Massimo Santantonio

Jurassic rifting evolution of the Apennines and Southern Alps (Italy): Parallels and differences

Jurassic rifting in the southern Alps and Northern Apennines occurred within a relatively short (2–4 m.y.) interval of tectonic activity (late Hettangian–early Sinemurian) in proximal areas (central-eastern southern Alps and Northern Apennines), and was followed by calm postrift sedimentation. The main axis of the rift jumped in the late Early Jurassic to the previously unaffected, mostly nonsubsiding and/or uplifted distal areas of southwestern Tuscany and the western southern Alps. Synchronous stretching occurred in the Helvetic-Brianconnais domains of the Alps and in the Longobucco-Caloveto area (Calabria), here interpreted as the conjugate margin of western southern Alps and southwestern Tuscany. Major differences occur in the extensional structural style of the southern Alps and Apennines. The Northern Apennines are characterized by diffuse thin-skinned stretching at shallow depths and by localized thick-skinned stretching at deeper crustal levels. This style contrasts with the well-known thick-skinned nature of extensional tectonics in the southern Alps, which are also characterized by a larger spacing between major normal faults. It is suggested that these different extensional styles were controlled by contrasting rheologies induced by the different stratigraphies. The strong strain partitioning and the diffuse shallow thin-skinned tectonics of the Northern Apennines basins are here related to the occurrence of thick (up to 2 km) evaporites that underlie a relatively thin (up to 1.3 km) carbonate platform.

Control of differential compaction on the geometry of sediments onlapping paleoescarpments: Insights from field geology (Central Apennines, Italy) and numerical modeling

Basin strata onlapping pelagic carbonate platform margins in the Central Apennines commonly dip considerably (as much as 20°–30°) toward the basin when platform strata (Calcare Massiccio) are retrodeformed to horizontal in order to undo the tilting related to Apenninic compressional tectonics. These angular relationships are commonly ascribed to normal drag associated with synsedimentary faulting. We show that such angular relationships are fully consistent with results of numerical simulations that aim at modeling first-order geometric features associated with sedimentation and compaction of deposits onlapping the escarpment at the margin of basins. Therefore, growth of an underlying normal fault is not generally required to generate them. This conclusion is also supported by field investigations of the contacts at pelagic carbonate platform margins and by paleoescarpment analysis, which strongly suggest post–early Liassic tectonic quiescence.

Slab bending, syn‐subduction normal faulting, and out‐of‐sequence thrusting in the Central Apennines

In the Central Apennines, a Tertiary-Present eastward-vergent fold and thrust belt, thrusting mainly occurred in-sequence, cutting across a Mesozoic to Early Neogene succession, deposited in rifted (Early Jurassic) to passive continental margin, to foredeep (late Miocene) conditions. However, the Simbruini Mts were characterized by the occurrence of regional out-of-sequence thrusts (the Vallepietra-Filettino-Monte Ortara thrust fault) and ofTertiary prethrusting normal faults, associated with the deposition of thick breccia deposits (Brecce della Renga, Tortonian-early Messinian). A direct link between these two features is here proposed. Evidence for a prethrusting normal faulting origin for the Brecce della Renga is amply discussed. Although evidence for subduction-related normal faulting is growing in the Apennines literature, nowhere in the region are known extensional systems so vast and their syn-tectonic deposits so thick as in the Simbruini area. We propose that the Simbruini prethrusting normal faults were subduction related, i.e., they developed in the foreland due to anomalous bending of the lithosphere subducting in Late Tertiary time under the Apennines in the Simbruini Mts area. The associated breccia deposits were subsequently deformed during the development of the Simbruini Mts thrust front. We speculate that the prethrusting normal faults allowed the penetration of fluids within the subducting crust and possibly also in the mantle, weakening this part of the subducting plate. As a consequence, the weaker plate was anomalously down-bent, leading to a subcritical state of the Apennines wedge. The regional scale out-of-sequence thrust faults developed in order to bring the Apennines wedge back to the critical state.

