Lateral facies variations in the Triassic Dachstein platform: A challenge for cyclostratigraphy

Abstract

The Triassic Dachstein platform limestone at Steinernes Meer, Salzburg, Austria, includes 611 m of limestone with 222 peritidal cycles overlain by 273 m of subtidal, non‐cyclic and weakly cyclic limestone. Cycle patterns include both shoaling and deepening upward, symmetrical, truncated, and couplets without a depth vector. Beds are laterally discontinuous, and cycle bounding surfaces are laterally variable in the studied strata. Of 558 subtidal and intertidal beds measured, 121 (21.7%) disappear laterally. An additional 73 beds (13.1%) show significant (>10%) lateral variations in thickness. Mean thickness variation is 49%. Both lateral variations and terminations appear to lack a spatial vector. Disappearances toward the inferred platform interior (west) total 10% of the beds. East, toward the platform margin, 11.6% of the beds disappear. Thickness changes occur in 6.5% of beds in each direction. The lack of lateral continuity of beds precludes a simple allocyclic forcing model and is consistent with a non‐eustatic component to stratification. Erosion of intertidal intervals is the process that can be most readily documented. Non‐uniform rates of production, transport and distribution of sediments, superposed on stratigraphic sequences driven by eustasy, probably also contributed to the complex cycle patterns recorded in the Dachstein. Such composites of autocyclic and extrabasinal factors should not be uncritically interpreted as exclusive records of orbital forcing. Lateral discontinuities and thickness variations would also produce inaccuracies in spectral analysis of thickness patterns, typically conducted in search of ‘Milankovich frequencies’, as well as in construction of Fischer plots to analyse long‐period oscillations in accommodation. Any section subjected to cycle analysis should be examined for lateral changes, to the extent permitted by the exposures, in order to produce the most complete (composite) section possible.

Interplay of eustatic, tectonic and autogenic controls on a Late Devonian carbonate platform, northern Canning Basin, Australia

“…Although it was not a core objective of this study, the results from the three Hull platform sections emphasise the uncertainty that can arise in estimating sedimentation rates from shallow‐water carbonate successions (e.g. Eberli, 2013; Samankassou & Enos, 2019; Weij, Reijmer, Eberli, & Swart, 2018). For example, sedimentation rates based on the HD 14 section alone would be significantly underestimated because of the amount of missing section due to subaerial exposure/erosion.…”

Florida Bay: Modern analogue for Lofer cyclothems?

“…(1990), Satterley (1996), Enos & Samankassou (1998), Haas et al . (2007) and Samankassou & Enos (2019). The east–west extent of this platform is well‐constrained by transitions to Kössen Beds west of the Steinplatte and Hallstatt Beds east of Hochkönig, a distance of about 42 km (Fig.…”

“…Fischer's simple facies designations, ‘members’ A, B and C (Figs 7 to 9), encompass considerable variation, but have proved useful in subsequent studies (e.g. Goldhammer et al ., 1990; Samankassou & Enos, 2019).…”

“…The Dachstein is dominated (92% of total thickness; Samankassou & Enos, 2019) by light‐grey, bioturbated, lime wackestone or packstone with a moderately diverse biota, characterized by megalodont bivalves (Fischer, 1964; Enos & Samankassou, 1998). This is the ‘megalodont limestone’ or subtidal member C of Fischer (1964, p. 131).…”

Preface: Celebration of the Career of Robert Nathan Ginsburg

“…Bob never published further on this and therefore this abstract is often cited by those studying this phenomenon. This idea is taken up by Samankassou and Enos () in this volume. Another theme dear to Bob’s heart was the study of stromatolites.…”