The Mississippian depositional system in the subsurface of Oklahoma is a mixed carbonate and siliciclastic system that was interpreted as being deposited on a regional shelf, ramp, or distally steepened ramp (Handford, 1986; Wilhite et al., 2011; Le Blanc, 2014; Price, 2014; Childress, 2015; Flinton, 2016; Thompson, 2016). Recent work in both the subsurface of Oklahoma, as well as local outcrops in Arkansas and Missouri, indicates these rocks were deposited on a distally steepened ramp due to the lateral facies distribution and the vertical facies successions identified throughout the system (Handford, 1986; Wilhite et al., 2011; Le Blanc, 2014; Price, 2014; Flinton, 2016; Thompson, 2016).

There are numerous examples of “blocks,” “mounds,” or “reefs” exposed at various Mississippian outcrops in the tristate region of Oklahoma-Arkansas-Missouri. These blocks were variously interpreted as displaced bioherms (Mazzullo, 2011; Morris and Mazzullo, 2013; Mazzullo et al., 2019), Waulsortian-type in situ mounds (Unrast, 2012), slump blocks (Evans et al., 2011), olistoliths (Tennyson et al., 2008), and mounds (Manger and Thompson, 1982).

A significant component of the distally steepened ramp depositional model, as originally defined by Read (1995), is the presence of downslope mass transport deposits (especially debris fows) sourced from subtidal environments. The Compton Limestone at the Jane outcrop in southwest Missouri contains some of these anomalous blocks that were studied in the past by several other workers, many of which utilize different terminology and propose different depositional interpretations. The interpretation and conceptual model proposed here is that these blocks are best characterized as “outrunner blocks” deposited along a distally steepened carbonate ramp, a term utilized to describe blocks encased within debris flow deposits that have been transported downslope along with smaller clasts supported by a mud matrix. Herein, we discuss the characteristics of the interpreted debris flow deposits from the Jane outcrop in Missouri. The goals of this study are to: (1) characterize the composition and associated sedimentary structures of these deposits, (2) to propose a mechanism for their formation, and (3) to discuss likely distribution and possible reservoir potential of similar deposits in the subsurface.

The blocks present at the Jane outcrop in southwestern Missouri were the subject of much debate in recent publications (Unrast, 2012; Morris and Mazzullo, 2013). Features observed at the Jane outcrop have been termed “reefs” and defined as “limestone lithosomes of convex-up lensoid geometry with presumed relief above the seafloor during deposition whose allochemical composition is dominated by what are regarded as impoverished Mississippian reef building biota” (Morris and Mazzullo, 2013). In this case, the term reef may be more consistent with the term bioherm, defined by Wilson (1950) as consisting of any dome-like, mound-like or other mass, built exclusively or mainly by organisms such as corals, stromatoporoids, algae, brachiopods, mollusks, and crinoids, and enclosed in matrix material of different lithologic character.

Mississippian Waulsortian and Waulsortian-type mounds from multiple outcrop locations throughout the U.S. midcontinent were compared to Waulsortian mounds in Ireland (Unrast, 2012). Waulsortian mounds are described as mud-rich carbonate mounds primarily composed of bryozoans and crinoids. The mounds often contain sparry calcite cement-filled voids, including stromatactis. These mounds had depositional relief above the seafloor, were up to hundreds of meters thick, and are interpreted as being deposited below wavebase in carbonate ramp settings. Waulsortian-type mounds are characterized by smaller dimensions, lower depositional relief, and were deposited in higher energy settings (Webb, 1994; Unrast, 2012; Morris and Mazzullo, 2013). Two mounds recognized at the Jane outcrop were classified as Waulsortian-type, and interpreted to be in situ mounds (Unrast, 2012). Evidence to support the term Waulsortian-type included one example of stromatactis in thin section, and various geopetal structures documented to be at the same angle (Unrast, 2012). The stromatactis cavities were described as being characterized by an irregular, digitate roof and a flat base (Unrast, 2012). The cavities are filled with inclusion-rich radiaxial fibrous cement and late blocky, sparry calcite cement. This explanation was previously documented by Wright et al. (2003), Lees and Miller (1985, 1995), and Somerville et al. (1992). An alternative, inorganic origin for stromatactis suggests the stromatactis cavities were opened by creep, slumping, or compaction and held open by the hydrostatic pressure of water trapped in the cavities until precipitation of cement occurred (Heckel, 1972).

