The Latemar is a mainly aggrading platform, but shows repeated backstepping during its entire development. The behaviour of the slope does not reflect accommodation changes and lateral consistencies ...of the lagoonal interior; the Latemar contemporaneously reveals different, even contrasting depositional characteristics. The slope of the late stage platform evolution corresponds at least partially to the "base-of-slope apron" model. Controlling factors on slope evolution are of tectonic (proximity of the Stava Line) and autocyclic (repeated oversteepening) nature. Other factors are insignificant and/or overprinted. The reef-facies at Latemar reveals a complex facies pattern; it varies along and across the margin and is rich in encrusting sponges, corals, biogenic crusts and "Microproblematica". Some biota or fossil assemblages--e.g. foraminifers (Abriolina mediterranea, Turriglomina scandonei) or "Tubiphytes" multisiphonatus thrombolites--have not been described in the Dolomites before. Biostratigraphic evidence from the uppermost reef-facies confirms a mainly Anisian age of the outcropping platform interior.PUBLICATION ABSTRACT
Massive early marine cementation (MEC) is a major diagenetic feature of some carbonate platforms. The comparison of two Triassic buildups of similar size and preservation but contrasting degree of ...MEC (Latemar, Dolomites, and Concarena, Lombardic Alps) allows for the investigation of differential cementation on carbonate platforms. The assessment of the response of platform cementation to changes in accommodation/sedimentation led to the identification of fundamental boundary conditions for MEC: (1) the time interval available, i.e. a low rate of creation in accommodation space and (2) low carbonate production. Other important factors are: (3) margin topography (e.g. walled reefs) and (4) effective fluid flow (e.g. wave energy, open and connected cavities provided by rigid frameworks). The Latemar–mainly aggrading and locally retrograding–lacks MEC due to a high
A′/
S′ ratio (i.e. creation/destruction of accommodation in time,
A′=d
A/d
t, vs. changes in sediment supply in time,
S′=d
S/d
t) and a low relief of the reefal margin. In contrast, the Concarena–in the beginning slowly and later rapidly prograding–indicates MEC owing to a low
A′/
S′ ratio and a distinct topography of the reef. Particular features of the Concarena are cement arrangements of lenticular shape and considerable size in the back-reef domain (up to 3 m in diameter and 2 m in height). These arrangements consist of botryoids and isopachous crusts of radiaxial fibrous calcite cements. They represent one of the main components of the platform margin at Concarena. Cathodoluminescence analyses of cements from both platforms quantifies the influence of shallow and deep burial diagenesis and shows that the majority (60–90%) of all cements are of early marine origin.
The well exposed Late Paleozoic to Cenozoic succession in the western High Atlas (Morocco) documents the early rift to mature drift development of the eastern Central Atlantic continental shelf ...basin. Vertical sections, depositional geometries and unconformities have been used to reconstruct the basin architecture prior to Atlasian inversion. Two-dimensional reverse basin modeling has been performed to quantitatively analyze the development of the continental shelf between the latest Paleozoic to Early Cenozoic. Basin evolution stages include (i) early rift, Late Permian to Anisian; (ii) rift climax, Ladinian to Carnian; (iii) sag, Norian to Early Pliensbachian; (iv) early drift, Late Pliensbachian to Tithonian; (v) mature drift, Berriasian to Cenomanian; (vi) mature drift with initial Atlasian deformation, Turonian to Late Eocene; (vii) Atlasian deformation; Late Eocene to Early Miocene; (viii) Atlasian uplift and basin inversion, Early Miocene to Recent. The Late Permian to Late Cretaceous basin development comprises eight subsidence trends of 10–35
Myr duration. Trends were initiated by changes in thermo-tectonic subsidence, which in turn triggered positive and negative feedback processes between sediment flux, flexural and compaction-induced subsidence. Plate-tectonic reconfigurations in the Atlantic domain controlled the thermo-tectonic subsidence history and the basin development of the Agadir segment of the northwest African passive continental margin: (1) major shifts in the sea-floor spreading axis; (2) significant decreases in sea-floor spreading rates; (3) the stepwise migration of crustal separation and sea-floor spreading in and beyond the Central Atlantic; (4) African–Eurasian relative plate motions and convergence rates. During the Early Pliensbachian/Toarcian to Cenomanian the first three plate-tectonic reconfigurations triggered changes in ridge-push forces and modulated the extensional stress field of Central Atlantic plate drifting. Since the Turonian, African–Eurasian relative plate motions and convergence rates represented the dominant control on the thermo-tectonic subsidence history in the Agadir Basin. Major variations in sediment flux and total subsidence characterize the development of the northwest African passive continental margin. The explanation of typical stratigraphic sequences as caused predominantly by sea-level fluctuations, and rough assumptions on sediment input/production and subsidence, is not necessarily applicable to passive continental margins. The methodology applied in this study, including the newly developed tool of ‘Compositional Accommodation Analysis’, allows to develop more rigorous genetic models for the development of continental shelf basins.
