Early Permian Strata Research Articles

Mesozoic-Cenozoic Exhumation History of the Bogda Range, Eastern Tianshan: Insights from Apatite Fission Track Thermochronology

The Bogda Range (hereafter referred to as the Bogda) is located in the Eastern Tianshan. Interpreting its tectono-thermal history is critical to understanding the intra-continental evolution of the Tianshan. In this study, we report new apatite fission track data from the late Paleozoic–Mesozoic sedimentary rocks in the northern Bogda and the Late Paleozoic granites in the southern Bogda to investigate the exhumation history of the Bogda. Apatite fission track ages dominantly range from the Jurassic to earliest Cenozoic (~143–61 Ma), except for one siliciclastic sample from the Early Permian strata with an older age of ~251 Ma. Thermal history modeling, together with detrital apatite fission track age peaks, reveal that the Bogda underwent three episodes of cooling during the Late Triassic, the Late Cretaceous, and the Late Miocene. The Late Triassic rapid cooling may represent the initial building of the Bogda, which is probably related to the final closure of the Paleo-Asian Ocean. During the Late Cretaceous, the Bogda may have experienced a moderate exhumation, which was possibly triggered by the extensive tectonic extension in the central–eastern Asian regime during the Cretaceous. The Late Miocene rapid cooling may be a response to the rapid uplift of the whole Tianshan, due to the far-field effect of the continuous India–Eurasia collision since the beginning of the Cenozoic.

Atmospheric CO2 Consumption by Chemical Weathering in the Main Tributaries of the Yellow River: Tao He, Huang Shui, and Datong He, Originating From the Northeastern Qinghai-Tibet Plateau

The Tao He, Huang Shui, and Datong He originate from the northeastern margin of the Qinghai-Tibet Plateau (QTP) and flow into the Yellow River on the Loess Plateau (LP), all with a basin area exceeding 15,000 km2, and are the three largest tributaries of the Yellow River QTP sub-basin. Water samples were collected at the river outlets, the QTP section, the transition zone between the QTP and the LP, and the LP section of each river. These water samples were used to explore CO2 consumption by chemical weathering and its control mechanisms. Runoff and physical erosion are the main factors controlling chemical weathering in the three rivers. The increase of relief ratio in the transition zone between the QTP and the LP makes the chemical weathering particularly intense in this area. The total CO2 consumption rates by chemical weathering in the Tao He and Huang Shui transition zones are 1.4 times and 1.7 times greater than in their QTP sections, and 1.7 times and 2.3 times greater than in their LP sections, respectively. In contrast, due to the high relief ratio of 8‰ in the Datong He transition zone, the residence time of the water is extremely short, and unweathered fine-grained materials are delivered downstream to continue weathering. The influence of differential lithology distribution on chemical weathering includes that the Datong He QTP section with carbonate exposure presents the most intense carbonate weathering in that basin, and the Tao He transition zone has low silicate weathering resulting from the distribution of early Permian strata. In addition, groundwater recharge most likely influenced the silicate weathering of Huang Shui significantly. The total area of the three rivers accounts for 25% of the Yellow River QTP sub-basin, while their contribution to the total CO2 consumption flux by chemical weathering approximates 36%. The silicate weathering of the northern QTP rivers is lower than the global average and significantly lower than those of the southern QTP rivers. However, carbonate weathering of the QTP rivers exhibit no north-south regional differences.

Ore Genesis for Stratiform Ore Bodies of the Dongfengnanshan Copper Polymetallic Deposit in the Yanbian Area, NE China: Constraints from LA‐ICP‐MS in situ Trace Elements and Sulfide S–Pb Isotopes