The differences in classification of these features as either in situ reefs or transported blocks, and the corresponding differences in depositional interpretations have resulted in significant confusion in terminology and lead to potential errors in the interpretation of the overall depositional system. These varying depositional interpretations may adversely affect the ability to predict facies distribution and potential reservoirs in the subsurface. This study incorporates a multistep approach to evaluate interpreted mass transport deposits that will complement the high-frequency sequence or high-frequency cycle framework and depositional models established in previous studies. The primary data set includes detailed outcrop analysis using the integration of Gigapan^® imagery, thin section analysis, bedding geometries, and the incorporation of a proposed depositional environment to explain movement and composition of each block within the Compton Limestone. Additionally, an understanding of mass transport deposition in a Mississippian ramp setting will assist in defining the controls and distribution of reservoir heterogeneity throughout the system.

Deposition of U.S. midcontinent Mississippian carbonate rocks analyzed in this study occurred at 10–15° south latitude in a foreland ramp setting as part of a system of shallow water facies bordered by deepwater deposits to the south and west (Mazzullo et al., 2013). Conodont biostratigraphy on Lower to Middle Mississippian strata in this region revealed a depositional geometry consisting of diachronous, prograding carbonate wedges (Boardman, 2013). Progradation of these wedges eventually led to a distally steepened ramp depositional setting for Mississippian strata (Wilhite et al., 2011).

Overall, the Mississippian was a period of global regression that occurs between Devonian submergence and Carboniferous emergence (Ettensohn, 1993; Buggisch et al., 2008). During the mid-Visean (late Osagean–Meramecian), eustatic sea level began to significantly decline relative to sea level during the Tournaisian (Kinderhookian and early Osagean), reaching a low in the late Mississippian–Serpukhovian (Chesterian; Figure 1; Haq and Schutter, 2008). This sea level change throughout the entire Mississippian represents a transitional period from overall greenhouse conditions present during the Devonian to icehouse conditions present during the Pennsylvanian and Permian. Multiple third-order composite sequences (duration of 1–6 million years) occur during the Mississippian and are well defined by Haq and Schutter (2008) as global in scale. Additional higher-frequency changes in relative sea level are distinguishable in outcrop and in subsurface cores. As the Mississippian was a transitional period between greenhouse conditions of the Devonian, and icehouse conditions in the Pennsylvanian, it is thought that obliquity (40 kyr) cycles (Read, 1995; Kerans and Tinker, 1997) are dominant during transitional periods, although the duration of these cycles is considerably below biostratigraphic or radiometric temporal resolution.

Gigapan^® EPIC Pro hardware and software was used in this study to allow over 800 individual photographs of the outcrop to be stitched together to produce a very high-resolution, seamless photograph of the entire outcrop (Figure 2) where individual beds and sedimentary structures are visible down to the centimeter scale. Once the high-resolution image was stitched together, individual blocks and beds were traced for lateral continuity and geometry, an important step in distinguishing each block from the surrounding bedding and allowing for the identification of potential mass transport (Figure 3).

A debris flow is a plastic, poorly sorted flow in which clasts “float” in a fine-grained matrix with finite shear strength (Tripsanas et al., 2008). The Gigapan^® photograph in Figure 2 highlights multiple outrunner blocks shaded in gray, each of which is set within debris flow deposits, shaded in orange. Figure 4 is a sample of the debris flows shaded in orange (Figure 2) and highlights the characteristics of the debris flows more closely. This sample shows subrounded mud clasts ranging in grain size from very coarse sand to very coarse pebbles (2–64 mm) supported by a crinoidal–bryozoan micrite matrix, confirming it is a debris flow deposit. There are a total of six blocks set within the outlined debris flows in Figure 2, and the size of each can be compared in Table 1.

