Biotic destruction of terrestrial plant debris in the Late Paleozoic marine environment

Biotic destruction of terrestrial plant debris in the Late Paleozoic marine environment ROYAL H. MAPES AND GENE MAPES

LETHAIA Mapes, R.H. & Mapes, G. 1997 01 1 5 Biotic destruction of terrestrial plant debris in the Late Paleozoic marine environment. Lethaia, Vol. 29, pp. 157-169. Oslo. ISSN 0024-1 164.

Small, oblong, limonitized coprolites (<0.5 mm) containing macerated terrestrial plant debris have been recovered in Westphalian and Stephanian (Upper Pennsylvanian) gray to black shales that were deposited in dysoxic outer-shelf marine environments. The internal structure and external surfaces of the coprolites are unlike those of vertebrate coprolites and unlike ejecta recovered in stratigraphically adjacent anoxic sediments. Stratigraphically adjacent oxygenated sediments have been homogenized by numerous kinds of mobile benthic invertebrates, whose activities have probably destroyed any trace of plant-bearing coprolites in the more nearshore environments. Coprolites of terrestrial origin that contain plant debris are considered to have been generally too loosely consolidated to survive long-distance transport from tens to perhaps several hundred kilometers from land. Thus, the coprolites in this report appear to represent a feeding pattern, by one or more kinds of marine macroinvertebrates. on drifted land-plant debris that sank into offshore marine environments. Distribution of such plant destruction rep- resents a previously undocumented taphonomic pathway, demonstrating an unsuspected plant-animal interaction for terrestrial macroscopic plant debris in Upper Paleozoic marine environments. ODysaerobic detritivore, dysoxic marine environments, permineralized land plants, plant-detritus coprolites, Stephanian, Westphalian.

Royal H. Mapes, Department of Geological Sciences, and Gene Mapes, Department of Environ- mental and Plant Biology, Ohio University, Athens, OH 45701, U.S.A.; *. *-, 199.; revised --. 1996.

Since their origin, land plants have littered the terrestrial landscape with stems, spores, leaves and fertile organs (Gensel & Johnson 1991). Many of these plant remains were preserved in situ or relatively close to their growing sites. Some land-plant remains, however, were transported from their source communities, by wind and water, for modest to long distances, until eventually becoming deposited as recognizable fragments in certain poorly oxygenated oceanic sediments.

Intensive collecting in excellent preservational sites in midcontinent North America has recovered thousands of anatomically preserved plants in selected offshore Upper Carboniferous marine units. Surprisingly, over forty small plant-bearing coprolites have been recovered in association with these plant remains. The presence of veg- etal remains in these coprolites reveals that land-plant debris provided an important food resource for some marine organisms. The coprolite-bearing units (Fig. 1) are interpreted as offshore dysoxic marine environments that represent parts of seven distinct cyclothems (West- phalian B through Stephanian C equivalents: Boardman etal. 1984, 1990, 1994; Heckel 1986).

The physical condition of the anatomically preserved plants that occur with the coprolites indicates that plant debris was commonly sorted and altered during transport. Most bark, leaves, and soft outer tissue layers were removed in transit, before sinking and subsequent fossili- zation. Most of the plant fossils show no evidence of epi- zoan attachments or borings.

Land-plant remains in the Carbonifero;s are generally assumed to have floated until they were either consumed, disintegrated or abraded into microscopic organic particles. Some, however, must have become partially or completely waterlogged. The waterlogged remains sank into a variety of seafloor environments. Before being preserved, the plant debris was available for partial or complete microbial degradation. Various organisms may have ingested fungi, bacteria, or other microbes as well as por- tions of the land-plant remains. The plant debris that was consumed passed through intestinal tracts; the more-or- less digested debris was deposited as coprolites. The partially consumed plant remains preserved within the coprolites reported here, range from small wood chunks to tubular cellular fragments and partial cell walls.

158 Royal H. Mapes and Gene Mapes LETHAIA 29 ( 1996)

Fig. 1. Stratigraphic distribution of the localities that have yielded limonitized coprolites containing terrestrial plant debris. Boundary positions between European and North American stages are approximate. The localities are in stratigraphic sequence and are shown in relative position within the North American stages.

