Graptolite reflectance and correlation with other diagenetic and very-low-grade metamorphic indicators

The correlation chart and references in this post have been updated as of November 28, 2020. In the chart, the mean maximum reflectance correlation of Malinconico has been changed and is based now on her (my) data from the prehnite-pumpellyite metamorphic terrane of northern Maine, USA, rather than a compilation with other published mean maximum graptolite reflectance published data. The mean random and mean maximum graptolite reflectance correlations of Luo et al. (2020) and the mean random equation of Bertrand and Malo (2012) have been added. Inclusion of Kübler Indices and associated metapelitic (anchizone, etc) zones have been removed (see text below).

My first independent organic petrology research project, in the late 1980's-early 1990's, was a graptolite reflectance study of the low- to very-low-grade metamorphic region of the northern US Appalachians in northern Maine. The goals were to 1) test the applicability of the technique, used in other anchizone regions, to these prehnite-pumpellyite grade rocks, and 2) outline in more detail the regional patterns or trends in metamorphism.

Silurian monograptid graptolites from Lawler Ridge, several miles north of Millinocket, Maine. Mean maximum reflectance 10.6% + 1.0 (n=20).

Graptolites are extinct colonial marine invertebrates of the Phylum Hemichordata with a geologic age range from Cambrian to Carboniferous. They derive their name from the pencil-mark appearance of preserved periderm on shales (Graptolithus= rock writing). Since the mid-1970's, the reflectance of graptolites, in a similar fashion to vitrinite reflectance, has been used to determine the diagenetic level or organic maturity of rocks that, either due to a marine environment of deposition (EOD) or age older than the flourishing of land plants (pre-Silurian), lack vitrinite derived from woody plant matter. Graptolite reflectance has been applied to both petroleum source rock evaluation and analysis of patterns of anchizone/subgreenschist metamorphism, the level of metamorphism between sedimentary rocks and greenschist facies metamorphic rocks where some diagenetic indicators may no longer be applicable and where big micas and flashy garnets, staurolites etc have not yet appeared. (In one talk in ~1992, I did compare the anchizone to the Neutral Zone of Star Trek, which separates Romulan space from Federation space: the anchizone is the area where neither those looking for liquid hydrocarbons nor those studying traditional metamorphic petrology care to go.)

However, the urge to correlate graptolite reflectance values to the well-known or more standard vitrinite-reflectance scale has been problematic for a number of reasons. Firstly, since vitrinite and graptolites are hardly ever found in the same rock, due again to age of rock or EOD, correlation has been made through intermediaries, such as solid bitumen/scolecodont/chitinozoan reflectance, conodont alteration indices (CAI), and Rock-Eval pyrolysis Tmax, that are found in or that can be applied to both vitrinite-bearing and graptolite-bearing rocks. However, a drawback particularly of using intermediaries such as CAI and subgreenschist mineral facies is the wide qualitative range of the categories within those indicators. 

Secondly, the percent graptolite reflectance has been reported in different forms: 

1) mean maximum reflectance: on each of numerous specimens in a single polished whole-rock sample, under polarized light (polarizer in light path), the microscopic stage is rotated to the orientation of the maximum reflectance of the highly anisotropic graptolite exoskeleton and then the reflectance is recorded; a mean and standard deviation is calculated from all the maximum reflectances for that sample; 

2) maximum-maximum or true maximum reflectance which is just the single highest maximum reflectance value of all specimens measured on a sample; no standard deviation; 

3) mean random reflectance, polarized light: the instantaneous measured value with no stage rotation is collected on numerous specimens in a sample, mean and standard deviation calculated; the range of reflectances collected can be quite variable depending on degree of anisotropy, and standard deviation can be large;

4) mean random reflectance, in non-polarized light. The reflectance of the non-polarized surface is theoretically an average of the anisotropic range of that specimen’s surface reflectivity. With a large enough number of measurements, the mean random reflectances in both polarized and non-polarized light should be equal, but the standard deviation in polarized light will be larger. 

Besides correlation to thermal maturation indices commonly used in sedimentary rocks and oil-gas exploration (CAI, vitrinite reflectance/coal rank), since graptolite reflectance has been used in zeolite/prehnite-pumpellyite subgreenschist terranes, proper correlation with related terminology such as diagenesis, anchizone/epizone, very-low-grade/low-grade metamorphism is also an issue. Discussions on the limits of the anchizone based on illite crystallinity and relationship to mineral facies and coal rank (bituminous/anthracite) have been ongoing for decades. In 2007, the International Union of Geological Sciences (IUGS) published a correlation classification for very-low to low-grade metamorphic rocks (Árkai and others, 2007), with vitrinite reflectance, diagenetic to low-grade metamorphic zones, subgreenschist mineral facies, and boundaries for metapelitic zones (diagenetic zone, anchizone, epizone) based on the illite crystallinity Kübler Index (KI). Lower and upper KI limits of the anchizone were 0.42-0.25˚ delta 2theta, respectively. Many of the boundaries were gradational or covered a range of values, but it appeared, to me, that there was international consensus. 

So, in 2016, partly for a couple papers still (and even now in 2020) in draft form and partly in response to a petroleum industry colleague asking how well constrained the vitrinite/graptolite correlations are, I made a huge spread sheet with the IUGS 2007 very-low-metamorphic indicators chart, CAI, and vitrinite-graptolite reflectance correlations from numerous collected graptolite reflectance papers (most source references following). From that, I posted in this blog entry, a correlation chart of metamorphic grade, mineral facies, KI with metapelitic zone, coal rank with vitrinite reflectance, and CAI, plus the mean random graptolite reflectance of Bertrand (1990) and Petersen et al. (2013), and mean maximum graptolite reflectance that was a consensus compilation of my own data from northern Maine and several publications that reported mean maximum graptolite reflectance data.

