508
tas fluvial sediments, laeustrine limestones and marls in a
series of strike-slip-indueed depressions (e.g. Manspeizer
1985' Kashai 1988; Niemi et al. 1997). In the northem part
of th~ transform zone, gabbroid to basaltie flows eontribute
to the graben fill. The basin fill of the Dead Sea reaehes a
thiekness of 8 to 10 km. The following interpretation is
mainly based on a previous synthesis (Zak and. Freut:d
1981), weil logs (e.g. Kashai 1988), and reeent radlOmetne
dating (Steinitz and Bartov 1992) of plateau basalts and
lava flows. However, there are still many uneertainties, for
example, in the dating of sediments, teetonie events,. and
subsidenee history. The preliminary geohistory analysIs of
Fig. 11.18e somewhat deviates from the Dead Sea basin
history summarized by Garfunkel (1997) who ~sumes an
earlier (Late Mioeene) onset of aeeelerated subsldenee than
shown in F ig. 1l.l8e.
In the Mioeene and early Plioeene, a sort of shallow depression (protorift, eomparable to that of the Gulf of Califomia; see below) seems to have existed with low to medium relief in its drainage area. This is doeumented by fluvial deposits of varying thiekness (Haveza and Biro-Lido
Fms. of some 200 m or more in thiekness) at the base and
at plaees along the margin ofthe graben fill. The long time
period (around 10 Ma) and the size of the drainage area
(possibly five times that of the depositional area) proyi~ed
mueh more elastie material than neeessary for the eXIstmg
sediment volume. Consequently, the protorift system was
sedimentologieaUy open to the west or south, and its floor
layabove sea level.
During the Early Plioeene (most !ikely after the
Messinian "salt erisis" in the Mediterranean (Fig. lU8e),
subsidenee ofthe Jordan rift and the Dead Sea basin aeeelerated in eonjunetion with rapid strike-slip motion. The
formerly eontinental basin beeame a salt lagoon eonneeted
(in the northwest) with the Mediterranean. Continued rapid
subsidenee lowered the basin floor deep below sea level
and provided aeeommodation spaee for a thiek marine
evaporite sequenee deposited in a very short time period
(Fig. 11.18b and e). After the eonneetion to the Mediterranean had been interrupted, the basin beeame both
hydrologieally and sedimentologieally elosed. Terrigenous
elasties and non-marine evaporites (Amora Fm. and other
time-equivalent and younger strata, ineluding dissolved
and repreeipitated older salts) on top of the marine roek
salt eould not fill the basin up to the niveau of sea level any
more. This signifies that mean denudation in the total
drainage area of the graben system was !irnited; even the
newly ereated high relief along the graben shoulders eould
not provide suffieient sediment to fill the further subsiding
basin. The suspended load of the Jordan River was trapped
by lakes to the north of the Dead Sea.
A erude estimate of the terrigenous sediment influx is
possible for the late Pleistoeene Lisan Fm. deposited in a
lake eovering most ofthe Dead-Sea Jordan graben during a
time period of about 50 ka (Fig. lU8a). The drainage area
ofthe graben (Ad=40 000 km 2 ) had beeome wider than before due to headward river erosion; it was about 13 times
larger than the lake area (Ab=3000 km 2 ). If the mean thiekness of the Lisan Fm. is 100 m (whieh is uneertain, porosity n ~ 30%) and one half of it eonsists of elasties (elose to
alluvial fans it is two thirds, e.g. Reid and Frostiek 1993), a
mean meehanieal denudation rate of ~55 mmlka (=135
tlkm 2 /a) is found for the drainage area. The modem sediment yield of the upper Jordan River entering Lake
Kinneret seems to be only 44 tlkm 2 /a (Inbar 1982).
Chapter 11 Sediment Supply, Subsidence, and Basin Fill
The relatively high mean mechanical denudation rate
(in the order of 50 mmlka) for the drainage area of
the Lisan Fm. is sirnilar to that of the Great Salt Lake
basin (43 mmIka, see above). It reflects the increased
relief of the elevated graben shoulders as well as the
somewhat wetter climate of the last pluvial period. It
would lead, if valid for a longer time period, to an
overall clastic sedimentation rate of about 700 mlMa
in the entire graben system. However, even this enhanced sediment supply would not have been sufficient to completely fill the subsiding basin during the
past 5 Ma.
The Gulf of California
The Gulf of Califomia is a young oceanic basin
formed by strike-slip movements and therefore
shows a complicated morphology with a number of
srnall deep basins separated by higher areas (cf. Figs.
