JOURNAL OF CREATION 30(1) 2016 || PERSPECTIVES The ‘Great Unconformity’ and associated geochemical evidence for Noahic Flood erosion Harry Dickens he Bible’s Flood account describes Tthe greatest rain event ever recorded. Forty days and nights of rain falling on the earth (Genesis 7:12) would have caused immense denud­ ation of landmasses around the globe. Evi dence for this is provided by a key stratigraphic surface and by associated geochemical signatures. Nature and extent of the ‘Great Unconformity’ The term ‘Great Unconformity’ was originally used to describe the prominent stratigraphic surface exposed in the Grand Canyon that separates the Lower Cambrian Tapeats Sandstone (of the Sauk cratonic sequence) from the underlying Precambrian strata (Granite Gorge Metamorphic Suite and tilted sedimentary rocks of the Grand Canyon Supergroup).1 The Great Unconformity can be traced across North America and globally, including most of today’s southern hemisphere landmasses, along with Western Europe and Siberia—this makes it the “most widely recognised and distinctive stratigraphic surface in the rock record”.2 This surface in most regions separates continental crystalline base­ ment rock from overlying undeformed Cambrian marine fossil­bearing sedimentary rock. It thus records the onset of the denudation of continental 8 PERSPECTIVES || JOURNAL OF CREATION 30(1) 2016 Geochemical signatures consistent with continental denudation Numerous geochemical signatures indicative of continental denudation have been described from Upper Proterozoic strata.2,17 Strong evidence for an increase in continental erosion and weathering products to the global ocean is Figure 1. Summary of major geochemical and sedimentary patterns derived from Upper Proterozoic provided by measurements of Ca2+ in to Phanerozoic strata (modified from Peters and Gaines2) fluid inclusions.2 Concentrations of Ca2+ show a precipitous increase from crust, followed by the first major surface of the crystalline basement Upper Proterozoic strata to a peak in marine transgression (Sauk Sequence) of the northernmost Arabian­Nubian Cambrian strata.18 Much of this near 9 and sediment accumulation on the Shield. threefold increase in Ca2+ has been 2 continents (figure 1). Evidence of sea level rise includes a at tributed to greater chemical we­ The Great Unconformity is a clear universal fining upward sequence that athering of continental crust during the case where uniformitarianism does has been observed in Cambrian and Sauk marine transgression.2 not apply. Extensive planation surfaces Lower Ordovician strata in locations The abundance and distribution of are not forming today but channel across the USA (Sauk Sequence), the phyllosilicate mineral glauconite, 3 erosion is occurring today. The very 3+ Greenland, UK, Russia, Australia, (K,Na)(Fe ,Al,Mg) (Si,Al) O (OH) , high energy erosion of the global 2 4 10 2 Bolivia, and Ghana.10 A classic fining in Cambrian sediments likely required Flood would have had the capacity upward succession occurs in Grand rapid authigenesis due to an unusually to wear down Precambrian cratons Canyon Cambrian strata.11 large flux of continental weathering to simultaneously form the Great products, particularly Fe3+, K+ and A Flood model has been proposed Unconformity as a peneplaned surface H SiO , during the formation of to explain the erosion of the Great 3 4 over tremendous areas of the earth. the Great Unconformity.2 Trough Unconformity and subsequent Most Flood geologists point to this cross-stratified deposits of glauconitic deposition of the Cambrian Tapeats widespread erosional discontinuity in mineral­rich accumulations (glau­ the geological record, known as the Sandstone, Bright Angel Shale, and carenites, i.e. coarse­grained glau­ Great Unconformity, as indicating the Muav Limestone as floodwaters conitic mineral pellets) found in Flood’s abrupt onset.4 advanced in areas now known as Cambro­Ordovician strata indicate The Sauk Sequence often has Nevada, Arizona, and New Mexico.11 a high energy environment. The quartz and feldspar­rich basal sands Along with tremendous erosion of abundance of thoroughly cross­ overlying Precambrian basement the exposed continental landmasses, stratified deposits also indicates that, across North America and North torrential rain would likely have at least on the cross­set scale, individual 2,5 Africa. Similarly, basal sandstone caused huge mass flows sweeping pellets were deposited and covered by units are widespread in the large down into the adjacent seas. Upper other laminae very rapidly.19 2 (2 million km surface area) Australian Proterozoic mixtites, interpreted by Precipitation of carbonate sedi­ intracratonic sedimentary basin known secular scientists as occurring during ments also reached a peak in the Phan­ as the Centralian Superbasin, which ‘glaciations’ (figure 1), are more likely erozoic, as recorded in the Cambrian­ is believed to have formed at the Lower Ordovician strata of the Sauk mass flow deposits formed in the early time of the break­up of the Rodinia Sequence of North America.20–22 stage of