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SEQUENCE STRATIGRAPHIC FRAMEWORK AND FACIES MODELS FOR THE LATE DEVONIAN TO EARLY MISSISSIPPIAN SAPPINGTON FORMATION (BAKKEN EQUIVALENT), SOUTHWEST MONTANA

By
Aaron P. Rodriguez
Aaron P. Rodriguez
Department of Geological Sciences, University of Idaho, 875 Perimeter Drive, Moscow, Idaho 83844 USA; Hess Corporation, 1501 McKinney Street, Houston, Texas 77010 USA
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George W. Grader
George W. Grader
PRISEM Geoconsulting, 823 West 25th Avenue, Spokane, Washington 99203 USA
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John C. Hohman
John C. Hohman
Hess Corporation, 1501 McKinney Street, Houston, Texas 77010 USA
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P. Ted Doughty
P. Ted Doughty
PRISEM Geoconsulting, 823 West 25th Avenue, Spokane, Washington 99203 USA
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John Guthrie
John Guthrie
Hess Corporation, 1501 McKinney Street, Houston, Texas 77010 USA
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Peter E. Isaacson
Peter E. Isaacson
Department of Geological Sciences, University of Idaho, 875 Perimeter Drive, Moscow, Idaho 83844 USA
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Published:
January 01, 2017
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ABSTRACT:

The Sappington Formation is a Late Devonian to Early Mississippian age, primarily siliciclastic, formation that outcrops in southwestern Montana. The Sappington Formation has been presented in the past as broadly analogous in lithologic character and age to other formations in the region, the Bakken and Exshaw Formations. The Sappington Formation was the focus of several studies in the 1950s through 1970s that extensively analyzed the fauna and distribution of the formation and established a lithostratigraphic and biostratigraphic framework. This study provides a needed present day look at the Sappington Formation, by incorporating extensive previous work with present day field observations and modern geologic concepts. The methodology applied to this work includes literature review, outcrop observations, and interpretations on lithofacies, depositional environments, and sequence stratigraphy. Results from this work include a sequence stratigraphic model, depositional models, and a summary of the effects of allocylic processes on deposition. Three sequences were identified using previous biostratigraphy and correlated throughout the study area using lithostratigraphy. Recently, intracratonic Late Devonian and Early Mississippian age formations have become of economic importance as “unconventional” hydrocarbon plays, owing to success in the Bakken Formation.

INTRODUCTION

The purpose of this paper is to document field observations, both new and previously published, of the Late Devonian to Early Mississippian Sappington Formation of southwestern Montana and to provide a modern interpretation of lateral and vertical facies relationships, depositional models, allocyclic processes, and sequence stratigraphy. Work presented here is based on outcrop observations from southwest Montana and eastern Idaho (Rodriguez 2014), supplemented with published data. This study provides an observation-based lithostratigraphic and sequence stratigraphic framework for future work on the Sappington and Bakken Formations. Research on the Sappington Formation has economic implications for industry because it relates directly to hydrocarbon production from the Bakken Formation, with which it is temporally and lithologically correlative.

Past and Present Work

The study area for this research is around the town of Three Forks, Montana, which lies at the headwaters of the Missouri River, and is one of the earliest areas in the western United States to be geologically examined. Lewis and Clark traveled through this area in the summer of 1805, and the first geologic observations of the area were documented by Hayden (1869). The earliest geologists (Peale 1893, 1896; Raymond 1907; Schuchert 1910; Haynes 1916a, 1916b) to study the Devonian and Mississippian in the Three Forks, Montana area classified the Sappington Formation as the uppermost member of the Three Forks Formation. This early work was focused on regional lithostratigraphy and brachiopod biostratigraphy. The brachiopod stratigraphy concluded that the uppermost Three Forks Formation contained brachiopod assemblages, indicating a transition from Devonian to Mississippian age (Peale 1893). Berry (1943) was the first to name the Sappington Formation, propose it as a formation, and designate the type locality at the Milligan Canyon outcrop. The Sappington Formation was studied intensively from the 1950s to the early 1970s (Sloss 1950; Holland 1952; McMannis 1955, 1962; Gutschick and Perry 1957, 1959; Achauer 1959; Gutschick 1962; Gutschick et al. 1962; Rau 1962; Sandberg 1962a, 1962b, 1963, 1965; Benson 1966; Gutschick and Moreman 1967; Gutschick and Rodriguez 1967, 1979; Sandberg and Klapper 1967; Gutschick and Sandberg 1970; MacQueen and Sandberg 1970; Gutschick and Lamborn 1975; Tysdal 1976). These authors made an extensive set of field based observations on the Sappington Formation and surrounding strata in western Montana, northwestern Wyoming, and eastern Idaho. The data were heavily weighted toward biostratigraphy and paleontology and were not done in the context of modern sequence stratigraphic principles.

Published work focused on the Sappington Formation largely ended after the 1970s, but renewed research began on the Sappington Formation in 2008 by PRISEM Geoscience Consulting and has been followed by others in academia and industry. Recent work on the Sappington Formation includes Doughty and Grader (2010); Adiguzel (2012); Adiguzel et al. (2012); Schietinger (2007); Doughty et al. (2014a, 2014b); Nagase (2014); Rodriguez (2014); Borski (2015); Cole et al. (2015); Phelps (2015); and Hohman et al. (2016). The new research is driven by a desire to better understand the Bakken Formation, from which a large volume of hydrocarbons have been produced by unconventional drilling methods, starting in the mid to late 2000s. The Bakken Formation is only present in the subsurface in the Williston Basin (Fig. 1) of eastern Montana, western North Dakota, and southern Saskatchewan. The Sappington Formation was first speculated to correlate to the Bakken Formation through lithostratigraphy (Sandberg 1965). The Bakken Formation does not outcrop in the Williston Basin, which makes the Sappington Formation the best outcropping analog to study the Bakken Formation.

Fig. 1.

—Paleogeographic map of the area of interest for this study. The dashed line represents the approximate depositional extent of the Sappington Formation from Adiguzel (2012), the Bakken Formation from Gaswirth and Marra (2015), Exshaw Formation from MacQueen and Sandberg (1970). The basin outlines represent the areas of thickest deposition. The location of the Antler Orogenic Highlands and Antler Foreland Basin are derived from Poole (1974).

Fig. 1.

—Paleogeographic map of the area of interest for this study. The dashed line represents the approximate depositional extent of the Sappington Formation from Adiguzel (2012), the Bakken Formation from Gaswirth and Marra (2015), Exshaw Formation from MacQueen and Sandberg (1970). The basin outlines represent the areas of thickest deposition. The location of the Antler Orogenic Highlands and Antler Foreland Basin are derived from Poole (1974).

Geologic Setting

In the late Devonian, Montana was situated on relatively stable continental crust adjacent to an active convergent plate margin to the west in present day Idaho (Dorobek et al. 1991). The orogenic event in Nevada associated with the coeval convergent margin is known as the Antler Orogeny (Roberts 1949, Roberts et al. 1958). In Idaho, the extension of the Antler Orogeny thrust belt complex is poorly preserved, but the extension of the Antler Foreland Basin is well documented by 3900+ ft of Devonian age Milligan Formation basin fill, as well as 790+ m of Mississippian age McGowan Creek Formation basin fill (Sandberg et al. 1975, Dorobek et al. 1991). East of the Antler Foreland Basin on the Montana Platform, low amplitude highlands and basins formed as a result of the translation of compressive stress at the Antler convergent margin (Dorobek et al. 1991). Areas of uplift and subsidence on the Montana Platform are set up by an area of potentially weaker crust associated with a Precambrian aulacogen (Dorobek et al. 1991). The Sappington Basin subsided within this area of weaker crust and acted as the primary depositional center for Sappington Formation sediment. Coeval to the deposition of the Sappington Formation, the Exshaw and Bakken Formations were being deposited in the South Alberta Basin and Williston Basin (Fig. 1) (Sandberg and Hammond 1958, MacQueen and Sandberg 1970, Doughty and Grader 2010). Subsidence of the area of weaker crust accelerated in the Mississippian age and acted with sea-level rise (Haq and Schutter 2008) to create accommodation for the deposition of the Madison Group carbonates (Dorobek et al. 1991).

The Sappington Formation outcrops are presently located within the Montana Disturbed Belt, a zone of deformation associated with Sevier and Laramide orogenic shortening originating from the west (Robinson 1959). All the outcrops in the study are allochthonous, with maximum east directed heave on some structures of 45 miles (Burton et al. 1998).

Biostratigraphy

Early brachiopod dating suggested much of the Sappington Formation was Early Mississippian age (Peale 1893, Gutschick and Rodriguez 1967). However, later conodont dating reported the Sappington Formation to be mostly Late Devonian in age (Knechtel and Hass 1953; Klapper 1966; Sandberg and Klapper 1967; Sandberg et al. 1972, 1988; Sandberg and Poole 1977; Gutschick and Rodriguez 1979). Sandberg et al. (1972) conducted a detailed conodont study of the Sappington Formation, in which each of the six Sappington Formation lithostratigraphic units, as well as the underlying Three Forks Formation and overlying Lodgepole Formation, were dated. The ages of these units, combined with lithostratigraphic correlation between outcrops, were used to create a chronostratigraphic framework (Fig. 2).

