Carboniferous quartz arenites and ganisters of the Northern Pennines
The Carboniferous succession of the Northern Pennines
contains a wide variety of texturally and mineralogically
mature quartz arenites. These occur interbedded with less
mature sandstones, shales and limestones and are common in
strata. of Brigantian to Westphalian A age.
The majority of these quartz arenites appear to have
achieved their mature, stable mineralogy by reworking of
less mature fluvial and deltaic sands in high energy shallowmarine
to shoreline environments. These quartz arenites
are up to approximately 18m. thick, and are particularly
common in Brigantian and Namurian E1 and E2 deposits on the
Alston Block. This suggests that during this period sediment
supply and subsidence on the Alston Block was often sufficiently
low to enable reworking to take place in the shallowmarine
to shoreline environments that commonly existed.
Preserved sedimentary structures and stratification sequences
suggest that the quartz arenites principally formed in barrier
island, beach and storm-dominated shallow-marine environments.
The remaining quartz arenites are generally <1 m. thick,
irregularly based deposits penetrated by rootlets. They are
common in the lowermost Westphalian A strata., and appear to
have formed pedogenically by the breakdown of unstable mineral
grains and downward mechanical eluviation of clays and other
alteration products. These deposits represent the fossilized
A2 -horizon of podzols and podzolic soils. Quartz
arenites formed in this-manner-which--contain >95% quartz
constitute the true ganisters.