Map Monday

The Mississippi River Alluvial Plain

The geology and geomorphology of large fluvial systems is extremely complex. This is especially true of the largest fluvial system in the United States, the Mississippi River. The Mississippi River Alluvial Plain as we know it today was formed during the last ice age. Our great river evolved throughout the Pleistocene epoch, cutting deep channels into the Coastal Plain as glaciers grew more than one mile high over parts of the mid-continent to the north and seasonally melted, causing drastic changes in sea level. Its valley was filled with thick sediments from the glacial meltwaters as they made their way to the Gulf. This is a testament to water’s immense power and ability to shape our earth, creating an environment that is now our state’s largest agricultural region. It was not until Mississippi was able to utilize the tools of LiDAR for geologic mapping, coupled with extensive borehole and archaeological data, that the true complexity and beauty of our Mississippi River Alluvial Plain was properly interpreted by our State Geological Survey scientists at MDEQ. We are proud to release a comprehensive geological map of the Mississippi River Alluvial Plain this week for #mapmonday. This publication serves as a new foundation for our understanding of the Mississippi Delta region and is a significant contribution to our state’s next geologic map.

Hard copies of this publication are available for order through our MDEQ, Mississippi Office of Geology publications and map sales department and available for free download here.

The powerful story of our coastal evolution—one only geology can reveal.

Our beautiful Mississippi Gulf Coast is a testament to the power of Mother Nature through deep time. The story of its natural history can only be unlocked through geologic mapping. The new tools of detailed lidar data coupled with test hole drilling and the study of fossils & outcrops helps our MDEQ’s State Geological Survey scientists tell the ancient story of our state’s coastal region.

The most influential part of this story can be found in the last few chapters of Earth’s history, recorded in the geology exposed at and near the surface. Our coastal region was largely shaped during the Pleistocene epoch, going back some 2.58 million years ago. During this time in earth’s history, sea levels rose and fell drastically due to cyclic glaciation. This left behind broad, coast-parallel terraces that were created during warm interglacial marine high-stands. Streams carved their valleys deep into the coastal plain as sea levels fell during the colder glacial episodes. The last glacial cycle ended some 11,700 years ago, as the last of the continental ice sheets melted. Sea levels finally rose to the coastline that we see today, only some 5,000 to 8,000 years ago.

We are proud to announce the release this week of a new publication by our State Survey scientists, the beautifully-detailed geologic map of our Mississippi coastal counties. This important project was funded by a cooperative grant with the USGS’s State Map geologic mapping program. It is a greatly updated interpretation of our coastal geology, depicted with detailed LiDAR, accompanying cross-sections, and unit descriptions. This map will provide an improved baseline for the understanding of the geologic framework of Mississippi’s amazing coastal region.

Hard copies of this publication are available for order through our MDEQ, Mississippi Office of Geology publications and map sales department and available for free download here.