Quaternary geological history is an integral part of the history of general natural environment change in Quaternary, which is controlled by the history of general natural environment change. Therefore, the geological and historical characteristics of the Quaternary are also an aspect of the general natural environment characteristics of the Quaternary, and are also determined by the general natural environment characteristics of the Quaternary. The basic characteristics of Quaternary geological history are as follows:
(1) The geological historical records are relatively complete.
Because the Quaternary period is very short, the results of various geological processes in Quaternary, that is, geological phenomena such as Quaternary topography, sediments and their biological remains, geological structures, magmatic rocks and related natural phenomena, are well preserved; Moreover, most of these phenomena are distributed on the surface or near the surface, which is easy to observe and study, thus contributing to the restoration of Quaternary geological history. In addition, various geological processes currently under way are a continuous process of Quaternary geological history, so we can directly study these processes and related phenomena, and make a more accurate analogy to trace the Quaternary geological history.
Major climate change
Another basic feature of Quaternary geological history is the remarkable climate change. The process of climate cooling since the Late Tertiary was obviously strengthened in the early Quaternary. The Quaternary climate change largely controlled the occurrence and development of Quaternary topography, sea surface changes, sediments, soil, biological communities and even human beings. Therefore, since the middle of the last century, geologists have always regarded the remarkable cooling of climate and the appearance of glaciers in vast areas of the earth's surface as a major symbol of dividing the Pliocene and Pleistocene boundaries. And this boundary is the boundary between Neogene and Quaternary.
Figure 1-2 only shows the climate change in the early Quaternary. As can be seen from the figure, although the tertiary climate has changed, it is not as obvious as the quaternary.
The research proves that the temperature changes greatly in Quaternary, and there are repeated processes of cooling and heating. Quaternary temperature changes are global, but there are differences in different latitudes and regions. The most obvious temperature change is in the mid-latitude zone, and the change range is small at the poles and near the equator. The maximum average temperature difference between cooling period (cold period) and heating period (warm period) in Quaternary is calculated as 16-25℃.
In the cold period, in the humid area, the snowfall exceeds the snowmelt, and the snowfall has accumulated for many years, and some of it melts and compacts, becoming glaciers. The period when glaciers appeared on a large scale on the earth is called the ice age. Glaciers first appeared at the top of mountains in polar regions, middle latitudes and even low latitudes. With the climate getting colder, the thickness of glaciers is increasing, and its distribution range is also expanding to the surrounding areas. This process is called ice propulsion. During the ice age, the maximum scale of glaciers reached 1/3 of the coverage surface area. The appearance of glaciers further aggravated the cooling of the climate. The calculation shows that the average temperature in the glacier area during the ice age was 8-65438 03℃ lower than that at present.
Figure 1-2 Average temperature changes in tertiary and quaternary in mid-latitude areas (according to Teichmuller)
In the warm period, the climate is 8- 13℃ higher than the current average temperature. Glaciers accumulated during the ice age melted in large quantities during the warm period. At the edge and end of the glacier, the amount of ablation is the largest. Melting makes the thickness of the glacier smaller, shrinking from its edge and end to the center and birthplace of the glacier. The thickness of glaciers continues to decrease, and the edges and ends of glaciers continue to shrink. The melting of glaciers leads to the thinning of glacier thickness, and the process that the edges and ends of glaciers retreat to the center and source is called glacier regression. The total area and volume of glaciers on the land surface are gradually reduced due to the retreat of ice. Due to the continuous process of glacier retreat, glaciers on the land surface disappeared in a large area.
The warm period between two glaciers is called interglacial period.
Holocene glaciers, including now, account for about110 of the land surface area. It is considered that this is the transitional period between glacial period and interglacial period, which is called post-glacial period. The post-glacial climate is in the transitional position between glacial and interglacial periods, which is relatively close to interglacial period.
Quaternary is a period in which glacial and interglacial periods alternate. In order to express this feature, Quaternary is called Ice Age in some geological documents.
Glacial period and interglacial period are the results of large-scale periodic changes of Quaternary climate. In the same ice age, it can also be divided into some smaller climate change cycles, that is, several cooling and heating periods with smaller climate change and shorter time. These periods caused a small range of short-term ice advance and retreat, which is called glacial period or stagal and interglacial period or stagal. Detailed study can further distinguish periodic changes from minor climate cooling and warming, resulting in minor ice advance and ice retreat.
