Deposition of a saline giant in the Mississippian Windsor Group, Nova Scotia, and the nascent Late Paleozoic Ice Age

    Deposition of a saline giant in the Mississippian Windsor Group, Nova Scotia, and the nascent Late Paleozoic Ice Age Laura A. Macneil, Peir K. Pufahl, Noel P. James PII: DOI: Reference:

S0037-0738(17)30236-1 doi:10.1016/j.sedgeo.2017.10.010 SEDGEO 5253

To appear in:

Sedimentary Geology

Received date: Revised date: Accepted date:

29 July 2017 23 October 2017 24 October 2017

Please cite this article as: Macneil, Laura A., Pufahl, Peir K., James, Noel P., Deposition of a saline giant in the Mississippian Windsor Group, Nova Scotia, and the nascent Late Paleozoic Ice Age, Sedimentary Geology (2017), doi:10.1016/j.sedgeo.2017.10.010

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Deposition of a saline giant in the Mississippian Windsor Group, Nova Scotia, and the nascent Late Paleozoic Ice Age

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LAURA A. MACNEILa,1, PEIR K. PUFAHLa,* and NOEL P. JAMESb

a) Department of Earth and Environmental Science, Acadia University, Wolfville, NS, B4P 2R6, Canada (E-mail: [email protected] & [email protected])

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b) Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, ON, K7L 3N6, Canada (E-mail: [email protected])

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* Corresponding author: Peir K. Pufahl

Current address: Royal Tyrrell Museum of Paleontology, Box 7500, Drumheller, AB, T0Y 0J0

ACCEPTED MANUSCRIPT Abstract Saline giants are vast marine evaporite deposits that currently have no modern analogues

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and remain one of the most enigmatic of chemical sedimentary rocks. The Mississippian Windsor Group (ca. 345 Ma), Maritimes Basin, Atlantic Canada is a saline giant that consists of

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two evaporite-rich sedimentary sequences that are subdivided into five subzones. Sequence 1 is

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composed almost entirely of thick halite belonging to Subzone A (Osagean). Sequence 2 is in

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unconformable contact and comprised of stacked carbonate-evaporite peritidal cycles of Subzones B through E (Meramecian). Subzone B, the focus of research herein, documents the

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transition from wholly evaporitic to open marine conditions and thus, preserves an exceptional window into the processes forming saline giants.

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Lithofacies stacking patterns in Subzone B reveal that higher-order fluctuations in

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relative sea level produced nine stacked parasequences interpreted to reflect high frequency

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glacioeustatic oscillations during the onset of the Late Paleozoic Ice Age. Each parasequence reflects progradation of intertidal and sabkha sediments over subtidal carbonate and evaporite deposits. Dissimilarities in cycle composition between sub-basins imply the development of contrasting brine chemistries from differing recharge rates with the open ocean. What the Windsor Group shows is that evaporite type is ostensibly linked to the amplitude and frequency of sea level rise and fall during deposition. True saline giants, like the basinwide evaporites of Sequence 1, apparently require low amplitude, long frequency changes in sea level to promote the development of stable brine pools that are only periodically recharged with seawater. By contrast, the high amplitude, short frequency glacioeustatic variability in sea level that controlled the accumulation of peritidal evaporites in Subzone B produce smaller, subeconomic deposits with more complex facies relationships. Keywords: marine evaporites, peritidal cycles, saline giant, climate, Late Paleozoic Ice Age 2

ACCEPTED MANUSCRIPT 1. Introduction Saline giants are large marine evaporite successions containing economic deposits of

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gypsum, anhydrite, salt and potash that can cover >1 000 000 km2 (Giles and Boehner, 2003; Kendall, 2010; Manzi et al., 2012). Most formed in restricted basins where intense evaporation

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of seawater under an arid climate promoted the precipitation of these soluble salts to create thick,

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aerially extensive beds (Sonnenfeld, 1984; Kendall, 2010). Thus, saline giants possess a sensitive

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record of paleoenvironmental change because lithofacies mineralogy and stacking reflect the complex interplay between climate, basin geometry, sea level and oceanography (Warren, 2010).

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Unfortunately, precise modern analogues are lacking as modern marine evaporite depositional systems are small in relation to ancient evaporite deposits (Warren, 2006; 2010).

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Modern evaporites are generally associated with sabkhas or salterns (Lokier, 2013), and have a

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maximum lateral extent of ca. 2 500 km2 (Warren, 2010). Many saline giants are interpreted to

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represent shallow and deep-water precipitation in large, restricted intracratonic basins and along platform margins (Schenk et al., 1994; Sarg, 2001; Kendall, 2010; Warren, 2010). Deposition in intracratonic basins produced basinwide evaporites containing deep-subtidal precipitates that shallow from gypsum to anhydrite, halite, and when basin restriction was severe, potash (Kendall, 2010). Platform evaporites are synonymous with basin-margin evaporites and generally reflect precipitation along the coast in peritidal environments (Kendall, 2010). The purpose of research herein is to further refine what is known about the accumulation of saline giants by investigating the Mississippian Windsor Group, Nova Scotia, Canada. The Windsor Group is a 1 to 2 km-thick saline giant recording ca. 14 million years of intermittent connectivity between the Maritimes Basin and the Rheic Ocean (Schenk et al., 1994; Giles, 2009; Jutras et al., 2015). It consists of two sequences that together record freshening of the Maritimes Basin through two complete sea level cycles (Gibling et al., 2008; this study). 3

ACCEPTED MANUSCRIPT The focus of this paper is to understand the paleoenvironments of deposition and oceanography marking the transition between these two sequences. This change is an intelligible

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record of the shift from basinwide to platform evaporites, and is therefore important for understanding how subtle differences in sea level, related basin restriction and climate,

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influenced the formation of saline giants. Such information is used to construct a depositional

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and oceanographic model for the Windsor Group, aspects of which are applicable to other

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ancient evaporites.

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2. Geological setting

The Windsor Group is a 1 to 2 km-thick carbonate-evaporite succession that accumulated

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between ca. 344 and 330 Ma in the Maritimes Basin of Atlantic Canada (Fig. 1; Schenk et al.,

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1994; von Bitter et al., 2003; Giles, 2009). The development of this intracratonic basin is related

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to the Acadian orogeny of the Appalachian Orogen (Fig. 2; Waldron et al., 2010; White and Barr, 2012). Subsidence began in the Late Devonian when rifting of Laurentia produced basalts and rhyolites of the Lower Mississippian Fountain Lake Formation and contemporaneous coarse clastics of the Horton Group (Boehner, 1989; von Bitter and Moore, 1992; Martel and Gibling, 1996; Sangster et al., 1998). Deposition of the Windsor Group began in the early Middle Mississippian when thermal subsidence and eustatic sea level rise flooded the Maritimes Basin with water of the Rheic Ocean (Lynch and Tremblay, 1994; Boehner et al., 2002). Strata rest on an angular unconformity produced when the underlying Fountain Lake Formation and Horton Group were tilted during the final stages of rifting (Gibling et al., 2008). Antecedent topography was an important barrier that restricted circulation in the newly formed Windsor Sea (Gibling et al., 2008; this study). Laurentia’s paleoequatorial position, an arid climate, and restriction from normal open marine conditions promoted widespread carbonate 4

ACCEPTED MANUSCRIPT and evaporite deposition in variably interconnected sub-basins (Fig. 3; Schenk, 1967; 1969; Schenk et al., 1994). The accumulation of the Windsor Group persisted into the late Middle

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Mississippian when sea level fall produced an unconformity that marks the change to the terrigenous clastics of the Upper Mississippian Mabou Group (Calder, 1998).

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The Windsor Group is ostensibly linked to an interglacial period that punctuated the Late

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Paleozoic Ice Age; at this time alpine glaciers dominated peripolar regions of southern

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Gondwana (Montañez and Poulsen, 2013). On several continents, this interglacial is characterized by high-frequency transgressive-regressive cycles, indicating that glacioeustasy in

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the Middle Mississippian was driven by rapidly waxing and waning glaciers under a dynamic

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2.1. Windsor Group stratigraphy

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climatic regime (Isbell et al., 2003; Rygel et al., 2008; Montañez and Poulsen, 2013).

