A SUMMARY ACCOUNT OF THE REGIONAL GEOLOGY OF SHANGHAI MUNICIPALITY

Shanghai is situated in the northeastern part of the Yangtze paraplatform. In the very long geological history, the paraplatorm underwent the stages of development of the geosyncline, platform and continental mrgins. Each stage has left records of its specific formations, structural deformation and biolog- ical evolution. The pre-Sinian witnessed a stage of geosyncline development. The folded basement of the platform of the area is composed of metamorphic rock series of the pre-Sinian Jinshan Group and Huinan slate. Through the Jinning move- ment, the Yangtze geosyncline was folded and inverted and transformed into a platform, forming a paleotectonic framework of uplifts and depressions that were distributed alternatively in a NE 60° direction. The Caledonian cycle was a stage of paraplatform development. "The first cover" of the paraplatform-the Caledonian tectonic layer-was developed completely, represented by marine and shallow marine continuous sediments, and did not undergo regional metamorphism and the sedimentary thickness was great. The changes of the lithofacies and thickness and the appearance of the biota all show the characteristics of a structural transitional region. The Caledonian movement was manifested by differential uplift and produced some folds of broad type. In this area, no Devonian-Middle Triassic sediments have been discovered up to now. The Indosinian movement caused original broad folds in the cover to develop into close composite linear folds, accompanied by fault structure of NE and NW trends. The Indosinian movement finished the history of long-con- tinued transgression in the area and ushered in a new era of the peri-Pacific continental-margin activity. The Yanshanian cycle witnessed very active struc- tural disturbances and magmatic activity. In the Jurassic, the volcanic structure was well developed, accompanied by intense eruption of intermediate-acid magmas, thus forming a volcanic-sedimentary rock series that is distributed throughout the area. In the Cretaceous the intrusion of intermediate-acid magmas predominated, the pre-existing fault structure exhibited inheritable activity, and besides NNE-trending faults were formed. In the Cretaceous several very thick down-faulted red basins were developed. In the Himalayan cycle, oscillating movements occurred frequently. In the early stage the late Yanshanian geological-structural characteristics were essen- tially inherited. The area has received several hundreds of meters of clays, sands and gravels since the Neogene. In the Neogene, there occurred eruption and intrusion of basaltic magmas. In the Quaternary, this area has undergone eight frigid stages and warm stages, accompanied by six transgressions.