SW UK Research Articles

Flame out! End-Triassic mass extinction polycyclic aromatic hydrocarbons reflect more than just fire

Global warming induced-wildfires of the 21st century reveal the catastrophic effects that widespread biomass burning has on flora and fauna. During mass extinction events, similar wildfire episodes are considered to play an important role in driving perturbations in terrestrial ecosystems. To better evaluate the record of biomass burning and potential carbon cycle feedbacks at the end-Triassic mass extinction (∼202 Ma; ETE), we investigated the relative abundances of a range of polycyclic aromatic hydrocarbons (PAHs) and the δ13C values of regular isoprenoids and n-alkanes at key sections in the SW UK. These data reveal little evidence for intensive wildfire activity during the extinction event, in contrast to what has been reported elsewhere in European, Chinese, and Greenland ETE sections. Herein, PAHs instead reflect greater contributions from an episode of soil erosion that we attribute to Large Igneous Province (LIP)-driven acid rain, and possible distal sources of smoke, suggestive of fire elsewhere in the UK/European basins. This terrestrial ecosystem perturbation is coincident with those in the marine realm, indicating ecosystem perturbations occurred across multiple habitats throughout the latest Rhaetian in the SW UK. Additionally, this geochemical approach reveals that the precursor carbon isotope excursion (CIE) routinely used in chemostratigraphic correlations is unrelated to LIP activity, but instead results from the increased input of terrestrially derived 13C-depleted plant material. Furthermore, we find the initial CIE (commonly used to mark the extinction level, but which is now known to precede the ETE) is also unrelated to biomass burning. Collectively, these data reveal that processes other than combustion of terrestrial material are important for the terrestrial phase of the ETE in the SW UK. Similar investigations are required on other ETE sections, both those in close proximity to the LIP driving the extinction and those further afield, to more clearly determine the negative effect(s) of LIPs and their geographic extent in the terrestrial realm.

Anatomy of a Late Triassic Bristol fissure: Tytherington fissure 2

The Late Triassic and Early Jurassic fissures around Bristol and South Wales are famous as sources of excellent fossils of early mammals, dinosaurs, sphenodontians, and other tetrapods. However, the ways in which these fissures filled with sediment have not often been documented. Moreover, systematic faunal sampling up a working face exposure has rarely been attempted for the UK Triassic fissures. Here we show in detail how a complex fissure in Tytherington Quarry, north-east of Bristol, filled in multiple steps, and document both sedimentary facies and faunas. Tytherington Quarry is a key Late Triassic Bristol sauropsid fissure site, having previously yielded abundant Thecodontosaurus remains and a new genus of sphenodontian, Diphydontosaurus. Our findings comprise specimens of terrestrial reptiles, including sphenodontians and archosaurs. However, abundant remains of fishes and marine invertebrates were also recovered, indicating a significant marine influence during parts of the fissure-filling process. Comparisons of our results with those of previous studies on Tytherington and other Late Triassic SW UK fissure sites indicate some consistent patterns of faunal association and provide further evidence of a Rhaetian age for the Late Triassic palaeo-island fissures north of Bristol. Our analysis supports a model of fissure formation and filling entailing punctuated episodes of sedimentation through a relatively short time.

A microbial carbonate response in synchrony with the end-Triassic mass extinction across the SW UK.

The eruption of the Central Atlantic Magmatic Province (CAMP)—the largest igneous province known—has been linked to the end-Triassic mass extinction event, however reconciling the response of the biosphere (at local and nonlocal scales) to potential CAMP-induced geochemical excursions has remained challenging. Here we present a combined sedimentary and biological response to an ecosystem collapse in Triassic-Jurassic strata of the southwest United Kingdom (SW UK) expressed as widely distributed carbonate microbialites and associated biogeochemical facies. The microbialites (1) occur at the same stratigraphic level as the mass extinction extinction, (2) host a negative isotope excursion in δ13Corg found in other successions around the world, and (3) co-occur with an acme of prasinophyte algae ‘disaster taxa’ also dominant in Triassic-Jurassic boundary strata of other European sections. Although the duration of microbialite deposition is uncertain, it is likely that they formed rapidly (perhaps fewer than ten thousand years), thus providing a high-resolution glimpse into the initial carbon isotopic perturbation coincident with the end-Triassic mass extinction. These findings indicate microbialites from the SW UK capture a nonlocal biosedimentary response to the cascading effects of massive volcanism and add to the current understanding of paleoecology in the aftermath of the end-Triassic extinction.