Noah’s Flood due to enormous supercontinent.6 The Heavitree Pet rographic textures (displasive rainfall on the continents.12–15 Other Quartzite is the basal sandstone unit growth of calcite crystals within the of the Amadeus Basin, which is in Upper Proterozoic mixtites are found claystone matrix) and depleted δ13C turn part of the Centralian Superbasin.7 in the Appalachian Mountains, values provide evidence of rapid The Heavitree Quartzite has been Scandinavia, Russian Platform, direct pre cipitation of carbonate described as an early Flood formation.8 Siberia, Caledonian Mountains, at the sediment­water interface.23 In southern Israel the fossiliferous northwest China, Brazil, central and Calcium carbonate precipitation does Cambrian sedimentary strata of the southern Africa, and northwest, central not require deep time as has been early Flood sit directly on the eroded and southern Australia.16 demonstrated by laboratory studies.24 9 JOURNAL OF CREATION 30(1) 2016 || PERSPECTIVES Thus huge volumes of Cambro­ weathering, and changes in global ocean 15. Austin, S.A. and Wise, K.P., The Pre­Flood/ Flood boundary: as defined in Grand Canyon, Ordovician carbonate globally could chemistry are indicated by numerous Arizona and eastern Mojave Desert, California; have precipitated rapidly, likely within geochemical signatures associated in: Walsh, R.E. (Ed.), Proceedings of the Third International Conference on Creationism, months during the year of Noah’s with this boundary. The evi dence is Creation Science Fellowship, Pittsburgh, PA, Flood. consistent with what would be expected pp. 37–47, 1994. During the early stage of the Flood, from the effects of enormous rainfall 16. Schermerhorn, L.J.G., Late Precambrian Mixtites: Glacial and/or NonGlacial? American the enormous runoff from continents and rising Flood waters/tsunami­like J. Science 274:673–824, 1974. may have contributed to the drawdown waves on the continents during the early 17. McKenzie, N.R., Hughes, N.C., Gill, B.C. of carbon dioxide described for the Noahic Flood. and Myrow, P.M., Plate tectonic influences on 25 Neoproterozoic­early Paleozoic climate and Cryogenian, since chemical weath­ animal evolution, Geology 42(2):127–130, 2014. ering of silicate rocks is a major car bon References 18. Brennan, S.T., Lowenstein, T.K. and Horita, dioxide sink.26,27 J., Seawater chemistry and the advent of 87Sr is a radiogenic daughter isotope 1. Yochelson, E.L., The Lipalian interval: a biocalcification,Geology 32:473–476, 2004. forgotten, novel concept in the geologic column, 87 19. Chafetz, H.S. and Reid, A. Syndepositional of Rb and is found in silicate rocks Earth Science History, 25:251–269, 2006. shallow­water precipitation of glauconite minerals, such as granite. The abundance of 2. Peters, S.E. and Gaines, R.R., Formation of Sedimentary Geology 136:29–42, 2000. radiogenic 87Sr relative to ‘common’ the ‘Great Unconformity’ as a trigger for the 20. Ronov, A.B., Khain, V.E., Balukhovsky, A.N. Cambrian explosion, Nature 484:363–366, 2012. 86Sr in a sample of sediment is related and Seslavinsky, K.B., Quantitative analysis 3. Oard, M., Flood by Design: Receding Water of Phanerozoic sedimentation, Sedimentary to the amount of sediment that orig­ Shapes the Earth’s Surface, Master Books, Green Geology 25:311–325, 1980. inated from erosion of continental crust Forest, AR, 2008. 21. Walker, L.J., Wilkinson, B.H. and Ivany, L.C., as opposed to that originating from the 4. Baumgardner, J., Could most of the earth’s U, Continental drift and Phanerozoic carbonate Th, and K have been in the mantle prior to the accumulation in shallow­shelf and deep­marine ocean. The observed increase in Upper Flood? J. Creation, 26(3), 47–48, 2012. settings, J. Geology 110:75–87, 2002. Proterozoic strontium isotope ratios 5. Clarey, T., Reading African strata, Acts & Facts 22. Ginsburg, R.N., Actualistic depositional models for the Great American Bank (Cambro­Ordovi­ 87 86 44(9), 2015. Sr/ Sr (figure 1) has been explained cian); in: Eleventh International Congress on by accelerated rates of erosion during 6. Allen, P.A. and Armitage, J.J., Cratonic Basins, Sedimentology, Abstracts of Papers, Inter­ in Tectonics of Sedimentary Basins: Recent national Association of Sedimentologists, Mc­ the so­called Pan­African orogeny, Advances, Edited by Busby, C. and Azor, A, Master University, Hamilton, Ontario, Canada, and high crustal erosion rates have Blackwell Publishing, 2012. p. 114, 1982. been inferred from Cambrian 87Sr/86Sr 7. Lindsay, J.F., Heavitree Quartzite, a 23. Gaines, R.R., Hammarlund, E.U., Hou, X., Qi, C., 28 Neoproterozoic (Ca 800–760 Ma), high­energy, Gabbott, S.E., Zhao, Y., Peng, J. and Canfield, D.E., values. tidally influenced, ramp association, Amadeus Mechanism for Burgess Shale­type preservation, The subsequent decline in 87Sr/86Sr Basin, central Australia, Australian J. Earth PNAS 109(14):5180–5184, 2012. Sciences 46:127–139, 1999. ratio in post­Cambrian strata indicates 24. Wojtowicz, J.A., Factors affecting precipitation 8. Walker, T., The sedimentary Heavitree Quartzite, of calcium carbonate, J.