Each outrunner block at the Jane outcrop was sampled for thin section analysis to aid in determining its composition. The debris flows were sampled at multiple locations to investigate its composition relative to the composition of the blocks. Fifteen thin section photomicrographs from the six outrunner blocks and four thin section photomicrographs from the debris flow deposits were examined and classified based on Dunham (1962) and Choquette and Pray (1970) classification schemes. Thin sections used in this study were standard size (27 × 46 mm [1 × 1.8 in.]) and vacuum impregnated with blue epoxy to illustrate presence of porosity. The abbreviations used to label skeletal grains are shown in Table 2.

The study area is located in southwestern Missouri, near Jane, Missouri, where Kinderhookian and Osagean strata are exposed (Figure 5). This location is approximately 100 miles (160 km) west of the Ozark uplift and 150 miles (240 km) north of the Arkoma Basin. Mississippian lithostratigraphic nomenclature throughout the U.S. midcontinent varies by state, which when combined with a general paucity of biostratigraphic data and the time-transgressive nature of the deposits (Boardman, 2013; Childress, 2015) leads to uncertainty in recognizing formations in the subsurface. Some of the most sought-after reservoir facies of the Mississippian were deposited during the Kinderhookian and Osagean (Mazzullo, 2011; Mazzullo et al., 2013). The units exposed at the Jane outcrop, from base to top, include the Bachelor, Compton, Northview, and Pierson formations (Figure 6).

The Bachelor Formation is the lowermost Mississippian unit in this region, which unconformably overlies the Devonian Woodford (Chattanooga) Shale. The general lithology of the Bachelor Formation consists of quartz arenite sandstone beds intercalated with green calcareous shale (Kreman, 2011; Friesenhahn, 2012). Thickness of the Bachelor Formation varies little throughout southwestern Missouri, reaching a maximum thickness of approximately 3.9 feet (1.2 m) with an average thickness of 1 foot (0.3 m; Mehl, 1961; Manger and Shanks, 1976).

This study focuses specifically on the depositional blocks within the Compton Limestone, which is generally described as a light gray crinoidal–bryozoan wackestone to packstone unit (Manger and Shanks, 1976; Kreman, 2011). The clasts within the debris flow deposits (Figure 4) are similar in texture and composition to the samples taken from the Compton Limestone. The Compton Limestone is Kinderhookian and overlies the Bachelor Formation in the Lower Mississippian. The average thickness of the Compton Limestone ranges from 5 to 15 feet (1.5–4.6 m), but can reach up to 30 feet (9 m) in some regions (Thompson and Fellows, 1970). Near Jane, Missouri, the average thickness of the Compton is 12–22 feet (3.7–6.7 m) thick (Wilhite et al., 2011).

The Northview Formation is the upper unit of the Kinderhookian and conformably overlies the Compton Limestone and is unconformably overlain by the Pierson Limestone. The Northview Formation occurs throughout southwestern Missouri, northwestern Arkansas, and northeastern Oklahoma (Shoeia, 2012). The lithology of the Northview Formation is olive green calcareous shale or marlstone with an average thickness of 2–5 feet (0.6–1.5 m), although it may reach over 80 feet (24 m) in places (Huffman, 1960). The amount of shale within the Northview Formation increases northward, where this unit becomes more calcareous to the south (Shoeia, 2012). The Northview Formation, along with the Bachelor, Compton, and Pierson Formations all thin to the south (Wilhite et al., 2011).

The Northview Formation was previously referred to as the “Northview Shale,” and interpreted as a deeper water facies due to contradicting lithologic correlations and lack of evidence to support a definite age assignment (McDuffie, 1964). Based on observations made in the field at the Jane outcrop, the Northview Formation is 2–5 feet (0.6–1.5 m) thick and contains flaser bedding, lenticular bedding, multiple subaerial exposure surfaces and bidirectional ripples at the top of the formation (Childress, 2015). The lithologies throughout the Northview include skeletal wackestone, packstone, and grainstone beds separated by two thin, discontinuous shaly beds. Each of these outcrop observations led to the current interpretation that at least the upper portion of the Northview Formation at Jane was deposited in a tidal flat environment.