The Dongfengnanshan Cu polymetallic deposit is one representative deposit of the Tianbaoshan ore district in the Yanbian area, northeast (NE) China. There occur two types of ore bodies in this deposit, the stratiform ore bodies and vein‐type ones, controlled by the Early Permian strata and the Late Hercynian diorite intrusion, respectively. Due to the ambiguous genetic type of the stratiform ore bodies, there has been controversy on the relationship between them and vein‐type ore bodies. To determine the genetic type of stratiform ore bodies, laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) in situ trace elements and S–Pb isotope analysis have been carried on the sulfides in the stratiform ore bodies. Compared with that in skarn, Mississippi Valley‐type (MVT), and epithermal deposits, sphalerite samples in the stratiform ore bodies of the Dongfengnanshan deposit are significantly enriched in Fe, Mn, and In, while depleted in Ga, Ge, and Cd, which is similar to the sphalerite in volcanic‐associated massive sulfide (VMS) deposits. Co/Ni ratio of pyrrhotites in the stratiform ore bodies is similar to that in VMS‐type deposits. The concentrations of Zn and Cd of chalcopyrites are similar to those of recrystallized VMS‐type deposits. These characteristics also reflect the intermediate ore‐forming temperature of the stratiform ore bodies in this deposit. Sulfur isotope compositions of sulfides are similar to those of VMS‐type deposits, reflecting that sulfur originated from the Permian Miaoling Formation. Lead isotope compositions indicate mixed‐source for lead. Moreover, the comparison of the Dongfengnanshan stratiform ore bodies with some VMS‐type deposits in China and abroad, on the trace elements and S–Pb isotope characteristics of the sulfides reveals that the stratiform ore bodies of the Dongfengnanshan deposit belong to the VMS‐type, and have closely genetic relationship with the early Permian marine volcanic sedimentary rocks.

Early Permian Strata Exist in the Olongbluk Block

Early Permian Strata Exist in the Olongbluk Block

Ages and Hf isotopes of detrital zircons from the Permian strata in the Bengbatu area (Inner Mongolia) and tectonic implications

The Central Asian Orogenic Belt (CAOB) was built up through protracted accretion and collision of a variety of terranes/micro-continents during Neoproterozoic–Mesozoic time. To understand potential links among Paleozoic subduction and accretionary processes that were operative during the development of the southeastern CAOB, we conducted a combined U-Pb and Hf-isotope analysis of detrital zircons from previously defined Devonian, Carboniferous and Early Permian strata in the Bengbatu area, Inner Mongolia. Detrital zircons from (meta-) sandstones in these strata commonly yield major Paleozoic age populations at ca. 300–261 Ma, 351–300 Ma and 517–419 Ma, and also give several Precambrian ages that range from 2687 Ma to 544 Ma. The youngest ages redefine the deposition of all these strata to be in the Middle Permian (Wordian–Capitanian) or later, much younger than previously considered. These ages, coupled with regional magmatic records, support an interpretation of most surrounding areas as possible detritus sources, including the Mongolian arcs to the north, the Northern Accretionary Orogen to the south, and the intervening Erenhot–Hegenshan Ophiolite Belt. Zircons with magmatic ages of ca. 500–350 Ma and ca. 300–261 Ma display a large range of εHf(t) values (−13.97 to +15.31), whereas ca. 350–300 Ma zircons are dominated by positive εHf(t) values (+0.14 to +16.00). These results support the occurrence of two significant shifts of the zircon εHf(t) values, which has tectonic implications for the understanding of the Carboniferous–Permian evolution of the southeastern CAOB. A marked shift from mixed to positive zircon εHf(t) values at 350–330 Ma likely manifests the incipient opening of the Hegenshan Ocean, due to the slab rollback of the subducting Paleo-Asian Oceanic lithosphere. Another shift from positive to mixed zircon εHf(t) values at ca. 300 Ma likely corresponds to a tectonic switch from syn-orogenic subduction-related to post-orogenic extensional setting, genetically related to the tectonic collapse of a formerly overthickened crust.

Global biostratigraphic comparison and correlation of an early Cisuralian palynoflora from Bolivia

This paper presents new data about Early Permian (Cisuralian) strata, palynostratigraphy and absolute dating from the Copacabana Formation in central Bolivia. Recent stratigraphic and palynologic data from marine and transitional rocks at Apillapampa refine the age of Cisuralian palynomorphs in South America. Twelve samples interbedded with five volcanic ashes (processed and productive) yielded 94 palynomorph species arranged in two informal palynoassemblages: the lower assemblage Vittatina costabilis corresponds to one sample near the base of the Copacabana Formation and the upper Lueckisporites virkkiae assemblage occurs in overlying marine and coal-bearing transitional intervals. Ages were also independently refined by a modern review of conodonts, fusulinids, along with those U–Pb radiometric ages (Isotope Dilution Thermal Ionization Mass Spectrometry [ID-TIMS] of zircon-bearing interbedded tuffs). These data suggest that the lower marine member of the Copacabana Formation at this location is Asselian and Sakmarian. Lueckisporites virkkiae is a key species of palynomorph utilised in South American and global Permian biostratigraphic reconstructions. Hence, a thorough global comparison of these palynofloras and correlations is addressed in this contribution, considering first appearances of mainly cosmopolitan diagnostic taxa. Correlations are established with many similar Permian palynofloras, some also constrained with radiometric data, in South America (Brazil, Uruguay and Argentina) and elsewhere.

