The paleoenvironment of this deposit should be studied according to the facies associations. But according to you, and as well as the roundness of the grains, it is probably a glaciofluvial deposit.

Dear Mr. Valero,

There are some important informations not shown on the images

1. Scale

2. Paleocurrent

3. Composition

I see an oligomictic grain-supported conglomerate with an intermediate degree of grain morphology.

To get an idea how the sediments have been emplaced I suggest the following tripartite gravel analysis

a) situmetric measurements as to their vertical and horizontal orientation

b) clast morphology (using the six-part categorization scheme)

c) granulometry of clasts and matrix minerals such as heavy minerals (the higher the glacier´s impact , the lower the hydrodynamic differentiation of the sediment load).

For comparison charts and more about gravel analyses recorded under a) to c) I suggest the following studies of mine covering the full range from the glacial to the fluvial landforms giving host to gravel-sized sediments. All methods are described there in detail.

They are available on request for download from the RG server

DILL, H.G., KUS J., BUZATU A., BALABAN S.-I. ,KAUFHOLD S., and BORREGO A. G. (2021) Organic debris and allochthonous coal in Quaternary landforms within a periglacial setting (Longyearbyen Mining District, Norway) - A multi-disciplinary study (coal geology-geomorphology-sedimentology).- International Journal of Coal Geology (on-line)

DILL, H.G., BUZATU A., BALABAN S.-I. , UFER K., TECHMER A. SCHEDLINSKY, W., and FÜSSL M., (2020) The transition of very coarse-grained meandering to straight fluvial drainage systems in a tectonized foreland-basement landscape during the Holocene (SE Germany) – A joint geomorphological-geological study.- Geomorphology (in print)

DILL, H.G., BUZATU A., BALABAN S.-I. , UFER K., GÓMEZ TAPIAS J., BÎRGĂOANU D. and CRAMER T. (2020) The “badland trilogy” of the Desierto de la Tatacoa, Upper Magdalena Valley, Colombia, a result of geodynamics and climate: With a review of badland landscapes.- Catena 194: 1-20.

DILL H.G., BUZATU A., GOLDMANN S., KAUFHOLD S., and BÎRGĂOANU D. (2020) Coastal landforms of “Meso-Afro-American” and “Neo-American” landscapes in the periglacial South Atlantic Ocean: With special reference to the clast orientation, morphology, and granulometry of continental and marine sediments.- Journal of South American Earth Sciences 98 (on-line)

[Antarctica and its periglacial foreland]

If you have used these three methods in combination with heavy minerals you will easily make up your mind with regards to the origin of transport and deposition of these coarse sediments.

I am looking forward to your response and wish you much success H.G.Dill

What is the source of your map?

According to french geological survey BRGM , it belongs to the unit: FGx5 Fluvio-glacial des couloirs de l'Est lyonnais from Würm age.

Glaciofluvial conglomerates from the Saalien (Riss) in Holland, quite similar. These have been deposited at the leeside of the Utrecht Ridge, a pushmoraine.

I am impressed as to their sedimentological attraction by the photographs taken at outcrops of conglomerates . But even taking a short glimpse at them will show us that they are significantly different with regard to the built-up in vertical, structure and texture. Coarse-grained sediments are variegated in origin from the coastal marine surf zone to the apical part of an alluvial fan so that a numerical approach will have to be taken on different scales unless a simple repetition of the previous mapping results is the aim.

Jérôme Juilleret The source of map is Mandier, 1984

The thesis () where I took the map (p56) :

"Caractérisation hydrogéophysique d’un dépôt fluvioglaciaire. Evaluation de l’effet de l’hétérogénéité hydrodynamique sur les écoulements en zone non-saturée.""

-David Goutaland

BRGM don't seem very precise for the location though.

Harald G. Dill Thank you Dr.Dill for your references.

I took several pictures from an other deposit where all the stratums are visible (you can zoom in).

Interestingly the circled area (small gravels) seem to be eroded in the other location.

Do you think these different textures indicate a fluctuation in paleocurrent ?

I extract one pebble and it seems that not all are rounded. Maybe they weren't deposited that far from their initial location ?

I suspect 3 different types of processes leading to mass wasting/ debris flows, glacial-fluvial/ braided streams and aeolian processes (deflation and deposition). Some gravels with beveled edges and characteristic shapes may be ventifacts , shaped during periods of time when the channel systems were abandoned and exposed to wind. For vertical sections I recommend to use the reference types of Miall , e.g., Scott- and Donjek-types. In plane view good hints you may deduce from Church´s descriptions (cited in my paper). He displays very well the relationship between sediment supply, sediment caliber, channel gradient and channel stability. Applying these aspects will help you make a great leap forward in relation to the results published in the existing map you use as basis. There are multiple-generation processes with abandoned and active drainage systems to be seen in the vertical section. Many of the clast-supported and matrix-supported conglomerates you will also find in photographs of the paper below:

DILL, H.G., KHISHIGSUREN, S., MAJIGSUREN, YO. , MYAGMARSUREN S. and BULGAMAA, J. (2006) Geomorphological studies along a transect from the taiga to the desert in Central Mongolia-Evolution of landforms in the mid-latitude continental interior as a function of climate and vegetation.- Journal for Asian Earth Sciences, 27: 241-264.

