Michael Kendall

Seismic imaging of a hot upwelling beneath the British Isles

The Iceland plume has had an important influence on vertical motions in the North Atlantic. The convecting mantle in this region contains a large-scale low-velocity seismic anomaly, which correlates with a long-wavelength gravity high and bathymetric feature. This suggests that an arm of plume material has extended, or is extending, from Iceland, in a direction perpendicular to the Mid-Atlantic Ridge. Here we present the results of a detailed teleseismic traveltime study that reveals the high-resolution morphology of this low-velocity anomaly beneath the British Isles. Our images provide insights into the nature of plume-lithosphere interactions. The low-velocity anomaly imaged in this study correlates geographically with a region of high gravity anomalies and high topography that was associated with Paleogene magmatism and phases of epeirogenic uplift during the Cenozoic Era. There is evidence that the distribution of British earthquakes is also related to the low-velocity anomaly. The low-velocity anomaly is interpreted to represent hot material from the original Iceland plume head that became trapped beneath thinned regions of lithosphere ca. 60 Ma.

The stability of the deposit feeding community of a mud flat in the River Tees

Abstract During an eighteen-month study of Seal Sands, a mud-flat in the Estuary of the River Tees, England, the numerical structure of the fauna proved to be highly stable. Comparison with earlier work suggests that this stability has been maintained for some time despite the faunal assemblage in question consisting of large numbers of both tube building and infaunal deposit feeding annelids. Although the salinity in the area is generally close to 33% the numerical dominant was Manayunkia aestuarina , a species usually regarded as being characteristic of brackish water.

Frontiers in Earth Sciences

In this study, we used data recorded by two consecutive passive broadband deployments on the Gulf of Aden northern margin, Dhofar region, Sultanate of Oman. The objective of these deployments is to map the young eastern Gulf of Aden passive continental margin crust and upper mantle structure and rheology. In this study, we use shear-wave splitting analysis to map lateral variations of upper mantle anisotropy beneath the study area. In this study, we found splitting magnitudes to vary between 0.33 and 1.0 s delay times, averaging about 0.6 s for a total of 17 stations from both deployment periods. Results show distinct abrupt lateral anisotropy variation along the study area. Three anisotropy zones are identified: a western zone dominated by NW–SE anisotropy orientations, an eastern zone dominated with NE–SW anisotropy orientations, and central zone with mixed anisotropy orientations similar to the east and west zones. We interpret these shorter wavelength anisotropy zones to possibly represent fossil lithospheric mantle anisotropy. We postulate that the central anisotropy zone may be representing a Proterozoic suture zone that separates two terranes to the east and west of it. The anisotropy zones west and east were being used indicative of different terranes with different upper mantle anisotropy signatures.

Variations in some morphological characteristics of Polydora ciliata (Johnston)

Summary On investigation of a dense population of mud tube building polychaetes tentatively identified as Polydora ciliata it was found that many individuals also showed morphological characteristics more usually associated with other members of the same genus. This prompted the examination of the morphology of P. ciliata from a number of different areas with the aim of assessing the stability of some of the characters used in the taxonomy of its genus. These proved to be highly variable, did not group together consistently and overlapped with some of those of P. limicola (Annenkova) and P. ligni Webster. No clear distinction between P. ciliata and P. limicola could be made on the grounds of the characteristics examined but the overlap between P. ciliata and P. ligni was small.