Chevron Marks Research Articles

Combined-Flow Generation of Sole Structures, Including Recurved Groove Casts, Associated with Lower Carboniferous Lacustrine Storm Deposits in Nova Scotia, Canada

ABSTRACT Sole structures are common on bases of sandstone beds in lacustrine shoreline deposits of the Horton Bluff Formation (Lower Carboniferous), Nova Scotia. The structures include recurved groove casts (the first reported occurrence), other curvilinear grooves, and opposed prod casts. Gutter casts and sinusoid-like chevron marks are associated with these sole marks, but flute casts and other undisputed indicators of unidirectional flow were not noted. Sole structures and gutter casts are oriented normal to the strike of wave-ripple crests and to the elongation direction of hummocky-cross-stratified lenses. Inclined strata within the lenses locally show a preferred migration direction parallel to the elongation direction. The erosional structures are inferred to have been generated during torms in a shallow lake by oscillatory and/or combined flow, the latter possibly associated with longshore currents. These storms also produced hummocky cross-stratification. Wave-formed sole structures may be common in the rock record, and can be recognized by curvilinear shapes, including rare recurved shapes, and bimodal orientations. Care should be taken when interpreting sole structures from wave-influenced settings, because they may not indicate directions of net sediment transport or the orientation of unidirectional currents.

Field observations on some dwarf chameleons (Brookesia spp.) from rainforest areas of Madagascar, with description of a new species

Six species of Brookesia dwarf chameleons were recorded during two rainforest expeditions in Madagascar. One of these is described as a new species Brookesia valerieae based on the arrangement of the nine pairs of dorso‐lateral spines, the lack of a pelvic shield, and dorsal chevron markings. Observations were made on the defence and roosting behaviours shown by these six species. Aspects concerning the evolution and conservation in Madagascar are discussed for this poorly studied group of endemic Malagasy reptiles.

Interlaminar and intralaminar fracture surface morphology in graphite/epoxy laminates

Fracture surface morphological studies of graphite/epoxy (T300/934) laminates have been performed to distinguish between mode I and mode II interlaminar and intralaminar fractures. Additionally, the effect of a few hygrothermal conditions on mode I fracture surface is also assessed. Centre notched tension, compact tension, double cantilever beam and cracked lap shear specimens have been used to study these fracture modes. While mode I fracture is characterized by branched cracks between fibers, river pattern and chevron markings on resin rich zones, the epoxy hackles dominate mode II fracture surface. The interlaminar and intralaminar fractures can be distinguished by fiber spacings and some matrix features. The effect of increase in temperature and/or moisture is seen to cause reduction in matrix microcracking and increase in fiber pullout in mode I.

Ａｌ‐２．０％Ｃｕ‐１．１％Ｍｇ合金の時効析出過程

Transmission electron microscopy and measurements of hardness and electrical resistivity were carried out on the alloy aged at various temperatures 40 to 300°C. This alloy follows a similar course of precipitation as common Al-Cu-Mg alloys. The pre-precipitation zones G. P. B. are considerably formable in the early stage of aging at temperatures bellow 200°C. The forming rate of the G. P. B. zones increases with concentration of the solutes in the alloys having a same ratio of Cu: Mg. High density of dislocation loops and helices are found in the stages of the G. P. B. zones formation at 120°C or bellow. The S' phase precipitates and grows in the distored lath form at aging temperatures above 120°C forming corrugated composite sheets and chevron markings as in the common Al-Cu-Mg alloys. The S phase precipitates and grows in the lath form at elevated temperatures above 250°C. The growth rate of it is considerably lowered in the prolonged aging at 250°C for more than 104min.

Sedimentary structures and palaeocurrent directions from the Silurian rocks of Kirkcudbright

New sedimentary structures are described from a thick greywacke/mudstone succession. The structures include modified ripple marks, nodule trails and orthocone prod marks. Further evidence is given and comment made on the genesis of longitudinal ridges, chevron marks and large-scale current bedding. Palaeocurrent directions statistically determined from 353 observations show that the dominant turbidity currents during Riccarton (Wenlock) and Upper (?) Silurian times came from the north-east ( i.e. parallel to the axis of the Caledonian geosyncline) with minor currents from the south-west. Currents at right angles to the axis of the geosyncline deposited the transverse ripples.