ABSTRACT Sedimentary cycles recorded in young sediments are often attributed to fluctuations of the Earth's climate on a 104−106‐year scale which in turn is governed by periodic variations in solar ...insolation linked to orbital (Milankovitch) parameters. A spectacular example of cyclic stratal patterns in ancient deposits is the Middle Triassic Latemar carbonate platform (W Dolomites, N Italy). Based on spectral analyses from previous studies, a superimposition of precession (∼20 ka) and eccentricity (∼100 ka) controlled sea‐level fluctuations has been suggested to account for the stacking hierarchy at Latemar, with ∼20 ka being assigned to each highest‐order depositional cycle. Zircon U–Pb isotopic ages from volcanic‐ash layers within the cyclic succession, corroborated by biostratigraphic constraints, suggest that the average time interval for every individual cycle is significantly smaller than the shortest Milankovitch period and therefore challenge previously published interpretations relating distinct spectral peaks to the above mentioned hierarchy. However, our new spectral data indicate that cyclicities resembling Milankovitch characteristics might exist, but on an entirely different scale. Our findings show that frequency spectra should only be interpreted in combination with robust age control. They also encourage the search for complementary mechanisms controlling carbonate deposition.
The Rosengarten and Latemar Middle Triassic carbonate platforms indicate similar subsidence patterns during equivalent times of platform evolution as calculated by numerical basin reverse modelling. ...In the case of Rosengarten and Latemar, thermo-tectonic subsidence is the most significant among all three subsidence components (thermo-tectonic s., flexural s., compaction-induced s.). Hence, the influence of differential tectonics–as recorded in the formation of structural highs and lows in the Dolomites during the Lower to Middle Anisian–almost ceases in Late Anisian times.
Basin modelling of Rosengarten and Latemar requires the correlation and integration of two sets of chronostratigraphic data from Buchenstein Fm (basin) and Schlern Dolomite Fm 1 (platform). Subsidence modelling argues for a microcycle (i.e. a single shallowing-upward cycle) duration of less than 1.97 ka in the cyclic succession at Latemar. However, previous time series analyses identify Milankovitch-cyclicities in larger-order cycle stacking patterns and thus indicate a microcycle duration of 4.2 ka. According to each model, total subsidence reaches values of 650–700 m/Ma (4.2 ka model) or 780–850 m/Ma (1.97 ka model) during the first stage of platform evolution. As both platforms successfully keep up with this subsidence peak, it is evident that the carbonate factory–despite its low diversity–must have recovered from the P/T faunal crisis. After this regionally observed peak, subsidence drops and triggers fast progradation at Rosengarten.
Subsidence in the study area is controlled by active strike-slip tectonics and the subsequent formation of a magmatic chamber (Predazzo/Monzoni) above the deep-reaching Truden/Stava line. The area close to this tectonic line and to the volcanic centre of Predazzo/Monzoni undergoes a higher heat flow pulse during the Late Ladinian and is possibly buried at shallower levels than the Rosengarten area. As shown by fission tracks in apatites, the heat flow pulse almost disappears laterally underlining the localised thermal influence of the Late Ladinian volcano-thermal event of Predazzo/Monzoni.
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