Geology Reference
In-Depth Information
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Lowstand shedding
is indicated by skeletal grains
in association with reef-derived (or slope-derived) li-
thoclasts. Primarily calcitic grains are common. Depo-
sition of carbonate breccias and blocks transported by
debris flows will punctuate the pelagic sedimentation
in the basin.
16.1.2.3 Case Studies: SeaLevel Fluctuations
and Systems Tracts Documented by Microfacies
The case studies in this section dealing with carbonate
ramps and platforms demonstrate the potential of
microfacies criteria and microfacies types in sequence
Plate 141 Microfacies, SeaLevel Fluctuations and SequenceStratigraphic Analysis: Case Study Part 1
The microfacies types shown in Pl. 141 and Pl. 142 characterize an Early Jurassic succession from the central
Peloponnesus in Greece. The section consists of 33 limestone beds, each one with a thickness of 25 to 40 cm.
The succession exhibits alternations of shallow-marine and deep-marine limestones. Pl. 141/1 shows the
microfacies of a sample from the bottom of the section, Pl. 142/20 the microfacies of the topmost sample.
Microfacies criteria and SMF types can be used to recognize changes in paleobathymetry, sequence boundaries
and systems tracts.
The section starts with a sample characterized by reworked and redeposited, possibly reef-derived mate-
rial (-> 1). The samples shown in -> 2 and 3 correspond to SMF 10 typically developed in the Standard Facies
Zones FZ 7 or FZ 2. Sedimentation in FZ 7 (open-marine platform interior) is reliable because of the association
of ooids, benthic foraminifera and diverse biota. Figs. 4-6 correspond to SMF 9. Sedimentation in a deep shelf
environment (FZ 2) is indicated by the association of echinoderms, bivalves, ostracods and foraminifera, and by
strong burrowing. The samples of -> 7 and 8 display pelagic criteria (filaments, ammonites) supporting an
attribution to SMF 3 and FZ 3 (deep shelf margin).
Regarding the sample shown in -> 1 as allochthonous intercalation in the open-marine platform facies re-
corded by -> 2 and 3, the microfacies of -> 1 to 8 reflects a deepening-upward succession of a HST connected
with sea-level rise.
A distinct sequence boundary and subaerial exposure at the top of basinal sediments and LST conditions are
recorded by the paleocaliche shown in -> 9 and 10. This boundary would demand a significant sea-level fall
corresponding to a Type1 sequence boundary.
1
Poorly sorted packstone.
Larger grains are recrystallized fragments of chaetetid coralline sponges (C). Smaller grains are
foraminifera, shell debris and peloids. The microfacies indicates allochthonous redeposition. Sample B 1.
2
Bioclastic packstone.
Grains: Small micritized radial ooids, coated echinoderm clasts (E) surrounded by rim cement,
foraminifera (F;
Involutina
), ostracods (O). SMF 10 (indicating textural inversion and redeposition). Sample B 3.
3
Oolitic-bioclastic packstone.
Grains: Radial ooids, echinoderms (E), bivalve and brachiopod shells, foraminifera (F). The
matrix is inhomogeneous micrite. SMF 10. Sample B 4.
4
Strongly burrowed, fine-bioclastic wackestone.
Larger grains are micritized echinoderm fragments, smaller grains are
shell debris, ostracods and rare foraminifera (arrow). SMF type 9 (defined by a bioclastic wackestone in which diverse
organisms have been jumbled through burrowing). Sample B 8.
5
Burrowed bioclastic wackestone.
Grains: Ostracods, echinoderm debris (E), foraminifera (F), small gastropods (G). Grains
with black Fe/Mn coatings and fossil molds filled with dark micrite indicate reworking. SMF 9. Sample B 10.
6
Burrowed fine-bioclastic packstone.
Larger grains are foraminifera (F) and ostracods (O), smaller grains are densely
packed shell debris, foraminifera and ostracods, some echinoderm debris (E). SMF 9. Sample B 12.
7
Pelagic bioclastic wackestone.
Grains: Juvenile ammonites (A), filaments (arrows), some echinoderm fragments (E).
SMF 3. Sample B 14.
8
Pelagic 'filament' wackestone.
Grains: Filaments are very thin shells of pelagic bivalves (see Sect. 10.2.4.2), echinoderm
(E) fragments. SMF 3-F
IL
. Sample B 15.
9
Paleocaliche.
Diagnostic criteria are the nonfossiliferous clotted and microfractured, dark matrix (M) and the abundance
of quartz grains (Q). Sequence boundary. Sample B 18.
10
Paleocaliche.
Diagnostic criteria are the laminated texture (L), in-place brecciation (black arrows), fissures filled with
quartz grains (white arrow), clasts exhibiting alveolar texture (A), and dark-colored reworked grains ('black pebbles',
BP). Sequence boundary. Sample B19.