Broad scale agreement between intertidal habitats and adaptive traits on a basis of contrasting population genetic structure

Understanding the extent to which neutral processes and adaptive divergence shape the spatial structure of natural populations is a major goal in evolutionary biology and is especially important for the identification of significant levels of biodiversity. Our results identified replicated habitat-specific (adaptive) phenotypic divergence in the brown macroalga Fucus vesiculosus that is independent of population (neutral) genetic structure. F. vesiculosus inhabits contiguous and contrasting marine to estuarine intertidal habitats. Combining analyses of genetic and phenotypic traits of populations living under differential selective regimes (estuaries and open coast), we investigated levels of neutral genetic differentiation and adaptive physiological responses to emersion stress. In southwest England (SW UK) and northern Iberia (N. Iberia), populations living in estuaries and marine coastal habitats were genetically characterized at six microsatellite loci. In N. Iberia, two clades with limited admixture were recovered, each including one open coast site and the adjacent estuarine location. In contrast, SW UK samples clustered according to habitat and formed three distinct groups of genotypes; one including the two open coast locations and the other two representing each of the estuarine sites. Temperature loggers revealed distinct emersion regimes that characterized each habitat type independently of the region, while water and air temperature profiles showed site-specific trends. Despite acclimation under usual conditions, trait means of emersion stress resilience showed a strong phenotypic divergence between habitats, consistent with environmental clines in exposure time observed in the different habitats. We demonstrate that neutral genetic clusters do not reflect locally adapted population units. Our results identified replicated habitat-specific (adaptive) phenotypic divergence that is independent of population (neutral) genetic structure in F. vesiculosus. The significance of such findings extends beyond the theoretical evolutionary and ecological interest of discovering parallel adaptive responses to the broader implications for conservation of intraspecific biodiversity.

Large-scale, linked drainage systems in the NW European Triassic: insights from the Pb isotopic composition of detrital K-feldspar

Pb isotopic data from K-feldspars in Middle Triassic (Anisian) sandstones in the Wessex Basin, onshore SW UK, and the East Irish Sea Basin, some 350 km to the north, show that the same grain populations are present. This indicates that the drainage system (the ‘Budleighensis’ river) feeding these basins originated from the same source/s, most probably the remnant Variscan uplands to the south. Fluvial and aeolian sandstones have the same provenance, suggesting that if water- and wind-driven sands were originally derived from different sources, this has been obscured through reworking prior to final deposition. Significant recycling of feldspar from arkosic sandstones in earlier sedimentary basins can be ruled out. The provenance data agree with previous depositional models, indicating transport distances in excess of 400 km, with a drainage pattern that linked separate basins. This supports the idea that the regional fluvial system was driven by topography and episodic flooding events of sufficient magnitude to overcome evaporation and infiltration over hundreds of kilometres. Importantly, this drainage system appears to have been isolated and independent from those operating contemporaneously to the NW of the Irish and Scottish massifs, where the remnant Variscan uplands apparently exerted no influence on drainage or sand supply.

Particulate Thiol Peptides Along a Salinity Gradient of a Metal-Contaminated Estuary

The thiol peptide phytochelatins (PC2; the polymer with n = 2) are efficient metal-chelating compounds produced by phytoplankton and higher plants. Both PC2 and their precursor glutathione (GSH) are related to detoxification mechanisms. GSH and PC2 were quantified using liquid chromatography with fluorescent detection and observed in the particulate phase along a salinity gradient of the Tamar Estuary (SW UK), a heavily metal impacted site, at concentrations up to 274 and 16.5 μmol (g chl a) -1, respectively. The peptides predominated within low (0-5) and mid-salinities (5-20). Down-estuary, at sites farther from metal sources and salinities higher than 20, PC2 showed a sharp decrease or were not detected. High PC2/GSH ratios indicated areas with augmented concentrations of bioavailable metals at the tidal limit, near Cu mines and the mid-estuary where resuspension of sediments occurs. By following typical partitioning patterns previously reported for dissolved Cu and Zn, the production of thiol peptides, notably PC2, reflected a rapid interaction between the particulate and dissolved phases. © 2011 Coastal and Estuarine Research Federation.

Reproductive patterns in central and marginal populations of a large brown seaweed: drastic changes at the southern range limit

Understanding the factors determining geographic ranges and range shifts of species is a central issue in ecology and evolutionary biology. Research addressing distributional borders from a demographic perspective frequently focused on reproductive traits, finding reproduction reductions or failure at the range margin. However, some of the observed changes in marginal locations could be the result of adaptive adjustments to local, unfavourable conditions, though they have been rarely interpreted from this point of view. In this study we investigated the reproductive patterns of the seaweed Fucus serratus in central and southern marginal locations (SW UK, N Spain) over a 3-yr period. Our main goals were: 1) to determine the spatial (centre-margin) and temporal variation in reproductive traits and 2) to test if this variation fits with life-history predictions for stressful environments. Threshold size for reproduction declined at the range margin, in accordance with life-history predictions. Nevertheless, we also observed parallel drastic reductions in the percentage of reproductives, reproductive allocation and plant size. The reproductive capacity of marginal locations was thus dramatically reduced in relation to central ones. Furthermore, the decline became more pronounced over the study period. Our results suggests that the viability of marginal populations is at risk. This situation clearly differs from the pattern observed during the last decade. At that time, the species was able to growth and reproduce beyond its distributional boundary at similar rates than inside its range in N Spain. The seaweed was then expanding its distribution and the position of the boundary was set by dispersal limitations. At present, the southern boundary of this species seems to be directly influenced by very unfavourable abiotic conditions, which may be linked to the present scenario of climatic change or to environmental fluctuations acting at shorter-time scales.

