Judith A. Schiebout

Paleogene paleosols and changes in pedogenesis during the initial Eocene thermal maximum: Big Bend National Park, Texas, USA

This paper tests the hypothesis that continental chemical weathering increased during the initial Eocene thermal maximum (IETM) by comparing paleosols that formed before and during the event in western Texas. The chemical index of alteration (CIA) was used to investigate the weathering of silicate minerals. Paleosols generated before the IETM have CIA values ranging from 62 to 72, and CIA values during the IETM range from 67 to 82. The CIA values for pre–initial Eocene thermal maximum paleosols indicate moderate weathering conditions, and CIA values during the event indicate moderate to extreme weathering conditions. The clay mineralogy of the paleosols is dominated by smectite, and it is only within paleosols that formed during the IETM that there is a change. There is a notable increase in the amount of kaolinite in one paleosol horizon that is associated with the carbon excursion. In addition, there is an increase in the translocation of clays and iron, and an increase in the leaching of calcite and plagioclase in initial Eocene thermal maximum paleosols. The differences between soils that formed before and during the initial Eocene thermal maximum indicate that chemical weathering did increase during this ancient global warming event. The mechanism responsible for increased weathering is interpreted to be an increase in hydrolysis reactions caused by an increase in humidity and an increase of carbonic acid in the soil due to elevated CO2 levels during the initial Eocene thermal maximum. Documentation of an increase in chemical weathering during the initial Eocene thermal maximum is significant because it may have served as a negative feedback to reduce atmospheric CO2.

The cranial morphology of an early Eocene didymoconid (Mammalia, Insectivora)

ABSTRACT An early Eocene didymoconid skull with perfect basicranial region from Hubei Province of China is described. Important cranial features include a small orbit, a broad temporal region, a maxilla–frontal contact in the orbit, absence of the jugal–lacrimal contact, a broad dorsal process of the alisphenoid, an extensive squamosal, absence of the postglenoid foramen, a transversely elongate glenoid fossa, a fully ossified bulla, an external auditory canal floored by the squamosal and mastoid of the petrosal, a greatly expanded mastoid of the petrosal, and a large foramen for the epitympanic sinus in the tympanic roof. In addition, the internal carotid artery may be reduced, although the stapedial artery is well developed. Analyses of the cranial features reveal that this skull is already highly specialized. The analyses also indicate that the North American genus Wyolestes and the Asiatic didymoconids form a paraphyletic group and that derivation of both Wyolestes and didymoconids from a Paleocene Ya...

NEW EARLY EOCENE MAMMALIAN FOSSILS FROM THE HENGYANG BASIN, HUNAN CHINA

Abstract New fossil mammal materials found in the upper Lingcha Formation of the Hengyang Basin, Hunan, China, include a complete skull of Hapalodectes hetangensis and a taxon new to the fauna, Dissacus zengi, n. sp. H. hetangensis is the morphologically least derived species of the genus and currently is the earliest known record of the genus. D. zengi, n. sp. is the second Asian early Eocene record of the genus and represents the last occurrence of the genus in Asia. The Lingcha Formation includes two fossiliferous intervals. The upper contains about 12 species belonging to 7 mammalian orders, and the lower has yielded one mammalian species and one reptilian species. Biostratigraphic, chemostratigraphic, and magnetostratographic study in the Lingcha Formation indicates that the transient carbon isotope excursion that marks the Paleocene–Eocene boundary as currently advocated is present in the upper Lingcha Formation. The fauna from the upper Lingcha Formation occurs within the excursion interval, and is of earliest Eocene age. It is correlative with the Wasatchian-0 faunal zone in the Big Horn Basin, Wyoming, North America. The lower Lingcha Formation is of Paleocene age.

