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Re: geo The Sfakian gorges

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gorge The Sfakian gorges
17 February, 2010 15:02
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The Sfakian gorges - speculation

Conventional wisdom interprets the Sfakian gorges as the result of water erosion of a fault scarp, taking place over millions of years. While water erosion is obviously a factor, it never seemed to be the whole story to me.

A recent question, regarding the Fliskounias ‘dam’ in the Eligias gorge, got me thinking about the matter again. In particular, an entry by Erno ( [www.sfakia-crete.com] Fig 9c) prompted me to take a look at my photos (and search through dim memories of incidental field observations) for evidence of tectonic activity in Sfakia.



I have settled on an hypothesis that there are two types of gorge structures in Sfakia. And, in the accepted tradition of scientific classification, there is also one major anomaly which doesn’t fit the scheme (see separate entry which follows). I stress that this is only informal speculation, not answers. It represents questions about the geology of Sfakia that I’d like to have answers for.

TYPE 1: water erosion. The area covers the Ilingas gorge and all gorges east. The most distinctive evidence for long term water erosion is in the extensive alluvial fans which comprise most of the Frangokastello plain. The structure of the gorges plus alluvial fans is practically textbook water erosion of a fault scarp.

TYPE 2: faulting. The area covers Tripiti gorge to Eligias gorge. This area has the most visual evidence for faulting as a major cause of the gorge structure and height differential, with water erosion playing a secondary role. I can’t say anything about the timing of the faults or the direction of movement. Noteworthy is the absence of sea level alluvial fans, considering the presumed volume of mass wasting from the gorges in this area. Also, the distinctive feature of the Samaria gorge is it’s rapid height loss quite far inland. It can be almost 1000m ‘deeper’ than equivalent levels of gorges on either side. This implies some differences in the mechanisms creating the gorges.

Here's a sketch, using Google earth. Green dashed lines indicate possible fault areas, red lines fade AWAY from downward tilt direction (bright end defines the direction of downward tilt).


The simple story is as follows:
(i) One (or more) fault line(s) runs roughly north-south along the Eligias gorge. This may be scarp faulting, characterized by a slope on the west side of the gorge, and a steep cliff on the east side of the gorge. The tilt in a roughly NW to SE direction. In this photo it is easy to see the strata tilting down to SE from east side of Samaria Gorge into Eligias.


Here is a view from inside the gorge at Fliskounias. Zaranokefala to the east (right side).


(ii) a west-to-east fault appears to be along a line Linoseli (Gingilos) saddle - Xiloscala - Kalergi - Poria - and further east). The north side strata tilt down towards the north. This line either bends in a north-south direction at Tripiti gorge or joins a separate north-south fault (parallel to Eligias) somewhere in the area of Tripiti gorge.
Here is a photo looking west to Gingilos-Volakias from Poria. The dashed green line encircles light grey lower strata which makes up Gingilos. This is overlaid with a harder, dark grey limestone with strong plate structure. Red lines indicate direction of tilt on either side: to the south at Volakias, to the north at Kalergi.


Here is a photo taken on road from Kalergi (looking south in direction of Melindaou) - so on opposite side of Samaria gorge from Gingilos. The same structure of strata is clearly visible, lighter rock underneath harder more plated limestone. This is what implies the continuity of fault line cutting across north end of Samaria.


(iii) Might the entire Ginglios-Volakias massif, including Tripiti, Klados, and Samaria be the result of one massive block? In the Gingilos-Volakias photo the tilting of Volakias strata appears to be downward north-to-south (sometimes almost vertical), markedly different from either the NW-to-SE tilt of Eligias or the S-to-N downward tilt of Kalergi etc. or the apparent E-to-W downward tilt of the west end of Tripiti.



Edited 5 time(s). Last edit at 17/08/2010 23:52 by Erno.
Re: geo The Sfakian gorges
17 February, 2010 15:05
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THE ARADENA ANOMALY: The anomaly is defined by the two distinctive and very sharp kinks in the gorge bed. This results in three parts to the gorge, which itself traverses the flat Anopoli plateau, and not eroding a scarp face.
I have marked a GoogleEarth photo to illustrate:


This is not simple Type 1 water erosion at work. The lower section (marked green), runs roughly N-S and includes secondary ravines to the west, draining the Ag. Ioannis hills. The middle (marked blue) section runs SW-NE. The upper section (marked red) runs almost parallel to the W-E face of Lefka Ori, and drains the mountain face as well as upper end of Ag Ioannis hills. The gorge bed is generally flat, except for three distinctly steep sections (if memory is correct). The first is close to the coast where the gorge cuts through the hill. The second is at the first kink to the east. The third is at the huge rock fall. When following the gorge north of Aradena up and into the branch ravines into the mountains there is usually again only a slight grade, nothing steep.