The Pierson Formation occurs at the base of the Osagean, and unconformably overlies the Northview Formation. It is unconformably overlain by the Reeds Spring Limestone and has been described as a fine-grained limestone (Heinzelmann, 1964; Shoeia, 2012). The Compton and Pierson Formations are lithologically similar and differentiated primarily through the identification of the overlying and underlying strata, particularly through the identification of the intervening Northview Formation (Manger and Shanks, 1976). Regionally, the Pierson Formation occurs in southwestern Missouri, northeastern Oklahoma, and northwestern Arkansas (Wilhite et al., 2011). The Pierson Formation consists of skeletal grainstones and packstones, suggestive of a relatively high-energy depositional environment. Average thickness of the Pierson Formation is 4–18 feet (1.2–5.5 m; Kreman, 2011; Wilhite et al., 2011).

To define the controls and distribution of heterogeneity observed within the units of the Jane outcrop, samples were collected to identify facies types and vertical stacking patterns (Childress, 2015). The Dunham (1962) and Choquette and Pray (1970) classifications and descriptions were used to define texture, classification, and pore types observed in hand specimen and thin section. Four primary lithofacies, Facies 1–4, were defined based on specific attributes, which include sedimentary structures, texture and fabric, composition, size and geometry of grains, bedding geometry, and stratigraphic stacking patterns (Figure 7; Childress, 2015).

Depositional models assist in understanding sediment deposition, regional geometries, and facies stacking patterns of the area of interest. Based upon observed facies types and vertical successions at the Jane outcrop in southwestern Missouri, the best fit for a depositional model for the units described in this study is a distally steepened ramp, consistent with other recent studies in the region (Handford, 1986; Wilhite et al., 2011; Boardman, 2013; Le Blanc, 2014; Price, 2014; Childress, 2015; Flinton, 2016; Thompson, 2016) and similar to other distally steepened ramps described in the literature (Handford, 1986; Handford and Loucks, 1993; Kerans et al., 1994; Grafe and Wiedmann, 1998). The predominant facies types at the Jane outcrop range from crinoidal–bryozoan wackestone to crinoidal–bryozoan mud-lean packstone with an average ratio of 65% skeletal grains to 35% micritic mud. These facies types fall between the boundaries of fair weather wave base and storm wave base in a distally steepened ramp setting (Childress, 2015). This succession of lower-energy facies suggests deposition more distal and further from the shelf margin region originally defined by Gutschick and Sandberg (1983) and Lane and De Keyser (1980). Significant complexity and heterogeneity of facies distribution exists within the Mississippian distally steepened ramp setting (Figure 8). Deposition of the Jane outcrop facies would have likely occurred within the red outline of Figure 8, which includes the tidal flat environment of the Northview Formation and common mass transport features deposited along the ramp.

Third-order sequences were constrained throughout the U.S. midcontinent using distinctive conodont types to recognize biostratigraphic correlations (Boardman, 2013). The biostratigraphic framework from Boardman (2013) does not specifically constrain temporal resolution due to overlapping conodont zonations. In an attempt to gain a better understanding of temporal resolution at the Jane outcrop, the stratigraphic framework defined by stacking patterns of primary depositional facies (Childress, 2015) and the biostratigraphic framework from Boardman (2013) was compared to the eustatic sea-level curve from Haq and Schutter (2008) to identify two probable third-order sequences represented by the Kinderhookian and Osagean strata exposed at the study area (Childress, 2015). The sequence stratigraphic framework defined by stacking patterns of primary depositional facies and biostratigraphy was further refined to delineate higher-frequency stratigraphic cycles (herein termed fourth-order high-frequency sequences and fifth-order high-frequency cycles), identified by a combination of exposure horizons, flooding surfaces, and vertical stacking patterns. An understanding that this system is influenced by high-frequency (probable Milankovitch band) sea-level change, in addition to the third-order sea-level changes constrained by biostratigraphy, is fundamental to understanding facies migration through time, and at the Jane outcrop, underscores the vertical and lateral heterogeneity of facies and potential reservoirs within such a system (Grammer et al., 1996).

The transgressive phase of the first third-order sequence occurs within the Bachelor and Compton limestones. The regressive phase occurs as the Northview Formation. A flooding event occurred after the subaerial exposure surface at the top of the Northview. The second third-order sequence is represented by the Pierson Formation, deposited during the next third-order sequence.

