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The Origin and Occurrence of Subaqueous Sedimentary Cracks

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The Origin and Occurrence of Subaqueous Sedimentary Cracks Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021 The origin and occurrence of subaqueous sedimentary cracks SEAN MCMAHON1*, ASHLEIGH VAN SMEERDIJK HOOD1 & DUNCAN MCILROY2 1Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, New Haven, CT 06511, USA 2Department of Earth Sciences, Memorial University of Newfoundland, St John’s, NL, A1B 3X5, Canada *Correspondence: [email protected] Abstract: The rock record attests that sediments have cracked at or below the sediment–water interface in strictly subaqueous settings throughout Earth history. In recent decades, a number of hypotheses have been advanced to explain this phenomenon, but these are widely regarded as being mutually exclusive and there is little consensus about which model is correct. In this paper, we first review the geometries, lithologies and range of facies in which subaqueous sedimen- tary cracks occur in the geological record, with particular attention to cracks in carbonates. We then evaluate current models for subaqueous cracking, emphasizing that different models may be cor- rect with respect to different sets of cracks, but that cracking is generally a two-step process involv- ing sediment stabilization prior to disruption. We also present the results of some simple new experiments designed to test the dominant models of crack formation. These results demonstrate for the first time that microbial mats can produce thin, shallow cracks at the sediment–water inter- face. We conclude that the presence of cracks in marine, brackish and lacustrine rocks should not be used uncritically to infer fluctuations in salinity in the depositional environment. Supplementary material: A video showing a micro-CT scan of a hand-sample from the Monte- ville Formation, South Africa is available at https://doi.org/10.6084/m9.figshare.c.3580673 Gold Open Access: This article is published under the terms of the CC-BY 3.0 license. Marine and lacustrine rocks throughout the geolog- or partially correct, in particular contexts. How- ical record preserve cracks demonstrably opened ever, because many workers assume a gel de- in soft substrates at or below the sediment–water watering (synaeresis) origin for subaqueous cracks interface, without any possibility of desiccation. (e.g. Fairchild 1980; Carroll & Wartes 2003; Here, we reserve the term ‘crack’ for originally Bhattacharya & MacEachern 2009; Buatois et al. sharp-walled, approximately planar cavities formed 2011) – and also because it has become a con- predominantly by brittle failure rather than fluid ventional descriptive term uncritically used for interpenetration or dissolution. Most are filled either all non-desiccation cracks – the term ‘synaeresis by sediment or by authigenic minerals and super- crack’ retains wide currency. Harazim et al. ficially resemble desiccation cracks, although they (2013) preferred ‘intrastratal shrinkage crack’ as a typically lack mud curls (Tanner 2003). This resem- more neutral alternative, which is appropriate for blance has tempted some researchers to suggest that cracks that form by sediment shrinkage below the subaqueous cracking, like sub-aerial cracking, has a sediment–water interface. Here, we use the broader single universally applicable explanation (e.g. Pratt term ‘subaqueous sedimentary cracks’ to avoid 1998a), whereas others have explicitly rejected this implying either a causative mechanism or a position assumption (Davies et al. 2016). The most widely with respect to the sediment–water interface. cited models invoke shrinkage due to the expulsion of water from swelling clays or flocculating par- ticles, either as a result of salinity changes, gravi- Subaqueous cracks in the rock record tational compaction or seismic disturbance (Burst Subaqueous sedimentary cracks representing a wide 1965; Plummer & Gostin 1981; Pratt 1998a). In range of ages, morphologies, sediment compositions recent decades, several occurrences have been and palaeoenvironments have been documented attributed to the effects of microbial biostabilization (Table 1). Occurrences have been reported from (e.g. Pflueger 1999; Gehling 2000; Harazim et al. marine, marginal, lacustrine and fluvial deposi- 2013). Each of these explanations may be correct, tional environments, with a possible shoaling trend From:Brasier, A. T., McIlroy,D.&McLoughlin, N. (eds) 2017. Earth System Evolution and Early Life: A Celebration of the Work of Martin Brasier. Geological Society, London, Special Publications, 448, 285–309. First published online November 30, 2016, https://doi.org/10.1144/SP448.15 # 2017 The Author(s). Published by The Geological Society of London. