Argentine (& Uruguayan) Escoria

Full Page update underway 19 December 2012

Escorias from Chapadmalal (= Mar del Plata), Chasico, La Paloma, and Monte Hermosa added


Escoria!!!

To the best of my knowledge, this is the first and only batch of this peculiar material to reach the market.




Here's the general story:


At least six different impactite layers have been discovered within the last few years in the extensive loess deposits of Argentina, and another is reported in Uruguay (La Poloma, offered below). The specimens originally presented on this page were from what is likely the most important of these, the Chapadmalal Impact. (Only a few pieces remain, but ask me to get more---) Dated at 3.3 million years, this event is associated with the extinction of at least 36 genera of land animals and a temperature shift that may have been of global proportions. It has been suggested that this may have been the event that triggered a climatic destabilization leading to subsequent ice-age cycles, as the timing is about right.

No source crater has yet been identified, but the presence of splatted glass bombs with maximum dimensions up to 2 meters having baked soil horizons underneath suggests that the impact was very nearby. It is speculated that the advancing shoreline in this areMar del Plata, Argentinaa may have destroyed the crater.

Today, the impact glass, termed "Escoria", is found in sea cliff exposures extending at least 30 kilometers eastwards from the Mar del Plata area of the Buenos Aires Province, pictured at left. Relatively fragile material eroded onto the beaches is quickly destroyed by abrasion, so it is necessary to rappel down the cliffs to obtain quality specimens.

The impactite glass reportedly contains anomalous iridium and chromium relative to the associated loessoid deposits, and like many impactites, has an exceptionally low water content relative to other natural glasses. Protolith zircon grains have been transformed into baddeleyite, implying temperatures of formation in excess of 1700°C. This temperature constraint eliminates most natural possibilities other than extraterrestrial impact. Contorted schlieren bands are evident in thin sections. Magnetic spots similar to those seen in Monturaqui glass are sparingly present, but I have not yet seen metallic fragments on cut surfaces.
Vesicle cross-section
The material is highly vesiculated, often with about 30% vesicles by volume (15 to 50% range). The voids are commonly irregular and show moderate vertical flattening. They are complexely interlinked, and mostly under 1 cm in maximum dimension. Where open to the surface of the specimen, the vesicles are sometimes packed with sand containing well-rounded white zinfandel-colored garnets. The glass is mostly nearly opaque, dark champagne-bottle olive green, but includes streaks of creamy yellow-green similar to Trinitite color. Most is opaque to translucent, but occasional vitreous transparent seams are present in less vesiculated material. A few specimens show blockly angular enclaves (engulfed clasts?) of denser, finely vesicular dark glass. The latter is commonly attracted to a strong magnet. There are no visible phenocrysts or inclusions.
Skin Character

Where surface skin is visible, it has the ropy , bubble-punctured, pahoehoe character of fluid lavas, some trinitite, and the peculiar Australian Edieowie glass.

From the distribution and maximum known size of the glass bombs, an original crater size on the order of 10 to 15 kilometers has been inferred. Investigators speculate that the responsible bolide was an order of magnitude smaller than Chicxulub, perhaps something around a one km diameter.

Because the Chapadmalal impact appears to be involved in extinctions and significant climate change, the event continues to be a topic of extensive research funded by NASA and the NSF. While not a monster killer like the K-T event, Chapadmalal may represent something approaching a lower limit on the bolide size necessary to produce global effects, and is thus significant in assessing risks posed by potential future impacts.



Sold items updated 12/19/2012 Most of the Chapadmalal is gone, but several pieces remain---

I have just posted a shipment of Escorias from Chasico, Argentina (10.1 m.y.), and some weird charcoal-bearing material from La Paloma, Uruguay. I'll try to get background info posted soon. Chasico is dated at 10.1 million years. La Paloma is less well studied and is mostly found on beaches after big storms. It has been compared in character to Wabar glass (but the charcoal reminds me more of Egyptian Dakhleh glass---).



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Be sure and check out the 672 gram giant following this table! It is for sale.

Take notice of the relative size of my hands in the following photos. Because of cropping, you may get the impression that the pieces are all of similar size. They are not.

Chapadmalal Escoria (sometimes called Mar del Plata). Dated at 3.3 my. Recovered by rappelling down poorly consolidated loess seacliffs!

Chapadmalal, Argentina

86.7 gms $110 Preserved surface skin along right edge in photo indicates that this is a cross-sectional slice. Textural variations hint at a subtle breccia agglomerate.

Chapadmalal, Argentina

50.8 gms $65 Fragment from formerly 820 gram giant (decrepitated to 672 grams in storage and transport---). No external skin preservation.

