Carbonate platforms across the peri-Mediterranean region were extended in the Early Jurassic, as a result of intracontinental rifting which would lead to seafloor spreading in the western Tethys. The Northern Apennines provide spectacular field evidence enabling researchers to tackle a well known subject in new, stimulating ways, but still using "old" tools.
Initially (late Hettangian) footwall platforms prograded, through the growth of low-angle clinoform slopes, taking advantage of the accommodation space provided by incipient hangingwall subsidence. The clinoforms hosted in-situ subtidal production, largely microbial, with tubular Cyanophyceae, Thaumatoporella, and microproblematica (Lithocodium-Bacinella) dominating. Tectonic subsidence rates soon exceeded the carbonate growth potential, so hangingwall carbonate factories, including those initial prograding wedges, were drowned and foundered as room was created to host thick pelagic and resedimented successions. Faulting produced a submarine relief of about 1km, locally up to about 2km. Constraints for computing slip rates come unexpectedly from an hands-on examination of exhumed submarine fault escarpments. As fault activity declined, a thin drape of condensed pelagic epi-escarpment deposits could settle, and locally remain preserved, on the pre-rift peritidal limestone exposed at the footwall. Ammonite biostratigraphy of these condensed deposits, coupled with geological mapping, serves to constrain the minimum rates of footwall unroofing as the beds of the peritidal substrate they overlie unconformably can be traced laterally to reveal how much deep into the footwall stratigraphy had fault-displacement progressed at the times when the pelagic drape was sedimented. Plotting the oldest age of the epi-escarpment deposits against the lowest stratigraphic level in the footwall they rest upon provides the minimum slip rates for the local rift fault. Numerical results are in the order of 100's of metres/million year, but actual rates could have been one order of magnitude higher. In addition, the paleoescarpment dataset reveals that the total displacement along synsedimentary faults was attained in a short burst (late Hettangian-early Sinemurian), so the accommodation space produced by rift faults was essentially filled by a post-rift succession.
The tectonically-driven drowning of hangingwall platforms is documented by a drowning succession, with mixed components of the planktonic (calcareous nannoplankton) and benthic carbonate factories. This is older than that observed on structural highs, where an association with dominant microbial oncoids, crinoids, siliceous and calcareous sponges and benthic foraminifera documents sedimentation on a deeper carbonate bank that persisted for a few million years, until the earliest Pliensbachian. The disappearance of coated grains, and appearance of ammonite-dominated assemblages, marks a super-regional, synchronous drowning event interpreted as unrelated with tectonics, and driven instead by paloceanographic perturbation. Following this, the footwall blocks became Pelagic Carbonate Platforms (PCPs), hosting a condensed succession documenting the Pliensbachian-Tithonian in few tens of metres or less. While the geometry of the PCP-top succession was a wide convex-up lens, with stratigraphic units thinning out towards PCP-edges, scattered condensed deposits are also found along the marginal paleoescarpments, or draping megabreccia piles or house-size olistoliths at basin margins. The basin-fill history ended in the Early Cretaceous as the calpionellid limestone (Maiolica) eventually onlapped the uppermost escarpment and PCP-top succession.