Artemia is a filter-feeding organism, and its fecal composition reflects its living environment, that is, the composition of domestic water (organic and inorganic components) and the nature (composition) of the bottom salt layer under the surface brine, the salt precipitation in the biological-water-salt system and the reproductive status of seasonal microorganisms. The author thinks that when the bottom layer of the surface brine is silt, the composition of Artemia dung particles is mainly silt and organic matter (bacteria and algae), as well as a small amount of feldspar, timely and carbonate mineral debris; When the bottom layer of surface brine is mirabilite, the composition of Artemia dung particles is mainly mirabilite debris (sharp angle or sub-sharp angle), followed by bacteria and algae, gypsum, carbonate and clay minerals. When the bottom layer of the surface salt water is an alkali-mirabilite layer or an alkaline mineral layer, the components of fecal particles are alkaline minerals, mirabilite fragments, bacteria and algae and other mineral fragments, such as gypsum, carbonate and clay minerals; In the environment where the bottom layer of surface brine is halite layer, fecal particles are mainly composed of halite debris, bacteria and algae, gypsum, carbonate and clay minerals. When the bottom layer of surface brine is a halite-sylvite deposit, its fecal particles are composed of mineral debris such as halite, sylvite minerals, bacteria and algae. For example, the study of Ordovician potassium-bearing rocks in Ordos Basin shows that Artemia feces not only contain halite, anhydrite, dolomite, authigenic time, calcite, illite and chlorite, but also contain potassium salt (plates 9-25 and 9-26).

Through microscope observation, X-ray diffraction analysis, infrared absorption spectrum analysis and scanning electron microscope observation, it is determined that the complete fecal particles in the brine sediment of Barkun Salt Lake are mainly composed of aragonite, calcite and gypsum, followed by clastic minerals such as illite, chlorite, timely and feldspar. This is basically the same as the fecal particles in the sludge of the Great Salt Lake in the United States are mainly composed of calcium carbonate and magnesium carbonate, a small amount of clay and fine mineral debris.

What is particularly significant is that when the author studied Artemia feces in Balikun Salt Lake, he also found that some feces were composed of glauberite (Figure 6- 1, Figure 6-2). This provides a new geological occurrence for glauberite hydrate, that is, biogenetic geological occurrence, and its genesis may be primary (Wei Dongyan, 199 1). Therefore, it is of great significance to study the genesis of glauberite.

In Jurassic glauberite-halite deposit in Anning, Yunnan, it was found that the feces of Artemia and Artemia larvae were mainly composed of glauberite minerals. This is very similar to the fact that some Artemia dung fossils in Quaternary salt beds of Barkun Salt Lake are composed of glauberite. The question is whether the glauberite in the coprolites is dehydrated and transformed from glauberite hydrate. Or was it glauberite when it was first formed? This is also one of the long-standing debates about the causes of glauberite.

Fig. 6- 1 infrared absorption spectrum of glauberite in Artemia dung fossils

Fig. 6-2 Differential Thermal Curve of Glauberite in Artemia Fecal Fossils

In the study of the composition of Artemia feces, a prominent feature is that the feces contain Artemia and Artemia fossils, including Artemia eggs (panel 6-2), Artemia nauplii fossils (panel 7- 13) (panel 6-9), Artemia larvae, secondary adult fossils and Artemia larvae fossils (panel 7-65438) with appendages.

It is of great significance to study the material composition of Artemia dung fossils: firstly, according to the material composition of dung fossils, the biological-water-salt system, salt lake types and salt precipitation in the salt-forming environment at that time can be accurately distinguished; Secondly, we can judge the development of the biological food chain in the biological-water-salt system at that time, especially the species and reproduction of bacteria and algae; Third, we can distinguish paleoclimate, paleoenvironment and paleoecology.

Second, the structure of Artemia faeces fossils

Artemia dung fossils have a unique structure and are related to Artemia filter-feeding organisms. According to whether the Artemia faeces fossils are accounted for, they can be divided into three types: primary structure, metasomatic texture and primary-metasomatic texture. Now describe them separately.

