Sedimentary Rocks Contain Clues to Ancient Environments

As climate changes over time, so do the environments that are present in a region. For instance, at one time a region might contain a vast lake and river system, but millions of years later there may be no trace of water at all. While water may have left the region, traces of the lake and rivers might remain in the sediment that was deposited by the water and the shape of the landscape as well. These traces allow us to figure out what environments were like in the past!

Different types of environments contain different types of sediments. The type of sediment and the way that it is deposited determines the types of sedimentary rocks that will eventually be formed. Thus, sedimentary rocks formed in a lake will be different from those formed in a desert.

Geologists look at ancient sedimentary rocks to figure out the type of environment that once was in the location where the rock formed. The table below lists environments that are common on Earth and the physical features that characterize them. Click on the images below to compare modern environments and the rocks that are made from them.

Environment Sediment Size Sediment Sorting Structures and Features The Environment Today: Evidence Preserved in Rock:
Lake Mud Fair
  • Thin layers called laminations
  • Sometimes mud cracks
Swamp Mud
  • Organic material makes coal
Desert Dunes Sand Very good
  • Cross-beds
  • Rounded grains
Alluvial Fan Sand and gravel Poor
  • Angular fragments of rock
River Silt, sand, and gravel Poor
  • Rounded pebbles, channel shape
  • Cross-beds and ripple marks
Lagoon Mud
  • Mud cracks and ripple marks
Beach Silt, sand, or gravel Good
  • Mud cracks and ripple marks
  • Laminations and other thin layers
Shallow Ocean Silt and sand Good
  • Thick or thin layers
  • ripples and cross-beds
Deep Ocean Mud, with thin layers of sand or silt Fair
  • Layers of mud.
  • Thin sand layers form as sediment flows downslope.
Tropical Ocean Sediment made of Calcite (and other carbonate minerals) Good to poor
  • Most sediment comes from the skeletons of marine life.
Last modified January 6, 2004 by Lisa Gardiner.

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more


Rivers are very important to Earth because they are major forces that shape the landscape. Also, they provide transportation and water for drinking, washing and farming. Rivers can flow on land or underground...more

Step 3: Deposition (Sediments Settling Down!)

When water or wind loses energy and slows down, sediment can no longer be carried in it. The particles of sediment fall through the water or air and form a blanket of sediment on the bottom of a river,...more

Scientists Search for the Cause of Ancient Global Warming

An abrupt release of methane, a powerful greenhouse gas, from ice sheets that extended to Earth's low latitudes some 635 million years ago caused a dramatic shift in climate, scientists funded by the National...more

A Rover on the Red Planet! Spirit Will Look at the Geology of Mars

NASA’s rover, named Spirit, has successfully landed and will soon be scouting the surface of Mars for interesting geology! Scientists are interested to know whether the depression where Spirit landed...more

Prehistoric Fossil Snake is Largest on Record

Scientists have recovered fossils from a 60-million-year-old South American snake whose length and weight might make today's anacondas seem like garter snakes. Named Titanoboa cerrejonensis by its discoverers,...more

Life in an Antarctic Field Camp

Organizing a science camp for a field party of twelve people to conduct research for six weeks in Antarctica seems like an insurmountable task. And yet, here we are. It took much planning and hard work...more


Evolution is the process of change through time. Many things evolve. Language evolves so that English spoken four hundred years ago during the time of playwright Shakespeare was very different than English...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA