Figures & Tables
The vertical tectonics inherent in the scheme of lateral motions of plates of lithosphere affords a coherent logic for the analysis of sedimentary basins. Subsidence may stem from crustal attenuation, thermotectonics, flexure of lithosphere, or combinations of these influences in space or time. Key facets of basin evolution include geometric configuration, the nature of the stratigraphic fill, the types of structural features, and the location of fluid hydrocarbons in space and time. Critical attributes favorable to hydrocarbon occurrence include the presence of organic-rich source beds, a history of thermal flux appropriate for thermal maturation, effective migration paths to allow concentration, and adequate reservoir capacity within suitable traps.
Both divergent and convergent plate motions embody vertical tectonics within the zone of plate interaction, but pure transforms do not. At divergent plate junctures, which are associated with the generation of new oceanic lithosphere, crustal attenuation causes eventual subsidence that is delayed by thermotectonic effects but may later be enhanced by plate flexure under sedimentary loading that forces isostatic adjustment. At convergent plate junctures, which are associated with the consumption of old oceanic lithosphere, crustal thickening causes uplift of subduction complexes and of arc or collision orogens, but plate flexure associated with plate subduction and with tectonic or sedimentary loading induces subsidence in basins that lie along the flanks of orogenic belts. Most sedimentary basins can thus be grouped generally into those in rifted settings and those in orogenic settings. A given basin may occupy several settings of either kind sequentially in time, and gradational examples also occur.
Basins in rifted settings include (1) infracratonic basins and (2) marginal aulacogens where continental separation is incomplete; (3) protoceanic rifts where the initial emplacement of fresh oceanic crust occurs; (4) miogeoclinal prisms of terrace, slope, and rise assemblages that mask rifted continental margins and (5) continental embankments where sedimentary progradation of the continental edge is important; (6) nascent ocean basins in which expansion by accretion of new lithosphere at midoceanic rise crests is dominant; (7) transtensional basins along complex transform systems where pull-apart or fault-wedge features occur; and (8) interarc basins formed as marginal seas behind intra-oceanic arc-trench systems from which remnant arc structures have been calved.
Basins in orogenic settings include (9) oceanic trenches where plate consumption occurs, (10) slope basins formed above accretionary subduction complexes, and (11) forearc basins in the arc-trench gap related to subduction zones; pericratonic basins of (12) peripheral forelands adjacent to collision orogens, (13) retroarc forelands adjacent to arc orogens, and (14) broken forelands where differential basement deformation is significant; (15) transpressional basins along complex transform systems where wrench or fault-warp features occur; and (16) remnant ocean basins in which shrinkage by consumption of old lithosphere at bounding arc-trench systems is dominant.
Useful for comparative basin analysis are plots of the following parameters against time: paleolatitude, subsidence rate (maximal or volumetric), net cumulative subsidence (maximal or volumetric), heat flux, geothermal gradient, and temperature at key source horixons.