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12. Inverse modelling of extensional sedimentary basins and margins

Author

Edwards, G. R. H.

Subjects
551.7
Abstract

In this dissertation, a fully depth-dependent 2D kinematic model of the litho­sphere is developed. This forward model forms the basis of an inversion scheme capable of recovering the temporal and spatial strain rate history of a basin from present-day observed stratigraphic and subsidence data. The inversion scheme does not assume any a priori form for the strain rate distribution and unlike previous inversion schemes does not assume that the strain rate is invariant with depth (White and Bellingham, 2002). The depth-dependent inversion is applied to two sedimentary basins. Data from the Northern North Sea is used to benchmark the new code against the previous 2D inversion scheme and the Gulf of Suez is studied in detail using newly collated stratigraphic profiles from across the region. The Gulf of Suez is found to have stretched by 12-18 km in two rift phases at 23-18 Ma and 14-11 Ma. Depth­-dependent stretching appears to be more important in the Southern Gulf than in the north. In the south, stretching factors beneath uplifted regions are higher in the mantle than in the crust. Data from three passive margins is also inverted. The inversion scheme provides little evidence for depth-dependent stretching in the Eastern Black Sea. However, the stratigraphic data from the Pearl River Mouth basin and Angolan Margin can be more faithfully reproduced when depth-dependent effects are included. In all cases, recovered strain rates and timings of rift events are consistent with published values. Using the inversion scheme developed within this dissertation allowed results to be obtained with no a priori assumptions about the form or timing of the rifting periods.

Published
2006

46. Modelling feeding strategies to improve milk production, rumen function and discomfort of the early lactation dairy cow supplemented with fodder beet.

Author

Fleming, A. E., Dalley, D., Bryant, R. H., Edwards, G. R., and Gregorini, P.

Abstract

Feeding fodder beet (FB) to dairy cows in early lactation has recently been adopted by New Zealand dairy producers despite limited definition of feeding and grazing management practices that may prevent acute and sub-acute ruminal acidosis (SARA). This modelling study aimed to characterize changes of rumen pH, milk production and total discomfort from FB and define practical feeding strategies of a mixed herbage and FB diet. The deterministic, dynamic and mechanistic model MINDY was used to compare a factorial arrangement of FB allowance (FBA), herbage allowance (HA) and time of allocation. The FBA were 0, 2, 4 or 7 kg dry matter (DM)/cow/day (0FB, 2FB, 4FB and 7FB, respectively) and HA were 18, 24 or 48 kg DM/cow/day above ground. All combinations were offered either in the morning or afternoon or split across two equal meals. Milk production from 2FB diets was similar to 0FB but declined by 4 and 16% when FB increased to 4 and 7 kg DM, respectively. MINDY predicted that 7FB would result in SARA and that rumen conditions were sub-optimal even at moderate FBA (pH < 5.6 for 160 and 90 min/day, 7FB and 4FB respectively). Pareto front analysis identified the best compromise between high milk production and low total discomfort was achieved by splitting the 2FB diet into two equal meals fed each day with 48 kg DM herbage. However, due to low milk response and high risk of acidosis, it is concluded that FB is a poor supplement for lactating dairy cows. [ABSTRACT FROM AUTHOR]

Published
2020
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