Santa Fe Impact Structure, Santa Fe, New Mexico

 

 Please proceed to revised paper at http://www.scribd.com/tmcelvain_1 

 

In the spring of 2004 I discovered shatter cones approximately 10 kilometers north east of the Historic Santa Fe Plaza on NM Highway 475.

 

Santa Fe Impact Structure, Santa Fe, NM

Location map of the Santa Fe Impact Structure in north central New

Mexico,USA.

 

 

Further investigation revealed a road cut with a beautiful nest of shatter cones rivaling those of Vredefort, Sudbury, and other well-known shatter cone exposures. The road cut contains shatter cones ranging in size from a few centimeters up to 2 meters in a large tabular lensof resistant crystalline rock striking north south and dipping 65 degrees to the west. The lens is composed of several rock types which are cut by a dominant fracture system striking plusor minus 10 degrees from due north, dipping 65 degrees to the west. The rocks in the lensare schist exhibiting varying degrees of schistosity and grain size. There is a black, isotropic (except for some elongation of the grains), fine grained quartz, hornblende, biotite schist exhibiting very little schistosity that produces the best nestled, convex, horsetail striations (shatter cones) with the sharpest detail. There is a soft, grey schist exhibiting a high degree of schistosity which contains numerous, convex, horsetail striations (shatter cones), but without the fine grained detail found in the hard black schist. The schist is intruded by a granitic rock of at least three different grain sizes; very fine grained granite, and fine to medium grained granite, and a pegmatite. There are shatter cones developed in all these granites of varying grain sizes, but as with the schist the finer the grain and more isotropic the rock the sharper and more precise the horsetail striations are.

 

 

Santa Fe Impact Structure, Snta Fe, New Mexico

 

Nest of shatter cones in fine grained granitic rock; some of the cones are

over 1.5 meters in length.

 

Santa Fe Impact Structure, Snta Fe, New Mexico

Santa Fe Impact Structure, Shatter Cone

 

Photo of a beautiful shatter cone in a black, hard, isotropic (except for some elongation of the grains), fine grained quartz, hornblende, biotite schist exhibiting very little schistosity.

 

 

Santa Fe Impact Structure, Snta Fe, New Mexico

Santa Fe Impact Structure, Shatter Cone

 

Photo of a small shatter cone in a fine grained granitic rock found approximately 1 kilometer west of the above mentioned road cut verifying that the shatter cones were not caused by blasting during road construction. 

 

 

 

The discovery of Shatter Cones precipitated an investigation into their origin. Siobhan P. Frackelman et. al. published the following paper:

Shatter cone and microscopic shock-alteration evidence for a post-Paleoproterozoic terrestrial impact structure near Santa Fe, New Mexico, USA

Siobhan P. Fackelman, Jared R. Morrow, Christian Koeberl, Thornton H. McElvain, 2008 Elsevier B.V. All rights reserved.

  This paper verified that the horsetail striations are indeed shatter cones and they also found Planar Deformation Features within the shatter cones confirming that they were caused by a bolide impact. The authors speculate the age of the impact to be between early Mississippian and Mesoproterozoic. My research which has continued through 2008 and will continue, leads me to believe that the impact event occurred in Mid-Tertiary. The balance of this page is my interpretation of continuing research on the Santa Fe Impact

 

Structure

 

The morphological Santa Fe Impact Structure has yet to be defined and may be completely destroyed; however, the following oblique view downloaded from Google Earth is an elongated circular structure that could represent the remnants of the Santa Fe Impact Structure or a smaller slightly younger impact structure that helped destroy an earlier larger impact structure that actually was responsible for generating the nest of shatter cones.

 

 

 

Marker 05021 is the location of the nest of shatter cones in the road cut, I have found shatter cones all along the valley from the road up to markers 05049, 05050 and 05051. the other markers are locations where I have taken samples looking for planar microstructures. Markers 05056, 0fo57, 05058, 05060 are locations of samples of Pennsylvanian and Mississippian sandstone where I have samples of quartz grains with planar microstructures whose angles to the C-Axis I have measured and indexed fitting the requirements for Planar Deformation Features (see below).

 

 

 

 

I have found breccia, mega-breccia, melts, and probable allocthonus slideblocks all containing quartz with planar microstructures (PM's) that fit the scale of planar deformation features (PDF's) and histograms of the angle of the pole of the planar microstructure to the c-axis resemble those of known impact structures. Waypoint Numbers on the following two maps 05055, 05057, and 05064.2 marks the location of samples of sandstone in which I have found grains of quartz with planar microstructures. Waypoint 05051 marks the location of the clastic dike described below.Santa Fe Impact Structure, Snta Fe, New Mexico

Santa Fe Impact Structure, Waypoints

 

 

Santa Fe Impact Structure, Snta Fe, New Mexico

 

 

The above map plots the location of the sandstone samples on a geologic map of the Santa Fe Impact Structure. The Geologic Map was cut and pasted from the Preliminary Geologic Map of the Santa Fe Quadrangle Bauer, May, 2000 Last Revised: 8-October-2003

 

