Geology Reference
In-Depth Information
• Measure the thickness of the units and compare the
thickness with the thickness of the layers representing
the background sedimentation.
high- and low-energy reefs, or upper and lower parts
of slopes (see Sect. 15.7.5).
• Consider the preservation of fossil shells. Strongly
bored and worn shells may indicate a source area with
reduced sedimentation and high nutrient input (e.g. la-
goons).
• Look for burrowing at the top of the turbidite or
within individual sedimentary units. The latter indicate
an arrested deposition of turbidite material.
Microfacies
• Use vertically and horizontally oriented thin sec-
tions. Vertical sections exhibit the composition and
boundaries of individual internal units. Sections paral-
lel to bedding planes allow sediment transport to be
recognized.
• Determine the type and frequency of skeletal grains,
lithoclasts, extraclasts and other particles. Frequency
should be determined by point counting (Sect. 6.2.1.1).
Differentiate between particles that were already lithi-
fied at the time of erosion and redeposition, and par-
ticles that were not lithified.
• Note the shape and roundness of litho- and extra-
clasts. Distinguish lithoclasts of different texture and
microfacies.
• Look for orientation patterns of particles indicating
type of grain settling and current transport.
15.7.2.6 Sliding and Slumping
A slide is the movement of a rigid, internally unde-
formed mass. A slump originates from mass sliding and
the creeping of semi-consolidated sediment. The de-
tachment surface of slides is called an intraformational
truncation surface. The study of detached submarine
slide masses aids in recognizing slope failures. Slide
masses can be preserved either downslope or within
the adjacent basins. The reasons for sliding are varied
and interrelated (Vortisch 1964; Bernoulli and Jenkyns
1970; Schwarz 1975; Nardin 1979; Mills 1983; Eberli
1988; Coniglio and Dix 1992). Sediment overloading
and seismic activity as well as excessive pore pressures
are the most obvious reasons. Evidence of slide masses
Grain size and packing
• Perform a thorough grain-size analysis. The maxi-
mum grain size of lithoclasts and bioclasts reflects the
degree of transport energy. At least 50 grains should be
averaged. Relate maximum grain size and grain size
ranges with bed thickness and the thickness of sedi-
mentary units within the turbidite bed. Consider dif-
ferences in porosity and the density of grains that could
influence settling behavior.
Calculate grain-size parameters (Sect. 6.1), particu-
larly the mean, standard deviation and skewness (see
Table 6.1). Parameter diagrams indicate the type and
strength of transport energy. Sect. 6.1.2.2 gives an ex-
ample using Barmstein limestone samples.
• Use packing indices (Sect. 7.5.1), e.g. the number
of grain cross sections per square centimeter. A high
grain number indicates the deposition of many small
grains; low grain numbers indicate the predominance
of coarse grains.
Box 15.3.
Selected references on ancient carbonate tur-
bidites. Many of these papers include descriptions not
only of turbidites but also of other gravity flow deposits.
Tertiary:
Betzler et al. 2000; Engel 1974; Gawenda
et al. 1999; Reijmer et al. 1992; Skaberne 1989;
Westphal 1998.
Cretaceous:
Carrasco and Baldomero 1977; Cazzola
and Soudt 1993; Colacicchi and Baldanza 1986; Everts
1991, 1994; Ferry 1979; Harloff 1989; Hesse and Butt
1976; Mutti et al. 1978; Sagri 1979.
Jurassic:
Bosellini 1967; Carozzi 1955; Eberli 1987,
1988; Ebli 1997; H.W. Flügel and Fenninger 1966; H.W.
Flügel and Pölsler 1965; Garrison and Fischer 1969;
Marcinowski 1970; Matyszkiewicz 1996; Misik and
Sykora 1982; Mutti et al. 1978; Scheibner and Reijmer
1999; Schlager 1980; Steiger 1981.
Triassic:
Matzner 1986; Reijmer and Everaars 1991;
Reijmer et al. 1994; Watts 1988.
Permian:
Brown and Loucks 1993, Flügel et al. 1991.
Carboniferous:
Davies 1977; Franke et al. 1975;
Hemleben and Reuther 1980; Herbig and Bender 1992;
Herbig and Mamet 1994; Izart et al. 1997; Meischner
1962, 1964; Yurewicz 1977
Devonian:
Babek and Kalvoda 2001; Carozzi and
Banaree 1984; Cook et al. 1972; Eder 1971; Junge 1992;
Lütke 1976; Szulczewski 1968; Tucker 1969, 1974.
Ordovician:
Pohler and James 1989.
Cambrian
: Cook and Taylor 1977; Demicco 1985;
Reinhardt 1977.
Biota
• Differentiate between benthic and planktonic fos-
sils. Benthic fossils should be determined by their as-
signment to groups or taxonomic units. The occurrence
of dasyclad green algae in calciturbidites should indi-
cate a source area in very shallow, well-lighted, plat-
form interior environments. Specific foraminifera can
be used to distinguish source areas within different parts
of reef complexes (see Sect. 14.2.2 and Pl. 111). Con-
sider the assemblages of microfossils that may reflect
the major source environments, e.g. platform interior,
