Reading the Sedimentary Record: A Multiple-Hypotheses Working Methodology
Reading the sedimentary record to decipher Earth history and predict future changes is one major task for sedimentologists. One of the objectives and challenges is to interpret the main controlling factor (e.g., tectonics, climate, autogenic processes, etc.) on the preserved strata. Recent development of sequence stratigraphy and the realization of the autogenic processes have led the author to reconsider some of the best known interpretations, and suggest that the method of multiple working hypotheses may work best for interpreting sedimentary record. There are three main reasons why we need a multiple-hypotheses working methodology. First, there are multiple controls on preserved strata. The multiple controls inevitably lead to non-uniqueness in stratal patterns. One example is the transgression of a delta front, which can result from 1) purely autogenic processes, 2) reducing sediment supply during steady accommodation changes, 3) increasing rate of accommodation changes during constant sediment supply, and/or 4) a combination of both autogenic and allogenic changes. This requires us to keep an open mind and have multiple hypotheses at the initial stage of research. Secondly, all the allogenic and autogenic processes have complex and non-linear responses. One common practice of interpreting the main controlling factor is linking the specific time of certain events in source area (e.g., climate change) to the preserved strata. If the time intervals of a certain event and the deposition of the strata match with each other, then the event is usually believed to be responsible for deposition of the strata. This reasoning process, however, might be problematic. This is proved by the increasing numbers of studies on the environmental signal propagation within the source-to-sink system. Thirdly, the limitation of data can lead to misinterpretation or ignorance of other possibilities if we use a single working hypothesis. This phenomenon is common in earlier studies of sequence stratigraphy, which are usually based on one- or two-dimensional datasets. Recent study by Madof et al. (2016) has shown how evaluation of along-strike variability can change our interpretation of the controlling factor. The change of mindset for interpreting depositional sequences will obviously alter our view of how sedimentary systems evolve, and this helps to increase the success rate of reservoir prediction and play exploration.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017