5.4 Gravity Mass Flow
matter from their source area (e.g., slope sediments
under regions of upwelling) can alternate with deep
sea sediment poor in organic carbon (Fig. 5.17 c). In
contrast, slow "normal" black shale deposition can be
interrupted by turbidite interbeds poorer in organie
matter.
Both types of alternating host sediments and turbidite beds
can be used for paleoceanographic reconstructions (e.g.,
Berger and von Rad 1972; Hesse 1975; Hesse and Butt
1976; Degens et a1. 1996).
A specific problem is the discrirnination of distal
tempestites, deposited on the rnidd1e to outer shelf
(cf. Sect. 3.1), from deep-water distal turbidites originating main1y from slope failure. Both types of event
deposits result from suspension currents and tend to
display grading and the same internal sedimentary
structures (i.e. the upper divisions of the Bouma sequence). In the case of tempestites, however, body
fossils and trace fossils are both of shallow-water
origin. In contrast, turbidites contain displaced
shallow-water fauna but alternate with host sediments characterized by deep-water faunal elements
(Einseie and Seilacher 1991).
Bed Sets and Proximal-Distal Trends in
Turbidite Sequences
Proximal turbidites inc1uding channel fills are often
relatively coarse-grained and thick-bedded, and their
tops may be truncated by a subsequent turbidity current (amalgamation). Many turbidites displaya striking correlation between the dimension of their sole
marks, their grain size distribution, and their bed
thicknesses. Large flute or groove casts, for example,
are often associated with particularly thick and
coarse sandy turbidites (Fig. 5.15e). Downslope, i.e.
more distal, the percentage of sand layers in the total
fan volume often decreases, a tendency which was
also observed in the modem ocean basins (Pilkey et
al. 1980). Distal turbidites, far away from the sediment source, become thinner and finer grained, and
they suceessively lose their basal divisions with sole
marks (Fig. 5.15d; see also, e.g., Macdonald 1986;
Stowet al. 1996).
However, the proximal-distal concept should be
applied with caution if deep-sea fan associations with
channe! systems (e.g. thick beds) and overbank deposits are considered (thin beds, see below). Taking
into aecount channelized sediment distribution systems and variations in the size of turbidity currents, it
is obvious that bed sets and vertical sequences of
turbidites can be quite irregular (e.g., alternating
thick and thin beds, or coarse and fine-grained beds;
Fig. 5.16a). Nonetheless, thiekening and coarseningupward or thinning and fining-upward trends can be
frequently observed within larger sequences. Minor
223
trends (asymmetrie eyc1es) of some meters up to several tens of meters in thickness can be interpreted by
prograding, retrograding, or laterally shifting channel
systems and fan lobes (e.g. Mutti 1992; Stowet al.
1996; Einseie et al. 1994).
5.4.4 V olumes, Travel Distances and
Frequency of Mass Flow Deposits
The various types of mass flow deposits and
turbidites can be regarded as a farnily of related phenomena. Here, some of their charaeteristics are discussed together in one section.
(1) Volumes. Many mass movements range between
0.001 and several 100 km 3 in volume. The same orders of magnitude are characteristic of the volumes
of large mud flows and turbidity currents which
evolved from slides and slumps. The famous 1929
Grand Banks earthquake off Newfoundland led to
the dislocation of sediment in the order of 100 km 3 ,
including current-induced erosion on the upper slope
(Hughes Clarke et al 1990). In addition, a number of
extremely large slides and slumps (1000 to 20 000
km 3 ) has been reported from the modem ocean margins (summary in Schwarz 1982).
However, many of the mass flow deposits and
turbidite beds to be observed in normal field exposures represent smaller sediment displacements with
volumes between 10 3 and 10 6 m 3 •
(2) Travel distances. Debris flows and mud flows
can travel distances of several 100 up to about 1000
km, as observed in the present-day oceans (Akou
1984; Simm and Kidd 1984). Turbidite flows may
redeposit sediments as far as several 1000 km away
from their primary location (cf. Sect. 5.4.2).
In ancient rocks (e.g. in the Eastern Alps, Apeninnes, Pyrenees) it was possible to trace specific marker beds across
100 to 170 km (Hesse 1974; Ricci Lucchi and Valmori
1980; Mutti et a1. 1984). Pure calcareous gravity flows,
lacking clayey matrix, show shorter travel distances or
higher bed thickness/lateral extent ratios than their
siliciclastic counterparts (Colacicchi and Monaco 1994).
(3) Frequency. It is obvious that the frequency of
gravity mass flows and turbidite events is a fimction
of both their volumes and sediment supply. Therefore, deep-sea fans with average sedimentation rates
from 100 to more than 1000 mlMa are also locations
where event deposits have short recurrence intervals.
