Page 93 - Carbonate Facies in Geologic History

80 Outline of Carbonate Petrography

platy shells in the mud, rotting of the form of some unknown organism (Philcox,
1963, p. 905; Heckel, 1972 a, p.12, 13).
32. Injection dikes
Beds cutting vertically through massive or normally bedded strata and fIlled
by material squeezed up from below through loading of the substrate by the
carbonate mass. May be somewhat irregular and anastomozing or straight and
sharp-sided.
33. Filled fissures, Neptunian dikes
Discordant sediment filling fissures which cut across massive to normally
bedded strata; sediment filled from above and generally composed of sand or
coarser material. The fissures may have been opened by slumping or tectonic
activity at an early stage in the geologic history of the mound (Shrock, 1948,
p.212; Fischer, 1964).
34. Geopetal sediment fillings in mound cavities (Plate XXV B)
Structures that indicate the relations of top to bottom during, or shortly after,
sedimentation. Various types of sediment fIllings may occur in bottoms of cavi-
ties. Color changes, textural differences, and cross lamination generally mark
these internal sediments which may also occur in several generations. Spar-filling
in upper parts of cavities, only partly filled with sediment, indicates top. Vadose
silt of Dunham (1969) is a special type of internal sediment resulting from early
breakdown and deposition of partly lithified lime mud, presumably under condi-
tions of meteoric water flow (Sander, 1936, p.31, 1951, p.2; Shrock, 1948, p.4).

Disconformities-Surfaces of Non-Deposition or Very Slow Deposition
Marking "Stratigraphic Breaks" (Standard Facies Belts 5-8)
35. Planar corrasion zones
Abrasion and truncation of surfaces by marine currents, meteoric water solu-
tion of organic activity. The structure may be indistinguishable from some "hard
grounds". The processes of formation are partly the same.
36. Hard grounds or bored surfaces
Organically bored marine or littoral surfaces encrusted commonly with fossils
in growth position. The sediment was syngenetically lithified by marine micritiza-
tion or void space cementation. Such surfaces are encountered at tops of regres-
sive carbonate sequences (Hallam, 1969, p.240; Purser, 1969, p.217; Shinn, 1969,
p.109).
37. Oyster plasters and other encrusters
Oyster-encrusted surfaces are commonly associated with "hard grounds", typ-
ically within Mesozoic and younger sediments (Kliipfel, 1917, pI. III).
38. Oxidation films
Red-stained zones due to thorough oxidation of iron in the top of the sub-
strate beneath a disconformity surface. Commonly but not exclusively due to
meteoric water (Krumbein, 1942).