Past studies Although numerous studies of Late Paleozoic plant taphonomy have focused on various terrestrial environments (e.g., Behrensmeyer & Hook 1992; Gastaldo 1992; Scott 1977b, 1978, 1979) and similar modern analogs (Burnham 1989,1990,1993; Gastaldo & Huc 1992), there has been little documentation of the fate of plant debris that was transported out to the marine environments (Mapes & Mapes 1989; Gastaldo 1992; Robbins et al. 1985; Porter & Robbins 1981). White (1912), an early pi- oneer of paleobotanical taphonomy, concluded the fol- lowing on land plants in the marine environment:

‘The deductions drawn from the occurrence and conditions of land plant material in the oceanic areas of today

and from the stratigraphic relations and state of the cor- responding fossils found in the older deposits, appear fully to justify the conclusion that the presence of clean and well preserved leaf material in limestones or other marine sediments constitutes satisfactory proof of prox- imity of the deposit to land; as, conversely, the occurrence of water-worn, partially decayed, incrusted, or corroded material permits the conclusion that the specimens may have been for some time in water and are therefore liable to have been transported for some distance. Unfortu- nately, the evidence of fossil plants, though of the highest value in paleogeographic deductions, is so rare as usually to be wanting on the occasions of greatest need.’

Since White’s (1912) report, studies on preservation and distribution of land plants in the marine environment have been minimal. One factor contributing to the paucity of such data is that land plants are typically poorly preserved in most oxygenated nearshore transitional marine environments. In addition, well-preserved land plants in fossiliferous marine sediments may often have been overlooked as investigators focused on animal remains. Most organismal lists merely include ‘plants’. Lithic descriptions primarily extol1 the invertebrate and/ or vertebrate fossils of special interest, with a casual note that ‘some fossil plants are also present’. With the ready availability of rich and diverse plant communities preserved as compressions and as permineralizations in terrestrial sediments, even paleobotanists have tended to ignore the occurrence of terrestrial plants in marine sediments.

During the past 25 years, however, more than 40,000 well-preserved Late Carboniferous terrestrial-plant permineralizations have been recovered from midcontinent North American rock units deposited in outer-shelf open-marine environments (Mapes & Mapes 1989). These anatomically preserved fossil plants are preserved by means of phosphate, calcite and pyrite. Where preserved as original pyrite, permineralizations are commonly altered to iron oxides such as limonite by weather- ing. Diverse marine invertebrate and vertebrate biotas are often found with the land-plant remains. Well established stratigraphic and sedimentological constraints provide a definitive paleogeographical and paleoecological model for interpreting the biological and geological context of these deposits (see Boardman et al. 1984 for summary). Rare, plant-bearing coprolites in specific marine environments (Mapes & Mapes 1993, and this report) support the conclusion that woody plant debris was part of the diet of some Late Paleozoic offshore marine invertebrates. Based on the preservational conditions and the interpreted paleoenvironmental sequences, and using the Upper Car- boniferous of midcontinent North America as a model, it is possible now to reconstruct part of the taphonomic pathway traversed by some terrestrial plant debris into marine environments.

LETHAIA 29 (1996) Destruction ofplant debris 159

Land Seaward Fresh to brackish to lully marine enviknents

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Terrestrial environments

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Sea level

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Limonite plant remains usually absent ?- mold/casts, and

permineralizations

* Coprotites

Fig. 2. Cross-sectional view of generalized distributions of land-plant remains and marine invertebrate paleocornmunities as observed vertically in cyclothem sequences in the North American midcontinent. The size of the balloon at the base generally indicates the quantity of plant debris preserved in each environment. The asterisk indicates the dysoxicloxic interface interval in the community sequence where the coprolites containing plant fragments were recovered.

Paleoenvironmental interpretation

Critical to understanding the distribution of the coprolites containing terrestrial plant remains in Upper Paleo- zoic marine environments are data combining plant ‘pet- rifaction’ (cellular permineralization sensu Schopf 1975), mineralogy, and paleoenvironmental interpretations of associated faunal assemblages. During Late Carbonifer- ous and Early Permian time in the interior midcontinent of North America, numerous (>75) eustatic sea-level shifts produced a more-or-less rhythmic vertical succession of carbonate and clastic rock units (i.e. cyclothems). Since the sea-level changes were driven by continental- scale glaciation in the southern polar regions, the eustatic oscillations were worldwide and synchronous (Heckel 1986). However, the rhythm and magnitude of advance and retreat of the marine environment onto the craton were tempered locally by tectonic events and by terrestrial paleogeography and deltaic sequences, which combined to produce a complex interplay of local to regional sedimentation rates, lithic types, and related biofacies (see

Heckel 1991 and Boardman 1984,1990 for the debate and summaries on cyclothem origins).

Considerable debate continues to revolve around the glacial eustatic model for cyclothems, which relies on the marine black shale being the deepest-water facies in the cycle (e.g., Heckel 1977, 1991; Boardmiin & Barrick 1989; Boardman & Heckel 1989, and others). The most recent objections are based on subsidence models (Kline 1992; Klein & Kupperman 1992) and on new geochemical arguments concerning the depositional environment of black shales (Coveney et al. 1991), which have been contested by Heckel & Hatch (1992). We favor the models of Heckel (1977,1991) and Boardman et al. (1984), which are based on extensive stratigraphic and paleontological field data rather than subsidence models and controversial geochemical arguments.