Fig. 2.

—Sappington Formation chronostratigraphic chart synthesis with the absolute ages of Sappington Formation 2012 conodont zones (Becker et al. 2012, Davydov et al. 2012), Sandberg 1972 conodont zones (Sandberg et al. 1972), global sea-level curve (Haq and Schutter 2008), global onlap curve (Haq and Schutter 2008), global sequence boundaries (Haq and Schutter 2008), and global glaciation events (Haq and Schutter 2008). The Sandberg et al. (1972) conodont zones are correlated to the 2012 conodont zones, which have been correlated to absolute ages in the 2012 time scale. The absolute ages from the Haq and Schutter (2008) data are correlated to the absolute ages from the 2012 time scale.

Fig. 2.

—Sappington Formation chronostratigraphic chart synthesis with the absolute ages of Sappington Formation 2012 conodont zones (Becker et al. 2012, Davydov et al. 2012), Sandberg 1972 conodont zones (Sandberg et al. 1972), global sea-level curve (Haq and Schutter 2008), global onlap curve (Haq and Schutter 2008), global sequence boundaries (Haq and Schutter 2008), and global glaciation events (Haq and Schutter 2008). The Sandberg et al. (1972) conodont zones are correlated to the 2012 conodont zones, which have been correlated to absolute ages in the 2012 time scale. The absolute ages from the Haq and Schutter (2008) data are correlated to the absolute ages from the 2012 time scale.

DATA SET AND METHODS

The majority of the 14 outcrops in Figure 3 were originally documented in past literature (Berry 1943, Gutschick and Perry 1957, Achauer 1959, Gutschick et al. 1962, Gutschick 1962, Benson 1966, Klapper 1966, Gutschick and Rodriguez 1990). These outcrops have been revisited by recent efforts from PRISEM Geoscience Consulting, the University of Idaho, Hess Corporation, and others in academia and industry. All of the outcrops were described and measured using a Jacob Staff and a Brunton Compass. Rock samples of representative facies were collected for closer examination, and an extensive set of facies photographs and outcrop photo mosaics were collected.

Fig. 3.

—Map of Sappington Formation outcrop locations used in this study. ANC2 = Antelope Creek; ASC2 = Ashbough Canyon; BRBG = Brown Back Gulch; COC2 = Copper City; DH10 = Dry Hollow; FRL = Frazier Lake; LOG = Logan Gulch; MIC = Milligan Canyon; MOC = Moose Creek; NIG = Nixon Gulch; POP = Pomp Peak (Peak 9559); RH = Red Hill; RES = Rekap Station; SC4 = Storm Castle.

Fig. 3.

—Map of Sappington Formation outcrop locations used in this study. ANC2 = Antelope Creek; ASC2 = Ashbough Canyon; BRBG = Brown Back Gulch; COC2 = Copper City; DH10 = Dry Hollow; FRL = Frazier Lake; LOG = Logan Gulch; MIC = Milligan Canyon; MOC = Moose Creek; NIG = Nixon Gulch; POP = Pomp Peak (Peak 9559); RH = Red Hill; RES = Rekap Station; SC4 = Storm Castle.

RESULTS

Lithostratigraphy

The Sappington Formation is located stratigraphically between the Devonian Three Forks Formation below and the Mississippian Lodgepole Formation above (Fig. 4). Conodont biostratigraphy (Sandberg et al. 1972) places the Devonian–Mississippian boundary within the silty Middle Member of the Sappington Formation. The Sappington Formation is informally subdivided into three lithologically distinct members: the Lower Member (black shale), Middle Member (siltstone), and Upper Member (black shale), in the same way as the Bakken Formation. Previous work further subdivided the Sappington Formation into nine (Gutschick et al. 1962) lithostratigraphic units and five lithostratigraphic units (Sandberg 1965). The lithostratigraphic unit nomenclature used in this paper adapts both the Sandberg (1965) numbering scheme of Unit 1–5, as well as the Gutschick et al. (1962) A–I lettering scheme. The equivalency of the current and historical lithostratigraphic subdivisions is illustrated in Figure 4. Subdividing the Sappington Formation into lithostratigraphic units is needed to align with previous authors, but it is preferred that the Sappington Formation be herein subdivided and referenced in terms of the sequence stratigraphic framework presented in this paper.

Fig. 4.

—Sappington Formation stratigraphic chart with stratigraphic nomenclature, stratigraphic column, lithostratigraphic nomenclature (historical and proposed), lithofacies, depositional environments, dominant depositional processes, relative macrofauna abundances, bioturbation intensity index (BI), surfaces, sequences, and systems tracts.

Fig. 4.

—Sappington Formation stratigraphic chart with stratigraphic nomenclature, stratigraphic column, lithostratigraphic nomenclature (historical and proposed), lithofacies, depositional environments, dominant depositional processes, relative macrofauna abundances, bioturbation intensity index (BI), surfaces, sequences, and systems tracts.

This paper identifies 16 lithofacies in the Sappington Formation. The descriptions of these lithofacies are presented in Table 1. The correlations of the lithofacies to the lithostratigraphic and sequence stratigraphic framework are illustrated in Figure 4.

Table 1.

—Table of Sappington Formation lithofacies and their respective lithology, grain size, sedimentary structure/feature, fauna, recognizable ichnogenera, other features, and depositional environments. BI = bioturbation index, HCS = hummocky cross stratification, NA = not available.

Lithofacies Lithology Depositional / diagenetic features Fauna Recognizable ichnogenera B.I. Interpreted depositional environment 
6C bluish gray silly mudstone bioturbation none unknown NA unknown 
6B dark gray siltstone bioturbation none Zoophycos, Teichichnus dysoxic shallow marine 
6A black shale laminations none unknown NA anoxic deep marine 
5E orangish beige sandstone tabular cross bedding none none eolian 
5D bluish gray oolitic grainstone tabular cross bedding none none NA carbonate shoal 
5C orangish beige siltstone amalgamating wave ripples, climbing ripples, trough cross beds none Lockeia upper shoreface 
5B orangish beige siltstone bioturbation, HCS, wave ripples, calcite cemented beds none Nereites (background lithology), Teichichnus(storm beds) lower shoreface 
5A orangish beige siltstone bioturbation none Nereites lower shoreface 
4B greenish gray silty shale heterolithic bedding, HCS, wave ripples, combined flow ripples none Arenicolites (Bifimgites), Planolite, Chondrites upper ofEshore/tidal flat 
4A greenish gray silty shale heterolithic bedding, starved ripples none Arenicolites (Bifimgites), Planolites, Teichichnus lower ofishore/tidal flat 
3B yellowish beige silty wacketstone calcite cementation brachiopods, crinoid stems none NA sediment starved shallow marine 
3A yellowish beige siltstone bioturbation, HCS, wave ripples brachiopod fragments Nereites, Planolites, Teichichnus lower shoreface 
2A bluish gray silly oncolitic wackestone beds of oncolites brachiopods, bryozoans, crinoid stems none NA carbonate bank 
ID greenish gray shale thin bedded brachiopods, bivalves unknown NA estuarine (marine) 
1C black shale thin bedded, conchoidal fracturing conchostracans, echinoderms (brittle starfish) unknown NA dysoxic estuarine (brackish) 
1A black shale thin bedded, chert interbeds radiolarians, tasmanites unknown NA anoxic deep marine 
Lithofacies Lithology Depositional / diagenetic features Fauna Recognizable ichnogenera B.I. Interpreted depositional environment 
6C bluish gray silly mudstone bioturbation none unknown NA unknown 
6B dark gray siltstone bioturbation none Zoophycos, Teichichnus dysoxic shallow marine 
6A black shale laminations none unknown NA anoxic deep marine 
5E orangish beige sandstone tabular cross bedding none none eolian 
5D bluish gray oolitic grainstone tabular cross bedding none none NA carbonate shoal 
5C orangish beige siltstone amalgamating wave ripples, climbing ripples, trough cross beds none Lockeia upper shoreface 
5B orangish beige siltstone bioturbation, HCS, wave ripples, calcite cemented beds none Nereites (background lithology), Teichichnus(storm beds) lower shoreface 
5A orangish beige siltstone bioturbation none Nereites lower shoreface 
4B greenish gray silty shale heterolithic bedding, HCS, wave ripples, combined flow ripples none Arenicolites (Bifimgites), Planolite, Chondrites upper ofEshore/tidal flat 
4A greenish gray silty shale heterolithic bedding, starved ripples none Arenicolites (Bifimgites), Planolites, Teichichnus lower ofishore/tidal flat 
3B yellowish beige silty wacketstone calcite cementation brachiopods, crinoid stems none NA sediment starved shallow marine 
3A yellowish beige siltstone bioturbation, HCS, wave ripples brachiopod fragments Nereites, Planolites, Teichichnus lower shoreface 
2A bluish gray silly oncolitic wackestone beds of oncolites brachiopods, bryozoans, crinoid stems none NA carbonate bank 
ID greenish gray shale thin bedded brachiopods, bivalves unknown NA estuarine (marine) 
1C black shale thin bedded, conchoidal fracturing conchostracans, echinoderms (brittle starfish) unknown NA dysoxic estuarine (brackish) 
1A black shale thin bedded, chert interbeds radiolarians, tasmanites unknown NA anoxic deep marine 

Lithostratigraphic Units

Unit 1: Unit 1 is located between the Three Forks Formation below and Unit 2 of the Sappington Formation above (Fig. 4). Within the study area, Unit 1 has a maximum thickness of 14 m (46 ft) at the Ashbough Canyon outcrop, and a minimum thickness of <0.3 m (1 ft) at the Moose Creek outcrop. The maximum documented thickness of Unit 1 is 22.9 m (75 ft) at the Long Canyon outcrop in eastern Idaho (Sandberg et al. 1975). Unit 1 contains three shale lithofacies: 1A, 1C, 1D (Table 1; Fig. 5). Lithofacies 1A is a black shale with chert interbeds; lithofacies 1C is a black shale with conchostracans and brittle starfish (Fig. 6); and lithofacies 1D is a gray shale with abundant brachiopods. Gutschick et al. (1962) first subdivided the Sappington Formation lower black shale into four shale lithostratigraphic units. Lithostratigraphic unit B from Gutschick et al. (1962) is interpreted in this paper as a diagenetic feature and therefore is not acknowledged as a lithologic unit.