A good interpretation of what it all means has to take account of the following:
(i) the east edge of the mid-section is higher than the Anopoli plateau. Does this suggest local fault tilt?
(ii) the entire Aradena plateau as such, a distinctive scarp at south side from, say, Sellouda to Sfakia, quite distinct from rest of Sfakia coastline.
(iii) relation of the Ag Ioannis hills on west side of Aradena to both the Anopoli plateau and to the Lefka Ori to the north. The upper and mid sections of Aradena gorge encircles these hills.



Edited 3 time(s). Last edit at 17/02/2010 17:11 by Erno.
Re: geo The Sfakian gorges
17 February, 2010 16:26
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Very interesting, Mike. Thank you for your elaborate article.

This is what I can find on the matter in this unsurpassed book:

From: Field guide to the geology of Crete
Charalampos G. Fassoulas
Heraklion 2001
ISBN 960-367-008-1

page 58 and on:

Quote

The road to Omalos Plateau crosses through the Phyllite-quartzite nappe *, and after Laki village, through the trypali nappe. [...] At the entrance of the gorge (the Xiloskalon area) begin the occurence of the middle and upper horizons of the Plattenkalk-nappe. The Gigilos beds are outcropped at the first five-Km, as the path crosses the big fault separating the beds from the typical platy limestones. [...] Many of the pebbles and rocks occuring at the riverbed belong to the stromatolitic dolomites **, which probably occur at the steep, nothern sides of the gorge.

At the first half of the gorge [...] impressive cliffs offer beautiful exposures of the folded Plattenkalk rocks. These folds were formed during the Oligocene compressional tectonics and indicate a southward vergence. [...] The platy limestones are outcropped until Agia Roumeli village, where large normal faults cut the mountain slopes forming the coastal zone. [...]

The cliffs of the coast lie parallel to the big, east-west trending normal fault zone that uplifted the Leyka Ori area. The activity of this fault zone, in combination with the karstic weathering, is responsible for the formation of the Samaria gorge and several other parallel gorges:



By the small harbour of Chora Sfakion is a small occurrence of chloritoid bearing schists [...].



All the eastern low lands are part of a paleorivage, emerged now due to normal faulting. Some of these onshore faults can be observed north of the Frangokastelo area.


* nappe = In geology, a nappe is a large sheetlike body of rock that has been moved more than 2 km (1.2 miles) or 5 km from its original position. Nappes form during continental plate collisions, when folds are sheared so much that they fold back over on themselves and break apart. The resulting structure is a large-scale recumbent fold.

Numerous signs can be determined on the frame of the word 'nappe'. The frontal part in the direction of movement is called the leading edge of the nappe. Numerous folds and secondary thrusts and duplexes are common here. These features are commonly called digitations.



From: [en.wikipedia.org]

** dolomite is the name of a sedimentary carbonate rock and a mineral, both composed of calcium magnesium carbonate CaMg(CO3)2 found in crystals. Dolomite rock (also dolostone) is composed predominantly of the mineral dolomite. Limestone that is partially replaced by dolomite is referred to as dolomitic limestone.



All the best,

Erno
webmaster Sfakia-Crete.com
Re: geo The Sfakian gorges
18 February, 2010 10:11
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Thanks for the addition, Erno. I'm glad to see that I have correctly applied my Geology 101 knowledge, at least regarding the Samaria area.

The university in my town does not have much on Geology. I did a search of the electronic journals, going back 40 years. Unfortunately the geologists writing articles are either only interested in the big picture (entire east Mediterranean) or they focus on central and east Crete when looking at the fine details.