Combining the depositional model for cyclothems pro- posed and expanded by Heckel (1977, 1980, 1984, 1986, 1991) and the paleocommunity succession documented by Boardman et al. (1984) and Boardman & Malinky (1985) provides substantial insight into the empirically

160 Royal H . Mapes and Gene Mapes LETHAIA 29 ( 1996

Fig. 3. Representative plant remains recovered from dysoxic marine zones. Specimens are reposited at the Ohio University Paleobotanical Herbarium (OUPH). These are permineralized as pyrite (A) or limonite after pyrite (B-F), and are from localities TXV-200 (A) and TXV-120 (B-F). See locality appendix. Individual plant organs are illustrated at same magnification ( ~ 2 ) to facilitate comparison. OA. Suavitas imbricata (Rice et a/. 1996), lycophyte cone with one functional megaspore per megasporangium. LS419 = O.U.P.H. 12338-12356. OB. Gall or unknown fructification. LS 630. OC. Presumed cordaitean axis bearing two partial cones. LS708. OD. Medullosan ovule showing seed coats and seed interior. LS482. OE. Synangium. LS 429. OF. Ser- geia neubergii (Rothwell et al. 1996), vojnovskyalean cone. P 72.

observed distribution and preservational modes of the Upper Carboniferous plants and plant-containing coprolites that occur in the cyclothemic units in Oklahoma and Texas (Fig. 1). By utilizing sequence stratigraphy and invertebrate fossils such as conodonts, ammonoid cepha- lopods, and fusilinids, Boardman & Heckel (1989), Boardman & Barrick (1989), and Boardman et al. (1994) have generated Carboniferous sea-level curves and have greatly refined biostratigraphic correlations across the multibasinal continental interior of North America. While not being unanimously accepted (See Van Veen tk Simonsen 1991), their work currently provides the best insight into the age of the plant-bearing coprolites and how they became preserved in the marine realm.

Preservation in the marine realm probably depends largely on the absence or near absence of oxygen in the marine bottom sediments. Empirical observations based on surface and some in situ collections derived from midcontinent North America suggest that, in Upper Paleo- zoic epicontinental seas, fossil plant debris is only rarely preserved in offshore environments with low paleoslopes and oxygenated sediments. In such oxygenated sedi-

ments, fossil plant debris is usually limited to small (< 0.5 cm) non-diagnostic particles and occasional degraded fragments. Such fragmented plant remains most often occur as carbon impressions in shale and more rarely in concretions composed primarily of carbonate. Addition- ally, mold/casts and impressions sometimes occur in lit- toral sandstones or in sedimentologic units such as tur- bidites that allowed rapid’burial (Fig. 2). Even more rarely, some plant debris is preserved in transitional (terrestrial to marine) fine-grained carbonates.

By contrast, in certain dysoxic environments, fossil plant material can be very abundant and include excel- lently preserved petioles, seeds, sticks, roots, pollen organs and cones (Fig. 3). All of these plant remains are differentially preserved either as pyrite (or more commonly as products of oxidized pyrite such as limonite, hematite and goethite), or as carbonate or phosphate permineralizations in carbonate or phosphate concretions. The abundance of plant fossils in the dysoxic sediments underscores the substantial influence of biodegradation that occurs in the more shoreward oxic sediments. In the oxygenated environments there is greater influx of land-

LETHAIA 29 (1996) Destruction of plant debris 16 1

plant debris, but it is accompanied by extensive bioturba- tion and biodegradation. In contrast, for the pieces of plant debris that sink into dysoxic sediments, there is relatively less biodegradation and greater probability of permineralization. Fortuitously, the limonitized coprolites reveal that even in these dysoxic environments certain marine animals were adapted to foraging on the waterlogged land-plant detritus that sank into their realm.

The plant-bearing coprolites described in this report are from twelve Upper Carboniferous localities represent- ing seven distinct cyclothems in the southern midcontinent. Stratigraphically the localities range (Fig. 1 ) from the Atokan (Westphalian B) through the Virgilian (Steph- anian C-D). Geographic and stratigraphic details on the twelve localities are given in Appendix 1. The coprolites from these localities are all preserved as limonite after pyrite. All of the specimens were recovered from marine shales that are dark when fresh and tan when weathered. In paleoenvironmental context, the majority of the coprolite-bearing localities that are sufficiently well exposed to permit analysis are on the dysoxic side of the oxic-dysoxic boundary. Additionally, we suspect but cannot prove that at some of the localities the water column from the paleo-ocean surface to the water-sediment interface was relatively well oxygenated, but the muddy sediment was dysoxic.

