Tor Bay Research Articles

Nature and significance of rift-related, near-surface fissure-fill networks in fractured carbonates below regional unconformities

Fissure-fill networks are a widely recognized, but relatively little described, near-surface phenomenon (<1–2 km) hosted in carbonate and crystalline basement rocks below regional unconformities. Faults and fractures in otherwise tight Devonian carbonate basement rocks of the Tor Bay region, Devon, SW England are associated with the development of millimetre- to decametre-wide fissures containing red-coloured early Permian sedimentary material, vuggy calcite mineralization and wall rock collapse breccia. These features preserve evidence about the style and history of fault deformation and reactivation in near-surface settings and on fluid-related processes, such as elutriation and/or mineralization. Field observations, palaeostress analysis and fracture topology analyses show that the rift-related faults and fractures created a network of long-lived open cavities during the development of the Portland–Wight Basin in the early Permian. Once formed, they were subjected to episodic, probably seismically induced, fluid fluxing events and local karstification. The large, well-connected networks of naturally propped fractures were (and possibly still are) important fluid migration pathways within otherwise low-permeability host rocks. These structures are probably equivalent to those observed in many other rift-related, near-surface tectonic settings and suggest that the Tor Bay outcrops can be used as a global analogue for sub-unconformity open fissure systems hosted in low-permeability basement rocks. Supplementary material: Appendix A is available at https://doi.org/10.6084/m9.figshare.c.5023103

Differential recolonization of Atlantic intertidal habitats after disturbance reveals potential bottom-up community regulation.

In the spring of 2014, abundant sea ice that drifted out of the Gulf of St. Lawrence caused extensive disturbance in rocky intertidal habitats on the northern Atlantic coast of mainland Nova Scotia, Canada. To monitor recovery of intertidal communities, we surveyed two wave-exposed locations in the early summer of 2014. Barnacle recruitment and the abundance of predatory dogwhelks were low at one location (Tor Bay Provincial Park) but more than 20 times higher at the other location (Whitehead). Satellite data indicated that the abundance of coastal phytoplankton (the main food source for barnacle larvae) was consistently higher at Whitehead just before the barnacle recruitment season, when barnacle larvae were in the water column. These observations suggest bottom-up forcing of intertidal communities. The underlying mechanisms and their intensity along the NW Atlantic coast could be investigated through studies done at local and regional scales.

Persistence of gametophyte predominance in Chondrus crispus (Rhodophyta, Gigartinaceae) from Nova Scotia after 12 years

Gametophytes predominated clearly over tetrasporophytes in an intertidal population of Chondrus crispus at Tor Bay (Nova Scotia, Canada) in the summer of 1991. Since this species is perennial and the rocky substrate is stable at this site, we predicted that gametophyte predominance would persist after several years. We confirmed this hypothesis by re-sampling the same area in the summer of 2003. This is one of the first long-term studies of the relative abundance of life-history phases done unequivocally at the same site for the Gigartinaceae.

Artificial hybridization between Ascophyllum nodosum and Fucus vesiculosus (Phaeophyceae) from Nova Scotia, Canada

Reciprocal crosses between male and female gametes of Ascophyllum nodosum (L.) LeJolis and Fucus vesiculosus L. were made from plants collected at Tor Bay, Nova Scotia. Crosses within each species were viable and resulted in normal zygote development. Hybrids occurred in low frequency in the cultures (ca. 1–5%) and developed either an initial rhizoid or underwent one or two internal divisions. Hybrid zygotes did not develop further. More developing embryos were observed in crosses when F. vesiculosus provided the eggs, and these zygotes developed longer rhizoids. Maximum development was to three or four cells, which occurred in ca. 10 days. By 5 weeks, all zygotes had disintegrated. Nuclear diameter was the same in both species (6 μm) although almost twice as much nuclear DNA was present in A. nodosum than in F. vesiculosus. Nuclei in hybrids were larger than in the parental species. Key words: Ascophyllum nodosum, Fucus vesiculosus, Fucales, hybridization, Phaeophyta.

Reproductive Ecology of Chondrus crispus (Rhodophyta, Gigartinales) from Nova Scotia, Canada

Spore production and viability were studied in Chondrus crispus based on monthly samples from June to October 1991 at Tor Bay on the Atlantic coast of Nova Scotia. Random collection of fronds showed a gametophyte: tetrasporophyte ratio of about 3: 1. Two reproductive periods were distinguished based on number and diameter of cystocarps and number of tetrasporic sori g −1 frond weight, with reproductive fronds in June and July having larger and fewer cystocarps, and fewer tetrasporic sori g −1 than fronds collected from August to October. The pattern of daily spore release was variable among months. Spore viability varied between monthly means of 4-16% for carpospores and 6-26% for tetraspores, with maximum viability in June and August for carpospores and tetraspores, respectively

The raised beaches and shore platforms of Tor Bay: A re-evaluation

This paper describes a re-examination of the Quaternary stratigraphy and palaeoenvironments represented by the well known raised beaches and shore platforms of Tor Bay. A complex history of head formation and sea level change is identified. Major problems of correlation and dating within Tor Bay and with sites farther afield in southwest Britain still remain.

