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Objective Abundant ichnofossils present in the Eocene Pinghu Formation and Baoshi Formation in the Pingbei area， Xihu Sag. It is of practical significance for the division of sedimentary systems in the Xihu Sag to study the characteristics and distribution of its ichnofabrics and their indication of sedimentary environment. Methods Using core observations， the study identified ichnofossils and ichnofabrics in the Pingbei area. The IDIPA technique was employed to objectively quantify ichnofossil abundance and accurately determine both the bioturbation index and the ichnofabric index. By integrating these findings with ichnological indices， this study summarizes the characteristics of the planar distribution and vertical evolution of ichnofabric in the study area. Results （1） The study identified six ichnogenera of ichnofossils and divided them into four types of ichnofabrics： Planolites ichnofabric， Thalassinoides ichnofabric， Teichichnus ichnofabric and Beaconites ichnofabric. （2） The study area features a high landform in the northwest and a low landform in the southeast. Seawater invades from south to north， and the sedimentary environment transitions from a subtidal zone to an intertidal zone， and finally to a supratidal zone in the northwest where the highest terrain is located. The evolution pattern of the corresponding ichnofabrics follows the sequence Thalassinoides → Teichichnus → Planolites → Beaconites， consistent with regional sedimentary zoning and paleoclimate analysis. （3） From the Pinghu Formation to the Baoshi Formation in the study area， the study found an increase in the size， diversity and abundance of ichnofossils. The tiering transitioned from simple and shallow to complex and deep. The variety of organisms and the degree of bioturbation increased， and the biological habits evolved continuously， indicating that the sedimentary environment changed from anoxic to oxic. Conclusions Based on the characteristics of ichnofossils， ichnofabrics and sedimentary structures， the response relationship between the ichnofabrics and the sedimentary environment was established in the Pinghu Formation⁃Baoshi Formation in the Pingbei area. These findings provide new evidence for the changes in sedimentary environment from the perspective of ichnology in the Xihu Sag during the Eocene.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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