Unlike phosphatized invertebrate and vertebrate coprolites and ejecta from stratigraphically adjacent anoxic sediments, the limonitized coprolites in this study are all relatively small, averaging less than 1 cm long, and none show any appreciable disaggregation. The lack of disaggregation suggests that pyritization occurred relatively quickly after defecation. All of the limonitized coprolites co-occur with larger (>1 cm) pieces of excel- lently preserved fossil plant remains and an extensive, diverse, well preserved marine invertebrate macrofauna (See Boardman et al. 1984 for lists of characteristic dysoxic faunal elements). Despite their wide stratigraphic distribution, these small limonitized coprolites are always a rare component in the combined totals of the plant and invertebrate fossils recovered from surface collecting and microsample processing.

Coprolites The limonitized coprolites are somewhat variable in surface features and interior texture (Figs. 4-7). The majority of the coprolites (n=43) are small, compact, cylindrical units. Individual coprolites generally range in length from 3 to 9 mm, are oval to round in cross-section and, with one exception, average 2.5 mm in maximum width (Fig. 9). While some coprolites are clearly broken and incomplete at one or both ends (Fig. 6A, left side), many appear to have been deposited and preserved as completed units

Fig. 4. Large coprolite from TXV-I20 (See locality appendix), (LS438 = C2 = O.U.P.H. 12478-12482). Surface morphology of somewhat flattened coprolite (X 10) containing numerous partially macerated wood fragments. Arrow indicates one wood fragment.

Fig. 5. Close-up of ground thin section of coprolite interior from Fig. 4; arrow indicates wood fragments with groups of tracheids intact (x60). LS438, Slide 4 = O.U.P.H. 12482.

(Fig. 6C,G; Fig. 7D,E). Unbroken ends vary in shape from tapered wedges (Fig. 6F, I) to bluntly rounded flattened ends with shallow centers that either protrude or are sunken (Fig. 6A, right side). Some coprolites are covered with a complete or discontinuous homogeneous iron

162 Royal H. Mapes and Gene Mapes LETHAIA 29 (1996)

Fig. 6. Typical coprolites illustrating surface features and textures of broken interiors. All surface views are at the same magnification (x IO) , while the interior views are 50% larger (x15). Specimens are ail from OKD-15 (see locality appendix). OA. Incomplete coprolite with broken end at left and abruptly flattened truncation with central depression at right end. Note smooth incomplete limonite coating. C24 = O.U.P.H. 12483. OB. Broken interior view from center of A; homogeneous to granular with no complete cells. C24 = O.U.P.H. 12483. OC. Complete coprolite with bluntly rounded ends and granular limonite coating. C15 =O.U.P.H. 12484. OD. Broken interior view from center of C; shredded subunits packed tightly with no apparent order. CIS = O.U.P.H. 12484. OE. Broken interior view from center of C29 with two distinct textural layers; majority of innermost interior comprises relatively large but unidentifiable subunits, exterior layer comprises swirled fiber-like areas. C29 = O.U.P.H. 12485. OF. Fibrous swirled surface of C29; ends are both angled and rough and may be incomplete. C29 =O.U.P.H. 12485. OG. Complete coprolite slightly flattened; end at left is bluntly wedged, end at right is slightly rounded with central protrusion. Weathered surface reveals partially cellular shredded fragments. C7 = O.U.P.H. 12486. OH. Broken interior view of C7 with shredded fragments. Note greater homogeneity than illustrated for C15 in Fig. D. 01. Complete coprolite slightly curved and somewhat flattened with coarsely granular limonite coating. End at left is more abruptly angled than rounded end at right. C10 = O.U.P.H. 12487. OJ. Broken interior view with homogeneous to granular contents with no recognizable cell walls. C10 = O.U.P.H. 12487.


oxide coating that is either smooth or granular, or may include small oxidized pyrite crystals. These variations in coating may result from fluctuation of microbiogeo- chemical (Robbins & Norden 1995) or other sedimentologic conditions, or from biological factors such as original mucilage. Other coprolites display shredded (Fig. 7G), fibrous (Fig. 7A, B) or granular surfaces (Fig. 7J), parallel striations (Fig. 7C), or small chunks of wood (Figs. 4,7F) on their surfaces.