The Decline of the Gastropod Nucella Lapillus Around South-West England: Evidence for the Effect of Tributyltin from Antifouling Paints

A survey of the gastropod Nucella lapillus around the south-west peninsula of England has revealed that the incidence of ‘imposex’, the induction of male sex characters in the female, is widespread, that all populations are affected to some degree and that the phenomenon is most prevalent along the south (Channel) coast. Populations close to centres of boating and shipping activity show the highest degrees of imposex, especially those within the vicinities of the Helford, Fal, Salcombe and Dart estuaries and in Plymouth Sound and Tor Bay. Within Plymouth Sound the degree of imposex increased markedly between 1969 and 1985, coinciding with the introduction and increasing usage of antifouling paints containing tributyltin (TBT) compounds.

The stratigraphy and structure of the Devonian rocks around Liskeard, east Cornwall, with regional implications

A formal stratigraphy based on new macrofaunal evidence is proposed for a little-known area of slates, thin limestones, and volcaniclastic rocks of Lower Devonian to early Upper Devonian age around Liskeard, between South Devon and north Cornwall. Open shallow marine shelf conditions persisted from the Emsian until the onset of basinal sedimentation in the Frasnian, with the local development of pillow lavas and pillow fragment breccias during Eifelian and Givetian times. Regional stratigraphic correlations identify a Middle Devonian axial ridge which runs from Tor Bay to Bodmin, and separates a redefined Trevone (north Cornwall) Basin from the south Cornish Basin. A moderate to steeply dipping slaty cleavage (Dl) dips southward throughout the area and is associated with early E–W major folds, inferred to be north- or upward-facing, which plunge gently east. A penetrative, closely spaced crenulation cleavage (D2) is developed in a zone, >0.7 km thick, which trends E–W and dips at 15º to 30º south. This fabric, previously misidentified as the D1 slaty cleavage, is associated with major D2 folds which have near horizontal, east–west trending axes; structures of this age and geometry have not been reported from elsewhere in the region. The Portwrinkle Fault has been traced NW–SE across the area and passes west of Liskeard; it shows a large dextral strike-slip displacement and may have developed early in the history of the thrust belt.

Facies variations in the Devonian limestones of eastern South Devon

SummaryThe Middle and Upper Devonian limestone successions at Torquay and in the Lemon Valley SW of Newton Abbot are described. Lithostratigraphic units are proposed for the Torquay succession. The compositions of the coral faunas in both successions are outlined and contribute, together with the other available faunal evidence, towards a broad internal dating of these limestone sequences. Successions elsewhere in the limestones of eastern South Devon are briefly outlined. On the basis of this evidence facies variations from the margin towards the centre of the carbonate platform in eastern South Devon are demonstrated and interpreted as reflecting the development of barrier reefs along parts at least of the platform margin in Givetian times. The character of the reef-complex, named the Tor Bay Reef-Complex, is briefly compared with Devonian reefs elsewhere.

Natural distribution of trace metals in sediments from a coastal environment, Tor Bay, England

The distribution of cadmium, chromium, cobalt, copper, lead, manganese, mercury, nickel and zinc, in the sediments of Tor Bay, a coastal area relatively free of industrial pollution, has been investigated. The aim of this study was to provide base line information which could be used for comparison with similar areas receiving industrial wastes.

On the New Red Sandstone Neptunian dykes of the Tor Bay area (Devonshire)

Beyond the main outcrop of the New Red Sandstone there occur in the Middle Devonian Limestone of the Tor Bay area certain dykes and pockets of New Red Sandstone material. While these generally represent the infilling of small caves which were caused by solution, genuine sandstone dykes appear in the more or less flat-lying limestone sheet around Brixham. They are of great depth and are persistent. Lithological differences indicate certainly two, and possibly three, generations of sandstone dykes. The genesis of the clastic dykes is referable to tectonic stretching.

V.—On the Geology of Tor and Babbacombe Bays, Devon.

The district to be noticed in this communication enables us to trace the disturbance of the Exeter red conglomerate, carboniferous limestone, and old red sandstone of the coasts of Tor and Babbacombe Bays, to the intrusion of trap rocks, subsequent to the formation of the Exeter red conglomerate. The following is a general sketch of the coast. There is no beach to the cliffs from near the Ness-point, at the mouth of the Teign, to Hope’s Nose, the northern point of Tor Bay, with the exception of the bottom of a few coves, and the Babbacombe-sands, and their continuation the Oddicombe-sands, both misnomers, for they are shingle beaches. The cliffs plunge directly into the sea, and are well seen only from a boat. The coast is equally bold from Hope’s Nose to Torquay, with the exception of Meadfoot-sands, which are, however, backed by a high broken hill. After passing the hill between Torquay and Tor Abbey, the coast assumes a milder character: the cliffs, where they occur, are of no great elevation; and there are extensive sands both at Paington and Goodrington, separated by Roundham Head. Further south, low cliffs intervene between Goodrington-sands and the Broad-sands. Beyond the low rocky land of Galmpton Point, the cliffs are bolder, and continue so to the Berry Head, being, in a few places, broken into coves, the most considerable of which is occupied by the harbour of Brixham. This range of coast is backed by hills, varying in height from 200 to 500