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The Windsor Group consists of two depositional sequences recording two complete sea level cycles that can be subdivided into five subzones, A through E (Fig. 4; Giles, 2009; this study). Sequence 1 is composed entirely of Subzone A, which rests with angular unconformity over lower Middle Mississippian terrestrial deposits of the Horton Group (Schenk, 1969; von Bitter et al., 2003). The ubiquity of halite at the top of this sequence suggests evaporative concentration under severely restricted conditions (Schenk et al., 1994). The upper contact is a disconformity marked by continental red beds recording a few million years of terrestrial sedimentation (von Bitter et al., 2003; Giles, 2009). Sequence 2 contains Subzones B, C, D and E, all of which are in conformable contact. These subzones are formed of stacked, aggradational, brining-upwards peritidal cycles (Boehner, 1979). The diversity of evaporitic and limestone facies implies deposition under variably restricted conditions (Boehner, 1989; Giles, 2009). The upper contact of Sequence 2 is the 5

ACCEPTED MANUSCRIPT present-day erosion surface. Deposition of the Windsor Group spans nearly the entire Middle Mississippian (von

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Bitter et al., 2003). Age determination is primarily through biostratigraphic correlation using conodonts, benthic foraminifera and miospores with similarly aged peritidal successions in Great

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Britain and Ireland (Barnett et al., 2002; von Bitter et al., 2003; Somerville, 2008). These

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relationships suggest that Subzone A began to accumulate at ca. 344 Ma during the Osagean

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stage, when initial marine incursion produced thin organic-rich limestone and tufa deposits of the Macumber and Gays River formations (Jutras et al., 2006; Giles, 2009). These basal units are

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conformably overlain by 500 m of anhydrite and halite composing the White Quarry Formation and the correlative Carroll’s Corner and Stewiacke formations, respectively (Schenk et al.,

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1994), which are in turn capped by terrestrial red beds of the Tennycape and Meaghers Grant

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formations (Jutras et al., 2006). The thickness and aerial-extent of evaporites indicate saline giant

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development through widespread evaporative drawdown under severely restricted conditions (Schenk et al., 1994; Jutras et al., 2006, 2015). Red beds are separated from Subzone B by a prominent disconformity spanning the early Meramecian stage (ca. 340 to 338 Ma; von Bitter et al., 2003; Giles, 2009).

Subzone B, the focus of research herein, records renewed flooding of the Maritimes Basin. It constitutes the Miller Creek, Wentworth Station and Pesaquid Lake formations of the Windsor sub-basin, and laterally equivalent Macdonald Road Formation of the Shubenacadie and Musquodoboit sub-basins (Boehner, 1979; Giles and Boehner, 2003). Subzone B began to accumulate during the middle Meramecian (ca. 337 Ma; von Bitter et al., 2003) and consists of stacked, decametre-scale shallowing and brining-upward peritidal cycles (Schenk, 1969; Giles, 2009). These parasequences are carbonate-evaporite-siliciclastic cycles recording aggradation in environments that became increasingly restricted. 6

ACCEPTED MANUSCRIPT Subzones C, D and E form the Murphy Road Formation in the Windsor sub-basin and laterally equivalent Green Oaks Formation in the Shubenacadie and Musquodoboit sub-basins.

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Subzone C is separated from Subzone B by a sharp, but conformable contact (Boehner, 1979) that correlates to the late Meramecian stage (ca. 334 Ma; von Bitter et al., 2003). Cycles in

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Subzones C, D and E consist of structureless red sandstone and wavy-laminated fossiliferous

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limestone that host an array of normal-marine corals and fish remains (Globensky, 1967; Moore

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and Boehner, 2005). Evaporites are uncommon and generally occur as nodular anhydrite capping parasequences. Accumulation of the Windsor Group is interpreted to have ceased in the early

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Chesterian by ca. 330 Ma.

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3. Methods

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Fieldwork was conducted in Hants and Kings counties, central Nova Scotia, and involved

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the description of Windsor Group strata in drill core and outcrop. Four drill cores archived at the Nova Scotia Department of Natural Resources Drill Core Library (Stellarton, NS) were analyzed to obtain information on vertical stratal relationships, whereas three quarries were chosen to understand lateral facies trends (Fig. 3). Cores are from Riverside Corner in the Windsor subbasin (core RC 85-1) and Alton in the Shubenacadie sub-basin (cores SB-1, ALT 87-1 and ALT 06-01). Quarries that were investigated include the Antigonish Limestone Quarry, Mosher’s Quarry, and Miller Creek Quarry. Lithofacies were described based on their composition, primary sedimentary structures, and preserved fossil assemblages. Parasequences were identified in drill core based on the presence of flooding surfaces between subtidal deposits and overlying supratidal or non-marine beds. Changes in the brining-upward packaging of lithofacies were analyzed for fluctuations in sub-basin restriction. Emphasis was placed on understanding lithofacies associations of Subzone 7

ACCEPTED MANUSCRIPT B because it contains a sensitive record of environmental change and the processes producing saline giants.

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Macrofossil characteristics of Subzone B were determined in the field and drill core by assessing type, abundance, and diversity within dolostone and limestone lithofacies. Fossils were

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assigned an abundance index in individual beds of rare (1 to 10 fossils), uncommon (11 to 20

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fossils), common (21 to 40 fossils) or abundant (>40 fossils). Similarly, percentages of bioclastic

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and terrigenous silt- and sand-sized grains as well as microfossils were estimated from thin section using a ranking of rare (1 to 5 vol. % particles), uncommon (6 to 30 vol. % particles),

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common (31 to 60 vol. % particles), or abundant (>60 vol. % particles). The Droser-Bottjer ichnofabric index was also used to measure the bioturbation of units and were assigned an index

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of 1 (no bioturbation), 2 (<10% bioturbation), 3 (10 to 40%), 4 (40 to 60%), 5 (60 to 100%), or 6

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(bed is completely homogenized; Droser and Bottjer, 1986). Such an approach permitted the

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assessment of the range of limiting factors affecting faunal abundance and diversity in depositional and oceanographic context. Systematic evaluation of the effects of climate-induced changes in salinity, oxygen levels, nutrient concentrations and terrigenous clastics input on paleoecology was a primary focus. Forty polished thin sections from samples representative of all lithofacies were analyzed using standard petrographic techniques and cathodoluminescence to understand paragenesis. Petrographic analysis was performed using a Nikon OPTIPHOT-POL transmitted and reflective light microscope. A Nikon eclipse E400-POL microscope fitted with a Reliotron III cathodoluminescence (CL) system was also used to analyze carbonate and evaporite microfabrics. X-ray powder diffraction analysis of five samples was performed to confirm evaporite and carbonate phases. Samples were analyzed on an X-pert-Pro Philips powder diffractometer across scattering angles of 5º to 70º using a cobalt X-ray target sources. These 8

ACCEPTED MANUSCRIPT data were integrated into the sequence stratigraphic framework to develop a depositional and

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oceanographic model for evaporite accumulation in the Maritimes Basin.

4. Sedimentology and paleoenvironments

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Ten lithofacies were identified in Subzone B of the Windsor Group (Table 1). Like other

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ancient evaporite successions, interpretation of several of these facies (Facies 2, 3, 4, 6, and 9) is

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challenging because they lack sedimentary structures and have a complex paragenesis that obscures primary textures (Dean, 1975; Hardie et al., 1985; Hardie and Lowenstein, 2004).

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Nevertheless, their association with lithofacies containing unequivocal shallow-water synsedimentary features (Facies 1, 5, 7, and 8), and a close affinity to karst surfaces with

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paleosols (Facies 10), suggest accumulation in peritidal environments under a salinity range of

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ca. 35 to >350‰. Detailed facies descriptions are presented in Table 1.

