The 'second parameter': a memory from the globular cluster formation epoch

We study the correlations between the distribution of stars on the horizontal branch (HB), the HB morphology, and some other properties of globular clusters (GCs) in a large sample of GCs. We strengthen previous results that a general correlation exists only between HB morphology and metallicity. Correlations with other properties, e.g. central density and core radius, exist only for GCs within a narrow metallicity range. We conjecture that the lack of correlations with present properties of GCs (besides metallicity) is because the variation of the HB morphologies between GCs having similar metallicities is caused by a process, or processes, the effect of which was determined at the formation time of GCs. This process (or processes) is historically termed the 'second parameter', metallicity being the 'first parameter'. We then argue that the 'planet second parameter' model, where the presence of planets and to a lesser degree brown dwarfs and low-mass main-sequence stars is the 'second parameter', fits this conjecture. This is because the processes that determine the presence of planets and their properties occur during the formation epoch of the star and its circumstellar disc.     

Hydrothermal dolomite marbles associated with charnockitic magmatism in the Proterozoic Bamble Shear Belt,south Norway

Deformed and metamorphosed dolomite marbles in the Kragerø area of the Bamble Shear Belt occur as lenses within metasupracrustal sequences, as matrix in bodies resembling magmatic breccias, and as veins/dykes cutting amphibolites and metagabbros. A common origin is not evident from the field relationships, but is nevertherless probable due to great geochemical similarities between dolomite from the different occurrences. They are characterized by higher REE, Ni, Co, Cr and Sc, and lower Ba and Sr contents relative to metasedimentary marbles occurring nearby. Sm-Nd isotope data shows that the dolomites are of Sveconorwegian age (1175±37 Ma). The dolomite marbles are very weakly LREE-enriched and display in most cases positive Eu anomalies. Their stable isotope compositions are uniform (¹⁸O=+9.6 to +10.7; ¹³C=-8.5 to-6.2), their initial ⁸⁷Sr/⁸⁶Sr ratios are high (0.706–0.709), whereas their age corrected _Nd varies from +0.7 to-1.5. Geochemically the dolomitic marbles differ considerably from sedimentary or metasedimentary marbles as well as from carbonatites. The Kragerø dolomite marbles represent deformed and metamorphosed hydrothermal veins or vein-complexes deposited in tensional fractures in the deep crust. Although the dolomitic marbles regionally are of minor volume, the dolomite deposition represents a specific and important event in the geological evolution of the Bamble Shear Belt. Their geochemical and isotopic homogeneity on a regional scale suggest that the hydrothermal solutions were supplied from a very large, homogeneous reservoir. Trace elements, stable and radiogenic isotopes, and field and isotopic age relationships are consistent with a deposition from hydrothermal solutions which were exsolved from crystallizing charnockitic intrusions and subsequently interacted with the crust. The parental magma to these intrusions underplated the crust and raised the geotherm of a carbonated ultramafic uppermost mantle, and imposed decarbonation and fluid release. These fluids were channelled into a large degassing zone now found as a deformed, regional zone with hydrothermal dolomite deposits, albitites, apatite-veins and widespread scapolitization. Whether the CO₂-rich fluids, which precipitated the Kragerø dolomites, pervasively infiltrated crustal rocks at a deeper level and caused granulitization is ambiguous, but possible.     

Modelling the DC electrical response of fully and partially saturated Permo-Triassic sandstone

Results from a laboratory investigation into the electrical properties of fully and partially saturated Wildmoor Triassic Sandstone have been modelled using the Archie, Waxman–Smits and Hanai–Bruggeman equations. The results demonstrate the limitation of using simple relationships to describe samples when the matrix resistivity ρ_r is not significantly greater than the saturating electrolyte resistivity ρ_w. In these situations Archie's parameters m and n are not accurately determined. Conversely, the more sophisticated Waxman–Smits and Hanai–Bruggeman models provide parameters that better describe the electrical properties of the rock and are able to identify heterogeneity between samples that would otherwise be missed. The ranges of values for matrix resistivity (49 < ρ_r < 161 Ωm) and cementation factor (1.6 < m < 2.1) obtained from the Hanai–Bruggeman model indicate significant variation between samples. Comparison of laboratory‐determined values for cation exchange capacity (0.06 < Q_v < 0.51 meq/mL) and those obtained from the Waxman–Smits model (0.09 < Q_v < 0.55 meq/mL) indicates a very strong correlation, suggesting this model is appropriate for describing the rock. There is good agreement between parameters modelled using fully and partially saturated versions of both the Hanai–Bruggeman and Waxman–Smits equations, indicating that the data are consistent with these models and that the assumptions made are appropriate.     

