To be allochthonous or autochthonous? The late Paleocene–late Eocene slope sedimentary succession of the Latium–Abruzzi carbonate platform (Central Apennines, Italy)

Margins, slopes, and toe-of-slopes represent regions of sediment transfer and bypass from shallow-water settings to the basin. They are zones of sediment flux triggered by different types of physical process including sediment-gravity flows, storm-driven currents, unidirectional currents, and oscillatory flows. As a consequence, they are zones where sediment can be remobilized and strongly reworked from inner environments to offshore settings and deposited as a mixture of autochthonous/allochthonous sediments. In the Monte La Serra and Monte Torretta (Central Apennines) lower-to-upper Eocene reworked sedimentary succession, two main facies associations are differentiated on textural characteristics and tested for robustness by hierarchical cluster analysis: a grain-supported (packstone-to-grainstone) facies FA1 and a mud-supported (mudstone-to-wackestone) facies FA2. The outcrops allow investigation of the transition zone between the margin of the Latium–Abruzzi platform and the adjoining basin and especially the identification of the carbonate factories that supplied the sediment to the slope zone of the Latium–Abruzzi platform. During the Paleogene, this platform was a shaved isolated platform under the action of waves, with sediment deposition during the transgressive and highstand phases of sea level, and erosion of this material during a subsequent lowstand phase. During these phases, storm-driven currents acted on the carbonate platform, remobilizing, resuspending, and reworking sediments. The remobilized material was transferred from the inner platform on to the slope, generating a mixture of detrital shallow- and deep-water biotic assemblages and depositing autochthonous/allochthonous units mainly constituted by alveolinids, large rotaliids, hooked gypsinids, nummulitids, and orthophragmines (discocyclinids and orbitoclypeids) assemblages. This mixture of shallow- and deep-water biotic assemblages demonstrates that a systematic study of the provenance of carbonate-producing biota, even if they are not preserved in their original context, can be useful in palaeoenvironmental reconstruction of the original carbonate factory system.