4.5 and 12.37a, Sect. 12.8). The balanced drainage
and basin areas shown in Fig. 11.19b have a ratio of
A d /A b =1.4. The sediment volume ~fthe gulfha~ be~n
deterrnined for the last 4 Ma (Emsele and Nlemltz
1982), i.e. for the so-called post-rift sediments which
were deposited after the initiation of ocean spreading
(Fig. 11.19a; Curray and Moore et al. 1982a).
Prior to the building of artifieial dams, the northem gulf
was fed with substantial amounts of sediment by the Colorado River draining a large hinterland. In the south the gulf
has a wide, deep opening to the Paeifie Oeean. To assess a
hemipelagic sediment budget, the influenee of the Colorado as a souree of terrigenous material was exeluded by
ehoosing some gulf islands as the northem boundary of the
studied basin area (Fig. 11.19b). These islands aet as a barrier whieh traps the Colorado sediments. In the south and
southwest the boundary !ine of the study area separates a
gulf region still influeneed by hernipelagie ~edim.ents fro~
the deeper oeean floor, where pelagie deposlts (wIth a sedimentation rate ofless than 20 mmIka) prevail.
Prior to 4 Ma ago, a "protogulf" existed, in whieh sediments of eonsiderable thiekness aeeumulated, partieularly
below the eastem shelf of the present gulf (Fig. 11.19a and
d). The protogzilj sediments rest on subsiding eontinental
ernst, while the younger, post-rift sediments were deposited
either on new oeeanie erust in the deep main part of the
gulf, or on top of protogulf sediments separated by an uneonformity.
Based on seismie reeords and holes drilled during Leg
64 ofthe Deep Sea Drilling Projeet, an isopaeh map for the
post-rift sediments eould be drawn, whieh sho:ws ~xtremely
varying sediment thieknesses (EinseIe and Nlemttz 1982).
In order to ealculate the sediment volume of the
depositional area, the different ~ediment thieknes~es were
subdivided into slabs of equal thlekness and POroSlty. Wet,
uneompaeted sediment volume was the!? eon~erted into
volume of eompaeted, solid (dry) rnatenal (Flg. lUge)
using the porosity/depth relationship found in the boreholes (Fig. lUge).
tas fluvial sediments, laeustrine limestones and marls in a
series of strike-slip-indueed depressions (e.g. Manspeizer
1985' Kashai 1988; Niemi et al. 1997). In the northem part
of th~ transform zone, gabbroid to basaltie flows eontribute
to the graben fill. The basin fill of the Dead Sea reaehes a
thiekness of 8 to 10 km. The following interpretation is
mainly based on a previous synthesis (Zak and. Freut:d
1981), weil logs (e.g. Kashai 1988), and reeent radlOmetne
dating (Steinitz and Bartov 1992) of plateau basalts and
lava flows. However, there are still many uneertainties, for
example, in the dating of sediments, teetonie events,. and
subsidenee history. The preliminary geohistory analysIs of
Fig. 11.18e somewhat deviates from the Dead Sea basin
history summarized by Garfunkel (1997) who ~sumes an
earlier (Late Mioeene) onset of aeeelerated subsldenee than
shown in F ig. 1l.l8e.
In the Mioeene and early Plioeene, a sort of shallow depression (protorift, eomparable to that of the Gulf of Califomia; see below) seems to have existed with low to medium relief in its drainage area. This is doeumented by fluvial deposits of varying thiekness (Haveza and Biro-Lido
Fms. of some 200 m or more in thiekness) at the base and
at plaees along the margin ofthe graben fill. The long time
period (around 10 Ma) and the size of the drainage area
(possibly five times that of the depositional area) proyi~ed
mueh more elastie material than neeessary for the eXIstmg
sediment volume. Consequently, the protorift system was
sedimentologieaUy open to the west or south, and its floor
layabove sea level.
During the Early Plioeene (most !ikely after the
Messinian "salt erisis" in the Mediterranean (Fig. lU8e),
subsidenee ofthe Jordan rift and the Dead Sea basin aeeelerated in eonjunetion with rapid strike-slip motion. The
formerly eontinental basin beeame a salt lagoon eonneeted
(in the northwest) with the Mediterranean. Continued rapid
subsidenee lowered the basin floor deep below sea level
and provided aeeommodation spaee for a thiek marine
evaporite sequenee deposited in a very short time period
(Fig. 11.18b and e). After the eonneetion to the Mediterranean had been interrupted, the basin beeame both
hydrologieally and sedimentologieally elosed. Terrigenous
elasties and non-marine evaporites (Amora Fm. and other
time-equivalent and younger strata, ineluding dissolved
and repreeipitated older salts) on top of the marine roek
salt eould not fill the basin up to the niveau of sea level any
more. This signifies that mean denudation in the total
drainage area of the graben system was !irnited; even the
newly ereated high relief along the graben shoulders eould
not provide suffieient sediment to fill the further subsiding
basin. The suspended load of the Jordan River was trapped
by lakes to the north of the Dead Sea.
