Eolian deposition and its significance in the claron formation indicated by grain-size end members in the Bryce Canyon, Utah, USA

The Cenozoic Claron Formation spanning the Paleocene to Eocene， which is widely exposed in the western United States, is suitable for studying climatic and environmental change in this period. The Claron Formation has generally been interpreted as a fluvial-lacustrine deposit, but eolian deposit features are evident from field observations. Therefore, identifying eolian components in the strata and discussing their significance is of vital importance for interpreting the sedimentary environment of the Claron Formation. The area of the Claron Formation covered by this study was the Bryce Canyon National Park. The eolian deposits in the strata were firstly identified by field observation of the sedimentary characteristics and the surface textures of quartz grains. Then the eolian components of the rock were determined by non-parametric grain-size end-member analysis to unmix the grain-size components. It was found that most of layers are red in color, and the deep-to-light variation of the red color of the strata and the off-white color vary overall with the bedding/horizon. The sediments were found to be homogeneous, mainly composed of silt and clay and rich in carbonate, with well developed vertical joints. Aggradational deposit properties were clearly observed in the red layers, evidence that the sedimentation and weathering processes were simultaneous. These field sedimentary characteristics indicate that the red layers are mainly eolian deposits. The quartz grains in the red samples were found to have surfaces characterized by large and small mechanical saucer-shaped pits, deep troughs, round pits, upturned plates and precipitation of SiO_2, all of which are indicative of an eolian environment. This provides further evidence of eolian deposition in the red layers. Six end members with different sedimentary significance were obtained from the non-parametric grain-size end-member analysis model: soil-forming components; components of hydrostatic sedimentation formed in soak/ephemeral lake; components transported by high altitude air streams over long distances; components of dust settling after storms; alluvial-diluvial components; and near-source or far-source components transported by storms. End members 3, 4 and 6 (first mode grain size 5.33, 11.93 and 42.34 μm, respectively) were identified as eolian components, with an average content of approximately 50% in the strata. This indicates that eolian deposition accounted for more than half of the sediments in the strata. Moreover, the eolian components were found to occupy a large proportion in each layer, indicating that they were a stable strata component. Obvious variation of the content of each end member in the strata indicates inconsistent sedimentary environments at different times. The strata consist of alternate layers of eolian sediments, alluvial-diluvial deposition and soak/ephemeral lake deposition. The climate was humid during the periods of alluvial-diluvial and soak/ephemeral lake sedimentation, and arid during eolian deposition and soil formation.