Fig. 5.

—Unit 1 lithofacies. A) 1A (hand sample), black shale with marine fauna; B) 1A (outcrop), black shale and chert beds; C) 1A (hand sample), common appearance of 1A in high deformation areas (lithofacies 1B of Gutschick et al. (1962); D) 1C (outcrop), black shale with brackish fauna; E) 1D (hand sample), fossiliferous gray shale; F) outcrop photo of lag with phosphatic fish fragments and conodonts; G) diagenetic rock located beneath S_0.

Fig. 5.

—Unit 1 lithofacies. A) 1A (hand sample), black shale with marine fauna; B) 1A (outcrop), black shale and chert beds; C) 1A (hand sample), common appearance of 1A in high deformation areas (lithofacies 1B of Gutschick et al. (1962); D) 1C (outcrop), black shale with brackish fauna; E) 1D (hand sample), fossiliferous gray shale; F) outcrop photo of lag with phosphatic fish fragments and conodonts; G) diagenetic rock located beneath S_0.

Fig. 6.

—Sappington Formation fauna. A) Brittle starfish (red circle) in lithofacies 1C, B) Conchostracan (red circle) in lithofacies 1C, C) Mollusk (red circle) and other shelly debris in lithofacies 1D, D) Crinoid stem (red circle) and other fossil debris in lithofacies 2A, E) Oncolite with brachiopod nucleus (red circle) and other fossil debris in lithofacies 2A.

Fig. 6.

—Sappington Formation fauna. A) Brittle starfish (red circle) in lithofacies 1C, B) Conchostracan (red circle) in lithofacies 1C, C) Mollusk (red circle) and other shelly debris in lithofacies 1D, D) Crinoid stem (red circle) and other fossil debris in lithofacies 2A, E) Oncolite with brachiopod nucleus (red circle) and other fossil debris in lithofacies 2A.

Unit 2: Unit 2 is located between Unit 1 below and Unit 3 above (Fig. 4). The character of the gradational contact between Unit 2 and Unit 3 contact makes differentiating thicknesses difficult. The combined thickness of the Unit 2 and Unit 3 succession is a minimum thickness of 4.0 m (13 ft) at the Nixon Gulch outcrop and a maximum thickness of 10.4 m (34 ft) at the Rekap Station outcrop. Unit 2 is a silty oncolitic wackestone (Fig. 7) with brachiopods and sponges composing the nucleus of the oncolite (Gutschick and Perry 1959). Oncolites have been found in equivalent age formations to the Sappington Formation in Nevada (Pilot Shale Formation) and Utah (Leatham Formation) (Gutschick and Rodriguez 1979). Similar fauna to what is seen at the nucleus of the Sappington Formation oncolites has been found at the base of the middle siltstone member of the Bakken Formation (Smith and Bustin 2000).

Fig. 7.

—Unit 2 lithofacies. A) 2A (outcrop), silty oncolitic wackestone; B) 2A (outcrop), less developed oncolites with less algal coatings around fauna.

Fig. 7.

—Unit 2 lithofacies. A) 2A (outcrop), silty oncolitic wackestone; B) 2A (outcrop), less developed oncolites with less algal coatings around fauna.

Unit 3: Unit 3 is located above Unit 2 and below Unit 4 (Fig. 4) and is a yellowish burrowed siltstone composed of two lithofacies, 3A and 3B (Fig. 8). Lithofacies 3A is a highly bioturbated siltstone with interbeds of siltstone containing hummocky cross stratification and wave ripples. Lithofacies 3B is a bluish yellow silty wackestone with brachiopods. The two lithofacies have distinctly different outcrop weathering patterns (Fig. 8A). Lithofacies 3B is most commonly positioned overlying lithofacies 3A in uppermost Unit 3, although additional occurrences of 3B have been found interbedded within 3A. Gutschick et al. (1962) and Sandberg (1965) were the first to recognize Unit 3 as a lithostratigraphic unit of the Sappington Formation.

Fig. 8.

—Unit 3 lithofacies. A) Photo showing the outcrop expression of lithofacies 3A and 3B; B) 3A (cut hand sample), highly bioturbated siltstone with Nereites (Ne) and Planolites (P) ichnogenera; C) 3B (cut hand sample), silty fossiliferous limestone with fragments of brachiopods.

Fig. 8.

—Unit 3 lithofacies. A) Photo showing the outcrop expression of lithofacies 3A and 3B; B) 3A (cut hand sample), highly bioturbated siltstone with Nereites (Ne) and Planolites (P) ichnogenera; C) 3B (cut hand sample), silty fossiliferous limestone with fragments of brachiopods.

Unit 4: Unit 4 is positioned between Unit 3 below and Unit 5 above (Fig. 4). Unit 4 reaches a maximum thickness of 7.6 m (25 ft) at the Milligan Canyon outcrop and a minimum thickness of 1.5 m (5 ft) at the Moose Creek outcrop. Unit 4 is a greenish gray shaley siltstone that is subdivided into two lithofacies 4A and 4B (Fig. 9). Lithofacies 4A is a laminated and bioturbated shale with silty thin beds. Lithofacies 4B is a shaley bioturbated siltstone with hummocky cross stratification and ripples. Lithofacies 4A and 4B have not been observed in the same outcrop, but similarities in character and stratigraphic position imply they are gradational laterally and vertically. To the west in the study area (i.e., Red Hill, Ashbough Canyon) the lithologic appearance of Unit 4 described in lithofacies 4A and 4B is not present. From the data it is unclear whether Unit 4 has been erosionally removed or Unit 4 is present in a different lithologic character. Gutschick et al. (1962) reported fauna in Unit 4 only in one outcrop (Antelope Creek), but no fauna was observed in any Unit 4 locations from this study.

Fig. 9.

—Unit 4 lithofacies. A) 4A (outcrop), bioturbated silty shale with starved ripples; B) 4A (outcrop), magnified photo of 4A showing bioturbation and laminae; C) 4B (outcrop), bioturbated shaley siltstone with storm beds; D) 4B (cut hand sample), magnified photo of 4B showing hummocky cross stratification in a storm bed and bioturbation in the background lithology.

Fig. 9.

—Unit 4 lithofacies. A) 4A (outcrop), bioturbated silty shale with starved ripples; B) 4A (outcrop), magnified photo of 4A showing bioturbation and laminae; C) 4B (outcrop), bioturbated shaley siltstone with storm beds; D) 4B (cut hand sample), magnified photo of 4B showing hummocky cross stratification in a storm bed and bioturbation in the background lithology.

Unit 5: Unit 5 is located between Unit 4 below and Unit 6 above (Fig. 4). Unit 5 is the most resistant to erosion of the six Sappington Formation lithostratigraphic units, and as a result it is the unit that first distinguished the Sappington Formation to early geologists such as Peale (1896). Gutschick et al. (1962) conducted the first detailed study of Unit 5, in which multiple sedimentary structures were described. Unit 5 is a maximum thickness of 10.1 m (33 ft) at the Milligan Canyon section and at the Rekap Station outcrop. Unit 5 is a minimum thickness of 4.0 m (13 ft) at the Moose Creek outcrop. Unit 5 is an orangish variably sandy siltstone, and it has been subdivided into five lithofacies: 5A, 5B, 5C, 5D, and 5E (Fig. 10). Lithofacies 5A is an intensely burrowed siltstone, and lithofacies 5B is an intensely burrowed siltstone with hummocky cross stratification and wave ripples. Lithofacies 5C is a silty very fine grained sandstone with wave ripples and trough cross bedding, lithofacies 5D is an oolitic very fine grained sandstone with tabular cross bedding, and lithofacies 5E is a very fine grained sandstone with tabular cross bedding. A composite lithofacies stacking pattern for Unit 5 is illustrated in Figure 4.

Fig. 10.

—Unit 5 lithofacies. A) 5A, bioturbated siltstone; B) 5B, bioturbated siltstone with storm beds; C) 5C, siltstone with wave ripples; D) 5E, very fine grained sandstone with tabular cross bedding; E) 5D, oolitic grainstone with tabular cross bedding; F) 5D, (from cut hand sample) very fine grained sandstone with inverse graded bedding.

