Page 94 - Carbonate Facies in Geologic History

Intertidal Environments, Tide Flats, Channels, Levees, Ponds, Beaches 81

39. Small serpulid mounds
Commonly cup-shaped patches with raised rims, actually colonies of serpulid
worms. Size may vary from that of a bread loaf up to several m across. Serpulids
may thrive in very shallow marine or hypersaline, very warm water, covering wide
shallow areas on hard bottoms of very shallow subtidal and intertidal zones.
40. Blackened pebbles
Dark-colored, brecciated limestone and isolated blackened particles may indi-
cate subaerial exposure in salina areas filled periodically with hypersaline water.
Algal mats flourish here during high-water periods but are intermittently exposed
to times of extensive decay on the edges of ponds which dry out completely. The
black color of the bed rock is derived from decaying organic matter, chiefly from
microfilamentous boring algae which thrive in the mats and residual "stewy"
water and thoroughly impregnate the underlying substrate. The reworking of this
brecciated material into overlying beds is common (Ward et aI., 1970, p.549;
Rose, 1972, p.98).
41. Lag deposition, glauconite and phosphatic bone beds (Plate IX C)
The accumulation of chemically and physically resistent coarser particles in
thin beds formed through long periods of non-deposition and persistent winnow-
ing of the sediment on the sea floor. Lithoclasts and blackened coated particles
may also mark such deposits along with fish bones and teeth, phosphatized
organic remains, glauconite and quartz sand grains (Krumbein, 1942; see discus-
sion of SMF-14).
42. Brecciation of lithified bed rock
Polygonal cracking and shrinkage causing brecciation of hardened or semi-
lithified bed rock owing to temperature changes and force of crystal growth
within sediment (Ward et aI., 1970).
43. Karstic collapse
Collapse of limestone in sink holes, fissures, and irregular caverns may be
common as much as tens of meters beneath unconformities. These represent
fillings of caves and various underground drainages formed by solution. Dolomi-
tization is known to follow some of these pathways (Shrock, 1948, p.66-{)9).

Intertidal Environments, Tide Flats, Channels, Levees, Ponds, Beaches
(Standard Facies Belt 8)

These many subenvironments have been recognized and closely studied. Mani-
fold sedimentary structures are described in the Symposium Tidal Flat Deposits,
1973, Comparative Sedimentology Laboratory, Miami University.
44. Homogeneous and unusually thick storm layers
Such widespread, commonly unfossiliferous and well-marked layers result
from major storms and are deposited when rising tides and high winds mobilize
mud on bottoms of normally quiescent shallow ponds and lakes and deposit
single thick layers on shoal areas (Shinn et al., 1967, p.583; Shinn et aI., 1969,
Fig. 22).