Discussion on palaeoecology of the Late Triassic extinction event in the SW UK Journal , Vol. 165, 2008, pp. 319–332

Jonathan Radley writes: The Penarth Group (of Late Triassic and possibly ranging to Early Jurassic age) of the southern UK marks a marine transgression and the establishment of a shallow epicontinental seaway (Hallam & El Shaarawy 1982; Warrington & Ivimey-Cook 1992), influenced by regressive–transgressive pulses and characterized by rapid facies changes (Hallam & Wignall 2004; Hesselbo et al . 2004). A well-documented invertebrate macrofauna includes corals, brachiopods, molluscs and echinoderms (Swift & Martill 1999). Facies developments range from storm-influenced, shallow-marine mudrocks (Westbury Formation) upwards into calcareous mudstones, siltstones and essentially fine-grained carbonates (Lilstock Formation) demonstrating extremely shallow-water conditions: wave ripples, storm beds, desiccation and omission surfaces (Swift 1999 a ; Wignall 2001; Hallam & Wignall 2004). The low-diversity macrofauna of the Lilstock Formation has frequently been attributed to salinities deviating from that of normal seawater within shallow-water, partly landlocked settings, isolated from the open sea (Hallam & El Shaarawy 1982; Swift 1995; Allison & Wright 2005). However, widespread occurrences of stenohaline marine macrofossils such as corals and echinoderms (Swift & Martill 1999) suggest that salinity fluctuations were at most slight (Wignall 2001). Mander et al . (2008) have presented high-resolution benthic macrofaunal data, principally from molluscan macrofossils, for significant palaeoecological change within the Penarth Group of two key sections in the SW UK. Their detailed results demonstrate loss of taxonomic richness within the uppermost Westbury Formation–lower Lilstock Formation (Cotham Member) interval (latest Rhaetian), followed by a poorly fossiliferous interval represented by the latest Rhaetian or early Hettangian upper Lilstock Formation (upper Cotham Member–lower Langport Member). They attributed this pattern to an extinction event followed by a post-extinction ‘Dead Zone’; the latter coinciding with the onset of a negative organic carbon-isotope excursion, and an extinction event recorded in the terrestrial palynoflora. The relatively diverse shelly …

Palaeoecology of the Late Triassic extinction event in the SW UK

A high-resolution palaeoecological study of the shelly invertebrate macrofauna across two marine Triassic–Jurassic boundary sections in the UK (St. Audrie's Bay and Lavernock Point) is presented. Loss of taxonomic richness occurs in the upper Westbury Formation to lower Lilstock Formation (late Rhaetian), but if sample size is taken into account there is little convincing evidence of a catastrophic marine extinction. There is, however, good evidence for significant palaeoecological change in the benthic marine ecosystem at this time. The immediate post-event recovery interval in the upper Lilstock Formation is characterized by assemblages of low abundance, low diversity, high dominance and low evenness. Body-sizes of taxa that survived the event and originated afterwards were low until the later Hettangian. Recovery to higher abundance, higher diversity and higher evenness is recorded in the Psiloceras planorbis Zone. Recovery of the benthic ecosystem in the aftermath of the Late Triassic event was disrupted by marine anoxia and shows additional similarities to the (much slower) recovery that followed the Late Permian event. The pattern of body-size changes recorded in the shelly fossil record closely matches that of the trace fossil record. Shell thickness trends do not support a biocalcification crisis during the Late Triassic biotic event.

Bounding surfaces in a mixed aeolian–fluvial system (Rotliegend, Wessex Basin, SW UK)

The Dawlish Sandstone Formation is a Late Permian succession of mixed aeolian and fluvial deposits in the Wessex Basin (SW England). It is used to illustrate two contrasting types of fluvial/aeolian bounding surface (planar and incised). Planar bounding surfaces separate tabular bodies of fluvial conglomerate and aeolian dune sandstone. They were produced primarily by wind scour to groundwater table, with the later emplacement of conglomerates resulting in local fluvial erosion of cemented aeolian dune sandstones. Incised bounding surfaces were produced by fluvial downcutting. The erosive relief was infilled with mixed aeolian/fluvial deposits. The Dawlish Sandstone Formation may provide the first outcrop example of these incised valley fills, which have recently been identified as a major component of the subsurface Rotliegend in the Southern North Sea Basin. The potential variability of aeolian/fluvial sedimentary architecture has important implications for well-to-well correlation and reservoir modelling.