However, since my 2016 chart, there has been an increasing interest in graptolite reflectance and publication of important papers, particularly from China and Denmark. The surge in interest is due to large unconventional petroleum discoveries in Lower Paleozoic black shales. I am also finally getting around to finalizing my graptolite reflectance study in the prehnite-pumpellyite region of northern Maine. Coincidently, however, there has been changes in standardization used for illite crystallinity studies that has changed the KI limits of the anchizone (Warr and Ferreiro Mählmann, 2015) plus continuing discussion on the variability of the boundaries of the anchizone relative to mineral facies and to coal ranks in different regions (Ferreiro Mählmann and Frey, 2012; Warr and Cox, 2016).

It should be pointed out that the anchizone is defined specifically by illite crystallinity: Kisch wrote in 1990 (p. 42), “The main argument against such re-definitions […in terms of the metamorphic grade in associated materials…] is that the notion of the anchizone is intractably bound to phyllosilicate mineralogy in clastic sedimentary rocks, and particularly defined in terms of illite ‘crystallinity’…Such re-definition of the anchizone in terms other than illite ‘crystallinity’ should therefore be rejected.” In the Alps, there is a range of vitrinite reflectance values associated with the lower and upper boundaries of the anchizone depending on geothermal gradient or heating rate indicating that there are material differences in the chemical and mechanical kinetics of the transformation of clay crystallinity and the physiochemical structure of vitrinite. In addition, the influence of pressure varies between clay and organic matter. Warr and Cox (2016) also reported that in the famous zeolite to prehnite-pumpellyite facies metamorphic region of New Zealand, the epizone, previously interpreted to be equivalent to chlorite-grade greenschist metamorphism, should now include pumpellyite-actinolite facies, formerly in the anchizone.

Therefore, my new 2020 table below, does not include any reference to Kübler Index and related metapelitic zones, despite my fondness for the term “anchizone”. I so far have only found one researcher that reports KI and associated graptolite reflectance (Rantitsch 1995, 1997). Most graptolite reflectance practitioners are working in gas exploration, rather than very-low-grade metamorphic terrane studies, and the co-existing indicators in my area of northern Maine are CAI and zeolite/prehnite-pumpellyite mineral facies. 

The new table BELOW has FIVE correlative relationships of graptolite reflectance: three from studies reporting random reflectance, but that use different intermediaries to relate graptolite to vitrinite reflectance and are from different geological provinces, and two correlations of graptolite mean maximum reflectance.

TABLE (click on it to enlarge): Correlation of metamorphic grade, mineral facies, coal rank, vitrinite reflectance from the IUGS Subcommission on the Systematics of Metamorphic Rocks (Árkai et al., 2007); general boundaries of zeolite facies to vitrinite reflectance (Kisch, 1981); CAI (conodont alteration index) to vitrinite reflectance (Repetski et al., 2008); mean random graptolite reflectance, non-polarized light, from equation based on natural and heat-treated graptolites plus previously published sources (Luo et al., 2020); mean random graptolite reflectance, non-polarized light (to vitrinite reflectance through chitinozoan reflectance: Bertrand, 1990); mean random graptolite reflectance, non-polarized light (to vitrinite reflectance combining results in Bertand, 1990, 1993: Bertrand and Malo, 2012); mean random graptolite reflectance, non-polarized light (to vitrinite reflectance through RockEval pyrolysis Tmax: Petersen et al., 2013); mean maximum graptolite reflectance equation based on natural and heat-treated graptolites plus previously published sources (Luo et al., 2020); mean maximum graptolite reflectance to CAI (Bradley et al., 2000)  and metamorphic facies (Richter and Roy, 1976) of northern Maine, USA (Malinconico, 1992, 1993, unpublished data).

Another useful correlation chart is that of Hartkopf-Fröder (2015; their Figure 26). They comprehensively include not just coal rank, reflectance of vitrinite and graptolites and CAI, but other zooclasts, coloration of spores/pollen and other microfossils, and hydrocarbon generation zones. They did not include mineral metamorphic facies, which were important for my work. Three graptolite reflectance scales are in their chart: Petersen and others (2013) and two by Bertrand and colleagues (1990, 2012); I included those in my chart. Their bibliography includes graptolite reflectance citations (such as several by Bertrand) that are not listed below. Another bibliographic list (Microsoft Word document) of “Zooclast Reflectance” citations is on the website of The Society for Organic Petrology (TSOP) (https://www.tsop.org/references.html). Luo et al. (2020) have a useful graph (Figure 13) for visualization that plots several graptolite-vitrinite reflectance correlations against each other. 

These tables do not solve the graptolite/vitrinite reflectance correlation problem. They do, however, show state of the current publicly available knowledge.

Selected GRAPTOLITE REFLECTANCE 

and diagenetic to very-low-metamorphic indicator references 

including those examined for construction of the correlation table.

(Citations specifically mentioned or used in the table are in bold.) 

Árkai, P., Sassi, F., Desmons, J., 2007, Very low- to low-grade metamorphic rocks (Chapter 2.5), in Fettes, D., and Desmons, J., eds., Metamorphic Rocks: A Classification and Glossary of Terms (Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Metamorphic Rocks): Cambridge, UK, Cambridge University Press, p. 36-42.

Bertrand, R., 1990, Correlations among the reflectances of vitrinite, chitinozoans, graptolites, and scolecodonts: Organic Geochemistry, v. 15, no. 6, p. 565-574.

Bertrand, R., 1993, Standardization of solid bitumen reflectance to vitrinite in some Paleozoic sequences of Canada, in F. Goodarzi and R.W. Macqueen, eds., Geochemistry and petrology of bitumen with respect to hydrocarbon generation and mineralization: Energy Sources, v. 15, p. 269-287.

Bertrand, R., and Heroux, Y., 1987, Chitinozoan, graptolite and scolecodont reflectance as an alternative to vitrinite and pyrobitumen reflectance in Ordovician and Silurian strata, Anticosti Island, Quebec, Canada, American Association of Petroleum Geologists Bulletin, v. 71, p. 951-957.