This sentence from your own citation - The activity of this fault zone, in combination with the karstic weathering, is responsible for the formation of the Samaria gorge and several other parallel gorges - encapsulates my dilemma. Given this general statement, I'm now getting curious about the details. Geological reasoning basically involves trying to solve a Rubic cube. You have all these displaced pieces and you have to try to figure out the order of moves to get back to the ancient, and simpler, landscape. It would be fun to interpret all of the Sfakia area geologically, but nobody seems to have done it yet.

By the way, perhaps you can adjust the name of this branch to "Maps, GPS, and Geology of Crete". Geology is one of the topics, which is why I posted here, but it's not in the title.
Re: geo The Sfakian gorges
18 February, 2010 12:41
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Hi Mike,

I have just adjusted this forum's name, as you suggested.

"The university in my town" ... is the same as the university in my town smiling smiley

All the best,

Erno
webmaster Sfakia-Crete.com
Re: geo The Sfakian gorges
26 February, 2010 10:48

Mike:

A potential complication for you to think about:

I had not noticed until I looked closely at the photo below that Livaniana sits in a distinct depression that probably has something to do with water—note the vegetation in the depression, no vegetation on either side of the depression.

[www.panoramio.com]

The interesting bit is that this depression appears to intersect with, and cross, the Aradena gorge. Indeed, one of the “secondary ravines” marked by the green line going off to the left in your photo in the “Aradena anomaly” posting appears to be the continuation of this depression.

This can be seen more clearly in Google Earth. If you look at the barren southern lip of the Livaniana depression, it appears to continue with the barren southern lip of the secondary ravine on the west side of the Aradena gorge. This western ravine is vegetated in much the same way as the Livaniana depression.

It appears to me that there was a shallow depression, having something to do water. The Aradena gorge came later and cut across this older depression.

This also is pure speculation. But I find it interesting.

Ray.
Re: geo The Sfakian gorges
26 February, 2010 20:19
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I've asked my brother, a Cambridge University geomorphologist, to look at these posts and pictures. He says the terrain is water-worn, but water needs a weakness to exploit. There is obviously a complex tectonic situation, with faulting and some folding, leading to fractures etc which the water has exploited. As the fracturing is complex, so are the paths which the water has exploited and eroded downwards during uplift. The photos show a clear fault line with rocks displaced and not matching on either side.
Re: geo The Sfakian gorges
04 March, 2010 11:46
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I may have to become a semi-professional geologist to figure all this out (I'm working on it). The timing of events is crucial. You have to deal with large scale land rise and subsidence over a period of 60 million years or so (geologists sometimes work with estimate variation of 4-5 million years!). The Cretan mountains had their origins in this way. The periodic rise and fall of the underlying plate crated circumstances for land fill which connected the separate mountains this creating the island as we know it. Then there is the slower land rise. However high the Lefka Ori used to be in their origins, the entire area has risen 1000m over the past several million years. Added to that we have the sea rise and fall during the various ice ages. This can make a difference of 100m or more in average sea level. Also, some small scale glaciers are hypothesized to have created and filled the upper valleys of the Lefka Ori. Melt from the glaciers provided the water for some of the erosion we see (wasn't all rain).

If I could work out the timings, then it would be possible to describe a situation where at least some of the lower Aradena area could have been much lower and even periodically under water, then drained, then under water again. I also get the impression that the current course of the Aradena gorge cuts through some earlier structures which were made first, and then water flow patterns changed, and cut up the land in a different way. So, perhaps at some time in the past the drainage from the mountains followed a course which left its mark as the livianiana depression -- perhaps even the entire lower terraced area to the north on east side of the gorge channel.



Edited 1 time(s). Last edit at 04/03/2010 12:06 by Mike.
Re: geo The Sfakian gorges
04 March, 2010 13:09
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Hi Mike,

Perhaps this will help you to find the timing of events:

SCHEMATIC STRATIGRAPHIC COLUMN OF CRETE ISLAND



1. Alluvial deposits
2. Pleistocene deposits
3. Neogene formations
4. Complex nappe of the Internal Zones
5. Olonos-Pindos nappe
6. Tripolis nappe
7. Phyllite-Quartzite nappe
8. Trypali (or Omalos) nappe
9. Crystalline platy limestones (Vigla formations)
10. Dolomites (Pantokratoras formation)
11. Gigilos formation
12. Sisses formation
13. Fodele formation

All the best,

Erno
webmaster Sfakia-Crete.com
Re: geo The Sfakian gorges
05 March, 2010 20:06
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More info from Cambridge University: The material at [www.sfakia-crete.com] is entirely accurate. The uplift happened during the Oligocene, which was from 40-25 million years ago, when the Alps were built as the plates moved north against Eurasia. 25 million years gives plenty of time for water to carry out erosion. Any uplifted landforms are bound to be faulted and somewhat folded, deformed and then water-worn. This would have been in the pluvial periods when the rain belts moved south and then north before and
after each ice advance.
Re: geo The Sfakian gorges
05 March, 2010 21:46
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Thank you Peter, that is good to hear.

