Raymond C. Gutschick

Problems in Interpreting Unusually Large Burrows

Although marine burrows of unusually large dimensions have long been known in certain areas, they are probably much more widespread in the rock record than is generally recognized. Such burrows constitute a heterogeneous group, having little in common other than “exceptional” size. Yet their size alone unites them in difficulty of interpretation: e.g., densely spaced?dwelling burrows or combined dwelling-escape burrows as much as 12 cm in diameter and 5 m long; vertical dwelling burrows only 0.5 cm in diameter but up to 9 m long; possible escape structures as much as 24 cm in diameter and 3 m long, subsequently penetrated in some cases by secondary burrow-like structures.

Middle Ordovician agglutinated foraminifera including Reophax from the Mifflin Formation, Platteville Group of Illinois

Agglutinated siliceous foraminifera occur in the Middle Ordovician (Blackriveran) Mifflin Formation of the Platteville Group in northern Illinois. The fauna consists of globular saccamminids and a new form Reophax blackriveranus n. sp. which records the oldest validated representative of this genus. This marks the earliest known occurrence of agglutinated foraminifera with multichambered uniserial tests of progressively expanding chambers from the proloculus to the aperture. This early innovation of test morphology was probably developed to control unfavorable changes in the water chemistry of the environment. Mifflin lithofacies consist of light gray, thin, wavy-bedded, lithographic limestone and fine-grained dolomite with green shale interbeds, thin calcarenite layers with graded bedding, a K-bentonite ash layer and hardground corrosion bedding surfaces. Mifflin biofacies include the foraminiferan fauna, brachiopods and molluscan shelly faunas, bryozoans, trilobites, ostracodes, echinoderms, solitary corals, conodonts, chitinozoans, scolecodonts, sponges and trace fossils particularly Chondrites . The Mifflin strata were deposited on an exceedingly gentle slope off the Pecatonica carbonate platform which flanked the Wisconsin Arch. Thin Mifflin clinothem limestone beds wedge out into shales in the moderately deep ( Reophax is associated with saccamminids in the benthos of the marine upper foreslope. Apparently slope-dwelling Reophax foraminifera of the Ordovician were displaced downslope into the basin by the rapid development and expansion of hyperamminids which occupy the lower and middle foreslope in the Mississippian.

Mississippian Wood-grained Chert and its Significance in the Western Interior United States

ABSTRACT Wood-grained chert is nodular chert which has internal light- and dark-colored, concentric, three-dimensional, compositional banding resembling grain in wood. The light-colored bands are dolomitic and the dark-colored bands are quartzose with carbonaceous matter. Wood-grained chert is recognized in the Mississippian Lodgepole, Deseret, and Great Blue Limestones and some correlatives of these formations in Montana, Utah, and Idaho. The Deseret starved basin model (Sandberg and Gutschick 1980; Gutschick and Sandberg 1983) provides a paleogeograpic framework that restricts the wood-grained cherts in this basin to the foreslope between the oxygenated carbonate platform margin ( 300 m) basin. Wood-grained chert may mark th approximate position of the lower limit of the pycnocline in the Deseret starved basin. Upwelling of nutrient-rich water along the foreslope generated high biological productivity which in turn supplied abundant biogenic silica and organic matter to the sediments of the foreslope and basin. Siliceous microfossils dissolved and provided a source of silica for the formation of porcellanite (opal-CT) nodules within the foreslope sediments during burial and compaction. Calcium carbonate diffused into the nodules from the surrounding mixed calcareous/siliceous muds and early diagenetic conversion of opal-CT to quartz released magnesium. Reduction of sulfate, a dolomite inhibitor, in the associated anoxic, organic-rich sediments below the pycnocline permitted dolomite formation. Dolomite precipitated in bands as a result of a periodic supersaturation-precipitation-nucleation-d pletion process (Ostwald-Prager theory of Liesegang band formation), possibly augmented by competitive particle growth. Petrographic evidence and the apparent inverse relationship between band spacing and time support our theory.

