Carbonate production of ancient debris-dominated reefs: An outcrop-based example from the Upper Jurassic reef complex of the central Apennines (Italy)

Abstract

This study provides the fi rst quantitative carbonate production estimate of an ancient debris reef, represented by the Upper Jurassic reef complex of the central Apennines. The components of carbonate production (Pnet, Psed, and Pgross) have been defi ned entirely on the basis of outcrop data. The reef volume (Pnet) was reconstructed based on the present distribution of the Upper Jurassic reef complex and its relationship with coeval successions of platform and slope. The volume of sediment exported along the slope (Psed) was obtained through the reconstruction of the thickness reduction pattern of the reef-derived sediments, at increasing distances from the platform margin. Several variables have been introduced to overcome the lack of data in some areas.The estimates obtained indicate that the Upper Jurassic reef complex produced a total amount of calcium carbonate equal to 1.7-2.3 times the amount of material retained in the reef complex. This excess volume of sediment produced was redistributed along the slopebasin system, up to a distance of ~55 km from the platform margin. According to the indices commonly used for quantifying carbonate production, the Upper Jurassic reef shows values that are consistently lower than other ancient and Holocene reef systems. The interaction between the sedimentologic characteristics of the reef structure and the hydrodynamic processes is ultimately seen as the main mechanism responsible for the low growth potential and reduced export of reef material. The methodology and the procedure used were designed specifi cally for the site being studied but could potentially be adapted for use in other regions where the data required are diffi cult to access. Isolated coral colonies are a few decimeters to 1 m wide, in life position, toppled or as large coral fragments, apparently without an evident preferential direction of dispersion. Preserved coral colonies have branching and massive morphologies. Bioerosion and microencrusters represent relevant features. They are mainly present in the back-reef zone and are more rare in the reef fl at.Calcifi ed demosponges are present as whole specimens or as large fragments with variable dimensions, growth fabric, degree of reworking, and distribution across the reef complex. Chaetetids are generally more abundant, larger, and better preserved in the back reef, where they form closely packed colonies, whereas they are fairly scarce in the external zones of the reef complex. Stromatopores show the opposite distribution pattern: They are very rare and small in the back reef, whereas they increase in frequency, degree of preservation, and dimensions toward the external reef zones, where several tens of whole stromatopore specimens form densely packed, moundshaped structures, 0.5 to 10 m 2 wide (stromatopore mounds).Microencrustations actively contribute to the reef construction by binding and cementing sediment and other reef components. They are micropeloidal microbialites, organized into different structures (stromatolitic, trombolitic, leioli...

Geological mapping reveals the role of Early Jurassic rift architecture in the dispersal of calciturbidites: New insights from the Central and Northern Apennines

“…A larger amount of resedimented carbonates characterizes the Sabina region, traditionally considered the transitional belt connecting the LACP with the Umbria‐Marche Basin s.s. (Cantelli, Castellarin, & Praturlon, 1978; Cosentino & Parotto, 1989; see also discussion in Galluzzo & Santantonio, 2002). However, the occurrence of Lower Jurassic syn‐rift resediment‐rich stratigraphic intervals is also well‐documented in ‘pure’ basinal settings of the Umbria‐Marche region (Cipriani, 2016; Coltorti & Bosellini, 1980; Fabbi, 2015; Galdenzi, 1986; Santantonio, Fabbi, & Bigi, 2017), and the same holds true for post‐rift Jurassic‐Cretaceous shallow water‐derived resediments (Bartoccini & Rettori, 1991; Cipriani, Citton, Romano, & Fabbi, 2016; Citton, Fabbi, Cipriani, Jansen, & Romano, 2019; Colacicchi & Monaco, 1994; Fabbi et al, 2016; Giannini, Lazzarotto, & Zampi, 1970; Monaco et al, 1994; Monaco, Nocchi, & Parisi, 1987; Pierantoni et al, 2013; Rusciadelli et al, 2009; Rusciadelli & Ricci, 2013).…”

Post-rift extensional tectonics at the edge of a carbonate platform: insights from the Middle Jurassic-Early Cretaceous Monte Giano stratigraphic record (central Apennines, Italy)

“…For these reasons, it is partly correlated with the nerineid and diceratid limestones fm. of Rusciadelli and Ricci (2013).…”

“…This unit is a shallowing and coarsening upward sequence, which testifies the progradation of the margin of the Latium-Abruzzi platform onto the previous slope, with large-scale clinoforms made up of shallow water debris. The occurrence of rare pelagic organisms (Saccocoma sp., radiolarians and calpionellids) testifies sedimentation developed on a very broad marginal environment (Rusciadelli and Ricci, 2013) with unrestricted water circulation. The thickness ranges between 400 and 180m, from the southern to the northern part of the area, due to the lateral transition with the Velino Gorge limestones Fm.…”

“…5E-F). Turbidites are related to a general recovery of healthy carbonate production throughout the Latium-Abruzzi platform due to the bloom of producers (Damiani et al, 1991b(Damiani et al, , 1998Chiocchini et al, 1994), documented elsewhere in the central Apennines by broad platform rim/margin complexes (Rusciadelli and Ricci, 2013).…”

“…are thought to represent Upper Jurassic marginal facies around the Latium-Abruzzi platform and the Apulian platforms, both at surface (Miccadei et al, 2014) and subsurface (Santantonio et al, 2013). This evolution from distal to proximal facies during the whole Tithonian could be the result of a combination of two important factors: i) the geometry of the carbonate platform, which was not a rimmed platform with a marginal area gently dipping towards the basin (Rusciadelli and Ricci, 2013); and ii) the strong global regressive character of sedimentation (Gill et al, 2004;Hardenbol et al, 1998;Jacquin et al, 1998), with three prominent sea-level drops found in eustatic-cycle charts (Haq, 2017). Remarkably, the punctuated occurrence of deep-photic zooxanthellate corals in PCPs, in the Umbria-Marche Basin, related to these eustatic fluctuations in the Apennines was reported by Santantonio et al (1996) and Gill et al (2004).…”