James Lawrence

Shoal choice in zebrafish, Danio rerio: the influence of shoal size and activity

Shoaling fish are expected, in many cases, to gain fitness benefits from being in a larger shoal and previous experiments have shown that fish are indeed capable of choosing between shoals of different sizes. We investigated the influence of shoal activity on shoal size preference in the zebrafish. We gave test fish the choice between shoals of one to four stimulus fish, presented at two different water temperatures, and so differing in their activity levels. Where all stimulus fish were in water of the same temperature, test fish generally preferred the larger shoal. However, this preference could be reduced by presenting the larger shoal in colder water and so reducing its activity. We discuss these findings with reference to the factors that may influence shoal activity, the effect of temperature on shoaling behaviour and the mechanisms that may be used by fish to discriminate shoal size.

Fish shoal composition: mechanisms and constraints

Observations were made on three fish species (banded killifish (Fundulus diaphanus), golden shiner (Notemigonus crysoleucas) and white sucker (Catostomus commersoni)) in a temperate lake (New Brunswick, Canada) in order to investigate the relationship between shoal choice behaviour of individual fishes and shoal composition. Encounters between shoals were observed to take place every 1.1 min per shoal and an encounter lasted 3.7s on average. The duration of shoal encounters was influenced by shoal size but not by differences between shoals in either body length or species. Conversely, the outcome of shoal encounters (i.e. whether or not an individual changes shoal) was influenced by body length and species differences but not by shoal size. Together, these results suggest that encounter duration itself is unlikely to have an important influence on encounter outcome. The collection of ten entire fish shoals showed that they were assorted by species and body length. A simulation model demonstrated that individual shoal choice behaviour alone could account for the generation and maintenance of the observed levels of size assortedness of shoals without invoking the existence of other sorting mechanisms such as differential swimming speeds. However, the generation of species assortedness was not predicted by the model. Furthermore, our data suggest that fish density acts as a constraint on shoal choice, influencing both shoal size and composition. This work has implications for studies on information transfer and reciprocal altruism within populations.

Coastal cliff geohazards in weak rock: the UK Chalk cliffs of Sussex

Abstract Geohazards related to chalk coastal cliffs from Eastbourne to Brighton, Sussex are described. An eight-fold hazard classification is introduced that recognizes the influence of chalk lithology, overlying sediments and weathering processes on location, magnitude and frequency of cliff collapses. Parts of the coast are characterized by cliffs of predominantly a single chalk formation (e.g. Seven Sisters) and other sections are more complex containing several Chalk formations (Beachy Head). Rock properties (intact dry density or porosity) and mass structure vary with each formation and control cliff failure mechanisms and scales of failures. The Holywell Nodular Chalk, New Pit Chalk and Newhaven Chalk formations are characterized by steeply inclined conjugate sets of joints which lead to predominantly plane and wedge failures. However, the dihedral angle of the shears, the fracture roughness and fill is different in each of these formations leading to different rock mass shear strengths. In contrast the Seaford and Culver Chalk formations are characterized by low-density chalks with predominantly clean, vertical joint sets, more closely spaced than in the other formations. Cliff failure types range from simple joint controlled conventional plane and wedge failures to complex cliff collapses and major rock falls (partial flow-slides) involving material failure as well as interaction with discontinuities. Other hazards, related to sediments capping the Chalk cliffs, include mud-slides and sandstone collapses at Newhaven, and progressive failure of Quaternary Head and other valley-fill deposits. Weathering, including the concentration of groundwater flow down dissolution pipes and primary discontinuities, is a major factor on rate and location of cliff collapses. A particular feature of the Chalk cliffs is the influence of folding on cliff stability, especially at Beachy Head, Seaford Head and Newhaven. A new classification for cliff collapses and a new scale of magnitude for collapses are introduced and used to identify, semi-quantify and map the different hazards. Climate (and climate change) and marine erosion affect the rate of development of cliff collapse and cliff-line retreat. This was particularly evident during the wet winters of 1999–2000–2001 when the first major collapses along protected sections of coastline occurred (Peacehaven Cliffs protected by an undercliff wall; Black Rock Marina the Chalk cliffs and the Quaternary Head). It is the geology, however, that controls the location and scale of erosion and cliff failure.

