Characteristics of geological hazards in South China coastal areas and impact on regional sustainable development
Prevention and treatment of geological hazards is important for the sustainable development of human society. Surface geological hazards alone caused direct economic losses of ¥3.47 billion, with 768 deaths and 785 injuries in Guangdong Province, South China, from 1994 to 2005. The major factors causing geological hazards can be categorised into three types: geo-environmental, climatic-meteorological and human activity. Accompanied by rapid economic development and population growth, human activities can cause geological hazards that are as serious as those caused by natural factors. The authors propose some suggestions for prevention and treatment of geological hazards to achieve sustainable development on the Chinese coast.
Interaction of tectonic and depositional processes that control the evolution of the Iberian Gulf of Cadiz margin
Abstract This study provides an integrated view of the growth patterns and factors that controlled the evolution of the Gulf of Cadiz continental margin based on studies of the tectonic, sedimentologic and oceanographic history of the area. Seven sedimentary regimes are identified, but there are more extensive descriptions of the late Cenozoic regimes because of the larger data base. The regimes of the Mesozoic passive margin include carbonate platforms, which become mixed calcareous–terrigenous deposits during the Late Cretaceous–early Tertiary. The Oligocene and Early Miocene terrigenous regimes developed, in contrast, over the active and transcurrent margins near the African–Iberian plate boundary. The top of the Gulf of Cadiz olistostrome, emplaced in the Late Miocene, is used as a key horizon to define the `post-orogenic' depositional regimes. The Late Miocene progradational margin regime is characterized by a large terrigenous sediment supply to the margin and coincides with the closing of the Miocene Atlantic–Mediterranean gateways. The terrigenous drift depositional regime of the Early Pliocene resulted from the occurrence of high eustatic sea level and the characteristics of the Mediterranean outflow currents that developed after the opening of the Strait of Gibraltar. The Late Pliocene and Quaternary regimes are dominated by sequences of deposits related to cycles of high and low sea levels. Deposition of shelf-margin deltas and slope wedges correlate with regressive and low sea level regimes caused by eustasy and subsidence. During the highstand regimes of the Holocene, inner shelf prograding deltas and deep-water sediment drifts were developed under the influence of the Atlantic inflow and Mediterranean outflow currents, respectively. A modern human cultural regime began 2000 years ago with the Roman occupation of Iberia; human cultural effects on sedimentary regimes may have equalled natural factors such as climate change. Interplay of tectonic and oceanographic controls dominated the evolution of the Cadiz margin during the Cenozoic. Depositional sequences formed where the tectonic setting provided the accommodation space and the shape of the deposits has been greatly influenced by the strong unidirectional Atlantic inflow currents on the shelf and Mediterranean outflow currents on the slope. The entire cycle of the inflow and outflow deposition along the margin has been controlled first by the tectonic evolution of the Betic and Rif gateways, which become closed during the Late Miocene, and after the Messinian by the opening of the Strait of Gibraltar. Strong current development during eustatic sea level highstands of the Pliocene and Quaternary has controlled deposition because of maximum sill depths at Gibraltar for water circulation. Lowstand sea levels slowed circulation and resulted in mud drapes over the slope and regressive stratigraphic sequences over the shelf. More recently, the human industrial revolution has caused heavy metal contamination of sediment and water over the Cadiz margin. Human activity also has affected sedimentation rates because of deforestation that caused increased depositional rates near undammed rivers and decreased rates where rivers have been dammed. Future research efforts will need to focus on: (1) the effect of increased Mediterranean outflow caused by river damming plus global warming and the increased outflow as a potential trigger for new ice ages; (2) assessments of geologic hazards for planning man-made shoreline structures, developing offshore petroleum resources and maintaining undersea communications cables; and (3) confirmation of the general geologic history of the Cadiz margin.
Evolution of the North Atlantic--An Overview: Chapter 8: North Atlantic Perspectives
The Mesozoic North Atlantic rift systems are superimposed on Precambrian and Paleozoic basement complexes and are only partly aligned with their structural grain. The Triassic to mid-Jurassic evolution of the North Atlantic rift system can be related to the southward propagation of the late Paleozoic Norwegian-Greenland Sea rift and the westward propagation of the Permo-Triassic Tethys rifts. Following mid-Jurassic crustal separation in the central Atlantic, rifting and later sea-floor spreading propagated during the Late Jurassic and Cretaceous northward into the Labrador Sea-Baffin Bay. During the Late Cretaceous and Paleocene, compressional intraplate stresses emanating from the Alpine collision zone impeded crustal separation between Greenland and Europe. When the e stresses were relaxed, the North Atlantic sea-floor-spreading axes propagated during the earliest Eocene into the Norwegian-Greenland Sea. The evolution of rifted basins in the North Atlantic domain shows great variations in duration of the rifting stage, thermal doming, and volcanism. Upper crustal extension values derived from seismic reflection profiles can provide new constraints for palinspastic reconstructions of the North Atlantic. It is believed that the Moho can become seriously destabilized during rifting processes. Rifting models need to be tested against Trans-Atlantic paleotransects covering conjugate margins.