For those of you interested in a little more background on the geology of Crete: here is a pilot publication of the Greek Institute of Geology and Mineral Exploration (IGME) :

[www.igme.gr]

At the bottom of the listed areas there you can find a link to download the entire brochure on GeoTrails in West-Crete and Gavdos. [30 pages, 3764 KB!]

I can give this link here now, because I have checked that the downloads are allowed, and not against the wish of the publisher.

I hope you will all enjoy!

All the best,

Erno
webmaster Sfakia-Crete.com
Re: geo The Sfakian gorges
05 March, 2010 22:36
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And even more from Cambridge University:
The webpage [www.sfakia-crete.com]
has the entirely plausible idea that the gorges formed DURING the uplift along the fault line so the gorge formation is contemporaneous with the uplift - each earthquake would have lifted the block at the back higher (they would have been at about the frequency of what we see in Chile e.g one in Darwin's time and some more recently so maybe 1-2 earthquakes per human generation) but which is ample time for the river to cut back down all through the Tertiary era (so the limestones must be earlier, maybe very early Tertiary, but probably Cretaceous) and then the glaciations and sea level changes followed which probably, as they lasted only 1-2 MY while significantly deepening the gorges, probably didn't do a lot compared with the erosion during the 20 - 40 MY or so of the uplift.
For time scales see [en.wikipedia.org], where Paleogene and Neogene = Tertiary.



Edited 1 time(s). Last edit at 05/03/2010 22:37 by Peter.
Re: geo The Sfakian gorges
05 March, 2010 23:24
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Rackham and Moody's Making of the Cretan Landscape has lots of authoritative detail about all of this: several different limestones of different ages, complete complex geological history, tectonic uplift, and everything about the formation of the gorges, uplift, erosion, and glaciation.
Re: geo The Sfakian gorges
09 March, 2010 15:51
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The Devil is in the Details


Some interesting posts, Peter, kept me busy for a couple of days. I do detect a specialist bias in the interpretation of the data, emphasizing the water erosion factor. I will expand on a few points.

The detail of scientific models
The suggestion that “The material at [www.sfakia-crete.com] is entirely accurate” is not entirely accurate. The word “entirely” requires some qualification.
We can ask: is the material on the website accurate? Yes, but we have to take account of the level of generality. For example, a general statement such as ‘the Cretan landscape is shaped by processes of erosion working on a tectonically modified rock profile’ is accurate. But it is not adequate as a description of specific circumstances. Detailed models need to select from several types of erosion processes and several types of tectonic activities. Detailed models would also have to specify the proportion or balance in how the various processes work.
This problem of proportion is sometimes confounded with scientists' specialist focus on types of problems. Even a simple statement such as “Any uplifted landforms are bound to be faulted”, while correct, can be the subject of intense primary study by some specialists, where tracking the timing and location of these faults is the essential task. For example, some articles which I’ve read (a couple given to me by simon-78) do not even mention erosion. For the specialists in tectonic activity, erosion only constitutes noise in their data. They aim for a pristine model best represented in the block figure in my original post. They’d say something like ‘Of course erosion is bound to occur, but we’re interested in what tectonics has done’. A different specialist might reverse the story and say, ‘Of course there is tectonics, but that only makes the weaknesses which water erosion exploits’.

Even granting ‘true in general’, is it the whole story? We still need to ask, (i) is the specific model adequate (does it take all factors into account and in the proper balance of importance”) and (ii) is the model applicable to all circumstances?
Regarding point (ii): the model – that the gorges are caused by water erosion of a scarp face – is precisely what does not fit some parts of the Sfakian coast. It fits the area roughly Illingas gorge eastward. It does not fit the Samaria area (no scarp being cut into) and it does not fit the ‘Aradena anomaly’ (same reason plus other details). So, while we do have the same general processes to work with – tectonics and erosion – we need to adjust our selection of specific processes to account for regional differences. We need a different story for different gorges.

