# High-Resolution Mapping of Subsurface Sedimentary Facies and Reservoirs Using Seismic Sedimentology
## 3 Methodology and Workflow
### Step 3: Interpret Stratal Slices for Seismic Geomorphology  
If processed correctly, the horizontal resolution of a 3D seismic cube should be roughly equivalent to its vertical resolution [48]. However, the effectiveness of either resolution in seismic investigation is subject to the natural stacking pattern of lithofacies in the geological strata. The proportion of a lithofacies unit's horizontal to vertical dimensions in the formation controls its spatial resolution status.  
From outcrop observations, most thin sedimentary units are prominent in horizontal dimensions (tens to thousands of meters) and minor in vertical dimensions (several meters to low tens of meters). Such thin beds can only be detected in the vertical dimension, although they can be resolved in the horizontal dimension. Thin beds are volumetrically critical in both marine and lacustrine formations. Luckily, many of these beds can be reliably interpreted using seismic geomorphology on stratal slices or horizontal seismic attribute display following depositional surfaces. Therefore, the seismic interpretation of thin beds is limited only to what can be detected.  
In a case study [12] (Figure 7), a 50 Hz dominant-frequency data set in a lacustrine basin in China is adjusted to a 90\({}^{\circ}\) phase, such that the seismic reflection amplitude indicates lithology: positive (red) amplitudes are associated with sandstones, while negative (black) amplitudes indicate shale. Seismic geomorphic patterns of sandstones are ranked by size and thickness and include channels (distributary sands), irregular sheet-like amplitudes between channels (sandy mixtures formed in marginal environments such as crevasse spalys), and random patchy amplitudes (residual sands interspersed in shales, probably formed during transgression). The patterns indicate the presence of two shallow-water deltaic systems originating from the basin's upper-side (northern) margin. Such deltas are typical of lacustrine shallow-water deltas and are characterized by well-developed straight-to-networked distributary channel systems and poorly developed mouth bars and sand sheets at the delta front. In wells, the thickness of the sandstone in this delta varies from about 0.5 (prodelta) to 10 m (delta plain). It is confirmed with wireline-log verification that distributary channel sands as thin as one meter (\(\lambda/80\)) can be spatially resolved (Figure 7)--much thinner than the \(\lambda/25\) speculated by [PERSON] [49] decades ago.  
Seismic geomorphology can be analyzed on time, reflection horizon, and stratal slices [7; 50], as long as they are made following geologic-time-equivalent depositional surfaces. Ideally, stratal slices are the preferred option, as they are created by proportional slicing between two reference geologic events (e.g., maximum flooding surfaces) without significant internal depositional hiatuses (e.g., angular unconformities) [7]. Readers are referred to [PERSON] and [PERSON] [10] for the relationship between stratal slice and system tracts during deltaic development.