Three-dimensional seismic geomorphology and analysis of the Ordovician paleokarst drainage system in the central Tabei Uplift, northern Tarim Basin, western China

TLDR

The Ordovician karst system in the central Tabei Uplift is analogous to the modern Guilin tower karst and, during burial, intrastratal and suprastratal collapse formed extensive damage zones. The study aims to use high‑quality 3‑D seismic data to detail the geomorphology of a deeply buried Ordovician unconformity and its paleokarst drainage system. An integrated approach combining seismic data with core, wireline logs, and age‑equivalent outcrops was applied to interpret the system. The high‑resolution seismic data revealed karst features smaller than 75 m horizontally and 6 m vertically, identified fluvial channels, valleys, sinkholes, tower karsts, and hills, showed that surface canyons and river valleys align with subsurface collapse zones, and allowed interpretation of coalesced paleocave systems from circular fault patterns.

Abstract

High-quality three-dimensional seismic data acquired in the central Tabei Uplift, Tarim Basin, western China, provide a rare opportunity to characterize in exceptional detail the three-dimensional geomorphology of a deeply buried (5500–6500 m [18,045–21,325 ft]) Ordovician unconformity and the related paleokarst drainage system. An integrated approach was applied that emphasized integration of seismic data with available conventional core, wireline logs, and age-equivalent outcrops. The exceptional quality of the seismic data allowed a seismic detection limit of karstified features of less than 75 75 m (246 246 ft) horizontally and 6 m (20 ft) vertically. Interpreted geomorphologic and depositional elements include fluvial channels and canyons, fluvial valleys, sinkholes, and tower karsts and hills. The modern tower karst-drainage system in Guilin, China, is very similar to the mapped Ordovician karst-drainage system and is used as a modern analog. The interaction between the surface karst-drainage system and the shallow-subsurface cave-passage system is evidenced by the observation that surface canyons appear to initiate in areas associated with intense sinkhole development. Also, surface river valleys tend to correspond to dip-oriented surface depressions partly related to near-surface cave collapse. During burial into the deeper subsurface, the combination of intrastratal collapse (karstified strata) and suprastratal collapse (postkarst-deposited strata) created large damage zones hundreds of meters thick and kilometers wide. Coalesced-collapsed paleocave systems can be interpreted from the unique circular pattern of faults (observed in map view) that are associated with seismic bright spots.