Rocks and soils of Timorasso's Colli Tortonesi DOC

I have previously treated the geology of Colli Tortonesi DOC but, while the treatment was comprehensive, the final product was unconsolidated. I address that shortcoming in this post.

The Villalvernia-Varzi Line is a key feature of the regional geology. It is an east-striking, slightly dipping fault zone which separates the sedimentary structures of the Tertiary Piedmont Basin to its south of from the Epiligurian Unit sediments in the wedge-top basin to its north. The role that this line has played is evidenced in the two charts following which show the comparative parent-rock geology. The Line is represented by the Antognola Formation in both of the charts.

In the charts below, we see evidence of at least four tectonic events south of the line and no equivalent activity in the north.

The chart immediately following shows a lack of alignment in sediment deposition within the two basins except for Sant'Agata Marl in the middle of the Late Miocene and no evidence of deposition in the Epiligurian Units post that phase. It is unclear as to whether that lack of deposits post the Sant'Agata phase was due to erosion in the Epiligurian column or an early uplift.

Screen shot from Festa, et al., 
Geological Map of the Villalvernia-Varzi Line

As shown in the chart below, the parent rocks have eroded down to primarily limestone, clays and marls. 

Descriptions of these soil types can be found on my soils page but I have also used the wein+ glossary to construct the table shown below.

Table 1. Soil types described in Colli Tortonesi (Descriptions curated from Wein+)

Soil Type	Description
Limestone	Rocks with a dominant proportion of calcium carbonate and smaller proportions of magnesium carbonate Widespread asa light grey or yellowish mineral and sedimentary rock Formed as sedimentary rock in the sea by deposition of calcareous shells and skeletons of small marine animals and as lake sediment Iron poorly available to plants in calcareous soils Usually yield wines with good acidity; particularly well-suited to white wine varieties Appreciated in cooler wine growing areas but require lime-tolerant rootstocks
Chalk	White, soft, fine-grained limestone that breaks down into a white powder Often contains flint Good water drainage due to its great porosity Soil easily penetrable by vine roots
Clay	A mixture of sand, silt, and clay Depending on the ratio, distinction made between sandy, silty, or clayey loam Colored yellow=brown by iron compounds Usually already decalcified Produces full=bodied, powerful wines
Marl	Grey or yellowish sedimentary rock of about half clay and half limestone Formed where clay particles were deposited on the fossil seabed with simultaneous lime precipitation Fertile, heavy soils with high pH values
Sand	Weathering products of hard rocks Grain size between 63 micrometers and 2 millimeters High proportions of quartz and feldspar Water-permeable, dry, and often infertile Produces fragrant, low-acid wines
Lime Tuff	Deposition of lime with air inclusions Porous structure caused by swelling mosses on whose plant  bodies lime precipitates Mosses eventually calcify and die, while new mosses are already growing above them

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