The excursion will take in areas (Figure 1) that exemplify the contrasting
scenery of Charnwood Forest, with its craggy knolls separated by featureless
tracts or smooth-sided valleys. This landscape is controlled by geology, and is
caused by the influence of erosion on rocks with very different physical
properties. The Precambrian rocks, which are the subject of this excursion, are
extremely resistant to erosion. They represent the tips of an ancient, rugged hill
range that is only now beginning to protrude through a covering of younger and
much softer Triassic strata, the latter in turn blanketed by Quaternary deposits.
Past workers have viewed Charnwood Forest’s topography as being a ‘fossil’ or
an ‘exhumed’ landscape, because a mountainous topography on the
Precambrian rocks was already in existence before being buried by younger
strata in Triassic times, about 240 million years ago. This ancient landscape is
dramatically revealed in the walls of Bardon Hill Quarry, which will be viewed
from the summit of the hill. It is only now emerging because the covering of
Triassic strata (and also Quaternary deposits) is being preferentially removed
by modern-day erosion (see inset to Figure 2).
Abstract High‐ P granulites contained in two allochthonous tectonic units were thrust southwards onto the northern margin of the Zimbabwe craton during the Pan‐African Zambezi orogeny. In the lower sheet, the Masoso Metamorphic Suite contains mafic garnet granulite assemblages formed during a high‐ P‐T metamorphic event, although the suite as a whole is predominantly granitic. The garnet granulites occur as relicts within narrow mafic layers characterized by migmatitic and mylonitic fabrics. The annealed mylonites represent surfaces of deep‐crustal tectonic imbrication that formed immediately before the Pan‐African orogeny. Gabbros which intruded the granulites after the main phase of migmatization have formed corona textures that document a low‐ P‐T metamorphic event at mid‐crustal levels. The style of deformation then changed and the Masoso Suite with its mylonitic layers was folded and thrusted southwards onto the Archaean Zimbabwe craton.
Abstract The Avalon Assemblage (Ediacaran, late Neoproterozoic) provides some of the oldest evidence of diverse macroscopic life and underpins current understanding of the early evolution of epibenthic communities. However, its overall diversity and provincial variability are poorly constrained and are based largely on biotas preserved in Newfoundland, Canada. We report coeval high-diversity biotas from Charnwood Forest, UK, which share at least 60% of their genera in common with ones in Newfoundland. This indicates that substantial taxonomic exchange took place between different regions of Avalonia, probably facilitated by ocean currents, and suggests that a diverse deepwater biota may already have been widespread at the time. Contrasts in the relative abundance of prostrate versus erect taxa likely record differential sensitivity to physical environmental parameters (hydrodynamic regime, substrate) and highlight their significance in controlling community structure.
The landscapes and drainage systems of southern Britain are widely considered to have developed during the Cenozoic Period, following the destruction of the shelf sea in which Jurassic and, ultimately, Cretaceous strata were deposited (see review in Gibbard & Lewin, 2003). When this region is studied in greater detail, however, it can be argued that its modern physiography is the culmination of a more fundamental geological inheritance, over hundreds of millions of years. The trunk streams of the Trent catchment system (Fig. 1) demonstrate this, in that they are spatially related to outcrops of Triassic strata (Fig. 2). What are not so obvious are the tectonic factors that have exerted an underlying control over drainage and landscape development. This article briefly assesses the structural framework of the Trent Basin, emphasizing the role that plate tectonics has played in controlling geological and geomorphological evolution through time.
Discrete, funnel-shaped structures consisting of downwarped and disrupted strata are described from a restricted stratigraphical interval in the Late Neoproterozoic Charnian Supergroup, just above the base of the Bradgate Formation at exposures in Bradgate Park, in Charnwood Forest, Leicestershire. The structures occur within a deep-water marine turbidite succession and have attracted much attention, with a variety of explanations advanced to account for their origin including volcanic bomb-impacts and burrowing organisms. This article describes these structures, interprets their mode of origin, and concludes that they compare with features known as 'thixotropic wedges'. The latter have been described from various other parts of the world and are commonly placed within a category of soft-sediment deformation phenomenon known as 'seismites'. Such an association may have important implications for the style of turbidite sedimentation in the Charnian Supergroup as a whole. In south-eastern Charnwood Forest, Bradgate Park exposes the younger formations of the Charnian Supergroup (Moseley and Ford, 1985), which is of latest Neoproterozoic (Ediacaran) age (Fig. 1). With respect to conditions of sedimentation and palaeoenvironments, one particularly interesting part of this sequence occurs within the Maplewell Group at the transition from the Beacon Hill Formation into the overlying Bradgate Formation. The latter's base is delineated by a horizon of disturbed bedding that includes the Sliding Stone Slump Breccia Member, the type locality (SK 5304 1133) for which was designated by Moseley and Ford (1985) as the partially wooded crags immediately west of the Sliding Stone enclosure (Fig. 1). Narrow zones of strongly downwarped bedding and lamination occur in strata capping the Sliding Stone Breccia at its type locality. These structures have been a source of debate among visitors to the park for many years, but they are comparable with an unusual type of soft-sediment deformation phenomenon that has been described from a variety of sedimentary environments in other parts of the world.
Lower to Middle Miocene sediments on Maewo contain clasts derived from the 'Vitiaz arc', a former tholeiitic volcanic belt similar in age, lithology and geochemistry to Upper Eocene-Middle Miocene rocks on Viti-Levu, Fiji. The configuration of Outer Melanesia from the New Hebrides through Fiji to Tonga-Lau in the Early to Middle Miocene was a double arc compising a frontal arc (Vitiaz arc — Viti Levu — Tonga Ridge) and a rear arc (Western Belt-Lau Ridge) couple. Tectonism in the Middle Miocene brought about inter-arc rifting between the Vitiaz arc-Western Belt couple and the anti-clockwise rotation of Viti Levu into a rear arc position; further fragmentation and the development of marginal basins had also affected the Tonga-Lau couple by the Early Pliocene. Mio-Pliocene lavas of the New Hebrides Eastern Belt were erupted in the Vitiaz arc-Western Belt inter-arc basin in response to further rifting and crustal thinning associated with the developing proto-North Fiji Basin. Expansion of this basin was accompanied by subduction reversal from the eastern to western margins of the New Hebrides Ridge which then migrated south-westwards to its present position. The present configuration of the New Hebrides Ridge is atypical of that usually attributed to SW Pacific arc systems.
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