One exceptional coprolite (Fig. 4) is relatively large (14 .5~12 mm), amorphously subrounded and somewhat flattened, with partially macerated wood fragments visible on the surface and in ground thick section (Fig. 5). Although the wood cannot be identified systematically, the tracheids are presumably gymnosperm, the most common woody plant remains in these Paleozoic marine deposits. Many wood fragments are incompletely digested. Some tracheids remain in groups as part of the original wood structure, indicating their dissociation or removal from the source plant debris as small chunks. Individual fragments are up to 1000 pn long, with the longer dimension parallel to the tracheids long axes.

By contrast, examination of the more typical (small, cylindrical) coprolite interiors (Fig. 6B, D, E, H, J) reveals considerable variability in degree of content disaggregation and digestion. Cell wall fragments, wood fragments, and smooth tubular fragments are recognizable in some sections, but none are systematically diagnostic. Addi- tional specimens used in this study, but not illustrated here, are reposited at Ohio University Paleobotanical Herbarium as O.U.P.H. 12500-12541.

Interpretations and conclusions While relatively compact, these coprolites are all considered too loosely consolidated to have survived much aquatic transport from land without disaggregation. Though we understand that some modern, and presumably fossil, millipedes have relatively compact fecal pellets (See Scott 1992 and others), the transport distances and geologic span represented cause us to consider terrestrial coprolite sources less likely for this material. We therefore interpret the fossil coprolites described here as support for the presence of marine detritivores at the site of deposition and preservation. Internal organization of individual coprolites ranges from finely homogenized granular contents to swirled fibrous layers and coarse chunks of wood. In combination with the stratigraphic range represented by the coprolites, the internal textural variations suggest that more than one source animal was able to obtain nutrient value, directly or indirectly, from the terrestrial plant debris.

Worms, arthropods, and molluscs such as gastropods and chitons are among the possible coprolite source ani-

mals co-occuring with the fossil plant debris (See Board- man et al. 1984). The limonitized coprolites do not display characteristic layers or other surface features associated with known vertebrate coprolites or enteros- pirae (Williams 1972); nor do any display patterns of parallel tubes characteristic of certain crustaceans (Parejas 1948). Most do conform in general shape to coprolites of certain worms and gastropods (Brotzen 1951; Kornicker & Prudy 1959; see also illustrations in Scott 1992).

It is not known whether the food resource being ingested was actually the plant cellulose and cell contents, or the bacteria, fungi, or other biotic residents or residues on the plant surfaces. The coprolite source animal(s) may have foraged in the oxic-water-dysoxic-sediment interface, preferentially consuming the waterlogged plant debris and/or associated microbiota. Molluscan grazers commonly use radulae to rasp at almost any substrate on which algae has grown (Parsons & Brett 1991). Tapho- nomically, the physical process of shredding and disag- gregating plant remains containing fungal, bacterial, or other microbiota is a separate part of the biodegradation process, resulting in increased surface area for further microbial colonization. Though cellular remains assigna- ble to specific microbial organisms have not yet been rec- ognized in, on, or with these coprolites, there is no reason to believe that bacteria, algae, fungi and other microbiota have not been present to colonize and biodegrade dead terrestrial and aquatic plants from Precambrian time to the present (Gall 1990; Taylor & Taylor 1993; Robbins et al. 1987; Robbins et al. 1985; Porter & Robbins 1981; Sherwood-Pike & Gray 1985; Scott et al. 1992).

The plant-eating, coprolite producers are presumed to have been megafaunal detritivores, rather than specialized herbivores. The wood fragments present in some coprolite specimens may have been swallowed inadvertently as some detritivores consumed surface microbiota. How- ever, the volume of plant debris in other coprolites suggests that some of the necrophytovores may have specifi- cally selected sunken plant debris as a direct food resource.

Most marine coprolite studies center'on fecal remains of vertebrates eating other vertebrates (McAllister 1988; Amstutz 1958; Price 1927). Studies of Paleozoic coprolites containing plant debris, however, focus on terrestrial herbivory, emphasizing vertebrates (TifTney 1992; Olson, Hotton & Beerbower 1991) or insects and other invertebrates preferentially eating various plants or plant parts in the terrestrial environments (Scott 1977a; Baxendale 1979; Cichan & Taylor 1982; Scott &Taylor 1983; Scott et al. 1985; Shear 1991; Behrensmeyer etal. 1992; Scott etal. 1992). The absence of previous studies examining necro- phytophagy in marine environments is due in part to the paucity of direct evidence that has been available for investigation. Another crucial factor may also be the development of reliable conceptual models for regional

