Sea level changes versus hydrothermal diagenesis: Origin of Triassic carbonate platform cycles in the Dolomites, Italy: Discussion

Peterhänsel, Arndt; Egenhoff, Sven

doi:10.1016/j.sedgeo.2005.03.004

Cited by 5 publications

(3 citation statements)

References 22 publications

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“…Lower values are characteristic of blocky calcite in cements precipitated in the burial realm, associated with high temperatures and oxygen-depleted waters. The narrow range of δ 13 C values can be explained by the fact that the samples were derived from a marine source and remained unchanged despite their transformations into diagenetic products (Peterhänsel and Egenhoff 2005). In Text- fig.…”

Section: Diagenetic Historymentioning

confidence: 99%

An early Middle Anisian (Middle Triassic) Tubiphytes and cement crusts-dominated reef from North Dobrogea (Romania): facies, depositional environment and diagenesis

Popa¹,

Panaiotu²,

Grădinaru³

2014

Acta Geologica Polonica

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ABSTRACT:Popa, L., Panaiotu, C.E. and Grădinaru, E. 2014. An early Middle Anisian (Middle Triassic) Tubiphytes and cement crusts-dominated reef from North Dobrogea (Romania): facies, depositional environment and diagenesis. Acta Geologica Polonica, 64 (2), 189-206. Warszawa.A well-developed Triassic carbonate platform is exposed in the eastern part of the Tulcea Unit, in the Cimmerian North Dobrogean Orogen, southeastern Romania. Facies analysis of the 200 m thick succession of lower Middle Anisian limestones exposed in a large limestone quarry south of the village of Mahmudia suggests a transition from upper slope towards toe-of-slope carbonate facies, reflecting sea-level fluctuations and tectonic tilting. The slope is dominated by in situ microbialites in the upper portion, consisting of reefal boundstone facies, and by molluscan coquina and cement boundstones. A key role is played by the cosmopolitan micro-encruster Tubiphytes, which became common in the aftermath of the mass extinction at the Permian/Triassic boundary, and by autochthonous micrite and synsedimentary marine cement. The absence of metazoan reef builders, such as sponges and corals, reflects the fact that microbes were the first organisms to recover after the Permian/Triassic crisis under unusual marine conditions and that their main role in reef formation was sediment stabilization along the upper slopes. The lower slope is mostly detrital, being dominated by platform-derived bioclastic rudstones and crinoidal floatstones, which are interbedded with basinal carbonate hemipelagics. The toe-of-slope is composed of pelagic wackestones framed by thin tongues of intraclast breccia. All these observations are in agreement with the slopeshedding model described for the Pennsylvanian microbial margin in Asturias (northern Spain) and the AnisianLadinian flat-topped, steep-rimmed Latemar platform (Dolomites, Italy).As most of the Anisian reefs were described from western and eastern Tethys (Southern Alps, Hungary, China), the occurrence of the early Middle Anisian Tubiphytes-reef from North Dobrogea (Romania) contributes to resolving the puzzle of the geographic distribution of reef recovery in the Middle Triassic.

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Section: Diagenetic Historymentioning

confidence: 99%

An early Middle Anisian (Middle Triassic) Tubiphytes and cement crusts-dominated reef from North Dobrogea (Romania): facies, depositional environment and diagenesis

Popa¹,

Panaiotu²,

Grădinaru³

2014

Acta Geologica Polonica

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“…These fluids produced stratiform diagenetic features, including tepees, and favored growth of cyanobacterial mats and early dolomitization. However, the Latemàr facies and its distribution patterns argue against Blendinger's (2004) hydrothermal model, and stableisotope data from Latemàr are equivocal (Preto et al, 2005;Peterhänsel and Egenhoff, 2005).…”

Section: The Latemàr Controversymentioning

confidence: 99%

Lateral Variabilities of Cycle Stacking Patterns in the Latemàr, Triassic, Italian Dolomites

Peterhänsel¹,

Egenhoff²

2008

Controls on Carbonate Platform and Reef Development

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The well-known cyclic carbonate succession of the Middle Triassic Latemàr Massif in the Italian Dolomites reveals significant lateral variability in cycle numbers in platform-interior strata. Within an interval of 60 m, a 25% increase in the number of marine flooding surfaces was detected when approaching the several-hundred-meters-wide tepee belt in the backreef area, which represents the maximum elevation of the isolated Latemàr buildup. The impact of high-frequency-low-amplitude sea-level fluctuations on this elevated zone resulted in the development of spatially restricted intermittent emergence and marine flooding surfaces bounding small-scale upward-shallowing cycles. It is postulated that these alternations of submergence and subaerial exposure have favored tepee formation. Sediment collecting in the saucer-shaped tepee megapolygons further expedited upward shallowing of small-scale cycles. Conversely, deeper parts of the lagoon remained largely unaffected by high-frequency, lowamplitude sea-level oscillations: marine flooding surfaces disappear and cycles amalgamate. It is concluded that tepee structures are generally confined to topographically elevated areas where low-amplitude sea-level fluctuations were recorded. Lateral variations in cycle stacking pattern should be commonplace in shallow carbonate buildups throughout the geological record, where paleorelief existed in the platform interior.