Cores from the Miocene Castor Creek Member of the Fleming Formation, Fort Polk Louisiana: Relationship to the Outcropping Miocene Terrestrial Vertebrate Fossil-Bearing Beds

ABSTRACT A series of clays and silty clays with moderately developed paleosols were recovered from three 15 m cores drilled in the Castor Creek member or the Fleming Formation in western Louisiana. These cores were taken to provide stratigraphic control for the outcropping conglomeratic beds bearing small Miocene terrestrial mammal teeth. These fine-grained core sediments and outcropping conglomeratic units were deposited in a fluvial setting. The conglomeratic units were not penetrated by coring indicating that they are very discontinuous, localized deposits. The sedimentology and distribution of these deposits and a thin interval of poorly sorted, cross-bedded sandstone found in one core, suggest that these coarse deposits formed at the bases of minor channels or gullies. The fine-grained core sediments are floodplain deposits. These thick sequences of massive gray clays with paleosol features such as mottles, roots, root casts, carbonate nodules and slickensides reflect deposition in moderate to well-drained, seasonally wet floodplain backswamps. Intervals of relatively unaltered parallel and wavy laminated silts and clays may represent crevasse-splay development or lacustrine delta-fill. Moderately developed soil profiles, containing A, B, and C horizons, characterize these fine-grained sediments. Mottle coloring indicating oxidation and possible water table fluctuations is prevalent throughout the paleosols. Roots and large root burrows which characterize A horizons are abundant. Stage II carbonate development is common in most B and some C horizons. Slickensides, resulting from the alternating wetting and drying of soils, are common. In general, these paleosol features support the interpretation of a moderately-drained, seasonally wet fluvial setting.

Fossil Vertebrates from the Castor Creek Member, Fleming Formation, Western Louisiana

ABSTRACT The first Miocene terrestrial vertebrate fauna from Louisiana has been recovered from exposures within Fort Polk in central western Louisiana. Remains of eight orders of mammals, including insectivores, rodents, perissodactyls, artiodactyls, and proboscideans, as well as crocodile and fish remains, have been recovered. Small vertebrate teeth are recovered from several conglomeratic layers in the Castor Creek Member of the Fleming Formation, and isolated bones and teeth of sheep-sized to horse-sized mammals are found in both the conglomerates and the surrounding nodule-rich mudstones. Nodules winnowed from the mudstone formed the layers of conglomerate. Small, resistant vertebrate remains from the normal accumulation on the land surface were concentrated and incorporated in them. After dissolution in dilute acetic acid and screening, the rocks yield a diverse fauna of terrestrial microvertebrates, particularly rodent teeth. Fossils found so far indicate an early late Barstovian Land Mammal Age.

Vertebrate paleontology of the lower Tertiary Baca Formation of western New Mexico

A paleontologic survey of the western outcrops of the terrestrial Baca Formation has yielded the first Chadronian fossils from New Mexico. Three sites of Chadronian (latest Eocene–early Oligocene) age have produced the cameloid Eotylopus , the creodont ? Hyaenodon , the entelodont Brachyhyops , the oreodont Protoreodon , and a large-horned titanothere, ? Menodus . These genera also are found in the Chadronian Porvenir local fauna of Trans-Pecos Texas. Vertebrate finds indicate a greater time span for the formation9s isolated outcrops than previous workers had accepted. The formation had been considered Eocene, in part on the strength of a specimen of Protoreodon pumilus , an oreodont from alluvial-fan deposits north of Datil. The Chadronian sites lie in fluvial deposits north of Quemado, approximately 60 km to the west. Most Baca vertebrates have been recovered from channel deposits or from float. No site with a concentration of small fossils suitable for screening has yet been discovered; thus, future goals for Baca Formation paleontological work include location of fossils in the still unfossiliferous outcrop areas and location of screening sites.

A skull of Pantolambdodon (Mammalia, Pantodonta) from Ningxia, North China

ABSTRACT A pantodont skull with a strongly retracted nasal incision and a mandible fragment were recently found in Yan chi County, Ningxia, Peoples Republic of China. Comparison with ancient and modern proboscis-bearing forms indicates that this pantodont had a proboscis, unlike any previously-known pantodont. It and several other gracile Chinese pantodonts have expanded our view of pantodont diversity beyond the common, heavy, graviportal North America types. The form most similar to it is Pantolambdodon inermis from Inner Mongolia for which, unfortunately, there is no comparable skull material.

