20. Cretaceous Period

66 Million Years Ago

Sediments, Extinction

Cretaceous 145 Mya - Name derived from Latin creta (chalk) from extensive chalk beds

The Cretaceous period was the last and longest period of the Mesozoic era, spanning approximately 79 million years from 145 million to 66 million years ago. It was a time of significant change on Earth, marked by the gradual breakup of the supercontinent Pangaea and the evolution of many new plant and animal species.

One of the most notable features of the Cretaceous period was the proliferation of dinosaurs, which were the dominant terrestrial animals during this time. The Cretaceous saw the evolution of many new species of dinosaurs, including the fearsome Tyrannosaurus rex and the iconic Triceratops. Many other reptiles, such as crocodilians, turtles, and pterosaurs, also thrived during this period.

In addition to the dinosaurs, the Cretaceous was a time of rapid diversification for many other types of organisms, particularly marine invertebrates. The oceans were home to a wide variety of creatures, including ammonites, belemnites, and rudists, which left behind a wealth of fossils that provide important insights into the evolution of life on Earth.

The climate of the Cretaceous period was generally warm and humid, with high levels of atmospheric carbon dioxide leading to higher temperatures and more rainfall. This climate was favorable for the growth of lush forests and the evolution of many new plant species, including flowering plants (angiosperms), which began to dominate terrestrial ecosystems during this time.

Towards the end of the Cretaceous period, significant changes began to occur that would eventually lead to the extinction of the dinosaurs and many other species. These changes included a cooling and drying of the climate, as well as the impact of a massive asteroid that struck the Earth approximately 66 million years ago, triggering a mass extinction event that wiped out more than 75% of all plant and animal species on Earth.

Physics of the impact

GEOLOGY - Chalk Beds, Calcareous Ooze and Calcium Carbonate (CaCO3)

The chalk beds of the Cretaceous period refer to extensive layers of sedimentary rock made up of calcium carbonate (CaCO3) that were deposited during the Late Cretaceous period, approximately 100 to 66 million years ago. These chalk beds are widespread across many regions of the world, including Europe, North Africa, and North America.

The deposition of the chalk beds was the result of the accumulation of tiny marine organisms, such as planktonic algae, foraminifera, and coccolithophores, which produced hard skeletal structures made of calcium carbonate. As these organisms died, their remains sank to the ocean floor and were compacted and cemented together over time, forming the chalk rock.

The chalk beds of the Cretaceous period are of particular interest because they contain a wealth of information about the ancient environment and the evolution of life on Earth. For example, they provide valuable insight into the ocean chemistry and climate of the time, as well as the diversity and distribution of marine organisms.

In addition, the chalk beds have played an important role in human history, as they have been used for a variety of purposes, including building materials, art, and agriculture. The famous White Cliffs of Dover in England, for example, are made up of Cretaceous chalk beds, and have been an important landmark for mariners for centuries.

calcareous ooze is a type of biogenous sediment that is composed of the calcium carbonate (CaCO3) skeletons and shells of marine organisms such as foraminifera, coccolithophores, and pteropods.

When these organisms die, their remains sink to the ocean floor and accumulate over time, forming a layer of sediment. The calcium carbonate in their shells and skeletons is particularly resistant to dissolution, so it tends to accumulate in areas where the rate of sedimentation is high and the rate of dissolution is low, such as in deep ocean basins.

Calcareous ooze can be found on the ocean floor at depths greater than 4,500 meters (14,764 feet) and covers approximately 48% of the ocean floor. It is particularly common in regions of the ocean that have a high rate of biological productivity, such as in upwelling zones, where nutrient-rich waters rise from the deep ocean to the surface and support large populations of phytoplankton and other organisms.

Calcareous ooze can provide important clues about past ocean conditions and climate, as well as the evolution of marine life, as it is often found in association with other types of sedimentary rock and can be dated using a variety of techniques.

LOCAL GEOLOGY

Niobrara Chalk in Kansas

Austin Chalk of central Texas

The Western Interior Seaway was a large inland sea that covered a vast area of North America during the Late Cretaceous period, approximately 100 to 66 million years ago. The seaway stretched from the Arctic Ocean in the north to the Gulf of Mexico in the south and separated the western portion of North America from the eastern portion.

The Western Interior Seaway was formed as a result of the gradual separation of North America from other continents during the Mesozoic era, which created a series of shallow basins and troughs that were gradually flooded by seawater. The seaway was a shallow and relatively warm body of water that was home to a diverse range of marine life, including ammonites, belemnites, mosasaurs, and a variety of bony fish and invertebrates. The seaway had a significant impact on the development of life in North America, as it created a barrier that isolated different populations of organisms and allowed for the evolution of many unique species. It was also an important habitat for numerous species of planktonic organisms, which formed the basis of the marine food web. It also had a major influence on the deposition of sedimentary rock in the region, with thick layers of sandstone, shale, and limestone accumulating in the seaway over millions of years. The combination of organic material combined with sedimentary rocks result in the formation and storage of hydrocarbons which are an important resource of the region.