Shelf-margin clinoforms and prediction of deepwater sands

Early Eocene successions from Spitsbergen and offshore Ireland, showing well‐developed shelf‐margin clinoforms and a variety of deepwater sands, are used to develop models to predict the presence or absence of turbidite sands in clinoform strata without significant slope disturbance/ponding by salt or mud diapers. The studied clinoforms formed in front of narrow to moderate width (10–60 km) shelves and have slopes, 2–4°, that are typical of accreting shelf margins. The clinoforms are evaluated in terms of both shelf‐transiting sediment‐delivery systems and the resultant partitioning of the sand and mud budget along their different segments. Although this sediment‐budget partitioning is controlled by sediment type and flux, shelf width and gradient, process regime on the shelf and relative sea‐level behaviour, the most tell‐tale or predictive signs in the stratigraphic record appear to be (1) sediment‐delivery system type, (2) degree of shelf‐edge channelling and (3) character of shelf‐edge trajectory through time. The clinoform data sets from the Porcupine Basin (wells and 3‐D seismic) and from the Central Basin on Spitsbergen (outcrops) suggest that river‐dominated deltas are the most efficient delivery systems for dispersing sand into deep water beyond the shelf‐slope break. In addition, low‐angle or flat, channelled shelf‐edge trajectories associate with co‐eval deepwater slope and basin‐floor sands, whereas rising trajectories tend to associate with muddy slopes and basin floors. Characteristic features of the shelf‐edge, slope and basin‐floor segments of clinoforms for these trajectory types are documented. Seismic lines along the slope to basin‐floor transects tend to show apparent up‐dip sandstone pinchouts, but most of these are likely to be simply sidelap features. Dip lines aligned along the axes of sandy fairways show that stratigraphic traps are unlikely, unless slope channels become mud‐filled or are structurally partitioned. Another feature that is prominent in the data sets examined is the lack of slope onlap. During the relative rise of sea level back up to the shelf, the clinoform slopes are generally mud‐prone and they are characteristically aggradational.     

Separation of multi-component NRM: A general method

A method is presented which can successfully isolate components of remanent magnetization having intermediate relative stability in a single rock sample which contains any number of remanence components with overlapping coercivity or blocking temperature spectra. The approach consists of analysis of the path swept out by the vector destroyed during a detailed alternating field or thermal demagnetization run. The point of intersection determined for any two neighboring great circle segments identified in such a difference vector path defines the direction of such a component. Samples cored from a fragment of a Jurassic pillow basalt, shown to contain several components of magnetization, serve to illustrate the utility of the method for the case when the Zijderveld approach is unsuccessful.     

Devonian basins of western norway - sedimentary response to tectonism and to varying tectonic context

The Devonian basins of western Norway are notable for their small size (<2000 km) and for the great stratigraphie thickness (up to 25 km) and the cyclic nature of their coarse-grained, alluvial infilling. These general features alone strongly suggest that tectonism was the dominant control on sedimentation but it is argued in particular that a coarsening-upwards motif, which permeates the three main basins usually on a scale of less than 200 m, was the direct sedimentary response to basin-floor subsidence. The coarsening-upwards is interpreted in terms of progradation of alluvial plain and alluvial fan facies in response to rapid lowering of the basin floor, while the overall cyclicity of the basin fills reflects repetition of such tectonic events. Detailed study within Hornelen Basin shows that the repeated coarsening-upwards theme overprints different sedimentary facies, and, in particular, the clastic wedges on opposite sides of the basin have contrasting thicknesses, radii, grain-size gradients and conglomerate types. These features suggest differing rates or degree of continuity of fault movement on opposite margins of the basin. Hornelen and Solund Basins, the two largest, are strongly contrasted in their differing mode of filling and sediment grade. It is suggested that this may reflect their development under strike-slip and dip-slip dominated regimes, respectively.