Fig. 10.

—Unit 5 lithofacies. A) 5A, bioturbated siltstone; B) 5B, bioturbated siltstone with storm beds; C) 5C, siltstone with wave ripples; D) 5E, very fine grained sandstone with tabular cross bedding; E) 5D, oolitic grainstone with tabular cross bedding; F) 5D, (from cut hand sample) very fine grained sandstone with inverse graded bedding.

Unit 6: Unit 6 is positioned between Unit 5 below and the Lodgepole Formation above (Fig. 4). Unit 6 reaches a maximum thickness of 3.4 m (11 ft) at the Ashbough Canyon outcrop and is not present at Antelope Creek, Brown Back Gulch, Copper City, Dry Hollow, Milligan Canyon, and Red Hill outcrops. Unit 6 is subdivided into three lithofacies of a wide range of lithologic character (Fig. 11): lithofacies 6A is a silty black shale, lithofacies 6B is a bioturbated dark gray siltstone with the Zoophycos ichnogenera, and lithofacies 6C is a limestone (mudstone). A composite lithofacies stacking pattern of Unit 6 is illustrated in Figure 4. Unit 6 has been described as a part of the Sappington Formation (Gutschick et al. 1962) and as a separate formation named the Cottonwood Canyon Formation (Sandberg and Klapper 1967).

Fig. 11.

—Unit 6 lithofacies. A) Lag (hand sample), composed of phosphatic fish parts and conodonts; B) 6A (hand sample), black shale; C) 6B (hand sample), bioturbated siltstone; D) 6C (hand sample), limestone.

Fig. 11.

—Unit 6 lithofacies. A) Lag (hand sample), composed of phosphatic fish parts and conodonts; B) 6A (hand sample), black shale; C) 6B (hand sample), bioturbated siltstone; D) 6C (hand sample), limestone.

Ichnogenera

The relative intensity of bioturbation of the Sappington Formation stratigraphic units was estimated by assigning a bioturbation index (BI) (Fig. 4). Classifying BI and identifying ichnogenera was made difficult by poor outcrop quality. Therefore, a BI was not assigned to lithofacies where there was a low confidence factor.

Lithofacies 3A has a maximum BI of 5, which is too thorough to identify specific ichnogenera. At outcrops of lithofacies 3A where there is a relatively lower BI, Arenicolites, Planolites, Teichichnus, and Thalassinoides were observed (Fig. 12A, B). The form of Arenicolites that is present in the Sappington Formation is a rare form called Bifungites bisagitta, which is first noted by Gutschick and Lamborn (1975) (Fig. 12C). Lithofacies 4A and 4B have a BI of 3–4 and the following ichnogenera: Arenicolites, Chondrites, and Planolites. Lithofacies 5A and 5B have a BI of 3–4 with the following recognizable ichnogenera: Nereites and Teichichnus. Lithofacies 5C has a BI of 1, and ichnogenera include Lockeia and Nereites (Fig. 12D). Lithofacies 5E has a BI of 0. Lithofacies 6B has a BI of 3, and ichnogenera include Teichichnus and Zoophycos (Fig. 12E, F).

Fig. 12.

—Sappington Formation Ichnogenera. A)Planolites (P) and Bifungites (B) (bedding plane view of location of arrow in C inset) ichnogenera in lithofacies 3A (bedding plane view); B)Thalassanoides (Th) ichnogenera in lithofacies 3A (bedding plane view); C)Bifungites (B) ichnogenera rare bedding plane view of basal most horizontal burrow (bedding plane view), inset is a rare cross section view of vertical portion of Bifungites (B) ichnogenera in lithofacies 4A; D)Lockeia (Lo) and Nereites (Ne) ichnogenera in lithofacies 5A (bedding plane view); E)Teichichnus (Te) ichnogenera in lithofacies 6B (cross section view); F)Zoophycos (Z) ichnogenera in lithofacies 6B (Bedding plane view). See Gutschick and Lamborn (1975) for Bifungites schematic.

Fig. 12.

—Sappington Formation Ichnogenera. A)Planolites (P) and Bifungites (B) (bedding plane view of location of arrow in C inset) ichnogenera in lithofacies 3A (bedding plane view); B)Thalassanoides (Th) ichnogenera in lithofacies 3A (bedding plane view); C)Bifungites (B) ichnogenera rare bedding plane view of basal most horizontal burrow (bedding plane view), inset is a rare cross section view of vertical portion of Bifungites (B) ichnogenera in lithofacies 4A; D)Lockeia (Lo) and Nereites (Ne) ichnogenera in lithofacies 5A (bedding plane view); E)Teichichnus (Te) ichnogenera in lithofacies 6B (cross section view); F)Zoophycos (Z) ichnogenera in lithofacies 6B (Bedding plane view). See Gutschick and Lamborn (1975) for Bifungites schematic.

The ichnogenera assemblages found in the Sappington Formation support placement into the Cruziana ichnofacies. Cruziana ichnofacies are indicative of marine and moderate to high energy environments found typically in the lower shoreface to upper offshore depositional settings (Pemberton et al. 2011).

Diagenetic Features

The most prominent diagenetic features in the Sappington Formation are calcite cementation and large scale soft sediment deformation. The calcite cementation occurs in two forms, nodules and storm beds. The nodules are a light blue color and have a disk geometry that is longer along the x and y axes than along the z axis (Fig. 13B, C). The storm bed calcite cementation is a light blue color, and the cementation is restricted to the extents of the storm bed. The internal stratification of the parent rock is preserved in both forms of cementation (Fig. 13A, E). The nodules have been observed in lithofacies 5A, 5B, and 5C, and the storm bed cementation has been observed in lithofacies 3A and 5B. The cementation is interpreted to have occurred relatively soon after deposition based on differential compaction of the nodules vs. the surrounding rock.

Fig. 13.

Sappington Formation diagenetic features. A) Calcite cemented storm bed with preserved bedding in lithofacies 5B from Dry Hollow (cross section view); B) Calcite cemented nodules (red circles) from storm bed in lithofacies 5B from Milligan Canyon (bedding plane view); C) Calcite cemented nodules in lithofacies 5C at Milligan Canyon just below contact with overlying Lodgepole Fm (cross section view); D) Soft sediment deformation in Unit 5 at Milligan Canyon just below the contact with the Lodgepole Fm (cross section view); E) Inset of D, calcite cemented nodule in soft sediment deformation in Unit 5 at Milligan Canyon just below contact with the Lodgepole Fm. The features in E indicate that calcite cementation happened prior to soft sediment deformation.

Fig. 13.

Sappington Formation diagenetic features. A) Calcite cemented storm bed with preserved bedding in lithofacies 5B from Dry Hollow (cross section view); B) Calcite cemented nodules (red circles) from storm bed in lithofacies 5B from Milligan Canyon (bedding plane view); C) Calcite cemented nodules in lithofacies 5C at Milligan Canyon just below contact with overlying Lodgepole Fm (cross section view); D) Soft sediment deformation in Unit 5 at Milligan Canyon just below the contact with the Lodgepole Fm (cross section view); E) Inset of D, calcite cemented nodule in soft sediment deformation in Unit 5 at Milligan Canyon just below contact with the Lodgepole Fm. The features in E indicate that calcite cementation happened prior to soft sediment deformation.

Soft sediment deformation on various scales occurs in Unit 5 of the Sappington Formation. The soft sediment deformation forms detached inclined to recumbent isoclinal folds ranging in size from several inches to several feet (Fig. 13D, E). The folds were first referred to by Gutschick et al. (1962) as “flow rolls,” and they have been reported on more recently by Adiguzel et al. (2012) and Phelps (2015). The folds have been observed at outcrops in the Bridger Mountains, as well at outcrops along the Dry Hollow–Milligan Canyon outcrop belt. The folds formed after calcite cementation, since calcite nodules are observed to be folded within the soft sediment deformation (Fig. 13D, E). The formation of these features could be the result of slumping or dewatering due to rapid burial by overburden sediment.

Surfaces

Six regionally correlatable key surfaces have been identified from outcrop of the Sappington Formation (Fig. 4). Ages of the surfaces are derived from conodont biostratigraphic dating by Sandberg et al. (1972) of the six Sappington Formation lithostratigraphic units, the Three Forks Formation, and the Lodgepole Formation (Fig. 2). Surfaces were then correlated using lithostratigraphy of the Sappington Formation. The key Sappington Formation surfaces are numbered 0 through 5 (S_0, S_1, S_2, S_3, S_4, S_5).

Surface 0 (S_0) is located between the underlying Three Forks Formation and Unit 1 of the overlying Sappington Formation (Fig. 14). The surface is characterized by a distinct lithology change, a surface of discoloration, and an irregular erosional surface. The lithology of the Three Forks Formation is a green fossiliferous shale and/or a light blue wackestone, and the lithology of Unit 1 of the Sappington Formation is a black shale with interbeds of chert. The surface of discoloration marking S_0 is a rusty orange brown color.

Fig. 14.

A) outcrop photo of the surfaces (S_0 and S_1) that bound sequence 1; B) annotation of the outcrop photo from A showing observed fauna, sedimentary structures, lithostratigraphy, and key surfaces. P = paleosol.