The Western Interior Seaway began to recede during the Late Cretaceous period, as the land began to rise and the seaway gradually drained into the surrounding oceans. This drainage event is thought to have played a significant role in the extinction of the dinosaurs and many other species, as the changing sea levels and climate disrupted ecosystems and led to widespread extinctions.

K-Pg Boundary - End of the Cretaceous

A Closer Look at The Deccan Traps

is a large volcanic province located in west-central India that covers an area of over 500,000 square kilometers. The term "traps" refers to the step-like topography that is characteristic of the region.

The Deccan Traps are composed of multiple layers of flood basalt, which are massive outpourings of lava that occurred over a period of several million years during the late Cretaceous and early Paleogene periods, around 66 to 60 million years ago. The volcanic activity that produced the Deccan Traps is thought to have been related to the rifting of the Indian subcontinent from the rest of Gondwana and the subsequent opening of the Indian Ocean.

The Deccan Traps are one of the largest volcanic provinces in the world, and the volcanic activity associated with the formation of the Deccan Traps is thought to have played a significant role in the mass extinction event that occurred at the end of the Cretaceous period, along with the impact of an asteroid at the Chicxulub crater in Mexico.

The Deccan Traps have been extensively studied by geologists and paleontologists, and are of particular interest because of their role in the evolution of life on Earth. The massive outpourings of lava associated with the Deccan Traps would have had a significant impact on the environment, causing changes in climate, sea level, and atmospheric composition that may have contributed to the extinction of the dinosaurs and other groups of organisms at the end of the Cretaceous period.

Large igneous provinces (LIPs)

Also known as large volcanic provinces (LVPs), are massive regions of volcanic and/or intrusive rock that are believed to have formed by intense and sustained volcanic activity over a geologically short period of time, usually several million years or less. LIPs are considered to be among the largest features on Earth's surface, covering areas that can range from tens of thousands to millions of square kilometers.

LIPs are typically associated with large-scale tectonic events such as continental rifting, mantle plume activity, or subduction zone magmatism, and are thought to represent some of the most extreme and voluminous expressions of magmatism on Earth. They are often characterized by the emplacement of huge volumes of magma into the Earth's crust and the extrusion of vast quantities of lava onto the surface, leading to the formation of massive basaltic plateaus or flood basalts.

The formation of LIPs can have significant impacts on the environment, including the release of large amounts of volcanic gases and aerosols that can alter atmospheric composition, cause climate change, and trigger mass extinction events. LIPs have been implicated in several major extinction events throughout Earth's history, including the end-Permian extinction, the end-Triassic extinction, and the end-Cretaceous extinction.

Despite their size and importance, many aspects of LIP formation and evolution remain poorly understood, and ongoing research is focused on unraveling the complex interactions between tectonic, magmatic, and environmental processes that give rise to these massive features. They have occurred frequently in earth’s history, below is a list of the most significant LIPs around the world from oldest to youngest.

  • Franklin Large Igneous Province (Late Devonian to Early Carboniferous, around 375 million years ago)

  • Emeishan Traps (Late Permian, around 260 million years ago)

  • Siberian Traps (Permian-Triassic boundary, around 252 million years ago)

  • Karoo-Ferrar LIP (Late Permian to Early Jurassic, around 252 to 183 million years ago)

  • Central Atlantic Magmatic Province (Triassic-Jurassic boundary, around 200 million years ago)

  • Viluy Traps (Jurassic, around 165 to 160 million years ago)

  • Ontong Java Plateau (Late Jurassic to Early Cretaceous, around 160 to 120 million years ago)

  • Parana-Etendeka LIP (Late Jurassic to Early Cretaceous, around 140 to 120 million years ago)

  • Maranhão Basin (Early Cretaceous, around 130 million years ago)

  • Kerguelen Plateau (Late Cretaceous to Early Eocene, around 118 to 35 million years ago)

  • Madagascar LIP (Late Cretaceous to Early Eocene, around 90 to 40 million years ago)

  • Deccan Traps (Late Cretaceous, around 66 to 60 million years ago)

  • North Atlantic Igneous Province (Paleocene to Eocene, around 60 to 55 million years ago)

  • Columbia River Basalt Group (Miocene, around 17 to 14 million years ago)

  • Chilcotin Group (Early to Middle Miocene, around 20 to 10 million years ago)