Lithofacies
The kind of comparison that never ceases to amaze. Left: Very large, tabular-like crossbedding in the Jurassic Navajo Sandstone, spectacularly exposed at Zion National Park. The dune bedform containing these foresets, at least 18 m high, marched in unison with other dunes across the Middle Jurassic sand-sea. Right: Detail of dune crossbedding in the 3.7 – 2.9 billion year old Stimson formation, probably of aeolian origin, exposed in Gale Crater, Mars (see the recent paper by Banham et al. 2021, Open Access). Contact between crossbed sets is outlined by the dashed line. Note the strongly tangential foresets on lower left. Bar scale is 1 metre. Image credit: enlarged from NASA/JPL-Caltech/MSSS image PIA19818
This series of articles deals with the description and interpretation of sedimentary rocks. The focal point in each article is the lithofacies, the basic descriptive unit for all sedimentary rocks; it is the starting point for any investigation. The key elements of lithofacies descriptions are that they derive from reasonably objective criteria, and they simplify the complex geology.
Lithofacies are the cornerstone for a hierarchy of analytical tools: Bounding surfaces, lithofacies assemblages, architectural elements, and facies models.
Sandstone lithofacies
Sedimentary lithofacies – An introduction
Ripple lithofacies: Ubiquitous bedforms
Ripple lithofacies influenced by tides
Tabular and trough crossbed lithofacies
Laminated sandstone lithofacies
Low-angle crossbedded sandstone
Hummocky and swaley cross-stratification
Lithofacies beyond supercritical antidunes
Subaqueous dunes influenced by tides
The three pycnals: Hypo-, homo-, and hyper
Storms and storm surges: Forces at play
Evolving tempestite lithofacies models
Gravel lithofacies
Introducing coarse-grained lithofacies
Crossbedded gravel lithofacies
The lithofacies of mountain streams
Three posts on tempestites
3 Evolving tempestite lithofacies models
2 Storm surges and tempestites
1 Storms and storm surges: Forces at play
Seagrass, mangrove, and salt marsh lithofacies
Seagrass meadows and ecosystems
Seagrass lithofacies in the rock record
Geological models
Geological models: An introduction
Model dimensions and dimensional analysis
Analogue models of faults: scaling the materials
