Map of Tuscany and Emilia Romagna, covering the Northern Apennines and the Tuscan extensional province.  The projected (not actual) path of our field trip is shown

We did not drive through Siena on Day 1, but rather took the Autostrade from Roma to Firenze with a long afternoon stopover at Mount Cetona, which is located south of the topo map boundary.  On Day 2, we stopped short of Bologna and the Po Valley, shifting across a ridge to join the Reno River valley near Sasso Marconi. We overnighted after Day 1 just north of Firenze.  The point marked 2.3 is approximately where we overnighted after Day 2.  After day 3, we overnighted in the coastal town of Pietrasante, just SW of the Alpi Apuane.
 
 
 
 
 

Roll 1  (seven photos) On day one (2/14/01):  Mount Cetona, looking for the peneplain with Mauro Coltorti, of University of Siena, as our guide.  The field map for Mount Cetona, with J. Park's markings, is shown below.  There are three images.  First is a full-page JPEG of the field map with my red-pen scribbles. Next is a blowup of the map legend. Third is a zoom of the central portion of the map, where we spent most of our time.



Here we are maybe 40 minutes north of Roma off the road to Firenze, near the boundary of Umbria. Travelling in five cars.  Lunch in the little town of Sarteano.  Chilly winter day.  Russell Pysklywec is at left, then Peter Reiners, then Vadim Levin.  Mark Brandon is in leather jacket, right of center, Darrell Cowan is in orange sweater. Frank Pazzaglia in the baseball cap at the left. Maria Laura Balestieri of Univ Firenze in center with blue jacket.


This is the view from the cars near Mount Cetona.  This is an unpretentious plowed field that lies flat at 700-meter elevation.  Coltorti identified this surface as the "peneplain" a residual surface that in the Pliocene accumulated a shallow water carbonate layer.  This layer is called the Amphistegina limestone, recognized in many places in central Italy.  The interpretation of "peneplain" was much discussed during the trip.  In traditional geomorphic terminology (I was told) a peneplain is an elevated surface whose topography can be ridden upon easily while on horseback.  Coltorti took us here to demonstrate that central Italy had uplifted quite a bit since the Pliocene (~2.5 Ma), without much folding and thrusting. The paradox is that Tuscany is an extensional province behind the northern Apennines, so that its uplift was contemporaneous with crustal thinning.

Different view of the peneplain, with Mt. Cetona and the Cetona Ridge in the distance.  Mount Cetona itself is Jurassic evaporate of the "Tuscan unit," inferred by Coltorti to have been an island during the Pliocene submersion of Italy.   Fragments of the Pliocene carbonate layer can be found all around the mountain.  The peneplain interpretation has been extended to other high-elevation low-relief surfaces in Central Italy, but not all places have the Pliocene carbonate preserved, so the interpretation must rely on weaker evidence, that the surface now exposed was a marine erosional surface (perhaps a wave-cut bench) that failed to accumulate or to preserve sediment.


Here is a roadcut of the Amphistegina limestone unit, a Pliocene carbonate layer that underlies the Mt. Cetona "peneplain."   Mark Brandon is waving at the center of the frame, confused about where the outcrop is.  Although it is a little difficult to appreciate in a long shot of the outcrop, the strata dip about 20 degrees towards the right.


Another view of the Pliocene carbonate outcrop.  Sean Willett faces the camera and Daryl Granger has his back to the camera.


Coltorti took us to several places around Mt. Cetona where the Amphistegina was underlain by a gravel/conglomerate layer, also inferred to be of lower-middle Pliocene age.  This is directly west of the Cetona peak.  The conglomerate lies above a clay layer of the Val Di Chiana basin, also Pliocene.  In many places the conglomerate has slid down the gentle slopes of the landscape after the sequence was uplifted and eroded.  It can be followed in the landscape easily because trees grow readily on the conglomerate flows, but not on surfaces where the underlying clay remains exposed.  Only meadow vegetation grows on the clay.


