Abstract

The thermal regime of a small basin is sensitive to the effects of intrabasinal conductive and advective heat transport. Deep, narrow basins require, at a minimum, a two-dimensional modeling scheme to accurately assess the effects of these heat transport mechanisms. Modeling of the thermal regime of a basin based on the lithology and dimensions of the Ventura Basin in southern California indicates that a two-dimensional modeling scheme is necessary when the width to depth ratio of the basin is less than 5 to 6:1. If no groundwater flow is present, the two-dimensional conductive modeling scheme is adequate; however, if permeabilities of units in the basin are greater than 1 x 10⁻¹⁸ m² and the topography in the basin area is sufficient to drive fluid flow, a two-dimensional model that couples the effects of conductive and advective heat transport must be used. Results of modeling the thermal regime of the model basin through its history imply that the effects of two-dimensional conductive heat transport are probably negligible early in the history of a small basin, but become significant as the basin matures, inducing temperature variations within the basin as great as ±30°C. When fluid flow occurs, the temperature regime may vary an additional 40 to 50°C from the purely conductive thermal field. Application of a conductive model to the current geometry of the Ventura Basin in California demonstrates that at present the thermal field is dominated by conductive effects and there are likely significant lateral variations in the temperature structure of that basin.