1. Primary structure

Primary structure refers to the characteristics of the original structure of fecal particles that have not been explained and preserved. According to its composition and debris characteristics, the structure can be subdivided into the following seven types:

1) debris structure can be divided into angular debris structure (fig. 6-8), secondary angular debris structure (fig. 6-27), directional debris structure (fig. 6-8) and annular angular debris structure (fig. 7- 15).

2) Structure of argillaceous organic matter (Plate 6-7).

3) Muddy structure with detritus (Table 6- 10).

4) Structure of clastic-argillaceous organic matter (Table 6-9).

5) Muddy debris structure with machine ring edge (Plate 6-8).

6) Fragment structure with asymmetric organic edges (plate 6- 16).

7) Detrital structure containing early fecal particles with detrital structure (Figure 6-28).

2. metasomatic texture

Metasomatic texture refers to the structure in which fecal fossils are basically or mostly occupied. According to the strength and morphological characteristics of metasomatism, it can be subdivided into the following five kinds of metasomatic texture:

1) fecal particles are completely occupied by mirabilite or anhydrous mirabilite, showing a pseudo-occupied structure (plates 6-29 and 6-30).

2) Fecal particles are metasomatism by mirabilite, forming metasomatic bright edge structure (Plate 6-4).

3) Explain the structure of silkworm erosion (Table 6-3 1).

4) The fecal fossils are island structures that are metasomatized by mirabilite or anhydrous mirabilite (Plate 6-32).

5) The dung fossils are partially metasomatic, forming a metasomatic serrated bright edge structure (the left side of plate 6-33).

3. Natural metasomatic texture

Primary metasomatic texture refers to the structure in which fecal fossils are partially explained and partially or mostly unexplained.

According to the characteristics of metasomatism, primary metasomatic texture can be further divided into the following four types:

1) The center of dung fossils is occupied by mirabilite, but the two ends are not, and the original cryptocrystalline-clastic structure is still preserved (plates 6-5 and 6-9).

2) The dung fossil part is mirabilite or anhydrous mirabilite, which gives people the illusion of muddy organic structure containing debris (Figure 6-34).

3) Both ends of dung fossils are occupied by mirabilite, but the central part is not occupied, but its original structural characteristics are still retained (Plate 9-35).

4) The coprolites were partially replaced by halite, showing a harbor-like structure. However, you can still see the outline of the original dung fossil (Plate 9-24).

The formation of this fecal fossil in metasomatic texture needs further study. After preliminary study, the author thinks that after Artemia dung particles were deposited and buried, some dung particles experienced the metasomatism of intercrystalline brine. This kind of explanation is gradual, selective and repeated. The gradual change of fecal particles is very obvious, that is, from sawtooth replacement → reaction side replacement → bright side replacement → silkworm erosion replacement → harbor replacement → residual island replacement until complete replacement. According to the metasomatism of Artemia feces in Quaternary mirabilite deposit in Barkun Salt Lake, the feces were first metasomatism by mirabilite and then by anhydrous mirabilite. It is often observed that mirabilite mineral remains in the illusion that feces are replaced by anhydrous mirabilite.

It should be pointed out that the fragments in the structure of fecal fossil fragments are worth studying. First of all, the composition of debris is related to the salt layer. For example, in the mirabilite bed, the debris in dung particles is mainly mirabilite, while in the alkali bed, it is mainly alkaline minerals. Secondly, the shape of the fragments is very distinctive. The larger the fragments, the more obvious the sharp corners, mostly triangular, polygonal, arrow-shaped, T-shaped and irregular. Most of the sharp edges of the debris are serrated, and there are few straight edges, which indicates that Artemia "processes" all the debris when eating. The size of debris in fecal particles is usually related to the size of fecal particles. The larger the fecal particles, the larger the debris. Furthermore, the debris in fecal particles is often arranged along its long axis, which is probably related to the peristalsis and squeezing of abdominal cavity when Artemia excretes.

Biological detritus can not be ignored in the study of fecal fossil detritus. Because Artemia is a filter-feeding organism, Artemia nauplii and larvae, Artemia larvae, their eggs and molting fossils may all be their food. The discovery of the above fossils in Artemia dung fossils fully illustrates this point. Therefore, the fecal particles of two kinds of insects are an important aspect of studying the fossils of two kinds of insects.