Clastic Sediment Partitioning in a Cretaceous Delta System, Western Canada: Responses to Tectonic and Sea-Level Controls

The early–mid Cenomanian Dunvegan Formation represents a large delta complex that prograded at least 400 km from NW to SE. A regional stratigraphy based on marine transgressive surfaces and equivalent subaerial interfluves allows the formation to be subdivided into ten transgressive–regressive allomembers, labelled J to A in ascending order, each with an average duration of <200 ky. Analysis of stacking patterns and facies distributions of parasequences within allomembers allows transgressive, highstand, falling stage and lowstand systems tracts to be identified. Extensive valley systems that average 1–2 km wide and 21 m deep can be traced for up to 320 km across the top surfaces of allomembers H to E. In their lower 20–40 km, valleys are filled with muddy heterolithic tidal facies but this changes to fluvial-dominated multi-storey channel-fills further up-valley. Interfluve surfaces are marked by palaeosols, the character of which indicate a protracted hiatus with extensive physical, chemical and biological modification of the parent material. Changes in flexural subsidence rate are indicated by isopach patterns. Allomembers J–F have a sigmoidal prismatic geometry, successively offlapping to the SE. There is no evidence of thickening toward the orogen. In contrast, overlying allomembers E–A show progressive development of a depocentre along the western margin of the basin. The increasing accommodation rate on the updip coastal plain caused marine deltas to be starved of sediment, leading to progressive backstep of shorelines. Simultaneously, alluvial deposits within the depocentre show an upward increase in the proportion of subaqueous to subaerial facies, culminating in the incursion of brackish and finally marine waters. Thus tectonic subsidence rate had a first-order affect on both the volume of sediment available to build marine deltas and also on the local character of facies that accumulated on the coastal plain. The onset of flexural subsidence in allomember E appears to have resulted in subtle uplift of a forebulge, resulting in dramatic deflection of river systems. Despite the clear tectonic signature, successive transgressions and regressions involved similar horizontal displacements of the shoreline, regardless of subsidence rate. This suggests that modest eustatic changes also influenced the accommodation available. Based on the measured horizontal excursions of the shoreline, the vertical thickness of alluvial strata, and realistic alluvial gradients, an average eustatic excursion of about 24 m is calculated. The incision of valley systems is attributed in part to periods of eustatic fall. However, valleys seem too long to be explained by eustasy alone, and hence secular changes in discharge are postulated as an additional forcing factor. Climatic cycles in the Milankovitch band may have been responsible for both eustatic and discharge variations

In-situ stylus profilometer for a high frequency reciprocating tribometer

Measuring the friction and wear characteristics of a tribological contact is essential to gaining a detailed understanding of its performance and predicted life. Wear rate and friction coefficient measurements are obtained from instrumented benchtop tribometers designed to replicate specific tribological contacts. Due to the difficulty of measuring wear in situ, measurements are typically made before and after an experiment. The wear rate must be assumed to be linear for it to be used to predict product life, however this is assumption can hide changes occurring during an experiment which indicate wear transitions. This paper details the design and validation of an in situ stylus profilometer for a reciprocating sliding tribometer to provide an insight into the wear transitions occurring during dry sliding of 52100 bearing steel against graphitic flake cast iron. The profilometer's performance was validated using ground roughness standards and the accuracy found to be approximately 110 nm. Incubation, run-in and steady state wear regimes were identified by the profilometer and corroborated with friction coefficient data, providing an enhanced understanding of the tribological contact behaviour

Reproducing automotive engine scuffing using a lubricated reciprocating contact

The frequency and severity of scuffing in automotive engines has the potential to increase due to new low-viscosity lubricants for fuel efficiency and increased cylinder power output. This work is to understand the fundamental causes and events resulting in piston ring and liner scuffing. A TE-77 high frequency reciprocating tribometer was used with a synthetic PAO base oil (4cSt) to reciprocate a 52100 G5 barrel against a ground pearlitic Grade 250 grey cast iron.Samples were run-in at 50 N and 10 Hz prior to a temperature ramp to 150 °C followed by a discreet load ramp to 1 kN (0.49 GPa). The tests were terminated when a sharp increase in the average friction force was observed indicating that scuffing had occurred. 3D optical profilometry showed that the scuffed cast iron surface consisted of smeared platelets and craters of View the MathML source35?m depth. SEM and EDX analyses suggested adhesive transfer of cast iron material to the counter-surface was occurring by failure along lamellar graphite interfaces. Tests were repeated using instantaneous high-speed friction data and indicated that micro-scuffing initiated at a load of 620 N. Focused ion beam cross-sections of the mildly scuffed surface confirmed the mechanism of sub-surface crack initiation occurring along lamellar graphite boundaries

Data supporting: Scuffing mechanisms of EN-GJS 400-15 spheroidal graphite cast iron against a 52100 bearing steel in a PAO lubricated reciprocating contact

This data supports the following publication (see below for paper abstract): Kamps, T.J., Walker, J.C., Wood, R.J., Lee, P.M. and Plint, A.G. (2017) Scuffing mechanisms of EN-GJS 400-15 spheroidal graphite cast iron against a 52100 bearing steel in a PAO lubricated reciprocating contact. Wear, 1-16 Scuffing of the automotive piston ring on liner contact is likely to increase due to engine downsizing and the use of low viscosity engine oils to achieve greater fuel efficiency. This work investigated the scuffing mechanism of EN-GJS 400-15 spheroidal graphite cast iron caused by reciprocating sliding of a 52100 roller bearing element lubricated with PAO base oil. The contact was conditioned at 100N and 15 Hz over a stroke of 25 mm at 180 oC. Subsequently the load was incremented in 100 N/min steps at 5 minute intervals until severe scuffing occurred, indicated by a rapid rise in the average friction coefficient. High speed friction was used to determine the onset of mild and severe scuffing. Stylus and 3D optical profilometery revealed that mild scuffing produced a smooth surface with small cracks compared to the severe scuffed surface which contained adhesive wear craters of 40 ?m in depth. Focused ion beam cross-sections of the mild scuffed surface and EDS analysis of the microstructure indicated that cracks were initiated by dross inclusions with a similar morphology to flake graphite. The transition to severe scuffing occurred at 700N when crack networks facilitated adhesive transfer of cast iron material to the counter-surface.</span