11.2 Denudation-Sediment Accumulation Systems
the river loads (bedloads and suspended loads). To determine the rates of chemical denudation and (biogenic) sedimentation, DR.:h and SReh, the dissolved river load entering
and leaving the lakes as well as biogenic carbonate and
silica production in the lakes were considered. Detrital carbonate derived from the drainage areas was added to the
mechanical sedimentation rate.
Lake systems with drainage areas dominated by crystalline rocks of the Central Alps (group I) show higher DR me
and S~ but lower DReh and SReh values than lakes with
drainage areas in the Northem Ca\careous Alps (group 2).
The DR,.jDR.:h ratio is 2 to 6 for group I and 2 lakes. Biogenic carbonate (and also biogenie silica) only
playa minor role in lake filling (10-30% in the centrallake
sediments; much less in delta sediments). Of the chemical
river load, 82-92% passes the lakes. Lake Balaton, a rifttype lake in Hungary (with low DR'otal and DRrne almost
negligible), is an example for the effects of low relief and
warmer, drier c1imate.
The present-day sediment storage capacity of these
perialpine lakes is limited. Using the data of Fig.
11.4b, the lifetimes of the lakes can be estimated.
They mainly range from ~ 15 to 40 ka.
Mass balances are also available for some glaciershaped lakes in British Columbia. The wide range in
their mean sedimentation rates (1-40 mmla) rnainly
results from differences in their ratios of drainagelbasin area, but variations in relief and climate
also play a role. The impact of the A d / Ab ratio is
shown for two examples, the Lillooet Lake and the
Stave Lake, British Columbia, both of which lie in
the humid zone close the Pacific coast.
About 13% of the Lillooet drainage area are covered by
glaciers (SY=560 t/km 2 /a or 225 rnrnIka); the lake (ratio
Aj Ab:::: 180) is mainly filled by rapid delta prograding
(Owens and Slaymaker 1993; Desloges and Gilbert 1994).
Thus the mean sedimentation rate (dry, related to a constant lake area) is 40 rnrnIa. In reality, the sedimentation
rate in the lake center is only 1.6-3 rnrnIa.
The larger Stave lake (Aj Ab:::: 15) receives less sediment (200 tlkm 2 /a) from a smaller drainage area and therefore displays a mean sedimentation rate of 1.2 mrnIa which
is much lower than that of the Lillooet lake.
Adjacent Semi-Closed Basins: The Black Sea
The modem Black Sea (cf. Sects. 4.3 and 9.6) represents an adjacent (backarc) basin with an opening to
the Mediterranean Sea. It is a gigantic catch basin for
the river discharge of half of Europe and part of Asia
(Fig. 11.5). Degens et al. (1978) have calculated denudation rates from river loads and compared these
values with observed sedimentation rates in the
Black Sea.
The total drainage of the Black Sea comprises an area of
1.98 x 10 6 km 2 ; the basin area is 0.45 x 10 6 km 2 and
AjAb=4.4. The shallow and narrow outlet ofthe Bosporus,
connecting the Black Sea with the Mediterranean, allows
489
all the incoming river sediments to be trapped by the Black
Sea.
The total suspended and dissolved river load transported
into the Elack Sea amounts to 237 x 10 6 tla. The suspended
load is slightly greater than the dissolved load. The Danube
River delivers about 60% of the total river load. The Don
and Kuban rivers discharge into the Sea of Asov, where
most of their material is deposited. The Caucasian rivers
from the east contribute about 20% of the total detritus.
As determined from their chemical and solid loads, the
present-day denudation rates in the principal source areas
vary from approxirnately 10 rnrnIka (drainage area of the
Dnepr River) to 80 rnrnIka (Danube River; average rock
density 2.5 t/m 3 ). The average denudation rate for the total
drainage system is 50 mmlka or 120 t/km 2 /a); if it is only
20 rnrnIka for the lowlands, it increases to 120 mmlka in
the mountainous regions (about 30% ofthe total area).
