Introduction
Kaş is a small town on the Mediterranean coast of Southern Turkey located 36.1999° N, and 29.6396° E. The location is on the southern edge of the Teke Peninsula, roughly midway between Fethiye and Antalya, where the Greek Island of Kastellorizo separates Kaş Bay from the open sea (Figure 1). The adjacent Turkish coastline forms a semicircular arc, with multiple, roughly concentric, curved, linear hills.
Google map image of Kaş Bay 2016, indicating the initial suggested crater rim, yellow curved lines. The unbroken yellow line demarcates the border between Greece and Turkey. Red circle shows the islands marking the central uplift.
The local bedrock is Cretaceous marine limestone, and because no local volcanism is evident, this potential geological origin of the circular structures can be excluded. An impact hypothesis was first suggested in 2016 after field investigations to ascertain the cause of the unusual geological features were undertaken. A small circular group of islands (Figure 2) in the SE part of Kaş Bay outlines an inverse cone-shaped area of shallow bathymetry. The top of this cone is ∼1 km in diameter, with a gentle dish profile down to 20 m depth in its centre. Around the outer margins of these islands, delineating the top of the cone, is a near-vertical drop to 85 m depth. This remarkable circular structure has been proposed as the central uplift of a complex hypervelocity impact structure [1].
View; the circular group of islands in Kaş Bay, looking southward with Strongili island in the background. Photo courtesy of David Talbot.
The reason that the Kaş Bay structure, despite its size, has not so far been recognized as an impact site is mainly because its northeastern margin, in its continuation onto the Turkish landmass, no longer bears any resemblance to a round impact crater and is more elongated in configuration, and its southern and western margins have disappeared. This shape is indicated in Figures 3 and 4.
The radial sea floor structures are suggested to be remnants of the southern part of the original Kaş circular crater, with distortion and displacement resulting from movement of the Aegean plate relative to the Anatolian plate. The African plate moves northwest at around 2.15 cm per year [4].
Digital Terrain Model images of the Kaş Bay impact structure onshore, mostly composed of an accumulation of smaller and bigger megablocks, some larger ones marked turquoise. The turquoise lines also represent probable transtensional troughs. Yellow lines indicate the proposed distorted crater rim.
We explain this shape as being due to the location of Kaş in the subduction zone of the African and Eurasian plates near the boundary of the smaller associated Anatolian and Aegean plates, which move in different directions and at different speeds (Figure 3). After the impact, proposed to have occurred in the Pleistocene epoch [2], this plate movement caused the original, presumably round crater, to be disrupted and deformed, even possibly made smaller. Consequently, transpressional ridges and transtensional troughs [3] from the modification stage of the cratering process, can still be observed on land in the Digital Terrain Model (Figure 4), and on the adjacent sea floor of the receding Aegean plate (Figure 3).
The Western Taurus Mountains, including the Kaş region, with their notably rugged terrain, run parallel to the Mediterranean Sea in southern Turkey as an extension of the Alpine orogenic belt, forming a primary geomorphological component of the region. This mountain range extends along the islands of Crete and Rhodes, from the Teke Peninsula to Uzunyayla and the Elbistan Plain in the east, for more than 900 kilometres. The study area is located in the southern (coastal) section of the Western Taurus Mountains, stretching in an arc across the Teke Plateau to the Taşeli Plateau. Akdağ mountain is located north of the area, while the Bey Mountains and the Tahtalı Mountains are situated to the northeast. These mountain ranges, which include the region’s highest summits (3070 m), are incised by deep canyons. Unlike the Central and Eastern Taurus Mountains, which continue in an east-west direction, the Western Taurus Mountains make a sharp bend along the line between Eğirdir Lake and Antalya Bay (Antalya Suture Belt) in a northeast-southwest direction.
Clayey and carbonate limestones deposited in the Tethys seas throughout the Mesozoic make up the lithological structure of the Western Taurus Mountains (Figure 5).
Geological-petrographic-mineralogical features, providing evidence for an impact, are widespread although, due to the lack of silicate rocks, shock metamorphism is restricted to carbonate rocks. In this case we suggest reconsidering the ‘law of proven impact’ commonly maintained within the impact community and giving substantially more credit to intrinsic geological evidence, especially when silicate rocks are lacking.
