Abstract
Submarine or sub-lacustrine lobe deposits are important reservoirs, but the fan fringe deposits form heterogeneities within deep water fan deposits. Fan fringe facies records the complex sediment gravity flow types. By understanding of the bed types and flow mechanisms, we can identify the fan fringe deposit, which aids in the reconstruction of deep water fan and reservoir evaluations. The Jiucaiyuanzi and Dalongkou sections in the West Bogda Mountains preserve well-exposed 536-m and 171-m thick successions, respectively, of a deep water lacustrine depositional system from the Middle Permian Lucaogou Formation. Bed types of the Lucaogou Formation include high-density turbidite, low-density turbidite, incomplete Bouma-type turbidite, hybrid event beds, and slump deposits. The Lucaogou Formation is interpreted here as a fan fringe facies due to the thin bed thickness that characterize turbidites and hybrid event beds, as well as the predominance of the isolated sheet architecture. Previous studies suggest that these deposits were considered as deposited in a deep water setting due to the absence of wave-related structures. The presence of abundant mud clasts in massive medium-coarse grained sandstone beds reflects the significant erosional capability and interactions between high-density turbidity currents and lake floor. The fan fringe facies here contains amalgamated and thick-bedded homolithic facies (~ 30%) and thin-bedded heterolithic facies (~ 70%). The examination of the bed type is of wider significance for facies prediction and reservoir heterogeneity in the sub-lacustrine fan fringe facies.
Highlights
Mass-flow processes deposit submarine fans, which correspond to distinct constructional sediment bodies on the sea floor that develop seaward of a major sediment point source (Normark 1978; Walker 1978; Reading and Richards 1994)
This study describes the bed types and depositional architectures of deep water sub-lacustrine fan fringe deposits from the Lucaogou Formation
The aims of the study are to (1) document the bed types and interpret the flow mechanism of the Lucaogou Formation; (2) describe the depositional architecture of the Lucaogou Formation and understand why the Lucaogou Formation is considered as a fan fringe facies, and (3) discuss the heterogeneities in fan fringe facies of the Lucaogou Formation
Summary
Mass-flow processes deposit submarine fans, which correspond to distinct constructional sediment bodies on the sea floor that develop seaward of a major sediment point source (Normark 1978; Walker 1978; Reading and Richards 1994). Important components of the submarine fan include the submarine channels, channel-lobe transition zones, and submarine lobes. Lobes are often incised by channels in the proximal area, the deposits of which are characterized by thick-bedded channel fills and sheets (Fildani and Normark 2004). Besides thick turbidites in the proximal lobe (lobe axis and off-axis), hybrid event beds, with a thick division in terms of the high-density turbidite (i.e., the H1 division in Haughton et al (2009)), occur in the proximal position Besides thick turbidites in the proximal lobe (lobe axis and off-axis), hybrid event beds, with a thick division in terms of the high-density turbidite (i.e., the H1 division in Haughton et al (2009)), occur in the proximal position (Ito 2008; Patacci et al. Vol.:(0123456789)
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