The youngest trigonotarbid <i>Permotarbus schuberti</i> n. gen., n. sp. from the Permian Petrified Forest of Chemnitz in Germany

A new trigonotarbid (Arachnida: Trigonotarbida) is described as <i>Permotarbus schuberti</i> n. gen., n. sp. from the Early Permian Petrified Forest (Rotliegend) of Chemnitz in Saxony (Germany). At ca. 290 Ma it represents the youngest record of this extinct arachnid order discovered to date. Its familial affinities are uncertain, but may lie close to the Aphantomartidae. The distribution of the trigonotarbid genera through time is summarised, together with a list of their seventy-seven fossil-yielding localities. Together they offer a broad overview of the group's fossil record, which is heavily biased towards the Moscovian Stage (ca. 307–312 Ma) of the Late Carboniferous in Europe and North America. This is due in no small part to numerous localities associated with coal mining districts, and trigonotarbids are found less frequently after this stage. While it is tempting to associate this with biological events – such as a putative "Carboniferous Rainforest Collapse" dating to ca. 305 Ma – it is difficult to differentiate the effects of genuine extinction patterns from artefacts caused by fewer appropriate localities in the economically less relevant latest Carboniferous and Early Permian strata. Nevertheless, trigonotarbids became extinct at some point after the Early Permian and loss of the Coal Measures forests remains one of the most likely possible causes. <br><br> doi:<a href="http://dx.doi.org/10.1002/mmng.201300012" target="_blank">10.1002/mmng.201300012</a>

The youngest trigonotarbidPermotarbus schubertin. gen., n. sp. from the Permian Petrified Forest of Chemnitz in Germany

A new trigonotarbid (Arachnida: Trigonotarbida) is described as Permotarbus schuberti n. gen., n. sp. from the Early Permian Petrified Forest (Rotliegend) of Chemnitz in Saxony (Germany). At ca. 290 Ma it represents the youngest record of this extinct arachnid order discovered to date. Its familial affinities are uncertain, but may lie close to the Aphantomartidae. The distribution of the trigonotarbid genera through time is summarised, together with a list of their seventy-seven fossil-yielding localities. Together they offer a broad overview of the group's fossil record, which is heavily biased towards the Moscovian Stage (ca. 307–312 Ma) of the Late Carboniferous in Europe and North America. This is due in no small part to numerous localities associated with coal mining districts, and trigonotarbids are found less frequently after this stage. While it is tempting to associate this with biological events – such as a putative "Carboniferous Rainforest Collapse" dating to ca. 305 Ma – it is difficult to differentiate the effects of genuine extinction patterns from artefacts caused by fewer appropriate localities in the economically less relevant latest Carboniferous and Early Permian strata. Nevertheless, trigonotarbids became extinct at some point after the Early Permian and loss of the Coal Measures forests remains one of the most likely possible causes. doi:10.1002/mmng.201300012

A late-Carboniferous to early early-Permian subduction–accretion complex in Daqing pasture, southeastern Inner Mongolia: Evidence of northward subduction beneath the Siberian paleoplate southern margin

A subduction–accretion complex is identified from previously defined late-Carboniferous and early-Permian strata in Daqing pasture, southern Xiwuqi, Inner Mongolia. The subduction–accretion complex is composed of a matrix of siltstone and exotic blocks of bioclastic limestone, pillow basalt, foliated basalt, chert and asbestos. The pillow basalt possesses the geochemical characteristics of mid-ocean ridge basalt (N-MORB), whereas the foliated basalt displays the geochemical characteristics of island arc basalt (IAB), indicating that these basalts are of different origins. U–Pb (zircon) dating indicates that the foliated basalt formed in the late-Carboniferous (314.5 to 318.4Ma) and the bioclastic limestone formed in the early early-Permian. Combined with regional geological data, the subduction–accretion complex and coeval calc-alkaline granitic belt to the north constitute the essential elements of the late-Carboniferous to early early-Permian subduction zone on the southern margin of the Siberian paleoplate. The zircon εHf(t) values of the foliated basalt are positive (+14.4 to +23.9), suggesting that this basalt originated directly from depleted mantle. The temporal–spatial distribution of the subduction–accretion complex and ophiolite belts in southeastern Inner Mongolia indicates that there was significant lateral crustal growth on the southern margin of the Siberian paleoplate in the late Paleozoic.

