Question

what is the difference between a marine transgression and a marine regression? what environmental factors cause this type of change to occur? your answer

Explanation:

1. Difference between Marine Transgression and Marine Regression:

• Marine Transgression: It is a geological process where the sea level rises relative to the land, and the shoreline moves landward (inland). This results in the sea covering more of the continental shelf, and sedimentary deposits (like shale, limestone) that are typically marine in origin are laid down over previously non - marine (such as terrestrial or fluvial) deposits.
• Marine Regression: In contrast, this is when the sea level falls relative to the land, and the shoreline moves seaward. As a result, non - marine (e.g., fluvial, deltaic, terrestrial) sedimentary deposits are laid down over previously marine deposits.

1. Environmental Factors Causing These Changes:

• For Marine Transgression:
• Eustatic (Global) Sea - Level Rise: This can be caused by the melting of large ice sheets (e.g., during interglacial periods when ice from glaciers melts, adding more water to the oceans). Another cause is thermal expansion of seawater as the Earth's climate warms; warmer water occupies more volume, leading to a rise in sea level.
• Tectonic Subsidence: If the landmass itself sinks (subsides) due to tectonic activity (e.g., in areas with active continental rifting or where the crust is being stretched), the relative sea level will rise even if the global sea level remains constant.
• For Marine Regression:
• Eustatic Sea - Level Fall: This can occur during glacial periods when large amounts of water are locked up in ice sheets on land, reducing the volume of water in the oceans. Also, if the Earth's climate cools, seawater can contract (thermal contraction), leading to a drop in sea level.
• Tectonic Uplift: When the landmass is uplifted due to tectonic forces (e.g., mountain - building events like orogenies), the relative sea level falls as the land rises above the ocean surface. Additionally, the accumulation of sediment in coastal areas (sedimentation) can cause the sea floor to rise, effectively leading to a relative fall in sea level with respect to the land.

Answer:

• Difference: Marine transgression is the landward shift of the shoreline due to rising sea - level (marine deposits over non - marine), while marine regression is the seaward shift due to falling sea - level (non - marine deposits over marine).
• Environmental Factors:
• Transgression: Eustatic sea - level rise (glacial melt, thermal expansion), tectonic subsidence.
• Regression: Eustatic sea - level fall (glacial formation, thermal contraction), tectonic uplift, sedimentation.