Chalk physical properties and cliff instability

Abstract Physical properties such as porosity and intact dry density (IDD) are compared with strength testing in relation to the Chalk formations in the cliffs of the English Channel. Natural moisture contents are close to saturation moisture contents for chalks with intact dry densities above 1.70 Mg/m3. Below this IDD, the natural moisture contents show a much greater range and greater divergence from the saturation line. There is also an indication that certain types of chalk retain water at saturation level while others gain and lose water more readily. Strength tests (Point Load Index, Brazilian Crushing Strength and Uniaxial Compressive Strengths) show up to four times reductions in strength between dry (higher strength) and saturated (lower strength) samples. Absence of a strong correlation between density and strength is interpreted as resulting from either mineralogical differences in the samples and/or textural differences between different chalks. The variation in physical properties and strength in the different chalks forming the cliffs indicates the strong stratigraphical and sedimentological controls on mechanical performance of the material and mass in cliff failures.

Engineering geological characterization of flints

The petrographic and mechanical properties of flints from the Burnham (North Landing, Yorkshire, UK), Seaford (East Sussex, UK, and Dieppe, France), and Lewes Nodular (Mesnil-Val, France) Chalk formations have been investigated. Microtexture and mineral composition of flints are studied to understand how the geological and petrophysical properties of the flint affect drilling responses to the rock and investigate any spatial variation. The flints are categorized based on physical observation into white crust and light brownish grey, dark brownish grey and grey flints. Scanning electron microscopy shows textural variation in the classes. The white crust, light brownish grey, brownish grey and grey flints from the Burnham Chalk Formation from North Landing contain more calcite and have coarser, more poorly cemented silica spherules in comparison with similar classes of flint from the Seaford and Lewes Chalk formations from the Anglo-Paris Basin. In these latter flints, the structure is dominated by massive quartz cement with trace calcite independent of location. Strength tests show that the grey flints from North Landing are weaker than equivalents from the Anglo-Paris Basin. It is suggested that variation in engineering properties between grey and the dark brownish grey flints is caused by mineral composition, microtexture, structure and the local or site geology of flint materials.

Stratigraphic correlation and paleoenvironmental analysis of the hydrocarbon-bearing Early Miocene Euphrates and Jeribe formations in the Zagros folded-thrust belt

The Lower Miocene Euphrates and Jeribe formations are considered as the main targets of the Tertiary petroleum system in the western part of the Zagros Basin. The formations consist of carbonates with some evaporate intercalations of the Dhiban Formation. This study utilized data from a field investigation including newly described outcrop sections and newly discovered productive oil fields within the Kirkuk embayment zone of the Zagros fold and thrust belt such as Sarqala and Kurdamir wells. This work is the first to show a stratigraphic correlation and paleoenvironmental interpretation by investigating both well data and new outcrop data. Three depositional environments were identified, (1) an inner and outer ramp belts environment, (2) shoal environment, and (3) restricted lagoon environment. Within these 3 environments, 12 microfacies were identified, based on the distribution of fauna mainly benthonic foraminifera, rock textures, and sedimentary structures. The inferred shallow water depths and variable salinities in both the Euphrates Formation and Jeribe Formation carbonates are consistent with deposition on the inner ramp (restricted lagoon and shoal) environments. Those found in the Euphrates Formation constrained the depositional environment to the restricted lagoon and shoal environment, while the microfacies in the Jeribe Formation provided evidence for an inner ramp and middle to outer ramp belt environments. This study represents the first detailed research that focuses on the stratigraphic correlation and changes in carbonate facies with the main aim to provide a wider understanding of stratigraphy of these carbonate reservoirs throughout the northern part of Iraq.