Studies in most parts of the earth believe that there are four distinct glacial periods, three interglacial periods between which there is a post-glacial period in Quaternary. However, there are still different opinions on this issue.
(3) Quaternary biology
According to the data of Quaternary biological remains collected in Quaternary strata, a clear outline of the distribution, classification and development of Quaternary biological world is obtained. These data include the remains of land and marine life. Because the Quaternary period is short, the biological development is not as remarkable as other geological periods, but it has its own characteristics.
The change of Quaternary organisms is caused by the change of Quaternary ecological environment. The change of ecological environment mainly depends on two factors: climate and tectonic movement. Repeated cooling and warming of Quaternary climate led to the alternation of glacial and interglacial periods, which caused the repeated rise and fall of sea level. However, the change of sea surface has caused repeated land and sea changes in a certain range, including the appearance and disappearance of some land bridges. At the same time, the strong Quaternary tectonic movement and related magmatic activity also greatly changed the landing site and ocean topography. All these natural changes have affected the drastic changes in the Quaternary ecological environment.
The change of Quaternary ecological environment caused the migration, recombination and morphological variation of Quaternary organisms, as well as the extinction of some species and the emergence of some new species.
Because the change of ecological environment varies from region to region and the adaptability of Quaternary organisms is also different, the change of Quaternary organisms is unbalanced between regions and categories.
Quaternary climate change and its accompanying ecological environment change are zonal phenomena at different latitudes. This change is more obvious in the mid-latitude region than in the polar and equatorial regions; And the changes on land are more obvious than those in the ocean. Therefore, the changes of Quaternary organisms are more obvious in mid-latitude, high-latitude and low-latitude areas. The change of terrestrial biota is more significant than that of marine biota.
The changes of Quaternary marine biota are mainly manifested in geographical distribution and combination. In addition to the changes in distribution and combination, there have been significant morphological variations, some species have become extinct and some new species have emerged. In the Quaternary offshore and ocean, the change of marine biota is very small; This change is obvious in some inland seas or closed basins, such as the Black Sea, the Baltic Sea and the Mediterranean Sea.
The research of Quaternary marine biota is mainly invertebrates and micro-animals. The history of marine invertebrates in Quaternary is a history of settlement and migration, accompanied by the extinction and regeneration of some species. This conclusion is mainly inferred from the study of inland waters such as the North Sea and the Mediterranean Sea. The Mediterranean Quaternary fauna is basically similar to the present fauna, and there are some exotic species of distant northern cold-loving animals, which shows the migration of Quaternary marine animals.
Quaternary terrestrial biota is obviously affected by climate change. Although the Quaternary terrestrial biota migrated, recombined, died out, regenerated and mutated during the alternation of glacial and interglacial periods, their reactions in vertebrates, invertebrates and plants were different.
In an area, when the climate becomes unsuitable for animals to live, the change of animals from warm period to cold period or from cold period to warm period is usually due to their slow and continuous migration to more favorable residential areas. Different animal distribution changes are caused by mixed living. When the glacier shrinks and disappears, some members of periglacial fauna, an ice species living near the ice sheet, migrate in the direction of glacier retreat; However, other members remain in place and become part of non-glacial animals. When glaciers occur and expand, cold-loving fauna appears, and its distribution expands with the ice, so the fauna in non-glacier areas contains exotic species left over from glacier fauna. During the alternation of Quaternary glacial and interglacial periods, the mixing process of this fauna was repeated many times, so that there were some mixed components in the mammalian fauna of general glacial and interglacial periods.
The formation of the characteristics of Quaternary land plants Group is more due to the repeated migration of the poles to the equator than the evolution of the plants themselves. Quaternary glaciation interrupted the development of polar flora, and the flora recovered during the interglacial period.
In the mid-latitude zone, the glaciers in the ice age are not continuous, but scattered, isolated and polycentric. The climate in mid-latitude glacier area is not conducive to plant growth. Therefore, the flora of each region changes greatly. The general trend of ice age is that the flora in the mid-latitude zone migrated to the equator; During the interglacial period, the flora returned from the equator to the poles.
Near the equator, Quaternary climate change has little effect on flora.
Because the migration of flora is slow and difficult, some plants can't return to the original zone during the alternation of Quaternary Glacial Period and Interglacial Period, and some plants mutate in order to adapt to the new climate environment. The other part couldn't adapt to the new environment, so it became extinct.
