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MEEHAN, Kimberly C.1,BARTLETT, Kimberly1, KOWALSKI, Cody1, LASH, Gary G.2, BEMBIA, Paul
(1)Department of Geology, University at Buffalo, 126 Cooke Hall, Buffalo, NY 14260, (2)Department of Geosciences, SUNY Fredonia, Fredonia, NY 14063
Abundant microspherules associated with carbonate concretion beds have been discovered at the contact of the Upper
Devonian Rhinestreet and overlying Angola formations of on Eighteenmile Creek of Western New York. Similar objects have
also been recovered from near the contact of the Cashaqua Formation and overlying Rhinestreet Formation, also on
Eighteenmile Creek. The latter occurrence is associated with an abrupt negative stable carbon isotope excursion that appears
to define the termination of the Upper Devonian punctata event in the Appalachian Basin. Microspherules have also been
collected from shale and concretions near the Rhinestreet-Hatch contact in the Genesee River Valley. Most spherules are
spheroidal or teardrop in shape and range in size from approximately 150 to >500 microns in diameter. Nearly opaque dark
and exceptionally clear microspherules occur in both concretions and host shale. However, microspherules were found in
higher concentrations within the carbonate concretions; up to several thousand per gram. Evidence of transport is lacking.
Electron dispersive microscopy results show that both light and dark glass spherules are Si-Na rich, which differs markedly
from the host shale chemical composition. Their origin is still in question as these spherules can be considered either natural
(biological or mineral) or an artificial product (fly-ash or contaminants of local manufacturing). However, timing and
proximity do not eliminate these as potential evidences for the known Devonian Alamo, Charlevoix or Siljan impact events but
may also give credence to the suspected impact event at Panther Mountain, New York.
The Upper Devonian succession exposed along Eighteenmile Creek near the village of Derby, New York (Fig. 1B) includes the
Cashaqua Formation of the Sonyea Group, and the Rhinestreet Formation of the West Falls Group (Fig. 2). The studied
deposits accumulated in the relatively enclosed northern part of the northeast-southwest trending Appalachian foreland basin
bounded on its east and southeast by the rising Acadian Highlands (Ettensohn, 1985, 1987; Scotese and McKerrow, 1990;
Blakey, 2016) (Fig. 1A).To the west lay the Laurentian epicontinental sea breached by the Findlay-Algonquin Arch or a
precursor arch (Scotese and McKerrow, 1990; Rast and Skehan, 1993; Bose and Bartholomew, 2012; Blakey, 2016) (Fig. 1B).
Late Devonian paleogeographic reconstruction (Blakey, 2016) depicts the Appalachian Basin connection with the global Rheic
Ocean to the southwest as a narrow seaway (Fig. 1B).
The upper 2.3 m of the Cashaqua comprises dark-gray shale hosting the styliolinid- and barite-bearing Shurtleff Septarian
Horizon and several cm-thick black shale layers (Kirchgasser et al., 1994; Over and Sullivan, 2016) (Figs. 1C and 5).
Microtektite-like spherules discussed later were recently recovered from an interval 20 to 41 cm below the base of the dark-
gray shale (Fig. 5). The Cashaqua Formation is sharply overlain by the organic-rich Rhinestreet Formation, more than 50 m
of heavily fractured black and gray, commonly finely laminated, pyritic shale, several m-scale intervals of organic-lean gray
shale and thin black shale beds, sparse thin siltstone beds, and horizons of calcium carbonate concretions (Lash and Blood,
2004) (Fig. 2). The Rhinestreet transitions upward into the Angola Formation, approximately 78 mof silty gray shale and
subordinate black shale containing occasional calcareous siltstone beds and calcium carbonate concretion horizons.