Bifungites, trace fossils from Devonian-Mississippian rocks of Pennsylvania and Montana, U.S.A

Abstract The trace fossil Bifungites Desio 1940, first recognized in Late Devonian rocks of Libya and later in Algeria, is common in Late Devonian rocks of Montana, Pennsylvania, Ohio, and Michigan, and Early Mississippian rocks of Pennsylvania. Its manifestations are given for seven stratigraphic units from forty localities in Pennsylvania, Montana, and Michigan. Bifungites commonly occur on bedding planes and consist of a horizontal shaft with doubly terminating arrow- or dumb-bell-shaped projections. Less apparent are paired vertical cylindrical sediment-filled tubes connected at their base to the bi-arrow or dumb-bell shaft. The combination represents the mud or silt casting of an inverted pi-shaped, μ, infaunal tubular burrow (domichnia). Siltstone slabs have been transversely sectioned to reveal this π-shaped, double-arrow burrow pattern with undisturbed stratification between the vertical tubes. Three new ichnospecies are proposed based on markedly different size and shape of the fossil traces in three stratigraphic zones. A Late Devonian Girard Shale type is the smallest with wide, short arrows on a narrow shaft whose median overall length is 12.5 mm. The latest Devonian Sappington type has well-formed, shortly barbed arrow terminations and median length of 28 mm. An Early Mississippian Meadville type is the largest with median length of 36 mm and prominently barbed broad arrows. The Bifungites organism is unrecognized but it was probably a sedentary, soft-bodied, infaunal suspension-feeding animal inhabiting shallow nearshore marine and brackish water environments. The identified biota directly or indirectly associated with Bifungites is extremely limited to a few brachiopods, clams, and other trace fossils.

By-the-Wind-Sailors from a Late Devonian Foreshore Environment in Western Montana

Three remarkable fossil medusoid hydrozoans (Plectodiscus latinautilus n. sp.) with disc, topsail, and pendant tentacular appendages were recovered from the latest Late Devonian beds of the Sappington Member of the Three Forks Formation in the Gallatin Range, southwest Montana. This is the first velellid reported from a Paleozoic beach paleoenvironment. Top and underside patterns of these chondrophorine velellids display well-preserved casts and mold imprints in fine siltstone. Outlines of the circular disc and the profile of the wide sail and tentacular structures embedded in soft tissue can be recognized. These floating colonial animals were moved along the southeast shores of the Sappington Basin during a time of eustatic sea level lowering and regression in a tropical setting. Colonies were washed up on the upper beach where they were stranded in the bubbling swash left behind by the surf. The foreshore was constructed of tabular, planar cross-bedded, seaward-dipping, foreset accretionary beds which contain parallel laminations and lime-coated grains. Bedding is inclined 17? to 24? seaward.

Stratigraphic and Economic Significance of Mississippian Sequence at North Georgetown Canyon, Idaho

Recognition of the Mississippian sequence exposed at North Georgetown Canyon, Idaho, as a facies belt largely different from those already known in ranges on the east and west adds significantly to knowledge of the Mississippian stratigraphy and petroleum geology in the Overthrust belt of Idaho, Wyoming, and Utah. In the newly recognized facies belt in the Aspen Range, the Madison Group is represented by the Lodgepole Limestone and Mission Canyon Limestone, but only the lower part of the latter is present. The greatly thinned Mission Canyon is the westernmost known occurrence of the formation. The overlying beds of middle Osagean to middle Chesterian age are a unique combination of deep-basin shallowing upward to peritidal lithofacies that are included in a new formation, the Aspen Range Formation. An organic-rich phosphatic member at the base of the Aspen Range Formation is a possible petroleum source rock. Also, westward thinning of the Mission Canyon Limestone into the Aspen Range and its absence farther west suggest a westward pinch-out that may provide stratigraphic traps for petroleum beneath a seal formed by the phosphatic member of the Aspen Range Formation.

