Cracking in soils that are undergoing drying is controlled by soil suctions and by soil properties such as compression modulus, Poisson's ratio, shear strength, tensile strength, and specific surface energy. The paper reviews the occurrence and morphology of cracks in dry-climate regions of Australia and Canada. After reviewing the behaviour of unsaturated soils and the mechanics of cracking, solutions are developed based on ( i ) elasticity theory, ( i i ) the transition between tensile and shear failure, and (iii) linear elastic fracture mechanics. The solutions are compared and related to crack depths observed in the field.La fissuration dans les sols subissant une dessiccation est contr81Ce par la succion et par les propriCtCs du sol telles que le module de compression, le rapport de Poisson, la rksistance au cisaillement, la rCsistance en tension, et 1'Cnergie de la surface spkcifique. L'article passe en revue la distribution et la morphologie de fissures dans les rCgions B climat sec de 1'Australie et du Canada. Aprks avoir pass6 en revue le comportement des sols non saturts et la mCcanique de fissuration, des solutions ont Ct C dCveloppCes sur la base de ( i ) la thCorie d'ClasticitC, ( i i ) la transition entre la rupture en tension et en cisaillement, et (iii) la mCcanique de fissuration Clastique 1inCaire. Les solutions sont comparCes et relikes aux profondeurs des fissures observCes sur le terrain.

The particle size of the bed sediments in or on many natural streams, alluvial fans, laboratory flumes, irrigation canals and mine waste deltas varies exponentially with distance along the stream. A plot of the available worldwide exponential bed particle size diminution coefficient data against stream length is presented which shows that all the data lie within a single narrow band extending over virtually the whole range of stream lengths and bed sediment particle sizes found on Earth. This correlation applies to both natural and artificial flows with both sand and gravel beds, irrespective of either the solids concentration or whether normal or reverse sorting occurs. This strongly suggests that there are common mechanisms underlying the exponential diminution of bed particles in subaerial aqueous flows of all kinds. Thus existing models of sorting and abrasion applicable to some such flows may be applicable to others. A comparison of exponential laboratory abrasion and field diminution coefficients suggests that abrasion is unlikely to be significant in gravel and sand bed streams shorter than about 10 km to 100 km, and about 500 km, respectively.

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A theoretical model is presented which shows that streams with low solids concentrations and low lateral inflows, whose bed load sediments undergo either comminution or hydraulic sorting under steady or quasi-steady conditions, have exponential profiles. Similar streams in which both communition and sorting are significant have exponential profiles only if they are short.Sediment threshold and flow depth estimates based on the theoretical model are consistent with field and laboratory data from the literature. A comparison of the model and communition and sorting data from the literature strongly suggests that hydraulic sorting and comminution dominate in short and long natural streams, respectively. No examples of natural streams of intermediate length with exponential longitudinal profiles were found, suggesting that neither sorting nor comminution is dominant in such streams.

The micropalaeontological biostratigraphy of the Magnus Sandstone Member of Kimmeridgian-Early Volgian age is described for the first time using data from 27 Magnus Field wells (blocks 211/12a and 211/7a). Despite extensive re-sedimentation within the Magnus Sandstone Member turbidite reservoir, a consistent sequence of nine bioevents is recognized field-wide. These include both regionally extensive bioevents and localized extinction and acme bioevents. The microfaunas are documented and key taxa, which include numerous radiolarian species, are described and figured.The bioevent scheme provides the basis for the chronostratigraphic and genetic sequence stratigraphic subdivision (sensu Galloway) of the Magnus Sandstone Member. It allows the recognition and biostratigraphic calibration of three maximum flooding surfaces (MFS) which in ascending stratigraphic order comprise: the pre-Magnus Sandstone Member top J62-basal J63 'Eudoxus' of Partington et al.