The formation symbols on the map are hard to read at this scale; however, the buff yellow represents the Nambe Member of the Tertiary Tesuque Formation, the blue represents the Paleozoic Formations and the grey represents the Precambrian formations, all of which are described below. The descriptions have been cut and pasted from the Preliminary Geologic Map. Ttn Nambé Member (upper Oligocene(?) to lower Miocene) – Poorly sorted sandy pebble to cobble conglomerate, sandstone, and minor mudstone composed of detritus eroded from pre-Tertiary rocks. Color is typically red to pink but is locally white to very pale pink or buff. Base is unconformable on Proterozoic or Pennsylvanian rocks atvarious locations in the map area. Basal contact is highly irregular in part because of erosional relief along the basal unconformity and also because of interpreted deposition of lower parts of the member in small half grabens. In the Big Tesuque watershed there are at least 400 m of Nambé Member locally present below the Bishop’s Lodge Member. These lowest Nambé strata are distinctive for their abundance of Paleozoic clasts (25-60%, typically 50-60%). Nambé strata between Bishop’s Lodge volcaniclastic intervals in the Bishop’s Lodge-Arroyo de la Piedra area contain 25-35% Paleozoic clasts and Nambé beds above the Bishop’s Lodge Member contains <10% Paleozoic clasts. These variations in clast composition have been demonstrated through 16 conglomerate-clast counts (100 clasts per count) and provide a basis for tracing stratigraphic intervals in the Nambé Member. The abundance of Paleozoic clasts in the lower Nambé Member is curious since these strata rest on Proterozoic rocks. Although one cannot discount the possibility of Paleozoic rocks cropping out in the vicinity of the current Santa Fe Range during Tesuque deposition, it is also possible that the Paleozoic clasts originated from localities east of the Picuris-Pecos fault. The latter interpretation would require Neogene west-side up motion of that fault zone, which has been suggested previously but has not been supported by structural studies along the fault. A zone of unusually coarse blocks of Paleozoic limestone and sandstone at the base of the Nambé Member near Big Tesuque Creek is indicated on the map by closed-box symbols ( ). These clasts are 2->4 m across. Spiegel and Baldwin portrayed a dip slope containing such clasts above Proterozoic rocks on the north side of Big Tesuque Creek as Pennsylvanian bedrock. Despite the large size of the Paleozoic clasts found on that slope, there is no outcrop of such rocks and exposures along the USFS Winsor Trail, at the southern end of that slope, clearly show the large blocks to be in the basal Tesuque Formation. The origin of these large clasts is unknown and is especially puzzling in the absence of nearby Paleozoic outcrops. They may be a residual lag of Pennsylvanian clasts resting on exhumed Precambrian outcrops and then buried beneath Tesuque Formation. Otherwise, clast sizes in the Nambé Member are generally 2-20 cm, with Paleozoic limestone and some Proterozoic granite clasts approaching 40-50 cm in easternmost exposures. IPm Pennsylvanian Madera Group undifferentiated – Limestone, calcareous siltstone, shale, and minor fine to medium grained sandstone, includes isolated thin outcrops of Mississippian rocks and some coarse sandstones that may represent Pennsylvanian Sandia Formation. Mu Mississippian(?) limestone (undifferentiated) - Approximately 10 m of brecciated gray limestone, with red silty matrix in fractures, present only on a low ridge about 0.6 km northeast of Bishop’s Lodge. Limestone overlies Proterozoic mylonite and wedges out to the south below a calcareous siltstone more typical of basal Pennsylvanian strata seen elsewhere. The crackle-breccia texture and red-silt fracture filling material is suggestive of karst dissolution prior to deposition of the overlying calcareous siltstone. The brecciation and abrupt lateral pinchout of the limestone strongly suggest that these strata are Mississippian, rather than Pennsylvanian, in age. Madp Del Padre Member of the Mississippian Espiritu Santo Formation – a distinctive silica-cemented white sedimentary quartzite sometimes seen in float along the Paleozoic/Proterozoic unconformity. Generally exposures are to thin to differentiate on the map. Proterozoic Rocks Ymg Megacrystic granitoid (Mesoproterozoic?) – Coarse unfoliated granite contains quartz, biotite, and large (up to 10cm) K-spar megacrysts. looks quite similar to the Sandia Granite. High magnetic susceptibility suggests that this rock may be responsible for pronounced magnetic highs in the Seton Village quadrangle (Mark Hudson, personalcommunication, 2003). Yg Microcline-qtz-muscovite granitoid (Mesoproterozoic) – Fine to medium grainedunfoliated to weakly foliated granitoid. Ypeg Pegmatite (Mesoproterozoic?) – Simple pegmatite veins and pods, unfoliated Xgd Granodiorite to Diorite (Paleoproterozoic?) – Weakly to undeformed pods and irregularly shaped bodies of intermediate intrusive rocks best exposed along the lower end of the Ski Basin Road. Xd Granodiorite to Diorite (Paleoproterozoic?) – Generally medium-grained dark, weakly foliated-to-unfoliated massive diorite. Forms pod-like bodies within surrounding gneisses suggesting late emplacement. Cut by Ypeg. Xpg Pink Granitic Gneiss (Paleoproterozoic) – Fine-grained quartz-Kspar mylonitic gneiss is distinctly pink in outcrop. This rock appears to be more resistant to weathering than the coarser biotite-bearing gneisses and forms the bulk of the Sunlit Hills. Xbg Biotite-rich granitic gneiss (Paleoproterozoic) – Coarse grained strongly foliated biotite-bearing gneiss often contains microcline augen and appears to be less resistant toweathering than Xpg. Forms much of the broad valley east of the Sunlit hills that I-25 travels along. Unit is broadly generalized due to poor exposure. Xqm Quartz muscovite schist (Paleoproterozoic) – Generally strongly foliated and often crenulated quartz-muscovite schist. Muscovite is often very coarse suggesting pervasive annealing similar to that seen in other nearby uplifts. Xms Quartz biotite schist (Paleoproterozoic) Xa Paleoproterozoic strongly foliated amphibolite and mafic schist, may include Xd in places. Mafic units tend to weather poorly and are often mantled by Yg and Xbg float. Consequently, Xa and other mafic units are probably vastly under-represented on the map.

 

 

 

Measurements of the Angle of the Pole of the Planar Microstructure to the C-Axis

 

 

 

 

On the above maps I have plotted the GPS Waypoint number where I collected the samples analyzed below of quarts grains with planarmicro structures. 

