From river to shelf, anatomy of a high‐frequency depositional sequence: The Late Pleistocene to Holocene Tiber depositional sequence

Abstract

The Late Pleistocene/Holocene Tiber delta succession represents the most recent and one of the best preserved, high-frequency/low-rank depositional sequences developed along the Latium continental margin of the Italian peninsula. Several previous studies have established a robust data set from which it has been possible to describe the stratigraphic architecture of the entire Tiber depositional sequence from the landward to seaward sectors and over a distance of 60 km. The Tiber depositional sequence shows many characteristics found in other Late Pleistocene to Holocene deltaic and coastal successions of the Mediterranean area. The stratigraphic architecture of the Tiber depositional sequence is controlled mainly by glacioeustasy, although factors such as tectonic uplift, volcanism and subsidence, exert an influence at a local scale. The resulting depositional model allowed discussion of some important points such as: (1) the genesis of the Tiber mixed bedrock-alluvial valley, extending from the coastal plain to the innermost portion of the shelf, recording (i) multiple episodes of incision during relative sea-level fall, and (ii) a downstream increase of depth and width of the valley during the base-level fall and the subsequent base-level rise; (2) the different physical expression of the Tiber depositional sequence boundary from landward to seaward, and its diachronous and composite character; (3) the maximum depth reached by the Tiber early lowstand delta at the end of the sea-level fall is estimated at ca 90 m below the present sea-level and not at 120 m as suggested by previous works; (4) the backward position of the Tiber late lowstand delta relative to the deposit of early lowstand; (5) the change of the channel pattern and of the stacking pattern of fluvial deposits within the Lowstand Systems Tract, Transgressive Systems Tract and Highstand Systems Tract. All of these features indicate that the Late Pleistocene/ Holocene Tiber delta succession, even if deposited in a short period of time from a geological point of view, represents the result of the close interaction among many autogenic and allogenic factors. However, global eustatic variations and sediment supply under the control of climatic changes can be considered the main factors responsible for the stratigraphic architecture of this sedimentary succession, which has been heavily modified by human activity only in the last 3000 years. 1886

Three‐fold nature of coastal progradation during the Holocene eustatic highstand, Po Plain, Italy – close correspondence of stratal character with distribution patterns

“…Anthropic land use influence probably reached a peak near the end of this phase – agriculture achieved maximum development between 2·8 kyr bp and 1·75 kyr bp (e.g. Pinhasi et al ., ; Kaplan et al ., ; Milli et al ., ; Ward et al ., ), probably increasing clastic sediment yields.…”

“…An example of human influence might be the boundary between the lower and upper HST that spans a period of relatively stable climate but coincides with a significant change in soil use (during the Late Bronze Age to Early Iron Age). This change could record, in part at least, the impact of anthropogenic activities on sediment discharge, probably due to deforestation and intense and widespread agriculture (Maselli & Trincardi, ; Milli et al ., ; Di Rita et al ., ). Increasing human influence, especially over the last 3000 years, has been interpreted to have been an important driver of changes in sediment supply, strongly modulating deltaic development worldwide (Wang et al ., ; Maselli & Trincardi, ; Anthony et al ., ).…”

“…On the other hand, a significant climate signal has been interpreted to exist in the coeval Holocene record of other river systems in Italy (such as the Tiber, Volturno and Garigliano) that had generally similar anthropic activities and climate (Milli et al ., ; Di Rita et al ., ). These systems are, however, considerably smaller than the Po River system and would be expected to be more responsive to rapid climate changes ( cf .…”

“…Sediment supply rates also varied due to changing climatic and land use conditions: increased flood activity in the southern Alps between 1·3 kyr bp and 0·1 kyr bp , northern European climate change from Sub‐Atlantic to the Little Ice Age (0·4 kyr bp ), and Alpine glaciers advance and retreat throughout interval (Table ; Mangerud et al ., ; Hormes et al ., ; Wirth et al ., ). Land use for agriculture peaked at the very beginning of this period (2·0 to 1·75 kyr bp ), followed by a period of reforestation (with decreasing sediment yields; ca 1·75 to 1·2 kyr bp ) and then agricultural renaissance, since ca 1·2 kyr bp (Pinhasi et al ., ; Kaplan et al ., ; Milli et al ., ; Ward et al ., ; Di Rita et al ., ; Cacciari et al ., ). Since the Porto Viro cut, in the 17th Century ( ca 400 cal yr bp ), the evolution of the delta was no longer a natural process, and progradation took place under considerable anthropogenic influence (Correggiari et al ., 2005b).…”

Late Quaternary multiple incised valley systems: An unusually well‐preserved stratigraphic record of two interglacial valley‐fill successions from the Arno Plain (northern Tuscany, Italy)

“…Thus, incised valley systems (IVSs), and especially their infilling successions, are natural laboratories for deciphering stratigraphic patterns and better understanding the hierarchy of controlling factors under unstable climate-sea-level conditions. Indeed, several allogenic and autogenic factors are known to work together at Milankovitch and sub-Milankovitch time scales driving physical and biological processes in alluvial-coastal areas (Blum & T€ ornqvist, 2000;Tanabe et al, 2003Tanabe et al, , 2015Rees, 2006;Hoffmann et al, 2010;Mattheus & Rodriguez, 2010;Notebaert & Verstraeten, 2010;Blum et al, 2013;Anthony et al, 2014;Milli et al, 2016).…”