4.1. F1 - Interbedded crinoid packstone and carbonate mudstone Facies 1 (F1) is composed of 1 to 3-m-thick intercalated crinoid packstone and carbonate mudstone beds (Fig. 5A). Planolites is common in crinoid packstone layers that have an ichnofabric index of 4 and contain fragments of bryozoans, echinoids, brachiopods, ostracods, bivalves, benthic foraminifera and phylloid algae. Lime mudstone is organic-rich, generally unbioturbated, and has been recrystallized to micrite. The interbedding of crinoid packstone with organic-rich mudstone devoid of macrofossils suggests deposition in a mesotrophic subtidal environment that alternated between periods of near normal marine salinity and hypersaline conditions (Stickle and Diehl, 1987; Lukasik and James, 2003; Mutti and Hallock, 2003; Hardie and Lowenstein, 2004). The ubiquity of Planolites in some packstone beds suggests sediment accumulation was slow and organic matter 9

ACCEPTED MANUSCRIPT production was ideal for infaunal grazing (Wetzel, 1987; Savrda and Bottjer, 1991). Lower ichnofabric indices in mudstones imply higher salinities and/or the development of a dysoxic

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4.2. F2 - Unbioturbated anhydrite-rich carbonate mudstone

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seafloor (Savrda and Bottjer, 1991).

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Facies 2 (F2) is similar to F1, but body and trace fossils are absent. Beds are ca. 2-m-

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thick, structureless, and have gradational upper and lower contacts. Anhydrite occurs as 1 to 2cm-wide nodules and rosettes in carbonate mud that is now fine-grained ankerite and dolomite

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(Fig. 5B). Uncommon dull, pitted, angular silt-sized quartz grains and rare muscovite are also disseminated throughout beds.

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F2 is interpreted to record carbonate mud production and the accumulation of wind-

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blown silt in a hypersaline environment just seaward of the tidal flat (Facies 7 & 8). Evaporation

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in this subtidal environment likely drove the growth of anhydrite just beneath the sediment-water interface. The pitted and uniform silt-sized nature of quartz grains suggests aridity was accompanied by delivery of aeolian sediment to the coast. Aeolian sediment is typically dull and pitted from wind abrasion and more angular than grains reworked subaqueously (Windom, 1975; Mazzullo et al., 1986; Vandenberghe, 2013). The lack of coarse terrigenous clastics in Subzone B further implies that wind was the dominant transport mechanism.

4.3. F3 - Structureless anhydrite Facies 3 (F3) is composed of bluish-white, structureless microcrystalline anhydrite beds that are 10 to 20-cm-thick (Fig. 5C). Beds also contain cubic halite and abraded, silt-sized quartz grains. Fabric destructive, bladed anhydrite crystals overprint these minerals (Fig. 5E).

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ACCEPTED MANUSCRIPT The massive nature of anhydrite suggests cumulate deposition of microcrystalline gypsum precipitated in the water column of a low-energy subtidal to intertidal environment with

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brine salinities of >133‰ (van den Belt and de Boer, 2009; Kendall, 2010). As in F2, the presence of silt-sized quartz grains is interpreted to record aeolian input. The occurrence of

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fabric destructive anhydrite suggests that the dehydration of gypsum, to form anhydrite during

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burial diagenesis, destroyed primary sedimentary layering. When brine salinities increased to

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>350‰, cubic halite became the primary cumulate phase (F4; Hovorka, 1987).

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4.4. F4 - Diffusely layered halite

Facies 4 (F4) consists of peach to white coloured, diffusely-layered halite beds that are

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intercalated with convolute or enterolithic beds of bluish-white, microcrystalline anhydrite (Fig.

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5C&D). Halite beds are 3 to 100-cm-thick and characterized by foam texture (Fig. 5F&G;

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Lowenstein and Hardie, 1985; Cathro et al., 1992). Lower and upper contacts are sharp with anhydrite layers, which range in thickness from 1 to 20 cm. F4 is interpreted to have accumulated in low-energy subaqueous brine pools with salinities consistently >350‰ (Kendall, 2010; Warren, 2010). Halite precipitated at the air-water interface where evaporation rates were highest (Aref et al., 1997) to form rafts of crystals that eventually coalesced and sank through the water column (Hovorka et al., 2007). The diffuse layering that characterizes this facies probably reflects the establishment of perennial brine sheets in this shallow subaqueous setting (Kendall, 1978; Lowenstein and Hardie, 1985; Lowenstein, 1988). Anhydrite beds are interpreted to record rapid freshening events that induced the precipitation and deposition of gypsum as a cumulate (Manzi et al., 2012). Their convolute nature is probably the result of diagenetic volume changes, and plastic deformation associated with compaction during burial. Such enterolithic anhydrite is common in modern sabkha 11

ACCEPTED MANUSCRIPT environments where cyclic dehydration-rehydration of calcium sulfates records seasonal changes

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in rainfall and evaporation (Hussain and Warren, 1989; Lokier et al., 2013)

4.5. F5 - Oolitic grainstone

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Facies 5 (F5) is a grainstone composed of fine-grained to granule-sized radial ooids and

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rare monospecific bivalve fragments cemented by blocky calcite. Ooids are replaced and

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cemented with blocky low Mg calcite. Beds are 1 to 10-cm-thick and when bioturbated have an ichnofabric index no higher than 3 (Droser and Bottjer, 1986).

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This facies is interpreted to represent carbonate precipitation and grain production in a high-energy subtidal environment (Duguid et al., 2010). A depauperate bivalve assemblage and

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low bioturbation index suggests salinity stress. The presence of radial ooids and near-complete

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replacement by blocky calcite formed during meteoric diagenesis implies precipitation from

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aragonite-saturated seawater (Sandberg, 1975; Duguid et al., 2010).

4.6. F6 - Structureless quartz wacke This wacke is grey in colour and composed of nearly equal proportions of mud and pitted, subangular, fine quartz grains (Fig. 6D) cemented with ankerite. Individual beds are 1 to 5-cm-thick, have diffuse lower and upper contacts, and intensely bioturbated to an index of 6. Some beds also contain uncommon crinoid columnals and benthic foraminifera. Facies 6 (F6) probably records the deposition and biologic reworking of aeolian-derived sediment in an upper subtidal environment (Plint, 2010). The presence of crinoids implies accumulation in seawater with near-normal marine salinities of ca. 35‰ (Lukasik and James, 2003).

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ACCEPTED MANUSCRIPT 4.7. F7 - Flaser-bedded quartz arenite Facies 7 (F7) is a red to green-grey flaser-bedded sandstone (Fig. 6A&E). Bidirectional

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ripples are composed of fine sand-sized, subangular quartz grains and rare mollusc shell fragments. In rare instances, 5 to 10-cm-thick oncolitic rudstones are interbedded.

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Microcrystalline hematite commonly coats quartz grains and pore spaces are occluded with

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ankerite and halite. Mud drapes are organic-rich with framboidal pyrite. Where bioturbated, this

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facies contains rare crinoid fragments and has an ichnofabric index of 4. Flaser bedding generally records deposition on intertidal mudflats (Reineck and Singh,

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1980; Reynaud and Dalrymple, 2011). Bidirectional ripples and the presence of mollusc and crinoid fragments record transport of sediment over mudflats through tidal action (Dalrymple,

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2010). Mud drapes reflect slack-water suspension rain of clays during high tide slack water

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(Reineck and Singh, 1980). The presence of framboidal pyrite indicates microbial respiration of

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sedimentary organic matter through bacterial sulfate reduction (Flügel, 2004). Oncoid-rich layers characterize high-energy deposits that typically accumulate just seaward of the tidal flat (Carozzi et al., 1983; Dahanayake, 1983; Cecil, 1990). Their presence suggests sediment was periodically transported onshore during storms.

4.8. F8 - Anhydrite-rich microbialite Facies 8 (F8) consists of a brown microbialite with crinkly, fenestral, or planar laminated fabrics (Fig. 6B&C; Demicco and Hardie, 1994; Harwood and Sumner, 2011). Microbial layers contain silt-sized, abraded quartz grains and are commonly intercalated with thin laminae of grey acicular anhydrite. In rare instances, thinly bedded grainstone composed of ostracods, brachiopod spines, filamentous algae and carbonate peloids are also interbedded. Fenestrae are filled with euhedral halite that is displacive and distorts these pores (Fig. 6F). 13

ACCEPTED MANUSCRIPT F8 is interpreted to record the establishment of cyanobacterial communities in evaporative intertidal ponds that experienced varying degrees of recharge (Burne and Moore,

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1987; Babel, 2004; Kendall, 2010). Communities trapped and bound windblown quartz grains as they developed. Anhydrite laminae formed when salinities were at least 133‰ (Schreiber and

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Tabakh, 2000) through dehydration of primary gypsum (Sørensen et al., 2005; Warren, 2006), or

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direct precipitation during subaerial exposure above 50°C (Billo, 1986). Intercalated grainstone

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layers likely record tide and storm transport of grains from the subtidal realm into microbial-

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lined intertidal pools (Dalrymple, 2010).

