Characteristics and sedimentary processes of lamina-controlled sand-particle imbricate structure in deposits on Lingshan Island, Qingdao, China

Imbricate structure is a common sedimentary structure and is well developed in sandy sediments. Here, we report a lamina- controlled fine-sand-particle imbricate structure in a set of very fine grained sedimentary rocks （fine sandstone, siltstone, and mudstone） at the Dockyard and Qianceng Cliff areas of Lingshan Island, Qingdao, Shandong, China. Sets of up to 300 laminae are found in stratigraphic profiles in these areas. The laminae are generally less than 1 mm thick, with most being 0.3-0.4 mm thick and the thinnest being 〈0.1 ram. The dip angle of the imbricate structure varies widely, between 0° and 90°, with an av- erage dip angle of about 40°-50°, which is higher than that of imbricate riverbed gravels （about 34°）. The dip angle is a func- tion of the shape and sorting of the particles, as well as the hydrodynamic conditions under which these fine-grained sediments were deposited. Several profiles show well-developed multiscale, soft-sediment deformation structures. Flute casts, load casts, and groove casts are also common. Fragments of carbon remains occur widely and commonly constitute stringers several mil- limeters thick and up to 10 cm long, together with fine clasts. Vitrain lenticles are also common. Based on the imbricate struc- ture of the Lingshan Island deposits, it is shown that in addition to paleocurrent analysis, the imbricate structure can be used to infer information about fluid properties, transport characteristics, and sedimentary processes of the depositional environment. A near-bottom underflow, either of authigenic origin or derived from cold river water in winter in a delta interdistributary bay or delta-front environment, is inferred to have provided the hydrodynamic setting in which this imbricate structure formed. The imbricate structure, together with other sedimentary structures and features, shows that the sedimentary rocks on Lingshan Is- land were deposited in an inland, shallow-water environment, such as a delta, and not in a deep-water or submarine continen- tal-slope environment.

Imbricate structure of the Otakeyama area, Okayama Permian Yoshii Group in the Prefecture, southwest Japan

The Yoshii Group of the Akiyoshi terrane is distributed over the Otakeyama area, Okayama Prefecture, southwest Japan. The Yoshii Group is composed of siliceous rocks and clastics, comprising chert-clastic sequences. The Yoshii Group is divided into four structural units （Units Ot 1, Ot 2, Ot 3, and Ot 4） in structurally ascending order. Lithological similarities and radiolarian age suggest that these units exhibit almost identical ocean plate stratigraphy. These units are structurally-repeated to form an imbricate structure. This structure was possibly formed by off-scrape accretion at a toe of an accretionary complex. Additionally, a review of previous studies indicates that an imbricate structure is common in the Akiyoshi terrane. The presence of an imbricate structure in the Akiyoshi terrane, Permian accretionary complex, indicates the possibility that a specific horizon of Permian pelagic sequences acted as a drcollement zone.