The origin of the regional and stratigraphical variation in the Triassic authigenic clay assemblages of England is discussed in relation to new estimates of the palaeotemperatures experienced by their host sediments and a preliminary study by transmission electron microscopy of their microtextural features. Spore colour index measurements, based on the spore type Deltoidospora s.l. occurring in the sediments (Penarth Group) at the very top of the Triassic sequence, give estimated palaeotemperatures ranging from 60–74°C (south Devon) to 89–97°C (northeast Yorkshire). Calculated palaeotemperatures, based on a gradient of 25°C/km, for the main zone of authigenic clay minerals range from 63–77°C to 89–97°C for the top to 71–85°C to 94–104°C for the base. Irregular mixed-layer smectite-chlorite, corrensite and Mg-rich chlorite are associated with calculated palaeotemperatures of 66–86°C, 66–104°C and 75–104°C respectively. The suggestion that elsewhere in the UK corrensite and Mg-rich chlorite were formed at temperatures in excess of 100°C finds no support. Geothermal gradients would have to have been of the order of at least 100–300°C/km to obtain these temperatures within the Triassic sediments; such values are associated typically with high-level magmatic intrusions or geothermal systems of which there is no geological evidence. The balance of evidence suggests that the Triassic authigenic clay assemblages formed by neoformation during the early stages of sediment diagenesis under the influence of variation in the alkalinity of the depositional environments.

Field studies were conducted in 1986-87 and 1988-89 to compare chiseling, disking, and skewtreading to no-till and to compare 0.3 and 0.4 kg ai ha−1 pronamide applied before or after fall tillages for weed control in fallow. Chiseling or disking in October 1986 when weeds were emerged reduced the dry weight of volunteer wheat about 90% the following spring; however, only disking reduced the dry weight of downy brome 90%. Disking or skewtreading in October 1988 before weeds germinated reduced the dry weight of volunteer wheat about 95% 6 mo later, but none of the three tillages reduced the dry weight of downy brome. Pronamide applied at 0.3 and 0.4 kg ha−1 to emerged downy brome and volunteer wheat with either chiseling or disking before or after herbicide application reduced the dry weight of both species 90% or more 6 mo later compared with tillage alone. If weeds did not emerge until early November, then only pronamide at 0.4 kg ha−1 applied in no-till or after fall tillage controlled both species at least 90%.