Thin-bedded (some mm to some cm) silt and mud
turbidites, as observed in interchannel areas or in
some modem backare basins, have recurrence intervals of tens to hundreds of years. Thicker turbidite
sands and muds in middle and lower fan regions as
well as in adjaeent marine basins (Mediterranean,
matter from their source area (e.g., slope sediments
under regions of upwelling) can alternate with deep
sea sediment poor in organic carbon (Fig. 5.17 c). In
contrast, slow "normal" black shale deposition can be
interrupted by turbidite interbeds poorer in organie
matter.
Both types of alternating host sediments and turbidite beds
can be used for paleoceanographic reconstructions (e.g.,
Berger and von Rad 1972; Hesse 1975; Hesse and Butt
1976; Degens et a1. 1996).
A specific problem is the discrirnination of distal
tempestites, deposited on the rnidd1e to outer shelf
(cf. Sect. 3.1), from deep-water distal turbidites originating main1y from slope failure. Both types of event
deposits result from suspension currents and tend to
display grading and the same internal sedimentary
structures (i.e. the upper divisions of the Bouma sequence). In the case of tempestites, however, body
fossils and trace fossils are both of shallow-water
origin. In contrast, turbidites contain displaced
shallow-water fauna but alternate with host sediments characterized by deep-water faunal elements
(Einseie and Seilacher 1991).
Bed Sets and Proximal-Distal Trends in
Turbidite Sequences
Proximal turbidites inc1uding channel fills are often
relatively coarse-grained and thick-bedded, and their
tops may be truncated by a subsequent turbidity current (amalgamation). Many turbidites displaya striking correlation between the dimension of their sole
marks, their grain size distribution, and their bed
thicknesses. Large flute or groove casts, for example,
are often associated with particularly thick and
coarse sandy turbidites (Fig. 5.15e). Downslope, i.e.
more distal, the percentage of sand layers in the total
fan volume often decreases, a tendency which was
also observed in the modem ocean basins (Pilkey et
al. 1980). Distal turbidites, far away from the sediment source, become thinner and finer grained, and
they suceessively lose their basal divisions with sole
marks (Fig. 5.15d; see also, e.g., Macdonald 1986;
Stowet al. 1996).
However, the proximal-distal concept should be
applied with caution if deep-sea fan associations with
channe! systems (e.g. thick beds) and overbank deposits are considered (thin beds, see below). Taking
into aecount channelized sediment distribution systems and variations in the size of turbidity currents, it
is obvious that bed sets and vertical sequences of
turbidites can be quite irregular (e.g., alternating
thick and thin beds, or coarse and fine-grained beds;
Fig. 5.16a). Nonetheless, thiekening and coarseningupward or thinning and fining-upward trends can be
frequently observed within larger sequences. Minor
223
trends (asymmetrie eyc1es) of some meters up to several tens of meters in thickness can be interpreted by
prograding, retrograding, or laterally shifting channel
systems and fan lobes (e.g. Mutti 1992; Stowet al.
1996; Einseie et al. 1994).
5.4.4 V olumes, Travel Distances and
Frequency of Mass Flow Deposits
The various types of mass flow deposits and
turbidites can be regarded as a farnily of related phenomena. Here, some of their charaeteristics are discussed together in one section.
(1) Volumes. Many mass movements range between
0.001 and several 100 km 3 in volume. The same orders of magnitude are characteristic of the volumes
of large mud flows and turbidity currents which
evolved from slides and slumps. The famous 1929
Grand Banks earthquake off Newfoundland led to
the dislocation of sediment in the order of 100 km 3 ,
including current-induced erosion on the upper slope
(Hughes Clarke et al 1990). In addition, a number of
extremely large slides and slumps (1000 to 20 000
km 3 ) has been reported from the modem ocean margins (summary in Schwarz 1982).
However, many of the mass flow deposits and
turbidite beds to be observed in normal field exposures represent smaller sediment displacements with
volumes between 10 3 and 10 6 m 3 •
(2) Travel distances. Debris flows and mud flows
can travel distances of several 100 up to about 1000
km, as observed in the present-day oceans (Akou
1984; Simm and Kidd 1984). Turbidite flows may
redeposit sediments as far as several 1000 km away
from their primary location (cf. Sect. 5.4.2).
In ancient rocks (e.g. in the Eastern Alps, Apeninnes, Pyrenees) it was possible to trace specific marker beds across
100 to 170 km (Hesse 1974; Ricci Lucchi and Valmori
1980; Mutti et a1. 1984). Pure calcareous gravity flows,
lacking clayey matrix, show shorter travel distances or
higher bed thickness/lateral extent ratios than their
siliciclastic counterparts (Colacicchi and Monaco 1994).
(3) Frequency. It is obvious that the frequency of
gravity mass flows and turbidite events is a fimction
of both their volumes and sediment supply. Therefore, deep-sea fans with average sedimentation rates
from 100 to more than 1000 mlMa are also locations
where event deposits have short recurrence intervals.
Thin-bedded (some mm to some cm) silt and mud
turbidites, as observed in interchannel areas or in
some modem backare basins, have recurrence intervals of tens to hundreds of years. Thicker turbidite
sands and muds in middle and lower fan regions as
well as in adjaeent marine basins (Mediterranean,