Fig. 14.

A) outcrop photo of the surfaces (S_0 and S_1) that bound sequence 1; B) annotation of the outcrop photo from A showing observed fauna, sedimentary structures, lithostratigraphy, and key surfaces. P = paleosol.

Beneath S_0 is a low density rock with a brecciated fabric and red staining (Fig. 5G). S_0 is interpreted as an unconformity (Gutschick et al. 1962) and a sequence boundary (Cole et al. 2015).

Surface 1 (S_1) is located between the lower portion of Unit 1 and the upper portion of Unit 1 of the Sappington Formation (Fig. 14). The surface is characterized by a lithology and faunal change, a surface of discoloration, and a bed containing fish bones and conodonts (lag) above S_1. The lithology below S_1 is a black shale with interbeds of layered chert (lithofacies 1A), and the lithology above is a black shale composed of conchostracans and brittle starfish (lithofacies 1B). Conchostracans have previously been reported from lithofacies 1C of the Sappington Formation by several authors (Gutschick and Perry 1959, Gutschick et al. 1962, Gutschick and Lamborn 1975, Cole et al. 2015). Surface 1 can easily be overlooked as a chronostratigraphic significant surface because it is often not well exposed in outcrop due to the recessive nature of the bounding strata, as well as the similarity in the lithologic character of the bounding strata. Additionally, the contact between Unit 1 and Unit 2 can be easily misidentified as a time significant surface due to a stark contrast in lithology. However, that lithologic contact is conformable and is not of chronostratigraphic significance. S_1 is interpreted as an unconformity and a sequence boundary (Cole et al. 2015).

Surface 2 (S_2) is located between Unit 3 and Unit 4 of the Sappington Formation (Fig. 15). The surface is rarely exposed well in outcrop due to the recessive character of Unit 4. The surface is characterized by an abrupt change in lithology from a silty fossiliferous limestone (lithofacies 3B) below to a heterolithic argillaceous siltstone (lithofacies 4A/4B) above. The surface is recognizable throughout the majority of the study area, but at western outcrop locations (i.e., Red Hill and Ashbough Canyon) the surface is not distinguishable because the lithologic character of Unit 4 becomes more similar to Unit 3 and Unit 5. S_2 is interpreted to be a significant surface, but the type of sequence stratigraphic surface that S_2 represents is not clear due to uncertainties in the depositional environment interpretation of Unit 4.

Fig. 15.

—A) annotation of the outcrop photo from B showing observed sedimentary structures, lithostratigraphy, and key surfaces; B) outcrop photo of surfaces S_2 and S_3, which are bounding the middle systems tract of sequence 2 (Unit 4 in terms of lithostratigraphy).

Fig. 15.

—A) annotation of the outcrop photo from B showing observed sedimentary structures, lithostratigraphy, and key surfaces; B) outcrop photo of surfaces S_2 and S_3, which are bounding the middle systems tract of sequence 2 (Unit 4 in terms of lithostratigraphy).

Surface 3 (S_3) is located between Unit 4 and Unit 5 of the Sappington Formation (Fig. 15). It is distinguished by an abrupt change in lithology from a heterolithic argillaceous siltstone (lithofacies 4A/4B) below, to a sandy siltstone (Unit 5 lithofacies) above. Surface 3 is a sharp contact with recessive rocks below S_3 and the presence above of a bed several inches thick of very fine grained sandstone and phosphatic bioclasts (lag?). As with S_2, the surface is not distinguishable in select western outcrop locations. S_3 is interpreted to be a significant surface, but as with S_2, the type of sequence stratigraphic surface that S_3 represents is uncertain.

Surface 4 (S_4) is located between Unit 5 and Unit 6 of the Sappington Formation (Fig. 16). The surface is characterized by a distinct lithology change, a surface of discoloration, an erosional rugose surface, and a bed (lag) containing fish bones and conodonts. The lithology underlying S_4 is a sandy siltstone (various Unit 5 lithofacies), and the lithology above is a black shale (lithofacies 6A). S_4 is interpreted as an unconformity (Gutschick et al. 1962, Sandberg 1965, Cole et al. 2015) and a sequence boundary.

Fig. 16.

—A) outcrop photo of the surfaces (S_4 and S_5) that bound sequence 3; B) Annotation of the photo from A showing observed fauna, weathering profile, lithostratigraphy, and significant surfaces.

Fig. 16.

—A) outcrop photo of the surfaces (S_4 and S_5) that bound sequence 3; B) Annotation of the photo from A showing observed fauna, weathering profile, lithostratigraphy, and significant surfaces.

Surface 5 (S_5) is located between Unit 6 of the Sappington Formation and the Scallion Member of the Lodgepole Formation (Fig. 16). The surface is characterized by a subtle lithology change, an orangish brown surface, and truncation of underlying units. The lithology of the Sappington Formation below S_5 is a lime-mudstone (lithofacies 6C), and the lithology of the Lodgepole Formation above S_5 is a crinoidal packstone. Based off lithology and weathering character, the significant chronostratigraphic surface could be improperly placed at the contact beneath lithofacies 6C, when in actuality S_5 is the real surface of chronostratigraphic significance. S_5 is interpreted as an unconformity (Gutschick et al. 1962) and a sequence boundary, which is in contrast with the conformable interpretation of Sandberg and Klapper (1967).

At a significant number of western outcrop locations (Antelope Creek, Brown Back Gulch, Copper City, Red Hill) Unit 6 has been erosionally truncated, and the Lodgepole Formation is sitting disconformably on top of Unit 5.

DISCUSSION

Sequences

There are six significant surfaces (Fig. 4) in the Sappington Formation, from which surfaces S_0, S_1, S_4, and S_5 are interpreted as unconformities and sequence boundaries, and S_2 and S_3 are interpreted as significant surfaces subject to various sequence stratigraphic interpretations. The sequence boundaries constrain three sequences: sequence 1, sequence 2, and sequence 3. Sequence 1 is bound by S_0 and S_1, sequence 2 is bound by S_1 and S_4, and sequence 3 is bound by S_4 and S_5. Sequence 2 is subdivided into three systems tracts: lower systems tract, middle systems tract, and upper systems tract. The equivalency of the lithostratigraphy of the Sappington Formation with this sequence stratigraphic framework is presented in Figure 4.

Depositional Environment

The depositional environments of the Sappington Formation’s three sequences reflect predominantly clastic deposition in the low-accommodation Sappington Basin. The sequences are by definition not in lateral relationship with each other during any time and at any location within the basin (Catuneanu 2006). As a result, three depositional models have to be applied to the Sappington Formation (Fig. 17).

Fig. 17.

—Depositional models. These figure illustrate the succession of lithofacies and depositional environments for A) sequence 1, B) sequence 2, C) sequence 3.

Fig. 17.

—Depositional models. These figure illustrate the succession of lithofacies and depositional environments for A) sequence 1, B) sequence 2, C) sequence 3.

Sequence 1

The depositional environment for sequence 1 is interpreted as a low energy, anoxic, and relatively deep water setting. The chert interbeds in sequence 1 represent periods of elevated deposition of siliceous pelagic microfossils that underwent diagenetic alteration to chert beds. The up-dip lithologic expression of sequence 1 has not been located in the basin because of erosional truncation at S_1, as well as the uncertainty of the geographic extent of sequence 1 deposition. Within the study area, sequence 1 thickens to the west and north into areas interpreted to have greater accommodation and less erosional truncation (Fig. 18).

Fig. 18.

—Cross section A–A′. This is a representative cross section through four outcrops showing the range of observed thicknesses and facies variation within the study area. The eastern portion of the cross section through Rekap Station, Nixon Gulch, and Moose Creek indicates shallowing on to the eastern margin of the basin. Ashbough Canyon is interpreted as a deep portion of the basin during sequence 1 and sequence 3 (its location during sequence 2 is unknown).

Fig. 18.

—Cross section A–A′. This is a representative cross section through four outcrops showing the range of observed thicknesses and facies variation within the study area. The eastern portion of the cross section through Rekap Station, Nixon Gulch, and Moose Creek indicates shallowing on to the eastern margin of the basin. Ashbough Canyon is interpreted as a deep portion of the basin during sequence 1 and sequence 3 (its location during sequence 2 is unknown).

Sequence 2

The depositional environment for sequence 2 is interpreted as a predominantly marine, normally oxygenated, high energy, and relatively shallow setting. The heterogeneous character of the rocks of sequence 2 reflect deposition along a mixed energy (wave, tidal, storm) shoreface margin with environments ranging from upper offshore to eolian. Based on the shoreface classification scheme established by Dashtgard et al. (2012), sequence 2 of the Sappington Formation would be classified as a storm dominated shoreface (SDS).

Sequence 2 is characterized by a mixed deepening and shallowing-up depositional package in the lower systems tract, a deepening-up depositional package in the middle systems tract, and a shallowing-up depositional package in the upper systems tract (Fig. 4). The shallowing-up portion of the lower systems tract, as well as the shallowing-up upper systems tract, have similar lithofacies successions. However, the lower systems tract is typically located considerably down depositional dip from the upper systems tract. Sequence 2 is thickest in the central portion of the study area and thins to the east toward Moose Creek and to the west towards Ashbough Canyon.