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics 286 Downloaded from Table 1. Occurrence of subaqueous sedimentary cracks in the geological record Stratigraphy/ Age Shape Host lithology Infill CO3 MISS Inferred Reference location setting Kauai, Hawaii Quaternary P: semi-polygonal Carbonate None 33Speleothem Le´ve´ille et al. (2000) speleothems in basalt http://sp.lyellcollection.org/ West Basin Lake, Quaternary V: jagged, curved Aragonite, dolomite, Void space; 33Lacustrine Van Leeuwen (2013); Victoria, hydromagnesite carbonate field observations Australia cements Green River Fm, Eocene V: ptygmatic Siltstone– Carbonate mud/ 3 ND Sublittoral To¨ro¨ et al. (2013) Wyoming, USA carbonate– silt mudstone S. M Xialiao Basin, Palaeogene V: ptygmatic Mudstone Sand 66Lacustrine/ Hsiao et al. (2010) C China swamp MAHON Cujupe Fm, Brazil Cretaceous– P: polygonal Mudstone (with ND 6 ND Estuarine/ Rossetti (1998) Palaeogene interbedded bay (*) sandstone) Austral Basin, Late Cretaceous V: ptygmatic Mudstone Sand 6 ND Fluvio-deltaic Buatois et al. (2011) ET AL. byguestonSeptember29,2021 Argentina Dunvegan Fm, Cretaceous V: ptygmatic Mudstone Silt–fine sand ND ND Fluvio-deltaic Bhattacharya & Alberta, Canada spindles MacEachern (2009) Dunga oilfield, Cretaceous V: V-shaped, Black heterolithic Sand 3 6 Shoreface/ Cazier et al. (2011) Kazakhstan branching sandstone deltaic (*) downwards Raimalro Lst., Middle Jurassic P: curlicue Micritic sandstone Calcite 3 6 Marine Patel et al. (2013) Kuar Bet Mb, India Lockatong Fm, Triassic P: sinuous Calcareous siltstone Analcime, 3 ND Lacustrine Van Houten (1962) New Jersey/ dolomite Philadelphia, USA Liard Fm, British Middle Triassic V: vertical spindles Dolomitic ND 33Lagoonal Zonneveld et al. Columbia, mudstone/ (2001) Canada sandstone Lucaogou Fm, Late Permian V: branching Dolomitic mudstone 3 ND Lacustrine Carroll & Wartes NW China spindles (2003) Pebbley Beach Fm, Early Permian V: ptygmatic, Carbonaceous Carbonaceous 6 ND Estuarine/ Fielding et al. (2006) New South V-shaped mudstone deltaic Downloaded from Wales, Australia Orcadian Basin, Devonian P: bird’s foot, Shale Coarse silt 3 ND Lacustrine Donovan & Foster UK spindles (1972) V: ptygmatic Murzuk Basin, Silurian P: bird’s foot, Sandstone and Sand ND 3 Shallow Pflueger (1999) Libya sinuous, curlicue, (inferred) marine rectangular mudstone Beach Fm, Early Ordovician V: ptygmatic Shale Sand 6 3 Marine Harazim et al. (2013) Newfoundland, http://sp.lyellcollection.org/ ORIGIN OF SUBAQUEOUS SEDIMENTARY CRACKS Canada Petit Jardin, Berry Late Cambrian V: straight, jagged, Dolomitic Mud chips and 3 6 Shallow Cowan & James Head Fms, pinching and mudstone–oolite ooids, calcite marine (1992) Newfoundland, swelling, spar, fine Canada branching dolomite downwards cement Gushan and Late Cambrian P: reticulate Thin limestone Dolomitic 3 6 Shallow Chen et al. (2009) Chaomidian V: vertical interbeds marlstone carbonate Fms, China platform St Lawrence Fm, Late Cambrian P: isolated curving Fine dolomitic Sand 3 Kinneyia Marine Hughes & Hesselbo Mississippi spindles argillite (1997) Valley, USA V: ptygmatic byguestonSeptember29,2021 spindles Reno Mb, Lone Late Cambrian P: spindles forming Thin clay-bearing ND 6 3 Marine Eoff (2014) Rock Fm, partial polygons sandstone Wisconsin, USA Hales Limestone Late Ordovican– P: polygonal Calcareous shale Calcite spar 3 6 Marine slope Cook & Taylor case study, Early V: V-shaped (1977); this paper Nevada, USA Cambrian Bonahaven Fm, Neoproterozoic P: spindles; Dolostone, silty Sand 3 6 Shallow Fairchild (1980) Mb 3 incomplete dolomite subtidal polygons V: ptygmatic Bonahaven Fm, Neoproterozoic P: curving, Sandstone Sand ND 6 Intertidal/ Tanner (1998) UK quasi-polygonal shallow V: V-shaped, marine branching, with flaring of host layers (Continued) 287 288 Table 1. Occurrence of subaqueous sedimentary cracks in the geological record (Continued) Downloaded from Stratigraphy/ Age Shape Host lithology Infill CO3 MISS Inferred Reference location setting Irby Siltstone, Neoproterozoic V: Ptygmatic, Dolostone Dolospar, silt 3 ND Low energy, Calver & Baillie Tasmania, tapered marine (1990) Australia Brachina Fm, ABC Ediacaran P: Isolated spindles Mudstone Sand, silt 6 ND Shallow Plummer & Gostin http://sp.lyellcollection.org/ Range Quartzite, marine (1981) South Australia Masirah Bay Fm, Ediacaran V: Branching Sandstone (70–80% Sandstone 66Shallow Allen & Leather Oman spindles and quartz) marine– (2006) incomplete shoreface polygons S. M Nuccaleena Fm, Ediacaran Sheet cavities, Dolomite Dolomite marine 3 6 Deep marine Field observations C South Australia straight to curved cements, spar MAHON Keilberg Mb, Ediacaran Sheet cavities, Dolomite Dolomite marine 3 6 Deep marine Hoffman & Namibia straight to curved cements Macdonald (2010); field observations Ediacara Mb, Ediacaran P: sinuous and Sandstone Sand 6 3 Marine Gehling (2000) ET AL. byguestonSeptember29,2021
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