The Blackbrook Reservoir Formation is an Ediacaran aged geologic formation in Leicestershire, and lies within the wider Blackbrook Reservoir area. It is primarily composed of tuffs, siltstone, and sandstone.
Geology The formation is roughly in thickness, which can be broken up into three distinct layers, although there are no members. At its base it is predominately composed of up to of tuffeceous pelites, dust tuff, and coarse-grained tuff. The middle layers of the formation only reaches up to , being composed primarily of weathered coarse-grained tuffs, with tuffeceous pelites. Throughout the top of the formation, the previous tuffeceous pelites, dust tuff, and coarse-grained tuffs from the lower layers return, making up the rest of the .
At its type section in Blackbrook Quarry, which is roughly thick, the formation is primarily composed instead of pale-gray to greenish-gray, finely laminated volcaniclastic mudstone and siltstones, which are intercalated with beds of fine-grained sandstone. At the contact point over the South Quarry Slump Breccia Member of the underlying Ives Head Formation, the composition of the rocks change to beds of laminated to massive volcaniclastic siltstone and sandstone, ranging between in thickness.
In the reference section in Newhurst Quarry, the formation is composed primarily of parallel laminated, massive, or normally graded volcaniclastic mudstone and siltstone. There can also be found, though more rarely, massive to normally graded beds of volcaniclastic sandstone, with individual sandstone beds graded down into massive matrix-supported breccia.
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