Middle Ordovician mass‐transport deposits from western Inner Mongolia, China: Mechanisms and implications for basin evolution

Abstract

Subaqueous mass-transport processes are one of the mechanisms for transport of sediment into the deep sea. Internal structures and depositional processes of carbonate mass-transport deposits are relatively poorly understood relative to siliciclastic facies due to their comparative paucity in the rock record. A variety of carbonate mass-transport deposits, including slumps, debrites and deep-channel-confined density flow deposits, occur in Middle-Upper Ordovician slope deposits in western Inner Mongolia (Wuhai), China. These provide a rare opportunity to illustrate the emplacement history of carbonate mass-transport deposits at the outcrop scale. The slumps and debrites host remarkable folds, chaotic beds and imbricated beds that reflect differences in both rheology and position on the slope. Individual slump sheets show gradations between undulating laminae, inclined and recumbent folds, highly deformed folds, and chaotic textures upslope from the toe region. Debrites are commonly interbedded with slump deposits, whereas imbricated beds are present in the middle and lower parts of the toes of slump sheets near the terminal wall. In the study area, thin-bedded limestone with slump deposits of the Kelimoli Formation are overlain by fine-grained, siliciclastic-dominated, slope deposits of the Wulalike Formation. A thick breccia of the Wulalike Formation was deposited in a main feeder channel in south-east Wuhai, but to the west-north-west the breccia was deposited in distributary channels possibly represented as a unique lower-slope pattern of gullies. At the latter locality, the breccia was deposited solely within the channels on a steep west-north-west dipping slope under density-driven flows. The mass-transport deposits documented herein records passive to foreland basin tectonic transitions, and associated platform foundering and steepening of the slope. A slope facies model was constructed to demonstrate the spatial and temporal variations of mass-transport deposits during basin evolution, and as such it provides a template for the interpretation of the deposits of ancient slopes that underwent passive to active tectonic transitions.

The Emu Bay Shale: A unique early Cambrian Lagerstätte from a tectonically active basin

“…2, C and D). The upper surface of one 25-cm-thick, parallel-laminated sandstone bed truncates the lamination, indicating that the upper surface is a slide scar produced by detachment and downslope movement of a mass of the bed ( 35 , 36 ). The middle unit also contains conglomerate in a wide variety of bed types (fig.…”

Shallow‐marine calciclastic mass‐transport deposits in an evolving thrust‐top basin: A case study from the North Dalmatian foreland basin, Croatia

“…Most MTDs described from foreland basins worldwide were deposited in deep‐marine foredeep environments or along the margins of piggyback, thrust‐top, wedge‐top, episutural and satellite basins (e.g. Payros et al ., 1999; Lucente & Pini, 2003; Ogata et al ., 2012a, 2014b; Festa et al ., 2016; Li et al ., 2019, 2022; Payros & Pujalte, 2020; Petrinjak et al ., 2021), with sediment being transported within, but also between, large submarine canyons, commonly due to slope failure (Field & Clarke Jr., 1979). Such submarine conduits are prone to form on steep slopes and commonly in response to major relative sea‐level falls, yet it is also known that subaqueous mass movements may occur on gentle slopes (Lewis, 1971; Field & Clarke Jr., 1979; Alsop & Marco, 2013), even as low as 0.2° (Coleman et al ., 1998).…”

“…The term MTD is generally used to describe the products of a single depositional event in outcrop‐scale studies (Sobiesiak et al ., 2017; Ogata et al ., 2020), whereas the term mass‐transport complex (MTC) refers to features that can be imaged on large seismic surveys, or complex MTDs where individual MTDs cannot be distinguished from one another (Weimer & Shipp, 2004; Sobiesiak et al ., 2017). Their emplacement involves various types of gravity mass movements (Einsele, 1991), including mass movements of lithified rocks (for example, rockfalls), creep, slumping and sliding of soft or semi‐solid sediments, and various types of sediment gravity flows (for example, blocky flows and debris flows) that can be triggered by seismic perturbations (Lewis, 1971; Sims, 1975; Pedley et al ., 1992; Papatheodorou & Ferentinos, 1997; Owen et al ., 2011; Myrow & Chen, 2015; Li et al ., 2019, 2022), overpressuring due to rapid sedimentation (Helwig, 1970; Postma, 1983, 1984; Spence & Tucker, 1997), slope oversteepening (Prior et al ., 1981; Nemec, 1990; Spence & Tucker, 1997; Payros et al ., 1999), dynamic loading from storm waves (Field & Clarke Jr., 1979; Myrow & Hiscott, 1991; Chen & Lee, 2013), sea‐level fluctuations (Spence & Tucker, 1997), halokinesis (Alves, 2015; Arfai et al ., 2016) and flow sapping from confined aquifers (Holz Boffo et al ., 2022). Among the mass‐movement mechanisms, the term blocky flow has been introduced more recently to describe highly competent and complex debris flows carrying large coherent blocks, metres to hundreds of metres wide (Mutti et al ., 2006; Ogata et al ., 2012a; Festa et al ., 2016; Ogata et al ., 2020).…”

“…It should be noted, however, that a single mass‐failure event may generate both mass flows and turbulent flows, and that their resulting depositional products are part of a continuum of depositional processes (Posamentier & Martinsen, 2011). Remobilized sediment masses range in size from a few cubic metres to several thousands of cubic kilometres (Field & Clarke Jr., 1979; Moscardelli & Wood, 2008) and hence they may represent significant sediment accumulations in both ancient and recent stratigraphic successions (Li et al ., 2022).…”

Paleoenvironmental Significance of Claystone in the Middle Ordovician Miboshan Formation of Ordos Basin, China: Evidence from Trace Elements

“…The Miboshan Formation in the study area deposited in the deep-water slope-basin environment of back-arc extensional basin located at the active continental margin, which is distinctly affected by fresh water and hardly affected by the submarine hydrothermal condition. A small highland or subaqueous uplift may have existed in the western margin of the Ordos Basin during Middle and Late Ordovician, such as the Yinchuan-Wuzhong highland [48][49][50], and pond turbidity current deposits were also found in the Northern Zhuozishan area [6]. Therefore, the Miboshan Formation may also be deposited in a small pond basin affected by subaqueous uplifts (Figure 8).…”