 

 

 

Santa Fe Impact Structure Quartz Grain with PM's

 

Photomicrograph of a typical sandstone grain with Planar Microstructures (PM’s). The scale of the microstructures fits the scale of Planar Deformation Features (PDF’s), and the pole of the plane of these microstructures fit the Low Miller Indices in more than 90 percentof the measurements that I have made. In my opinion the PM’s are PDF’s.

 

Santa Fe Impact Structure - Histogram of Orientation of PM's

 

05064.2 – Paleozoic sandstone collected at the contact between the Precambrian and the Paleozoic formations.

 

 Santa Fe Impact Structure - Histogram of Orientation of PM's

05055 – Paleozoic sandstone stringer about 300 meters higher in the section than the Paleozoic – Precambrian contact.

 

 

Santa Fe Impact Structure - Histogram of Orientation of PM's

The above histogram was made from measured planar feature in grains from sample 05057 – Sample of a Paleozoic clast in the basal Nambe Member of the Tesuque Formation (Ttn). In my opinion the Ttn Formation here is a mega breccia, containing large clasts of Paleozoic formation. 

 

 

Clastic Dike

 

 

 

05051 (see map above) – marks the location of a clastic dike composed of Precambrian basement rocks (maroon) penetrating upward into the Paleozoic limestone (buff color) formations. The clastic dike is macroscopic evidence, but not proof, that the impact event is post Paleozoic. 

 

 

Santa Fe Impact Structure - Breccia Dike

 

Along the contact at the upper left hand corner of the photograph there is evidence of the fluidization and mixing of competent limestone and basement rocks, the following photographs look similar to me to illustrations found in the web site Ernston Claudin Impact Structures, Azuara impact structure (Spain): Evidence of shock fluidization of competent limestones, which can be seen on this link - http://www.impact-structures.com/Archiv/archiv.html.

 

dsc00603-1 Santa Fe Impact Structure, Santa Fe, New Mexico

Varve like bedding of the Mississippian limestone broken and rotated by the forsefull intrusion of the clastic dike. The varve like bedding indicates that the limestone was deposited in a very quiet and sheltered enviornment unlikely to have moved and caused soft sediment deformation, which some geologists attribute this deformation to.

 

 

Santa Fe Impact Structure - Breccia Dike

 

Photograph the contact of the clastic dike and the basement rock where the friction caused by the movement and the confining pressure plasticised or  fluidized the limestone mixing it with pieces of brownish red basement rock with flow structures mixing competent limestone and basement rocks. 

 

 

dsc00602_edited-2 Santa Fe Impact Structure, Santa Fe, New Mexico

This and the following photograph are closeups of the above contact zone of the clastic dike and the basement rock illustrating the flow structure and mixing of the redish brown basement rock and the grey compent and fluidized limestone.

 

dsc00601_edited-1 dsc00601_edited-1 Santa Fe Impact Structure, Santa Fe, New Mexico

 

 

 

dsc00607 Santa Fe Impact Structure, Santa Fe, New Mexico

 

Photograph of a clast of basement rock with a reaction rind within the fluidized zone. 

 

 

dsc00608_edited-2 Santa Fe Impact Structure, Santa Fe, New Mexico

 

Clasts of competent limestone and basement rock within the fluidized zone. 

 

dsc00610Santa Fe Impact Structure, Santa Fe, New Mexico

 

 

 

The above two photographs illustrate competent limestone and clasts of basement rock within the clastic dike frozen within the fludizied zone in finer and finer detail.

 

Photomicrographs 

 

 

The following photomicrographs are of quartz grains disolved out of the fluidized limestone exhibiting up to three sets of planar microstructures.

 

06031b-3-400x Santa Fe Impact Structure, Santa Fe, New Mexico

 

06031b-3-400x-xp Santa Fe Impact Structure, Santa Fe, New Mexico

 

 

 

06031b-1-400x-xp Santa Fe Impact Structure, Santa Fe, New Mexico

 

 


 

 

 

Tertiary Megabreccia mapped as the basal Nambe Member of the Tertiary Tesuque Formation

 

Sample number 06055 (see map above) was collected from a Paleozoic sandstone clast, most probably of Pennsylvanian age within this megabreccia. Some of the larger clasts within this breccia are displayed in the photographs below. There is no road cut or stream channel that exposes a clean cross section of the formation; however, one can see in the following photographs that the makeup of this breccia resembles a diamictite.

 

 

Santa Fe Impact Structure - Nambe member of the Tesuque

 

Photograph of a large megabreccia sized limestone clast in the Nambe member of the Tertiary Tesuque Formation.

 

Santa Fe Impact Structure - Nambe member of the Tesuque

 

Sandstone clast similar to the one that I sampled and found Planar Microstructures (PM’s) in. These mega clasts appear to be rounded, but because of their fragile, bedded nature I do not believe they would survive stream transport. Kord Ernston and Fernando Claudin in their web site, Ernstson Cladin Impact Structures, The Perlarda Formation, http://www.impact-structures.com/ show examples of clasts rounded and polished in the excavation stage of an impact crater.

 

megaclastbit-tesu

Photograph of another megabreccia calcarious arenite clast located further to the north in Big Teseque Creekl Canyon that also seems to have been rounded during excavation.

 

 

 

 

 

Galisteo Formation outcrop at Arroyo Hondo, NM

 

 

Tertiary Galisteo Formation outcrops approximately 14 kilometers southwest of the shatter cone outcrop. I believe this formation mapped as Tertiary Galisteo Formation (?) is an impact melt and melt breccia. This formation is mapped in the Arroyo Hondo Canyon just down stream from where I-25 crosses the canyon. The Formation consists of a reddish orange, hematite rich melt breccia with siltstone sized angular quartz clasts and feldspar phenocrysts resting on the basement, some of the quartz clasts have planar microstructures. The melt is overlain and incised by a melt breccia gravity slide and reworked breccia, composed of pebble up to cobble size clasts with a melt matrix in which I found phenocrysts of feldspar.

