Studies of turbidite channel complexes in outcrops, wells, and 3D seismic-reflection data suggest a general model of turbidite channel behavior related to three critical measures: (1) the thickness of channel elements; (2)the thickness of abandonment facies within each element; and (3) the thickness of overbank aggradation. These measures constrain channel stacking pattern and can be integrated into event-based geostatistical reservoir models that provide probabilistic predictions of net reservoir volume and element stacking pattern. Although channel and overbank thicknesses are measured routinely, this model provides a predictive framework that also emphasizes the importance of recognizing the presence and thickness of shale-rich abandonment facies at the top of sand-rich channel elements in outcrops.
For a given flow composition, the deposits of thick channel elements (thickness of active fill plus abandonment facies) tend to have relatively low sand percentage, abundant bypass facies, and thick abandonment facies (underfilled channels). Underfilled channel elements with high topographic relief, from levee crest to channel thalweg, at the time of abandonment influence the location of subsequent elements, resulting in an organized channel stacking pattern. The deposits of relatively thin channel elements tend to have higher sand percentage, small volumes of bypass facies and thin/absent abandonment facies. Filled channel elements with low topographic relief at the time of abandonment had little influence on the location of subsequent elements, which resulted in a disorganized channel stacking pattern. Channel ‘‘relief ’’ corresponds to the depth of erosion plus the height of the levee crest above the initial sea floor. We observe that erosion relief can correlate strongly with downslope gradient. Flow composition also is critical because the rate of overbank aggradation is strongly influenced by mud volume. Muddy flows tend to produce thick overbank aggradation, high confinement, and under-filled channels with an organized stacking pattern. Sand-rich flows tend to produce relatively low overbank aggradation, low confinement (unless erosion relief is high), and filled channels with a disorganized stacking pattern.
Figures & Tables
Outcrops are fundamental to everything we hope to achieve in geological understanding. They are gateways to geological processes, earth history and they help ground-truth remote sensing applications. With increasing resolution of subsurface tools and techniques, one could be forgiven in believing that outcrops have had their day and their utility is less than in the past great eras of field mapping and the development of facies models. This premise is far from the truth and this new SEPM volume illustrates how new analytical techniques are revitalizing outcrops and in the process creating a wealth of new data and fresh geological understandings. In this book you will find a compilation of the growing arsenal of outcrop tools and techniques and a consideration of future developments. This collection of papers, delivered at a SEPM Research Conference on the West coast of Ireland in the summer of 2008, is a smorgasbord of case studies, workflows, modeling, and applications which spans clastic and carbonate settings. Whatever your interest in outcrop geology and its application there is something in this volume for you. If you are seeking guidance for using new outcrop tools, looking for efficiencies in data collection or desiring new insights for old and favorite outcrops, this volume is a must have. This volume also makes an excellent reference or textbook for any group of professionals or students working or studying the new technologies that have allowed new insights from outcrops. We also consider this a superbly timed publication because many new outcrop tools are now becoming mainstream via reduced purchase and operating costs. Once you read this volume, and there are reduced prices for SEPM members and students, please share your new experiences with the authors and editors and help continue the revitalization of our shared and continually surprising outcrop library of the earth.