4.9. F9 - Nodular anhydrite

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This facies is comprised of blue to white nodular anhydrite in metre-thick beds of green

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to brown quartz-silt-rich dolomicrite (Fig. 7A&D). Nodules are 0.5 to 3.0 cm in diameter,

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composed of acicular anhydrite, and commonly coalesce to form chicken-wire structure. Rare corroded gypsum crystals occur in some nodules. Framboidal pyrite is common and disseminated throughout the dolomicrite matrix. Facies 9 (F9) is interpreted to reflect subsurface evaporite precipitation in sabkha environments under moderate to high evaporation rates and average temperatures >40ºC (Kasprzyk, 2003; Aleali et al., 2013). Nodules likely formed as primary gypsum underwent early burial dehydration to produce anhydrite (Schreiber and Tabakh, 2000). Together, the precipitation of gypsum and framboidal pyrite facilitated the precipitation of dolomicrite by increasing the Mg/Ca ratio of pore water and reducing the concentration of sulfate, a kinetic inhibitor to dolomite nucleation. Sulfate was sequestered in growing nodules (Aleali et al., 2013), and bacterial sulfate reduction produced sulfide that combined with ferrous Fe to form framboidal pyrite (Schieber, 2002). 14

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4.10. F10 - Muscovite-rich quartz arenite

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Facies 10 (F10) is a red, muscovite and quartz-rich fine-grained sandstone cemented with microcrystalline hematite. This facies fills well-developed surface karst that penetrates subaerial

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exposure surfaces in anhydrite to a depth of 20 m (Fig. 7B). F10 also contains limestone clasts

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halite and saddle dolomite are common (Fig. 7E).

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consisting of calcareous microbialite and oncolitic grainstone (Fig. 7C). Displacive euhedral

F10 is interpreted to record non-marine accumulation of wind-blown silt at the interface

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between the terrestrial and marine realms. The presence of displacive halite implies precipitation from marine-derived pore water when karst surfaces were flooded during transgression. Deep

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corrosion along karst surfaces was likely caused by high summer humidities. Such conditions are

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characteristic of arid sabkha environments and occur today along the Abu Dhabi coastline, where

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annual rainfall is low but summer temperatures >50ºC causes relative humidity to exceed 90% (Lokier, 2013). Dew, formed overnight on the sabkha when temperatures drop, is substantial enough to cause dissolution of evaporites. The presence of saddle dolomite reflects an interaction with hydrothermal fluid during deep-burial diagenesis (Lavoie et al., 2014; Liu et al., 2014).

5. Parasequences and sequence stratigraphy Stratal stacking patterns suggest Subzone B accumulated during the onset of marine transgression that was punctuated by higher order fluctuations in relative sea level. These superimposed sea level oscillations produced at least nine shallowing-upward parasequences that also brine-upwards (Figs. 8 & 9). Each parasequence is a decametre-scale peritidal cycle that records evaporite deposition in subtidal to terrestrial settings, providing a record of how accommodation, basin restriction and climate regulate saline giant formation. Flooding surfaces 15

ACCEPTED MANUSCRIPT between peritidal cycles are interpreted to correspond to major brine-dilution events that accompanied minor sea level rise.

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Progradation of environments in parasequences PS1, PS2, and PS3 followed by aggradational stacking in PS4, PS5, PS6, PS7, PS8, and PS9 typifies the lowstand systems tract,

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as accommodation gradually increased during the onset of transgression (Catuneanu, 2009,

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2011). Progradational parasequences have thicker accumulations of supratidal facies that are

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deeply karstified, reflecting pronounced basinward migration of coastal facies as sea level began to rise. The presence of subtidal and open-marine facies in aggradational parasequences, as well

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as the decrease in karst diastems up-section, tracks increasing accommodation through the lowstand (Catuneanu et al., 2009). The contact between Subzones B and C is interpreted as the

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transgressive surface of Sequence 2. Across this sharp, but conformable contact, deepening is

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recorded by the juxtaposition of subtidal, organic matter-rich mudstone with rare crinoid-bearing

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beds (F1) over intertidal nodular anhydrite (F9). Progradational and aggradational parasequences can be subdivided into three types (Fig. 10). Their dissimilarities in composition and vertical stacking of lithofacies are interpreted to represent differences in available accommodation, degree of basin restriction, climate and thus, evolving brine chemistry between the Shubenacadie and Windsor sub-basins. In order of increasingly saline conditions, Type 1 parasequences reflect the most open-marine conditions, Type 2 parasequences accumulated under salinities between 35 and 133‰, and Type 3 parasequences record the consistently highest salinities from 40 to 350‰. Because Type 1 parasequences are most common directly beneath the transgressive surface, they are interpreted to record the transition to permanent open-marine conditions that dominate Sequence 2 of the Windsor Group.

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ACCEPTED MANUSCRIPT 5.1. Type 1 - Carbonate-siliciclastic parasequence Type 1 parasequences occur only in the Shubenacadie sub-basin (Fig. 3) and are

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composed of carbonate and siliciclastic lithofacies organized into 15 to 20-m-thick shallowingupward cycles (Fig. 10A). Cycles are bounded by sharp, undulatory flooding surfaces preserved

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in nodular anhydrite (F9). The basal flooding surface is overlain by crinoid and ostracod-rich,

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bioturbated carbonate mudstone (F1) with an ichnofabric index of 4. F1 changes gradationally

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upwards into bivalve-rich oolitic grainstone (F5) that changes into a crinoid and foraminiferarich, quartz wacke (F6). This facies is overlain by flaser-bedded quartz arenite that is bioturbated

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to an index of 5 (F7), which in turn grades into anhydrite-rich microbialite (F8) and then nodular anhydrite (F9). Parasequences are capped by muscovite-rich quartz arenite (F10).

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The nature and stacking relationship of lithofacies characterizing Type 1 parasequences

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define a shallowing-upward succession that accumulated in evaporitic peritidal environments

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that were well-oxygenated. Evaporites are restricted to upper intertidal and supratidal settings and reflect the establishment of evaporite-rich sabkha flats. Sharp, undulatory flooding surfaces bounding Type 1 cycles are interpreted as dissolution surfaces. This suggests flooding events caused significant brine refreshening that induced dissolution of underlying nodular anhydrite prior to the deposition of the next peritidal cycle. Crinoid-rich, bioturbated lime mudstone (F1) and oolitic grainstone (F5) above these surfaces suggest dissolution by seawater with normal to slightly elevated salinities (35 to 40‰; James et al., 2010; Stickle and Diehl, 1987; Boczarowski, 2012). The transition to structureless quartz wacke (F6) and bioturbated, flaser-bedded quartz arenite (F7) is interpreted to record progressive shallowing and accumulation of wind-blown silt and sand on the tidal flat. Aerobic conditions are inferred from the high ichnofabric indices of marine lithofacies, indicating sediment mixing by infaunal organisms. The muscovite-rich quartz arenite (F10) above evaporitic facies is a paleosol that marks parasequence tops. 17

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5.2. Type 2 - Carbonate-anhydrite-siliciclastic parasequence

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Type 2 parasequences consist of 10 to 60-m-thick carbonate-anhydrite-siliciclastic cycles that are bound by either sharp flooding surfaces or karst diastems (Fig. 10B). From base to top,

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cycles are generally composed of a crinoid-bearing intraclastic grainstone with an ichnofacies

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index between 2 and 5 (F1), anhydrite-rich carbonate mudstone (F2), structureless anhydrite

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(F3), anhydrite-rich microbialite (F8), and nodular anhydrite (F9). Where present, karst diastems penetrate microbialite (F8) and nodular anhydrite (F9) to a depth of 20 m. Muscovite-rich quartz

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arenite (F10) containing eroded anhydrite clasts define cycle tops and passively fills karst cavities.