Mississippian Continental Margins of Conterminous United States: ABSTRACT

The paleogeographic, paleotectonic, and paleobathymetric reconstruction of continental margins around the present western, southern, and eastern sides of the conterminous United States can be defined for a brief span (about 1.5 m.y.) of Mississippian time. Interpretations are made by applying a biostratigraphic and sedimentological model for the Deseret starved basin of Utah and Nevada to recently published shelf-margin studies. The time span is that of the middle Osagean anchoralis-latus conodont zone. Precise dating and paleobathymetric interpretations are based on the biostratigraphy and paleoecology of conodonts, and also of corals, calcareous and agglutinate foraminifera, and radiolarians. At this time, a shallow tropical sea covered most of the southern North Americ n craton and was the site for sedimentation of a broad carbonate platform. Surrounding this carbonate platform was a starved trough comprising several bathymetrically distinct starved basins. These starved basins lay on the inner (continentward) sides of foreland basins that were bordered on their outer sectors by orogenic highlands. The highlands formed in response to convergences or collisions with the North American continent by an oceanic plate to the west, by South America to the south, and by Africa and Europe to the east. During a eustatic rise of sea level that accompanied the orogenies and reached its maximum during the anchoralis-latus zone, the carbonate platform prograded seaward and carbonate sediments cascaded over the passive shelf margins to intertongue with thin carbonat slope deposits and very thin (~ 10 m) phosphatic basinal sediments. Simultaneously, thick (~ 500 m) flysch and deltaic terrigenous sediments, such as the Antler flysch on the west and the Borden and Pocono deltaic deposits on the east, were shed into the outer parts of the foreland basins from active margins along the orogenic highlands. This Mississippian reconstruction provides a unique opportunity for comparing and contrasting shelf-slope boundaries in parts of contemporaneous passive and active margins on three sides of Paleozoic continent. End_of_Article - Last_Page 933------------

Mississippian Shelf Margin and Carbonate Platform from Montana to Nevada: ABSTRACT

The Kinderhookian to middle Meramecian history of a carbonate platform and shelf margin, extending from Nevada to Montana, is documented through four time-rock correlation charts and five successive maps that are synchronized by foraminiferan, conodont, and coral zonations. The platform was bordered on the west by a starved basin, a flysch trough, and orogenic highlands. The history of platform development is an integral part of the sedimentary cycle of the deep-water Deseret starved basin. Antler orogenic activity produced epeirogenic movements on the craton, which affected sea level and caused episodic progradation and retreat of the carbonate shelf margin. The sequential history is: (1) in earliest Mississippian time a narrow, northeast-trending seaway bordered by low oastal plains received mostly fine clastic sediments; (2) during late Kinderhookian time, a carbonate platform and shelf margin formed as a result of eastward expansion of the seaway; (3) during early Osagean time, the shelf margin retreated and a broad, gentle (less than 0°5^prime) clinoform ramp developed; (4) during middle Osagean time, lowering of the basin and craton and rise of sea level changed the pattern and sedimentary regime of the carbonate platform. Progradation of the shelf margin over the former ramp resulted in maximum expansion of the platform concurrent with maximum deepening of the starved basin. The foreslope attained a maximum steepness of 5°; (5) in middle Meramecian time, uplift of the craton and lowering of sea level caused shoaling of the carbonate plat orm and development of a sabkha landward. With increased uplift a karst plain developed over most of the former carbonate platform, and some cratonic sands were transported westward by streams into the basin. Meanwhile, filling of the flysch trough allowed eastward spillover of distal-flysch sediments to almost completely fill the basin. End_of_Article - Last_Page 716------------

Sedimentation, Biostratigraphy, and Source-Rock Potential of Deseret Starved Basin (Mississippian), Western United States: ABSTRACT