Method
Since 2016, extensive field studies have been conducted on mainland Turkey, on islands in Kaş Bay, and the island of Kastellorizo. These have included mapping and looking for impact-event characteristics, such as impact-related rock deformation, impact ejecta, shatter-cones, shock metamorphism, and signs of possible melt and decarbonization [6]. Samples were collected for various analyses that included thin-section preparation, XRF and magnetic susceptibility. In addition, a comparison was made with the Spanish Rubielos de la Cérida impact structure.
Early research suggested that the Kaş Bay Impact structure was 8–10 km in diameter [7]. The distance between Kastellorizo and Kaş town is 7.1 km [8] (Figure 1). The procurement of Digital Terrain Modelling (DTM) in December 2022 from satellite data over the site [9] indicated a structure much larger than this original suggestion, possibly ∼20 km in diameter. This and further observations of the study area formed the basis of the latest field research executed in early 2023. In Figure 4, the yellow lines indicate the suggested new, albeit distorted, crater rim. Visual ground observations were undertaken to ascertain whether the field evidence supported this suggestion from the satellite imagery. The terrain is extremely scrubby and very steep (nearly vertical in places), but road cuttings and new building sites, along with old quarries, allowed visualisation of the geology.
A study of the geomorphology emphasized that the ground north of the Kaş peninsula has subsided. Turkey is highly active tectonically, and the proposed crater, along with the three aforementioned plates jostling for room, is no exception (Figure 3). A comparison of how different aspects of the geomorphology might reflect tectonic movement or an impact event was considered.
Results
Breccias
Breccias are a significant constituent of impact structures due to the established contact/compression, excavation, and modification stages of impact cratering [1]. The Kaş Bay structure is no exception, and the richness of both monomict and polymict breccias in the field, along with megabreccias and dyke breccias, is striking (Figures 6–9). Breccia dykes are a prominent feature in impact structures [10].
Breccia-in-breccia and Breccia Generations
Due to the various stages of impact cratering, breccias-within-breccias and, in particular, multiple breccia generations (Figures 10, 11), are a typical impact texture and rarely observed in other brecciation processes [11]. This unusual impact phenomenon is abundant throughout the study area.
Up to 4 generations of breccia-in-breccia have been observed many times around the study area. In image (a) a monomict clast (red) in a monomict dike (blue) is cutting through a limestone fragment (yellow) itself being a clast of polymict breccia (green).
Peculiar breccias, often referred to as fitted fragments [11] and containing coherent fractured clasts with preserved fitting (Figure 12), indicate movement under confining pressure conditions.
All the above impact-specific field evidence is abundant on mainland Turkey, the islands of the central uplift and Kastellorizo.
Spallation
In fracture mechanics, the spallation in solids (not to be confused with nuclear spallation) is well understood. Evidence of impact-induced spallation in rocks [12] is seen frequently on the beaches around the study area (Figure 13). Spallation is indicative of a rarefaction wave having passed through a structure, cracking it into slices, while still leaving the rock in its original form. This dynamic shock deformation is also observed on a microscopic scale [2].
Decarbonization/carbonate melt
In contrast to silicate rocks, carbonate rocks do not quench to form glass. Under impact high pressure/temperature (PT) conditions, limestone can melt or decarbonize with subsequent, in part immediate, recrystallization. Like in other impact structures with a partial carbonate target, e.g., Azuara/Rubielos de la Cérida, Spain [13]; Haughton Dome, Canada [14], such relics of carbonate melt/decarbonization are abundant in the investigated area. On Kastellorizo, a white, porous carbonate rock was observed in contact with a scour plane of a polymict breccia interpreted as a variety of pseudotachylite (Figure 14a) [15]. Limestone clasts from the central uplift show a vesicular and skeletal texture as probable relics of decarbonization and/or carbonate melt (Figure 14b). In many outcrops in the study area, white powder and agglomerations also suggest decarbonized limestone/dolostone (Figure 14c, d). Remnants of melting/decarbonization with a flow texture can be seen in Figure 15, along with probable carbonate melt remains of white filaments and plastically deformed limestone components.
Petrographic thin-section analyses
Impact shock deformation in quartz is well documented in contrast to shock effects on carbonate minerals like calcite [16]. However, we observe abundant occurrences of multiple sets of micro-twinning in calcite, frequently in combination with kink banding (Figure 16). Regularly the size of the twins is of the order of 1 μm (Figure 16), which points to high-pressure deformation similar to the development of shock-produced planar deformation features (PDFs) in quartz [16, 17].