Generally speaking, plants and invertebrates have poor adaptability, slow migration, easy extinction and variation, and their fossils are sensitive to climate; Mammals, especially terrestrial mammals, have strong adaptability and fast migration speed, so they are insensitive to climate. Therefore, in some cases, although we can infer the Quaternary climate environment from a single plant species, we cannot simply do so for mammals. We must study the characteristics of the whole mammal population to reduce the error of different species' response to climate. During the Quaternary Glacial and Interglacial Periods, the flora of most mammals was as complicated as it is now. For example, in a single stratum in the same place, mixed grassland and tundra fauna can appear, and forest animals can also be included.
Biota is generally continuous, but it can also be discontinuous due to the interference of ice age. This is also a feature of Quaternary biology.
(4) Basic characteristics of Quaternary sedimentary environment
1. Continental Sedimentary Environment The emergence and disappearance of Quaternary glaciers formed three sedimentary environments in the mainland, namely, glacial environment, periglacial environment and non-glacial environment. In every environment, there are some specific sedimentary processes and symbiotic combinations of sediments.
(1) Glacier environment Glacier environment refers to the environment of glacial areas in the Quaternary Glaciation and Post Glaciation. In the glacial environment, there is a denudation and deposition system dominated by glaciation, including wind, mechanical weathering, gravity, denudation and accumulation of glaciers and ice water. In this environment, the above processes form a symbiotic combination of aeolian deposition, mechanical residue, gravity deposition, glacier deposition and ice water deposition.
(2) Periglacial environment Periglacial environment refers to the cold environment around the Quaternary glacier or outside the glacier area. The geological processes of this environment include freezing and thawing, mechanical weathering, biological erosion and accumulation, ice water, lakes and swamps, wind and mud (stone) flows, etc. The deposits formed by these actions include frozen soil, mechanical residues, mud (stone) flow deposits, biological deposits, lake deposits, wind deposits and so on.
(3) Non-glacial environment Non-glacial environment refers to an environment without glaciers in vast inland areas during interglacial and post-glacial periods. During the ice age, this kind of environment can also appear in the warmer low latitudes during the ice age. Non-glacial environment can be divided into cold and wet areas, arid areas and hot and humid areas.
In cold and humid areas, glaciation occurred in Quaternary glaciers. However, in the interglacial and post-glacial periods, with the warming of climate, the disappearance of glaciers and the thawing of frozen soil, the erosion and deposition environment similar to that before the glacial period was restored again. Running water, lakes and swamps, biological and chemical weathering developed, which transformed sediments during the ice age and formed a symbiotic combination of sediments with warm and humid climate characteristics. These include alluvial sediments, lacustrine sediments and biological sediments (peat, humus mud, etc.). ) and chemical residues. In addition, the violent action of organisms on Quaternary loose deposits during this period also formed soil layers. This symbiotic combination and soil layer of Quaternary sediments in non-glacial environment can also appear in the low latitude zone of Quaternary glacial period.
In areas with Quaternary glacial periods, the alternation of glacial periods and interglacial periods leads to the alternation of interglacial sediments and interglacial sediments (soil).
Arid areas In such areas, even if the climate is cold, Quaternary glaciers cannot be formed due to dryness. Most of these areas are located on the mainland. The relationship between the shore and bottom sediments of many lakes in arid areas, and the relationship between the topography and sediments of these lakes and the topography and sediments of glaciers and ice water show that the periods of lake expansion and contraction correspond to glacial and interglacial periods; The main reasons for the rise of lakes in these areas are the increase of precipitation and the decrease of evaporation. This is the characteristic of the ice age climate in these areas. During the ice age, due to the decrease of temperature and the increase of temperature gradient, the ice sheet formed and expanded in the adjacent areas, the intensity and contact frequency of cold air mass and warm air mass increased, and the precipitation increased. Due to the lower temperature and the temporary scattered snow, evaporation can be reduced. As a result, the amount of water melted by ice and snow increased and the flow of rivers increased. Therefore, in some closed lakes, the water level rises and some waterless arid basins collect water to form lakes. The period of increasing precipitation is called rainy season. Due to the increase of precipitation, it will lead to the increase of floods and the production of a large number of proluvial, so the rainy period is also called rainy period. The period of decreasing precipitation is intermittent rain (drought), which is also called intermittent flood age because of the decrease of drought and flood accumulation. In this way, in arid areas, the rain period (flood period and lake flood period) corresponds to the glacial period, and the intermittent rain period (drought period, flood intermission and lake contraction period) corresponds to the interglacial period and post-glacial period. The above phenomenon is most obvious in the desert areas with dry and non-glacial environment, especially in the desert edge of northern China, Central Asia, North Africa, North and South America and near the equator.