 

Santa Fe Impact Structure - Galisteo Formation, Arroyo Hondo, NM

Topographic map illustrating the relationship between the shatter cone area and the outcrop of the Tertiary Galisteo Formation (?) which I am mapping as consisting of a melt, melt breccia, fallback crater fill and reworked breccia.

 

 

 

Santa Fe Impact Structure - Galisteo Formation, Arroyo Hondo, NM

 

The Tg? Symbol and purple color in the center of the map has been mapped as the Tertiary Galisteo Formation primarily because of its stratigraphic position underlying the Tertiary Espinosa Formation. There is a question mark after the symbol because the Galisteo formation is usually sandwiched between the Paleozoic formations and the Espinosa Formation. Here the breccia is deposited directly upon the basement rocks, and appears to come to a feather edge to the east.

 

 

Santa Fe Impact Structure - Galisteo Formation, Arroyo Hondo, NM

 

In this photograph the fine grained glass melt rests directly upon the granite and has been channeled into and overlain by a gravity slide melt breccia that channeled into the impact melt.

 

Santa Fe Impact Structure - Galisteo Formation

 

In this photograph the dark maroon basement rocks are about 1 meter below the feet of the two geologists, overlain by the light orange red impact melt glass, which in turn is overlain by the coarser grained gravity slide melt breccia.

 

 

 

 

 

 

 

Santa Fe Impact Structure - Galisteo Formation - Arroyo Hondo, NM

 

Close up of the impact melt illustrating ball and pillow structure.

 

Santa Fe Impact Structure - Galisteo Formation Arroyo Hondo, NM

 

Close up of a pillow with indentations and impressions caused by plastic deformation.

 

 

 

 

 

 

 

 

Santa Fe Impact Structure - Galisteo Formation, Arroyo Hondo, NM

 

Photomicrograph of the impact melt with the angular siltstone sized clasts of quartz and feldspars in a glassy matrix highly stained with hematite, photomicrograph has a larger quartz crystal that has been embayed by melt, and a phenocryst of feldspar illuminated by plain polarized light.

 

 

Santa Fe Impact Structure - Galisteo Formation, Arroyo Hondo, NM

 

Same photomicrograph as above illuminated with crossed polarized light illustrating the glassy nature of the matrix. These photomicrographs and the description of the impact melt is very similar to the photo and description of a lithic breccia in Bevan M. French’s book Traces of Catastrophe on page 71.

 

 

 

 

 

Traces ofCatastrophe

A Handbook of Shock-Metamorphic Effects in

Terrestrial Meteorite Impact Structures

Bevan M. French

Research Collaborator

Department of Mineral Sciences, MRC-119

Smithsonian Institution

WashingtonDC20560

LPI Contribution No. 954

 

 

 

 

 

 

 

 

 

 

Bevan M. French - Traces of Catastrophe

Figure 23

 

 

 

5.4.2. Lithic Breccias (Allogenic)

Melt-free breccias (lithic breccias) form a common and distinct lithology in both large and small impact structures (Figs. 3.7 and 3.13). In small impact structures, e.g., Brent(Canada) (Dence, 1968; Grieve and Cintala, 1981), lithic breccias may form units hundreds of meters thick that extendover much of the final crater. At the larger Ries Crater (Germany), a distinctive allogenic polymict lithic breccia [the Bunte (“colored”) Breccia] occurs beneath the overlying melt-bearing suevite breccias both inside and outside  the crater (Hörz, 1982; Hörz et al., 1983), with a sharp contact between the two units. In some impact structures, especially those formed in carbonate target rocks, lithic breccias may be the only type of crater-fill material present (Roddy,1968; Reiff, 1977). Lithic breccias consist of rock and mineral fragments in a clastic matrix of finer-grained similar material (Fig. 5.8). The breccias are poorly sorted; fragment sizes generally range from  <1 mm to tens of meters. Fragments are typically sharp to angular in appearance. Unlike the lithic breccias found in parautochthonous rocks, crater-fill lithic breccias are more apt to be polymict because their fragments have been derived from a wider region of the original target rocks. Because most of the material in lithic breccias is derived from less-shocked regions around the walls and rim of the transient crater, distinctive shock effects are only rarely observed in the fragments. Within the crater-fill deposits, lithic breccias are often associated, both horizontally and vertically, with units that contain a melt component as discrete fragments or as a matrix for lithic fragments. Breccias with a few percent or more of a melt component are regarded as melt-bearing breccias, but the transition between these breccia types appears continuous, and no formal boundary has been established. Such melt-bearing breccias typically form a smaller proportion of the crater fill, perhaps 10–25 vol%, and the amount of melt component they contain varies from a few percent to >90 vol% (e.g., Hörz, 1982; Masaitis, 1983; von Engelhardt, 1990, 1997). Two basically different types of melt-bearing breccias can be distinguished. In melt-fragment breccias (suevites), the melt component occurs as large (centimeter-sized) discrete bodies; in melt-matrix breccias (impact melt breccias), the melt forms a matrix for rock and mineral fragments (Stöffler and Grieve, 1994, 1996).

 

Santa Fe Impact Structure - Galiseo Formation

 

Partially melted and quenched crystal within the impact melt illuminated with plane polarized light.

 

 

 

Santa Fe Impact Structure - Galiseo Formation

 

Same as above but illuminated with cross polarized light.

 

 

Santa Fe Impact Structure - Galiseo Formation

 

Photomicrograph of a phenocryst of feldspar within the impact melt.

 

 

Santa Fe Impact Structure - Galiseo Formation

 

Silt sized quartz crystal with planar microstructures that fit the scale of planar deformation structures within the impact melt.