Multiple sets of densely grouped micro-twinning and kink banding in calcite indicating shock metamorphism equivalent to PDFs in quartz.
Accretionary lapilli and lapillistone, usually associated with volcanic eruptions but also occurring in meteorite impacts, add to geological conspicuousness (Figure 17).
Magnetic susceptibility analyses
A handful of breccias were tested for magnetic susceptibility (Figure 18) using a Bartington MS2 meter with MS2K sensor. This revealed relatively strong readings (up to 108 × 10−5 SI) for the carbonate matrix, in comparison to the embedded limestone clasts. Enhanced magnetic susceptibilities in silicate impact breccias are common, but they have also been measured in purely carbonate impactites, though with a more subdued signature [18].
Shatter cones
This accepted indication of an impact structure [1] does not always exist and has not been located in the study area. Shatter cones are usually found around the central uplift, and, as this part of the structure is underwater, any that formed may have suffered dissolution.
Comparison with the Rubielos de la Cérida Structure
The Kaş structure has crystallized in many ways similar to the large Spanish Rubielos de la Cérida impact structure (Figure 19), and the extensive geological impact inventory of Rubielos de la Cérida was a helpful guide in the terrain exploration of the Kaş structure. What is special is that both structures are laid out in a purely sedimentary target, which is also largely formed in carbonate facies.
The Azuara and Rubielos de la Cérida impacts in the digital map of Spain 1: 250,000 (courtesy M. Cabedo). Central uplifts (peak ring, Kaş, and chain, Rubielos de la Cérida).
While the products of meteorite impacts into dense, mostly crystalline and mixed targets are relatively well understood, and macroscopic and microscopic deformation of these target rocks is the norm, the response to an impact into volatile-rich sedimentary rocks, in particular carbonate rocks, remains debated.
Although the impact basin of Rubielos de la Cérida is much more extensive than the Kaş basin and offers more exploration possibilities, it is striking that the morphologies are very similar. This similarity applies to comparable structural conditions, deformation features and rock types right down to the micro range, and it has not been difficult to compare findings of the most varied but impact-typical kind with each other, which is done below (Figures 20–23). Comparable scenarios in the field and in hand-specimen samples are much more extensive but are not presented here in detail. It should first be noted that, in the illustrations, the letters K and R indicate the respective assignment to the two impact structures.
Similarity of photomicrographs under crossed polars of accretionary lapilli (left) and twinning (right) from Kaş (K) and Rubielos de la Cérida (R).
Scour planes showing similarity with Kas (K) and the Rubielos de la Cérida (R). a, b, c and d, indicate the brecciated structure of these features in the Kaş structure.
Scour planes are gigantic landslides of mega blocks containing breccias and megabreccias and are typical in larger impact structures. Enormous mass movements often lead to impressive sliding surfaces, partly with mirror polish [19]. They look very similar to tectonic fault planes, but closer inspection reveals the brecciation within the rock face. Several layers of scour can be observed (Figure 21a–d).
Digital Terrain Modelling
The recently acquired DTM data [9] gave rise to a new area of research, comparing the geology inside the proposed new suggested crater rim (Figure 4) with that outside. The field results were compelling. Quarries on or inside the proposed rim revealed rocks of generally shattered appearance (Figure 24). Outside the rim, quarrying of large blocks of clean solid limestone was possible to the east of the structure, along with natural tabular limestone (Figure 25a–c), whilst tilting of conglomerates has occurred to the west (Figure 25d–f). None of these latter phenomena were found inside the suggested rim.
Shattered, brecciated limestone in quarries and main road cuttings on and inside the proposed new crater rim.
a, and b, quarried large blocks of limestone for building stone outside of the proposed crater rim to the east, c, tabular limestone block, d, Conglomerate clast ̴1m in length, e, conglomerate blocks, looking south-tilting east, f, conglomerate blocks, looking north-tilting east.
A new observation in the limestone inside as opposed to outside the proposed crater was obvious calcite crystals (Figure 26a), observable with the naked eye. The limestone is of a sugary texture (Figure 26b), which indicates that it had been subject to high pressure and temperature, causing the calcite to reorganise into larger crystals, i.e., low- grade metamorphism [20], which can be associated with an impact. This low-grade metamorphism can also explain why the limestone around the water ‘s edge of Kaş Bay is hard and sharp (Figure 26c) and does not weather the same way outside the study area; limestone in equivalent settings is more rounded and typical of a karstic landscape.