The problem of timing
The statement “The uplift happened during the Oligocene, which was from 40-25 million years ago” is correct except for the ‘The’. The ‘The’ implies a single uplift event followed by a long process of (water) erosion over a 40-60 m year period. It would be more accurate to say that things only got started at that time:

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Crete consists of a structural pile within which up to seven major nappes and several minor slices have been recognized. The nappes [see diagram provided by Erno] were emplaced between the early Eocene and early Miocene and the nappe pile uplifted in the Miocene. Subsequently, the whole island has been extended by normal faulting which is related to Neogene and Quaternary extension in the region north of the Hellenic Trench complex.

So, an initial phase created the pile-up of rock strata [again, see diagram provided by Erno] presumably related to plate compression (African plate bumping against Eurasian plate). This was followed by a second phase of tectonic activity mainly involving extension, and this has been creating faults, fractures, and so on. Then the story gets more complicated.

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Stratigraphic basin analysis of the Neogene (23Ma-3Ma ago) made it possible to reconstruct eleven successive intervals for the evolution of the Cretan area from the Middle Miocene to the Late Pliocene. The transitions from one interval to another were marked by pronounced changes in basin configuration and sedimentation patterns. One of the most dramatic changes occurred in the Late Serravallian-Early Tortonian boundary interval between about 12 Ma and 11 Ma ago. At that time the Southern Aegean landmass, hitherto connecting Crete with the European mainland, started to break up: Crete itself became transformed into a mosaic of culminations and depressions. One of the primary targets of our renewed investigation of the Neogene basins was to unravel the tectonic processes which controlled the paleogeographic revolution in the latest Serravallian to Early Tortonian and the ensuing repeated changes in basin configuration from the Early Tortonian onward. These processes ultimately led to the uplift of parts of Crete to a height of about 2500 m.

That last sentence in crucial, since it suggests yet another phase of uplift more recent than 12 million years ago. It is possible to get an even more detailed picture of local tectonic activity.

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Within the Lefka Ori range, lithified marine sands containing Calabrian age marine fossils outcrop at an altitude of 1000 m, indicating that the range has undergone 1100m of uplift since the Lower Pleistocene. [i.e., ‘only’ [about 2million years ago].

The following illustration is where such a coastline would be (1000 meters higher, the Lefka Ori only 1500m above sea level).


I did another test, because I was puzzling over yet another detail: the scarp face defining the south side of the Anopoli plateau. The Anopoli plateau has a height of 600m. I traced a line at that altitude starting at Eligias gorge and going east, just to see what I’d find. Interestingly enough, the 600m level extends quite consistently right across the ‘top’ of all of the eastern gorges.

This is consistent with the location of the Sfakian fault scarp. But this is something more recent, and a different process than the original block uplift. We also have to explain why the east end is riddled with gorge outlets, and the west end only has the Aradena gorge. When you start looking more closely, the model needs to be more detailed.

Back to the Aradena anomaly

I have settled some details. My speculation that the Aradena gorge follows a fault line (blue line in earlier entry above) turns out to be correct. Notice that we have the same general activities, tectonics and erosion, but this time it is water exploiting the weakness of a fault line, not eating into a fault scarp.

My question about timing had to do with the age of the rocks comprising the Anopoli plateau. One possibility was that the material was fairly ‘recent’ comprised primarily of sediment from the Lefka Ori (this would be the top 3 layers in the stratigraphic column Erno gives above). It turns out that, for Aradena, the rock layers are much older, going back to Jurassic times, and so even predating the onset of uplift. Presumably, the age of the rock layers is the same for all of the Anopoli plateau. I realized I had taken some photos of rock strata in the Sfakiano gorge. It is consistent with a general west to east slope starting even at the Eligias gorge.

Left photo looks at a cut perpendicular to the uplift, so the strata look more horizontal. Right photo (compare to photo of Eligias gorge) is parallel to angle of up-lift, and so the angle of tilt is more visible.

