Geology Reference
In-Depth Information
Box 3.1.
Checklist for field description of paleontological data in carbonate rocks.
Bedded limestones
Bedding and sedimentary structures
Bedding types (lithology, thickness, bedding boundaries, texture; see Fig. 3.1, Fig. 3.2)
'Event beds' ? (beds caused by physical and biological events of short duration, e.g. storms, turbidity currents,
earthquakes, sudden death of organisms resulting in mass acummulations; see Sect. 5.1.3)
Cyclic patterns ? (see Sect. 16.1)
Sedimentary structures and diagenetic features (see Fig. 3.4)
Types and preservation of fossils
Classification of fossils (group, taxa)
Evaluation of fossil types with regard to ecological criteria
Trace fossils and/or body fossils ?
Burrowing and bioturbation (see Sect. 5.1.4)
Taphonomic criteria (see Chap. 10)
Abundance and distribution of fossils
Fossil concentrations
Abundance of fossils based on bulk samples or on counts using various grids (see Sect. 6.2.1)
Distributional patterns of fossils on bedding planes (random, patchy, oriented)
Lateral distribution of fossils within the beds
Distribution and type of fossils within underlying and overlying beds
Massive limestones (e.g. reef limestones)
Geometry of the carbonate body
Mapping of the boundary and geometry of the buildup
Mapping of major litho- and biofacies types
Establishing time lines (tracing bedding surfaces in the flank facies), discontinuities and event marker beds, e.g.
storm layers, synsedimentary breccias)
Look for bottom-top structures (particulary at the flanks of buildups)
Types and preservation of fossils
Classification of fossils
Taphonomic criteria
Analysis of the principal fossils with regard to their inferred role in buildup formation (e.g. framebuilders, binding
and encrusting organisms)
Differentiation of growth forms of sessile organisms
Abundance and distribution of fossils
Vertical and horizontal cover (density) and size of reefbuilding organisms (using a gridded overlay, the quadrat
method orthe line method, see Sect. 6.2.1)
Recognition of significant vertical sequential changes in growth forms, taxonomic composition or abundance
Relation between sediment, texture and fossils
Description of the 'matrix' between and around autochthonous reefbuilders (see Sect. 16.2.5.2)
Description of growth cavities, shelter structures, open-space structures and solution voids (see Sect. 5.1.5) with
regard to geometry, dimension, distribution and filling (sediment, spar, crystal silt, still open)
Description of fissures with regard to setting, size, orientation, filling and fossils
Abundance of fine-grained sediment and carbonate cements in relation to benthic fossils
Diagenetic features:
see Sect. 7.45
3.1.1.3 Fossils and Biogenic Structures
Fossil concentrations
are relatively dense accumu-
lation of biologic hardparts (irrespective of taxonomic
composition, state of preservation, or degree of post-
mortem modification).
By taking into consideration the taxonomic compo-
sition, bioclastic fabric, geometry and internal struc-
ture of the deposit, skeletal concentrations can be
grouped genetically according to the inferred relative
importance of biogenic, sedimentologic and diagenetic
processes (Kidwell et al. 1986; Fig. 3.6). This approach
is useful for interpreting 'shell beds' composed of mol-
lusks and brachiopods, and understanding the processes
Fossils, fossiliferous sediments and biogenic sedimen-
tary structures are key sources of information on paleo-
environments, sedimentation patterns and diagenesis.
Strategies necessary for describing paleontological data
in the field were summarized by Goldring (1991). Field
strategies are different for bedded sediments and for
dominantly autochthonous buildups. Box 3.1 is based
on a
field classification of fossiliferous sediments
pro-
posed by Goldring (1991). Of special interest are 'fos-
sil concentrations', bioclastic fabrics, and ichnofabrics.
