Three-dimensional burrow systems and taphofacies in shallowing-upward parasequences, lower Jurassic carbonate platform (Calcari Grigi, Southern Alps, Italy) (original) (raw)
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Multivariate analysis of taphonomic data in Lower Jurassic carbonate platform (northern Italy)
Comptes Rendus Palevol, 2005
Taphonomical analysis on skeletal concentrations and taphofacies has been carried out in the Lower Jurassic deposits of the Trento carbonate platform (northern Italy). The interpretation of the taphonomic categories used has been refined applying three statistical processes to the semi-quantitative values of taphocharacter abundance in eight types of skeletal concentrations. Analysis of correlation allowed the taphocharacters to be subdivided into four genetic categories: (1) palaeobiological processes on shelly ground; (2) palaeobiological activity on the substrate; (3) mechanical processes induced by currents; (4) infilling processes induced by currents. Cluster analysis on the eight types of skeletal concentrations defined six genetic processes. Moreover, principal-components analysis offered three factors which explained 75% of the variance. Factor 1 shows the contribution of hydrodynamic vs. bioturbation processes in the genesis of the resulting skeletal concentration. Factor 2 displays the degree of transport undergone by bioclasts before burial. Finally, factor 3 points out the dominance of superficial taphodistortion and colonization of the substrate, or deeper colonization in the substrate. Numerical analysis on taphonomical data has been proved to be a powerful tool for palaeoenvironmental studies, thereby aiding in the understanding of the shell beds genetic processes.
Sedimentary Geology, 2012
The so-called Umbria-Marche Domain of Northern Apennines represents a vast depositional system, also stretching across the Adriatic Sea subsurface, that was characterized by dominantly pelagic sedimentation through most of its Jurassic to Oligocene/Early Miocene history. The pelagic succession is underlain by Hettangian shallow-water carbonates (Calcare Massiccio Fm.), constituting a regional carbonate platform that was subjected to tectonic extension due to rifting of the Adria/African Plate in the earliest Jurassic. While tectonic subsidence of the hangingwalls drove the drowning of the platform around the Hettangian/ Sinemurian boundary, the production of benthic carbonate on footwall blocks continued parallel to faulting, through a sequence of facies that was abruptly terminated by drowning and development of condensed pelagites in the early Pliensbachian. By then rifting had ceased, so that the Pliensbachian to Early Cretaceous hangingwall deposits represent a post-rift basin-fill succession onlapping the tectonically-generated escarpment margins of the highs. During the early phases of syndepositional faulting, the carbonate factories of footwall blocks were still temporarily able to fill part of the accommodation space produced by the normal faults by prograding into the incipient basins. In this paper we describe for the first time a relatively low-angle (b10°) clinoform bed package documenting such an ephemeral phase of lateral growth of a carbonate factory. The clinoforms are sigmoidal, and form low-relief (maximum 5-7 m) bodies representing a shallow-water slope that was productive due to development of a Lithocodium-dominated factory. Continued faulting and hangingwall subsidence then decoupled the slope from the platform top, halting the growth of clinoforms and causing the platform margin to switch from accretionary to bypass mode as the pre-rift substrate became exposed along a submarine fault escarpment. The downfaulted clinoform slope was then buried by base-of-escarpment proximal turbidites, forming a bypass wedge. Such a contact would be imaged along a seismic section as an unconformity, suggestive of shut-off of the local carbonate factory and onlap by pelagic mud. The composition of the turbidites, however, at least initially duplicates that of the clinoforms, indicating that the footwall top was still productive, yet the mechanisms of sediment shedding into the basin had changed due to the modifications of submarine topography induced by synsedimentary tectonics.
ISBN: 9781444304411. 03/2009: pages 367 - 400
The Barcellona Pozzo di Gotto Basin of northeastern Sicily, central Mediterranean, is a Plio-Pleistocene peri-Tyrrhenian shelf embayment that formed by the collapse and marine inundation of bedrock fault-blocks in response to regional tectonic extension. The study focuses on the well-developed transgressive systems tract of the lower bay-fill sequence. This succession of Middle Pliocene to Lower Pleistocene marine deposits has a mixed siliciclastic to bioclastic composition and is ~73 m thick in mid-bay outcrop section. The deposits are sandy to silty facies indicating a wavedominated bay influenced by storms and tidal currents and water rich in suspended sediment. Facies associations represent upper and lower shoreface, offshore-transition and mid-bay offshore zones. The abundance of silty to sandy suspension is attributed to the entrapment of fine sediment entrained by storms and tides and possibly derived from nearby streams. The supply of sediment from the bay's shoreline zone probably combined with fine-grained sediment drift from offshore areas, as is also suggested by admixtures of outer circalittoral benthic microfauna. Facies-based estimates indicate a water depth of ≤ 25 m for the mid-bay area, with a mean depth of ~10 m for fairweather wave base and ~15 -16 m for storm wave base. The shallow bay hosted circalittoral benthic fauna typical of deeper water Mediterranean shelves, which can be attributed to the high turbidity of the bay water.