Here we have the Val Di Chiana Pliocene clay layer in outcrop.  This is the layer that lies beneath the conglomerate, which itself lies beneath the Amphistegina limesones.


Roll 2

West of Mt. Cetona.  Conglomerate landslide atop clay layer, can be followed by the trees that have taken root in the  landslide, surrounded by grass on the clay lithology.  Note that Coltorti argues that the clay is not likely of volcanic origin, as it is not dominated by smectite.  He would argue that it was an erosional product, rather than weathered volcanic ash.


Jurassic carbonate block within the Pliocene clay layer, taken to be an erratic.  The circular holes near the base of the boulder are mussel borings.  These mollusks lived in shallow water, so the presence of their borings argues that the clay was not deposited in deep water.  Not a surf zone either, I guess.  Hi-Res image.



Peneplain in the distance, seen from the location of the Jurassic carbonate erratic, looking westward.  Coltorti noted that the "badlands" topography of central Italy is a very recent development, caused mainly by continuous agricultural use since the first Bronze Age human settlements.  The surface soil has eroded away during this time.  There are no examples of "weathered soil profiles" in the area, topsoil long gone.



Here we have a debris flow with large angular blocks.  The outcrop is along the wall of a small abandoned quarry in a hillside west of Mt Cetona.  The blocks are limestone.



 Another view within the quarry of the preserved landslide, evidence of active tectonic processes since the uplift of Mt. Cetona, since the Pliocene.



Another view within the quarry of the preserved landslide, evidence of active tectonic processes since the uplift of Mt. Cetona, since the Pliocene.   Granger and Brandon in foreground.  Mauro Coltorti, Paula ?  and Francesco Dramis (Univ Roma Tre) in middle ground.


Fault scarp SW of Mt. Cetona peak, seen behind the automobiles.  The fault is a normal fault, but Coltorti does not believe that it is the expression of the recent extension of Tuscany.  He argues that the scarp developed before deposition of the Pliocene Amphistegina limestone.  Indeed, the scarp does not look fresh.   The geologic map suggests that the Amphistegina does not exist on this quadrant of the mountain, as the fault divides older Pliocene clay units and the much older "Tuscan unit."


On the east side of Mt. Cetona peak.  This is a landslide that Coltorti places beneath the Amphistegina limestone.  There are several landslides on this side of the mountain. This field trip stop marked the presumed location of the east-dipping low-angle detachment fault that Balchi et al report in their analysis of seismic reflection profile CROP3.  There is no expression of the fault near the surface.  The main evidence for the low-angle fault is a faint bounding reflector beneath a handful of west-dipping steeply-angled normal faults that outcrop to the east of here (in Umbria?).


This is an outcrop of the Amphistegina limestone, draped over the east side of the Cetona ridge at a dip angle of 30 degrees.  The unit is truncated by a landslide, the past collapse of the unit into an incising river valley.  There are clays, sands and gravels of the Pliocene Radicofani Basin deposited below the Amphistegina east of Mt. Cetona (towards the *town* of Cetona), with facies suggestive of shoreline and shoreface environments.


This is a photo at the same roadstop, looking farther east down the slope of Mt Cetona.  The outcrop is light colored and laminar, suggesting past continuity with the Amphistegina limestone, but it is actually a travertine deposit.  It is the first of a succession of travertine layers down a river valley (Mattaiolo Creek?).  The uppermost travertine is proximal to a hot spring.  Water from the hot spring cascades down into a succession of pools, each of which forms a travertine deposit.  The travertine layers have caves with Paleolithic artifacts, evidence of early-human campsites.  No nearby volcanic activity to cite as the cause of the hot spring.  Coltorti noted that a mastodon fossil was found near this location in the Pliocene clay layer.  This is additional evidence that the Pliocene Val Di Chiana clay was deposited in shallow water.



After this stop the group stopped for a beer and conversation in Sarteano, where we had eaten lunch.  We then drove north past Firenze on the Autostrade to a roadside motel in the town of Barberino.