It should be noted that the change of the lake may also be caused by other reasons, including the rise and fall of the crust, fault movement, volcanic activity, erosion and accumulation in the area where the lake basin is located, and so on. Therefore, when studying the changes of lakes, it is necessary to distinguish the changes caused by these reasons from those caused by climate.
Hot and humid areas are hot and humid areas near the equator, and the Quaternary climate became cold, which caused glaciers in local alpine areas. Most areas are generally non-glacial, and the natural environment changes little. The alternation of glacial and interglacial periods in hot and humid areas is characterized by the alternation of rainy periods equivalent to glacial periods and less rainy periods equivalent to interglacial periods. This alternation of rainy and rainy periods in hot and humid areas not only caused the changes of running water and lake sediments here, but also clearly reflected in the residual red soil profile, which is one of the typical sediments in this kind of area. In rainy season, residual red soil develops; In the period of little rain, the development of residual red soil often stops or slows down.
2. Coastal sedimentary environment The research on coastal topography, sediments and biological debris proves that the sea surface experienced many large-scale ups and downs in Quaternary.
There are many reasons for sea level change, including glacial factors and non-glacial factors. Non-glacial control factors include coastal and submarine tectonic movement, magmatic activity, submarine sediment accumulation, seawater temperature change and equilibrium adjustment movement. These factors are not unique to Quaternary, but the special controlling factor of Quaternary sea level change is the alternation of glacial and interglacial periods. During the ice age, a large amount of water was sealed on the land in solid form, and the amount of water flowing from the land to the sea decreased, which led to the decline of the sea surface. On the contrary, during the interglacial period, due to the decrease of snowfall, a large amount of land ice was melted, and the ice melt water returned to the sea, which led to the rise of the sea surface. According to calculation, the sea level can rise by about 50m after the land glaciers melt. During the Quaternary interglacial period, there were basically no glaciers on the land. So the interglacial sea level should be 50 meters higher than the current sea level. The volume and area of glaciers in the Quaternary Ice Age were much larger than now. In the Quaternary Ice Age, the calculated sea level drop can reach 80- 150m.
The alternation of sea level rise and fall controlled by Quaternary glaciers led to the alternation of coastal and shallow sea deposits and land deposits in coastal areas. During the ice age, a part of the coast and shallow sea floor surfaced and deposited continental sediments, including glaciers and ice water sediments, lake sediments, alluvium, aeolian sediments and residual sediments. When the sea level rose during the interglacial period, the terrestrial sediments deposited during the glacial period were submerged by seawater and covered by new coastal sediments and shallow sea sediments. Therefore, in coastal areas, the sequence of glacial deposits and interglacial deposits shows the alternation of regressive deposits and transgressive deposits.
3. Marine sedimentary environment If the records of Quaternary geological events in the mainland are often incomplete or destroyed due to sedimentary discontinuity and erosion, then in some areas of the deep sea and ocean floor, such records are continuous and quite complete. The study of these records proves that the change of marine sedimentary environment is not as drastic as that of continental environment, and the deposition of seawater is continuous to a great extent. However, in many sea areas, Quaternary sediments are disturbed and eroded by turbidity current, collapse, ground slide, submarine current and earthmoving animals on the continental shelf and slope, which will also lead to discontinuous sedimentary sequence of normal marine products and more complicated distribution and types of sediments.
Marine sediments include terrigenous clastic sediments, chemical sediments, organic sediments and volcanic sediments.
