Characteristics and causes of platform-like layered fractures

Stair-step Fractures

Stair-step fractures are a type of fracture that has been observed in many geological surfaces. These fractures typically have a stepped, or stair-stepped, appearance, created by alternating layers of varying thickness. The steps occur when subsurface layers or elements are of different strength or are eroding at different rates, leading to uneven frequency of cracking. In some cases, stair-step fractures form as surface-area increases and gravity pulls the layers of the rock downward.

Formation of Stair-Step Fractures

Stair-step fractures are commonly formed in sedimentary rocks, like sandstone or limestone, as a result of surface irregularities caused by erosion. When surface elements erode, they take longer to wear away when they are thicker, causing the surface to form a series of steps as the thinner layers are eroded away more quickly. The fracture that forms is then a stepped surface feature.

Stair-step fractures can also form as a result of differential weathering. Differential weathering occurs when two surface layers experience different rates of weathering due to a contrast in chemical composition or physical strength between the layers. When the layer of rock on top of the other erodes, cracks form in the layers causing them to get wider apart. Over time, this causes the surface to form a staircase-like feature.

Other causes of stair-step fractures are thermal expansion, pressure release, and tectonic activity. Thermal expansion occurs when the Earth’s temperature rises, causing the pressure within rocks to expand and contract. If a rock has many layers with different densities and strengths, the expansion causes them to fracture. Pressure release occurs when the pressure inside a rock is released outward, causing the layers to separate and crack, forming staircase-like features. Tectonic activity is also known to create stair-step fractures by causing the layers of rock to shear or break apart from each other.

Applications of Stair-Step Fractures

Stair-step fractures are an important indicator of past and present geologic events and have several real world applications. They can be used to determine the strength and composition of rocks and minerals, as different types of rocks and minerals can have very different responses to weathering. The understanding of these processes can also inform engineering decisions, providing an indication as to the durability of a given structure or landscape.

Stair-step fractures can also provide insight into the history of a given landscape, as they are often formed by very slow processes over long periods of time. By studying the size, spacing, orientation and number of stairs, we can begin to understand how the underlying rock layers have deformed, weathered and eroded over time.

Conclusion

Stair-step fractures are an important sign of past and present geologic activity and can provide clues as to the composition and strength of the underlying rocks and minerals. They also provide insight into the history of a landscape, allowing us to understand how the landscape has changed over time. Stair-step fractures are an important indicator of geologic activity and have a variety of real-world applications.

Stratigraphic discontinuity refers to the special feature of the sedimentary layer where there is a gap in the deposition. It can be described in similar terms to a ‘step’ in the section of the rock or sediment layers. It is often in the form of what is called a ‘stratified platform’, where the surface of the surface of the stratigraphic layer is flat, yet the underlying bedrock is not. This can occur due to several different factors.

One of the primary reasons for a stratigraphic discontinuity is when a new layer of sediment is deposited on top of an older layer. Since the new layer of sediment tends to be of different grain size or type of material, it can make the new layer of sediment noticeably different from the underlying layer. This type of discontinuity is usually called a ‘non-conformity’.

Another reason for stratigraphic discontinuity is tectonic deformation. When tectonic plates move apart or together, the forces created can cause the underlying strata to break and slide down against one another. This can cause a substantial jump between the layers, as well as a noticeable break that looks like a ‘platform’. This type of discontinuity is called an ‘unconformity’.

Finally, a third type of stratigraphic discontinuity can occur due to eolian erosion or marine erosion. These processes can gradually erode away the tops of stratigraphic layers, leaving a platform-like surface with a gap between the remaining layers. This type of discontinuity is known as an ‘erosion surface’.

No matter what causes it, stratigraphic discontinuity is an important feature of the sedimentary record that can tell us a lot about how the rocks and sediments were formed and how they have changed over time.