Geomorphology
The topographic view in the southern section of the Teke Peninsula often consists of valleys running parallel to the mountains, which are at varying altitudes and stretch in a northeast-southwest direction; see green lines in Figure 27.
Annotated Google map image, August 2023: Green lines indicate the general northeast-southwest trend in the terrain surrounding the study area in contrast to the yellow lines indicating the concentric geomorphology around Kaş Bay.
On the other hand, terrace-like structures at various altitudes border Kaş Bay in a circular pattern on its immediate eastern side; see yellow lines in Figure 27. These circular terraces, which contrast with the general morphological pattern, are suggested to be marginal collapse zones from the impact cratering modification stage (Figure 28a, b), as opposed to landslips resulting from general slope instability or from an earthquake. These alternatives would be more linear in their formation.
Diagrammatic view of the final structure - ‘The development of a complex impact structure’ [1].
Eastern marginal collapse zone of the Kaş Structure looking south. Numbers indicate terraces.
With the suggested increase in size of the study area from the DTM data, the marginal collapse zone, already clearly observed to the east of the structure (Figure 28b), can now also observed to the north (Figure 29). Although less curved than their eastern counterparts, each terrace to the north conjoins to the corresponding eastern terrace (Figure 28b). This connection of terraces from the north to the east is curved, observable in the foreground of Figure 28b, which implies an impact as the source as opposed to tectonic movement.
Marginal collapse zone to the north of the structure showing 3 terraces which correlate to the eastern marginal collapse zone. The turquoise lines correspond to two of the probable transtensional troughs indicated in Fig. 4.
The impact is thought to have occurred around 2.5 million years ago, based on stratigraphical evidence, uplift and subsidence in the region [2]. During this time, the shape of the larger suggested study area, indicated in Figure 4, has lost the general concentric configuration expected in an impact structure. This is explained by conflicting tectonic plate movement (Figure 3). Furthermore, with the implied increased size of the structure, the lack of the southern edge is explained not only by the movement of the three aforementioned tectonic plates but also by the proximity of the continental shelf edge (Figure 3). Due to its location, this southern part of the structure will most likely have been less stable than its northern mainland counterpart, and with ˜2.5 million years of plate movement and local tectonic activity, this structural instability will have been compromised into collapsing and sliding down the shelf edge as indicated in (Figure 3). Additionally, the prevailing weather is from the southwest adding erosion to the depletion of the structure.
