Fig. 2: Core photographs of the different deposits observed in the Yu’anshan Formation. All scale bars represent 10 mm.
a, b Hummocky cross-stratified and climbing oscillation-ripple cross-laminated (cor), fine-grained sandstone of the oscillatory-flow deposits. Note strongly aggradational component of oscillatory climbing ripples in b. c, d Current-ripple (cr) and climbing-ripple (clr) cross-laminated, very fine-grained sandstone, interbedded with bioturbated intervals (biot), representing hyperpycnal or turbidity flow deposits. Massive fine mudstone (Mm) and coarse mudstone laminae (Msh) are interbedded. e Normal-graded (white triangles) and current-ripple cross-laminated (cr), fine-grained sandstone with minor soft-sediment deformation structures (ssd) of the hyperpycnal flow deposits, interbedded with massive mudstone (Mm) with erosive bases (eb) typical of the wave-enhanced fluid mud deposits. Burrows (bu) occur on top of the mudstone beds. f Rippled fine-grained sandstone (cr) with sharp-lined firmground burrows (bu) penetrating from the base of a hyperpycnal flow layer into an intensely bioturbated mudstone initially colonized under softground conditions. Fluid mud deposits with normal-graded mudstone (white triangles), coarse mudstone laminae (Msh), and erosive bases (eb) are observed, interbedded with bioturbated intervals (biot). g–i Low-angle cross-laminated (la), current-ripple cross-laminated (cr), and hummocky cross-stratified (hcs), very fine-grained sandstone of the hyperpycnal flow deposits, interbedded with fluid mud intervals with erosive bases (eb). These beds alternate with successions of plug flow and low-density turbidity current deposits consisting of massive mudstone (Mm) with some parallel coarse mudstone laminae (Msh), current-ripple cross-laminated coarse mudstone (Msr), and normal and inverse grading (white triangles), and with dark, organic-rich mudstone (Mor) of the hemipelagic deposits. Note bioturbation structures (bu) and bioturbated intervals (biot) at the top of beds. j Massive mudstone (Mm) of the plug flow and low-density turbidity current deposits, with local normal grading (white triangles) and faint lamination (fl), locally intercalated with bioturbated intervals (biot), the latter representing the hemipelagic deposits. Burrows (bu) can be observed towards the top of mudstone beds.
