There are many colors of sand. Where do these colors come from?

Although the desert is not as colorful as the humid area, it is not completely monotonous.

Different deserts have different colors. For example, between the sand dunes on the south bank of Ebinur Lake, the thick black sand seems to be a wide "asphalt road" paved in the desert; The sand dunes on the shore of Lake Ulungu are like salt deposits, and the sparkling flowers are dazzling; The sand dunes near the Gobi desert reveal the earth color of red soil in taupe. In addition, various plants that grow and bloom in different regions and seasons put colorful coats on the desert.

Why are deserts colorful? In fact, it is the color of sand itself that constitutes the basic color of desert; In addition to the taupe main color, there are red, orange, yellow, green, blue and purple, and all kinds of particles are available. When the sun shines on the sand containing mica particles, it will also reflect dazzling brilliance. Why does sand have such rich colors?

Seasonal and feldspar are the main components of sand, but the proportion is small; Although the content of heavy minerals in sand is small, there are many kinds. In the desert of China, amphibole, epidote, metallic minerals and garnet are the main heavy minerals. From the names of epidote, garnet, kyanite, rutile, biotite and muscovite, we can already imagine their colors. It is these mineral-rich colors that give sand a colorful side. In the Taklimakan desert, mica content accounts for almost 65,438+0/5 of the total mineral weight; In other deserts in China, mica content generally accounts for less than 3% of the total heavy minerals, so Taklimakan always gives people a "sparkling" feeling.

Many deserts in the world are named after the color of sand. For example, the Karakum Desert (Black Desert) in Central Asia has a complex mineral composition, reaching more than 40 kinds. The mixing of various minerals makes the Karakum desert have a strong color, so it is called "Kara" (black). Another desert in Central Asia, the Kizilkum Desert (Red Desert), is mainly composed of broken cuttings and residues deposited in red soil, hence the name "Qizil" (Qizil).

After learning about colorful deserts, let's take a look at two important periods of Taklimakan Desert in China-Red Desert Period and Yellow Desert Period. They are only divided by color, because they reflect the synchronization of Taklimakan desert evolution and global climate and environmental changes. This is the latest knowledge summed up by researcher Dong Guangrong, a Quaternary geologist and vice-captain of Taklimakan desert scientific expedition team, and his colleagues after years of research.

Debate on the age of Taklimakan Desert There are different opinions about the age of Taklimakan Desert. The authoritative desert scientist in China and the former researcher of Lanzhou Desert Research Institute of China Academy of Sciences believe that the Taklimakan Desert was formed and developed since the middle Pleistocene in the Quaternary, which means that it is only1.4000 years old. This understanding has long been accepted and recognized by most scholars. However, since 1980s, some petroleum geologists and paleontologists have put forward different opinions. They believe that the Taklimakan Desert was formed in Miocene or Pliocene of Tertiary, and this inference raised the age of the desert to 1 20-25 million years. Even the more conservative ones believe that the Taklimakan Desert was formed at least in the early Pleistocene of Quaternary, that is, 654.38+0.2 million years ago. However, a few people think that the Taklimakan Desert was formed at the end of the late Pleistocene or even the Holocene, with an age of only 1 10,000 to 20,000 years.

According to the above statement, the age of Taklimakan desert is more than 2000 times that of 1 10,000 years to more than 20 million years. Who is more accurate?

First of all, it should be explained that the formation and evolution of desert environment is different from the development stage of desert landform. The age of the former can be very early, and the age of the latter is very different due to different stages of landform development. For example, the Silk Road and towns in the Taklimakan desert were in a desert environment at that time, but the location could not be called a desert, otherwise people would not build towns there. However, after these places were abandoned, many of them have been lost in the wind and sand and become real deserts. Their history of formation and development is only a few hundred to several thousand years. In addition, due to different reasons, even in the same area, there may be many times of desert development history, but this desert is not another desert. The two development periods of Taklimakan Desert are two completely different deserts, which are quite different in matrix and appearance.

Researchers' understanding of the formation age of Taklimakan Desert in Red Desert and Yellow Desert has made a big step forward compared with predecessors. His upper limit extended to the last period of Mesozoic-the late Cretaceous, that is, 97.5-65 million years ago. At this time, scattered deserts have been distributed on the banks, lakes and coasts of Tarim Basin. After entering the Cenozoic Tertiary, the desert further expanded and activated. After entering the Quaternary, the desert began to shrink. After the Middle Pleistocene 654.38+400 million years ago, aeolian clay silt was widely developed and the desert was further expanded. Although in the past 65438+ million years, the development of desert has experienced many iterations, but the general trend is continuous expansion, and finally formed today's pattern.

In order to clearly explain the changing history of Taklimakan Desert, the researchers divided the formation and development of Taklimakan Desert into pre-Quaternary and Quaternary. Pre-Quaternary is a period before Quaternary, including Late Cretaceous of Mesozoic and Tertiary of Cenozoic, with a time span of 95 million years. The time span of Quaternary is 2.5 million years.

In the pre-Quaternary, the global temperature dropped, the environment in Taklimakan changed from subtropical and tropical to tropical and warm temperate, the climate became more arid, the vegetation gradually changed from savanna to desert grassland, and the desert gradually formed, mainly showing the nature of fixed and semi-fixed grassland desert. Because the sediments at this time are mostly purplish red or brownish red substances rich in gypsum, mirabilite and calcium nodules, the desert appearance is mainly red, so it is called "red desert period".

With the further decline of global temperature, the climate of Taklimakan changed to temperate zone after Quaternary, and changed from warm temperate zone to cold temperate zone with the fluctuation of ice age. The trend of drought has further developed, forming a warm-dry and cold-dry climate combination with "dryness" as the basic feature, which is very different from other parts of the world, such as the warm-wet, cold-dry combination in monsoon area and the cold-wet, warm-dry combination in westerly area, indicating the drought characteristics in this area. At this time, the desert changed from grassland type to desert type, and the quicksand gradually increased and the scale was also expanding. It is also called "yellow desert period", because the color of aeolian sand and primary aeolian clay silt that provide deposition is brownish yellow, which makes the desert appear yellow theme tone.

It seems that it is not entirely unreasonable to think that the Taklimakan Desert was formed since Holocene.

According to the dating of quartz sand collected from the underlying surface of mobile sand dunes in the hinterland of Taklimakan desert, it is proved that in the early Holocene, large-scale river and lake deposits appeared in the hinterland of the desert, and the desert should be in the stage of contraction and transformation to immobilization. After the Middle Holocene, with the strengthening of wind-driven activities, sandstorm accumulation entered a vigorous period, and modern tall mobile sand dunes were formed during this period, only four or five thousand years ago. And the big sand dunes on the old channel of Tarim River are only 500 years old.

According to this, it can be considered that Taklimakan is ancient in terms of the history of desert formation, with a history of nearly 100 million years; As far as the formation of modern sand dunes is concerned, Taklimakan is young and may bring us more surprises and discoveries in the future.