The depositional package of the lower systems tract has a depositional environment transition from a brackish and dysoxic lagoonal setting (lithofacies 1C and 1D), to a moderate energy marine silty carbonate shoal (lithofacies 2A), to a storm dominated shoreface (lithofacies 3A and 3B).

The lithologic character of the middle systems tract is distinctly different from the lower and upper systems tracts. The middle systems tract is composed of heterolithic bedding of silt and clay grain sizes and combined flow ripples/current ripples, wave ripples, and hummocky cross stratification. The two alternative depositional environment interpretations are tidal flat or lower shoreface/offshore. Neither the sedimentary structures, lithology, ichnology, nor fauna lead to a definitive conclusion on environment. The environment interpretation for Unit 4 has large implications for the sequence stratigraphic interpretation. If Unit 4 is interpreted as tidal, then there is a base level fall at S_2 and a base level rise at S_3. If Unit 4 is interpreted as offshore, then there is a base level rise at S_2 and a base level fall at S_3. This uncertainty is the reason for the non-classification of the systems tracts of sequence 2.

The upper systems tract has a (Fig. 4) depositional environment transition from a storm influenced upper offshore/lower shoreface (lithofacies 5A and 5B), to a wave dominated upper shoreface (lithofacies 5C), to a carbonate shoal (lithofacies 5D), to a wind dominated eolian environment (lithofacies 5E).

Sequence 3

The depositional environment interpretation for sequence 3 is a low energy, relatively deep water, and dysoxic setting. Two shallowing-up depositional packages are interpreted for sequence 3 (Fig. 4). The lower shallowing-up package transitions from anoxic relatively deep water (lithofacies 6A) deposition to anoxic relatively shallower water (lithofacies 6B) deposition. The upper shallowing-up package transitions from anoxic relatively deep water (lithofacies 6A) deposition to relatively shallower water (lithofacies 6C) deposition (Fig. 17C). Sequence 3 is absent in the western half of the central portion of the study area, and sequence 3 is the thickest near the Bridger Mountains and to the far west at Ashbough Canyon.

Depositional Controls

Sea Level: Sea level and tectonics both are responsible for the creation of accommodation within which Sappington Formation sediment was deposited. Sea level is proposed as the dominant driver of accommodation creation during Sappington Formation deposition. This interpretation is supported by the correlation between the timing of Sappington Formation deposition/nondeposition and the position of sea level (Fig. 2). Global sea-level fluctuations, driven by glaciation, controlled when deposition occurred. Supporting evidence for Late Devonian to Early Mississippian glaciation includes an increase in the ratio of the oxygen 18 isotope to the oxygen 16 isotope (Popp et al. 1986), as well as a replacement of tropical foraminifera, miospore, and brachiopod assemblages with temperate assemblages (Caplan and Bustin 1999).

The chronostratigraphic chart in Figure 2 was created to illustrate how the ages of the Sappington Formation sequences equate in time to global sea-level cycles, global onlap curves, global sequence boundaries, and glaciation events from Haq and Schutter (2008). Three sea-level cycles occurred during the time period of Sappington Formation deposition. Relative high sea level is reflected by periods of deposition, and relative low sea level is represented by unconformities. The globally recognizable sequence boundaries identified by Haq and Schutter (2008) at 363.4, 361, 359.2, and 353.3 Ma, correspond to surfaces S_0, S_1, S_4, and S_5 in the Sappington Formation.

Tectonics: The timing of Antler tectonic events are loosely constrained in Idaho and Montana based off the age of basin fill in the Antler Foreland Basin and the Montana Platform basins. Subsidence began in the Antler Foreland Basin in Idaho in the Early Devonian, and subsidence began in Montana on the cratonic interior in the Late Devonian (Dorobek et al. 1991).

There was significant sediment supply from the Antler thrust belt complex to the west of the Antler Foreland Basin, as demonstrated by the tremendous thickness of Devonian and Mississippian age sediment in the Antler Foreland Basin. Thicknesses of equivalent age formations on the Montana Platform are dramatically thinner and finer grained than their Antler Foreland Basin counterparts. Sappington Formation sediment is characterized by an abundance of silt grain sizes and general absence of sand grain sizes, which suggests the lack of proximal mountain building and sediment supply. The abundance of silt leads to the interpretation of wind as the dominant sediment transport mechanism for Sappington Formation sediment. The Sappington Basin acted as a catchment for wind transported sediment to be deposited. Wind energy has been proven to effectively carry silt grain sizes long distances (Soreghan et al. 2008), which could make provenance work difficult.

Observations on measured thickness of the Sappington Formation sequences suggest subtle active tectonics during the deposition of Sappington Formation sediment. Sequence 1 is thickest in the southwest portion of the study area at Ashbough Canyon and thins out in the eastern portion of the study area at Moose Creek (Fig. 18). Sequence 2 is thickest in the central part of the study area, thins to the east at Moose Creek, and thins to the west at Ashbough Canyon (Fig. 18). Sequence 3 is thickest to the west at Ashbough Canyon, thins out in the central part of the study area, and thickens again to the east at Moose Creek (Fig. 18). The patterns of relative thickness changes of the Sappington Formation sequences infers changes in accommodation driven by tectonics. Observations on facies character support the conclusions of the changing accommodation. The facies of sequence 2 have the most proximal signature at Moose Creek, which indicates shallowing of depositional environments to the east. Sequence 3 facies in the central portion of the field area are the most proximal in character and become more distal to the east at Moose Creek and to the west at Ashbough Canyon.

Climate: The Late Devonian to Early Mississippian is a time period of known anoxia, based off the abundance of black shale formations deposited across North America during that time: Antrim, Bakken, Chattanooga, Exshaw, Ohio, New Albany, Pilot, and Woodford (Gutschick and Moreman 1967). Eutrophication is commonly invoked for the creation of anoxic conditions, although the global event(s) responsible for the eutrophication is a matter of debate (Caplan and Bustin 1999). The most prominent of the anoxic events of this time period is the Hangenberg Event in Germany, which represents an extinction event and black shale deposition (Kaiser et al. 2009). A carbon isotope excursion has been documented from this interval in Europe as well as in North America (Kaiser et al. 2009, Myrow et al. 2011, Cole et al. 2015). Sequence 1 of the Sappington Formation is proposed to be equivalent to the Hangenberg Event due to its age relation, as well as anoxic character and carbon isotope signature

The Sappington Formation is an enigmatic unit when compared with typical deposition in the region during the Late Devonian and Early Mississippian. It is a relatively thin anomalous siliciclastic unit deposited between two prolific carbonate systems. It is evident from these observations that during Sappington Formation deposition, the carbonate system was being disrupted. At the onset of Sappington Formation deposition is a significant extinction event (Hangenberg), which eliminated a significant percentage of the population of Devonian reef builders (Caplan and Bustin 1999). In addition, during this same time period, nutrient levels increased due to the evolution of land plants (Caplan et al. 1996, Algeo and Scheckler 1998, Caplan and Bustin 1999). These are the two most apparent factors that lead to the demise of the carbonate factory during the deposition of the Sappington Formation.

CONCLUSIONS

This paper provides a sequence stratigraphic framework for the Sappington Formation that should be used to replace the existing lithostratigraphic framework. Three sequences are identified in the Sappington Formation that can be used to properly correlate time equivalent packages of rock. In addition to the sequence stratigraphic framework, this paper adds more outcrop based observations to the existing body of work and synthesizes the timing and effects of allocyclic processes on Sappington Formation deposition. This contributes to an improved understanding of low-accommodation intracratonic depositional settings (i.e., Sappington, Bakken, and Exshaw Formations).

ACKNOWLEDGMENTS

The funding of this research was provided by: University of Idaho, Hess Corporation, PRISEM Geoconsulting, the American Association of Petroleum Geologists (AAPG), the Rocky Mountain Section of the Society for Sedimentary Geology (SEPM), and the Tobacco Root Geological Society (TRGS).

Thank you to the following reviewers for their feedback and patience with the process: Ted Playton, Peter Holterhoff, David Katz, and Orion Skinner.

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Figures & Tables

Fig. 1.

—Paleogeographic map of the area of interest for this study. The dashed line represents the approximate depositional extent of the Sappington Formation from Adiguzel (2012), the Bakken Formation from Gaswirth and Marra (2015), Exshaw Formation from MacQueen and Sandberg (1970). The basin outlines represent the areas of thickest deposition. The location of the Antler Orogenic Highlands and Antler Foreland Basin are derived from Poole (1974).

Fig. 1.

—Paleogeographic map of the area of interest for this study. The dashed line represents the approximate depositional extent of the Sappington Formation from Adiguzel (2012), the Bakken Formation from Gaswirth and Marra (2015), Exshaw Formation from MacQueen and Sandberg (1970). The basin outlines represent the areas of thickest deposition. The location of the Antler Orogenic Highlands and Antler Foreland Basin are derived from Poole (1974).

Fig. 2.