Day 2:  In the Northern Apennines:  The day split into two halves, the morning spent looking at the lithologies and structures that comprise the compressional crustal-wedge tectonics south of Bologna, mostly led by G. Andrea Pini of Univ Bologna.  The afternoon was spent looking at uplift structures that (hopefully) will document the recent rise of the northern Apennines, mainly on the Rona River.  In the afternoon it was mostly Frank Pazzaglia (Lehigh Univ.) who chose the stops and described the rocks.


We departed from the Autostrade and climbed up a narrowing river valley towards the crest of the Apennines near the town of Firenzuola.  The crest of the Apennines forms (approximately) the boundary of the extensional (Tuscan) and contractional (Emilia-Romagna) tectonic regimes.   The Apennines are characterized by nappes, formed from forearc sediments.  Many of the forearc sediments are turbidites, and the nappe compressional tectonics often exposes them in an overturned state.  The largest recent (since 1980) earthquakes in central Italy have been normal-faulting events along the normal fault(s) that align with the crest of the mountain range.  Incipient normal faults have been mapped beyond the crest in the contractional region, suggesting an advance of the extensional process to the northeast.

Sedimentary unit names include

Marnoso Arencea ("marly sandstone")  These refer to lithologic components of turbidite sequences, which are often overturned -- the turbidites typically are composed of sandstone under siltstone under clay.  There is some carbonate in the sediments, hence they were deposited in the foredeep above the CCD.

Cervarola formation -- Covers much of the Emilia Romagna province, borders the Ligurian unit.  The morning drive travelled the border of the two units, mostly thrusted foredeep sediments.

Ligurian Nappe  or Ligurian Unit -- This overturned section of oceanic crust overlies much of the westernmost Apennines, and has many odd characteristics.  Its formation lies within Mesozoic tectonics, as it contains oceanic crust of this vintage and supports several later depositional basins, called "epi-Ligurian" basins, which seem to have ridden largely undisturbed on the nappe as it has saddled the Apennines.  This suggests that the Ligurian was emplaced in its distorted position early in its history, and has not been chewed up much since.
There are ophiolites scattered in the nappe's exposures.  Many of these are "ophicalcites," peridotite melanges mixed with calcite.  Ophicalcites are thought to occur where peridotite gets exposed on the seafloor.  It is observed in situ in transform fault environments and in the Marianas fore-arc.   The proximity to the seafloor means that ophicalcites are usually heavily serpentinized.  The ophicalcites of the Ligurian unit are overlain by mesozoic sediments.  In the Ligurian unit are also sometimes found fragments of continental crust.  Were these captured in the oceanic crustal unit when continental crust rifted?

This photo is near the crest of a winding road where a plaque commemorates the Allied breakthrough of the German Gothic Line in late 1944.  Not a nice place to launch an attack and get shot at.  The road leads to the town of Firenzuola, which lies next to a river that drains to the Po Valley.  At the overlook here (not pictured) you can view the bounding normal faults that define the Mugello graben, a basin within the Apennines.  There are 100s of meters of motion evident in the fault scarp, as the graben is deep, and the motion is recent.   The steeply-dipping strata surrounding the plaque are overturned turbidites, deposited in water when the Po foredeep was a marine basin.  For the last 5 My or so the Po foredeep has been subaerial, as more recent sediments are "molasse" type, a terrestrial equivalent to a marine turbidite.

Rock face at the Sassode Castro quarry.  The section is overturned, and all Mesozoic in age.  Dark units at top are the ophiolite.  At the bottom are light-colored turbiditic carbonates.  Up close, we were told that one can make out, above the carbonates, a thin chert layer, then a layer of weathered (and therefore reddish) basalt pillows.  Above this is massive basalts, then fine-grained gabbro.   The overturned units can extend for kilometers, undisturbed by faulting.  This implied that the structural units that overturned were quite large when they did it.   One hypothesis for such emplacement is that the ophiolite fell downslope into an accretionary wedge.  Strata overturn would be accomplished by a caterpillar rollover, like the tire-tread of a tank.  The ophiolite could be formed whaen back-arc rifting splits an island arc along its axis e.g. Tonga-Kermadec. A very steep trench face might be necessary for something as large as the Ligurian nappe to fall into it.