The estimation of the sediment volume in the Black Sea
is based on data available for the deep part of the basin
(Fig. 11.5) comprising ab out two thirds of the total basinal
area. In the past 5000 years, the sedimentation rate of uncompacted sediment (70% porosity), including coccolith
ooze, sapropel, and intercalated turbidites, was approximately 1000 mmlka (cf. Sect. 4.3) or about 300 mmIka for
compacted, solid material. Normalized on the drainage area
(Ad=4.4xAb), this value yields an average total denudation
rate of about 70 mmlka.
The somewhat revised results of this study are shown
in Fig. 11.5 (also cf. Fig. 9.19). The average denudation rates of 80 and 70 mmlka, determined independently by applying river load data and sedimentation
rates, respectively, agree fairly well. Most of the dissolved river load is probably used up by organisms
and deposited in the basin as biogenic carbonate and
opaline silica. There is, however, also some exchange
of dissolved material via the narrow passage of the
Bosporus, but present-day water outflow from the
Black Sea is greater than inflow (Sect. 4.3).
The denudation rates obtained in this study are characteristic of the steppe vegetation present in large parts of the
drainage area. During times of more extensive forest
growth, denudation was probably reduced by more than
half. During such times, sapropels were preferentially deposited in the Black Sea basin. Similarly, in the course of
Pleistocene glacial melting and loess mobilization in the
hinterland, denudation and sedimentation rates increased
considerably and may have reached values of up to about
five times greater than those found for the Holocene.
Longer-term Quaternary sedimentation rates in the
Black Sea were somewhat higher (up to about 1500
mmlka) than in the Holocene. The Quaternary sediments reached thicknesses up to 2.5 km in the western and 3 km in the eastern subbasin. For the entire
Tertiary, the average sedimentation rates were lower
than in the Holocene (in the order of 200 mrnIka,
leading to a Tertiary sediment of 11 to 12 km in
thickness; Okay et al. 1994; Robinson et al. 1996).
The basin floor must have subsided at a rate of at
least 200 mrnIka in the Neogene. Thus, the long-term
the river loads (bedloads and suspended loads). To determine the rates of chemical denudation and (biogenic) sedimentation, DR.:h and SReh, the dissolved river load entering
and leaving the lakes as well as biogenic carbonate and
silica production in the lakes were considered. Detrital carbonate derived from the drainage areas was added to the
mechanical sedimentation rate.
Lake systems with drainage areas dominated by crystalline rocks of the Central Alps (group I) show higher DR me
and S~ but lower DReh and SReh values than lakes with
drainage areas in the Northem Ca\careous Alps (group 2).
The DR,.jDR.:h ratio is 2 to 6 for group I and 2 lakes. Biogenic carbonate (and also biogenie silica) only
playa minor role in lake filling (10-30% in the centrallake
sediments; much less in delta sediments). Of the chemical
river load, 82-92% passes the lakes. Lake Balaton, a rifttype lake in Hungary (with low DR'otal and DRrne almost
negligible), is an example for the effects of low relief and
warmer, drier c1imate.
The present-day sediment storage capacity of these
perialpine lakes is limited. Using the data of Fig.
11.4b, the lifetimes of the lakes can be estimated.
They mainly range from ~ 15 to 40 ka.
Mass balances are also available for some glaciershaped lakes in British Columbia. The wide range in
their mean sedimentation rates (1-40 mmla) rnainly
results from differences in their ratios of drainagelbasin area, but variations in relief and climate
also play a role. The impact of the A d / Ab ratio is
shown for two examples, the Lillooet Lake and the
Stave Lake, British Columbia, both of which lie in
the humid zone close the Pacific coast.
About 13% of the Lillooet drainage area are covered by
glaciers (SY=560 t/km 2 /a or 225 rnrnIka); the lake (ratio
Aj Ab:::: 180) is mainly filled by rapid delta prograding
(Owens and Slaymaker 1993; Desloges and Gilbert 1994).