Bertrand, R., and Malo M., 2012, Dispersed organic matter reflectance and thermal maturation in four hydrocarbon exploration wells in the Hudson Bay Basin: regional implications: Geological Survey of Canada, Open File 7066, 52 p. http://publications.gc.ca/collections/collection_2012/rncan-nrcan/M183-2-7066-eng.pdf 

Bradley, D. C., Tucker, R. D., Lux, D.; Harris, A. G., and McGregor, D. C., 2000, Migration of the Acadian orogen and foreland basin across the northern Appalachians of Maine and adjacent areas: U.S. Geological Survey Professional Paper 1624, 49 p. 

Bustin, R., M., Link, D., and Goodarzi, F., 1989, Optical properties and chemistry of graptolite periderm following laboratory simulated maturation: Organic Geochemistry, v. 14, p. 355-364.

Cao, C., Sang, Q., Fang, Y., 2000, The study of graptolite reflectance as the indicator of source-rock maturation in Ordovician and Silurian of Tarim basin, Ordos, Jiangsu areas: v. 39, issue 1, Acta palaeontologica sinica, p. 151-156. (In Chinese; English abstract and figure captions)

Cardott, B. J., and Kidwai, M. A., 1991, Graptolite reflectance as a potential thermal-maturation indicator, in K. S. Johnson, ed., Late Cambrian-Ordovician geology of the southern Midcontinent, 1989 symposium: Oklahoma Geological Survey Circular 92, p. 203-209.

Clausen, C.-D. and Teichmüller, M., 1982, Die Bedeutung der Graptolithenfragmente im Paläozoikum von Soest-Erwitte für Stratigraphie und Inkohlung: Fortschritte in der Geologie von Rheinland und Westfalen, v. 30, p. 145-167.

Cole, G. A., 1994, Graptolite-chitinozoan reflectance and its relationship to other geochemical maturity indicators in the Silurian Qusaiba shale, Saudi Arabia: Energy & Fuels., v. 8, p. 1443-1459.

Ferreiro Mählmann, R., Frey, M., 2012, Standardisation, calibration and correlation of the Kübler-index and the vitrinite/bituminite reflectance: an inter-laboratory and field related study: Swiss Journal of Geosciences, v. 105: 153-170.

Gentzis, T., T. de Freitas, F. Goodarzi, M. Melchin, and A. Lenz, 1996, Thermal maturity of lower Paleozoic sedimentary successions in Arctic Canada: AAPG Bulletin, v. 80, p. 1065-1084.

Goodarzi, F., 1984, Organic petrology of graptolite fragments from Turkey: Marine and Petroleum Geology, v. 1, p. 202-210.

Goodarzi, F., 1985, Dispersion of optical properties of graptolite epiderms in increase maturity in early Paleozoic organic sediment: Fuel, v. 64, p. 1735-1740.

Goodarzi, F., 1990, Graptolite reflectance and thermal maturity of Lower Paleozoic rocks, in V. F. Nuccio and C. E. Barker, eds., Applications of thermal maturity studies to energy exploration: SEPM, Rocky Mountain Section, p. 19-22.

Goodarzi, F., Gentzis, T., Harrison, C., and Thorsteinsson, R., 1992, The significance of graptolite reflectance in regional thermal maturity studies, Queen Elizabeth islands, Arctic Canada: Organic Geochemistry, v. 18, no. 3., p. 347-357.

Goodarzi, F., and Norford, B. S., 1985, Graptolites as indicators of the temperature histories of rocks: International Journal of Coal Geology, v. 11, p. 127-141.

Goodarzi, F., and Norford, B. S., 1989, Variation of graptolite reflectance with depth of burial: International Journal of Coal Geology, v. 11, p. 127-141.

Hartkopf-Fröder, C., Königshof, P., Littke, R., Schwarzbauer, J., 2015, Optical thermal maturity parameters and organic geochemical alteration at low grade diagenesis to anchimetamorphism: A Review: International Journal of Coal Geology, v. 150-151, p. 74-119.

Kemp, A. E. S., Oliver, G. H. I. and Baldwin, J. R., 1985, Low-grade metamorphism and accretion tectonic: Southern Uplands terrain, Scotland: Mineralogical Magazine, v. 49, p. 335-344.

Kisch, H.J., 1981, Coal rank and illite crystallinity associated with the zeolite facies of Southland and the pumpellyite-bearing facies of Otago, southern New Zealand: New Zealand Journal of geology and Geophysics, v. 24, p. 349-360.

Kisch, H.J., 1990, Calibration of the anchizone: a cricial comparison of illite 'crystallinity' scale used for definition: Journal of Metamorphic Geology, v. , p. 31-46.

Kurylowicz, L. E., Ozimic, S., McKirdy, D. M., Kantsler, A. J. and Cook, A. C., 1976, Reservoir and source rock potential of the Larapinta Group, Amadeus Basin, Central Australia: Australian Petroleum Exploration Association Journal, v. 16, p. 44-65.

Luo, Q., Goodarzi, F., Zhong, N., Wang, Y., Qiu, N., Skovsted, C. B., Suchy, V., Schovsbo, N. H., Morga, R., Xu, Y., Hao, J., Liu, A., Wu, J., Cao, W., Min, X., Wu, J., 2020, Graptolites as fossil geo-thermometers and source material of hydrocarbons: An overview of four decades of progress: Earth-Science Reviews, v. 200, Article 103000. doi:10.1016/j.earscirev.2019.103000 

Luo, Q., Hao, J., Skovsted, C.B., Luo, P., Khan, I., Wu, J., Zhong, N., 2017. The organic petrology of graptolites and maturity assessment of the Wufeng–Longmaxi Formations from Chongqing, China: insights from reflectance cross-plot analysis: International Journal of Coal Geology, v. 183, p. 161–173. 

Luo, Q., Hao, J., Skovsted, C.B., Xu, Y., Liu, Y., Wu, J., Zhang, S., Wang, W., 2018. Optical characteristics of graptolite-bearing sediments and its implication for thermal maturity assessment: International Journal of Coal Geology, v. 195, p. 386–401. 

