Sequence: A coupled sequence-stratigraphic model built using Landlab

Landlab is an open-source Python package that streamlines the creation, combination, and reuse of 2D numerical models and is a key element of the Community Surface Dynamics Modeling System (CSDMS) Workbench. The Landlab Toolkit provides building blocks for model development such as grid data structures, input/output functions, and a library of several dozen components that each model a separate physical process. Additionally, it provides a framework for assembling integrated models from component parts. We've found that Landlab significantly accelerates model development, encourages user-developers to adopt standard practices and contribute new components to the library. It serves as a platform that nurtures a community of model developers, assisting them in creating coupled models to investigate non-linear interactions between geologic processes.

Using the Landlab toolkit, we developed a new model, Sequence, which is a modular 2D (i.e., profile) sequence stratigraphic model that incorporates key geophysical processes influencing accommodation space in both terrestrial and marine environments. These factors include tectonics and faulting, eustatic sea level changes, flexural isostatic compensation of sediment and water, sediment compaction, and hypopycnal sediment plumes. Each process is encapsulated as an individual, standalone Landlab component, providing flexibility in the construction of new models. Sequence serves not only as a distinct model, but also as a scaffold for the development of new models.

Sequence simulates the evolution of stratigraphy on a continental margin over time scales ranging from thousands to millions of years. Sediment transport and deposition primarily occur during infrequent, high-energy events like storms and floods. For these extended time frames, Sequence employs a scale-integral approach. This method utilizes differential equations to summarize the cumulative effect of sediment transport and deposition across different depositional environments over longer periods (e.g., on the order of a hundred years). The model features a moving-boundary formulation to track shoreline changes and partitions the domain into distinct areas: coastal plain, continental shelf, and upper and lower slope/rise. Submarine sediment transport and deposition are modeled through nonlinear diffusion, with a diffusion coefficient that varies inversely with water depth. The model tracks evolving stratigraphic layers and sediment lithology that is a mixtuer of two grain sizes (sand and mud) each with separate transport functions.