 

 

 

 

 

 

 

 

 

 

 

Santa Fe Impact Structure - Galiseo Formation

 

Silt sized quartz crystal with planar microstructures that fit the scale of planar deformation structures within the impact melt.

 

 

 

 

 

 

 

Santa Fe Impact Structure - Galiseo Formation

 

Photomicrograph of the melt breccia composed of angular fragments of quartz and feldspar illuminated with plane polarized light.

 

 

 

 

 

Santa Fe Impact Structure - Galisteo Formation

 

 

Photomicrograph of the same section of the melt breccia showing the glassy matrix along with some carbonate cement illuminated with cross polarized light.

 

 

 

Santa Fe Impact Structure - Galisteo Formation

 

Blob of impact melt within the melt breccia under plain polarized light.

 

 

 

 

 

 

 

 

 

 

Santa Fe Impact Structure - Galiseo Formation

 

Blob of impact melt within the melt breccia illuminated by cross polarized light.

 

 

Santa Fe Impact Structure - Galiseo Formation

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Phenocryst of feldspar within the melt breccia illuminated with plane polarized light.

03126 6-25x-xp

 

 

 

 

Phenocryst of feldspar within the melt breccia illuminated with cross polarized light.

 

 

 

 

 

 

Distal Ejecta

The Los Dos Quartzite, Los Dos Subdivision, Santa Fe, County, New

Mexico

The most recent published description of Tesuque Formation and the Los Dos Quartzite is found in the following description, cut and pasted from the digital copy of the: Preliminary Geologic Map of the Horcado Ranch Quadrangle, Santa Fe County, New Mexico by, Daniel J. Koning and Florian Maldonado, May, 2001, New Mexico Bureau of Geology and Mineral Resources

Open-file Digital Geologic Map OF-GM 44

Lower mixed Lithosome A-B, fine-grained (middle Miocene) – Sandstone, siltstone, and claystone with 1-15% conglomerate beds. Conglomerate is commonly pinkish-gray (7.5YR 7/2), clast­ supported, and consists of pebbles with subordinate cobbles. Conglomerate beds are very thin to medium, lenticular, and commonly indurated by calcium carbonate to form resistant ledges up to about 2 m thick. Within a bed there may be cross-lamination or planar lamination. Conglomerate clasts are granitic with 1-5% amphibolite, 3-15% yellowish Paleozoic siltstone and sandstone, trace­ 10% grayish to yellowish Paleozoic limestone, trace-5% muscovite- schist, 1-5% brownish chert, and up to 40% quartzite. Coarse to very coarse pebbles and cobbles are rounded to subrounded; very fine to medium pebbles are subangular to subrounded. Conglomerate clasts are moderately to poorly sorted within a bed. Siltstone and claystone beds are very thin to thick, tabular, and range in color from brown (7.5YR 5/4), reddish-brown (2.5YR-5YR 46/3-4), light-reddish-brown (5YR 6/4), light­ yellowish-brown (10YR 6/4), light-brown (7.5YR 6/3-4) to pink (7.5YR 7/3-4). Sandstone and silty sandstone are light-brown (7.5YR 6/3-4), pink (7.5YR 7/4), or reddish-yellow (10YR 6/6). Sandstone is commonly in very thin to thick, tabular or lenticular beds. Sandstone is very fine- to very coarse- grained, subrounded to subangular, mostly well sorted with some moderate sorting, and arkosic. Within 3 km of the south border of the quadrangle, the sediment is more reddish, sandy, and the clasts more granitic (with 5-10% quartzite) than to the north. The non-gravelly sediment is weakly to moderately consolidated. Unit correlates to the Skull Ridge Member of Galusha and Blick (1971). Smith (2000b) has interpreted the Skull Ridge Member to represent an alluvial slope environment fed by drainages in the Sangre de Cristo Mountains, and we concur. The age of the Skull Ridge Member on this quadrangle is interpreted to be 15.1 to 16 Ma based on its Barstovian fossil assemblage and paleomagnetic correlations (Galusha and Blick, 1971; Barghoorn, 1981; Tedford and Barghoorn, 1993) in 40 39 addition to Ar/ Ar dates of ash beds (Izett and Obradovich, 2001). Total thickness is approximately 250-430 m. Silica cementation of quartz-rich sandstone Within 0.5 km of the south boundary of the quadrangle, local silica-cementation of gravel and sand of unit Tts1has been observed at three locations. These locations are noted on the map (see "explanation of map symbols" below). The cementation has resulted in a very well-indurated, pebble- and cobble-conglomerate and sandstone that looks like the sediment of unit Tts1 except that these rocks have low amounts of feldspar grains and lack granitic clasts; instead, quartz grains and quartzite clasts dominate. These well-indurated and erosionally resistant rocks generally form angular blocks up to 3 m in diameter, some of which are still in place (based on their geometry and consistent attitudes between the beds within these blocks and the surrounding strata of the Tesuque Formation). Calcium carbonate nodules (1-7 cm in diameter) may coat the outside of the in-situ blocks. The clast lithology is: 85-90% quartzite and quartz, 10% yellow, green, and black chert, and trace to 5% schist and amphibolite. Sand grains are estimated (using a hand lens) to have 75% quartz and 25% feldspar and are generally medium to very coarse. Granitic clasts are generally not observed except near the margins of the in-situ blocks, where they comprise approximately 1% of the clasts. These silica-indurate rocks commonly occur along a north-south or northwest-southeast trend. In an exposure located in the extreme southeast corner of the quadrangle (NW1/4, NE1/4 of Section 32, T. 18 N., R 9 E.; UTM coordinates: 3,956, 810N 408, 975 E, zone 13), silica cementation occurs adjacent to a fault that strikes N10°W and similar faults may be located adjacent to the other outcrops as well. The authors agree with the interpretations by Borton (1979) that these outcrops are not from an upthrown fault block. Rather, we speculate that quartz-rich, mud- free sand beds of relatively high permeability were preferentially cemented by silica-rich fluids that flowed up from relatively deep depths adjacent to faults. A somewhat similar, silica-indurated, sandstone dike occurs on the northeast corner of Pueblo Road and U.S. 84/285 (3-5 mi south of Espanola and 8 mi north of Pojoaque). 

