Lithological maps are geological maps with the graphic, spatial representation of rock type, distribution, and other physical features, including that of unconsolidated surficial materials.
These maps show the lithology of a selected area of study. And since these maps define rock types, characteristics, formation, and association, they can help interpret, identify, and map valuable mineral resources, including oil.
You can also use these maps to create a correlation between areas, and knowledge gained is a vital variable in landscape evolution, river composition, fluxes of water pathways, etc.
Discover more about lithological maps and mapping, including symbols and pattern charts, color codes, abbreviations used, and much more.
What are lithological maps and mapping?
Lithology studies physical properties like color, grain size, composition, etc., of visible rock outcrops, hand, or core samples, including using a low-magnification microscope or conducting simple chemical tests. More lithology descriptions include rock type, small-scale features, surficial lithology, and fabric.
In the gross summary sense, examples of lithologies are limestone, slate, basalt, chert, coal, claystone, shale, sandstone, halite, anhydride, tuff, gypsum, chert, claystone, limestone, etc. All fall into three categories, igneous, sedimentary, and metamorphic.
A lithologic map, on the other hand, is a spatial, graphic representation of rock types, distribution, color, and other characteristics, including their association. Also, these maps will include lithologies of unconsolidated surficial materials.
We use lithologic knowledge to subdivide rock sequences into individual lithographic units. Afterward, we use lithology symbols, patterns, colors, abbreviations, and codes to represent lithologies spatially graphically. This entire exercise is called lithological mapping and is often aided by remote sensing.
Lastly, you can have maps of various lithologic areas like Wolfcamp, Louisville, Hell Creek, Bone Spring Formation, Permian basin regions, or the whole world.
Lithology symbols, patterns, codes, colors, and abbreviation
To help represent various lithologies on maps, we use standardized symbols and pattern charts, color codes, and abbreviations. Most maps will come with legends of all these to help with interpretation.
In the US, the Federal Geographic Data Committee provides various assets and guidelines for preparing geologic maps, including lithological ones. The FGDC Digital Cartographic Standard for Geologic Map Symbolization has geologic map symbols, color charts, and pattern charts, including lithological patterns. Other countries and regions may have their own lithologic patterns and colors.
Let us look at each briefly:
a). Lithology symbols and pattern charts
They refer to a mark or a set of marks that depicts certain lithology, such as rock type or texture. You will find lithologic pattern charts for sedimentary, igneous, vein matter, and metamorphic rocks.
For instance, a brick emblem represents limestone, while the stippled region will depict a sandstone. Coal is represented by solid black, crystal tuff by a set of X patterns and Zeolitic rock by Z.
b). Lithology color colors
Colors will help distinguish various lithologies in these maps, such as metamorphic rocks, igneous rocks, or sedimentary rocks, such as claystone, plutonic, acidic, mafic, etc. Also, they may indicate wetness and other things.
c). Lithological abbreviations
These are standard abbreviations used to describe certain lithological features on the map.
You can go for a PDF version intended for plotting and viewing. Also, you can go for downloadable PostScript intended for use with Adobe Illustrator or other software used in graphic design, including the USGS lithology patterns. Also, you can go for the ESRI version, i.e., compatible with ArcGIS Online and ArcGIS Pro.
Global or world lithological maps
Currently, three lithological world maps cover the globe, not just a region. Bluth and Kump built the first one in 1991 and later revised by Gibbs and Kump in 1994]. Based on Ronov’s group work, this map has a resolution of 2° and 13 distinguished lithological classes.
The second map by (Amiotte Suchet et al., 2003) is also based on the Ronov group with a 1° resolution and six distinguished lithological classes.
Lastly, a more recent global lithological map, GLiM (Hartmann & Moosdorf, 2012), has a very high resolution. It has a map scale of 1:3,750,000 with 1,235,400 polygons.
Remove sensing and lithological maps.
Remote sensing will help in lithological mapping to identify mineral-rich areas, classify surficial features, and draw lithological boundaries. Also, it will help mineral exploration (help miners), locate study areas, and produce lithological maps.
It is less hazardous and may help capture changes over time compared to physically visiting various study places.
References
- Hartmann, J., & Moosdorf, N. (2012). The new global lithological map database glim: A representation of rock properties at the Earth’s Surface. Geochemistry, Geophysics, Geosystems, 13(12). https://doi.org/10.1029/2012gc004370
- Bluth, G. J., & Kump, L. R. (1991). Phanerozoic paleogeology. American Journal of Science, 291(3), 284–308. https://doi.org/10.2475/ajs.291.3.284
- Gibbs, M. T., & Kump, L. R. (1994). Global chemical erosion during the last glacial maximum and present: Sensitivity to lithology and hydrology changes. Paleoceanography, 9(4), 529–543. https://doi.org/10.1029/94pa01009
- Dürr, H. H., Meybeck, M., & Dürr, S. H. (2005). Lithologic composition of the Earth’s continental surfaces derived from a new digital map emphasizing riverine material transfer. Global Biogeochemical Cycles, 19(4). https://doi.org/10.1029/2005gb002515