A erude estimate of the terrigenous sediment influx is
possible for the late Pleistoeene Lisan Fm. deposited in a
lake eovering most ofthe Dead-Sea Jordan graben during a
time period of about 50 ka (Fig. lU8a). The drainage area
ofthe graben (Ad=40 000 km 2 ) had beeome wider than before due to headward river erosion; it was about 13 times
larger than the lake area (Ab=3000 km 2 ). If the mean thiekness of the Lisan Fm. is 100 m (whieh is uneertain, porosity n ~ 30%) and one half of it eonsists of elasties (elose to
alluvial fans it is two thirds, e.g. Reid and Frostiek 1993), a
mean meehanieal denudation rate of ~55 mmlka (=135
tlkm 2 /a) is found for the drainage area. The modem sediment yield of the upper Jordan River entering Lake
Kinneret seems to be only 44 tlkm 2 /a (Inbar 1982).
Chapter 11 Sediment Supply, Subsidence, and Basin Fill
The relatively high mean mechanical denudation rate
(in the order of 50 mmlka) for the drainage area of
the Lisan Fm. is sirnilar to that of the Great Salt Lake
basin (43 mmIka, see above). It reflects the increased
relief of the elevated graben shoulders as well as the
somewhat wetter climate of the last pluvial period. It
would lead, if valid for a longer time period, to an
overall clastic sedimentation rate of about 700 mlMa
in the entire graben system. However, even this enhanced sediment supply would not have been sufficient to completely fill the subsiding basin during the
past 5 Ma.
The Gulf of California
The Gulf of Califomia is a young oceanic basin
formed by strike-slip movements and therefore
shows a complicated morphology with a number of
srnall deep basins separated by higher areas (cf. Figs.
4.5 and 12.37a, Sect. 12.8). The balanced drainage
and basin areas shown in Fig. 11.19b have a ratio of
A d /A b =1.4. The sediment volume ~fthe gulfha~ be~n
deterrnined for the last 4 Ma (Emsele and Nlemltz
1982), i.e. for the so-called post-rift sediments which
were deposited after the initiation of ocean spreading
(Fig. 11.19a; Curray and Moore et al. 1982a).
Prior to the building of artifieial dams, the northem gulf
was fed with substantial amounts of sediment by the Colorado River draining a large hinterland. In the south the gulf
has a wide, deep opening to the Paeifie Oeean. To assess a
hemipelagic sediment budget, the influenee of the Colorado as a souree of terrigenous material was exeluded by
ehoosing some gulf islands as the northem boundary of the
studied basin area (Fig. 11.19b). These islands aet as a barrier whieh traps the Colorado sediments. In the south and
southwest the boundary !ine of the study area separates a
gulf region still influeneed by hernipelagie ~edim.ents fro~
the deeper oeean floor, where pelagie deposlts (wIth a sedimentation rate ofless than 20 mmIka) prevail.
Prior to 4 Ma ago, a "protogulf" existed, in whieh sediments of eonsiderable thiekness aeeumulated, partieularly
below the eastem shelf of the present gulf (Fig. 11.19a and
d). The protogzilj sediments rest on subsiding eontinental
ernst, while the younger, post-rift sediments were deposited
either on new oeeanie erust in the deep main part of the
gulf, or on top of protogulf sediments separated by an uneonformity.
Based on seismie reeords and holes drilled during Leg
64 ofthe Deep Sea Drilling Projeet, an isopaeh map for the
post-rift sediments eould be drawn, whieh sho:ws ~xtremely
varying sediment thieknesses (EinseIe and Nlemttz 1982).
In order to ealculate the sediment volume of the
depositional area, the different ~ediment thieknes~es were
subdivided into slabs of equal thlekness and POroSlty. Wet,
uneompaeted sediment volume was the!? eon~erted into
volume of eompaeted, solid (dry) rnatenal (Flg. lUge)
using the porosity/depth relationship found in the boreholes (Fig. lUge).