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Flooding events that produced Type 2 parasequences were of sufficient magnitude to

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dilute hypersaline waters and promote abiotic carbonate precipitation. The transition from

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crinoid-bearing, intraclastic grainstone (F1) to anhydrite-rich carbonate mudstone (F2) is interpreted to reflect an increase in seawater salinity to between 40 and 80‰, excluding carbonate-producing organisms (James et al., 2010; MacEachern et al., 2010). The range of bioturbation indices characterizing F1 are interpreted to reflect aerobic to dysaerobic seafloor conditions (Bottjer and Droser, 1991). The lack of carbonate producing organisms in the anhydrite-rich carbonate mudstone (F2) suggests evaporitic concentration drove the abiotic precipitation of carbonate (Babel and Schreiber, 2014). The gradational transition from carbonate mudstone (F2) to massive anhydrite (F3) represents a gradual increase in water column salinities to 133‰, the point of gypsum saturation (Kendall, 2010). The presence of anhydrite-rich microbialite (F8) is interpreted to record progradation of intertidal evaporitic microbial mats over subtidal gypsum. Nodular anhydrite is interpreted to have precipitated from saline pore fluids beneath established microbial mats (Schreiber and 18

ACCEPTED MANUSCRIPT Tabakh, 2000). Terrestrial sandstone infilling karst cavities that penetrate diastems (F10) indicates Type 2 cycles terminate with the subaerial dissolution of evaporites and deposition of

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regolith. The conspicuous absence of layered halite (F4) suggests that connectivity with the open

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ocean was sufficient to preclude salt precipitation.

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5.3. Type 3 - Carbonate-anhydrite-halite-siliciclastic parasequence

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Type 3 parasequences are 15 to 40 m-thick brining upward peritidal cycles that contain abundant halite (Fig. 10C). In stratigraphic order, flooding surfaces are overlain by carbonate

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mudstone devoid of bioturbation and body fossils (F1), structureless anhydrite (F3), diffusely layered halite (F4), anhydrite and halite-rich, flaser-bedded quartz arenite (F7), anhydrite-rich

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microbialite (F8), nodular anhydrite (F9), and muscovite-rich quartz arenite (F10).

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Type 3 cycles are interpreted to record evaporation in restricted, low energy peritidal

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environments. The lack of traction deposits and the abundance of evaporite minerals in lithofacies suggest extreme evaporitic concentration along restricted segments of the shoreline with little wave and current activity (Hovorka et al., 2007). The conspicuous presence of halite indicates that the salinities producing this type of brining-upward succession were consistently higher than those forming Type 1 and 2 parasequences. As in these parasequences, the sharp nature of flooding surfaces between cycles is interpreted to record pervasive dissolution that accompanied flooding and deposition of the overlying peritidal cycle. These freshening events reduced the salinity to allow bioturbation of lime mud by annelids, but not enough to permit the establishment of skeleton-producing invertebrates (MacEachern et al., 2010). The absence of skeletal carbonate producers suggests salinities were consistently above 40‰ (James et al., 2010). Progressive brine concentration through evaporation and increased restriction is interpreted to have produced salinities 19

ACCEPTED MANUSCRIPT favourable for the precipitation of gypsum (F3) and eventually halite (F4). The presence of evaporite-rich, flaser-bedded quartz arenite (F7) and microbialite (F8) containing fenestrae

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reflects progradation of evaporitic intertidal mudflats over subtidal halite (Schreiber and Tabakh, 2000; Hardie and Lowenstein, 2004). As accommodation continued to fill, the accumulation of

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severely desiccated nodular anhydrite (F9) and terrestrial sandstone (F10) mark the onset of

6. Shubenacadie and Windsor sub-basins

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sabkha and terrestrial sedimentation.

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Paleogeographic reconstructions of the Maritimes Basin suggest accumulation of the Windsor Group occurred in an intracratonic pull-apart basin bounded by topography created

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during the Acadian Orogeny (Late Silurian to Late Devonian; Boehner, 1989; Schenk et al.,

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1994). Early Mississippian alluvial fans of the Horton Group preserved in contact with normal

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faults support this interpretation (Gibling et al., 2008). Extensional rifting during the Late Devonian to Early Mississippian produced high relief, right lateral east-west to northeastsouthwest trending oblique normal faults that controlled basin geomorphology (Gibling et al., 2008). Post-rift thermal subsidence in the Osagean is interpreted to have allowed for marine flooding of these half-grabens, creating a system of restricted sub-basins (Schenk, 1967, 1969; Schenk et al., 1994). A semi-arid climate promoted widespread evaporite deposition to produce the saline giant of Subzone A, which corresponds to Sequence 1 of the Windsor Group (Fig. 4). Subzone B records the onset of a second major flooding event that led to the accumulation of Sequence 2 (Fig. 4). The onlapping relationship of Subzone B onto Horton Group rocks inboard of the maximum aerial extent of Subzone A, indicates a higher amplitude rise in relative sea level flooded existing sub-basins (von Bitter et al., 2003; Giles, 2009). Lithofacies character, composition, and stacking patterns suggest that low energy peritidal 20

ACCEPTED MANUSCRIPT environments developed as sea level rose. Facies associations in parasequences represent a complex spatial distribution of evaporite environments that, unlike the basinwide evaporites of

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Subzone A, reflect the accumulation of cyclic, platform evaporites in coastal settings (Warren, 2006, 2010).

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The Shubenacadie sub-basin apparently had a higher degree of connectivity with the

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Rheic Ocean (Fig. 11A). The occurrence of Type 1 and 2 parasequences with bioturbated and

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macrofossil-rich limestone (F1, F5) indicate salinities were not as high as in the Windsor subbasin. In the Shubenacadie sub-basin the subtidal realm contained a diverse community of

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stenohaline, benthic organisms that thrived in normal-marine to slightly elevated salinities (ca. 35 to 40‰; James et al., 2010). As connectivity diminished through the progradation of

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environments to form aggradational cycles (Warren, 2006, 2010), increasingly restricted

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conditions produced brines (ca. 41 to 80‰) that resulted in the gradual disappearance of

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calcareous fauna and proliferation of halotolerant bacterial communities (Kendall, 2010). With continued shallowing and increased restriction, brine salinities (ca. 80 to 132‰) eventually precluded infaunal, soft-bodied organisms. Such aggradation and hypersalinity is marked by the widespread deposition of abiotic, evaporitic carbonate (F2), cumulate gypsum (F3), and extensive sabkha deposits (F8, F9) as accommodation filled. The Windsor sub-basin contains Type 2 and halite-rich Type 3 peritidal cycles, indicating salinities were consistently higher than in the Shubenacadie sub-basin. Type 3 parasequences are characterized by gypsum and anhydrite (F3) that brine-upward into layered halite (F4), reflecting sustained restriction and high evaporation rates with salinities >350‰ (Fig. 11B). Minimal to zero seawater influx is interpreted to reflect the presence of a topographical barrier to circulation and recharge (Schenk et al., 1994). The dense brines produced are interpreted to have been focused by gravity into the centre of the Windsor sub-basin to create the thickest deposits of 21

ACCEPTED MANUSCRIPT cumulate halite (F4; Roveri et al., 2008; Manzi et al., 2012). As in the Shubenacadie sub-basin, intertidal and supratidal environments were extensive and dominated by sabkha flats colonized

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by halotolerant bacteria (F7, F8, F9). The conspicuous absence of calcareous fauna suggests the Windsor sub-basin remained hypersaline (>40‰) during the entirety of Subzone B deposition.

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important process delivering terrigenous clastic sediment.

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The abundance of silt and fine sand in peritidal facies suggests aeolian input was the most

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With these differences between sub-basins an image emerges that circulation in the Maritimes Basin was controlled by the geomorphology of pre-existing half-grabens. Although

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this system of variably connected sub-basins contains similar physical facies attributes their chemical character is markedly different. Such differences relate to variability in the recharge

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rate, which affected the salinity and thus, evaporite facies that precipitated from evolving brines.