Pay also attention to imbrication. These structures enable you to measure paleocurrent directions. By and large, your sections are an ideal site for the application of the GMS tools (granulometry-morphology-situmetry)- see my first post in this thread for more detail.

I wish you much success

H.G.Dill

Quel est le but de ton etude Olivier?

Jérôme Juilleret Merci pour l’intérêt que vous portez au projet. Il s'agit de reconstituer l’environnement d'après ces affleurements de conglomérat (probablement du Pléistocène) et éventuellement associer une période. Tout cela dans le contexte d'une étude de Paléontologie.

Avez vous trouvé des fossiles? Le mieux serait une datation de ces sediments pour lever les doutes, mais leur cartographie systematique et leur position geomorphologique permet deja de mieux apprehender leur age relatif.

Jérôme Juilleret Pour l'instant aucun fossiles sur cette localité, mais ce n'est qu'une question de temps.

Selon vous, si on tient compte du temps nécessaire à un dépôt type conglomérat, peut-on exclure l'Holocène et envisager une période plus ancienne ?

Je reste sceptique sur l’environnement de ce dépôt : un climat chaud et humide me semblent plus vraisemblable qu'une période de glaciation.

On ne peut exclure, la compaction et la cimentation ne sont pas des bons indicateur de temps.

Par contre il faut apprecier sa position dans le paysage. Ya t'il une riviere proche?

Pour apprecier sa position geomorphologique et avoir une appreciation de sa datation "relative", il faut voir l'altitude. Pouvez vous la prendre?

Ensuite, vous pouvez regarder les altitudes des depots datant du Riss ou Wurm au alentours d'apres la carte geologique et voir avec lequels votre depot se correle.

Pourquoi un climat chaud? Ce genre de depots est issu du remaniement des depots morainiques par les eaux de ruisselement. De maniere generale, plus ils sont arrondis plus ils ont subis de deplacements. Vous voyez que leur nature (lithologie) est diverse, cela permet d'apprecier la zone de depart des differents galets.

Jérôme Juilleret Je vous remercie pour votre retour. L'affleurement a été exposé suite à la création d'un canal, à flanc de colline. Le seul cours d'eau à ''proximité'' serait le Rhône, mais il reste éloigné. La plaine de l'Isère a certainement habrité de nombreux alluvions, marais au cours des derniers milliers d'années.

J'ai pensé à un climat chaud (interglaciaire), en raison de l'absence de ventifacts.

Pourtant j'ai extrait un galet du même gisement, assez érodé et très crevassé (ci-dessous). Il me semblait plus altéré que les autres.

Pensez-vous que le gel et le vent peuvent produire cette texture ?

Je ne saurais pas vous repondre, de toute facon un galet peut avoir subis plusieurs remaniement, désolé.

Je parle seulement un peu le français pour survivre dans la « Légion étrangère ». So I can no longer follow your scientific discussion which I am interested in.

Harald G. Dill

Harald G. Dill I'm Sorry, I should have reported here the message that I sent to you yesterday. Do you have received it ?

For the sake of the conversation, I will copy the text :

''I require your attention on the texture of this pebble that I extracted from the conglomerate (in the precedent discussion). The pebble appears to be badly weathered and pocked with holes. What environment has produced such eroded material ? Frost, turbulent waters ? Do you have any references that I could use to further identify pebbles ?''

The pebble is ilustrated in my latest reply, 3 hours ago.

I suspect of a quartz pebble subrounded to rounded by a fluvial transport. There are two characteristic surface textures. It is the frosted surface texture of sand-sized quartz grains which they adopt being transported and polished by aeolian processes and the parallel oriented striae of fragments transported by glaciers. Both of them cannot be seen on the surface. The moderately wrinkled surface is due to the primary origin of the quartz as a mobilizate. Such notches and rills get sometimes accentuated and sometimes beveled at their edges. I would not read too much into this texture when it comes to the analysis of sedimentary processes. I am currently dealing similar gravel derived from straight to low-sinuosity mountain rivers. I agree with you gravel fragments can be like a letter and tell you a story.

Harald G. Dill Jérôme Juilleret Dear colleagues, I found this rock on the same slope from where I took the picture of the sediments above. It seems limestone : perhaps some Cretaceous chalk from the Alps ? If I take a sample and dissolve it with weak acid, perhaps I could determine the nature of the block (erratic or not) ?

Harald G. Dill Dear Dr.Dil, I found these conglomerates nearby, they are more impressive than the first above. They piled up to several meters, and the pebbles seem homogeneous. There seem to have some limestone inclusion. The energy of the paleocurrent seems to have been high enough to transport this quantity.

But I don't see any stratifications or change in current.

What do you think of these new profiles ?

In Pakistan, along Hunza river, Glacio-fluvial (first moved by glacier then fluvial action) deposits are know commonly.

regards

ijaz