Luo, Q., Zhong, N., Dai, N., Zhang, W., 2016. Graptolite-derived organic matter in the Wufeng–Longmaxi Formations (Upper Ordovician–lower Silurian) of southeastern Chongqing, China: implications for gas shale evaluation: International Journal of Coal Geology, v. 153, p. 87–98. 

Malinconico, M. L., 1992, Graptolite reflectance in the prehnite- pumpellyite zone, northern Maine, U.S.A.: Organic Geochemistry, v. 18, p. 263-271.

Malinconico, M. L., 1993, Reflectance cross-plot analysis of graptolites from the anchi-metamorphic region of northern Maine, USA: Organic Geochemistry, v. 20, p. 197-207.

Oliver, G. J. H., 1988, Arenig to Wenlock regional metamorphism in the paratectonic Caledonides of the British Isles- a review, in Harris, A. L. I., and Fettes, D. J., eds., The Caledonian-Appalachian Orogen: Geological Society (London) Special Publication 38, p. 347-363.

Petersen, H. I., Schovsbo, N. H., Nielsen, A. T., 2013, Reflectance measurements of zooclasts and solid bitumen in Lower Paleozoic shales, southern Scandinavia: Correlation to vitrinite reflectance: International Journal of Coal Geology, v. 114 , p. 1-18.

Rantitsch, G., 1995, Coalification and graphitization of graptolites in the anchizone and lower epizone: International Journal of Coal Geology, v. 27, p. 1-22.

Rantitsch, G., 1997, Thermal history of the Carnic Alps (Southern Alps, Austria) and its palaeogeographic implications: Tectonophysics, v. 272, p. 213-232.

Repetski, J. E., Ryder, R. T., Weary, D. J., Harris, A. G, and Trippi, M. H., 2008, Thermal maturity patterns (CAI and %Ro) in Upper Ordovician and Lower-Middle Devonian rocks of  the Appalachian basin: A major revision of USGS Map I-917-E using new subsurface collections: U.S. Geological Survey Scientific Investigations Map 3006, one CD-ROM.

Richter, D. A., and Roy, D. C., 1976, Prehnite-pumpellyite facies metamorphism in central Aroostook County, Maine, in Lyons, P. C., and Brownlow, A. H., eds, Studied in New England geology: Geological Society of America Memoir 146, p. 239-261.

Riediger, C., Goodarzi, F., and MacQueen, R. W., 1989, Graptolites as indicators of regional maturity in lower Paleozoic sediments, Selwyn Basin, Yukon and Northwest Territories, Canada: Canadian Journal of Earth Sciences, v. 26, p. 2003-2015.

Ruble, T. E., Knowles, W. R., Selleck, B. W., Wylie, A. S., 2013, Assessment of thermal maturation in outcrop samples of the Utica Shale, northern Appalachian basin, New York: American Association of Petroleum Geologists 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, AAPG Search and Discovery Article #90163 (www.searchandiscovery.com; accessed August 2013). 

Taylor, G. H., Teichmüller, M., Davis, A., Diessel, C. F. K., Littke, R., Robert, P., 1998, Organic petrology: Gebrüder Borntraeger, Berlin, 704 pages.

Teichmüller, M., 1978, Nachweis von Graptolithen-Periderm in geschieferten Gesteinen mit Hilfe kohlenpetrologischer Methoden: Neues Jahrbuch für Geologie und Paläontologie, Mh. 7, 430-447.

Wang, X. F., Hoffknecht, A., Xiao, J. X., Chen S. Q., Li Z. H., Brocke, R. B., and Erdtmann, B-D., 1993, Graptolite, chitinozoan, and scolecodont reflectances and their use as indicators of thermal maturity: Acta Geologica Sinica, v. 6, no. 1, p. 93-105.

Warr, L. N., and Cox, S. C., 2015, Correlating illite (Kübler) and chlorite (Árkai) “crystallinity” indices with metamorphic mineral zones of the South Island, New Zealand: Applied Clay Science, v. 134, p. 164-174. 

Warr, L. N., Ferreiro Mählmann, R., 2015, Recommendations for Kübler Index standardization: Clay Minerals, v. 50, p. 282-285.

Watson, S. W., 1976, The sedimentary geochemistry of the Moffat Shales: a carbonaceous sequence in the Southern Uplands of Scotland [Ph.D. dissertation]: St. Andrews, Scotland, UK, St. Andrews University, 818 pages. (https://research-repository.st-andrews.ac.uk/handle/10023/15471)

Yang, C., and Hesse, R., 1993, Diagenesis and anchimetamorphism in an overthrust belt, external domain of the Taconian Orogen, southern Canadian Appalachians—II. Paleogeothermal gradients derived from maturation of different types of organic matter: Organic Geochemistry, v. 20, p. 381-403.

Zheng, X., Sanei, H., Schovsbo, N.H., Luo, Q, Wu, J., Zhong, N., Galloway, J.M., Goodarzi, F., 2021, Role of zooclasts in the kerogen type and hydrocarbon potential of the lower Paleozoic Alum Shale: International Journal of Coal Geology, v. 248, doi.org/10.1016/j.coal.2021.103865 (This article does not mention reflectance but is an important discussion of non-granular and granular graptolite texture, generative potential, and relationship to Rock-Eval pyrolysis results.)