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7. Windsor Group and Middle Mississippian climate The Windsor Group is interpreted to have begun accumulating during the Osagean at the beginning of an interglaciation following Glaciation I of the Late Paleozoic Ice Age (Fig. 12; von Bitter et al., 2003; Gibling and Rygel, 2008; Giles, 2009). The deposition of Sequences 1 and 2 correspond remarkably well to episodes of glacial retreat and rising eustatic sea level, whereas unconformities and continental red beds marking sequence tops correlate to glacial advance and falling sea level (Fig. 12). Thus, parasequences are interpreted to record minor glacially related adjustments to accommodation superimposed on major episodes of glacioeustatic sea level change. It is unlikely that parasequences record tectonic re-adjustments of the Maritimes Basin because the Windsor Group was deposited during a long period of slow thermal subsidence (Gibling and Rygel, 2008).

22

ACCEPTED MANUSCRIPT Subzone A of Sequence 1 was deposited in the Osagean during a transgression early in this interglacial period (Giles, 2009). Evaporative drawdown in highly restricted sub-basins

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produced the halite-rich saline giant characterizing Subzone A (von Bitter et al., 2003). The unconformity between Sequence 1 and Sequence 2 is late Osagean to early Meramecian in age

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(von Bitter et al., 2003), and correlates with a purported period of glacial advance that is

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recognized in South America (Caputo and Crowell, 1985; Caputo et al., 2008). In the Windsor

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Group, this third glacial episode is interpreted to correspond to biozones Perotrilites tessellatusSchultzospora campyloptera and Raistrickia nigra-Triquitrites marginatus (von Bitter et al.,

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2003), which record subaerial exposure, desiccation and the development of the unconformity between Sequences 1 and 2.

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Deposition of Sequence 2 began with Subzone B in the early to mid Meramecian, a time

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that is interpreted to have been characterized by moderate glacioeustatic fluctuations (Barnett et

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al., 2002; Gibling and Rygel, 2008; Rygel et al., 2008). These 10 to 50-m-amplitude changes are well documented in Euramerican karst-bearing cyclothems (Barnett et al., 2002; Waters et al., 2007) and localized glaciogenic deposits in Australia and South America (Wright and Vanstone, 2001; Fielding et al., 2008). This supports the notion that Subzone B and related brining-upward parasequences record high-amplitude, glacioeustatic changes in relative sea level (Smith and Read, 2000; Wright and Vanstone, 2001; Barnett et al., 2002; Fielding et al., 2008). Subzones C, D and E of Sequence 2 record a transition to open-marine conditions (Giles, 2009). The lower and upper portions of Subzone C are correlated to the late Meramecian (von Bitter et al., 2003). The late Meramecian is characterized by a minor greenhouse period that resulted in eustatic sea level rise (Iannuzzi and Pfefferkorn, 2002; Pfefferkorn et al., 2014). The occurrence of warm and temperate floras at 60° N and S and paleotemperatures calculated from δ13O data from late Meramecian brachiopods suggests a short-lived global warming event during 23

ACCEPTED MANUSCRIPT this time (Mii et al., 1999, 2001; Iannuzzi and Pfefferkorn, 2002; Fielding et al., 2008; Giles, 2009; Pfefferkorn et al., 2014). The presence of bryozoans, corals and crinoids in Subzones C, D,

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and E (Moore, 1967; Moore and Ryan, 1976) indicate that the amplitude of sea level rise during the deposition of Sequence 2 was high enough to create unrestricted connectivity with the Rheic

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Ocean.

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Termination of Windsor Group deposition near the Meramecian-Chesterian boundary

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coincides with the first major glacial advance of Glaciation II across Gondwana and eastern Australia (Isbell et al., 2003, 2012; Fielding et al., 2008; Montañez and Poulsen, 2013). Such

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glacial growth is interpreted to have caused regression of the Windsor Sea to produce non-

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marine evaporitic lacustrine environments of the Mabou (Canso) Group (Gibling et al., 2008).

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8. Windsor Group and saline giants

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The three types of parasequences that characterize Subzone B contain a detailed record of changing eustatic sea level, basin circulation and climate during the Middle Mississippian. Thus, Subzone B provides an important window into how the interplay of these factors influenced evaporite accumulation. Of these, glacioeustasy was the most important because it was the primary control on accommodation, which in turn governed the degree of connectivity with the open ocean and ability to create evaporitic brines. This influence of sea level on evaporite accumulation is most pronounced in Sequence 1 of the Windsor Group during the accumulation of Subzone A when eustatic sea level was just high enough to produce restricted sub-basins with minimal recharge (Schenk et al., 1994; Warren, 2010). Such conditions, coupled with intense evaporation, produced highly stratified brines from which basinwide-like evaporites of economically important gypsum, halite and potash precipitated (Schenk et al., 1994; Jutras et al., 2006). 24

ACCEPTED MANUSCRIPT In Sequence 2, an overall marine transgression punctuated by higher order fluctuations in sea level produced the evaporite-rich, parasequences of Subzone B that become progressively

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less restricted in nature stratigraphically upwards (Moore, 1967; Boehner et al., 2002; Giles, 2009). This trend from lowstand, evaporite-rich peritidal cycles to transgressive, more open

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marine parasequences in Subzones C, D and E highlight the influence of eustatic sea level on

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circulation and basin recharge on two different timescales. Higher order cyclicity caused

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aggradation and restriction in shallow settings to produce stacked, successions of platform evaporites (Catuneanu et al., 2011). Rising glacioeustatic sea level, which was continually

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punctuated by these shorter duration fluctuations, eventually flooded the Maritimes Basin to promote unrestricted circulation and carbonate deposition with open-marine fauna (Globensky,

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1967; Legrand-Blain and von Bitter, 2003).

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Although cyclic evaporite successions also exist in Subzone A (von Bitter et al., 2003),

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minor flooding events recharged sub-basins just enough to sustain prolonged halite and potash precipitation (Giles and Boehner, 2003). The higher amplitude change in sea level (Rygel et al., 2008) that led to the accumulation of Sequence 2 created progressively more open-marine conditions because flooding eventually connected this system of restricted sub-basins to the open ocean (Gibling et al., 2008).

What these relationships demonstrate is that the accumulation of true saline giants that are more akin to basinwide evaporites (Warren, 2010) requires low amplitude, longer frequency changes in sea level to promote the development of persistent, stable brine pools that are only periodically recharged with seawater. Higher amplitude, shorter frequency variability produces thinner platform evaporites with more complex facies relationships that are aerially restricted and generally less economic. The Windsor Group highlights how basinwide and platform evaporites

25

ACCEPTED MANUSCRIPT can form at different times in the same depositional system depending on the nature of sea level

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cyclicity.

9. Conclusions

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1. The Windsor Group records the accumulation of two depositional sequences through two

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complete sea level cycles. Sequence 1 is formed entirely of Subzone A and constitutes the saline

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giant phase of basin development. Sequence 2 is composed of subzones B, C, D and E and reflects peritidal evaporite deposition under less restricted conditions. Together these sequences

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reflect freshening of the Maritimes Basin through the Middle Mississippian.

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2. Subzone B, the focus of research herein, records evaporite deposition during the onset of the

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transition to more open marine conditions. Stacking of aggradational, brining upward

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parasequences forming Subzone B indicates lowstand deposition as sea level began to rise. Variability in the composition of lithofacies forming parasequences reflects differences in the degree of restriction and thus, brine chemistry between sub-basins.

3. Lithofacies associations and correlation with other Middle Mississippian peritidal cycles indicate that higher-order glacioeustatic sea level changes during the accumulation of Sequence 2 produced extensive platform evaporites. These peritidal deposits are much smaller and less well developed than the economic, basinwide-like evaporites of Sequence 1.

4. This marked difference in evaporite style is interpreted to record glacioeustasy during the Late Paleozoic Ice Age on differing timescales. True saline giants require low amplitude, long frequency changes in sea level to promote the development of persistent, stable brine pools that 26

ACCEPTED MANUSCRIPT are only periodically recharged with seawater. Higher amplitude, short frequency variability produces thinner peritidal evaporites with more complex facies relationships that are aerially

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restricted and generally subeconomic.