Long-period Milankovitch cycles from the Late Triassic and Early Jurassic of eastern North America and their implications for the calibration of the Early Mesozoic time–scale and the long–term behaviour of the planets

During the Late Triassic and Early Jurassic the Newark rift basin of the northeastern US accumulated in excess 5 km of continental, mostly lacustrine strata that show a profound cyclicity previousl...

Variscan structure and its influence on post-Carboniferous basin development, Western Approaches Basin, SW UK Continental Shelf

Reflection seismic records from the Western Approaches Basin (SW UK Continental Shelf) reveal SSE-dipping reflection packages within the Variscan basement. These have been mapped and are believed to originate from Variscan thrusts. Orthogonal transfer faults are apparent as NNW-trending zones of discontinuity. Structural trends in the Permian-Mesozoic Western Approaches Basin parallel those of the underlying basement. An end-Variscan structural high in the northern part of the basin was progressively onlapped from the south during Permian times. This high may have been formed by thrust-driven tectonic thickening of the crust. During Late Jurassic-Early Cretaceous times Variscan thrusts were reactivated in the western part of the basin (Melville Basin) to form a half-graben. However, in the east (St Mary's Basin), the basin is more symmetrical, and Mesozoic reactivation of Variscan thrusts cannot be unequivocally demonstrated.

Chalk porosity and Tertiary uplift, Western Approaches Trough, SW UK and NW French continental shelves

Porosities have been derived from sonic logs for the Cenomanian–Maastrichtian Chalk of 22 hydrocarbon exploration wells in the Western Approaches Trough. Although the burial depth of the Chalk studied ranges from 40–1500 m below sea-bed, porosities are all within the range 0–45%. The most deeply buried Chalk sequences exhibit close to normal porosity/depth relations for offshore chalks. Abnormally low porosities in the remainder of the wells result from burial at greater depth than that presently observed. Low porosities were preserved during Tertiary, Alpine-related uplift of the area. For a given well the magnitude of uplift not reversed by subsequent subsidence (apparent uplift) equals the displacement of its porosity/depth relation from the normal relation along the depth axis. Apparent uplift in the Western Approaches Trough ranges from 0–1.3 km. In the Western Approaches Trough, Chalk porosity data provide evidence of more widespread Tertiary uplift than do seismic reflection records. Alpine-related compression and uplift (fault-bounded basin inversion) is apparent only on seismic records in the southern part of the Trough (Brittany and South-West Channel Basins), whereas Chalk porosity data suggest regional uplift occurred throughout the Trough and adjacent highs. Chalk porosity data were also used to quantify Tertiary uplift in the Cleethorpes-l well of the East Midlands shelf. The resultant value of 1.1km is considerably greater than that previously derived from shale sonic velocities (approximately 0.3 km) and slightly less than that based on apatite fission track analysis (1.3–1.7 km).

Species distribution in marine phytoplankton : Braarud T., 1962. J. Oceanogr. Soc., Jap., 20th Ann. Vol.: 628–649

Understanding the extent to which neutral processes and adaptive divergence shape the spatial structure of natural populations is a major goal in evolutionary biology and is especially important for the identification of significant levels of biodiversity. Our results identified replicated habitat-specific (adaptive) phenotypic divergence in the brown macroalga Fucus vesiculosus that is independent of population (neutral) genetic structure. F. vesiculosus inhabits contiguous and contrasting marine to estuarine intertidal habitats. Combining analyses of genetic and phenotypic traits of populations living under differential selective regimes (estuaries and open coast), we investigated levels of neutral genetic differentiation and adaptive physiological responses to emersion stress. In southwest England (SW UK) and northern Iberia (N. Iberia), populations living in estuaries and marine coastal habitats were genetically characterized at six microsatellite loci. In N. Iberia, two clades with limited admixture were recovered, each including one open coast site and the adjacent estuarine location. In contrast, SW UK samples clustered according to habitat and formed three distinct groups of genotypes; one including the two open coast locations and the other two representing each of the estuarine sites. Temperature loggers revealed distinct emersion regimes that characterized each habitat type independently of the region, while water and air temperature profiles showed site-specific trends. Despite acclimation under usual conditions, trait means of emersion stress resilience showed a strong phenotypic divergence between habitats, consistent with environmental clines in exposure time observed in the different habitats. We demonstrate that neutral genetic clusters do not reflect locally adapted population units. Our results identified replicated habitat-specific (adaptive) phenotypic divergence that is independent of population (neutral) genetic structure in F. vesiculosus. The significance of such findings extends beyond the theoretical evolutionary and ecological interest of discovering parallel adaptive responses to the broader implications for conservation of intraspecific biodiversity.