Abstract
Palaeodrainage basin, as an important component of the source-to-sink system, contains critical information on provenance and palaeoenvironment. Previous studies indicate that the scaling relationships of source-to-sink system components generally follow power laws, and channel-belt thickness represents a reliable first-order proxy for the drainage area. In this study, a database of borehole cores and geophysical well logs of the Jurassic coal measures from Saishiteng area in the northern Qaidam Basin was used to reconstruct the palaeogeography, and to identify single-story channel-belts. Three palaeochannels, namely, River A, River B and River C, were identified which were persistent throughout the Dameigou and Shimengou Formations during the Middle Jurassic. The mean channel-belt thicknesses of River A, River B and River C in the Dameigou Formation were 9.8 m, 8.9 m and 7.9 m, respectively, and those in the Shimengou Formation were 7.4 m, 6.2 m and 5.4 m, respectively. We estimate the drainage area of three major rivers by using scaling relationships between drainage area and channel-belt thickness. The drainage areas of River A, River B and River C in the Dameigou Formation were 63.0 × 103 km2, 50.1 × 103 km2 and 37.7 × 103 km2, respectively, and those in the Shimengou Formation were 32.3 × 103 km2, 21.2 × 103 km2 and 15.3 × 103 km2, respectively. The drainage basin lengths of River A, River B and River C in the Dameigou Formation were 300.4 km, 239 km and 180.2 km, respectively, and those in the Shimengou Formation were 154.3 km, 101.3 km and 73.1 km, respectively. For both the Dameigou and Shimengou Formations, River A showed the largest scale, followed by River B and River C succeedingly, which was mainly determined by the stretch direction of provenance in the southern Qilian Mountains. The variations of channel-belt thickness, drainage area and drainage basin length between Dameigou and Shimengou Formations are the response of source-to-sink system to the transformation from extension to compression depression during the Middle Jurassic in the northern Qaidam Basin.
Highlights
The comprehensive study on source-to-sink systems was originally proposed in the sub-project of Margins Program Science Plans 2004, which took the tectonic setting and denudation of source area, the transport process of sediments, and the final depositional pattern as a complete system (Allen 2008; Fuller and Marden 2010)
We focus on the variation of channel-belt thickness from the Dameigou Formation to the Shimengou Formation of the Middle Jurassic, and try to reveal the relationship between river dimensions and tectonic evolution, and to improve the comprehension of the Jurassic source-to-sink system in the northern Qaidam Basin
1) Based on a database of 81 well logs, Middle Jurassic single-story channel-belts were identified in the Saishiteng area, northern Qaidam Basin, and channelbelt thickness of three major rivers developed in the study area were measured
Summary
The comprehensive study on source-to-sink systems was originally proposed in the sub-project of Margins Program Science Plans 2004, which took the tectonic setting and denudation of source area, the transport process of sediments, and the final depositional pattern as a complete system (Allen 2008; Fuller and Marden 2010). As an important component of sourceto-sink system (Fig. 1a), controls sediment supply from provenance to sedimentary basin, and affects distribution characteristics and accumulation patterns of the strata in the sink (Davidson and Hartley 2014). It contains critical information of provenance and palaeoenvironment, due to late erosion, reconstruction of the source is difficult. A number of studies have investigated river data such as river channel dimensions, drainage area, and bankfull discharges, demonstrating that the scaling relationships of source-to-sink system components generally follow power laws, in which the channel-belt thickness (bankfull thickness) is positively correlated with the drainage area (Fig. 2; Syvitski and Milliman 2007; Blum et al 2013; Anderson et al 2016)
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