Normal Fault at Blue Anchor Bay

Normal fault at Blue Anchor Bay, Somerset, showing Triassic Mercia Mudstone (red, continental) faulted against Jurassic marine strata (grey) – capturing the continental-to-marine transition.

The normal fault at Blue Anchor Bay in Somerset is a striking geological feature that highlights the transition from Triassic continental deposits to Jurassic marine sediments.

Key Features:

Triassic Mercia Mudstone (Red, Continental):

• Formed in arid to semi-arid continental environments (playa lakes, floodplains).
• Distinctive red coloration due to iron oxide (hematite) from oxidizing conditions.
• Represents a time when the area was part of the vast Pangaea supercontinent, far from the sea.

Jurassic Marine Strata (Grey):

• Deposited in shallow marine environments as sea levels rose (Early Jurassic).
• Includes limestones, shales, and clays rich in marine fossils (ammonites, belemnites).
• Marks the flooding of the region due to tectonic subsidence and global sea-level rise.

Normal Fault:

Shows vertical displacement where the Mercia Mudstone has been downthrown against younger Jurassic rocks.

Reflects crustal extension, possibly related to the opening of the Atlantic Ocean or later tectonic activity.