Origin of Late Turonian and Coniacian Unconformities in the San Juan Basin
Dag Nummedal, Gregory W. Riley, 1991. "Origin of Late Turonian and Coniacian Unconformities in the San Juan Basin", Sequence Stratigraphy Applications to Shelf Sandstone Reservoirs: Outcrop to Subsurface Examples, J. C. Van Wagoner, C. R. Jones, D. R. Taylor, D. Nummedal, D. C. Jennette, G. W. Riley
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The objective of this field research conference is to address basic issues in shallow marine sequence stratigraphy. One central issue is the origin of the many discontinuities (unconformities and diastems) we observe: Three possible mechanisms may produce such discontinuities: (1) eustatic sea level fall, (2) tectonic uplift or tilting of the basin, and (3) lateral shifts in depositional environments (the origin of most diastems). Late Turonian and Coniacian rocks of the western San Juan Basin provide an excellent section of rocks in which to address these questions, because we believe that the three major discontinuities present within this part of the stratigraphic column are examples of all these listed modes of origin.
The analysis of the origin of these unconformities is based on: (1) a synthesis of relevant biostratigraphic data (including much not previously published) in order to constrain their ages with the highest possible precision, (2) documentation of parasequence stacking patterns and depositional systems to relate unconformities to their correlative deposits, and (3) subsurface data that demonstrate local tectonic movement.