--> Abstract: Pinning Points: A Method That Provides Quantitative Constraints on Relative Sea-Level History, by R. H. Goldstein and E. K. Franseen; #90987 (1993).

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GOLDSTEIN, ROBERT H., and EVAN K. FRANSEEN, The University of Kansas, Department or Geology, Lawrence, KS

ABSTRACT: Pinning Points: A Method That Provides Quantitative Constraints on Relative Sea-Level History.

To understand the controls on development of depositional sequences, it is important to develop quantitative constraints on relative sea-level history. We hereby define a "pinning point" as a position of ancient sea level relative to a geologically useful starting elevation. Pinning point elevations can be plotted relative to time to construct a "pinning point curve" that illustrates the quantitative basis for the history of relative sea-level change. To develop a pinning point curve, ancient stratigraphic positions of sea level and their relative elevations must be determined.

This can be accomplished by identification of facies deposited at or just below sea level such as reef crest deposits, tidal flat deposits, shallow water oolites, and beach deposits, from diagenetic evidence of subaerial exposure of marine rocks, or from an upward transition of marine to nonmarine deposits.

Determining relative elevation of pinning points is accomplished if paleoslope is preserved without deformation, or if paleoslope can be determined using geopetal fabrics or thickness of onlapping units at their termination. Stratigraphic thickness also may serve to define minimum relative elevation between pinning points. For each application, compaction and lateral variation in amount of compaction must be either determined or assumed.

Upper Miocene strata from Las Negras, southeastern Spain provide excellent outcrops for demonstrating the usefulness of pinning points. These strata preserve paleotopography, contain ancient surfaces of subaerial exposure, and contain facies deposited near sea level. The pinning point curve developed illustrates a complex history with large-scale relative sea-level changes of greater than 100-150 meters combined with smaller scale relative sea-level changes.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.