Index - Sample analysis
Sample analysis by pXRF - Niton XL3t 900 and XRF - Rigaku NEX-CG - produced some interesting results, although nothing conclusive. See Tables 1 and 2. These will be further analysed using SEM – EDS.
Initial XRF and pXRF results.
| Mg | Al | Si | S | Cl | K | Ti | Zr | Cr | Fe | Ni | Cu | Zn | Rb | Sr | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| XRFppm | |||||||||||||||
| 69 | 10600.00 | 13800.00 | 21600.00 | 160.00 | 128.00 | 1250.00 | 996.00 | 2600.00 | 26.00 | 8540.00 | 18.00 | ND | 27.00 | 12.00 | 45.00 |
| 72 | 4850.00 | 35000.00 | 42700.00 | 153.00 | 237.00 | 1760.00 | 2610.00 | 3650.00 | 51.00 | 22500.00 | 43.00 | ND | 53.00 | 24.00 | 41.00 |
| 73 | 6070.00 | 45300.00 | 57800.00 | 218.00 | 183.00 | 2550.00 | 3260.00 | 3750.00 | 80.00 | 29900.00 | ND | ND | 71.00 | 30.00 | 40.00 |
| 76 | 2720.00 | 8630.00 | 12600.00 | 289.00 | 139.00 | 708.00 | 688.00 | 2860.00 | 22.00 | 5670.00 | 18.00 | ND | 16.00 | 7.00 | 73.00 |
| 77 | 1750.00 | 15300.00 | 22900.00 | 335.00 | 160.00 | 119.00 | 118.00 | 3250.00 | 25.00 | 12200.00 | ND | ND | 37.00 | 12.00 | 44.00 |
| 80 | 1970.00 | 911.00 | 956.00 | 170.00 | 96.00 | 162.00 | 81.00 | 2630.00 | ND | 167.00 | ND | 11.00 | 12.00 | ND | 241.00 |
| 82 | 2690.00 | 471.00 | 378.00 | 590.00 | 650.00 | 93.00 | 55.00 | 2470.00 | 4.00 | 78.00 | ND | 10.00 | 12.00 | ND | 199.00 |
| 84 | 7090.00 | 67300.00 | 87400.00 | 183.00 | 228.00 | 4430.00 | 5170.00 | 4270.00 | 194.00 | 54600.00 | ND | ND | 96.00 | 46.00 | 63.00 |
| 85 | 1480.00 | 814.00 | 677.00 | 166.00 | 428.00 | 108.00 | 82.00 | 2650.00 | ND | 277.00 | ND | 4.00 | 7.00 | ND | 92.00 |
| 88 | 73800.00 | 512.00 | 586.00 | 1160.00 | 1670.00 | 145.00 | 38.00 | 2210.00 | 13.00 | 193.00 | ND | 10.00 | 11.00 | ND | 310.00 |
| 94 | 1390.00 | 2060.00 | 1640.00 | 45.00 | 71.00 | 141.00 | 150.00 | 2520.00 | 10.00 | 1220.00 | ND | 5.00 | 10.00 | ND | 10.00 |
| 96 | 9610.00 | 12200.00 | 16600.00 | 182.00 | 135.00 | 781.00 | 866.00 | 2930.00 | 51.00 | 8310.00 | 21.00 | ND | 33.00 | 6.00 | 30.00 |
| 101 | 4180.00 | 13200.00 | 21800.00 | 456.00 | 2200.00 | 1700.00 | 1010.00 | 3360.00 | 36.00 | 7470.00 | 16.00 | ND | 28.00 | 11.00 | 31.00 |
| 102 | 2850.00 | 500.00 | 456.00 | 722.00 | 702.00 | 112.00 | ND | 2920.00 | 9.00 | 136.00 | ND | 15.00 | 19.00 | ND | 214.00 |
| pXRF ppm | |||||||||||||||
| 70-1 | < LOD | 57027.19 | 117155.6 | < LOD | < LOD | 5820.02 | 4456.83 | 141.8 | 124.49 | 33002.04 | 156.83 | < LOD | 57.13 | 30.07 | 71.2 |
| 70-2 | < LOD | 34880 | 70930.96 | < LOD | < LOD | 2801.96 | 1990.84 | 119.59 | 62.24 | 12969.54 | 248.3 | < LOD | 19.82 | 16.02 | 42.77 |
