Lower Cretaceous facts for kids
The Lower Cretaceous was the first part of the Cretaceous Period. It's a huge chunk of time in Earth's history, like a long chapter in a very old book! This epoch started about 145 million years ago and finished around 100.5 million years ago. That means it lasted for about 46 million years. It's actually the longest part of the entire Phanerozoic eon, which is an even bigger division of time!
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Ancient Environments in England
Scientists can learn a lot about the Lower Cretaceous by studying rocks in England. Here, the rocks show us two main types of environments that existed back then. Between these two times, the sea level changed a lot!
The Wealden Beds: Rivers and Lagoons
The older rocks from this time are called the Wealden Beds. These rocks formed in places with either freshwater (like rivers) or brackish water (a mix of fresh and salty water, like in estuaries).
- Sand from the Wealden Beds came from the wide floodplains of a giant tropical river. This river had many channels, like a braided rope.
- Clay in these beds formed in coastal lagoons, which are shallow bodies of water separated from the sea by sandbars.
The Greensands and Gault Clay: Deeper Seas
Later in the Lower Cretaceous, the environment changed. The younger rocks are called the Greensands and the Gault Clay.
- The Greensands are a type of sandstone that looks olive-green. These rocks were laid down in the sea, showing that the area was covered by water.
- The Gault Clay is a thick, blue clay. It formed in a calm, fairly deep part of the ocean. This clay sits on top of the Lower Greensand.
Sea Level Changes
The different types of rocks from the Lower Cretaceous tell us a lot about how sea level changed. During the early part of the Lower Cretaceous (when the Wealden Beds formed), the sea level was much lower. Southern England was a huge river delta in a tropical area. Later, when the Greensands formed, these same areas were just off the coast.
However, in the Upper Cretaceous (the next part of the Cretaceous Period), the sea level rose even higher. The rocks from that time were laid down in much deeper water, on what was then the continental shelf. The sea level during the Upper Cretaceous was the highest it had been in the entire Mesozoic Era!
See also
In Spanish: Cretácico inferior para niños