This raises a new question for me: why the Anopoli plateau even exists. It implies a differential lift of the Lefka Ori relative to the plateau. Possibly, this means another area of faulting along the south base of the Lefka Ori. Then, the entire area (Lefka Ori plus plateau) has again undergone uplift as one big unit. That is why we have the scarp face on the coast. It is a yet more recent uplift phase.

This relative uplift difference, plus the changes in sea-level, might clarify several other ambiguities. Presumably, much earlier phases of relative land and/or sea movement created the origins of water drainage routes (origins of the modern gorges). But when the sea level was much higher the drainage routes could have been different – thus, the ‘anomaly' that Ray commented on in the lower Aradena area. Similarly, we might understand some differences in the Illingas vs. the much bigger Sfakiano gorges, and even some shallower secondary gorges and ravines. When you examine the upper reaches, they share a common source. Yet at some stage it seems that the erosion cutting the ravines eventually resulted in the Sfakiano gorge pirating most of the water runoff.

One last detail for now. The Mavri Laki looks like a good candidate for the location of a cirque glacier. The positioning is perfect for feeding the Sfakiano gorge with water runoff, and for creating the quite large alluvial deposits at its base, upon which Hora Sfakia now rests.
Re: geo The Sfakian gorges
09 March, 2010 17:07
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Hi Mike,

I find this extremely interesting. Your findings are (partially) backed by the text that accompanies the stratigram I posted above.

The whole text might interest you, so here it is:

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The area is very interesting from a geological point of view, mainly due to the uplifting movements,
the paleobeaches and paleoshore lines, reaching 9 m in certain areas.

The uplifting movements are still taking place.

Throughout the area, there are still sites with intense tectonic activity, which is responsible for the
present morphology of the area, large gorges, lakes and plateaus (poljes). Graywackes with gypsum, the oldest rocks in the
area (Triassic), are also interesting.

Crete was formed from the remnants of Tethys Ocean, as a result of alpine orogeny. It submerged and emerged three times from the end of the Paleozoic to the base of the Miocene (early Neogene), when it was covered by the sea and it re-emerged as three separate islands (mountain ranges of Lefka Ori, Psiloritis and Lassithian Mountains).

When the sea withdrew in the Messinian (late Miocene), due to the dryness of the Mediterranean (Messinian salinity crisis), gypsum and anhydrite were formed because of the evaporation. Abundant fossils (gastropods, echinoderms, etc.) are found within the Neogene sediments and, in the Miocene sediments in particular.

At some locations, the fossils in the lacustrine Upper Miocene sediments co-exist with the fossils of mammal fauna.

During the Pliocene, the depth of the sea increased again, so the sedimentation appears to have been gradually formed deeper and deeper in the sea. The filling of the Neogene basins with sediments united the mountain ranges and then, the island emerged as a land due to tectonic processes, having a form, which resembled its modern form.

During the Pleistocene, there were changes on the relief and the fauna of Crete. Mammal fauna developed during the Pleistocene-Holocene; it can be found in caves (Gerani in Rethimno Prefecture, Cape Drapano in Chania Prefecture) or in old lakes (Katharos plateau in Lassithi Prefecture).

Characteristic fossils are those of dwarf hippopotami, elephants, deer, rodents, etc. Fauna became extinct at the end of Pleistocene, possibly due to lack of food.

The text on the geology of Chania Prefecture and the Island of Gavdos follows the stratigraphic series and the tectonic emplacement from the lower to the upper members of the formations.

Crete has a particularly complex and complicated geological structure, due to its direct adjacency with the place where the African plate subducts under the Eurasian plate. Its structure is characterised by tectonic nappes of pre-alpine and alpine rocks, as well as postalpine neogene basins, with E-W or N-S orientation and sediments, which unite the mountain ranges and form the island.

The pre-alpine - alpine nappes of Crete are:

• Platy limestones (Plattenkalk) (M. Jurassic-Oligocene, 170-28 m.y.), nappe of carbonate rocks deposited on neritic (shallow) environment, which was transformed into a pelagic (deep sea) environment. The deposit closes with the Oligocene flysch of the series, some remnants of which occur on Psiloritis Mountain. This is the only series that was formed in Crete, that is why it is called autochthonous.