—Sappington Formation chronostratigraphic chart synthesis with the absolute ages of Sappington Formation 2012 conodont zones (Becker et al. 2012, Davydov et al. 2012), Sandberg 1972 conodont zones (Sandberg et al. 1972), global sea-level curve (Haq and Schutter 2008), global onlap curve (Haq and Schutter 2008), global sequence boundaries (Haq and Schutter 2008), and global glaciation events (Haq and Schutter 2008). The Sandberg et al. (1972) conodont zones are correlated to the 2012 conodont zones, which have been correlated to absolute ages in the 2012 time scale. The absolute ages from the Haq and Schutter (2008) data are correlated to the absolute ages from the 2012 time scale.

Fig. 2.

—Sappington Formation chronostratigraphic chart synthesis with the absolute ages of Sappington Formation 2012 conodont zones (Becker et al. 2012, Davydov et al. 2012), Sandberg 1972 conodont zones (Sandberg et al. 1972), global sea-level curve (Haq and Schutter 2008), global onlap curve (Haq and Schutter 2008), global sequence boundaries (Haq and Schutter 2008), and global glaciation events (Haq and Schutter 2008). The Sandberg et al. (1972) conodont zones are correlated to the 2012 conodont zones, which have been correlated to absolute ages in the 2012 time scale. The absolute ages from the Haq and Schutter (2008) data are correlated to the absolute ages from the 2012 time scale.

Fig. 3.

—Map of Sappington Formation outcrop locations used in this study. ANC2 = Antelope Creek; ASC2 = Ashbough Canyon; BRBG = Brown Back Gulch; COC2 = Copper City; DH10 = Dry Hollow; FRL = Frazier Lake; LOG = Logan Gulch; MIC = Milligan Canyon; MOC = Moose Creek; NIG = Nixon Gulch; POP = Pomp Peak (Peak 9559); RH = Red Hill; RES = Rekap Station; SC4 = Storm Castle.

Fig. 3.

—Map of Sappington Formation outcrop locations used in this study. ANC2 = Antelope Creek; ASC2 = Ashbough Canyon; BRBG = Brown Back Gulch; COC2 = Copper City; DH10 = Dry Hollow; FRL = Frazier Lake; LOG = Logan Gulch; MIC = Milligan Canyon; MOC = Moose Creek; NIG = Nixon Gulch; POP = Pomp Peak (Peak 9559); RH = Red Hill; RES = Rekap Station; SC4 = Storm Castle.

Fig. 4.

—Sappington Formation stratigraphic chart with stratigraphic nomenclature, stratigraphic column, lithostratigraphic nomenclature (historical and proposed), lithofacies, depositional environments, dominant depositional processes, relative macrofauna abundances, bioturbation intensity index (BI), surfaces, sequences, and systems tracts.

Fig. 4.

—Sappington Formation stratigraphic chart with stratigraphic nomenclature, stratigraphic column, lithostratigraphic nomenclature (historical and proposed), lithofacies, depositional environments, dominant depositional processes, relative macrofauna abundances, bioturbation intensity index (BI), surfaces, sequences, and systems tracts.

Fig. 5.

—Unit 1 lithofacies. A) 1A (hand sample), black shale with marine fauna; B) 1A (outcrop), black shale and chert beds; C) 1A (hand sample), common appearance of 1A in high deformation areas (lithofacies 1B of Gutschick et al. (1962); D) 1C (outcrop), black shale with brackish fauna; E) 1D (hand sample), fossiliferous gray shale; F) outcrop photo of lag with phosphatic fish fragments and conodonts; G) diagenetic rock located beneath S_0.

Fig. 5.

—Unit 1 lithofacies. A) 1A (hand sample), black shale with marine fauna; B) 1A (outcrop), black shale and chert beds; C) 1A (hand sample), common appearance of 1A in high deformation areas (lithofacies 1B of Gutschick et al. (1962); D) 1C (outcrop), black shale with brackish fauna; E) 1D (hand sample), fossiliferous gray shale; F) outcrop photo of lag with phosphatic fish fragments and conodonts; G) diagenetic rock located beneath S_0.

Fig. 6.

—Sappington Formation fauna. A) Brittle starfish (red circle) in lithofacies 1C, B) Conchostracan (red circle) in lithofacies 1C, C) Mollusk (red circle) and other shelly debris in lithofacies 1D, D) Crinoid stem (red circle) and other fossil debris in lithofacies 2A, E) Oncolite with brachiopod nucleus (red circle) and other fossil debris in lithofacies 2A.

Fig. 6.

—Sappington Formation fauna. A) Brittle starfish (red circle) in lithofacies 1C, B) Conchostracan (red circle) in lithofacies 1C, C) Mollusk (red circle) and other shelly debris in lithofacies 1D, D) Crinoid stem (red circle) and other fossil debris in lithofacies 2A, E) Oncolite with brachiopod nucleus (red circle) and other fossil debris in lithofacies 2A.

Fig. 7.

—Unit 2 lithofacies. A) 2A (outcrop), silty oncolitic wackestone; B) 2A (outcrop), less developed oncolites with less algal coatings around fauna.

Fig. 7.

—Unit 2 lithofacies. A) 2A (outcrop), silty oncolitic wackestone; B) 2A (outcrop), less developed oncolites with less algal coatings around fauna.

Fig. 8.

—Unit 3 lithofacies. A) Photo showing the outcrop expression of lithofacies 3A and 3B; B) 3A (cut hand sample), highly bioturbated siltstone with Nereites (Ne) and Planolites (P) ichnogenera; C) 3B (cut hand sample), silty fossiliferous limestone with fragments of brachiopods.

Fig. 8.

—Unit 3 lithofacies. A) Photo showing the outcrop expression of lithofacies 3A and 3B; B) 3A (cut hand sample), highly bioturbated siltstone with Nereites (Ne) and Planolites (P) ichnogenera; C) 3B (cut hand sample), silty fossiliferous limestone with fragments of brachiopods.

Fig. 9.

—Unit 4 lithofacies. A) 4A (outcrop), bioturbated silty shale with starved ripples; B) 4A (outcrop), magnified photo of 4A showing bioturbation and laminae; C) 4B (outcrop), bioturbated shaley siltstone with storm beds; D) 4B (cut hand sample), magnified photo of 4B showing hummocky cross stratification in a storm bed and bioturbation in the background lithology.

Fig. 9.

—Unit 4 lithofacies. A) 4A (outcrop), bioturbated silty shale with starved ripples; B) 4A (outcrop), magnified photo of 4A showing bioturbation and laminae; C) 4B (outcrop), bioturbated shaley siltstone with storm beds; D) 4B (cut hand sample), magnified photo of 4B showing hummocky cross stratification in a storm bed and bioturbation in the background lithology.

Fig. 10.

—Unit 5 lithofacies. A) 5A, bioturbated siltstone; B) 5B, bioturbated siltstone with storm beds; C) 5C, siltstone with wave ripples; D) 5E, very fine grained sandstone with tabular cross bedding; E) 5D, oolitic grainstone with tabular cross bedding; F) 5D, (from cut hand sample) very fine grained sandstone with inverse graded bedding.

Fig. 10.

—Unit 5 lithofacies. A) 5A, bioturbated siltstone; B) 5B, bioturbated siltstone with storm beds; C) 5C, siltstone with wave ripples; D) 5E, very fine grained sandstone with tabular cross bedding; E) 5D, oolitic grainstone with tabular cross bedding; F) 5D, (from cut hand sample) very fine grained sandstone with inverse graded bedding.

Fig. 11.

—Unit 6 lithofacies. A) Lag (hand sample), composed of phosphatic fish parts and conodonts; B) 6A (hand sample), black shale; C) 6B (hand sample), bioturbated siltstone; D) 6C (hand sample), limestone.

Fig. 11.

—Unit 6 lithofacies. A) Lag (hand sample), composed of phosphatic fish parts and conodonts; B) 6A (hand sample), black shale; C) 6B (hand sample), bioturbated siltstone; D) 6C (hand sample), limestone.

Fig. 12.

—Sappington Formation Ichnogenera. A)Planolites (P) and Bifungites (B) (bedding plane view of location of arrow in C inset) ichnogenera in lithofacies 3A (bedding plane view); B)Thalassanoides (Th) ichnogenera in lithofacies 3A (bedding plane view); C)Bifungites (B) ichnogenera rare bedding plane view of basal most horizontal burrow (bedding plane view), inset is a rare cross section view of vertical portion of Bifungites (B) ichnogenera in lithofacies 4A; D)Lockeia (Lo) and Nereites (Ne) ichnogenera in lithofacies 5A (bedding plane view); E)Teichichnus (Te) ichnogenera in lithofacies 6B (cross section view); F)Zoophycos (Z) ichnogenera in lithofacies 6B (Bedding plane view). See Gutschick and Lamborn (1975) for Bifungites schematic.

Fig. 12.

—Sappington Formation Ichnogenera. A)Planolites (P) and Bifungites (B) (bedding plane view of location of arrow in C inset) ichnogenera in lithofacies 3A (bedding plane view); B)Thalassanoides (Th) ichnogenera in lithofacies 3A (bedding plane view); C)Bifungites (B) ichnogenera rare bedding plane view of basal most horizontal burrow (bedding plane view), inset is a rare cross section view of vertical portion of Bifungites (B) ichnogenera in lithofacies 4A; D)Lockeia (Lo) and Nereites (Ne) ichnogenera in lithofacies 5A (bedding plane view); E)Teichichnus (Te) ichnogenera in lithofacies 6B (cross section view); F)Zoophycos (Z) ichnogenera in lithofacies 6B (Bedding plane view). See Gutschick and Lamborn (1975) for Bifungites schematic.