How BIG is BIG? (Data out of context and spinning the message: US Atlantic OCS and other oil reserve estimates in the news)

Two weeks ago, the US Department of Interior announced that the US Atlantic Outer Continental Shelf (OCS) was removed from the 2017-2022 offshore lease sale (http://www.cnn.com/2016/03/15/politics/obama-drilling-atlantic-coast/index.html;

http://washpost.bloomberg.com/Story?docId=1376-O42VSQ6JTSEX01-2P7U5E8RTS87GP3EKFMV10Q903). The January 2015 Draft Proposed Program for the OCS 2017-2022 lease sale originally included parts of the Mid-Atlantic and South Atlantic planning areas from Virginia south to Georgia; the portion of the Mid-Atlantic planning area offshore of Delaware and Maryland, and the North Atlantic planning area (offshore New Jersey north to Maine) were not in the Draft Proposal (see Figure 1). On March 15, 2016, however, the Proposed Program (http://www.boem.gov/2017-2022-Proposed-Program-Decision/) was published and now excludes the entire US Atlantic OCS. This decision was welcomed by environmental groups, various members of the US Congress from Atlantic coastal states (http://www.menendez.senate.gov/news-and-events/press/east-coast-senators-introduce-bill-to-prevent-atlantic-offshore-drilling-say-killthedrill), NASA and the US Navy (https://www.washingtonpost.com/news/energy-environment/wp/2016/03/14/the-governments-atlantic-drilling-plan-takes-friendly-fire-from-the-pentagon/), and some coastal communities. However, industry (http://www.oilandgasinvestor.com/feds-nix-atlantic-five-year-offshore-lease-plan-842361), plus governors of southern states who were hoping offshore fossil fuel production would bring income to the states, were disappointed, to say the least. (It is important to note, that although there is federal revenue sharing from offshore lease royalties to some Gulf Coast states, there is no revenue sharing plan in place for Atlantic states.)

 

Figure 1: Draft proposed Atlantic OCS planning area (from http://www.pressofatlanticcity.com/news/breaking/offshore-drilling-meegting-today-in-atlantic-city/article_49dbb8ee-c992-11e4-a1db-670b91b0f8ed.html)

The news articles above mention the 2011 assessed mean amount of potential fossil fuel resources for the entire Atlantic OCS, which includes the North, Mid- and South Atlantic planning areas: 3.3 billion barrels of oil (Bbo) and 31.3 trillion cubic feet (Tcfg) of natural gas (http://www.boem.gov/uploadedFiles/2011_National_Assessment_Factsheet.pdf). The revised 2014 assessment adjusts those mean numbers upwards to 4.72 Bbo and 37.51 Tcfg. These numbers are for the "Undiscovered Technically Recoverable"* resources on the Atlantic continental shelf within the US Exclusive Economic Zone (EEZ) that extends 200 miles from the US coastline. The lease blocks, however, would start no closer than 50 miles offshore (contrary to Senator Menendez' tweeted anti-drilling but Photoshopped picture of an oil rig within sight of beachgoers**). The assessments are based on wells drilled, mostly dry or uneconomic, and seismic data collected before the early 1990’s moratorium on Atlantic OCS oil and gas resource development, and on study of "analogs" which are known hydrocarbon plays in similar geologic settings in other parts of the world. The assessment, besides reporting the mean estimated amount, also provides other probabilities of occurrence: for the entire Atlantic OCS, there is a 5% chance (2014 revised assessment) of 9.23 Bbo and 67.7 Tcfg, but a large (95%) chance there is only 1.32 Bbo and 11.8 Tcfg.

But is this estimated resource amount BIG? Is loss of access to the Atlantic OCS a major blow to the Nation's energy independence and security, as some articles suggest? Although industry and industry media outlets would understand the relevance of the assessed numbers in relation to oil reserves around the world, the general public does not. A BILLION sounds immense, so readers may think we are missing out on a large national resource by blocking development. Without context, that is, without comparisons to other data, the numbers may be misleading. From the map below (Figure 2), however, one can see that Atlantic mean assessed amounts are minor compared to the Gulf of Mexico, and less than offshore California where there is proven production. According to an article in Eos, March 17, 2016,

“The removal of that lease sale would lower the projection of future U.S. oil production by about 0.1% and would lower the U.S. natural gas production projection by 0.06%, according to the Interior Department’s Bureau of Ocean Energy Management (BOEM). ‘Thus, the energy security of the United States will remain strong without offshore leasing in the Atlantic during the 2017–2022 program,’ BOEM states in the new OCS proposal.”

 Figure 2: Figure 5-6 from http://www.boem.gov/2017-2022-DPP/ (p. 101 of pdf): Assessment of UTRR of the OCS, 2011 (Atlantic OCS Updated 2014)

Another example of numbers out of context is also related to oil reserves. In the early-2000’s, whether or not to open the Alaska National Wildlife Refuge (ANWR) 1002 Area to drilling was a contentious and controversial topic. Many against drilling said there was only several months of oil there, based on data in a US Geological Survey (USGS) report (https://www.nwf.org/News-and-Magazines/National-Wildlife/Animals/Archives/2010/Arctic-Refuge-Turns-Fifty.aspx). WHAT? This argument was used as a reason not to drill. The USGS 1998 petroleum assessment of the 1002 Area (http://pubs.usgs.gov/fs/fs-0028-01/fs-0028-01.pdf) states that the mean Technically Recoverable oil in the 1002 Area (not including Native Lands or offshore waters) is 7.7 Bbo.  According to the Congressional Record-Senate (April 18, 2002, p. 5027), Senator John Corzine (D-NJ) said ". . . Based on estimates from the U.S. Geological Survey, it is likely to have little more than 6 months' worth of capacity relative to 1 year of U.S. demand. The oil wouldn't even begin to be available for at least 10 years. And it wouldn't reach peak production for 20 years."

Corzine's statement does include the phase "relative to 1 year of U. S. demand" which is key to understanding what is meant by "6 months' worth of capacity". In 2002, US crude oil consumption was 19.761 million barrels of oil PER DAY. If you divide that daily consumption (million barrels per day) into the mean recoverable 1998 estimate for the entire 1002 area (7.7Bbo, undeformed plus smaller geologically deformed region), you get the equivalent of 388 days or, using 1 month=30 days, 12.9 months, of US oil usage. Using instead the 95%-probability estimate of 3.4 Bbo (in just the undeformed part of 1002), the result is 170 days or 5.7 months of US oil consumption. But, could the 1002 Area, if ever in production, produce 20 million barrels a day? Could it be the Nation’s sole source of petroleum? NO. The estimated 1002 Area peak production daily rate ranges from 600,000 - 1.9 million barrels/day from multiple wells over a total 50-60 year life of the field (http://dog.dnr.alaska.gov/Publications/Documents/OtherReports/Oil_Gas_in_ANWR_Review_2003-02.pdf, p.6; http://www.eia.gov/pub/oil_gas/petroleum/analysis_publications/arctic_national_wildlife_refuge/pdf/anwr101.pdf). For comparison, current daily production from the world's largest conventional oil field, Saudi Arabia's megagiant Ghawar field, is ~5 million barrels/day. For the 1002 Area, saying there is only 6 months of oil, without detailing how that number was calculated, without saying that it is supposed to be some sort of useful analogy, is deceptive.

