Footwall progradation in syn-rift carbonate platform-slope systems (Early Jurassic, Northern Apennines, Italy) Simone Fabbi, Massimo Santantonio ⁎ Dipartimento di Scienze della Terra, Università “La Sapienza”, Piazzale Aldo Moro 5, 00185 Roma, Italy abstract article info Article history: Received 27 March 2012 Received in revised form 16 July 2012 Accepted 17 July 2012 Available online 27 July 2012 Editor: Dr. B. Jones Keywords: Carbonate slopes Early Jurassic Clinoforms Synsedimentary extension 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 escarp- ment 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 (b 10°) clinoform bed package documenting such an ephemeral phase of lateral growth of a car- bonate 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 sub- strate became exposed along a submarine fault escarpment. The downfaulted clinoform slope was then bur- ied 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. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Over vast areas of present-day Italy, the deposition of shallow-water, tropical-type carbonates in the Hettangian is documented either as a con- tinuation of Triassic sedimentation history in a continental, marginal ma- rine to carbonate platform environment (Corna Fm., Lombardy, Southern Alps; Apulia Platform), or as a part of a blanketing succession deposited over regions that had previously experienced phases of extension and de- velopment of deeper-water basins during the Triassic (e.g. Calcari Grigi Fm., Dolomites, Southern Alps) (Santantonio and Carminati, 2011, and references therein). In the Northern Apennines (Umbria–Marche to much of Tuscany), the Hettangian limestone (Calcare Massiccio Fm. and allied units) overlies a carbonate/salt to pure carbonate Norian to Rhae- tian succession (Ciarapica and Passeri, 1998; De Paola et al., 2007). The region was then subjected to rift tectonics around the end of the Hettangian/early Sinemurian, which produced a diffuse frag- mentation of the Hettangian platform, with a suite of linked effects that ultimately led to widespread demise of benthic carbonate pro- duction. The drowning of the Calcare Massiccio platform is seen across the Umbria–Marche region and most of the Adriatic Sea sub- surface through a change to pelagic or pelagic/turbiditic sedimenta- tion occurring in the late Hettangian to early Pliensbachian (Centamore et al., 1971; Farinacci et al., 1981; Passeri and Venturi, 2005; Marino and Santantonio, 2010; Santantonio and Carminati, 2011). The relationships between rift-related synsedimentary ex- tension, oceanographic change, and the demise of benthic-factory dominated carbonate sedimentation are discussed in Morettini et al. (2002) and Marino and Santantonio (2010). These papers suggest rapid tectonic subsidence as the cause of platform drowning in Sedimentary Geology 281 (2012) 21–34 ⁎ Corresponding author. E-mail addresses: simone.fabbi@uniroma1.it (S. Fabbi), massimo.santantonio@uniroma1.it (M. Santantonio). 0037-0738/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.sedgeo.2012.07.008 Contents lists available at SciVerse ScienceDirect Sedimentary Geology journal homepage: www.elsevier.com/locate/sedgeo