Same  quarry, same ophiolite, different camera angle.

Flysch turbidite of the Ligurian nappe.  Constructed from "olistrostromes"  undersea landslides.


Another overturned turbidite of the Ligurian unit, siliclastic in the lower (younger) layer, carbonate in the upper (older) layer. Andrea Pini in the foreground.


Well northeast of the Apennines crest, there are basin sediments of disconnected epi-Ligurian basins.  These were deposited during the Miocene atop the overturned Ligurian unit.  I believe that these are sandstones. This epiLigurian unit is flatlying, right-side-up, with small normal faults. This means that the epiLigurian stratigraphy has been preserved largely undisturbed since that time, as the Ligurian unit rode the Apennine orogeny like a carpet.   This photo shows a normal fault in the basin sediments, probably developed as they adjusted to the underlying uplift.

The Upper Miocene is missing throughout the epiLigurian sequence.  There was a global lowstand in the late Oligocene, associat4ed with the formation of the Antarctic ice sheet.  In the middle Miocene (12-15 Ma) sea level rebounded to 60-100 m higher than at present.  These sediments were deposited then.  The cause of the eustatic sea level change is not known.  The Upper Miocene is a global lowstand, when the epiLigurian units presumably went subaerial. The Ligurian and EpiLigurian sequences were shallow and not exposed at high elevation during the last 10-20 Myr.  This may mean that fission-track dates from the sequences are unreliable.  Shallow burial may not have led to temperatures sufficiently high to anneal the apatite and zircon fission tracks.  This would lead to measurements that underestimate the recent erosion rates.


River terrace ("strath") in a slightly tilted part of the epiLigurian sequence.  Road runs along the stream that eroded the valley that the strath flanks.  There is thin soil atop the bedrock sandstones, documenting the chemical weathering involved in soil profile development.  If the stream cut is Holocene (its sharp topography suggests so) the ~25 m river terrace implies erosion rates ~ 3 mm/yr.


Lunch in the mountain town of northern Apennines, just south of Bologna.  J. Park poses in front of a poster advertising the 10-year anniversary of the "new" Communist party.  Vadim Levin was delighted to find this poster.

In the Reno river valley south of Sasso Marconi.  The mountain in the background is draped with a Pliocene deposit in a ramp anticline.  Peneplain time again!  Much more uplift is implied here than near Mt Cetona in southern Tuscany.


Set of photos of a large set of river terraces along the Reno river.  The river terraces are the yellow layers atop the gray mid-Miocene epiLigurian sedimentary bedrock.   There is a thin brown layer between the grey and the yellow, consisting of gravel.  The yellow-layer terrace has some lenses of gravel, but is mostly fine-grained, maybe loess (silt that is wind-blown and later concentrated and deposited as alluvial sediment).  The stratigraphy within the terraces is *not* layered, so its deposition is not orderly.  This photo is a long view from a quick car stop.   Terraces at two levels are seen.  To the left a tributary to the Reno cuts through the terrace, splitting one terrace level into two yellow-layer deposits.  In venter right, the upper terrace level can be seen. Close inspection atop te structure (Pazzaglia) reveals evidence for downslope flow of sediments from the upper to the lower level.  This suggests that two "straths" are present, and that the terraces formed at different times.  The Reno tributary contributes sediment to the river here, which may explain why terrqace structures have developed.

View from the stop within the Roman/Etruscan ruins on the grounds of an antiquities museum on the west bank of the Reno.  Tributary cuts the lower terrace at the extreme left.  Shown here are the two terrace levels and the slope between them.

View from the same location, here focussing on where the Reno tributary has eroded through the terrace at the lower level.

