High-resolution sequence stratigraphy of clastic shelves I: Units and bounding surfaces

The high-resolution sequence stratigraphy tackles scales of observation that typically fall below the resolution of seismic exploration methods, commonly referred to as of 4th-order or lower rank. Outcrop-and core-based studies are aimed at recognizing features at these scales, and represent the basis for high-resolution sequence stratigraphy. Such studies adopt the most practical ways to subdivide the stratigraphic record, and take into account stratigraphic surfaces with physical attributes that may only be detectable at outcrop scale. The resolution offered by exposed strata typically allows the identification of a wider array of surfaces as compared to those recognizable at the seismic scale, which permits an accurate and more detailed description of cyclic successions in the rock record. These surfaces can be classified as‘sequence stratigraphic’, if they serve as systems tract boundaries, or as facies contacts, if they develop within systems tracts. Both sequence stratigraphic surfaces and facies contacts are important in high-resolution studies; however, the workflow of sequence stratigraphic analysis requires the identification of sequence stratigraphic surfacesfirst, followed by the placement of facies contacts within the framework of systems tracts and bounding sequence stratigraphic surfaces. Several types of stratigraphic units may be defined, from architectural units bounded by the two nearest non-cryptic stratigraphic surfaces to systems tracts and sequences. The need for other types of stratigraphic units in high-resolution studies, such as parasequences and small-scale cycles, may be replaced by the usage of high-frequency sequences. The sequence boundaries that may be employed in high-resolution sequence stratigraphy are represented by the same types of surfaces that are used traditionally in larger scale studies, but at a correspondingly lower hierarchical level.