Chapadmalal, Argentina

35.2 gms $45SOLD Fragment from formerly 820 gram giant (decrepitated to 672 grams in storage and transport---). No external skin preservation.

Chapadmalal, Argentina

12.4 gms $18sold Fragment from formerly 820 gram giant (decrepitated to 672 grams in storage and transport---). No external skin preservation.
La Paloma, Uruguay. Poorly studied. Often found on beaches after major storms. Pumicious pieces will float. Often contains charcoal; has been likened to Wabar and is said to have similar variations.

La Paloma, Uruguay

94.7 gms $150SOLD Quite a dense piece; visible charcoal clast

La Paloma, Uruguay

41.5 gms $70 Quite dense, visible charcoal clast

La Paloma, Uruguay

37.0 gms $50 Pumicious---it will Float on water. Visible charcoal clast.

La Paloma, Uruguay

29.3 gms $45SOLD Moderately dense. Visible charcoal.

La Paloma, Uruguay

10.2 gms $20 Highly vesiculated. Will float on water.

La Paloma, Uruguay

5.7 gms $15sold Dense, glassy.

La Paloma, Uruguay

1.2 gms $10sold Highly pumicious. Floats high!
Monte Hermosa, Argentina. Darwin collected fossils at this seacliff during the voyage of the Beagle, and if I remember correctly, mentioned seeing glass fragments. I have no detailed references to this material.

Monte Hermosa, Argentina

25.3 gms $100 Only piece ever offered for sale.
Chasico, Argentina. Dated at 10.1 my. Many pieces have cryptic, but pretty convincing reedy and grassy plant fragment impressions that remind me of Egyptian Dakhleh glass.

Chasico, Argentina

111.2 gms $150 Our biggest ever. Ropy surface. Possible plant molds and impressions.

Chasico, Argentina

57.6 gms $72 Possible trace plant fragment molds, but debatable.

Chasico, Argentina

39.5 gms $80 Pretty convincing plant mold fans out at upper left of photo

Chasico, Argentina

33.0 gms $41 Scoriaceous, no likely plant frags.

Chasico, Argentina

32.7 gms $65 Nice skin with one pretty good reedy plant imprint.

Chasico, Argentina

31.5 gms $70 Our best skin preservation and overall morphology. No plants evident (top surface?).

Chasico, Argentina

31.1 gms $50 Has a couple of nice fanning imprints like the 39.5 gm specimen. Great skin features whatever they may be!

Chasico, Argentina

28.8 gms $40 Highly vesiculated. One cavity has possible plant-like impressions, but hard to be sure.

Chasico, Argentina

24.7 gms $50SOLD Take a hand lense to this one and confirmed skeptics will believe. There's a jackstraw pile of little grassy stem imprints with pretty sharp detail.

Chasico, Argentina

17.3 gms (a) $22 Vesiculated internal fragment. No plants or skin.

Chasico, Argentina

17.3 gms (b) $22 Vesiculated internal fragment. No plants or skin.

Chasico, Argentina

11.9 gms $25 Includes a fair, but cryptic, plant impression.

Chasico, Argentina

10.5 gms $15 Vesiculated internal fragment. No plants or skin.

Chasico, Argentina

10.4 gms $17 Some skin preserved. No obvious plants.

Chasico, Argentina

9.9 gms $14 Vesiculated internal fragment. No plants or skin.

Chasico, Argentina

9.8 gms $12 Vesiculated internal fragment. No plants or skin.

Chasico, Argentina

9.7 gms $12 Vesiculated internal fragment. No plants or skin.

Chasico, Argentina

7.3 gms $10 Vesiculated internal fragment. No plants or skin.

Chasico, Argentina

5.2 gms $15 Small patches of plant texture visible with a lense.

Chasico, Argentina

4.4 gms $6sold Possible single plant impression, but questionable.

Chasico, Argentina

3.5 gms $5 Vesiculated internal fragment. No plants or skin.

Chasico, Argentina

2.8 gms $5sold A bit of preserved skin. No plants.

Chasico, Argentina

2.6 gms $5 Vesiculated internal fragment. No plants or skin.
 

Chasico, Argentina

1.9 gms $5 Vesiculated internal fragment. No plants or skin.


Chapadmalal, Argentina

This big guy is the largest specimen commerically offered in the world today. At approximately 672 grams, I can provide it at $500. I'll supply more pictures if you are seriously interested. This is a very nice piece! (It used to be a bit bigger, but it shed some pieces in storage---)


Email us at nlehrman@nvbell.net to inquire or order.

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