164 Royal H . Mapes and Gene Mapes LETHAIA 29 (1996)

Fig. 7. Coprolites demonstrating partial range of size, morphology and surface features. All are from OKD-15, except A, which is from OW-10 (see locality appendix). AU specimens are at the same magnification (X 10) to facilitate size comparisons. OA. Narrow slightly curved incomplete coprolite; note fibrous swirls are predominantly parallel at a low angle spiral around the specimen. C4 = O.U.P.H. 12488. OB. Incomplete coprolite is recurved in opposite directions with large broadly swirled patterns of apparent fibers on surface. C38 = O.U.P.H. 12489. OC. Coprolite with smooth end at left and angled, possibly broken, end at right. Surface texture displays chevron-like pattern of aligned, fiber-like units at left, but not at right. C17 = O.U.P.H. 12490. OD. Complete coprolite C14 (= O.U.P.H. 12491) with limonite coating and bluntly truncated ends with slight central depressions. Note resem- blance to incomplete specimen C24 in Fig. 6A. OE. Complete coprolitewith partial limonite coating and three small limonite nodules on surface. Surface

LETHAIA 29 ( 1996) Destruction ofplant debris 165

depositional environments and paleocommunity succes- sions (primarily Heckel 1977 and Boardman et al. 1984) that allows us now to begin to consider these unobtrusive remains in a taphonomic and paleoenvironmental context.

The taphonomic pathways leading to preservation of terrestrial plants in Upper Paleozoic marine environments clearly are not identical to those in more modern oceans. Plant debris in modern marine environments is subject to an expanded host of destructive events, including but not limited to anaerobic and aerobic bacteria, gnawing by polyplacophorans (chitons) and gastropods, and boring by algae, echinoids, bivalves and worms. A large volume of literature deals with how to preserve modern wood pilings and underwater wood structures from the destructive effects of modern marine organisms (for example, see Lane 1961). Although Toredolites worm borings were apparently present by Jurassic or Cretaceous time (Kelly 1988; Savrda & King 1993, Savrda et al. 1993), many of these destructive influences had not evolved by the late Paleozoic, or at least had not left recognizable traces on the terrestrial plants recovered from marine units described here.

In order to understand these occurrences of plant-bearing coprolites, a speculative scenario is provided. During the Late Paleozoic, land plants from a variety of terrestrial environments, such as wetland mires or coal swamps, flood plains, coastlines, well-drained valley slopes, etc., regularly discarded various plant organs (Gensel et al. 1991; Tifiey 1992; DiMichele & Hook 1992) that were subsequently washed or blown into rivers emptying into the marine environment. Other plant debris was washed directly into the sea during storms or high tides or sometimes reworked into the nearshore marine environments from beach deposits (Collinson 1983; Scott & Collinson 1983).

However, the majority of the land-plant debris entering the sea probably did so by way of river systems (Fig. 8) and may have included plants from ecozones seldom preserved in the terrestrial fossil record. Thus, abundant quantities of miscellaneous land-plant debris generally

is granular to shredded with small wood fragments. C8 = O.U.P.H. 12492. OF. Complete coprolite with partial smooth limonite coating; ends are both rounded and small chunks of wood are apparent. C34 = O.U.P.H. 12493. OG. Complete coprolite, slightly curved, with subrounded to oval ends; surface is granular to fibrous. C39 = O.U.P.H. 12494. OH. Incomplete coprolite broken at both ends; surface has loosely packed shredded and fibrous areas. C27 = O.U.P.H. 12495.01. Complete coprolite with compact surface combining shredded and fibrous areas. C31 = O.U.P.H. 12496.01. Complete coprolite with compact granular surface. C33 = O.U.P.H. 12497. OK. Elliptic to globular coprolite with coarse granular surface comprising numerous small pyrite to limonite crystals extending beyond smooth limonite coating. C37 = O.U.P.H. 12498. OL. Curved coprolite with partial coating of smooth limonite; coprolite surface reveals granular texture interspersed throughout with narrow tubular fragments. C11 = O.U.P.H. 12499.

can be expected to have been deposited into a large number of transitional terrestrial-marine environments such as estuaries, lagoons, and beaches. Where exceptional preservational conditions exist, some of those transitional deposits develop extremely interesting lagerstatten such as Kinney quarry in New Mexico (Schultze & Maples 1992; Mamay & Mapes 1992) or Hamilton quarry in Kansas (Mapes & Mapes 1988; Feldman et al. 1993). More commonly, however, nearshore plant debris is extensively bioturbated, mechanically abraded, and deposited in coarse-grained sediments.

Despite the substantial amount of plant biomass intro- duced into various transitional terrestrial-marine depositional systems, the plant litter commonly becomes fragmented and degraded as it floats out to sea. Presence of the plant-bearing coprolites reveals that sooner or later some of the debris sank into dysoxic marine environments and provided a reasonably reliable food source for members of certain oceanic paleocommunities.