A bit farther upriver, we stopped at a location where we could see and touch a Reno river terrace.  Here Pazzaglia (left) gesticulates in front of the terrace to Mauro Coltorti and Massimiliano Zattin (Univ. Bologna).  Note the alluvium with a soil profile developed on top.  Note the gravel interspersed with the light clay.

Another shot with Mark Brandon, Associate Professor of Geology and Geophysics at Yale University, blocking the foreground.

Drove back over the crest of the Apennines to overnight in the mountain town of San Marcello de Pistoia.  The stream valleys in this section of the Apennines are very sharply incised.  Some exciting driving.

Day 3.  The morning was devoted to incision and uplift features on the Tuscan side of the Apennines.  After lunch at a taverna next to an abandoned marble quarry, we spent the afternoon in the Alpi Apuane.

View of the mountain valley from our motel in San Marcello Pistoia  (historical note, the "pistol" was invented in the Renaissance city-state of Pistoia, somewhat to the south).  I believe that this is the Lima river valley.


We made stop to view an incised river south of the town of Barga inland of the Alpi Apuane, near a small cemetery complex.  This photo is from a bridge over a creek, showing a river-cut cliff face.  The sediments are Pliocene and alluvial, so there must have been subaerial deposition in this part of Italy at roughly the same time the shallow marine Pliocene planation surface was formed.  (This wave-cut surface in central Italy is the base of the Amphistegina limestone that we saw on day on near Mt Cetona.)

another shot a a different exposure setting on the camera:


Opposite side of the same narrow river valley.  Two views of a normal fault in Pliocene sediments.  Thos location is along the old Barga-Lucca highway.  Note the shear of the sedimentary layers proximal to the fault itself.  The deformation is consistent with the normal sense of motion.

Coltorti is at the right, in the yellow jacket.

Close-up of the normal-fault contact, tipped on its side.  The gouge itself is roughly 6 cm wide, but the detachment zone itself is only a cm or so thick.

Views of the Alpi Apuane from the town of Barga.  The town of Barga is perched atop a river terrace.  From this vantage point, Pazzaglia traced the terraces high above the river.

In Barga the roadside discussion centered on an apparent paradox:  the Pliocene alluvial sediments Include rocks derived from the Alpi Apuane, but most of these are rounded pebbles.  The detritus must therefore have undergone considerable mechanical processing to smooth over the pebble surfaces.  Coltorti argued that the rounded pebbles must imply sea-level wave action at what is now high elevation.  He argued that conglomerates can be found at high elevation in the Alpi Apuane itself, implying that the metamorphic core was, prior to 3.5 Ma, at least partially submerged.  Also, some of the deeply cut river gorges have changed river-flow direction.  We drove south (upriver) on the Reno River on day 2 of the field trip, and downriver (also south) the Lima river from san Marcello de Pistoia on the AM of Day 3.  The Lima has been inferred to have flowed into the Po valley foredeep before the rising of the northern Apennines.


In the Alpi Apuane, from the roadside taverna where we had lunch. Map location, I believe, is called Tre Fiumi.  The structures belong to an abandoned marble quarry.  The marbles of the Alpi Apuane belong to a metamorphic core complex, exposed via deep erosion.  Some of the youngest fission-track dates in the region are from the Alpi Apuane, and we can be sure that the fission track clock was reset by the heat of metamorphism.  The mountain crest contains folded stratigraphy, very common in the metamorphic core complex.

Long shot of the abandoned marble quarry at Tre Fiumi.  Carbonate rocks tend to be resistant to erosian if a regolith does not form on them.  It soil forms atop a carbonate outcrop, it holds moisture and dissolved acids from plant life in contact with the Ca CO3 in the marble/limestone to enhance its dissolution.  Erosion is faster for marly limestones, for which calcite dissolution leaves a clay residual.  Pure chalk and marble, on the other hand, tend to form erosion resistant cliff faces.

Vadim Levin standing before a large marble block, showing a circular fracture surface.

Long shot of the entrance to the marble quarry.