| 98-1 | < LOD | 23337.15 | 61080.54 | 1879.1 | 2719.52 | 3690.52 | 1502.27 | 59.62 | 51.58 | 10624.33 | 172.04 | < LOD | < LOD | 17.38 | 185.23 |
| 98-2 | 26476.57 | 15190.04 | 30874.11 | 3674.41 | 1740.53 | 2059.99 | 1156.76 | 45.5 | 40.83 | 6881.87 | 109.46 | < LOD | < LOD | 13.97 | 134.54 |
| 98-3 | < LOD | 17468.63 | 46505.46 | 27061.71 | 2741.96 | 3188.25 | 1394.7 | 53.14 | 49.49 | 9831.03 | 162.18 | < LOD | 23.6 | 19.4 | 128.4 |
| 100-1 | < LOD | 16066.57 | 39084.72 | 461.13 | 5792.38 | 3670.06 | 1465.78 | 43.6 | 59.38 | 9100.79 | 121.05 | < LOD | 22.06 | 16.03 | 62.34 |
| 100-2 | < LOD | 7373.58 | 14711.19 | 1236.17 | 2205.55 | 1404.27 | 747.34 | 22.21 | < LOD | 2003.64 | 281.85 | < LOD | < LOD | 8.3 | 44.77 |
| 100-3 | < LOD | 11080.71 | 30753.76 | 254.56 | 30139.09 | 2941.88 | 1084.14 | 44.15 | 52.74 | 7129.06 | 103.92 | < LOD | < LOD | 15.82 | 43.86 |
| 74-1 | < LOD | 25002.88 | 45865.05 | < LOD | < LOD | 2381.65 | 1962.93 | 46.48 | 81.46 | 11708.53 | 177.58 | < LOD | 24.47 | 10.41 | 13.73 |
| 74-2 | < LOD | 38486.28 | 58992.88 | < LOD | < LOD | 2649.98 | 2007.64 | 59.53 | 78.48 | 13195.25 | 275.41 | < LOD | 28.34 | 9.8 | 17.92 |
| 74-3 | < LOD | 30927.37 | 54448.42 | < LOD | < LOD | 2695 | 1936.26 | 51.33 | 52.22 | 10176.97 | 228.63 | < LOD | 35.8 | 10.19 | 17.34 |
| 74-4 | < LOD | 42104.42 | 75765.19 | 217.5 | < LOD | 3087.72 | 3227.93 | 56.18 | < LOD | 16213.75 | < LOD | < LOD | 29.4 | 10.27 | 15.39 |
| 74-5 | < LOD | 21938.38 | 41188.92 | < LOD | < LOD | 1486.75 | 1658.79 | 65.87 | 60.33 | 9860.56 | 246.74 | < LOD | < LOD | 6.83 | 15.07 |
| 71-1 | < LOD | 30266.56 | 50836.77 | 1067.66 | 114.01 | 3438.24 | 1765.78 | 74.29 | 65.45 | 11754.7 | 199.84 | < LOD | < LOD | 11.97 | 20.1 |
| 71-2 | < LOD | 34082.46 | 59416.11 | < LOD | < LOD | 4383.84 | 2012.61 | 86.72 | 59.95 | 14344.48 | 207.96 | < LOD | < LOD | 19.18 | 27.89 |
| 71-3 | < LOD | 55410.29 | 83488.48 | < LOD | < LOD | 5923.84 | 3190.61 | 70.5 | 98.2 | 21496.53 | 275.2 | < LOD | 35.72 | 16.23 | 28.61 |
| 97-1 | < LOD | 10222.64 | 19683.76 | 328.82 | < LOD | 674.64 | 813.73 | 22.57 | < LOD | 2584.08 | 272.1 | < LOD | < LOD | < LOD | 55.85 |
| 97-2 | < LOD | 19398.5 | 40075.62 | 243.49 | 123.67 | 2324.37 | 1814.81 | 24.34 | 50.54 | 6448.21 | 108.39 | < LOD | 44.47 | < LOD | 22.27 |
| 85b-1 | < LOD | < LOD | 6189.35 | 877.71 | 37869.91 | 415.86 | 696.76 | < LOD | < LOD | 692.27 | 217.65 | < LOD | < LOD | < LOD | 39.4 |
| 85b-2 | < LOD | 7115.88 | 3037.84 | 2438.32 | 41499.86 | < LOD | < LOD | < LOD | < LOD | 370.35 | 577.52 | < LOD | < LOD | < LOD | 133.75 |
| 85b-3 | < LOD | < LOD | 2526.72 | 738.32 | 16125.51 | < LOD | < LOD | < LOD | < LOD | 1855.6 | 205.47 | < LOD | < LOD | < LOD | 17.69 |