The mountain ranges of Crete are formed by platy limestones. Their deeper members are encountered on Lefka Ori (Pantokratoras marbles). Platy limestones cover the mountain range of Lefka Ori, with its highest peak, Pachnes reaching an altitude of 2.453 metres.

Within this formation of Lefka Ori, two large plateaus, Omalos and Askifos, and a smaller plateau, Krambi, develop; they are poljes, which owe their formation to the combination of karstic erosion and tectonic influence. In the NE edge of this mountain complex, Kourna Lake has been formed: it is a huge lake-doline and it stands on the place where three large faults converge. Another characteristic of the formation are large gorges with a main N-S orientation and a secondary E-W orientation, which usually end up in the southern area of the Lefka Ori.

Some of them are the Imbros gorge, the Agia Eirini gorge, the Samaria gorge, etc. The large springs of Stylos and Armeni, the Kourna lake, the Agia and Georghioupoli springs are fed by the Lefka Ori mountain range and provide water for the largest part of the Prefecture. The upper members of the platy limestones formation are to be found on Psiloritis (thin-bedded limestones with siliceous intercalations or nodules). At some locations (e.g. Fodele - Sisses), at the base of the platy limestones there are carbonate rocks dating back to the Permian (300-250 m.y.), limestones and dolomites considered similar to the Gigilos rocks, in Lefka Ori. The Gigilos layers develop in the South of Omalos Plateau in Lefka Ori and cover Gigilos Mountain to which they owe their name. They could be a series underneath the platy limestones. These layers present a steep relief and large volumes of lateral scree.

• The Trypali nappe, of unknown age, “sits” right on the platy limestones at some places in Western Crete. It contains carbonate conglomerates, limestones and, mainly, dolomites. It is rare in Chania Prefecture; some small occurrences are to be found on Trypali Mountain, in the Southeast of the island, in the North of Omalos Plateau.

• The nappe of the Phyllitic-Quartzitic series is possibly a prealpine continental block, formed by phyllites, schists, quartzites, marbles, graywackes and gypsum.

They are metamorphic rocks in high pressure/ low temperature conditions. The nappe lies tectonically on the formation of the platy limestones.

In Chania Prefecture there are significant occurrences in the West of the Prefecture, in the Kissamos (Kasteli) area, in the southern part of the Prefecture (Paleochora-Chrissoskalitissa) department. In the lower members of this series (graywackes) gypsum is hosted. The thickness of the series exceeds 1,500 metres.

• The tectonic nappe of Tripolis zone and the tectonic nappe Pindos zone, constitute the continuation towards the South of
the continental Greece Gavrovo–Tripolis and Pindos nappes.

• At the base of the Tripolis nappe there is ravdoucha formation. It is of Middle-Upper Triassic (245-200 m.y.) age, formed by argillaceous schists and clastic sediments. In Chania Prefecture, they develop at Rhodopos peninsula, next to Ravdoucha village. The thickness of the series reaches 300-600 m. Within the formation there are iron ores, the presence of which is connected to the existence of an old mine in the area for the exploitation of iron ore.

The Tripolis zone is formed by carbonate rocks, dating back mainly to the Mesozoic Era, limestones and dolomites of neritic sedimentation, and “closes” with the flysch (clays, sandstones and conglomerates) dating back to the Upper Eocene (30 m.y.). In Chania Prefecture, the carbonate series occurs in the area of Paleochora, in Kasteli, in small remnants, in the Akrotiri area and in the two capes Spathas and Gramvoussa of the Kissamos area. The flysch of the series has small occurrences in the Kasteli wider area and in the Paleochora area.

The Pindos zone is formed by pelagic sediments (radiolarites, cherts, limestones) dating back to the Triassic-Jurassic (230-145 m.y.), followed by the first flysch of the Upper Cretaceous (65 m.y.), then by pelagic carbonate sediments dating back to the Paleocene (65-55 m.y.) and the series “closes” with flysch (clays, sandstones and conglomerates), of Paleocene-Eocene age (55-35 m.y.). It is not widely spread in western Crete; it is only to be found in the Paleochora area, in the Kasteli area (Topolia), as well as on the island of Gavdos.

• Over the Pindos nappe, in some locations, mainly in SE Crete, namely in the mountain range of Asteroussia, there are tectonic nappes (e.g. Arvi, Vatos, Miamos nappes) mixed with one another, forming a “mélange”. Over all the other nappes, there is the nappe of Asteroussia (metamorphic rocks, amphibolites, gneisses in high temperature/ low pressure conditions).