Fig. 13.

Sappington Formation diagenetic features. A) Calcite cemented storm bed with preserved bedding in lithofacies 5B from Dry Hollow (cross section view); B) Calcite cemented nodules (red circles) from storm bed in lithofacies 5B from Milligan Canyon (bedding plane view); C) Calcite cemented nodules in lithofacies 5C at Milligan Canyon just below contact with overlying Lodgepole Fm (cross section view); D) Soft sediment deformation in Unit 5 at Milligan Canyon just below the contact with the Lodgepole Fm (cross section view); E) Inset of D, calcite cemented nodule in soft sediment deformation in Unit 5 at Milligan Canyon just below contact with the Lodgepole Fm. The features in E indicate that calcite cementation happened prior to soft sediment deformation.

Fig. 13.

Sappington Formation diagenetic features. A) Calcite cemented storm bed with preserved bedding in lithofacies 5B from Dry Hollow (cross section view); B) Calcite cemented nodules (red circles) from storm bed in lithofacies 5B from Milligan Canyon (bedding plane view); C) Calcite cemented nodules in lithofacies 5C at Milligan Canyon just below contact with overlying Lodgepole Fm (cross section view); D) Soft sediment deformation in Unit 5 at Milligan Canyon just below the contact with the Lodgepole Fm (cross section view); E) Inset of D, calcite cemented nodule in soft sediment deformation in Unit 5 at Milligan Canyon just below contact with the Lodgepole Fm. The features in E indicate that calcite cementation happened prior to soft sediment deformation.

Fig. 14.

A) outcrop photo of the surfaces (S_0 and S_1) that bound sequence 1; B) annotation of the outcrop photo from A showing observed fauna, sedimentary structures, lithostratigraphy, and key surfaces. P = paleosol.

Fig. 14.

A) outcrop photo of the surfaces (S_0 and S_1) that bound sequence 1; B) annotation of the outcrop photo from A showing observed fauna, sedimentary structures, lithostratigraphy, and key surfaces. P = paleosol.

Fig. 15.

—A) annotation of the outcrop photo from B showing observed sedimentary structures, lithostratigraphy, and key surfaces; B) outcrop photo of surfaces S_2 and S_3, which are bounding the middle systems tract of sequence 2 (Unit 4 in terms of lithostratigraphy).

Fig. 15.

—A) annotation of the outcrop photo from B showing observed sedimentary structures, lithostratigraphy, and key surfaces; B) outcrop photo of surfaces S_2 and S_3, which are bounding the middle systems tract of sequence 2 (Unit 4 in terms of lithostratigraphy).

Fig. 16.

—A) outcrop photo of the surfaces (S_4 and S_5) that bound sequence 3; B) Annotation of the photo from A showing observed fauna, weathering profile, lithostratigraphy, and significant surfaces.

Fig. 16.

—A) outcrop photo of the surfaces (S_4 and S_5) that bound sequence 3; B) Annotation of the photo from A showing observed fauna, weathering profile, lithostratigraphy, and significant surfaces.

Fig. 17.

—Depositional models. These figure illustrate the succession of lithofacies and depositional environments for A) sequence 1, B) sequence 2, C) sequence 3.

Fig. 17.

—Depositional models. These figure illustrate the succession of lithofacies and depositional environments for A) sequence 1, B) sequence 2, C) sequence 3.

Fig. 18.

—Cross section A–A′. This is a representative cross section through four outcrops showing the range of observed thicknesses and facies variation within the study area. The eastern portion of the cross section through Rekap Station, Nixon Gulch, and Moose Creek indicates shallowing on to the eastern margin of the basin. Ashbough Canyon is interpreted as a deep portion of the basin during sequence 1 and sequence 3 (its location during sequence 2 is unknown).

Fig. 18.

—Cross section A–A′. This is a representative cross section through four outcrops showing the range of observed thicknesses and facies variation within the study area. The eastern portion of the cross section through Rekap Station, Nixon Gulch, and Moose Creek indicates shallowing on to the eastern margin of the basin. Ashbough Canyon is interpreted as a deep portion of the basin during sequence 1 and sequence 3 (its location during sequence 2 is unknown).

Table 1.

—Table of Sappington Formation lithofacies and their respective lithology, grain size, sedimentary structure/feature, fauna, recognizable ichnogenera, other features, and depositional environments. BI = bioturbation index, HCS = hummocky cross stratification, NA = not available.

Lithofacies Lithology Depositional / diagenetic features Fauna Recognizable ichnogenera B.I. Interpreted depositional environment 
6C bluish gray silly mudstone bioturbation none unknown NA unknown 
6B dark gray siltstone bioturbation none Zoophycos, Teichichnus dysoxic shallow marine 
6A black shale laminations none unknown NA anoxic deep marine 
5E orangish beige sandstone tabular cross bedding none none eolian 
5D bluish gray oolitic grainstone tabular cross bedding none none NA carbonate shoal 
5C orangish beige siltstone amalgamating wave ripples, climbing ripples, trough cross beds none Lockeia upper shoreface 
5B orangish beige siltstone bioturbation, HCS, wave ripples, calcite cemented beds none Nereites (background lithology), Teichichnus(storm beds) lower shoreface 
5A orangish beige siltstone bioturbation none Nereites lower shoreface 
4B greenish gray silty shale heterolithic bedding, HCS, wave ripples, combined flow ripples none Arenicolites (Bifimgites), Planolite, Chondrites upper ofEshore/tidal flat 
4A greenish gray silty shale heterolithic bedding, starved ripples none Arenicolites (Bifimgites), Planolites, Teichichnus lower ofishore/tidal flat 
3B yellowish beige silty wacketstone calcite cementation brachiopods, crinoid stems none NA sediment starved shallow marine 
3A yellowish beige siltstone bioturbation, HCS, wave ripples brachiopod fragments Nereites, Planolites, Teichichnus lower shoreface 
2A bluish gray silly oncolitic wackestone beds of oncolites brachiopods, bryozoans, crinoid stems none NA carbonate bank 
ID greenish gray shale thin bedded brachiopods, bivalves unknown NA estuarine (marine) 
1C black shale thin bedded, conchoidal fracturing conchostracans, echinoderms (brittle starfish) unknown NA dysoxic estuarine (brackish) 
1A black shale thin bedded, chert interbeds radiolarians, tasmanites unknown NA anoxic deep marine 
Lithofacies Lithology Depositional / diagenetic features Fauna Recognizable ichnogenera B.I. Interpreted depositional environment 
6C bluish gray silly mudstone bioturbation none unknown NA unknown 
6B dark gray siltstone bioturbation none Zoophycos, Teichichnus dysoxic shallow marine 
6A black shale laminations none unknown NA anoxic deep marine 
5E orangish beige sandstone tabular cross bedding none none eolian 
5D bluish gray oolitic grainstone tabular cross bedding none none NA carbonate shoal 
5C orangish beige siltstone amalgamating wave ripples, climbing ripples, trough cross beds none Lockeia upper shoreface 
5B orangish beige siltstone bioturbation, HCS, wave ripples, calcite cemented beds none Nereites (background lithology), Teichichnus(storm beds) lower shoreface 
5A orangish beige siltstone bioturbation none Nereites lower shoreface 
4B greenish gray silty shale heterolithic bedding, HCS, wave ripples, combined flow ripples none Arenicolites (Bifimgites), Planolite, Chondrites upper ofEshore/tidal flat 
4A greenish gray silty shale heterolithic bedding, starved ripples none Arenicolites (Bifimgites), Planolites, Teichichnus lower ofishore/tidal flat 
3B yellowish beige silty wacketstone calcite cementation brachiopods, crinoid stems none NA sediment starved shallow marine 
3A yellowish beige siltstone bioturbation, HCS, wave ripples brachiopod fragments Nereites, Planolites, Teichichnus lower shoreface 
2A bluish gray silly oncolitic wackestone beds of oncolites brachiopods, bryozoans, crinoid stems none NA carbonate bank 
ID greenish gray shale thin bedded brachiopods, bivalves unknown NA estuarine (marine) 
1C black shale thin bedded, conchoidal fracturing conchostracans, echinoderms (brittle starfish) unknown NA dysoxic estuarine (brackish) 
1A black shale thin bedded, chert interbeds radiolarians, tasmanites unknown NA anoxic deep marine 

Contents

Society for Sedimentary Geology

NEWADVANCES IN DEVONIAN CARBONATES: OUTCROP ANALOGS, RESERVOIRS AND CHRONOSTRATIGRAPHY

Ted E. Playton
Ted E. Playton
Tengizchevroil, Atyrau 060011, Kazakhstan
Search for other works by this author on:
Charles Kerans
Charles Kerans
Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas 78712, USA
Search for other works by this author on:
John A.W. Weissenberger
John A.W. Weissenberger
ATW Associates, Calgary, Alberta, T3E 7M8, Canada
Search for other works by this author on:
Society for Sedimentary Geology
Volume
107
ISBN electronic:
9781565763456
Publication date:
January 01, 2017

GeoRef

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