Since the four primary depositional facies are repetitive throughout each formation, an idealized facies succession was recognized within the biostratigraphically and eustatically constrained third-order sequences. Each facies, displayed in an asymmetrical, shallowing-upward sequence (Figure 9), represents the facies deposited during one rise and fall in sea level. The idealized facies succession begins with deposition of Facies 1 (crinoidal–bryozoan wackestone) at the base of the cycle. This facies contains the highest mud content and represents the transgressive portion of the succession. The overall succession is dominated by the regressive portion of the sequence, which starts with deposition of Facies 2 (crinoidal wackestone–packstone), followed by Facies 3 (crinoidal–bryozoan mud-lean packstone–grainstone) and Facies 4 (skeletal grainstone). The repetitive packages range in thickness from 3 to 10 feet (1–3 m). This repetition illustrates facies within the same depositional system were migrating laterally during specific times of deposition for the Bachelor, Compton, Northview, and Pierson formations. This succession, and associated facies partitioning, allows for recognition of a hierarchy of sequences and cycles, which can increase the predictability of facies distribution related to the reservoir architecture in the subsurface (Eberli and Grammer, 2004).

As evidenced from the repetitive nature of each facies within the idealized facies succession at different scales (thicknesses), a hierarchy of sequences and cycles is developed within the sequence stratigraphic architecture. The higher-frequency events, superimposed on the biostratigraphically and eustatically constrained third-order sequences, are referred to as fourth-order high-frequency sequences and fifth-order high-frequency cycles (Figure 10), unrelated to actual time (Grammer et al., 2000). It is not possible to constrain the time element in Paleozoic rocks well enough to determine an average cycle duration that is unequivocally definable at the fourth- and fifth-order scale, but evaluation of a general cycle hierarchy is useful for determining stratigraphic ordering (Kerans and Tinker, 1997). This was a vital step in building the high-resolution sequence stratigraphic architecture of the Jane outcrop because higher-frequency sea-level fluctuations often are responsible for controlling vertical and lateral reservoir heterogeneity within a unit, as shown in many carbonate reservoirs (Grammer et al., 1996).

In addition to the debris flows outlined in Figure 2, multiple lines of evidence support movement of the blocks at the Jane outcrop through analysis of the Gigapan^® images. Evidence for block movement includes multioriented geopetal structures, and truncated Compton beds. Geopetal fabrics can serve as guides to the normal or inverted position of strata within complex stratigraphic settings (Honjo et al., 1965). These features are partial sedimentary infillings of rock cavities that may form during times of minimal sedimentation or rapid burial (Wieczorek, 1979). Multiple geopetal structures in the form of partially infilled brachiopods occur at angles ranging from 15˚ to 45˚ on the exposed surface of Block 1 (Figure 11), indicating the feature is a block that may have undergone multiple phases of movement and/or rotation subsequent to initial formation. This is not an unequivocal interpretation, as oblique cuts through the brachiopod shells could give different orientations.

Additional evidence for movement of the blocks occurs within the bedding between Block 1 and Block 3. Movement of each block likely occurred during different times, as indicated by the parallel bedding between the debris flow deposits and the blocks. If one event stemmed the movement of every block in the Compton Limestone simultaneously, the debris flow beds surrounding the blocks would likely be continuous, homogeneous deposits with no intervening parallel bedding. The debris flow beds (orange) are heterogeneous and intermixed with flat-lying, horizontal bedding in between the blocks (Figure 2). This is evidence that at least two of the five blocks moved at different times, complicating the bedding geometry within the Compton Limestone. In the same area between Block 1 and Block 3, intraformational truncation surfaces occur throughout the bedding (Figure 12). These features were likely produced as blocks moved along the ramp and truncated the beds between Block 1 and Block 3 (Ilstad et al., 2004). Similar truncation surfaces were observed within a base-of-slope carbonate apron (western Newfoundland) and are interpreted to represent deposition on an unstable sloping surface (Coniglio, 1986).