p1000319_edited-1

Los Los Dos Quartzite Pile Waypoint number10002, the largest of the 8 quartzite piles found in the Los Dos Subdivision, Santa Fe County, NM

 

 

This enigmatic quartzite is also described by Robert L Borton in a paper published 1n the New Mexico Geological Society Guidebook, 30th Field Conference, Santa Fe County, 1979. Dr. Bolton in his article proved that the quartzite piles are not rooted, but resting on about 3 thousand feet of Tesuque Formation, which they do not resemble at all lithologically nor is the cementation and Overgrowth of the quartz grains similar. He also drew attention to the partially polished boulder found in Quartzite Pile10004. I interpret the origin and meaning of the Tesuque Formation and the associated Los Dos Quartzite(Silica cementation of quartz-rich sandstone) differently from the above authors. I believe that the Tesuque Formation -Lower mixed Lithosome A-B, fine-grained (middle Miocene) including the Los Dos Quartzite is either direct or reworked distal ejecta. I am suggesting that the enigmatic quartzite piles (Los Dos Quartzite) and the Tesuque Formation are directly related to the excavation, ejection and development of the Santa Fe Impact Structure. I will give evidence for my interpretation in the following discussion: I find the claim that the huge outliers of enigmatic quartzite represent selective silica cementation of the Lower mixed Lithosome A-B (Tts1) hard to believe. Please see photos of the Tts1 outcrop below, the lithology of the formation does not resemble the lithology of the quartzite. The quartzite piles are of much well sorted, quartz sandstone that is thicker and contains a higher percentage of quartz than any lithographic unit or bed in the Tts1 formation that I could see in the outcrop. The Tesuque Formation has the properties of a fluvial conglomerate and an impact ejecta breccia combined. The following photographs were taken of the Tesuque Formation in the vicinity of the Los Dos Quartzite piles. 

 

 

 

Photo of the Tesuque Formation with rounded clasts that indicate fluvial erosion and rounding; however, rounding can also be caused by the excavation and transportation of ejecta. 

 

 

 

Photo of the Tesuque Formation with angular clasts indicative of a breccia and the fact that an angular clast is found approximately 8 miles from the source indicates to me that it is an impact ejecta breccia. 

 

 

 

 

 

Photo of a massive sandstone lens within the Tesuque Formation, this sandstone is thick and massive enough to be cemented with silica and resemble the Los Dos Quartzite; however it is an arkosic arenite whereas the Los Dos Quartzite is a quartz arenite.

 

 

Close up of the above massive sandstone lens with both angular and rounded clasts.

 

The Los Dos Quartzite consists of large enigmatic clasts, boulders or slabs of quartz arenite that lie approximately 8 miles west of the shatter cone outcrop associated with the Santa Fe Impact Structure

 

relative location to other evidence

 

Map illustrating the relative location of the Los Dos Quartzite Piles in relation to other evidence of the Santa Fe Impact Structure that I have found in the area. 

 

 

 

They are unconformable and enigmatic in that they are huge clasts in relation to the clast size of the Tesuque Formation. The quartzite piles do not resemble any sedimentary outcrop within the Santa Fe immediate area, which are dated from the Mississippian through the Tertiary. Most of the  massive Paleozoic sandstone outcrops that I have seen are in the Pecos Watershed area over the divide approximately 8 miles east of the shatter cone outcrop, and the sandstones lithology is usually arkosic. There are Paleozoic and Mesozoic sandstone outcrops to the south and east, but as of this date I have not found any sandstone outcrop that resembles the Los Dos Quartzite. However: the Los Dos Quartzite does resemble the Cretaceous Dakota Formation in many respects. There are no outcrops of the Dakota Formation in the immediate area, but there are outcrops about 20 miles to the south and 45 miles to the east as well as outcrops a little more distant to the north and west. The Dakota formation was deposited and covered the entire southern Rocky Mountains and Colorado Plateau before the Tertiary event that raised the Colorado Plateau and Southern Rocky Mountains. The problem is how giant slabs of Dakota Formation come to lie on top of the Tertiary Tesuque Formation in Santa Fe County, NM. I will give my reason for assuming the Los Dos Quartzite piles are giant clasts in the Microscopic Section below.

 

 

On the map below I have plotted the location and approximate elevation of the Los Dos Quartxite piles.

 

I have attempted to contour the elevations of the quartzite piles and their elevation appears to place them on the same depositional sequence time line one would expect when the projected strike and dip (N-60-E, 10 degrees NW) of the sandstone lens located in the immediate vicinity of the Los Dos quartzite pile elevation 6682, see photograph of the sandstone lens below.

 

 

 

 

 

On the following illustration I have projected the locations of the quartzite piles onto the cross section published in the above captioned Horcado Ranch Quadrangle on a rough guess of the sequence time line. 

 

 

 

 

The black dots represent my projection of the quartzite piles on my estimation of the depositional sequence line in the Tesuque (Tts1) Formation.

If the Los Dos Quartzite Piles were deposited on the same depositional sequence time line it would indicate that the piles were all deposited at the same time, which would give credence to them being ejecta from one of the larger multi-impact events in the Santa Fe area. 

 

Except for quartzite pile 10002 all the quartzite piles consist of randomly placed boulders of 1 to 10 feet of coarsely weathered quartzite.

 

 

Randomly placed boulders of Quartzite pile 10004

 

In quartzite pile 10004 there is one large boulder of quartzite that has very highly polished surfaces and groove that looks like a flute on a Clovis Point. The inside surface of the flute has conchoidal fracture structures similar to those found in a fluted arrowhead.