Based on generalized paleogeographical and paleoenvironmental modeling, we interpret most of the dysoxic units in the Upper Carboniferous cyclothems of midcontinent North America to have been from tens to several hundred kilometers offshore. Based on the preserved faunal diversity, the paleoenvironments that yielded the plant-bearing coprolites had fully marine salinity and, perhaps in some areas, a moderately oxygenated water column. However, based on the large number of invertebrate and plant fossils preserved in limonite after pyrite, the sediments below the sediment-water interface were probably dysoxic to anoxic.

Although generally closer to shore and to the terrestrial plant source areas, the well-oxygenated sediments in our study areas are typically intensely burrowed and homogenized by benthic organisms. Such oxic sediments contain no coprolites and only rarely contain recognizable plant organs. Nearly all the plant detritus appears to have been fragmented into small particles or destroyed completely by the combination of physical, chemical and biological mechanisms. The very active biotic destruction is presumably due to the increased numbers 'and expanded diversity of both microorganisms and megafauna com- peting for food resources in the oxygenated sediments and oxygenated water column. In the relatively more oxygenated parts of the marine system, therefore, unless sealed off by rapid sedimentation or similar phenomena, neither plant debris nor coprolites produced by necro- phytophagy are likely to be preserved.

Anoxic sediments stratigraphically adjacent to the dysoxic zones also contain no plant-bearing coprolites. The anoxic sediments are generally poorly fossiliferous and paleogeographically farther from shore. Occasional plant remains occur as fragments or partial axes either preserved as compressions or differentially permineralized by phosphate and calcite. Additionally, the anoxic sedi-


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Middle shelf

Outer shelf

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Fig. 8. Diagrammatic model of the taphonomic pathways and lithologies by which land-plant debris could be transported, deposited, and preserved in marine sediments. The vast majority of the permineralized plants and coprolites are recovered from the dysoxic and anoxic shale units.

ments often contain phosphate concretions with verte- cephalopod mandibles and radulae (Mapes 1987; Tanabe brate coprolites or ejecta, presumably derived from fish & Mapes 1995; L. Doguzhaeva, R.H. Mapes, & H. Mutvei, consuming nektic or planktic organisms in the overlying unpublished ). Microscopic examination of thousands of oxygenated water column. Preservation of organic debris the phosphatized coprolites and other ejecta have in the phosphate concretions can be excellent, including revealed no recognizable plant debris in the ejectoid chitinous shells of articulated arthropods and chitinous masses from anoxic zones.


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I 0 2 4 6 8 10 12

Diameter (mm)

Fig. 9. OA. Scatter plot indicating coprolite width and length. OB. His- togram of coprolite width. N=43 specimens; coprolite specimen O.U.P.H. 12482 is unique in size and in contains very large fragments of wood. See also Figs. 4 and 5.

The complete lack of plant-bearing coprolites in anoxic sediments, despite the evidence of presence of both plant debris and animals, suggests the ‘necrophytovores’ contributing coprolites to the dysoxic zones were not nektic. We consider it more probable that the plant-detritus eat- ers were mobile benthic invertebrates making short-term foraging forays from better oxygenated adjacent environments into the food-rich, lower-competition, lower-oxygen territories. The discovery of plant-dominated coprolites in the dysoxic marine environments documents selective plant biodestruction in the Paleozoic marine realm and increases our understanding of the taphonomic pathways involving land plants in marine deposits.

Acknowledgments. - Our sincere thanks to David Kidder, Ohio Univer- sity, for his insightful and helpful comments on earlier drafts of this report. We wish to thank the Ohio University Research Committee and the Baker Award Fund for providing support for early stages of the field work that allowed collecting of these specimens. Part of this research was supported by a grant from the National Science Foundation (EAR 9117700) to Koyal H. Mapes and Gene Mapes. Specimen preparation and photography were ably assisted by Jennifer Rice; Gary Greer pre-

pared Fig. 9; and Ohio University Graphic Art Production staff prepared Figs. 1,2 and 8.

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Appendix Locality register Locality OKA-01: Atoka Formation: SW %, SW %, sec. 1, T2S, R8E; Wa- panucka North 7%" Quadrangle. The locality is on the north bank of Delaware Creek about 1.5 miles (2.4 km) north ofWapanucka, Johnston County, Oklahoma.

Locality OKD-04: Lower Holdenville Formation: NE %, NE %, sec. 11, T1 lN, RlOE; Clearview 7%" Quadrangle. The locality is an opening in a pasture on the west side of the road 5.0 miles (8 km) east and 018 miles (1.3 km) north of Okemah, Okfuskee County, Oklahoma.

