Download Michele Lacroce Italy Field Camp Dr. David Bice Mapping San

Michele Lacroce
Italy Field Camp
Dr. David Bice
Mapping San Vittore
Between May 23 to the June 1st our class; Alessio, Massimiliano, Stu, Giacomo, and Michielle
spent nine days mapping San Vittore with Dr. David Bice and Dr. Sandro. The town of San Vitore lies
between Umbria- Marches Apennines mountain range. The main goal of the project was to use mapping
techniques in field geology to map the geology of San Vittore and learn the geologic history of the this
section of the Apennine Mountain Range. After nine days of hiking and almost dying we have collected
enough data to construct a map and cross section of San Vittore.
The maps scale is 1:10,000 meaning one cm on the map is a 100 m. The west side of San Vittore
consists of a couple Mountain peaks. The mountains contain Monte La Croce, Monte Ginuno, and
Monte Di Frasassi. A river cuts through the mountains creating Grotta Di Frasassi. Following the river
east a valley flattens out around 200ft above sea level where San Vittore lies. To the north of San
Vittore, Piepsora and C. Collepeccio sit on the ridge of Monte Ginguno which seperates the San Vittore
from Genga Stazione. A railroad also follows the bottom of Monte Giguno and the Mountains to the
west of Genga Stazione.
During the early Jurassic Period San Vittore was a part of massive carbonate platform Figure 1.
Extension broke the entire platform into a complete series of horst and grabens. There are three horst
formations on the map by Monte Di Frassi into the Grotta Di Frassi, Il sassone, and in the upper right
corner in the 600m elevation level. These horsts are represented by the Massiccio formation which is
massive homogenous limestone. The two graben formations lie right along the Jurassic normal faults on
our map area covering the area between San Vittore and Genga Stazione and the quarries to the far
right of the map. Figure 2 show where the normal faults occurred. After the faults formed, the
formations that deposited in the grabens are Corniola and Diaspri . On top of the horsts lies the
Bugarone formation and on the sides is the Bugarola formation. Figure 3 shows how these formations
were deposited. The Bugarone/Bugarola formations contain ammonite fossils which is a distinctive
characteristic of the formation. The Diaspri has a variation of limestone color, thin bedding, and mostly
green chert. These formations are the key indicators for identifying the horst and grabens in the field.
Some outcrops had fault planes and where we could measure the direction of the faulting from slicken
lines, “steps”, and a large amount of pressure solution cleavage.
Along the western part of the Cretaceous Scaglia Rossa along the ridge of Monte Ginguno there
are huge turbidities that are slumped. Turbidites are formed by turbidity current causing a flow of
sediment instantly. These turbidite are caused by tectonic activity. As activity continued the turbidite
layer was slumped creating the turbidity formation we see in the Cretaceous. Plotting the strike and dips
of the turbidite folds and original bedding we can plot the fold axis of the turbidities fold. Perpendicular
to the fold axis shows the direction and of the turbidity flow as seen in Plot 2. The normal Jurassic fault
is in the same direction as the turbidity flow indicating that the tectonic activity that caused the
turbidites could have been a reactivation of the normal faults as seen in Figure 4.1.
There are three normal faults on our map that border the Massiccio formations. These normal
faults where caused during the Jurassic Period and reactivated as previously mentioned. The Miocene
Epoch was the start of compression from the Apennine Mountain range. This caused a thrust fault
through the Massiccio formation as seen in Figure 5. This caused the Massiccio to bulldozer the
formations above it causing folding as seen in Figure 5.1. After plotting the strike and dips of the beds
we can find the trend of the fold axis around the area where the syncline formed Plot 1. Minor folds
where also found around Dead Mans curve and by the turbidites. In the folds the pressure solution
bended with the fold, perpendicular to each limbs strike. This suggests that the pressure solution
happened before the bedding was folded. In Plots 3 to 5 the strike and dips of the pressure solution
trends fall in the bedding planes of the folds. This indicates that the same mechanism that formed the
fold created the pressure solution. The mechanism that formed the folds was caused by the thrust fault
in the Massiccio seen in Figure 5. With the cross section we can measure the shortening created by the
folding. The overall the shortening is about 2 km. This explains the uneven thickness in the Miolica layer
on our map because the western layer is being compressed from folding from the thrust fault. However
the thrust fault does not cut through the surface. Since this is a blind fault it is inferred that this is the
mechanism that caused the folding.
To conclude we can break up the geologic history of San Vittore into two parts extension and
compression of the Apennines. The extension period started in the Jurassic where normal faults caused
horse graben formations. The turbidities in the Cretaceous formation indicate a reactivation of the the
normal fault on the far west Massiccio horst this could be the end of the extensional period and the
start of the compressional period. The Miocene is where we see evidence of the start of the
compressional period where a thrust fault formed through the west Massiccio horst causing
compression of the younger formations creating the syncline seen in San Vittore. It is evident that the
Jurassic structures influence the genesis of the Micoene formations creating the compression state and
folding continuing in San Vittore today.