The White Cliffs of Dover facing the English Channel in Southeastern England are a part of a prominent chalk deposit that “underlies large portions of southern England as well as parts of northern France.”  Rising to a height of about 350 feet, the cliffs extend for about 8 miles along the English coast.  Chalk is formed from the calcium carbonate shells, called coccoliths, of coccolithophores, a type of algae that is still abundant in the seas today. Coccolithophores live in the upper layers of the ocean and when they die their shells slowly settle and accumulate in the ocean floor sediments. Like all forms of limestone, chalk is extremely pure calcium carbonate. French chalk ranges from 90 to 98% calcium carbonate and Kansas chalk is 88 to 98%.  Impurities in the cliff include “horizontal bands of dark coloured flint which is composed of the remains of sea sponges and other siliceous planktonic microorganisms...”
The purity of the chalk creates a problem for conventional geologists. Sea sediments measured today do not contain coccolith percentages anywhere close to the purity in chalk. Coccolith contents in ocean floor sediments are 5 to 33% by weight in the Atlantic and 4 to 71% in the Indian Ocean.  The purest chalky marine sediments today are being formed in deep oceans far away from land runoff contamination. But there is abundant evidence that the chalk was deposited and preserved in shallow water.   So why is the chalk so pure in these cliffs if “The present is the key to the past” as has been the guiding motto of conventional geology for the last 200 years? [a] One proposal speculates that the chalk’s purity resulted from a non-seasonal climate, probably arid, causing reduced erosion of nearby exposed rock.  This proposal, leads to a rate of deposition and duration problem.
Geologists conventionally estimate based on the current rates of deposition that it takes 100,000 years to produce three feet (one meter) of chalk.   At this rate, just considering the 350-foot-high portion of the White Cliffs of Dover’s chalk above sea level, it would take around 11.67 million years to form this cliff. But in millions of years, it is very difficult to imagine “how mud or sand could have been prevented from being washed in and mixed with it.”  Chalk purity therefore strongly supports rapid accumulation of chalk.
Rapid chalk accumulation is further supported by the preservation of macrofossils buried in chalk. Macrofossils common in chalk include belemnites, bryozoans, echinoids, bivalves, brachiopods, serpulids and sponges.”  These “must have been rapidly buried to account for their excellent preservation.”  Again considering the conventional estimated rate of chalk disposition, it equates to 0.01 mm per year, 1 mm per 100 years, 1 cm (0.4 in) in 1,000 years and 10 cm (3.9 in) in 10,000 years; this is obviously magnitudes too little to protect these fossils from deterioration by burial.
Not so common are the larger animal fossils found in chalk. In Europe, Mosasaur skulls were found in a chalk quarry in Maastricht, Netherlands.  “The western Kansas chalk beds” of North America include “largely complete fossils of giant swimming and flying reptiles known as mosasaurs..., plesiosaurs..., and pterosaurs ... as well as fossils of aquatic birds with teeth, 20-foot-long fish, and clams ... up to six feet in diameter.”  Also, found fossilized in the Kansas chalk beds is “the voracious predatory fish Xiphactinus audax, 13 feet (4 m) long with a nearly perfectly preserved 6-foot-long (1.8 m) fishGillicus orcuatus inside it.”  “To fossilize such large creatures, ginormous amounts of sediments had to bury them instantly before the creatures had time to escape. Fish are known to decompose quickly unless they are completely buried within a few days. Yet the fish found fossilized in the chalk beds show no signs of decay” 
How could such massive amounts of chalk be generated so rapidly? Coccolithophore concentrations vary depending on environmental factors. Intense white water coccolith blooms are known today in which numbers increase by two orders of magnitude.  Although these factors are poorly understood, suggested reasons for calcareous algae bloom rates to explode in number include turbulent conditions, warm water, high concentrations of calcium carbonate and nutrients. 