Special Lateral Increase in a Permian Rugose Coral Kepingophyllum aksuence Wu et Chow

Abstract:Well‐preserved specimens of Kepingophyllum aksuence Wu et Chow were collected from Early Permian strata in western Tarim Basin, Xinjiang. More than 100 serial thin sections were made for this study. Kepingophyllum aksuence displays a unique increase pattern. The bud appears in lonsdaleoid dissepiments between the corallites where the wall of parent corallite disappears and the area becomes aphroid. This increase pattern is different from other lateral increases of most colonial rugose corals, and therefore has taxonomic significance to differentiate Kepingophyllidae from other compound rugose corals. It is also discussed that Kepingophyllum aksuence has a high “reproductive integration”, which means a rapid growth of buds during the offsetting process. Kepingophyllum was possibly originated from Ivanovia and was also a probable ancestor of Wentzellophyllum, which is supported here by more or less the similarity of the blastogeny in different stages of three taxa.

Clay mineralogy of the Permo-Triassic strata of the British Isles: onshore and offshore

AbstractThe regional distribution, mineralogy, petrology and chemistry of the detrital and authigenic clay minerals associated with the Permo-Triassic strata (excluding the Rotliegend: see Ziegler, 2006; this volume), of the onshore and offshore regions of the British Isles are reviewed within their stratigraphical framework. The origin of these clay minerals is discussed in relation to current hypotheses on the developments of the Mg-rich clay mineral assemblages associated with the evaporitic red-bed Germanic facies of Europe and North Africa.Composite clay mineral successions are described for seven regions of the British Isles — the Western Approaches Trough; SW England; South Midlands; Central Midlands; the Cheshire Basin; NE Yorkshire; and the Central North Sea. The detrital clay mineral assemblages of the Early Permian strata are variable, consisting of mica, smectite, smectite-mica, kaolin and chlorite, whereas those of the Late Permian and the Trias are dominated by mica, usually in association with minor Fe-rich chlorite. The detrital mica consists of a mixture of penecontemporaneous ferric mica, probably of pedogenic origin, and recycled Pre-Permian mica. In the youngest Triassic strata (Rhaetian), the detrital clay assemblages may contain appreciable amounts of poorly defined collapsible minerals (irregular mixed-layer smectite-mica-vermiculite) and kaolin, giving them a Jurassic aspect. There are two types of authigenic clay mineral assemblages. Kaolin may occur as a late-stage diagenetic mineral where the original Permo-Triassic porewaters of the sediment have been replaced by meteoritic waters. A suite of early-stage diagenetic clay minerals, many of them Mg-rich, are linked to the evaporitic red-bed facies — these include sepiolite, palygorskite, smectite, irregular mixed- layer smectite-mica and smectite-chlorite, corrensite, chlorite and glauconite (sensu lato). The sandstones and mudstones of the onshore regions of the British Isles display little or no difference in their detrital and authigenic clay mineral assemblages. In contrast, the sandstones of the offshore regions (North Sea) show major differences with the presence of extensive chloritic cements containing Mg-rich and Al-rich chlorite, irregular mixed-layer serpentine-chlorite, and mica.

THE GENUSVESPERISPIRA(GASTROPODA: PLEUROTOMARIOIDEA) FROM THE PERMIAN OF TWO DISPLACED TERRANES, WESTERN UNITED STATES

Early permian strata in two displaced terranes of the McCloud belt contain a small biconic gastropod of distinctive appearance, Vesperispira humboldtiana new genus and species. This trochiform gastropod has a strongly oblique aperture with interrupted peristome, a small sinus on the peripheral margin of the shell, and lamellose shell. This gastropod is an easily recognized biogeographic indicator of the McCloud province biota, because of its lamellose ornamentation. Occurrence of this gastropod in strata of the Pine Forest Range of northwestern Nevada provides additional evidence for including rock units of the Black Rock terrane within the McCloud Belt, a grouping of several displaced terranes along the western margin of North America (Stevens et al., 1990) that contain fossil biotas rich in endemic species.

