The stratigraphy and composition of the Latterbarrow and Redmain sandstones, Lake District, England

Abstract

The Latterbarrow Formation, 400 m thick, has been mapped and subdivided informally into three members. These consist of quartz wacke sandstone and, in the upper member only, intercalated mudstones. The formation unconformably overlies the fossiliferous Skiddaw Group of late Tremadoc to middle Arenig age and is overlain disconformably by volcanic rocks that have been attributed to the Borrowdale Volcanic Group. Chemically, the sandstones are characterized by very low concentrations of CaO, Na2O, and K2O and unusually high total iron. MnO and MgO, such that iron, as Fe2O3, exceeds Al2O3. Mudstone in the upper member is illite rich, has a high K2O content and is compositionally similar to K‐bentonites derived from volcanic ash. Sedimentary structures and petrography suggest that the sediments were deposited in a sandy estuary and were derived from a similar source area to that of the Skiddaw Group. Throughout the succession there is evidence of distal volcanism, probably representing the earliest eruptions of the Borrowdale volcanic episode. The Redmain Formation, 100 m thick, is unconformably overlain by Carboniferous rocks but its relationship to the underlying Skiddaw Group is unknown. Though this lithic arenite shows some petrographic and geochemical similarities with the Latterbarrow sandstone, differences are such that it is possible they are not equivalent in age. The Redmain sandstone may be derived from the erosion of Skiddaw Group rocks.

The stratigraphy, correlation, provenance and palaeogeography of the Skiddaw Group (Ordovician) in the English Lake District

“…The Latterbarrow Sandstone (Eastwood et al 1931) was included at different stratigraphical positions in the group by all three authors. Allen & Cooper (1986) showed subsequently that the Latterbarrow Formation rests unconformably on the Skiddaw Group, and concluded that it is a basal deposit of the Borrowdale Volcanic Group. The Redmain Sandstone was considered by Eastwood (1927) to be equivalent to the Latterbarrow Sandstone, but was shown by Allen & Cooper (1986) to be a different unit.…”

“…Allen & Cooper (1986) showed subsequently that the Latterbarrow Formation rests unconformably on the Skiddaw Group, and concluded that it is a basal deposit of the Borrowdale Volcanic Group. The Redmain Sandstone was considered by Eastwood (1927) to be equivalent to the Latterbarrow Sandstone, but was shown by Allen & Cooper (1986) to be a different unit. They designated it the Redmain Formation but reached no conclusion about its stratigraphical position in the Skiddaw Group.…”

“…- Figure 10 about hereIn addition to these outcrops in the Buttermere area, slump-folded mudstones, siltstones and sandstones yielding Tremadoc trilobites and acritarchs (Molyneux & Rushton 1985;Rushton 1988) (Allen & Cooper, 1986) are also an olistolith.…”

The early Palaeozoic evolution of northwest England

“…In the Lake District, two dominantly sedimentary sequences occur locally at the base (Fig. 2), the Latterbarrow Formation in the northwest (Allen & Cooper, 1986) and the Whinneybank Tuffite on the south side of Black Combe in the southwest (N. A.…”

Field and biostratigraphic evidence for an unconformity at the base of the Eycott Volcanic Group in the English Lake District

“…Sheffield, 1986). West of the Ennerdale granophyre outcrop the mainly arenaceous Latterbarrow Formation also contains volcanic remains, but is composed mostly of quartzwacke sandstones (Allen & Cooper, 1986). The faunal ages of all these sequences is unknown (Allen & Cooper, 1986;Rushton & Molyneux, 1989), but all appear to be relics of the period between the end of Skiddaw Group deposition and the main period(s) of volcanism.…”