Page 168 - Carbonate Facies in Geologic History

Major Facies and Paleotectonic Patterns in Europe 155

miles 3
, ! ,
'km' 5
N
Massif facies
t

N.C.F. North Craven fault M.C.F. MiddleCraven fault
1 ... 1 Reef limestone forming knolls D Lower Carboniferous
1"-.::';::) Yoreda(e Series, Namurian ~ Pre-Carboniferous
and later rocks
Fig. V -8. Craven fault belt of Waulsortian lime mudstone mounds, West Riding of Yorkshire.
Mounds occur on downthrown side of Middle Craven fault. From Parkinson (1957, Fig. 11),
with permission of American Association of Petroleum Geologists

Some mounds are between 100 and 150 m high above the old sea floors and as
much as several km in diameter (Figs. V -8 and V -9). They are surrounded by dark,
fine-grained, terrigenous deposits. Submarine relief is indicated by the steep sides
of the sheet-like masses and the mounds which are from 30 to 50 degrees. Some
flanking beds of crinoidal grainstones occur, but are not common. Slump and
slide masses, breccias, and conglomerates derived syndepositionally from the
mounds, are also present but relatively rare compared to other types of mounds
and reefs known in the geological record. Evidence of local fault control on
mound deposition exists in the North Pennine block in England which is
bounded on the south by the Craven fault zones along which Waulsortian
mounds occur (Fig. V -8). The faults are of Early Carboniferous age but have been
rejuvenated by Tertiary movement and fine exposures occur along them (Fig. V-
10). Shelf deposits over the block consist of the Great Scar limestone and cyclic
Yoredale beds, the micritic Waulsortian mounds occurring only on the down-
thrown side of the fault zone. These are surrounded by thin and irregularly
bedded black, cherty, limestone with some beds of bioclastic material, including
encrinites. Black shale interbeds may be very fossiliferous. The mounds thus
accumulated bathymetrically below the shelf on the down thrown sides of growth
faults and in a deeper water environment forming a Type I shelf margin profile
(Chapter XII and Wilson, 1974). Figures V-8 and V-9 show two adjacent areas in
the English Midlands. The original mound topography along the Craven faults is
believed by Hudson to have been modified by pre-Namurian (Pennsylvanian)
erosIOn.