Although the alternation of Quaternary Glacial Period and Interglacial Period can't dramatically change the marine environment like the mainland, it affects the marine sedimentary environment. The alternation of Quaternary glaciers and interglacial periods affected the depth, temperature and density of seawater to some extent, thus changing the composition, salinity and living environment of marine life, and then changing the sedimentary environment. In the process of continental ice propulsion, part of seawater is extracted from the ocean and sealed on the continental surface in the form of ice; When the ice recedes and the snow melts, water can return from the mainland to the sea. During the ice age, due to the decrease of seawater temperature, the increase of density and salinity, the increase of chemical deposits and cold-loving organisms, ice raft deposits and ice shelf deposits appeared in land sediments, and some shallow sea sediments contained a large number of ice water deposits. During the interglacial period, due to the increase of seawater, the rise of sea level, the increase of depth, the increase of water temperature, the decrease of seawater density and salinity, and the increase of chemical solubility, the chemical deposits will decrease, and some glacial chemical deposits will even dissolve, and the deposition of thermophiles will increase. In marine sediments, the alternation of glacial and interglacial periods is characterized by the alternation of cold sediments and warm sediments.
(5) Basic characteristics of Quaternary sediments
The history of formation and development of Quaternary sediments is an important part of Quaternary geological history and is controlled by the whole Quaternary geological history. The basic characteristics of Quaternary sediments are determined by the above-mentioned basic characteristics of Quaternary geological history.
Quaternary sediments have the following basic characteristics:
1. Quaternary sediments generally cover the continental surface, and in most cases, they are unconformity or false conformity with the underlying pre-Quaternary strata. At the bottom of the ocean and some lakes, the deposition of Quaternary sediments is continuous with that of pre-Quaternary sediments.
2. The spatial distribution of Quaternary sediments is closely related to modern topography. In steep and concave terrain such as mountains and continental slopes, the distribution of Quaternary sediments is scattered, discontinuous or patchy in the horizontal extension direction. In the land plain, lake basin and sea basin plain, the extension of Quaternary sediments is relatively continuous.
3. Due to the short Quaternary period, in most cases, Quaternary sediments suffered slight erosion and structural deformation. Most Quaternary sediments have basically no structural deformation, and generally retain the original occurrence closely related to topography. The genetic types and ages of Quaternary sediments are closely related to topography.
4. The thickness of Quaternary sediments is related to Quaternary tectonic movement and topographic relief. In the convex terrain with forward movement, the thickness of Quaternary sediments is small, uneven or even lacking. In the low-lying areas where negative movement develops, the thickness of Quaternary sediments is large and uniform, reaching hundreds or even thousands of meters (the thickness of Quaternary sediments in parts of North China Plain can reach 2-3,000 meters), but in most cases the thickness is between several meters and tens of meters.
5. Due to the short formation time and the failure of diagenesis, most Quaternary sediments are loose. However, the term Quaternary sediments also includes hardened volcanic rocks, cemented breccia, chemical rocks and other hard rocks.
6. The bioclastic contained in Quaternary sediments has a shallow degree of fossilization.
7. Due to the drastic and frequent changes in the sedimentary environment, there are many discontinuities in the deposition process of Quaternary sediments, especially continental sediments. These discontinuities are characterized by denudation surface, structural unconformity surface and changes and replacement of various genetic types (such as the alternation of Quaternary glacial deposits and interglacial deposits). ).
8. The formation process of Quaternary sediments continues.
9. The genetic types of Quaternary sediments are complex. Due to the appearance of Quaternary glaciers, the sedimentary environment of Quaternary sediments is very complicated. Compared with the Tertiary sedimentary environment, the Quaternary increased the glacier-periglacial environment. Quaternary glacier-periglacial, drought, moist heat, seashore and marine environment all have their own geological action combinations, resulting in a certain symbiotic combination of Quaternary sediments. Therefore, the genetic types of Quaternary sediments are diverse, and their spatial distribution and temporal distribution are also significant, frequent and complex.
(6) Quaternary tectonic movement
Another feature of Quaternary geological history is strong tectonic movement. Compared with the past dynasties, the mountains on the surface of the earth in Quaternary are relatively high. Moreover, the overall height of the mainland is much larger than that of the previous Quaternary period. A large number of research data prove that the basic outline of modern terrain is mainly determined by the tectonic movement during Neogene-Quaternary. Quaternary tectonic movement played an important role in it. The development of some large topographic units (such as mountains and plains) and some secondary topographic units (such as mountain basins) is basically consistent with the new tectonic units formed by neotectonic movement.
Quaternary tectonic movement, accompanied by volcanic and seismic activities. Especially in the Pacific Rim and the Alps-Himalayan Belt, as well as some continental rifts and mid-ocean rifts, volcanic and seismic activities are extremely frequent.
Because the Quaternary tectonic movement controlled the formation and development of Quaternary landforms, it also indirectly controlled Quaternary sediments and biota.