¹Yoko Kebukawa,²Conel M. O’D. Alexander,¹George D. Cody
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13302]
¹Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, Washington, District of Columbia, 20015 USA
²Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, Washington, District of Columbia, 20015 USA
Published by arrangement with John Wiley & Sons

Past studies of the various separable carbonaceous fractions have been unable to account for all of C in primitive chondrites. In particular, up to 20–50% of the C is lost during acid leaching of bulk samples even after the C in carbonates and soluble organic matter is accounted for. To try to better characterize the nature of this “missing C,” we have compared the bulk infrared (IR) absorption spectra of a number of primitive chondrites with those of their previously reported insoluble organic matter (IOM). The aliphatic C–H stretching bands, in particular, allow us to compare the molecular structures of bulk C with that of IOM. The spectral differences between bulk C and IOM reflect “missing C” phases that were lost during acid leaching, although we cannot completely exclude the possibility that the OM was modified after demineralization. Comparing IR spectra of bulk meteorite powder and IOM suggests that the missing C varies in its molecular structure, and that mildly thermally metamorphosed type 3 chondrites tend to be richer in an aliphatic fraction with lower CH₂/CH₃ ratios, relative to IOM, compared to aqueously altered carbonaceous chondrites (CI/CM/CR). The missing C is most likely released from acid‐labile functional groups, such as esters, acetals, and amides, during demineralization, although it cannot be ruled out that some fraction of the missing C is in small grains that are difficult to recover from suspension, or in water‐soluble compounds trapped in phyllosilicates.

¹Anthony Gargano,²Zachary Sharp
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13303]
¹Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, 87131‐0001 USA
²Center for Stable Isotopes, University of New Mexico, Albuquerque, New Mexico, 87131‐0001 USA
Published by arrangement with John Wiley & Sons

The bulk chlorine concentrations and isotopic compositions of a suite of non‐carbonaceous (NC) and carbonaceous (CC) iron meteorites were measured using gas source mass spectrometry. The δ37Cl values of magmatic irons range from −7.2 to 18.0‰ versus standard mean ocean chloride and are unrelated to their chlorine concentrations, which range from 0.3 to 161 ppm. Nonmagmatic IAB irons are comparatively Cl‐rich containing >161 ppm with δ37Cl values ranging from −6.1 to −3.2‰. The anomalously high and low δ37Cl values are inconsistent with a terrestrial source, and as Cl contents in magmatic irons are largely consistent with derivation from a chondrite‐like silicate complement, we suggest that Cl is indigenous to iron meteorites. Two NC irons, Cape York and Gibeon, have high cooling rates with anomalously high δ37Cl values of 13.4 and 18.0‰. We interpret these high isotopic compositions to result from Cl degassing during the disruption of their parent bodies, consistent with their low volatile contents (Ga, Ge, Ag). As no relevant mechanisms in iron meteorite parent bodies are expected to decrease δ37Cl values, whereas volatilization is known to increase δ37Cl values by the preferential loss of light isotopes, we interpret the low isotope values of <−5‰ and down to −7.2‰ to most closely represent the primordial isotopic composition of Cl in the solar nebula. Similar conclusions have been derived from low δ37Cl values down to −6, and −3.8‰ measured in Martian and Vestan meteorites, respectively. These low δ37Cl values are in contrast to those of chondrites which average around 0‰ previously explained by the incorporation of isotopically heavy HCl clathrate into chondrite parent bodies. The poor retention of low δ37Cl values in many differentiated planetary materials suggest that extensive devolatilization occurred during planet formation, which can explain Earth’s high δ37Cl value by the loss of approximately 60% of the initial Cl content.

^1,2Mike Meyer,³Peter J. Harries,⁴Roger W. Portell
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13299]
¹Earth and Environmental Science Department, Harrisburg University, Harrisburg, Pennsylvania, 17101 USA
²Geophysical Laboratory, Carnegie Institution for Science, Washington, DC, 20005 USA
³Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina, 27695 USA
⁴Florida Museum of Natural History, University of Florida, Gainesville, Florida, 32611 USA
Published by arrangement with John Wiley & Sons

The Plio‐Pleistocene Upper Tamiami Formation (Pinecrest beds) of Florida is well known for its fossiliferous shell beds, but not for its extraterrestrial material. Here we report the first occurrence of tiny (~200 μm in diameter) silica‐rich microspherules from this unit and from the state. This material was analyzed using petrographic and elemental methods using energy dispersive X‐ray spectroscopy (EDS). The majority of microspherules are glassy and translucent in reflected light with some displaying “contact pairs” (equal‐sized micro‐spherules attached to each other). Broken microspherules cleave conchoidally, often with small internal spherical vesicles, but most lack any other evidence of internal features, such as layering. Using the EDS data, the microspherules were compared to volcanic rocks, microtektites, and cosmic spherules (micrometeorites). Based on their physical characteristics and elemental compositions these are likely microtektites or a closely related type of material. The high Na content in the examined material deviates significantly from the abundances usually found in micrometeorites and tektite material; this is enigmatic and requires further study. This material may be derived from a nearby previously unknown impact event; however, more material and sites are required to confirm the source of this material. Because of the focus on molluscan fossils in southwestern Florida shell beds, microtektite material has likely been overlooked in the past, and it is probable that these microspherules are in abundance elsewhere in these units and possibly throughout the region.