Rivista Italiana di Paleontologia e Stratigrafia
The trace fossil Desmograpton Fuchs, 1895, as many other graphoglyptids, has been considered to be a typical pre-turbidite, three-dimensional burrow system formed in mud and preserved as a casting at sole of turbidites. This classic interpretation was mostly based on hypichnial preservation, for the lack of direct evidences (e.g. modern seafloor pictures) for pre-depositional or post-depositional origin. Due to the accidental series of processes invoked to explain the perfect hypichnial preservation of this delicate trace fossil, several doubts and questions have been raised. To try to explain this aspect, many Desmograpton dertonensis Sacco, 1888 and Desmograpton ichthyforme Macsotay, 1967 specimens have been analysed at sand/clay interface of thin-bedded calcarenites in the Miocene marl deposits of Verghereto, Northern Apennines (Italy). Petrographic analysis of textures and grains of the burrow-filling sediments points out that most of the grains of burrows differs from those of ...
Italian Journal of …, 2011
Bipedal tridactyl dinosaur footprints dominate the Early Jurassic Coste dell'Anglone tracksite, located on the eastern slope of the Mt. Biaina-Mt. Brento chain (Trentino Alto-Adige, NE Italy). The site yielded 544 tridactyl footprints, arranged in 20 long trackways, and belongs to the upper part of the Calcari Grigi Group (lower portion of the Rotzo formation). All the tracks can be attributed to smalland medium-sized theropods. Trace fossils were discovered in a peri tidal carbonate succession deposited in a marginal area of the Trento carbonate Platform, which has so far been considered fully marine (subtidal) in origin. The Coste dell'Anglone outcrop represents one of the most extensive Early Jurassic dinosaur tracksites in the Southern Alps and is probably the last dinosaur occurrence on the Trento Platform. The ichnological and sedimentological analyses of the track-bearing sequence indicate a depositional setting corresponding to a tidal flat embayment, positioned on the westernmost sector of the Trento Platform, close to the Lombardy pelagic basin. Stratigraphical data indicate that dinosaur populations lived in this area until the Sinemurian.
The morphological expression of trace fossils varies according to whether they are preserved, within/between sandstone or mudstone beds. For this reason a toponomy has been proposed and a series of terms, the so-called Seilacher's and Martinsson's terms, has arisen to describe the preservation potential of trace fossils. They are: hyporelief or hypichnia (base of bed at boundary), full relief or endichnia (inside bed), full relief or exichnia (outside bed) and epirelief or epichnia (top boundary) (Seilacher, 1964; Martinsson, 1970). Both of these clas-sifi cations involve structures which are strictly related to the casting medium of an event bed or transition with underlying or overlying beds (Bromley, 1990). Typi-cal expression of hyporelief are graphoglyptids (Fuchs, 1895), a large supergroup of geometrical trace fossils usually preserved at soles of deep-water turbidite deposits of basin plains, which includes a very high diversity of ichnogenera and species (Seilacher, ...
Palaeogeography, Palaeoclimatology, Palaeoecology, 2001
Micropalaeontological investigation of one of a number of black shale horizons within the carbonate platform sediments of the Calcari Grigi Formation (Trento Platform, NE Italy) has yielded the ®rst recorded oligohaline, early Jurassic, ostracod assemblage. The shale is dated as late Sinemurian on the basis of large benthic foraminiferal biostratigraphy in the sediments above and below. The shale is devoid of foraminifera and ammonites, which supports a non-marine context. Three previously unknown ostracod species are identi®ed, however, the assemblage is dominated (.95%) by a single taxon which is erected as a new genus and species (Phraterfabanella tridentinensis Whatley and Boomer gen. et sp. nov.) which further supports the interpretation of a ªstressedº environment. The two remaining ostracod taxa are assigned to Klieana and Limnocythere both considered to represent non-marine or very low salinity conditions. This new genus includes probable members from the Rhaetian of Hungary and France as well as from the Liassic of France. The new genus is shown to be one of the earliest representatives of the Cytherideidae, a family which survives to the present and includes the modern pandemic, euryhaline species Cyprideis torosa.
Cretaceous Research, 2019
Carbonate platforms are sedimentary archives recording the evolution of the global carbon cycle. Their stratigraphic architecture depends on the regional tectonics, controlling subsidence rates and geometries, as well as the paleoceanography and evolutionary trends, controlling the different organisms thriving at their margins, such as frame-building corals or mound-building microbes. We present an integrated bio-and chemostratigraphic study of the Aptian to Santonian interval of a base-of-slope section located in the Southern Alps of northeastern Italy that we correlate with the classic section representing the Friuli-Adriatic Carbonate Platform, one of the largest isolated platforms of the low latitude Tethys. We show the effects of the end of the passive-margin stage and the interaction between foreland flexuring due to the growing Alps, to which the study area represented the retroforeland, and the approaching prowedge of the Dinarides. The Friuli-Adriatic platform margin shows an abrupt change from reef rimmed to ramp, where abundant microbial mounds provided the habitat for the rudists to thrive. This change occurred around the late Albian and likely correlates with the Oceanic Anoxic Event (OAE) 1d. The previous OAE's did not change the structure of this platform, whose margins were mostly rigid and colonized by corals and calcareous sponges. Late Albian was a time of important changes in paleoceanography in Tethys Highlights • Correlation of a carbonate platform with its base-of-slope by integrating nanno and foraminifera bio-and chemostratigraphy. • At the late Albian, the slope changed from sediment-starved to gravity flows supplied; the platform margin changed from rimmed to ramp. • Corals and calcareous sponges were replaced by rudists and microbes forming large mounds. • Alpine/Dinaric foreland tectonics and the environmental stress related to the OAE1d controlled this abrupt change.