type
According to the different division basis, the strata that make up the crust are divided into different types of strata. The international trend is to divide classes into three types:
① Rock stratum (lithologic layer) with lithology as the main division basis;
② Biostratigraphy based on fossils;
③ chronostratigraphy or chronostratigraphy based on formation time.
Another view is that chronostratigraphy is biostratigraphy. Although there are many dating methods, paleontology and isotope dating methods are of universal significance. It is pointed out that isotopic age value is an important method to compare the ages of pre-Cambrian and post-Cambrian deep metamorphic strata, but it is not perfect in the detailed division and correlation of Phanerozoic strata. Paleontology (biostratigraphy) method has global simultaneity in the division of geological periods and the comparison of stratigraphic ages. And so far, chronostratigraphic units (boundaries, series, sequences) are based on fossils, just like biostratigraphy, so chronostratigraphy is biostratigraphy, and then it is advocated to divide stratigraphy into two types.
Geologists have discovered that
The stratum is like a book that records the history of the earth, and the rocks and fossils in the stratum are like the words in this book.
Rock formations mainly include limestone, argillaceous limestone, argillaceous shale, shale and granite.
The general name of the state and orientation of rock strata in space. Except that horizontal strata are produced in a horizontal state, the occurrence of inclined strata is expressed by their strike, dip and dip angle, which is called the three elements of strata occurrence. The intersection line between the rock stratum and the horizontal plane or the horizontal line on the rock stratum is the strike line of the rock stratum, and both ends point to the strike of the rock stratum, which can be expressed by two azimuth angles with a phase difference of180, such as NE30 and SW2 10. The straight line that the vertical strike line leads downward along the inclined plane is the inclined line of the rock stratum, and the plane inclined direction indicated by the horizontal projection line of the inclined line is the inclination angle of the rock stratum. Strike and dip are 90 degrees apart. The angle between the oblique line of the rock stratum and its horizontal projection line is the (true) dip angle of the rock stratum. Therefore, the dip angle of strata is the included angle between the upper plane (trace) and the horizontal plane (trace) on the section perpendicular to the strike of strata.
There are two ways to express the occurrence of rock strata: ① Azimuth representation. Generally, the dip and dip angle are recorded, such as 205 ∠ 65, that is, the dip is 205 southwest and the dip angle is 65, and its trend is NW65 or SE65. ② Representation of quadrant angle. Generally, the strike, dip and dip angle are measured, such as n65 w/25 SW, that is, the strike is 65 northwest, the dip angle is 25, and it tends to southwest.