Although here in the USA, we are in the height of "spin" season with the coming Presidential election, sound bites or media reports with partial information or numbers out of context happen at any time in any field, not just the earth sciences. A piece of data or information, no matter how accurate can, without revelation of how it was derived or if isolated from larger trends or data sets, lead to an incorrect assumption on the part of the listener or reader. This can occur by design, to twist or “spin” a meaning, or inadvertently, but for greatest transparency, educated discussion and informed decision making, complete data and background derivations must be available.

* Technically Recoverable means we have the drilling and production technology to access and produce the resource. Sometimes assessment estimates are given as "Economically Recoverable" which means what can be produced with a profit at a particular market price of oil/gas: if the price is too low, as we have seen in the last year, production of some resources, such as unconventional shale gas and shale oil, may not be cost effective.

** (http://twitter.com/SenatorMenendez/status/560157585274572800/photo/1;

oil rig original photo: http://www.shutterstock.com/s/offshore+rig/search.html?page=3&thumb_size=mosaic&inline=214057231)

KEYWORDS AND TERMS: "Atlantic Outer Continental Shelf", OCS, "offshore lease sale"

Rubber duckies serving science (Plastic 1)

Having a young grandchild now, I am pulling out my children’s toys, boxed away for over 15 years, for a new round of use. Among the Brio train sets, Legos, stuffed animals, dolls, Bobo Fett’s space ship, and Teenage Mutant Ninja Turtles are a variety of bath toys. The tub toys include these simple floating animals that I bought in the mid to late-1980’s.

Three remaining tub toys from my original set of four.

In September 1994, I was surprised to see these tub toys on the front page (photo below) of the American Geophysical Union newsletter Eos (abstract:

http://onlinelibrary.wiley.com/doi/10.1029/94EO01056/full)!

The featured Eos tub toys had enjoyed a more cosmopolitan cruise venue than a bath tub, with about 29,000 of them floating across the Pacific to the northwest coast of North America (Gulf of Alaska) after the shipping container transporting them from their Asian birthplace fell off the ship during a storm in January 1992 and broke open. The full Eos article described their service to science tracking ocean currents. The authors, Curtis Ebbesmeyer and W. James Ingraham, modeled possible routes from "deployment" to landfall and predicted subsequent trajectories of duckies, etc that did not wash up on beaches.

Parameters affecting the pathway include, of course, ocean currents, plus "windage": the air resistance or effect of the wind on a moving object. Air currents had a greater effect on the early movement of the tub toys since they are light and ride high in the water. On the other hand, the Nike sneakers in the Eos photo above, from a shipment lost in the Central Pacific in 1990, usually floated upside down with the sole barely above the surface of the water. The higher windage of the tub toys increased their speed across the Pacific after initial entry into the sea, compared to models for objects with lower windage.

The Eos authors discussed the several types of planned and serendipitous ocean current trackers: messages-in-a-bottle (MIB), flotsam, scientific drift bottles. About 2% of planned scientific drift releases are recovered, so the ~400 tub toys recovered from November 1992-August 1993, and an equal amount reported subsequently, are the same order of magnitude. However, the absolute number found was large since typical scientific drift bottle releases at that time were usually only 500-1000 objects. For flotsam to be useful, their point of entry into the ocean must be known so that they aren't confused with other shoreline trash. The Nike shoes had unique identification numbers. The tub toys had no numbers, but from the rather sudden appearance of all four plastic animal types on beaches along the SE coast of Alaska, coupled with reports of the spill, confirmed the shipping flotsam connection.

Computer models projected that, after 2 years, some tub toys still at sea would enter the Bering Sea. Computer modeling of trajectories in earlier years (back to 1946) showed that due to interannual variability in currents, drift objects initially traveling eastward from the central north Pacific reached a turning point close to the west coast of North America, and then could go north, like the 1992 toys, and either circle counterclock-wise around an eastern sub-orbit of the Subarctic Gyre or continue west to the Bering Sea; go south and then float clockwise west towards Hawaii, or not turn at all and head straight on for the coast. The Eos authors speculated that some tub toys could eventually reach the North Atlantic though a combination of ocean water and pack ice transport into the Arctic Sea through the Bering Strait or traverse the Bering Sea and head south towards Japan. Historic examples since the late 19th century of shipwreck debris or planned bottle/container releases support both these long-term travel pathways (http://oceanmotion.org/html/gatheringdata/flotsam.htm).

With additional co-authors, Ebbesmeyer and Ingraham did a follow-up Eos article in January 2, 2007 (http://faculty.wwu.edu/wallin/envr325/tubtoys_ocean_circ.pdf or http://onlinelibrary.wiley.com/doi/10.1029/2007EO010001/pdf) on the toys and other cargo and natural flotsam looking at long-term trajectories. The speed of tub toys travel had eventually decreased, after initial passage to Alaska, due to decreased windage as the toys aged and leaked, barely floating above the surface. Computer simulations were combined with flotsam reports from western Canada and southern Alaska. In that period, the authors found toys had completed up to four round-trips on various sub-orbits of the Subarctic Gyre.

 

Subarctic Gyre and locations of various flotsam releases and finds (Ebbesmeyer and others, 2007).