 

Polished and Fluted Boulder in pile 10004, the concave fluted surfaces in the lower left side of the boulder could have been caused by the impact of a smaller boulder traveling at high speed striking the larger boulder.

 

The published papers either do not try to explain why the polished surfaces are there or they are passed off as sandblasting by wind action. The other blocks in the pile are not polished and there is not good reason why the wind would select this boulder and not the adjacent ones. If the polishing was not caused by man there is evidence in other impact craters that polishing can occur during the excavation phase of an impact event by particles in the cloud of material or be glazed by the heat generated by the impact.

 

Close up of one of the highly polished or glazed surfaces on the large boulder in Pile 10004

 

 

Quartzite pile 10002 consists of one overturned slab of quartzite 125 feet by 35 feet and 15 feet thick and covered at the east end by the typical randomly placed 1 to 10 foot boulders.

 

 

 

 

The surface of the big slab in quartzite pile 10002 is covered with what appear to be very complex sole marks that indicate that the formation is overturned.

 

Photograph of the very complex sole or clast marks on the big slab.

 

 

 

A large block of quartzite broken off the large slab giving a cross section view of the sole markes as shown in in the following photograph.

 

 

 

 

 

The above photograph illustrates the sole marks in cross section; there is little or no change in lithology from the edge of the sole marks and the interior of the quartzite.

I do not believe these casts or sole marks would have been formed by water circulating through an in

situ lens of Tesuque sandstone. 

 

 

Microscopic Evidence

In thin section the composition of the Los Dos Quartzite appears to me to be about 95% quartz and 5% feldspar and other minerals.

Thin sections of the Los Dos Quartzite do not look like sandstone metamorphosed into a quartzite, it is very porous, permeable, and well cemented with silica cement. The overgrowth on individual rounded grains has grown in such a way that the rounded grains have grown into small crystals with regular crystal faces and terminations.

 

 

Photomicrograph of a quartz grain illustrating original rounded edge and the straight edge of the crystal resulting from the overgrowth. The 2 following photomicrographs illustrate the same phenomenon.

 

 

 

 

 

I have been told that this overgrowth and cementation process requires much more time than the rapid cementation from percolating silica rich spring water as discussed in USGS Quadrangle Map of the Horcado Ranch Quadrangle, which prompts me to look for older sandstone formations. Next summer I intend to compare thin sections of the Dakota sandstone outcroping closest to the Los Dos Quartzite, Cambrian and Proterozoic sandstone in Colorado and Utah. In addition any water flowing up through a fault zone from depth would have to pass through approximately 2,500 feet of limestone rich Paleozoic formations that lie beneath the Quartzite Piles. The Yates Petroleum, La Mesa No.2, Sec. 24, T17N, R8E, Santa Fe County, New Mexico well was drilled to the basement about 4 miles southwest of the Los Dos Quartzite piles and in situ Paleozoic rock rich in limestone can be seen on the Schlumberger   Litho Density Compensated Neutron GR Log between the depths of 5021 feet and 7536 feet. Further interpretation of the stratigraphy penetrated by this well was published in August 2006, The Stratigraphic analysis of the Yates #2 La Mesa well and implications for southern Española Basin tectonic history, Caroline Myer* and Gary A. Smith, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, *Current address: Department of Geology, Utah State University, Logan, Utah 84322-4505 Can be downloaded at http://geoinfo.nmt.edu/publications/periodicals/nmg/downloads/28/n3/nmg_v28_n3_p75.pdf

This much limestone would have changed the chemistry of the water percolating through and would have most probably cemented the quartz grains with calcite instead of silica.

In thin section the sand grains show evidence of being accelerated into each other, damaging the overgrowth crystal faces, which would date the timing of the acceleration event after the formation of the overgrowth.

 

 

Shattered quartz grains that have been accelerated into each other and as a result damaging the overgrowth crystal faces.

 

 

Shattered quartz grains that have been accelerated into each other and as a result damaging the overgrowth crystal faces.

 

Shattered quartz grains that have been accelerated into each other.

 

 

There are a few quartz grains in the Los Dos Quartzite and in the Tesuque Formation with Planar Microstructures that fit the scale of PDF’s.

 

 

Photomicrograph of a quartz grain with 2 sets of planar microstructures that fit the scale of planar deformation features. Photomicrograph of a quartz  grain with 1 set of planar microstructures that fit the scale of both planar deformation features and planar fractures. Photomicrograph of a quartz grain with 1 set of planar microstructures that fit the scale of both planar deformation features and planar fractures. 

 

 

Quartz grain with 1 set of planar microstructures that fit the scale of both planar deformation features and planar fractures.

 

Quartz grain with 1 set of planar microstructures that fit the scale of both planar deformation features and planar fractures.

 

 

Quartz grain with 1 set of planar microstructures that fit the scale of planar deformation features that has subsequently been fractured and plastically deformed. 

 

 

Quartz grain with one set of planar microstructures that fit the scale of planar fractures.

 

 

The following photomicrographs of quartz grains with planar microstructures were found in the Tesuque Formation in the vicinity of the Los Dos Quartzite. The microstructures fit the scale of planar deformation features, but the grains have been plastically deformed resulting in either curviplanar microstructures, or they are Bohm Lamellae. In either case there has not been enough tectonic heat and pressure for these features to have been formed from tectonic action, meaning they have most probably been caused by an impact event. I hope to do more microscope work on this formation and find better examples.