Two contacts well exposed at Eighteenmile Creek, the Cashaqua-Rhinestreet and the Rhinestreet-Angola, and a poorly exposed outcrop
from Letchworth State Park in the Genesee River Valley, the Rhinestreet-Hatch, are known to contain distinct concretion beds. Concretions
at the Eighteenmile Creek localities were sampled (no concretions were exposed at Letchworth) and shale samples were taken at 3cm
(Rhinestreet-Angola) and 10 cm (Cashaqua-Rhinestreet; Rhinestreet-Hatch) intervals at these localities. Shale samples were roughly
crushed with a mortar and pestle and completely submerged an industrial grade quaternary surfactant (Betco Quat-Stat ammonium
surfactant) for up to two weeks until shale was completely dissolved. Concretion were left entact and submerged in a Hcl (50%) solution for
24 hours. Aliquots were then run through a series of nested sieves (250, 150, 90, and 63 μm) and weighed out to 0.05 gm for specimen
counts and collection. Microspherules were analyzed by scanning electron microscopy (SEM). Each sample was mounted on double-sided
adhesive carbon tape and analyzed on a Phenom ProX SEM operating at acceleration voltages between 5 and 15 keV and equipped with an
energy dispersive spectroscopy (EDS) detector. Elemental data collected included: O, Si, Na, Ca, Mg, N, Al, Te, Fe, S, C, K, N, and W.
Microspherules lack any crystalline structures and have been determined to be glass.
Microspherules, though predominantly spheroidal, also include lesser numbers of tear drop and conjoined shape are quite pristine,
particularly those from the Rhinestreet-Angola contact. Microspherules range in size from approximately 63 500 µm; the vast majority at
all three localities within an approximate size range of 63 90 µm (fig. 3 a-e). Coloration of microspherules range from perfectly clear to
amber to opaque black; the majority (>90%) being clear for 63 90 µm and the majority (>90%) being clear for microspherules > 90 µm.
Chemical analysis of clear, black, and concretion encapsulated microspherules render all microspherules silica-rich (~ 51.0%) with lesser
quantities of Na (~12.0%) , Ca (~3.8%) , Mg (~3.1%), among other elements (fig. 4 a-c). Microspherules from both localities sampling from
the upper Rhinestreet (Eighteenmile Creek Rhinestreet-Angola and Letchworth Rhinestreet-Hatch) show little to no signs of devitrification
or abrasion, whereas the microspherules from the Cashaqua-Rhinestreet contact show substantial abrasion. The two localities sampled from
known contacts containing concretions have distinctly higher concentrations of microspherules within the shale bedding of the concretion
formation and within the concretions themselves (fig. 5 & 6).
Figure 2: (A) Cashaqua-Rhinestreet contact
denoted by red dashed line, concretion beds
denoted by white arrows at 20 cm and 41 cm,
(B) K. Bartlett collecting at 10 cm intervals at
the Cashaqua-Rhinestreet contact denoted by
red dashed line, concretion beds denoted by
white arrows at 20 cm and 41 cm, (C)
Concretions insitu at the 41 cm bed at the
Cashaqua-Rhinestreet contact, at Eighteenmile
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3A B C D E
Figure 3: a-b) Spheroidal microspherules exhibiting conchoidal fracturing; c) teardrop microspherule; d-e) conjoined microspherules.
Figure 4 a-c: EDS element results for clear (CT),
black (5B), and concretion encapsulated(CC)
microspherules. Compositions of all
microspherules are the same despite coloration,
size, and shape variations.
Stratigraphic Column Rhinestreet-Angola at Eighteenmile Creek
Figure 5: Stratigraphic columns of the transitional contact of the Rhinestreet-Angola Formations (left) and the contact of the Cashaqua-Rhinestreet
Formations (right) at Eighteenmile Creek. Sampling of shale and concretions bearing microspherules was measured within the column at and above the
concretion bed (scraggy layer) for the Rhinestreet-Angola transitional zone while measurements taken at the Cashaqua-Rhinestreet were taken from the
contact. Measurements noted on figure do not represent height or depth within the shown formations.