| 89 | 47506.98 | < LOD | 4555.96 | 197.92 | 417.23 | < LOD | < LOD | < LOD | < LOD | 198.69 | < LOD | < LOD | < LOD | < LOD | 145.83 |
| 78-1 | < LOD | 21472.31 | 41488.76 | < LOD | < LOD | 3375.23 | 1085.03 | 79.43 | < LOD | 11223.9 | 281.21 | < LOD | 39.97 | 14.26 | 37.84 |
| 78-2 | < LOD | 20466.93 | 40336.02 | < LOD | < LOD | 2388.32 | 1297.16 | 81.57 | 115.75 | 12015.59 | 145.83 | < LOD | 34.24 | 12.26 | 42.63 |
| 78-3 | < LOD | 19509.17 | 36666.76 | < LOD | < LOD | 2008.54 | 1580.84 | 56.67 | 51.36 | 11819 | 286.98 | < LOD | < LOD | 14.34 | 39.2 |
| 78-4 | < LOD | 11988.76 | 24954.85 | < LOD | < LOD | 1083.3 | 646.08 | 76.93 | < LOD | 7433.44 | 516.3 | < LOD | 38.32 | 13.57 | 27.61 |
| 95-1 | < LOD | 56498.64 | 104402.09 | 140.63 | < LOD | 6486.88 | 4811.82 | 128.92 | 130.28 | 26996.53 | 218.22 | 45.55 | 74.73 | 33.37 | 41.67 |
| 95-2 | < LOD | 59581.9 | 105402.28 | 441.72 | < LOD | 5592 | 3458.93 | 127.64 | 80.33 | 22040.38 | 298.7 | < LOD | 76.13 | 31.79 | 41.35 |
| 95-3 | < LOD | 55927.81 | 100117.4 | < LOD | < LOD | 5059.09 | 3338.74 | 128.7 | 108.52 | 25311.62 | 252.54 | 38.68 | 52.39 | 36.33 | 44.91 |
| 78b | < LOD | 19110.58 | 40325.3 | 163.85 | < LOD | 1729.18 | 1102.88 | 55.06 | 32.17 | 6082.91 | 405.41 | < LOD | 25.59 | 4.97 | 34.33 |
| 78b2 | < LOD | 28526.65 | 51288.92 | 139.82 | < LOD | 3215.13 | 1523.29 | 55.25 | 71.07 | 11590.02 | 190.37 | < LOD | 31.1 | 11.26 | 32.97 |
| 78b3 | < LOD | 22793.32 | 61755.41 | 1464.23 | 114.89 | 2688.64 | 1184.09 | 45.72 | 80.85 | 5888.55 | 187.69 | < LOD | 85.02 | 7.07 | 48.3 |
| 78b4 | < LOD | 29321.06 | 56447.82 | 256.83 | < LOD | 3021.68 | 1730.47 | 72.15 | 45.8 | 13429.7 | 142.31 | < LOD | 39.53 | 12.47 | 49.4 |
| 92 | < LOD | 29783.8 | 48185.51 | < LOD | < LOD | 2995.61 | 1432.26 | 30.33 | 72.43 | 10147.57 | 231.91 | < LOD | < LOD | 7.15 | 64.32 |
| 92-2 | < LOD | < LOD | 5833.62 | < LOD | < LOD | < LOD | < LOD | < LOD | < LOD | 629.21 | 344.32 | < LOD | < LOD | < LOD | 7.59 |
| 92-3 | < LOD | 24080.79 | 33857.99 | < LOD | 707.75 | 2707.1 | 1303.13 | 54.53 | 65.44 | 13468.26 | 459.36 | 60.68 | 42.93 | 16.19 | 30.3 |
| 92-4 | < LOD | < LOD | 3486.64 | < LOD | < LOD | < LOD | < LOD | < LOD | 55.01 | 494.75 | 202.93 | < LOD | < LOD | < LOD | 259.37 |
| 87-1 | < LOD | 5206.93 | 18370.67 | 2196.68 | 7662.33 | 937.12 | < LOD | < LOD | < LOD | 1200.84 | < LOD | < LOD | < LOD | < LOD | 998.32 |
| 87-2 | < LOD | 4747.26 | 9735.93 | 5035.6 | 5133.4 | 1024.84 | < LOD | < LOD | < LOD | 463.44 | 270.63 | < LOD | < LOD | < LOD | 7313.26 |
| 87-3 | 38632.37 | < LOD | 8679.29 | 5025.84 | 17616.91 | 932.27 | < LOD | < LOD | < LOD | 530.84 | < LOD | < LOD | < LOD | < LOD | 2421.65 |
< LOD – less than limit of detection. Highlighted figures were shown in parentheses on the original data sheet. ND – No data.
XRF results showing REE along with Au and Ir.
