View source for Recognizing stacked depositional sequences from well data

==GOM basin example==
In the GOM basin, variations in well-log response and [[Fossil assemblage|biofacies]] distribution are analyzed for recognition of stacked depositional sequences. The [[Basic open hole tools#Gamma ray|gamma-ray]] log display provides a measure of sediment type, with curve deflections to the left suggesting increased sand content while high values to the right indicate increases in clay content. Use of multiple logs, especially [[Basic open hole tools#Spontaneous potential|spontaneous potential]], [[Basic open hole tools#Resistivity|resistivity]], density, and velocity logs calibrated by well-cutting descriptions and formation microscanner displays, provides a data set for reliable rock type identification. The figure below illustrates an interpretation template for log motif analysis.

Patterns of forestepping vs. backstepping log-motif funnels can define transgressive vs. [[Regression|regressive]] depositional trends and candidate systems tracts and sequences. Vail and Wornardt<ref name=ch04r101>Vail, P., R., Wornardt, W., W., 1990, Well log seismic stratigraphy: a new tool for exploration in the '90s: Proceedings, Gulf Coast Section SEPM 11th Annual Research conference, p. 379–388.</ref> and Armentrout et al.<ref name=ch04r8>Armentrout, J. M., S. J. Malacek, L. B. Fearn, C. E. Sheppard, P. H. Naylor, A. W. Miles, R. J. Desmarais, and R. E. Dunay, 1993, Log-motive analysis of Paleogene depositional systems tracts, central and northern North Sea: Defined by sequence stratigraphic analysis ''in'' J. R. Parker, ed., Petroleum Geology of Northwest Europe: Proceedings of the 4th Conference, The Geological Society of London, p. 45-57.</ref> detail the process.