The genus Vesperispira (Gastropoda: Pleurotomarioidea) from the Permian of two displaced terranes, western United States

Early permian strata in two displaced terranes of the McCloud belt contain a small biconic gastropod of distinctive appearance, Vesperispira humboldtiana new genus and species. This trochiform gastropod has a strongly oblique aperture with interrupted peristome, a small sinus on the peripheral margin of the shell, and lamellose shell. This gastropod is an easily recognized biogeographic indicator of the McCloud province biota, because of its lamellose ornamentation. Occurrence of this gastropod in strata of the Pine Forest Range of northwestern Nevada provides additional evidence for including rock units of the Black Rock terrane within the McCloud Belt, a grouping of several displaced terranes along the western margin of North America (Stevens et al., 1990) that contain fossil biotas rich in endemic species.

Tectonic and lithological constraints on the evolution of the Karoo graben of northern Malawi (East Africa)

The results of a lithostratigraphic, tectonic and kinematic study of the Karoo deposits of northern Malawi are reported. The objective of the lithostratigraphic study is to correlate the deposits of the Karoo basins of northern Malawi with the well-known deposits of southern Tanzania, thus establishing a stratigraphic framework through which the timing of faulting can be constrained. The kinematic analysis of faulting constrains the opening direction for the Karoo graben in this area and provides basic data to discuss the Karoo graben development within the regional tectonic framework of south-eastern Africa. The studied adults are defined by moderately to steeply dipping cataclastic zones with a width of up to 15 m and are characterized by an array of slickensided fault surfaces with different orientations and slip directions. In this study, small faults (offset 10 m, but generally not exceeding 30–40 m) have been distinguished. Methods used to analyse the kinematic data include the ‘pressure tension’ (PT) method, which estimates the principal axes for the bulk brittle strain, and the internal rotation axis (IRA) method, which estimates the axis of bulk internal rotation and the overall sense of slip at the faults. A mass balance calculation reveals a volume increase of up to 16% during cataclastic deformation in the fault zones. The PT method shows an approximately east trending extension direction for faults that occur only in the latest Carboniferous (?) and Early Permian strata, whereas the fault kinematics from faults that cut middle Permian to Early Triassic rocks is characterized by a ESE to SE trending extension direction. The small faults yield essentially the same kinematic results as the meso-scale faults. In a transport-parallel cross-sectional view, the principal extension axes are at an acute angle of approximately 60° to the major fault planes. Given the moderate fault density, the relatively high angle between the orientation of the principal extension axis and the fault planes suggest only a moderate amount of horizontal extension across the Karoo graben of northern Malawi. Riedel structures in the fault zones formed within two conjugate sets of localized shear zones; slip on one set was top to the W/NW and, on the other, top to the E/SE. The two conjugate sets of Riedel structures have an acute angle about the regional shortening axes, implying that no pronounced rotation of the strain axes occurred. The internal rotation axes for the Riedel structures reveal a largely bimodal distribution and inferred weakly monoclinic to orthorhombic symmetry. Therefore the overall deformation during Karoo rifting in northern Malawi is interpreted to be close to a coaxial deformation with a limited amount of horizontal extension.[/p]

Late Palaeozoic arc flank and fore‐arc basin sequence of the New England fold belt in the stanage bay region, central Queensland

Devonian and Carboniferous (Yarrol terrane) rocks, Early Permian strata, and Permian‐(?)Triassic plutons outcrop in the Stanage Bay region of the northern New England Fold Belt. The Early‐(?)Middle Devonian Mt Holly Formation consists mainly of coarse volcaniclastic rocks of intermediate‐silicic provenance, and mafic, intermediate and silicic volcanics. Limestone is abundant in the Duke Island, along with a significant component of quartz sandstone on Hunter Island. Most Carboniferous rocks can be placed in two units, the late Tournaisian‐Namurian Campwyn Volcanics, composed of coarse volcaniclastic sedimentary rocks, silicic ash flow tuff and widespread oolitic limestone, and the conformably overlying Neerkol Formation dominated by volcaniclastic sandstone and siltstone with uncommon pebble conglomerate and scattered silicic ash fall tuff. Strata of uncertain stratigraphic affinity are mapped as ‘undifferentiated Carboniferous’. The Early Permian Youlambie Conglomerate unconformably overlies Carboniferou...