Thus the mean sedimentation rate (dry, related to a constant lake area) is 40 rnrnIa. In reality, the sedimentation
rate in the lake center is only 1.6-3 rnrnIa.
The larger Stave lake (Aj Ab:::: 15) receives less sediment (200 tlkm 2 /a) from a smaller drainage area and therefore displays a mean sedimentation rate of 1.2 mrnIa which
is much lower than that of the Lillooet lake.
Adjacent Semi-Closed Basins: The Black Sea
The modem Black Sea (cf. Sects. 4.3 and 9.6) represents an adjacent (backarc) basin with an opening to
the Mediterranean Sea. It is a gigantic catch basin for
the river discharge of half of Europe and part of Asia
(Fig. 11.5). Degens et al. (1978) have calculated denudation rates from river loads and compared these
values with observed sedimentation rates in the
Black Sea.
The total drainage of the Black Sea comprises an area of
1.98 x 10 6 km 2 ; the basin area is 0.45 x 10 6 km 2 and
AjAb=4.4. The shallow and narrow outlet ofthe Bosporus,
connecting the Black Sea with the Mediterranean, allows
489
all the incoming river sediments to be trapped by the Black
Sea.
The total suspended and dissolved river load transported
into the Elack Sea amounts to 237 x 10 6 tla. The suspended
load is slightly greater than the dissolved load. The Danube
River delivers about 60% of the total river load. The Don
and Kuban rivers discharge into the Sea of Asov, where
most of their material is deposited. The Caucasian rivers
from the east contribute about 20% of the total detritus.
As determined from their chemical and solid loads, the
present-day denudation rates in the principal source areas
vary from approxirnately 10 rnrnIka (drainage area of the
Dnepr River) to 80 rnrnIka (Danube River; average rock
density 2.5 t/m 3 ). The average denudation rate for the total
drainage system is 50 mmlka or 120 t/km 2 /a); if it is only
20 rnrnIka for the lowlands, it increases to 120 mmlka in
the mountainous regions (about 30% ofthe total area).
The estimation of the sediment volume in the Black Sea
is based on data available for the deep part of the basin
(Fig. 11.5) comprising ab out two thirds of the total basinal
area. In the past 5000 years, the sedimentation rate of uncompacted sediment (70% porosity), including coccolith
ooze, sapropel, and intercalated turbidites, was approximately 1000 mmlka (cf. Sect. 4.3) or about 300 mmIka for
compacted, solid material. Normalized on the drainage area
(Ad=4.4xAb), this value yields an average total denudation
rate of about 70 mmlka.
The somewhat revised results of this study are shown
in Fig. 11.5 (also cf. Fig. 9.19). The average denudation rates of 80 and 70 mmlka, determined independently by applying river load data and sedimentation
rates, respectively, agree fairly well. Most of the dissolved river load is probably used up by organisms
and deposited in the basin as biogenic carbonate and
opaline silica. There is, however, also some exchange
of dissolved material via the narrow passage of the
Bosporus, but present-day water outflow from the
Black Sea is greater than inflow (Sect. 4.3).
The denudation rates obtained in this study are characteristic of the steppe vegetation present in large parts of the
drainage area. During times of more extensive forest
growth, denudation was probably reduced by more than
half. During such times, sapropels were preferentially deposited in the Black Sea basin. Similarly, in the course of
Pleistocene glacial melting and loess mobilization in the
hinterland, denudation and sedimentation rates increased
considerably and may have reached values of up to about
five times greater than those found for the Holocene.
Longer-term Quaternary sedimentation rates in the
Black Sea were somewhat higher (up to about 1500
mmlka) than in the Holocene. The Quaternary sediments reached thicknesses up to 2.5 km in the western and 3 km in the eastern subbasin. For the entire
Tertiary, the average sedimentation rates were lower
than in the Holocene (in the order of 200 mrnIka,
leading to a Tertiary sediment of 11 to 12 km in
thickness; Okay et al. 1994; Robinson et al. 1996).
The basin floor must have subsided at a rate of at
least 200 mrnIka in the Neogene. Thus, the long-term