 

 

 

 

 

 

 

 

 

 

In Summery

The very large clasts of the Los Dos Quartzite, if you want to call them clasts, they look like outliers or Klippe of a sandstone formation that has been thrust out away from the outcrop similar to Heart Mountain in NW Wyoming. In this case, however, the quartzite piles would have been propelled by the energy released by the Santa Fe Impact Structure, the blocks of sandstone formation gliding on the unconsolidated and fluidized ejecta (Lower mixed Lithosome). The thickness of the quartzite piles could represent a thick massive sandstone formation, or could have been formed by thinner bedded sandstone that was thrust over itself forming a pile of slabs at the end of its trajectory. If I tried to fit these quartzite piles into my hypothesis of the mid-Tertiary Impact Event the Lower mixed Lithosome member of the Tesuque Formation represents the settling of a very dense ejecta cloud caused by multiple and successive bolide impacts with numerous cross currents and various compositions of material graded into beds of sandstone, siltstone, claystone and conglomerate which could mimic fluvial deposition. The large clasts of quartzite would represent ejecta from a large bolide impact timed toward the end of the series of impacts from the space rubble or dirty snowball impact event.

 

 

Los Dos Quartzite – Possible deposition scenarios:

 

 1. Selective cementation of the Tesuque Formation (Tt) –

 

A large volume spring of deep seated, silica rich water was flowing up through the angular grains of the Tt Fm., that washed away all the fines and somehow all the feldspars leaving the larger clasts of primarily vain quartz, chert, and some mica schist, and a rather well sorted quartz arenite with rounded grains. The resulting deposit would then have to be buried deep enough and long enough for a quartz overgrowth to cover the grains forming a facetted crystal.

 

Problems with this scenario include the following:

 

Water flowing up through a fault zone from depth would have to pass through approximately 2,500 feet of limestone rich Paleozoic formations that lie beneath the Quartzite Piles. The Yates Petroleum, La Mesa No.2, Sec. 24, T17N, R8E, Santa Fe County, New Mexico well was drilled to the basement about 4 miles southwest of the Los Dos Quartzite piles and in situ Paleozoic rock rich in limestone can be seen on the Schlumberger   Litho Density Compensated Neutron GR Log between the depths of 5021 feet and 7536 feet. Further interpretation of the stratigraphy penetrated by this well was published in August 2006, The Stratigraphic analysis of the Yates #2 La Mesa well and implications for southern Española Basin tectonic history, Caroline Myer* and Gary A. Smith, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, *Current address: Department of Geology, Utah State University, Logan, Utah 84322-4505 Can be downloaded at http://geoinfo.nmt.edu/publications/periodicals/nmg/downloads/28/n3/nmg_v28_n3_p75.pdf

 

I am having a log expert look at the logs of the Yates well and determine the salinity of the water at depth, which may or may not give us a clue about the possibility of quartz rich water reaching the surface.

 

 

This much limestone would have changed the chemistry of the water percolating through and would have most probably cemented the quartz grains with calcite instead of silica. In addition the Tt Formation is a poorly consolidated aquifer 3,000+ feet thick that I believe would disperse the silica rich water flowing from deep seated faults.

 

In thin section the sand grains show evidence of being accelerated into each other, damaging the overgrowth crystal faces, which would date the timing of the acceleration event after the formation of the overgrowth.

 

2. Allochthonous boulders and slabs of an older formation propelled by the energy released by a Tertiary impact event, the blocks of sandstone formation gliding onunconsolidated and fluidized ejecta from the large impact event.

 

 The depositional environment for this sandstone, in my opinion, would have to include a source of sand, conglomeritic clasts up to cobbles, consisting of chert, vein quartz, mica schist and occasional granitic clasts. If this material was carried to the deposition site by a river with enough energy to carry cobble sized clasts it would also dump all sorts of material ranging is size from clay to cobbles. There would then have to be a mechanism to wash away the fines, clean the sediment of feldspars, sort and round the remaining quartz grains. The resulting deposit would then have to be buried deep enough and long enough for a quartz overgrowth to cover the grains forming a facetted crystal.

 

      

The Dakota Formation is one option that could fill the above requirements, although I have not found a perfect match yet.

p1000865

 

p1000862

 

 

The above photographs are of an outcrop of the Dakota Sandstone South of Las Vegas NM along the canyon carved by the Gallinas River above San Augustine NM. The grain size is similar to the Los Dos Quartzite and the rounded quartz grains are covered by an overgrowth covering the grains forming a facetted crystal. The formation is well cemented but not quite as well as the Los Dos Quartzite, and the formation has similar weathering characteristics, but the chert, vein quartz, and schist clasts are missing. The Dakota Formation here also has much more distinct bedding.

 

The clasts could form in the Dakota Formation if a transgressive sea began eroding a Burro Canyon Formation conglomerate similar to the conglomerate in the following photograph. The Burro Canyon conglomerate was photographed about 15 kilometers north of Blanding UT and contains all the required conglomeratic clasts and sandstone of about the correct grain size. The photograph is not very clear because at the time I was not considering illustrating this scenario. The eroded Burro Canyon material would then be cleaned, washed and rounded by wave action eliminating all the clay and other fines. The same depositional environment could be caused by a river eroding the Burro Canyon or some other source and dumping the material in a marine environment and reworked by wave action and long shore currents.

 

 burrocanyoncong

 Photo of Burro Canyon conglomerate.

 

 

 burrocanyonsandstone

Burro Canyon sandstone photographed at the same location as the conglomerate.

X

 

The Dakota Formation is not normally described as coming in direct contact with the Burro Canyon Formation, but the above photograph shows a turbulent sort of contact between the yellow Dakota Sandstone and the grey Burrow Canyon formation. This photograph was taken higher up in the Abajo Mountains and may not represent an erosional contact. I believe the Abajo Mountains represent the central uplift of a large impact crater which could drastically impact the contact between the two formations.

 DSC00371

 

 

I have not found a outcrop of the Dakota Formation that fits the Los Dos Quartzite, and the Dakota Formation may be the wrong place to look. There are other older quartzites that could be the source of the Los Dos Quartzite which I intend to explore.