The lack of crystalline structures within the glassy microspherules suggests that their origins were from melt. The disparate age of the beds suggests that
the two sets of microspherules are unrelated. Further, given the tectonic history of the area, it is unlikely that the spherules are of volcanic origin, thus,
suggesting that they are either remnants of 1) separate impact events or 2) potentially residue from local industrial contaminants.
Microspherules as Ejecta
It is noteworthy to point out that the chemistry of all the microspherules analyzed herein is consistent, whereas other investigations of microspherules
from comparable age found in Belgium have reported varying chemical compositions (Claeys et al.). These Western New York microspherules are
depleted in Al and K which contrasts the background shale which is Al-rich (Hosterman & Whitlow 1981) and suggests that the composition of the
microspherules reflects that of the target rock. Further research into potential target rock chemistry is needed. Known impact events that correlate to
the upper Cashaqua include the Alamo Event in Nevada. However, this does not rule out a potentially unknown impact event for this time. Similarly, the
age of the upper Rhinestreet Formation microspherules may be ejecta from known or suspected impacts in Charlevoix, Panther Mountain, or another
unknown event. Further research is needed to confirm which known or unknown impacts served as the event of origin for both contacts.
Microspherules as Contaminants
Western New York is historically an industrial manufacturing area. Noted types of production where flyash may have produced microspherules could
include former steel manufacturing plants and coal-fueled power plants among others. Publications that have reported on the chemical compositions of
varying anthropogenic contaminants including flyash show that the microspherules in their investigations are Al-rich (Kutchko & Kim 2006; Medina et al.
2010; Nyambura et al.2011). However, the disparate chemical compositions to previously reported and those found herein do not rule out the potential
for an unforeseen contaminant in fact several characteristics of the microspherules may suggest that these are indeed a product of anthropogenic
activity. These characteristics include: 1) their pristine shape and clarity, 2) their consistent geochemistry, and 3) the extent of their dispersal within the
Rhinestreet-Angola column. More research is needed to confirm or deny potential sources of flyash contaminants.
Further substantiating the need for this type of further research, recently, glassy microspherules, like those described and analyzed herein, have been
recovered from upper Chautauqua Creek as part of a course held with SUNY Fredonia this past fall semester. Additional questions to probe include
interest into how much of these materials make their way into Lake Erie and the surrounding water sources? What would the effect be to both human
and non-human life should such glassy microspherules be ingested or inhaled?
Transport and Stratigraphic Dispersal
Where the microspherules from the Cashaqua-Rhinestreet are altered, most likely due to transport, the microspherules lack such evidence suggesting
that they were preserved in situ. The microspherules recovered from the Rhinestreet-Angola contact were found to have far greater numbers and
dispersed over a larger extent of the stratigraphic column than those recovered from the Cashaqua-Rhinestreet contact. Considering the known
extinctions of the punctata event and the subsequent recovery during the hassi (fig. 1C), it is suspected that the dispersal of microspherules over >5 m
near the Rhinestreet-Angola transitional zone is most likely due to extensive bioturbation.
Microspherules as Concretion Condensation Nuclei
These microspherules may have served as condensation nuclei for these distinct concretion beds and may also be previously unrecognized in other
significant concretion beds/zones. Exploratory laboratory tests on Moqui Balls from an unknown locality of the Jurassic Navajo Sandstone in Utah has
also produced similar results suggesting that concretion beds may serve as secondary evidence for previously unknown impact events.
Figure 1: a) Localities of investigation in a global perspective
during the Devonian, b) detail map of the area of investigation in
Western New York, c) stratigraphic column for the Cashaqua-
Rhinestreet showing the zones of collection with the punctate
event for the concretion beds at the Cashaqua-Rhinestreet contact
and the subsequent recovery through the hassi, into the
Rhinestreet-Angola transition zone where the Rhinestreet-Angola
samples were retrieved.
Stratigraphic Column Cashaqua-Rhinestreet
at Eighteenmile Creek
Number of microspherules per gram
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