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“…Blendinger (2004) stated (p. 21) that 'an alternative interpretation to eustatically controlled cyclicity and repeated subaerial exposure is provided by diagenesis in a hydrothermal fi eld.' However, the interpretations of Blendinger (2004) are clearly open to debate (Blendinger, 2005a,b;Preto et al, 2005;Peterhänsel & Egenhoff, 2005).…”

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confidence: 99%

The Allocyclic Interpretation of the ‘Latemar Cycles’ (Middle Triassic, the Dolomites, Italy) and Implications for High‐Frequency Cyclostratigraphic Forcing

Forkner

Hinnov

Goldhammer

et al. 2009

Perspectives in Carbonate Geology

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The Middle Triassic Latemar Platform is an approximately 5 km wide, 700 m thick isolated carbonate platform succession containing over 500 cycles (<1 m average thickness), which have been attributed to allocyclic forcing by Milankovitch to subMilankovitch cycle driven composite eustasy. These interpretations are based on the facies composition of the cycles (thicker subtidal units overlain abruptly by thin, centimetre-scale, subaerial caps), the 5:1 bundling of the 'fundamental' metre-scale cycles into lower-frequency 'megacycles', and spectral analyses of thickness and rank series showing conspicuous matches to predicted Milankovitch periodicities. The infl uence of periodic Milankovitch cycle-driven composite eustasy on the development of the Latemar cyclic succession has been questioned based on the dating of ashfall tuffs, palaeomagnetic analysis of the platform, and correlation to biostratigraphic markers in nearby basinal deposits. In order to test the interpretation of allocyclic forcing for Latemar cycles, the cyclic succession preserved at Mendola Pass (located 30 km northwest of Latemar Platform) was investigated where Latemar-equivalent cyclic platform interior strata are well exposed. The Mendola cycles (average 0.70 m per cycle) are also bundled into upward-thinning packages with an approximate 5:1 ratio. However, unlike the subtidal deposits immediately overlain by vadose diagenetic caps found in the Latemar succession, Mendola cycles consist of a mud-rich subtidal unit gradationally overlain by a cryptomicrobial (peritidal) laminite cap. A measured section from Mendola Pass of 36 cycles correlates biostratigraphically and statistically to a unique interval within the Latemar succession. Although laminite-capped cycles are often attributed to autocyclicity, the similarity of the stacking patterns of the Mendola cycles to those of Latemar support an allocyclic interpretation. In addition, depositional rates calculated from dated Holocene shallow-water carbonate facies equivalent to those at Latemar and Mendola Pass are shown to be consistent with Milankovitch or multimillennial periodicities, rather than millennial (1 kyr) cycle periods. Finally, the question of whether comparative sedimentology can be relied upon for the interpretation of relative cycle duration is considered, or if comparative sedimentology has reached its useful limit for identifying facies and depositional environments with respect to the Middle Triassic. It is concluded that statistical and biostratigraphic correlations, in addition to comparative sedimentology, indicate that the Latemar and Mendola cycles were deposited under the control of an allogenic forcing mechanism, and that this mechanism generated depositional cycles with multimillennial individual periodicities.

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Sea level changes versus hydrothermal diagenesis: Origin of Triassic carbonate platform cycles in the Dolomites, Italy: Discussion

Cited by 5 publications

References 22 publications

An early Middle Anisian (Middle Triassic) Tubiphytes and cement crusts-dominated reef from North Dobrogea (Romania): facies, depositional environment and diagenesis

An early Middle Anisian (Middle Triassic) Tubiphytes and cement crusts-dominated reef from North Dobrogea (Romania): facies, depositional environment and diagenesis

Lateral Variabilities of Cycle Stacking Patterns in the Latemàr, Triassic, Italian Dolomites

The Allocyclic Interpretation of the ‘Latemar Cycles’ (Middle Triassic, the Dolomites, Italy) and Implications for High‐Frequency Cyclostratigraphic Forcing

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