--> How Accurate is the Triassic Global Sea-Level Curve?: Disturbing Results from the Dolomite Mountains, Italy, by L. A. Yose; #90986 (1994).

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Abstract: How Accurate is the Triassic Global Sea-Level Curve?: Disturbing Results from the Dolomite Mountains, Italy

Lyndon A. Yose

The global sea-level curve of Haq and others is controversial in terms of the type and quality of data that were used to construct the curve and the attendant reliability of the curve in constraining global stratigraphic correlations. This study presents results from an integrated sequence- and bio-stratigraphic study of Triassic carbonate platform and basin deposits in the Dolomites. These seismic-scale outcrops form the primary data base for the Ladinian and Carnian portion of the Triassic sea-level curve and, therefore, provide an opportunity to critically assess the data behind the curve. In using a region such as the Dolomites to reconstruct global sea-level patterns, three critical assumptions must hold true: (1) depositional sequences developed in response to relative sea-level changes were accurately identified; (2) sequences were accurately dated and correlated on a regional scale; and (3) local tectonics or variations in sediment supply did not significantly overprint the eustatic signal. This study of the data base for the Triassic portion of the curve reveals problems with all three of the above assumptions. First, significant ambiguities were found in previous sequence-stratigraphic models for the Dolomites. For example, a prominent interval of carbonate megabreccias that was previously attributed to a global lowering of sea level is interpreted in the present study to record the active growth of platform margins during a longer-term highstand of sea level. Second, an integration of new and existing ammonite and palynomorph data indicate major inconsisten ies in previous lithostratigraphic-based correlation schemes proposed for the Dolomites. The new time-stratigraphic model for the late Ladinian and Carnian differs from older schemes in terms of the time span of platform deposition, the correlation of potential sequences between buildups, and the number of sequences recorded. Third, late Ladinian and Carnian stratigraphic relationships were found to be strongly influenced by regional tectonic and volcanic processes: significantly different stratigraphic histories were observed from one buildup to the next.

Results of this study indicate that (1) major problems exist with previous sequence- and time-stratigraphic models for the Dolomites and, accordingly, the polarity and timing of sea-level changes depicted on the global curve may be erroneous, and (2) while some regional trends in platform development within the Dolomites may be related to eustasy, eustasy is secondary to local tectonic and volcanic processes as a control over buildup evolution. These findings highlight the need for a new look at Triassic sea-level patterns and the danger of interpreting global sea level from a single region, especially one characterized by active tectonics.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994