--> Mapping Fluvial Injection Points and Sediment Provenance in Rifted Basins Using Detrital Zircon U-Pb Geochronology, Paleogene of the Raoyang Sag, Bohai Bay Basin, China

AAPG ACE 2018

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Mapping Fluvial Injection Points and Sediment Provenance in Rifted Basins Using Detrital Zircon U-Pb Geochronology, Paleogene of the Raoyang Sag, Bohai Bay Basin, China

Abstract

Recent research on sediment input and provenance in ancient rifted basins has focused on seismic imaging of paleomorphologic indicators of sediment transport pathways. However not all basins are imaged to the quality necessary to use such techniques accurately. The Lixian Slope (LS) in the Raoyang sag is a Paleogene-aged gentle dipping region (less than 1°) in the Bohai Bay basin. Here, sediment provenance is a significant factor in controlling the quality and volume of deltaic sands. This study documents 117 cores, 85 well logs, and 500 km2 of 3D seismic data to discuss the source-to-sink sediment dispersal in the Paleogene-aged Shahejie formation. Combining paleomorphologic analysis with petrology and heavy mineral data, we mapped bedrock types and the general source locations and reconstruct the relationship between the bedrock distribution and the paleo-river systems in the sedimentary source area. It provides information on sediment ages in different paleo-river systems. Detrital zircon U-Pb dating of these sediments along the strike of the LS allowed for correlation of sediment ages with specific transverse paleo-river systems feeding the rift. Paleomorphologic and petrologic characteristics shows the LS can be classified into A, B, C areas, which corresponds to three sediment source provenances respectively. More specifically, for the northwest sediment source system, the bedrock is the Paleozoic-aged igneous rocks from the Xingmeng orogenic belt. These sediments were carried southeastward to the A region of the LS by the paleo-Daqing river system. For the west sediment source system, the various bedrock types include the Mesozoic-aged igneous rocks, the Meso-Neoproterozoic-aged intrusive rocks, and the Mesoproterozoic-aged metamorphic rocks in Laiyuan district. These sediments were carried by the paleo-Tang river system eastward to the B region of the LS. For the southwest sediment source system, the bedrock is the Paleoproterozoic-aged metamorphic rocks, which are carried by the paleo-Dasha River system from the southwest to the C region of the LS. Quantitative seismic geomorphologic analysis reveals a positive correlation between drainage area and sediment dispersed area. Zircon age distributions tie directly to the relative volumes of sediment input from different source provenances. According to this study, current exploration is focused on the southwestern-sourced sediment system (B region) in the LS, North China oil field.