All the above conditions could easily have occurred in conjunction with the worldwide flood described in the Book of Genesis. This cataclysmic flood’s origin is described as follows:
“In the six hundredth year of Noah’s life, in the second month, the seventeenth day of the month, the same day were all the fountains of the great deep broken up, and the windows of heaven were opened. And the rain was upon the earth forty days and forty nights.” Genesis 7:11
This account implies that there were enormous quantities of water within the earth’s crust and/or mantel and in the upper atmosphere before the flood. It is likely that the “fountains of the great deep” also referred to volcanic eruptions and magmatic releases. These subterranean sources coming from the great deep would have significantly warmed the oceans and atmosphere. Violent eruptions could have greatly increased the oceanic turbulence including causing tidal waves.
A turbulent ocean will capture carbon dioxide and nitrogen from the atmosphere. The torrential rain lasting 40 days and nights as described in Genesis would have added to the flood waters a significant amount of nitrogen and carbon dioxide captured from the atmosphere. Also, the volcanic emissions would have added huge quantities of hot gases including water vapor (the most abundant of these gases), carbon dioxide, sulfur dioxide, hydrogen sulfide and hydrogen halides.  The decay of massive amounts of plants and animals killed during the flood would have also supplied to the flood waters large amounts of carbon dioxide and nutrients including calcium and nitrogen.
The Genesis flood could therefore have supplied all the necessary conditions for explosive coccolithophore blooms including warmth, high quantities of carbon dioxide and calcium to form calcium carbonate plus other nutrients such as nitrogen. Very large quantities of almost pure chalk could then have conceivably been laid down very rapidly.
[a] What does “The present is the key to the past” mean and is it true? It generally is the idea that the slow rates of physical processes we experience today are the same rates that have always occurred in the past. This concept is known as uniformitarianism and is an unproveable assumption using questionable interpretations (flawed logic) to date ancient sedimentary geological features. Recently, many geologists have begun to move from a strict uniformitarian view recognizing that some geological features are the result of catastrophic events.
(a) Traveler100, CC BY SA 3.0, via Wikimedia Commons
(b) James St. John, CC BY 2.0, via Wikimedia Commons
(c) A Guide to Reptile Fossils and Fishes in the Department of Geology and Palaeontology in the British Museum (Natural History), (London: Harrison and Sons, 1896), 29
(d) Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC, NASA photo, Jun. 15, 2004
 Lutgens, Frederick and Tarbuck, Edward, Essentials of Geology, 9th Ed., (Upper Saddle River, New Jersey: Pearson Prentice Hall, 2006), 136
 White Cliffs of Dover, Wikipedia
 Snelling, Andrew, Earth’s Catastrophic Past: Geology, Creation & the Flood, Volume 2, (Dallas, Texas: Institute of Creation Research, 2009), 925
 The Geology of the Cliffs of Dover, The White Cliffs of Dover, cliffs of dover.com, viewed Jan. 5, 2022
 Snelling, Ibid.
 Garner, Paul, Set in Stone Evidence for Earth’s Catastrophic Past, Truth in Science, dvd
 Ineson, J.R.; Stemmerik, L and Surlyk, F, Sedimentary Rocks/ Chalk, Encyclopedia of Geology, 2005, 42-50
 Chalk, Wikipedia, viewed Jan. 10, 2020
 Snelling, Ibid.
 Garner, Ibid.
 Ineson, Ibid.
 Garner, Ibid.
 Mosasaur, Wikipedia, viewed Jan. 11, 2022
 Chalk, Kansas Geological Survey, University of Kansas, viewed Jan. 10, 2022
 Snelling, Andrew, Chalk It Up to a Global Flood, 6-19-2016, http://answersingenesis.org/bios/andrew-snelling/
 Snelling, reference 3, 927
 Snelling, Andrew, Can Flood Geology Explain Thick Chalk Beds?, Journal of Creation 8(`1):11-15, April 1994
 Garner, Ibid.
 Volcanic gases can be harmful to health, vegetation and infrastructure, USGS, viewed Jan. 19, 2022