Geology Reference
In-Depth Information
Plate 116 Standard Microfacies Types: SMF 6 and SMF 7
SMF 6:
For general explanation of SMF 6 see Pl. 115.
SMF 7. Organic boundstones
In the Standard Microfacies classification, the multifold kinds of reef limestones have been amalgamated
within a single SMF Type (boundstone) characterized by in-situ organic growth of potential reefbuilders. The
type was subdivided by growth forms and assumed growth patterns (framestone, bafflestone, bindstone; see
Sect. 8.2). SMF 7 and also the subdivisions are of limited value for microfacies studies. 'Reef limestones' look
very different! Compare Pl. 116/2 and Pl. 116/3, Fig. 14.18 and the reef limestones depicted in Figs. 8.2, 8.3 and
Pl. 41/1 and Pl. 42. Reef limestones require specific investigation methods that are discussed in Sect. 15.2
.
Additional pictures:
Pl. 41/1 (SMF 7-B
AFFLESTONE
), Pl. 42 (SMF 7-F
RAMESTONE
).
1
SMF 6
.
Mass-flow deposit.
Reef rudstone. The sample shows grains eroded from 'sponge reefs' and redeposited on a
slope. Grains are subrounded, micritic lithoclasts, reef dwellers and peloids, sometimes representing 'tuberoids' (inter-
preted as result of carbonate deposition during the decay of sponges and microbial crusts). Arrows point at longitudinal
and cross-sections of
Terebella lapilloides
. This name designates an annelid worm tube characterized by thick aggluti-
nated micritic walls.
Terebella
is a facies-diagnostic fossil in Late Jurassic sponge reefs. Originally living on the lower
macerated surfaces of siliceous sponges, the tubes became transported from the reef to the near-reef detrital facies. The
fossil is diagnostic of near reef deposits. Black structures with white 'eyes' (left margin) are reworked sessile foramin-
ifera. Late Jurassic (Kimmeridgian): Ludwag quarry northeast Bamberg, Northern Franconian Alb, Germany.
2
SMF 7F
RAMESTONE
.
Coralline sponge-microbe crust framestone
characterized by in-situ growth of sessile organisms.
The upright growth form of the sponges (SP) and the close intergrowth with microbial crusts (MC) resulted in the forma-
tion of an organic framework. The framework exhibits a large number of cryptic habitats between and below reef-build-
ing organisms and in small reef cavities. Cavity-dwelling microfossils (foraminifera, microproblematica, microbes, sponges
and others) are common criteria of this SMF Type, known since the Cambrian. Late Triassic (Dachstein limestone,
Norian): Gosaukamm, Austria.
3
SMF 7B
AFFLESTONE
.
Coral bafflestone.
Cross-section of a fasciculate coral colony (
Retiophyllia
) showing trapping of
sediment between the delicate coral branches. Solution cavities are filled with internal sediment (arrows). Note the excel-
lent preservation of the corals. Late Triassic (Zlambach Formation, Rhaetian): Gosaukamm, Austria.
-> 2, 3: Wurm 1982
Fig. 14.18. SMF 7.
Micro-framework reef limestone.
Many Permian reefs were formed by a micro-framework consisting of
very small, encrusting and low-growing organisms, abundant fine-grained trapped bioclastic sediment (often more than
50%) and marine carbonate cement (Weidlich 2002). Large reefbuilders are of minor or no importance in these reefs formed
in platform-marginal or upper slope positions. The sample shows
'Tubiphytes'
(T), trapped fine-bioclastic and peloidal sediment
(S), and recrystallized calcite cement (C). Middle Permian (Wordian-Early Capitanian): Hawasina Complex, eastern Oman
Mountains.
