Abstract：Contour current deposits are a common type of deep-water deposits. However,limited work has been done on identification and formative mechanisms of contour current deposits in the rock record. Here,a new type of contour current deposits(lenticular contour current deposits)is documented in the Ordovician Kelimoli Formation of the study area in the Ordos Basin. The results show that There are four types of lithofacies and lithofacies associations in the study area,including lenticular micrite(lithofacies 1),mainly lenticular silt-sized silt-crystalline limestone(lithofacies 2),micrite and sparry calcarenite or calcirudite(lithofacies 3),and bedded calcirudite(lithofacies 4). It is found that lenticular micrite,silt-sized silt-crystalline limestone,and calcarenite or calcirudite are present as fine-grained through coarse-grained to fine-grained facies sequences. These deposits are characterized by relatively thin bed thickness,wavy surface,lenticular geometry,and association with muddy lamina,stripe,and spot,which are attributed to the persistent effect of contour current. Silt-sized silt-crystalline limestones are usually mottled. Bedded calcirudites with imbricate structures and the inverse Chinese character of “small”are likely to be storm deposits. In addition,carbon and oxygen isotopes indicate that relative sea level and paleotemperature show two rising to falling cycles and a continously-rising half cycle. It is also found that the contour current in the study area are low energy thermohaline circulation and that the strength of the contour current is positively correlated with eustatic sea level and salinity change. Finally,the energy of the contour current increases gradually upsection with occassional transient extremes,which might be also effected by storms in the Kelimoli stage.
LI Hua,HE Youbin,YAO Fengnan et al. Contour current deposits in the Ordovician Kelimoli Formation,northwestern margin of Ordos Basin[J]. JOPC, 2024, 26(4): 962-971.
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