Flotsam study, of both planned and accidental releases, is the research focus of the Eos articles' lead author, Curtis Ebbesmeyer (http://oceanmotion.org/html/gatheringdata/flotsam.htm). For tracking specific flotsam debris, he uses reports from beachcombers (including beachcombersalert.org which he founded), and solicited information using local media, and beachcomber and lighthouse keeper networks and associations, an example of organized citizen science data collection (another citizen science example: http://app.budburst.org/web/budburst).

So WHY am I discussing PLASTIC in this blog? The current feedstock for plastic is petroleum (mostly in Europe) or natural gas (US manufacture), so it has a natural geologic carbon base. Plastic, and “synthetic” fibers such as rayon or nylon, are synthetic meaning that they are not naturally-occurring organic polymers (long chains of repeating organic units) (http://www.chemheritage.org/discover/online-resources/conflicts-in-chemistry/the-case-of-plastics/all-science-of-plastics.aspx).  Even in its anthropogenically transformed manufactured state, plastic remains part of the global carbon cycle, for better or worse.

Price of gasoline (and changes in other costs) during my post-college career . . .

We all have noticed that gasoline prices have plummeted in recent months. Getting gas several days ago, ($1.65/gallon regular in New Jersey USA), I noted to myself that, except for the oil price crash and immediate rebound in December 2008, prices had not been this low since late 2006.

Since owning my first car, a 1963 Volkswagen Beetle, in 1972-73 (my last year of undergraduate college), the price of gas at various times has stuck in my mind, frequently related to career milestones. In the spring of 1973, the price of regular grade gas was ~$0.35/gallon. In late 1973, the price rose to over $1 due to the Arab Oil Embargo in retaliation for US support of Israel during the October Yom Kippur War. During that shortage, I luckily only had to wait once in one of the infamous long gas station lines since, besides having the fuel-efficient VW, I used daily bus transportation to get to my first job, in Washington, DC.

The next gas price that sticks in my mind was in the summer of 1980 when I was driving 80 miles round-trip daily to my geology Master’s thesis field area in central New Hampshire USA. I was mapping Siluro-Devonian sillimanite-grade metasediments, and associated granites, as part of a revision of the bedrock geologic map of New Hampshire, and now driving a 1967 VW Beetle (green again). My transportation expenses were reimbursed, and I noted the amount, total cost, and price per gallon in my field books. In June 1980, I paid $1.25/gallon; in the autumn, it was $1.23/gallon. The historical charts below, one for crude oil price and one for US gasoline price, show a peak in prices during that time. In adjusted dollars, this was the highest crude price before 2008. The peak in crude oil is in December 1979, but, while rising since late 1979, the peak in the “price at the pump” is delayed until 1981. The Iranian revolution and dramatic decrease in Iranian oil production was the cause of the price increase in crude and refined products (https://en.wikipedia.org/wiki/1979_energy_crisis).

From http://inflationdata.com/articles/inflation-adjusted-prices/inflation-adjusted-gasoline-prices/

From http://inflationdata.com/Inflation/Inflation_Rate/Historical_Oil_Prices_Chart.asp

When I eventually went back to graduate school for a Ph.D., it was 1993, and I was commuting 180 miles round-trip four days a week from my home in Pennsylvania (PA) to the Lamont-Doherty Earth Observatory of Columbia University, just outside New York City. (I certainly was not the only person doing that daily commute: hundreds of people from eastern PA commute by car or bus to NYC for work.) I would buy my gas a couple miles from home in New Jersey where price of gas is historically a bit cheaper than Pennsylvania, and gas stations are only full-service. (New Jersey and Oregon are the only US states where self-service gas is illegal.) The general price was $1.15 - $1.25/ gallon during my several years of commuting, not really different from 13 years before. (I did visit Oregon in 1998, and the price there was notably higher : ~$1.80; I don’t know if that is due to distribution costs, wages, or taxes.)

From then until 2005, I don’t remember anything remarkable about the price of gas, but on my way in fall 2005 to visit the site of the ICDP-USGS deep drilling project into the moat of the Chesapeake Bay impact structure, I remember the gas price on the Delmarva peninsula was ~$1.80, definitely higher than NJ or eastern PA. The gas price chart above shows 2005 was the start of the steep increase in crude oil prices, culminating in the summer 2008. During that peak in gas prices, I was commuting 450 miles round-trip per week from PA to the US Geological Survey, outside Washington, DC, for my postdoctoral fellowship work (2006-08) on the Chesapeake Bay impact structure, and eventually paying over $4/gal for gas.

Before the recent fall in oil prices, in 2012-2013, the price of gas was around $3.50, so a tenfold (10X) increase since $0.35/gal in 1973. How does this 10X increase, compare to some other prices I can remember over the same general period? (I am listing actual or nominal prices, not adjusted for inflation.)

• In January 1968, my father bought a new Mustang convertible car for $3200 (price remembered by my brother). In 2016, a Mustang V6 convertible retailed for $30,045, a 9.4-times increase. This is comparable to the 10X increase in gas prices over approximately the same period.
• My first apartment, in the Riverhouse complex in Arlington, Virginia, was about $150/month in 1973-74. Today the same studio apartment in the same building is $1429/month, a 10X increase.
• My parents bought a house in 1971 for $90,000 (sold it in 1995); it most recently sold in 2013 for $1,445,000, an increase of 16X. 
• The tuition at Dartmouth College for 1972-73 for one year was ~$3100; for 2014-15, it was $46,764: an increase of 15 times over that 42 years before. The increase in these last two cases is similar, but both are more than the 10X increase in gasoline prices.

On the other hand, looking at changes in salaries and wages is not encouraging:

• In 1973, for my first job, I was a Foreign Service Officer (US diplomatic corps) earning a starting salary of $9500/year. Currently, an FSO just out of college living in Washington, DC, would annually earn $60,646 (http://www.pathtoforeignservice.com/foreign-service-officer-salary-a-comprehensive-guide/). The increase is 6.4 times.
• The minimum wage in 1973 was $1.60 (http://www.dol.gov/whd/minwage/chart.htm). Today it is $7.25, an increase of only 4.5 times.