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5. The unique record of climate, sea level and oceanography preserved in Subzone B has not

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only expanded what is known about evaporite accumulation in the Windsor Group, but has also

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provided new information on the factors controlling the formation of saline giants in general. What was underappreciated until now is that in addition to an arid climate, basinwide and

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platform evaporites likely record differences in the nature of sea level cyclicity. Such information will assist in the exploration of economic evaporites and refine our understanding of

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Acknowledgements

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the Earth system feedbacks that created evaporite basins through time.

K. Adams, M. Grey, and D. Skilliter are thanked for their assistance and discussions while in the field. Pam Frail prepared polished thin sections at Acadia University, and C. Koebernick assisted with drafting and CL microscopy. The paper was improved through critical review by T.M. Lowenstein and S.W. Lokier. This research was supported by a Natural Sciences and Engineering Research Council of Canada Discovery Grant to PKP and an Acadia Graduate Award to LAM.

27

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Moore, R. G., 1967. Lithostratigraphic units in the upper part of the Windsor Group, Minas Subbasin, Nova Scotia. Geological Association of Canada Special Paper, 4, 245-266.

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Moore, R.G., Ryan, R.J., 1976. Guide to the invertebrate fauna of the Windsor Group in Atlantic

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Moore, R.G., Boehner, R.C., 2005. Geology of the Windsor (Kennetcook) basin, Hants and Kings Counties, Nova Scotia. Open File Report, Nova Scotia Department of Natural

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Rygel, M.C., Fielding, C.R., Frank, T.D., Birgenheier, L.P., 2008. The magnitude of Late Paleozoic glacioeustatic fluctuations: a synthesis. Journal of Sedimentary Research 78,

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Sandberg, P.A., 1975. New interpretations of Great Salt Lake ooids and of ancient non-

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skeletal carbonate mineralogy. Sedimentology 22, 497-537. Sangster, D.F., Savard, M.M., Kontak, D.J., 1998. A genetic model for mineralization of Lower

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Windsor (Viséan) carbonate rocks of Nova Scotia. Economic Geology 93, 932-952. Sarg, J.F., 2001. The sequence stratigraphy, sedimentology, and economic importance of

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evaporite-carbonate transitions: a review. Sedimentary Geology 140, 9-42.

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Savrda, C. E., Bottjer, D. J., 1991. Oxygen-related biofacies in marine strata: an overview and

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Sonnenfeld, P., 1984. Brines and evaporites. Academic Press, University of California.

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Sørensen, K. B., Canfield, D. E., Teske, A. P., Oren, A., 2005. Community composition of a hypersaline endoevaporitic microbial mat. Applied and Environmental Microbiology

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Waters, C.N., Browne, M.A.E., Dean, M.T., Powell, J.H., 2007. Lithostratigraphical framework

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Wetzel, A., 1987. Ichnofabrics in Eocene to Maestrichtian sediments from deep-sea drilling

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White, C.E., Barr, S.M., 2012. Meguma terrane revisited: Stratigraphy, metamorphism, paleontology, and provenance. Geoscience Canada 39(1). Wright, V.P., Vanstone, S.D., 2001. Onset of Late Paleozoic glacio-eustasy and the evolving climates of low latitude areas: a synthesis of current understanding. Journal of the Geological Society, London 158, 579-582.

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ACCEPTED MANUSCRIPT Figure Captions Figure 1. Areal and sub-areal extent of Windsor Group in the Maritimes Basin is shown in blue

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(modified from Giles, 2009).

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Figure 2. Geologic map of Nova Scotia, Canada (modified from Keppie, 2000).

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Figure 3. Geologic map of central Nova Scotia with locations of drill cores and outcrops investigated. Refer to box delineating study area in Figure 2 for its location. Windsor Group

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strata are in blue. Cross-section from A to A’ is shown in Fig. 9.

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1976).

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Figure 4. Generalized stratigraphy of the Windsor Group (modified from Moore and Ryan,

Figure 5. (A) Interbedded crinoid packstone and carbonate mudstone (F1) with crinoids (Cr) and brachiopods (Br). White arrow indicates younging direction. (B) Unbioturbated anhydrite-rich carbonate mudstone (F2) cemented with ankerite (Ank) and halite (Ha). Displacive anhydrite (Anh) rosettes are coated with pyrite (Py). (C) Interbedded structureless anhydrite (F3; bluishwhite) and diffusely layered halite (F4; peach). Yellow circles denote sharp but gradational transitions between beds. (D) Diffusely layered halite (peach) with convolute anhydrite layers (white). (E) PPL photomicrograph of the contact between diffusely layered halite (F4; Ha) and structureless anhydrite (F3; Anh). (F) PPL photomicrograph of diffusely layered halite (F4) with triple junction foam texture. Yellow box indicates field of view in G. (G) PPL photomicrograph of microcrystalline cubic halite composing halite layers in F4.

39

ACCEPTED MANUSCRIPT Figure 6. (A) Flaser-bedded quartz arenite (F7). Dark grey laminae are mud drapes and light brown are ripple cross-laminated fine sand. (B) Anhydrite-rich microbialite (F8). Yellow circles

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highlight fenestrae. (C) Anhydrite-rich microbialite (F8) with crinkly microbial laminae that are enriched in anhydrite. (D) XPL photomicrograph of structureless quartz wacke (F6) composed

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predominantly of subangular, pitted quartz grains (Qtz) with uncommon silt-size plagioclase

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clasts (Pl). (E) PPL photomicrograph of flaser-bedded quartz arenite showing interbedded sand

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and mud laminae. Sandy layers are composed of silt-size, subangular and pitted monocrsytalline quartz grains. (F) Fenestral pores in anhydrite-rich microbialite (F8) that are occluded with cubic

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halite.

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Figure 7. (A) Nodular anhydrite (F9) in dolomitic mudstone. White arrow denotes younging

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direction. (B) Karst surface developed in structureless anhydrite (F3). Dissolution cavities are

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infilled with muscovite-rich quartz arenite (F10; red). (C) Structureless muscovite-rich quartz arenite (F10; red) with limestone clasts interpreted as regolith (white and grey clasts). (D) XPL photomicrograph of anhydrite nodules (F9; Anh) in quartz silt-rich (Qtz) dolomudstone (Dol). (E) XPL photomicrograph of muscovite-rich quartz arenite containing abundant abraded silt-size quartz grains (Qtz) and displacive halite (Ha).

Figure 8. Composite section displaying the stratigraphic architecture of the MacDonald Road Formation, Subzone B. Stratigraphic analysis identified three progradational (PS1, PS2, PS3) and six aggradational (PS4, PS5, PS6, PS7, PS8, PS9) parasequences. Lithologies, sedimentary structures, stratigraphic surfaces and palaeoenvironmental interpretations are also used in Figs 9 and 11. FS = flooding surface; FS/KS = flooding surface and karst surface; SB = sequence boundary; TS = transgressive surface; PS = parasequence. PS1 = parasequence 1; PS2 = 40

ACCEPTED MANUSCRIPT parasequence 2, et cetera. Cly = clay; Slt = silt; Ms = lime mudstone; Ws = wackestone; Ps = packstone; Gs = grainstone; Fs = floatstone; Rs = rudstone; Ba = bafflestone; Bi = bindstone; Fr

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grained; G = granule; Pbl = pebble; Cbl = Cobble; B = boulder.

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= framestone; Vf = very fine-grained; F = fine-grained; M = medium-grained; C = coarse-

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Figure 9. Regional stratigraphic correlation of lithofacies in the MacDonald Road Formation.

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Datum used for correlation is the flooding surface separating PS3 and PS4, which overlies a well-developed karst surface identifiable throughout the study area. For abbreviations and

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symbols, refer to Fig. 7.

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Figure 10. Parasequence types composing Subzone B. Variations in the stratigraphic

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architecture of each cycle reflect different salinity regimes during deposition. The Shubenacadie

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sub-basin contains predominantly Type 2 cycles and changes stratigraphically upwards to Type 1 parasequences through the thickness of Subzone B. The Windsor sub-basin contains mainly Type 3 cycles and changes upwards to Type 2 parasequences near the top of Subzone B.