Carbonate intercalations in a terrigenous foredeep: late Miocene examples from the Simbruini Mts. and the Salto Valley (Central Apennines - Italy)

Resedimented calcarenites and hybrid arenites are commonly found interbedded with various Upper Miocene terrigenous units (hemipelagic marls, “brecce della Renga fm.”, and siliciclastic turbidites) across the Simbruini Mts. and neighbouring areas of Central Apennines. Their distribution provides evidence for a complex, and rapidly evolving, paleogeography across a region that was experiencing the transition from foreland to accretionary wedge conditions during the Tortonian and Messinian. The bio-sedimentological features of the calcarenites indicate deposition through gravity flows (turbidity currents) sourced by areas of active benthic, heterozoan-type carbonate production, locally lying at photic depth. Thin-section analysis of >130 samples revealed that the resedimented levels are mainly composed by bioclastic calcarenites, with fragments of bivalves, echinoids, bryozoans, balanids, benthic foraminifera, anellids and red algae, along with subordinate planktonic foraminifera. The calcareous turbidites in the hemipelagic marls (Unita argilloso-marnosa) are characterized by the presence of Heterostegina sp., and their main source area was probably lying east, on the undeformed foreland. In contrast, evidence from field mapping, their common association with Cretaceous and Miocene carbonate lithoclasts, and the age of the encasing units, all suggest that the calcarenites in the “brecce della Renga fm.” and in the siliciclastic turbidites (“complesso torbiditico altomiocenico laziale-abruzzese”) could most likely have a different source. The presence of a carbonate ridge, corresponding today to the NW sector of the Simbruini range, bordered by normal faults exposing the Cretaceous substrate, is proven proven by mappable paleo-escarpment tracts onlapped by clastic and hemipelagic deposits. This ridge could have fed surrounding deeper areas with a mixture of lithoclasts and loose bioclastic material, produced through erosion of exposed bedrock coupled with export of sediment that was being produced topping and fringing the footwall blocks and their marginal downsteps. Carbonate production was apparently able to survive for a limited time in small productive areas until the early Messinian, shedding sediment into the siliciclastic foredeep.

Discussion on «Geological map of the partially dolomitized Jurassic succession exposed in the central sector of the Montagna dei Fiori Anticline, Central Apennines, Italy» by

In their paper on the Montagna dei Fiori area, [Storti et alii (2017][1]) present a new geological map and discuss the dolomitization pattern and the Jurassic extensional architecture of this sector of the Central Apennines. They conclude that their “field evidence does not support the gravity-

Discussion on «Geological map of the partially dolomitized Jurassic succession exposed in the central sector of the Montagna dei Fiori Anticline, Central Apennines, Italy» by G. Storti, F. Balsamo & A. Koopman (2017)

In their paper on the Montagna dei Fiori area, [Storti et alii (2017][1]) present a new geological map and discuss the dolomitization pattern and the Jurassic extensional architecture of this sector of the Central Apennines. They conclude that their “field evidence does not support the gravity-

Forward modelling of the Montagna dei Fiori fault-related fold (Central Apennines, Italy), using combined kinematic models .

The Subandean Basins of South America extending from Trinidad to Tierra del Fuego have been the object of intensive exploratory activities (Fig. 1). The largest amount of hydrocarbons discovered during the last 30 years in these basins was found in complex structural terrains. A total of 59 Billion Barrels of Oil Equivalent (BBOE) have been discovered in areas affected by compressional tectonics. Of these basins, the largest discoveries are in the Furrial Trend of Venezuela (24 BBOE), followed by the Chaco area in Bolivia and Argentina (13 BBOE), the Llanos Foothills of Colombia (4.4 BBOE), and the Madre de Dios Basin of Peru (4.2 BBOE).

The Terni “corridor”: new stratigraphic constraints for the reconstruction of the Jurassic paleotopography of Central Apennines.

Abstract from 88th Congress of the Italian Geological Society, 2016-09-07 - 2016-09-09, NaplesAbstract from 88th Congress of the Italian Geological Society, 2016-09-07, 2016-09-09, Naplesbook Edited by D. Calcaterra, S. Mazzoli, F.M. Petti, B. Carmina & A. Zuccari doi: 10.3301/ROL.2016.79