With the information on the Riverhouse apartment vs FSO salary, we can also examine what portion of that income goes to housing now compared to forty years ago. In 1974, 19% of my income went to apartment rent; today, that portion (same apartment, starting FSO salary) would be 28%.

Admittedly, these price change examples are few. Other commodities of daily living like eggs, milk, clothing are not included. My parents' house was in an upscale suburb of New York City, Dartmouth College is a selective private university, and, therefore, increases may not be representative. (And, I certainly am no economist.) But, these few examples of relative increase in cost put some numbers on the feelings, despite recovery from the Great Recession of 2008-09, of personal economic frustration in the US, particularly the affordability of US higher education and housing relative to income.

Geology and Gerrymandering: Anthracite and Congressional district boundaries in Pennsylvania (Geosciences Congressional Visits Day postscript)

In the last post, I wrote about Geosciences Congressional Visits Day, most recently held on September 30, 2015. My four-person Pennsylvania (PA) state team's first visit that day was to the office of my Representative, Matt Cartwright, of the northeast PA 17th district. As we were waiting for our appointment with a staff member, I was pointing out, to one of my western PA colleagues, where I lived (Easton) on the big district map on the wall, and it became apparent to me that the strange shape of the district encompasses most of the PA anthracite coal fields.

 

Above I have roughly drawn the general outline of the district onto the Coal Distribution Map of Pennsylvania, which includes county boundaries. The cities of Scranton and Wilkes Barre (Cartwright's home) are in the northernmost arm of the district in the north half of the Northern Anthracite Field. The ENE-WSW spine of the district skims along the north edge of the Blue/Tuscarora/Kittatinny Mountain ridge AKA Blue Mountain Structural Front (= the southern border of the Valley and Ridge province whose Lower to Upper Paleozoic strata were folded in the closing stages of the Late Paleozoic Alleghanian orogeny) and encloses the Southern Anthracite Field. The Middle Fields are mostly in the 11th Congressional district.

Our district truly looks like a lobster, or eurypterid (the New York state fossil), or a salamander without back legs. That brings up "gerrymandering" (https://en.wikipedia.org/wiki/Gerrymandering_in_the_United_States ): the drawing or partitioning of legislative district boundaries within a state to favor a particular party or group of voters. Although it was practiced even before the signing of the US Constitution in 1789, the term comes from 1812 when Massachusetts governor Eldridge Gerry redrew state senate districts to the advantage of the then-Democratic-Republican party: one Boston district's outline resembled that of a sala-"mander". Despite the arthropodian or reptilian shape of my district, it is certainly not the strangest: some parts of some districts are connected only by narrowest threads of land (https://www.washingtonpost.com/news/wonk/wp/2014/05/15/americas-most-gerrymandered-congressional-districts/). Another article published later than the original posting of this blog (https://www.washingtonpost.com/news/wonk/wp/2016/01/13/this-is-actually-what-america-would-look-like-without-gerrymandering/), and following the President's State of the Union speech request for thoughtful redistricting, includes a discussion on the pros and cons of computer-drawn districts, and includes an informative general video on gerrymandering.

Pennsylvania's federal Congressional districts were last redrawn by the Republican-dominated state legislature before the 2012 elections.* The number of districts decreased from 19 to 18, due to changes in population. The redistricting pitted some incumbents against each other in the 2012 election. It also eliminated some "blue-dog" Democrats, who sometimes voted more conservatively but whose party affiliation benefited Democrat numbers in the House (https://www.washingtonpost.com/blogs/2chambers/post/blue-dog-democrats-trying-to-stave-off-extinction-following-pennsylvania-losses/2012/04/25/gIQAjUoRhT_blog.html). The only Congressional districts currently with Democratic Representatives in Pennsylvania are around the big cities of Philadelphia (east) and Pittsburgh (west) and my 17th district. Much like the national electoral college maps after the 2008 and 2012 Presidential elections, the blue or Democratic Pennsylvania districts cover relatively little geographic area, but have large populations.

 

Pennsylvania Congressional districts (2013-2018) by political party affiliation of Representative (red-Republican; blue- Democratic) [https://en.wikipedia.org/wiki/Pennsylvania's_congressional_districts#/media/File:2012_Pennsylvania_congressional_districts_by_party.png]

Most of the 17^th district is geologically located in the Valley and Ridge Province (and similar but anomalous Lackawanna syncline of the Northern Anthracite Field). But Easton, where I live, is in the southeastern “claw” or “foot” extending across the Blue Mountain Structural Front into the Ordovician of the Great Valley province (see geologic map below). The Great Valley carbonates (southern part of valley) and shales (north) are commercially called the “cement belt” and the “slate belt” respectively, and in historic, but outdated, geologic nomenclature were the classic miogeosyncline (platform carbonates) and eugeosyncline (siliciclastic flysch) of the Laurentian margin. The Great Valley province, and Easton, are generally bordered on the south by slivers of the pre-Cambrian famously-radon-rich Hudson Highlands/Reading Prong metamorphic/igneous rocks.

So redistricting removed my city, Easton (the home of Crayola Crayons and the championship heavyweight boxer, Larry Holmes) from the rest of the Lehigh Valley (15^th Congressional district), with which it shares a common geologic setting and commercial/ educational/ health care infrastructure and historic heritage. HOWEVER, on the plus side, both districts do have representatives, Matt Cartwright (D-PA17*, my current district) and Charlie Dent (R-PA15*; former district and Representative), that value federally-funded STEM education and science research! 

* UPDATE: In early 2018, the Pennsylvania Supreme Court redrew the state's federal Congressional district map to remove effects of gerrymandering. My small city, Easton, rejoined the rest of Northampton county and the geographic Lehigh Valley. With new logical east-to-west renumbering, we are now the 7th district while Matt Cartwright won re-election in the new 8th district. Our 7th district Representative at that time, Susan Wild, was new to Congress since Charlie Dent did not seek re-election. District lines were re-drawn again for 2024 after the 2020 census, tweaking the 2018 boundaries. Matt Cartwright and Susan Wild (both Democrats) lost re-election in 2024.