Page 91 - Carbonate Facies in Geologic History

78 Outline of Carbonate Petrography

19. Nodular to wavy bedding
Layers which consist of undulose beds grading to loosely-packed nodular
bodies of rock in matrix oflike or unlike character (commonly shale); also termed
"lumpy bedding" (Pettijohn and Potter, 1964, p. 324, pI. 15 b, pI. 16 b and c).
20. Ball and flow, sedimentary boudinage, or flaser bedding
Differential compaction of originally patchily distributed shale and carbonate
resulting in irregular, closely spaced, almost nodular structure caused by a disrup-
tion of layers by stretching and flowage. Original inhomogenities in the fabric
may result from burrowing, patches of shells, or pebbles on the sea floor. The
argillaceous material compacts regularly while the calcareous material cements
early and resists compaction (McCrossan, 1958, p.3161; Pettijohn and Potter,
1964, p.287, pI. 16a). Similar to pull-apart structures (Natland and Kuenen, 1951,
p.89).
21. Local patch reefs
Recognized as small subequidimensional or irregularly shaped, flat-topped
organic buildups, less extensive than "platform reefs". Mostly dominated by
frame-building organisms. These occur locally as small, thick, generally unbedded
lenses of very fossiliferous carbonate, more or less isolated and surrounded by
rocks of unlike facies (Henson, 1950, p.222; AGI Glossary, 1973).
22. Foreset bedding or flank beds on slopes of knoll or patch reefs
Loosely used for any inclined bedding off flanks of carbonate buildups. Some
may be steeply inclined beds (about 25° but up to 45°) developed on seaward
slopes of major shelf margins (Stricklin et aI., 1971).
23. Bioturbation and burrows
Thorough homogenization of sediment by burrowing organisms. Sinuous or
straight burrow forms commonly preserved as traces through color mottling and
textural differences, or outlined by dolomitization. Tubular openings made and
refIlled bv worms, mollusks, echinoderms or other organisms (Pettijohn and Pot-
ter, 1964, p. 288; Seilacher, 1964 and 1967; Shinn, 1968b, p. 879; R.W.Frey in
Perkins, 1971, p. 91-124).
24. Trace fossils
Tracks, trails, grazing traces, nests, etc., on bedding planes and within the
substrate. F or references see No. 23 above.
25. Ripple mark
This structure is varied in the shallow marine environment. In general ripples
are either symmetric or asymmetric. (1) Symmetric marks have symmetric profIle
in cross section, and crest in plan view is predominantly straight. (2) Oscillation
ripple marks are straight with sharp, narrow, relatively straight crests between
broadly rounded troughs, formed by the orbital or to-and-fro motion of water
agitated by oscillatory waves on sandy bottoms above wave base. (3) Asymmetric
ripple marks are characterized by short and steep slopes facing down-current and
more gentle slopes facing up-current. (4) Current ripple marks are asymmetric
and formed by currents moving in a uniform direction over a sandy surface. They
are common in shallow water but may also form in deeper water (see above) (AGI
Glossary, 1973, p.4, 44,503, and 717 respectively).