Abstract

This paper discusses Amanz Gressly's (1814–1865) fundamental contributions to stratigraphy in three areas: facies concepts and applications, stratigraphic correlation, and paleogeographic reconstruction. To facilitate access to his discoveries, we present an English translation of his 1838 paper on facies and stratigraphic correlation. We discuss excerpts from this translation, which demonstrate that many of the fundamental principles of modern stratigraphy were understood and expressed by Gressly. We put this into the context of subsequent development and refinement of current stratigraphic principles.

Gressly explained the genesis of sedimentary facies by processes operating in depositional environments. He demonstrated regular lateral facies transitions along beds, which he interpreted as mosaics of environments along depositional profiles. He recognized the coincidence of particular fossil morphologies with particular sedimentological facies, and distinguished “facies fossils” from those that had time value and that were useful for biostratigraphy (“index” or “zone” fossils). He discussed the equivalency of vertical facies successions through a series of strata and lateral facies transitions along a bed, developing the same principle that later became known as Walther's Law of the Correlation of Facies. He distinguished between the time value of strata and properties that reflect their genesis, and introduced specific terms to reflect this distinction. He used this understanding to show how stratigraphic successions should be correlated across different facies tracts.

Gressly derived an internally consistent, logical, and comprehensive definition of a new stratigraphic paradigm, which was the basis for further developments and refinements. The five remaining principles of contemporary stratigraphic thought include: (1) the stratigraphic process-response system conserves mass; (2) sediment volumes are differentially partitioned into facies tracts within a space-time continuum as a consequence of mass conservation; (3) cycles of facies tract movements laterally (uphill and downhill) across the Earth's surface are directly linked to vertical facies successions, and are the basis for high-resolution correlation of stratigraphic cycles; (4) stratigraphic base level is the clock of geologic time, and the reference frame for relating the energy of space formation with the energy of sediment transfer; and (5) facies differentiation is a byproduct of sediment volume partitioning.

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