Locality OKD-10: Middle Wewoka Formation: SE %, SW %, sec. 10, T13N, R12E Okmulgee 7%" Quadrangle. The locality is a shale bank on the north side of Oklahoma Highway 56, 3.0 miles (4.8 km) west of Okmulgee, Okmulgee County, Oklahoma.

Locality OKD-12: Lower Wewoka Formation: SW %, NW %, SW lh, sec. 4, T3N. R7E Francis 7%" Quadrangle. The outcrop is a ravine now part- ly filled with trash about 2.0 miles (3.2 km) east and 1.8 miles (2.9 km) south of Homer, Pontotoc County, Oklahoma.

Locality OKD-13: Wetumka Formation: SW %, SW Ih, NE %, sec. 8, T7N, RlOE; Lake Holdenville 7%" Quadrangle. The locality is 5.2 miles (8.3 km) east and 0.6 miles (1 km) north of Holdenville, Hughes Coun- ty, Oklahoma.

Locality OKD-15: Wetumka Formation: NW %, NW %, NE %, sec. 18, T3N, R7E; Stonewall 71h" Quadrangle. The locality is a large ravine located 3.0 miles (4.8 km) south and 0.5 miles ( 0.8 km) east of Homer, Pontotoc County, Oklahoma.

Locality OKM-10: Muncy Creek Shale?: center of sec. 36, T20N, RlOE; Wekiwa 71h" Quadrangle. The locality is on the northeast comer of a filled refuse dump on the north side ofa small drainage creek. The refuse dump is located 1.0 miles (1.6 km) south of the Eagles Nest Landing Strip Air Facility near Sand Springs, Osage County, Oklahoma.

Locality OKM-31: Muncey Creek Shale: center of SW %, SW %, sec. 12, T21N, R11E Avant SE 7115" Quadrangle. The locality is a bulldozer cut on the side of a steep hill.

graphic correlation with curve for midcontinent North America'. Geology lY:l, 91-94.

White, D. 1912: Value of floral evidence in marine strata as indicative of nearness of shores. Geological Society ofAmerica Bulletin 22,221-227.

Williams, M.E. 1972: The origin of 'spiral coprolites'. The University of Kansas Paleontological Conm'butions 59, 1-19.

Locality TXV-31: Finis Shale: Pond dam on the west side of FM 717,4.2 miles (6.7 km) south of the FM 717 and Texas Highway 180 junction at Caddo, Stephens County, Texas.

Locality TXV-41: Finis Shale: The Knoll. 14 SNM58333367496. Jacksboro Northeast 7W" Quadrangle, Jack County, Texas. The locality is on the southeast side of an isolated circular knoll approximately 20 m in relief in an unnamed north-south valley on the south side of Lost Creek. The knoll is located 0.9 miles (1.5 km) north of U. S. Hwy. 380 at a point 1.7 miles (2.7 km) east of the junction of U. S. Hwy. 380 and U. S. Hwy 381 south of Jacksboro, Jack County, Texas.

Locality TXV-73 Finis Shale: 14 SNM %618%7778. Jacksboro 7%" Quadrangle. (This is not TXV-73 of Boardman et al. 1994, but is fossil landing and measured section of Boston, 1988 =BBTXV-I 14) Exposure on side of hill near a gas line compressor unit on the Stewart Ranch, 3.9 miles (6.4 km) due east of the old Lake Jacksboro spillway, which is about 1 mile (1.6km) northeast of Jacksboro, Jack County, Texas.

Locality TXV-92: Finis Shale: 14 SNM 58000366921. Jacksboro 7%" Quadrangle, Jack County, Texas. The exposure is an abandoned oil well pad located 0.4 miles (0.7 km) north northwest ofTXV-120.

Locality TXV-120: Finis Shale: 14 SNM 58019366826. Jacksboro 7%'' Quadrangle. (= fossil localities and measured section TXV-66 ravine and TXV-83 well pad of Boston, 1988). The two exposures are 2.8 miles (4.5 km) south of the U. S. Hwy. 380 and U. S. Hwy. 281 intersection south of Jacksboro, Jack County, Texas. The localities which have been combined here for convenience of reference are a ravine that is separated from an abandoned oil well pad by about 50 m of grassy slope, approximately 20 m below marker VABM 13332.

Locality TXV-200 Finis Shale: 14 SNM 58150367860. Jacksboro North- east 7%" Quadrangle. The locality is the floor and south side of theemer- gency spillway of the new Lake Jacksboro dam located approximately 2.0 miles (3.4 km) northeast of Jacksboro, Jack County, Texas.

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Biotic destruction of terrestrial plant debris in the Late Paleozoic marine environment