Page 90 - Carbonate Facies in Geologic History

Shelf Margin and Shallow Shelf in Front and behind Shelf Margin 77

bounded with a ferruginous rind while others are not; matrix contains higher
proportion of microscopic skeletal material (ostracods, foraminifers, etc.). Stylo-
lites commonly occur separating pebbles (Hollman, 1962, Garrison and Fischer,
1969, p. 26-27).
12. Resedimented clasts and retextured sediments
Beds in which slumped or otherwise dislocated complexes of rock occur.
Original stratification, or traces of it, may still be recognizable; locally, a slumped
mass may consist of a chaotic melange of large tilted blocks with no internal
deformation (see No.3 in this list). In other cases, beds are deformed plastically
and pass laterally into retextured sediments. The interstices between blocks and
slump folds are filled with slump rubble (Bernoulli and Jenkyns, 1970, p.512).
13. Current ripple mark or small scale cross-lamination
A common synonym for transverse asymmetrical ripple mark (Pettijohn and
Potter, 1964, p.297). Ripple mark formed with ridges transverse to current. Peri-
odic undulations of primary origin at the interface between water and granular
material on the sea floor cause such ripples. They are usually on a small scale and
are basically current-formed, below wave base (Shrock, 1948, p. 99-113; Pettijohn
and Potter, 1964, p.333).
14. Mud mounds on slope
Mounds of skeletal lime wackestone or relatively pure lime mudstone usually
enclosed by beds of dark laminated sandy beds, or shales (Dunham, 1972, p.III-
19,111-20).
15. Planar-bedded lime mudstone with even mm laminae (Plate XII A)
Common within thin beds of lime mudstone and reflected as color banding
caused by concentrations of organic matter, iron, or minor amounts of clay
(Wilson, 1969, p. 7). Where interbedded with CaS0 4 (see below) perhaps bacterial
reduction of the SO 4 augmented by associated lime precipitation will result in
dark fetid lime muds (Friedman, 1972).
16. Evaporites in basins with mm laminites of carbonate
Dark finely and planar laminate sediment, commonly interstratified carbon-
ate and anhydrite or even pure anhydrite resulting from thorough replacement of
the carbonate. May be minutely interstratified with thin graded carbonate beds
(Davies and Ludlam, 1973).

Shelf Margin and Shallow Shelf in front and behind Shelf Margin
(Standard Facies Belts 2,5-7)

17. Massive to medium-bedded strata, irregularly interbedded
Beds of varying thickness from homogenous thick massive strata to thinner
beds (less than 50 cm), commonly with shaly intervals. Common in shelf strata
(McKee and Weir, 1953; Pettijohn and Potter, 1964, p.321).
18. Flat lens-shaped beds with shale partings
Subplanar beds which taper gradually over distances of many tens of meters,
as opposed to regular planar beds. Also typical of shelf deposits.