Figure 11. (A) Depositional model of Subzone B in the Shubenacadie sub-basin. The subtidal zone includes deposits from F1 (blue), F2 (blue and yellow), F3 (yellow), F5 (blue) and F6. The intertidal and supratidal environments include sediment from F3 (yellow), F7 (pinkish-red), F8 (microbial mats), and F9 (nodular anhydrite). The terrestrial realm consists of F10 (pinkish-red). (B) Depositional model of Subzone B in the Windsor sub-basin. The subtidal zone includes deposits from F1 (blue), F2 (blue and yellow), F3 (yellow), and F4 (grey). The intertidal and supratidal environments contain sediment from F7 (pinkish-red), F8 (microbial mats), and F9 (nodular anhydrite). The non-marine realm consists of F10 (pinkish-red). 41

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Figure 12. Correlation of Windsor Group to major and minor glacial intervals. Minor glacial

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intervals 2 and 3 of Caputo et al. (2008) are highlighted in orange. Middle Mississippian biozone

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data are from Caputo et al. (2008), Somerville (2008), and von Bitter et al., 2003.

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ACCEPTED MANUSCRIPT Table Captions Table 1. Summary of facies descriptions and environmental interpretations Sedimentary

Petrography

Framboidal pyrite

Shallow to deep

common in organic

subtidal, normal

Structures Variably bioturbated

packstone and

organic-rich lime

carbonate mudstone

mudstone interbedded

rich beds; fine-

to elevated

with bioturbated

grained blocky

salinities, low

crinoid packstone.

calcite and crinoid

basin

Fossils include

epitaxial cements

restriction.

crinoids, bryozoans,

occlude interparticle

echinoids,

pores. Mechanical

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brachiopods,

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Interbedded crinoid

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F1

Interpretation

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Facies

compaction and

ostracods,

pressure solution

filamentous algae,

evident in ca. 30% of

uniserial and

bioclasts.

trochospiral benthic foraminifera. Bioturbation of Planolites ichnogenera; 0 to 6 index. Beds have gradational lower and upper contacts.

F2

Unbioturbated

Structureless,

Nodules and rosettes

Shallow to

anhydrite-rich

unbioturbated with

are 1 to 2 cm wide,

middle subtidal,

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secondary displacive

composed of 0.5-

arid, normal to

anhydrite nodules and

mm-long acicular

elevated

rosettes. Macro and

crystals. Framboidal

salinities, low

microfossils absent.

pyrite forms

to moderate

Anhydrite occurs as

isopachous rims

basin

around rosettes in

restriction.

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carbonate mudstone

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acicular crystal

organic-rich layers.

mud that is now

Pitted subangular

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rosettes in carbonate

quartz and rare

thick with gradational

muscovite

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ankerite. Beds 2-m-

anhydrite

contacts.

throughout beds.

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disseminated

Pure, structureless,

Very fine-grained

Subtidal to

bluish-white

acicular and bladed

intertidal, arid,

anhydrite and

anhydrite with

salinities

uncommon fine-

uncommon gypsum

>133‰,

grained gypsum and

forming interlocking

moderate to

microcrystalline cubic

crystal mosaics.

high basin

halite. Silt is

Cubic halite occurs

restriction.

uncommon. Beds

disseminated and as

have common sharp

aggregates

and uncommon

throughout. Dolomite

gradational contacts.

is present in organic-

All primary

rich wispy layers.

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Structureless

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F3

upper and lower

sedimentary structures have been destroyed through

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ACCEPTED MANUSCRIPT burial diagenesis. Peach to colourless,

Halite displays foam

Shallow to

halite

diffusely layered

texture encompassing

middle subtidal,

halite. Beds are 5 to

a mesh of subhedral

arid, salinities

100 cm-thick and

and euhedral 10 to

>350‰, high

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Diffusely layered

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F4

100-µm-wide

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defined by

microcrystalline

cm-thick layers of

cubic halite. Very

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interbedded 1 to 20

fine-grained acicular

white anhydrite.

anhydrite crystals

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planar and convoluted

restriction.

observed in F3 compose anhydrite layers.

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Oolitic grainstone

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F5

basin

Bioturbated

Ooid nuclei, cortical

Shallow

grainstone with fine-

layers and mud

subtidal, high

grained to granule-

matrix completely

energy

sized ooids and

replaced by blocky

environment,

monospecific bivalve

calcite. Poikilotopic,

low to medium

fragments; Beds are 1

bladed anhydrite

basin

to 10-cm-thick; B.I. =

crystals are common

restriction.

3. Ooid cortices

and overprint grains.

formed of radial layers accentuated by micrite envelopes. F6

Structureless quartz

Grey, structureless,

Detrital grains are

Shallow to

wacke

well-sorted muddy

angular to sub-

middle subtidal,

sandstone with 60%

angular pitted fine

low aridity, low

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ACCEPTED MANUSCRIPT sand-sized quartz,

basin

Muscovite,

<5% muscovite and

restriction.

plagioclase and

plagioclase in grey

bioclastic grains are

ankerite cement.

rare to uncommon.

Partially dissolved

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sand and 40% mud.

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crinoid remnants and simple septate

Flaser-bedded quartz

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arenite

Red to green-grey

foraminifera occur as relict black remnants and comprise ca. 1% of grains. Grains consist of

Lower to upper

flaser bedding

angular to sub-

intertidal, low

composed of

angular, pitted, well-

basin

alternating mm-thick

sorted quartz, <10%

restriction.

sand and mud

muscovite, crinoid

laminae. Hematite-

and mollusk

rich facies commonly

bioclasts. Cements

bioturbated to index

include hematite, salt,

of 4.

clay and ankerite.

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F7

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trochospiral benthic

Secondary framboidal pyrite is disseminated throughout greengrey beds. F8

Anhydrite-rich

Microbial mats with

46

Angular to sub-

Intertidal pools

ACCEPTED MANUSCRIPT angular sand;

dominated by

carbonate and

bioclastic grains lined

bacterial

evaporite minerals.

with druzy calcite

communities,

Calcareous

cement; commonly

medium to high

microbialite is

micritized.

aridity, low to

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varying quantities of

Microcrystalline

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organic- and quartz-

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microbialite

cubic halite fills

crinkly, fenestral and

remaining pore

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rich, with mm-thick

space. Anhydrite-rich

Bioclasts include

facies have 0.5-mm-

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planar laminae.

long whitish-blue

spines, filamentous

acicular and bladed

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ostracods, brachiopod

F9

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algae, and peloids.

Nodular anhydrite

high basin restriction.

anhydrite crystals

Anhydrite-rich

with interlaminated

microbialite has up to

light brown silty

50% anhydrite

dolomicrite

displaying mm-thick

containing pyrite.

crinkly fabrics. 0.02 to 40-mm-wide

Nodules are a

Upper intertidal

blue to white nodular

displacive mesh of

to supratidal,

anhydrite in m-thick

randomly oriented

precipitation of

beds of green to

acicular and bladed

anhydrite

brown silty

anhydrite crystals

within

dolomicrite.

that uncommonly

sediment, high

coalesce to form

aridity, low to

chicken-wire

high basin

structure. Angular to

restriction.

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ACCEPTED MANUSCRIPT sub-angular, siltsized quartz grains and framboidal pyrite

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disseminated

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throughout

Red, structureless

Grains consist of

Terrestrial-

quartz arenite

with common

well-sorted angular to

marine

limestone intraclasts,

sub-angular quartz,

interface, high

anhydrite nodules,

<5% muscovite and

humidity during

and nodular and cubic

plagioclase in

karst

halite. Limestone

hematite cement.

formataion.

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Muscovite-rich

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clasts consist of

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F10

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dolomicrite.

Halite consists of

calcareous

randomly oriented

microbialite and

microcrystalline

oncolitic grainstone.

cubes encompassing

This facies infills

saddle dolomite.

karst surfaces that occur in structureless and nodular anhydrite (Facies F3 and F9).

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Figure 1

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Figure 2

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Figure 3

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Figure 4

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Figure 5

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Figure 6

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Figure 7

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Figure 8

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Figure 9

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Figure 10

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Figure 11

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Figure 12

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