On Stratigraphy from Spatial and Temporal Perspectives: Review and Interpretation

Key words: 
• stratigraphic record /
• stratigraphic attributes /
• depositional sequence /
• diachronism /
• spatial and temporal order

Abstract: A series of branches of stratigraphy have formed since 1970's along with the development of multiple stratigraphic classification theory and the application of various testing methods and means, These stratigraphy branches have greatly extended their research fields, and made stratigraphic theories developed towards multi-laterals, multi-levels and multi-scales directions. However, the specific and simple research object has also made stratigraphy fragmented and narrowly-defined. Therefore, it is necessary to review the stratigraphic history and consider the different stratigraphic units based on independent characteristics and attributes as a whole. In this paper, from the philosophy of time and space, the incompleteness, cyclicity, punctuated equilibrium and irreversibility of stratigraphic records are systematically summarized and combed. It is found that although lithologic, biologic, physical and chemical changes are not strictly unified into temporal variations, the strata are distributed orderly and regularly in time and space. From the Steno's Laws stating that rocks laid down in vertical order with younger strata on the top of the older one to the Walther's Phase Law suggesting that the contiguous relation in space can be transformed into the chronological sequence in time, the stratigraphy not only expresses the concept of space by using concepts of top and bottom, left and right, but also reveals its time attribution. The unconformity, once supposed to be a tectonic-induced concept from the beginning, which represented its spatial incongruity caused by folds or orogeny, is now defined with the help of time attribute i.e. the prolonged absence of stratigraphic records. Similarly, the stratigraphic cycle, a term previously describing the repetition of strata, after the confirmation of the Quaternary Milankovitch cycle is redefined as the transgressive and regressive sequences bounded by unconformities in the stratagraphic record. The discovery and restoration of the spatial and temporal order in the complex stratigraphic record is therefore becoming the driving force in promoting the development and integration of all stratigraphy branches.