Question

In what nonmarine settings do gravelly sediments often accumulate?

Short answer

Gravelly sediments, which are clastic sediments larger than 2 millimeters in diameter, often accumulate in various nonmarine settings. These include river channels, where gravels are formed due to erosion and transported by the river's flow; alluvial fans at the base of mountain ranges, where rivers or streams deposit sediments as they slow down; glacial environments, where glaciers erode bedrock and transport and deposit gravelly sediments in landforms like moraines, outwash plains, and eskers; and landslide deposits, where mass wasting events generate a mixture of debris, including gravels.

Step-by-step solution

Understanding gravelly sediments

Gravelly sediments are clastic sediments containing rock fragments larger than 2 millimeters (0.08 inches) in diameter. These fragments can be rounded or angular, depending on the transportation and deposition processes.

Identifying different nonmarine environments

Nonmarine settings refer to locations on earth that are not influenced by marine (oceanic) environments. These include terrestrial and freshwater settings.

Listing nonmarine settings where gravelly sediments accumulate

Gravelly sediments can accumulate in a variety of nonmarine environments. Some common settings where gravelly sediments often accumulate are: 1. River channels: Gravel can be found in and alongside rivers, especially along the bends or downstream from a river's source. Erosion from the riverbanks and underlying bedrock contribute to the production of these gravelly sediments, which are then transported by the river's flow. 2. Alluvial fans: Alluvial fans are cone-shaped deposits of gravel, sand, and silt that accumulate at the base of mountain ranges. They form where a river or stream emerges from a steep slope onto a flat plain, causing the flow to slow down and deposit its load of sediments. 3. Glacial environments: Glaciers are large masses of ice that move slowly across the land, eroding the underlying bedrock and generating large amounts of gravelly sediments. These sediments are then transported by the glacial movement and/or meltwater outwash and deposited in various glacial landforms, such as moraines, outwash plains, and eskers. 4. Landslide deposits: Landslides, or mass wasting events, can generate gravelly sediments when large volumes of rock and soil on slopes become unstable and flow downhill. The resulting chaotic mixture of debris can include a range of sediment sizes, including gravels.

Key concepts

Nonmarine Environments

Nonmarine environments are crucial to understanding the accumulation of gravelly sediments as they form a significant part of the Earth's terrestrial landscape. Unlike marine settings, which are influenced by the sea and its processes, nonmarine environments include areas such as river valleys, deserts, mountains, and polar regions. These settings are governed by freshwater or terrestrial processes rather than by saltwater influences.

In these environments, sediment accumulation occurs through various processes, such as erosion from wind or water, volcanic activity, and gravitational actions like landslides. Gravelly sediments often deposit near water sources, like rivers and streams, or can be found in regions that were previously sculpted by glaciers, giving rise to unique geological formations. Understanding nonmarine environments is pivotal because they reveal earth's history and are indicators of past climatic conditions.

Clastic Sediments

Clastic sediments, such as gravelly sedimentary deposits, are collections of particles that originate from the mechanical breakup of rocks. These sediments can range in size from clays to boulders, with gravel representing the larger end of this spectrum with a diameter of over 2 millimeters.

Transported by water, wind, or ice, their shape and size can tell geologists a lot about their journey from origin to the point of deposition. Rounded gravel particles suggest they have traveled a long distance and have been smoothed by the constant abrasion of movement, while angular particles indicate a short travel distance from their source. The composition and layering of clastic sediments provide crucial information on the Earth's geological past, including insights into past environments and climatic conditions.

Alluvial Fans

Formation and Characteristics of Alluvial Fans

Alluvial fans are among the most visually distinct nonmarine sedimentary structures. They are formed when fast-flowing mountain streams exit narrow valleys and decelerate upon reaching a relatively flat plain. This decrease in velocity causes the water to spread out and drop its sediment load, with heavier, gravelly particles settling first, followed by finer sediments like sand and silt.

Importance of Alluvial Fans

These fan-shaped deposits often occur in arid or semiarid climates and can cover extensive areas. They are dynamic systems that can change quickly in response to precipitation events, and their deposits are stratified, recording the history of environmental changes and water flow within the region.

Glacial Deposits

Glacial deposits, also known as glacial drift, are the sediments left behind by retreating glaciers. These sediments can range in size from fine clays to large boulders and are typically unsorted due to the variety of transport methods, including ice movement and meltwater flow.

As glaciers advance and retreat, they carve out vast sections of the Earth's topography, creating U-shaped valleys, fjords, and circular lakes (kettles). The gravelly sediments within glacial deposits, such as moraines and eskers, provide evidence of the glacier's movement and are valuable indicators of the climate at the time of the glacier's presence. These sediments also influence the current landscape as they form rich farmland and aquifers, making them significant for environmental and economic reasons.