Mesozoic-Cenozoic tectonic evolution of the Zhuanghai area, Bohai-Bay Basin, east China: the application of balanced cross-sections

The technique of balancing cross-sections, an important method for studying the tectonic history of sedimentary basins, has many applications. It enables one to compile charts for petroleum exploration and development, and growth sections of ancient structures can be restored so that the structural growth history can be studied. In order to study tectonic evolution in the Zhuanghai area of the Bohai-Bay basin, we selected two seismic profiles and compiled two structural growth sections. Based on the two balanced cross-sections, the evolution can be divided into four phases: the Triassic-Middle Jurassic phase, Late Jurassic - Cretaceous phase, Palaeogene extension phase, and Late Palaeogene-to-present phase. The whole area was uplifted during the Triassic-Middle Jurassic phase because of intense extrusion stress related to the Indo-China movement. During the Late Jurassic and Early Cretaceous, intense extension occurred in east China, and the whole area rifted, leading to the deposition of a thick sedimentary sequence. In the Late Cretaceous, the area suffered uplift and compression associated with the sinistral strike slip of the Tanlu fault. In the Palaeogene, a rifting basin developed in the area. Finally, it became stable and was placed in its present position by dextral strike-slip motion. In addition, some problems associated with compiling balanced cross-sections are discussed.

Critical reappraisal of Late Mesozoic-Cenozoic Central and North Atlantic, Caribbean and Mediterranean evolution

(l) The Pacific basin (Pacific area) may be regarded as moving eastwards like a double zip fastener relative to the continents and their respective plates (Pangaea area): opening in the East and closing in the West. This movement is tracked by a continuous mountain belt, the collision ages of which increase westwards. (2) The relative movements between the Pacific area and the Pangaea area in the W-E/E-W direction are generated by tidal forces (principle of hypocycloid gearing), whereby the lower mantle and the Pacific basin or area (Pacific crust = roof of the lower mantle?) rotate somewhat faster eastwards around the Earth's spin axis relative to the upper mantle/crust system with the continents and their respective plates (Pangaea area) (differential rotation). (3) These relative West to East/East to West displacements produce a perpetually existing sequence of distinct styles of opening and closing ocean basins, exemplified by the present East to West arrangement of ocean basins around the globe (Oceanic or Wilson Cycle: Rift/Red Sea style; Atlantic style; Mediterranean/Caribbean style as eastwards propagating tongue of the Pacific basin; Pacific style; Collision/Himalayas style). This sequence of ocean styles, of which the Pacific ocean is a part, moves eastwards with the lower mantle relative to the continents and the upper-mantle/crust of the Pangaea area. (4) Similarly, the collisional mountain belt extending westwards from the equator to the West of the Pacific and representing a chronological sequence of collision zones (sequential collisions) in the wake of the passing of the Pacific basin double zip fastener, may also be described as recording the history of oceans and their continental margins in the form of successive Wilson Cycles. (5) Every 200 to 250 m.y. the Pacific basin double zip fastener, the sequence of ocean styles of the Wilson Cycle and the eastwards growing collisional mountain belt in their wake complete one lap around the Earth. Two East drift lappings of 400 to 500 m.y. produce a two-lap collisional mountain belt spiral around a supercontinent in one hemisphere (North or South Pangaea). The Earth's history is subdivided into alternating North Pangaea growth/South Pangaea breakup eras and South Pangaea growth/North Pangaea breakup eras. Older North and South Pangaeas and their collisional mountain belt spirals may be reconstructed by rotating back the continents and orogenic fragments of a broken spiral (e.g. South Pangaea, Gondwana) to their previous Pangaea growth era orientations. In the resulting collisional mountain belt spiral, pieced together from orogenic segments and fragments, the collision ages have to increase successively towards the West. (6) With its current western margin orientated in a West-East direction North America must have collided during the Late Cretaceous Laramide orogeny with the northern margin of South America (Caribbean Andes) at the equator to the West of the Late Mesozoic Pacific. During post-Laramide times it must have rotated clockwise into its present orientation. The eastern margin of North America has never been attached to the western margin of North Africa but only to the western margin of Europe. (7) Due to migration eastwards of the sequence of ocean styles of the Wilson Cycle, relative to a distinct plate tectonic setting of an ocean, a continent or continental margin, a future or later evolutionary style at the Earth's surface is always depicted in a setting simultaneously developed further to the West and a past or earlier style in a setting simultaneously occurring further to the East. In consequence, ahigh probability exists that up to the Early Tertiary, Greenland (the ArabiaofSouth America?) occupied a plate tectonic setting which is comparable to the current setting of Arabia (the Greenland of Africa?). The Late Cretaceous/Early Tertiary Eureka collision zone (Eureka orogeny) at the northern margin of the Greenland Plate and on some of the Canadian Arctic Islands is comparable with the Middle to Late Tertiary Taurus-Bitlis-Zagros collision zone at the northern margin of the Arabian Plate.