Thin section photomicrographs (Figure 13) document the core facies of Block 1 (Unrast, 2012). Blocks 2–6 were documented in this study and representative thin section photomicrograph for the blocks are shown in Figure 13. Each block at the Jane outcrop is similar in composition and can be classified as a crinoidal–bryozoan wackestone–packstone with localized skeletal grains consisting of crinoid and bryozoan fragments with local trilobites and ostracods. All blocks contain similar facies and skeletal components, indicating each block likely originated from the Compton Limestone at a location further updip on the ramp. Additionally, analysis of the debris flows show very poorly sorted, chaotic, unstratified clasts ranging in grain size from very coarse sand to very coarse pebbles (2–64 mm [0.08–2.5 in.]) supported by a deformed mud matrix, confirming the interpretation of the deposits surrounding each outrunner block are debris flow deposits (Figure 14; Asmus and Grammer, 2013).

A plausible explanation for the development of the outrunner blocks within the debris flow beds of the Compton Limestone at Jane includes the activation of a slump. A slump is defined as a rotational slide characterized by displacement of relatively intact blocks over curved or spoon-like slip surfaces with limited downdip transport (Tripsanas et al., 2008). Debris flows are produced from a slump as broken clasts supported by a mud matrix (De Blasio et al., 2006; Tripsanas et al., 2008). Also associated with the slump rotation and debris flows are outrunner blocks, described as nearly intact pieces of debris that detach from a slowing-down submarine slide and flow ahead of the front (De Blasio et al., 2006). Development of the blocks is due to hydroplaning, acceleration, and final detachment of the head of submarine landslides and debris flows (Ilstad et al., 2004; Tripsanas et al., 2008). Elements stimulating the movement of the block include gravity, velocity, shape, surface roughness, and block orientation (De Blasio et al., 2006). Multiple examples of similar mass transport processes can be found in recent and ancient analogs (Rigby, 1958; Crevellow and Schlager, 1980; Harris, 2004).

Formation and flow of outrunner blocks was documented to be closely related to channel systems, which may serve as an avenue for mass transport into the basin (Ilstad et al., 2004; Lee et al., 2008; Tripsanas et al., 2008; Gamberi et al., 2010). An example of a pathway for mass transport on a distally steepened ramp into a Mississippian basin in the U.S. midcontinent is shown (Figure 15). The Petrel image was provided by Devon Energy and shows a channel system entering the basin from the north direction. The image was produced using application of the sweetness attribute to highlight the channel feature. The image was then modified using Petrel’s geobody interpretation tool to create multiple box probes, which extracted the 3-D image in time.

The primary processes likely involved with initiating block movement include sediment loading (Coniglio, 1986; Schlager, 2005) and regional tectonism (Moore et al., 1976; Gawthorpe and Clemmey, 1985; Heubeck, 1992; Boardman, 2013; Mazzullo et al., 2019). Autochthonous micrite in the form of layers, lenses, or mounds serves as an in situ growth of a rigid body and adds additional weight to the slope or ramp (Wolf, 1965; Schlager, 2005). The mounds act as a rigid weight and represent localized loads capable of triggering slides and slumps (Schlager, 2005; Figure 16A). A similar form of sediment loading occurs within the Cow Head Group, in the form of a base-of-slope carbonate apron (Coniglio, 1986). In this case, synsedimentary shear zones evidenced by brecciation, truncation surfaces, and slide zones record deposition on an unstable sloping surface that eventually gives way to sediment failure.

The alternative explanation for triggering block movement is regional and/or local tectonism (Figure 16B; Moore et al., 1976; Gawthorpe and Clemmey, 1985; Heubeck, 1992; Evans et al., 2011; Boardman, 2013; Mazzullo et al., 2019). Conodont biostratigraphy and identification of unconformities throughout the US midcontinent region supports the interpretation for active syndepositional tectonism throughout Kinderhookian and Osagean strata (Boardman, 2013). Regional tectonic behavior in southwestern Missouri records northwest–southeast trending transpressional faults that would have effected sedimentation during the late Devonian and Early Mississippian (Evans et al., 2011). Flexure, loading, and tectonic subsidence were associated with the northwest–southeast regional faults (Evans et al., 2011). Recently, a strong case has been made for syndepositional tectonic activity related to a forebulge high where gravity induced dislodging of blocks and sediments likely occur (Mazzullo et al., 2019). Syndepositional tectonism is the favored mechanism for block movement within the Compton Limestone analyzed in this study (Evans et al., 2011; Boardman, 2013; Mazzullo et al., 2019).