• The ophiolite nappe consists of Upper Jurassic (145 m.y.) mafic and ultramafic rocks of the ocean lithosphere, such as peridotites, serpentinites and gabbros. In Chania Prefecture, they occur mainly on the island of Gavdos.

The post-alpine rocks of Crete are: Neogene – Quaternary deposits.

• The depositional environment during the Serravallian age (Neogene, 13 m.y.) is that of a shallow sea or a brackish stage,
with clastic formations, such as conglomerates, sands and clays. One such formation are the Topolia conglomeratic breccias (western Crete), consisted of carbonate pebbles and gravel, originating from the erosion of the alpine Tripolis and Pindos zones, tightly cemented with calcitic material. The Topolia formation is very thick (> 350 m). It is characterised by steep reliefs, cavernous forms and gorges.

• Beneath, there are sediments of a deeper sea (Tortonian-Lower Messinian, 11-7 m.y.), with deposits of bioclastic recifal limestones, alternating with marls, followed by open-sea sediments (e.g. white marls and clays). At the end of the Messinian (5,3 m.y.), with the salinity crisis and the retreat of the sea, there were new deposits of terrestrial, fluviatile, lacustrine and lagoonal sediments with gypsum and evaporites.

• During the Pliocene (5-2 m.y.), the depth of the sea increased again, so the sedimentation appears to have been gradually formed deeper and deeper in the sea; some examples are white marls and clays with alternations of diatomites at some places (particularly in the Iraklio and Chania areas). Namely in Chania Prefecture, Neogene formations cover a large part of the Kasteli Basin, the Chania Plain area and the town of Chania, the Frangokastello area, and the island of Gavdos.

• Finally, during the Pleistocene (2 m.y.), there are intense tectonic elevations and considerable fluctuations of the sea level, leading to the deposition of Quaternary terrestrial or marine formations, such as terraces, clays and conglomerates, especially along the southern coasts of the island. In Chania Prefecture, there are Quaternary deposits (2 m.y. until today), such as terraces, screes, conglomerates, raised paleobeaches and shore lines, on all the coasts and on the island of Gavdos.



1. Alluvial deposits
2. Pleistocene deposits
3. Neogene formations
4. Complex nappe of the Internal Zones
5. Olonos-Pindos nappe
6. Tripolis nappe
7. Phyllite-Quartzite nappe
8. Trypali (or Omalos) nappe
9. Crystalline platy limestones (Vigla formations)
10. Dolomites (Pantokratoras formation)
11. Gigilos formation
12. Sisses formation
13. Fodele formation

From: © Copyright IGME, Geotrails 2009

All the best,

Erno
webmaster Sfakia-Crete.com
Re: geo The Sfakian gorges
11 March, 2010 14:47
avatar

The detail is staggering, isn't it? The stratigraphic column answers the question "What is Crete made of, and where did it come from?".

It has been an interesting experience reading some of the scientific source material. Depending on how closely the researchers look, they emphasize different terminologies. The stratigraphy terminology is often correlated to the 'big picture' of the entire east Mediterranean and even to all of western Europe (Peter mentions this above):


The researchers are mostly interested in the major faults and trenches in the region. Crete is a little sliver in the region they are studying:


For a visual analogy on a small scale, this is what's happening to Crete (in photo, imagine the center of the image being Crete tilted vertical, e.g., east Crete pointing up):

Big blocks are broken into smaller blocks, and the smaller blocks get broken and cracked, and so on right down to the little pieces of rock you can hold in your hand.

Some scientists want to take an closer look at the details of Crete and ask the question "Why does Crete have the shape it has?" (irrespective of what it's made of):

They want to learn something about the smaller faults and fractures. I am amused by my own hesitant speculation at the start of this thread that there might be other faults and fractures in and around Anopoli plateau. Crete is littered with them!

And if that isn't a close look for someone, just power up the microscope. The following illustration is from a dissertation examining flood patterns in the Aradena gorge over the past 200 years, and relating flood frequency to changing weather patterns in the North Atlantic:




Edited 1 time(s). Last edit at 11/03/2010 14:48 by Mike.
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