Polyspermophyllum, a new Permian gymnosperm from Argentina, with considerations about the dicranophyllales

Polyspermophyllum gen. nov., a new primitive seed plant, is described. The material was found in early Permian strata, Chubut province, Argentina. It includes twigs that bear long, linear, once dichotomized leaves with two marginal longitudinal grooves in a compact helix. The fertile structures have proximal portions similar to sterile leaves and ultimate trusses with axes being several times dichotomized (or trichotomized) and bearing subsphaerical bodies composed of a distally curved segment (peduncle) enclosing a single oval structure (ovule). The vegetative organs ar closely comparable to taxa that have been referred to different genera while the fertile organs resemble those of the late Palaeozoic Trichopitys and Dicranophyllum. It is suggested that the Dicranophyllales are a primitive order of seed plants, including two families, the Trichopityaceae and the Dicranophyllaceae, in which Polyspermophyllum is placed. Possible relationships with Paleozoic pteridosperms and Mesozoic ginkgophytes are discussed, especially with regard to a putative “pre-ginkgophytic” line, already established during the Carboniferous in all palaeofloristic regions, viz. Angara, Equatorial Belt and Gondwana.

Globivalvulinid Foraminifera from the Permian of Queensland

Globivalvulinid foraminifera were found in late Early Permian strata of the Cattle Creek Formation from GSQ Eddystone 4 drilled in the central region of the Bowen Basin. A revision of foraminifera previously identified as Globivalvulina (= Valvulina auct.) in Australia and a review of species of the genus are attempted: most of the species of Globivalvulina were identified on random thin sections, all possess a calcareous microgranular test, and some may be construed to exhibit an essentially trochospiral, rather than biserial mode of growth; the Early Permian globivalvulinid under study possess a thin, microgranular and silicified test, and a trochospiral type of growth. Verispira jelli gen. et sp.nov. is proposed here to represent new trochospirally coiled free benthic globivalvulinid foraminifera. The abundance of Globivalvulina bulloides is considered to mark a new foraminiferal zone in late Early Permian strata of the Denison Trough (Bowen Basin).

Correlatives of the Greta Coal Measures in the Hunter Valley and Gunnedah Basin, New South Wales

Abstract Exposures of Early Permian strata in the Gunnedah Basin are described and it is shown that the Willow Tree, Werris Creek, Condadilly, and Wean Formations comprise similar successions consisting of prominent horizons of kaolinite clayrocks or flint clays at the base overlain by quartz‐lithic sandstone, siltstone, and conglomerate. It is concluded therefore that these formations pertain to the same stratigraphic unit and, since the flint clays do not differ appreciably from those characterizing the Greta Coal Measures at Wingen, that this stratigraphic unit represents extension of the measures in the Gunnedah Basin. The Willow Tree and Wean Formations are underlain by considerable thicknesses of kaolinitic soil that undoubtedly furnished the detritus for the alluvial and colluvial flint clay deposits. The presence of the soil indicates that during part of the Early Permian in northeastern New South Wales the climate was humid and at least subtropical.

Sedimentary Environments, Pennsylvanian and Early Permian, Southeastern Arizona: ABSTRACT

In southeastern Arizona, Pennsylvanian and Early Permian strata have 15 complex transgressive and regressive cycles. Sedimentary environments were influenced primarily by a stable central Arizona shelf (divisible into Papago inner shelf, San Pedro outer shelf, and Mogollon inner shelf) and an unstable Pedregosa basin on the southeast. Morrowan and earliest Derryan deposits (Black Prince Limestone) have a basal red clastic unit overlain by thin, sheetlike carbonate units. During late Derryan and early and middle Desmoinesian deposition (lower part of Horquilla Limestone), successive carbonate banks separated the 3 parts of the central Arizona shelf, but there was little differentiation of sediments on the San Pedro outer shelf and in the Pedregosa basin. During the latter part of the Desmoinesian, a clastic influx from the north initiated carbonate-poor depositional cycles. Missourian and Virgilian deposition (upper part of Horquilla Limestone) produced more clearly differentiated carbonate-bank margins around the Pedregosa basin and San Pedro outer shelf. Northward, these strata become dominantly clastic and pass into interdistributary bay and lagoonal deposits and supratidal, deltaic redbeds and conglomerates of the Supai Formation. Wolfcampian depositional environments (part of Supai and Earp Formations) shifted southeast with time. On the Mogollon inner shelf, supratidal deltas and gypsiferous lagoonal deposits form this part of the Supai Formation; and on the San Pedro outer shelf, shallow-shelf sandstones, siltstones and shales intertongue with a few thin limestones. Massive, lenticular carbonate banks enclosed the Pedrogosa basin, and within the basin, dark fetid clastics and carbonates suggest restricted environments. Latest Wolfcampian or early Leonardian sediments (part of Supai and Earp Formations) are sandy dolostones and siltstones with impoverished faunas that suggest a series of poorly aerated lagoons. End_of_Article - Last_Page 802------------