| Au | Sn | Y | Br | Th | Tm | Ta | Ir | Te | Pa | Eu | Re | Tb | Dy | Er | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| XRFppm | |||||||||||||||
| 69 | ND | 30.00 | 8.00 | 11.00 | ND | 30.00 | 13.00 | ND | ND | 10.0000 | 1080.00 | 14.0000 | 253.00 | ND | 67.00 |
| 72 | ND | 31.00 | 43.00 | 5.00 | 14.00 | 50.00 | 13.00 | ND | 13.000 | 14.0000 | 20000.00 | 21.0000 | 594.00 | ND | 73.00 |
| 73 | ND | 33.00 | 33.00 | 7.00 | 16.00 | 56.00 | ND | 17.000 | ND | 19.0000 | 2980.00 | 15.0000 | 736.00 | ND | 67.00 |
| 76 | ND | 28.00 | 6.00 | 7.00 | ND | 15.00 | ND | ND | 12.000 | 9.0000 | 1040.00 | 26.0000 | 280.00 | 54.00 | 113.00 |
| 77 | ND | 36.00 | 10.00 | 13.00 | ND | ND | 11.00 | ND | 18.000 | 17.0000 | 2000.00 | 16.0000 | 552.00 | ND | 109.00 |
| 80 | ND | 27.00 | ND | ND | ND | ND | 16.00 | ND | ND | ND | 622.00 | 15.0000 | 127.00 | 45.00 | ND |
| 82 | ND | 23.00 | ND | 5.00 | ND | ND | 14.00 | ND | ND | ND | 130.00 | 11.0000 | 43.00 | 29.00 | ND |
| 84 | 12.000 | 47.00 | 49.00 | 6.00 | 25.00 | ND | 37.00 | 21.000 | 26.000 | 25.0000 | 4150.00 | 25.0000 | 1340.00 | 178.00 | 72.00 |
| 85 | ND | 25.00 | ND | 3.00 | ND | ND | ND | ND | ND | ND | ND | 6.0000 | 58.00 | ND | ND |
| 88 | ND | 22.00 | ND | 8.00 | ND | ND | ND | ND | ND | 2.0000 | ND | 4.0000 | 32.00 | 18.00 | 12.00 |
| 94 | ND | 21.00 | ND | ND | ND | ND | ND | ND | 12.000 | ND | ND | ND | ND | ND | 18.00 |
| 96 | ND | 30.00 | 6.00 | 19.00 | 9.00 | 40.00 | 19.00 | ND | ND | 9.0000 | 1230.00 | 24.0000 | 311.00 | 61.00 | 77.00 |
| 101 | ND | 33.00 | 7.00 | 31.00 | 10.00 | ND | ND | ND | ND | 11.0000 | 2120.00 | 22.0000 | 492.00 | ND | 102.00 |
| 102 | 11.000 | 31.00 | ND | 6.00 | ND | ND | ND | ND | 11.000 | ND | ND | 13.0000 | 84.00 | 68.00 | ND |
Highlighted figures were shown in parentheses on the original data sheet. ND – No data.
Discussion/Conclusion
Very large impact structures in purely sedimentary, in particular predominantly carbonate targets, are rare and have not been much investigated to date. Even in recent publications, e.g., in Pilles et al “Review of impact melt and breccia dykes in terrestrial impact structures” [21], sedimentary targets are mentioned only casually in a single sentence about lithic breccia dykes, apparently forgetting that such an inventory exists to a much greater extent and variability as exemplified here. Below is the list of intrinsic geological, geomorphological, petrographic, and mineralogical field evidence found so far on the Kaş Bay impact site. We suggest this testimony should be given considerably more credit by the impact community when ascertaining the provenance of an impact structure, especially an all-carbonate structure such as Kaş Bay. To date 20 types of field evidence have been observed from macro scale to micro, as follows:
Macro:
- 1)
Central uplift.
- 2)
Marginal collapse zones.
- 3)
Impact Breccia – from mega to micro clasts.
- 4)
Polymict and monomict breccia.
- 5)
Breccia in breccia – up to 4 generations.
- 6)
Breccia dykes large and small on land and under water.
- 7)
Fitted fragments.
- 8)
Carbonate melt rocks, some with flow texture.
- 9)
Decarbonized limestone.
- 10)
Spallation.
- 11)
Scour planes.
- 12)
Sugary limestone containing visible calcite crystals.
- 13)
<indent>Possible transtension troughs and transpression ridges on land and underwater.
- 14)
Lapillistone.
Micro:
- 15)
Fitted fragments.
- 16)
Spallation.
- 17)
Accretionary lapilli.
- 18)
<indent>Multiple sets of calcite micro-twining often with kink bands.
- 19)
<indent>Regularly; Size of micro-twining to the order of 1 μm, similar development to PDFs in quartz.
Electromagnetism:
The DTM data indicating a larger structure is supported by the newly observed field evidence, making the Kaş Bay Impact Structure much larger than originally suspected, with a diameter in the region of 20 km. The alteration in the expected concentric geomorphology of an impact structure is explained by the movements of three tectonic plates over time.
Sample analysis by pXRF, XRF, petrology and magnetic susceptibility has produced some interesting data and is ongoing, with results to be provided in a future publication.
The abundance of field evidence and related geomorphology makes it increasingly difficult to envisage a cause other than an impact for the features of this study area. We, therefore, propose that the Kaş Bay Impact Structure be added to the list of known terrestrial impact structures.