, Ramat Aviv, 69978, Tel-Aviv, Israel
2. Geological Survey of Israel, 30 Malchei Israel St., Jerusalem, 95501, Israel
3. Geophysical Institute of Israel, P.O.B. 182, Lod, 71100, Israel
The Lebanese
offshore area is a key element for understanding the tectonic development of
the Levant margin. However, this area has hardly been studied over the years
and therefore its tectonic history is still very poorly known. We present previously
unpublished seismic reflection data obtained offshore southern Lebanon, extending
100 km into the Levantine Basin. The new data were combined with seismic reflection
surveys in adjacent areas to produce regional depth structural maps of the Levant
Basin, for the base Pliocene and base Messinian evaporites (traditionally marked
as the "M" and "N" markers, respectively).
Both maps, as well as the bathymetry, portray a similar general picture: a steep
(paleo) slope offshore Lebanon that gradually becomes moderate to the south,
with the anomalous widening of the shelf offshore the Carmel Structure. While
the bathymetry is dominated by the distribution of Nile sediments and their
gradual transport northward, the base Messinian shelf may have reflected older
tectonic settings. Similarities in the shapes of the present and base Messinian
margins, despite the intense sedimentation since the Messinian, insinuate that
the crustal structure dictates not only the tectonic behavior of the area, but
also the way that the sediments accumulate.
Thin Plio-Pleistocene sections were deposited on the shelf and slope, while
thicker sections were deposited at the easternmost part of the continental rise
(up to 1,000 m). The base slope also marks the point where Messinian evaporites
(mainly salt) start to thicken. At a later stage these evaporites became mobile
under the overburden layers. This is evident in the eastward tilting blocks
of the Plio-Pleistocene section, which are accompanied by growth faults that
appear as a coast-parallel disturbed zone with a generally constant width.
The only variation in the width of the disturbed zone is from the irregular
sedimentary section offshore the city of Damur, the 'Damur Disturbance'. Both
in its scale and mechanism this phenomenon resembles the Palmahim and Dor Disturbances,
located in the southern Levant continental margin.
Onshore, the area of southern Lebanon and northern Galilee is widely affected
by the Neotectonic activity of the Dead Sea Fault, manifested by two major fault
systems. The sinistral Roum Fault branches NNW from the Dead Sea Fault at the
south of the Lebanese restraining bend, while NE-SW trending dextral faults
slice up the southern Lebanon terrain. The new seismic data show several fault
systems. The dominant one consists of the growth faults associated with the
salt movement, but deep rooted faults also exist in the area. The presence of
the 'Damur Disturbance', in spite of the intense sedimentary faulting that masks
the tectonic activity, contributes to the debate surrounding the activity along
the Roum Fault.