Block deposition within the Compton Limestone has disrupted the sequence stratigraphy at the Jane outcrop. The newly defined conodont zonations do not definitively correlate to the eustatic sea-level changes throughout the Kinderhookian and Osagean (Figure 1; Boardman, 2013). The eustatic sea-level curve shows three third-order sequences in the Kinderhookian and two third-order sequences in the early Osagean. Based on conodont biostratigraphy at the Jane outcrop, there is only one third-order sequence in the Kinderhook formations and one third-order sequence in the Osagean formations. The discrepancy between the biostratigraphic zones and third-order sequences in the Kinderhookian strata at the Jane outcrop could be related to a sequence masked or eroded by deposition of the blocks and debris flows throughout the Compton Limestone or erosion at the top of the Northview Formation. The discrepancy between the biostratigraphic zones and third-order sequences in the Osagean strata at the Jane outcrop could be related to a combination of an incomplete Osagean section and erosion at the top of the Pierson Formation.

The blocks distributed throughout the Compton Limestone at the Jane outcrop are clearly not in situ features and are interpreted as outrunner blocks within debris flow deposits. These mass transport deposits are common in distally steepened ramp settings and were likely initiated by syndepositional tectonism throughout the Mississippian of the U.S. midcontinent. Outrunner blocks documented in the literature range in size from tens to hundreds of meters and can travel up to several kilometers on very gentle slopes (1–2˚).

A plausible explanation for the development of the outrunner blocks observed within the debris flow deposits of the Compton Limestone includes the activation of a slump. Debris flows are often produced from a slump as broken clasts supported by a mud matrix. The debris flow beds and block deposits are interpreted as being downslope from the original slump, which cannot be seen in the Jane outcrop. Often associated with the slump rotation and debris flows are outrunner blocks, defined as nearly intact pieces of debris that detach from a slowing-down submarine slide and flow ahead of the front. Development of the blocks is due to hydroplaning, acceleration, and final detachment of the head of submarine landslides and debris flows.

The outrunner blocks were deposited during the transgressive leg of the first third-order sequence, during a time when more accommodation space was available. This is reflected in the thickness of the high-frequency sequences and cycles in the Compton Limestone (1–2 m [3–6 ft] thick) relative to the Northview and Pierson formations (0.5–1.5 m [1.6–5 ft] thick). During this time of increased accommodation, the blocks and debris flow deposits were deposited across the outcrop in phases, indicated by parallel bedding in between each of the truncated beds.

Mass transport deposits and turbidites constitute a large volume of strata within subaqueous slope and basinal settings, making them a dominant strata type in most deepwater basins around the world (up to 50%; Posamentier and Walker, 2006). Due to this abundance, petroleum exploration efforts have focused much of their attention on these potential reservoirs (Asmus and Grammer, 2013). Although the Jane outcrop contains smaller outrunner blocks and thin debris flow deposits, if the flow is traced to more proximal settings, perhaps larger blocks and more laterally extensive debris flows could form limited targets, similar to examples in both recent and ancient analogs.

This work was completed as a part of Oklahoma State University’s Mississippian Consortium, funded by Devon Energy, Chesapeake, Marathon Oil, Sinopec, Maverick Brothers Energy, SM Energy, Newfield, Redfork Energy, Unit Petroleum, Chaparral Energy, Longfellow Energy, Samson Energy, American Energy Partners, and Trey Industries. Many thanks to the OSU students who helped with field work and data collection: Buddy Price, Stephanie LeBlanc, Beth Vanden Berg, Taylor Thompson, Scott Shelley, Ahmed Elbelasy, Ashley Dupont, Yulun Wang, Lara Jaeckel, and Ibukun Bode. Early versions of the manuscript were improved by Ashley Dupont’s individual reviews. Subsequent reviews by Mike Pope and an anonymous reviewer made the manuscript much stronger and are appreciated. We’d like to thank OSU faculty, Jim Puckette, Jay Gregg, and Darwin Boardman II for their valuable review and comments. We are grateful for the donation of the Petrel image provided by Devon Energy and Mouin Almasoodi’s assistance in extracting the image. The contents of this chapter were derived primarily from the first author’s master’s thesis.