Dark, organic-rich starved-basin sediments of the basal, phosphatic member of the Deseret Limestone and equivalents were deposited west of a westward-prograding carbonate platform in Osagean to early Meramecian time. These sediments comprise mainly pelletal, peloidal, oolitic, and conglomeratic phosphorite; phosphatic shale enclosing large calcareous concretions; bedded spiculitic and radiolarian chert; cherty micritic limestone; siltstone; and mudstone. The starved basin extends for more than 700 km from southeastern Nevada to southeastern Idaho. Rate of sedimentation of starved-basin sediments is calculated from the conodont zonation to be about 10 m/m.y. Slope sediments that intertongue westward with basinal sediments and eastward with carbonate-platform sediments cons st mainly of thin-bedded clinoform micrite interbedded with some debris-flow encrinite. These sediments were deposited on a gentle foreslope of 5° or less at a rate of 16 to 18.5 m/m.y. Time-equivalent carbonate-platform sediments were deposited at a rate of about 113 to 130 m/m.y. The biota of the basinal sediments is mainly planktonic radiolarians, nektonic goniatites and conodonts, benthonic agglutinate foraminifera and sponges, and infaunal traces of burrowing organisms. The sparse shelly fauna consists mainly of small solitary corals and a few brachiopods. The bathymetry of the foreslope and shelf, considered together with the character and biota of the basin sediments, suggests that the floor of the central basin lay in the dysaerobic zone at a depth of about 300 m. Organic-carbon and hydrocarbon content of outcropping phosphatic shales that have been deeply weathered, leached, and biodegraded are difficult to evaluate. Analyses generally produce values that are much lower than values that can be expected in the subsurface, where the same rocks have generated or are generating petroleum. Nevertheless, the following organic-carbon yields have been obtained from carefully selected outcrop End_Page 779------------------------------ samples: 1.50 to 7.95% (4.29 median) for phosphatic shales, 0.67 to 5.11% (2.64 median) for phosphorites, and 0.40 to 3.17% (1.25 median) for micrites. Hydrocarbon analyses range from 50 to 300 ppm in areas where conodont CAI values range from 1.5 to 4. End_of_Article - Last_Page 780------------

Mississippian Carbonate Shelf Margin Along Overthrust Belt from Montana to Nevada: ABSTRACT

A constructional carbonate platform and a generally north-trending shelf margin in Utah and southwestern Idaho were bordered on the west by a starved basin, flysch trough, and orogenic highland during Kinderhookian to middle Meramecian time. The Antler orogeny produced epeirogenic movements, which resulted in sea-level changes that caused the carbonate platform episodically to prograde and retreat. At different times the shelf was bordered either by a narrow foreslope or by a broad ramp. The sequential history is as follows: (1) Late Devonian thrusting raised the continental margin to produce the Antler orogenic highlands, which in earliest Mississippian time had a low eastern coastal plain that bordered a narrow, shallow marine basin lacking a distinct eastern shelf. (2) Widespread marine inundation of the craton on the east was followed by a stillstand, during which a low shelf margin that turned abruptly eastward in Montana was developed and deposition of clinoform micritic limestone beds occurred in moderately deep water across a very broad ramp. (3) Increased downwarping produced an incipient starved basin, separated by a shallow carbonate bank from the flysch trough on the west and by a broad ramp from the northeast-trending shelf margin on the east; coarse encrinites were deposited alternately with micrites on the ramp. (4) Maximum deepening and expansion of the starved basin were accompanied on the west by deepening of the carbonate bank and on the east by westward progradation of a carbonate platform with a narrow, steep foreslope. (5) Lowering o sea level produced a karst plateau on the former carbonate platform and caused cratonic sands to be carried westward into the basin. Meanwhile, filling of the flysch trough allowed an eastward spillover of distal flysch sediments into the basin. The starved-basin sediments, which have organic-carbon values as high as 7% in outcrop, are considered to be source rocks. Coarse sediments of the carbonate platform, particularly where dolomitized, may serve as petroleum reservoirs. End_of_Article - Last_Page 828------------