Cathedral-like entrance to the quarry.  Vadim Levin poses in middle ground.  Sean Willett in background.

Inside the quarry.  The blocky walls of the quarry are maybe 7-8 meters high from step to step.  Sean Willett and Vadim Levin pose for scale.  In the late winter sun the quarry seems impossibly white.

Vadim Levin and Russell Pysklywec pose in front of a marble block in the quarry.  Note the curved contact between undeformed marble and surrounding deformed rock.

Metamorphosed portion of the Macigno shale (i.e. a pelite), near the head of a valley within the Apli Apuane.  Vadim Levin poses in the right center. The shale dips slightly to the viewer's right in this outcrop. Atop this pelite is a thin slickensides paleofault zone.  The slickenside is located just about where Vadim Levin's head is.  Farther down the road is a glacial moraine, inferred by Coltorti to have been emplaced at the last glacial maximum.  A rough calculation for river incision from the incised moraine is 3 mm/yr, mighty fast.  At the top of the surrounding peaks here, one can find remnants of Hercynian basement, the platform atop which Mesozoic carbonates were deposited to form the marbles later, in Cenozoic metamorphism.

Views from the roadstop in the Alpi Apuane.  The Alpi Apuane is technically part of the Ligurian Nappe, but is the most deeply buried portion of it, and so the most highly metamophosed.

MARBLE QUARRIES CUT  INTO THESLOPES OFTHE MOUNTAINS.  High res photo

A zoomed view

We spent a large portion of the mid afternoon at this roadstop.  After talking about the rocks, we parted with Professors Andrea Pini and Mauro Coltorti, who returned to their homes.  This portion of the landscape drains into the western coastline of Liguria.  The blue of the Mediterranean was visible from the road, though the afternoon haze prevented me from taking a good picture.

Note the steep folding and overturned sequences in the Alpine rocks.  There is a hiking trail along the crest of the range, with huts spaced at intervals for overnight shelter.

Hi-res photo is here

This photo shows that we did not have a great deal of room for the road stop.  The cars are parked along the road on the other side of the tunnel.  There was very little car traffic, and we stood in the road for 90-120 minutes.  A herd of goats passed us on the road at one point.  The road stop happened to be at the contact between the Hercynian basement (metamorphosed Paleozoic shales) and the Mesozoic stratigraphy (carbonates).  Darryl Granger took the opportunity to find some surface rocks for a test of cosmogenic radionuclide dating of an erosional surface.  He took off up the steep rock slope to the right.  Far above our heads, he was able to pry loose a rock sample that had both carbonates and silicic rock exposed to the air, and therefore to cosmic ray flux.  Granger hopes that he may obtain a calibration between the two lithologies for this type of radiometric dating.

At the close of Day 3 we drove down off the Alpi Apuane (more exciting mountainslope roads!) to the Ligurian coast, and turned south to overnight in the town of Pietrasante.  This town is famed for its sculpture, owing to its proximity to the great marble quarries. This shot comes from one of the town squares, with a limestone-faced church and a brick campanile.

Day 4 -- return to Roma.  We stopped in the city of Lucca for a break, shopping and a recap of the proposed RETREAT project over lunch.  It was the warmest day since our arrival in Italy, so we were able to eat outside.  Lucca is a fine Renaissance city.  Here are some geologists loitering on one of its street corners

This weekends before Lent inspire some child-centered fun in Italy.  Here are some kids in costumes in the square of a church in Lucca.  We saw similar costumed children the weekend before milling about the streets of central Roma.


Many of the classic marble chuches of Italy are accented by lines of darker rock, actually often peridotite quarried from the Ligurian nappe.

Here are two shots of our group conferring over lunch in the "Ampitheatre" square in the northeast quadrant of the walled city, built over the site of an ancient Roman colosseum.  Pazzaglia and Granger at the left end of table, Pysklywec with back turned in center foreground, Reiners, Levin and Paula at right.

Brandon at left, then Pysklywec, and Willett.