Provenance and Depositional Environments of Eocene-Oligocene Baca Formation, Catron County, New Mexico: ABSTRACT

The Baca Formation, which crops out discontinuously in east-west-trending exposures from Socorro, New Mexico, to the New Mexico-Arizona border, is composed of fluvial, alluvial-fan, and lacustrine deposits. It was deposited in a basin which formed during the Laramide orogeny in New Mexico and Arizona. Uplifts bordering the basin include the Defiance, Zuni, Lucero, and Sierra-Sandia, and the Mogollon highland. In the late Eocene, volcanism began in the Datil-Mogollon volcanic field in southwestern New Mexico and adjacent Arizona, south of the study area. Sediments were derived from adjacent uplifts and from the volcanic rocks. The Mogollon highland and the Zuni uplift supplied metamorphic, sedimentary, and plutonic detritus to the Baca Formation. There is a westward increase in volcanic detritus in the Baca Formation, and faunal evidence shows an early Oligocene, Chadronian, age for western Baca outcrops north of Quemado, younger than outcrops further east which are Eocene in age. With the beginning of Eocene volcanism, volcanic detritus was supplied to the Oligocene Baca sediments which were deposited in a coarse-grained meander belt. Other depositional environments identified include fine-grained meander belt, alluvial fan, and distal, braided alluvial plain. Flow direction was dominantly eastward. End_of_Article - Last_Page 568------------

Effects of Sea Level Changes on Distribution and Evolution of Early Tertiary Mammals: ABSTRACT

Sea level changes in the early Tertiary affected mammalian End_Page 1688------------------------------ distribution and speciation by affecting paleogeography, climate, and deposition. Intercontinental links were broadened during regressions. Transgressions had moderating effects on climate, produced by lessening continentality. A middle Paleocene major regression probably marked the withdrawal of the North American interior seaway, and its absence was linked to Paleocene-Eocene transition climatic warming and drying. Shifts in sea level shifted loci of deposition, affecting rates of animal burial and diagenesis. Sea level effects on shape and disjunction of ranges on the Gulf Coast were of particular importance because southern sources were likely for the wave of new forms, many representing the first appearance of modern mammal orders, which marks the Paleocene-Eocene transition in northern sites. Gulf Coast regressions exposed a broad continental shelf producing terrestrial conditions analogous to those of the broad, stable epicontinental seas produced by major transgressions. An embayment in Texas at the location of the Cretaceous interior seaway could have functioned to produce eastern and western Gulf Coast terrestrial provinces as the Mississippi embayment did in the Pleistocene. Transgressions reduced the area of lowlands, constricted ranges, and promoted speciation by isolating demes n highlands. Regressions could also promote speciation, by lowering water tables, increasing the extent of savannas, and thus fragmenting the habitats of forest dwellers. The effects of sea level changes are important in the burst of mammalian speciation that characterizes the early Tertiary, just as they are in marine evolution. End_of_Article - Last_Page 1689------------

Vertebrate Paleontology of Lower Tertiary Baca Formation of Western New Mexico: ABSTRACT

A paleontologic survey of the western outcrops of the terrestrial Baca Formation has yielded the first Oligocene fossils from New Mexico. Three sites of Chadronian (early Oligocene) age are known, and their fauna included the small oreodont Leptomeryx, the cameloid ?Eotylopus, the carnivore Hyaenodon, the entelodont Brachyhyops, and a large-horned titanothere Menodus. All these genera are also found in the Porvenir local fauna, Chadronian of Trans-Pecos Texas. Vertebrate finds indicate far less contemporaneity of the formations isolated outcrops than previous workers had accepted. The formation had been considered Eocene, partly on the strength of the discovery of a specimen of Protoreodon pumilis, a late Eocene-early Oligocene oreodont, in alluvial-fan deposits north of Datil. The Chadronian sites lie in fluvial deposits north of Quemado, approximately 60 km west. Most Baca vertebrates have been recovered from channel deposits or from float. No site with a concentration of small fossils suitable for screening has yet been discovered. Future goals for Baca Formation paleontologic work include location of fossils in the still unfossiliferous outcrop areas and location of screening sites. End_of_Article - Last_Page 568------------