Significant Regional Uplift Research Articles

Euarchontans from Fantasia, an upland middle Eocene locality at the western margin of the Bighorn Basin

The fossil record of North American Eocene mammals is best known from relatively low-elevation ‘basin center’ fossil localities in intermontane depositional basins of the Western Interior. This sampling bias, largely drawn from preservational bias, has limited our understanding of fauna from higher elevation Eocene fossil localities. Here we describe new specimens of crown primates and microsyopid plesiadapiforms from a middle Eocene (Bridgerian) locality (‘Fantasia’) from the western margin of the Bighorn Basin in Wyoming. Fantasia has been considered a ‘basin-margin’ site and geological evidence suggests that it was already at a high elevation relative to the basin center at the time of deposition. New specimens were described and identified using comparisons across museum collections and published faunal descriptions. Linear measurements were used to characterize the patterns of variation in dental size. Contrary to expectations derived from other Eocene basin-margin sites in the Rocky Mountains, Fantasia has low anaptomorphine omomyid diversity and lacks evidence for the co-occurrence of ancestor-descendant pairs. Fantasia also differs from other Bridgerian sites in having low abundance of Omomys and unusual body sizes of several euarchontan taxa. Some specimens of Anaptomorphus and cf. Omomys are larger than those found in coeval sites, while specimens of Notharctus and Microsyops are intermediate in size between middle and late Bridgerian samples of these genera from basin-center sites. These findings suggest that high elevation fossil localities like Fantasia may record atypical faunal samples that should be more thoroughly explored to understand faunal dynamics during the periods of significant regional uplift like that represented by the middle Eocene record of the Rocky Mountains. Furthermore, modern faunal data indicate that species body mass may be influenced by elevation, which may further complicate the use of body mass to determine species identity in the fossil record in the regions of high topographic relief.

New schizothoracine from Oligocene of Qaidam Basin, northern Tibetan Plateau, China, and its significance

ABSTRACTThe schizothoracines (Cyprinidae) are a type of endemic freshwater fish in and around the Tibetan Plateau. They are the only taxa among the cyprinids capable of tolerating the harsh environments of the plateau. The origin and evolution of schizothoracines are thought to be closely linked to the rise of the Tibetan Plateau; however, complete fossil schizothoracines are rare. Herein, we report a new Oligocene genus and species of the subfamily Schizothoracinae, Paleoschizothorax qaidamensis, gen. et sp. nov., from the Qaidam Basin, northeastern Tibetan Plateau, China. This is the earliest credible fossil schizothoracine by far, and the discovery demonstrates that schizothoracines originated no later than the Oligocene. We deduce that the origin of schizothoracines is closely related to the global climate shift at the Eocene–Oligocene transition. Our findings contribute to efforts to comprehend the influence of the global climatic shift on Asian environments from a biotic perspective. Additionally, the fossils reflect a warm, low-altitude environment before the uplift of the Tibetan Plateau. The fossil fish records indicate that vast drainages existed in the northern Qaidam Basin during the Oligocene and that the basin has experienced significant regional uplift since the Neogene, leading to the extinction and migration of fishes.http://www.zoobank.org/urn:lsid:zoobank.org:pub:1E9D9016-5DF7-4A15-8F10-C713FD428DCACitation for this article: Yang, T., L. Zhang, W. Li, J. Jia, L. Han, Y. Zhang, Y. Chen, and D. Yan. 2018. New schizothoracine from Oligocene of Qaidam Basin, northern Tibetan Plateau, China, and its significance. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2018.1442840.

Engineering Prediction of Axial Wellbore Shear Failure Caused by Reservoir Uplift and Subsidence

Summary Injection and production can cause significant regional uplift or settlement. We analytically evaluate the potential for cement-annulus failure in response to injection-induced deformation in a coupled casing/cement/rock poromechanical vertical-well system. Deformation is calculated with respect to the initial near-wellbore stress state, occurring immediately after cement curing. Tensile-failure and shear-failure lengths along this well are predicted using a stress-development-length method. The analytical model is verified by Abaqus modeling. A sensitivity analysis identifies critical engineering-well-design parameters for ensuring wellbore-annulus integrity.

Reduced convergence within the Tibetan Plateau by 26 Ma?

AbstractUnderstanding the dynamics of double‐thickening and uplifting of the Tibetan crust requires constraints on the magnitude and timing of crustal shortening. New elongation/inclination (E/I)‐corrected paleomagnetic data from ~26–22 Ma sediments indicate that the latitude of southern Tibet in the early Miocene was 31.1/−6.8/+5.2°N, not significantly different from today. This implies that the southern margin of Asia, which was at 21–24°N latitude from the Late Cretaceous to the early Eocene, advanced 8–10° northward between the early Eocene and the latest Oligocene. Our results therefore suggest that at least 900–1100 km of continental shortening and significant regional uplift of the plateau occurred between the early Eocene and late Oligocene. Our results suggest that N‐S intra‐Asian convergence was considerably reduced around 26 Ma, corresponding to a transition from compression to extension within the Tibetan Plateau.

Paleocene‐Early Eocene uplift of the Altyn Tagh Mountain: Evidence from detrital zircon fission track analysis and seismic sections in the northwestern Qaidam basin

AbstractMost existing tectonic models suggest that the deformation and uplift of the northern Tibetan Plateau is the latest crustal response to the collision of the India Plate and Eurasian Plate. The tectonic evolution of Altyn Tagh Mountain (hereafter called simply the “Altyn Tagh”), on the northern margin of the Tibetan Plateau, has attracted considerable scientific attention. In this study, we use fission track age dates of detrital zircons from the northwestern Qaidam basin together with sedimentary observations to understand more fully the Cenozoic tectonic uplift of the Altyn Tagh. Detrital zircons from five borehole samples distributed in different folds in the northwestern Qaidam basin yielded ages mainly ranging from 88.5 to 49.2 Ma, older than their sedimentary deposition ages (43.8–22 Ma). The binomial distribution in grain age fitted peaks was generally dominated by one young peak, P1, which varied from 73.6 to 47.2 Ma. A thinning of the Cenozoic Lulehe Formation (53.5–43.8 Ma) stretched from the inner Qaidam basin to the slopes of the Altyn Tagh in the seismic sections of the northwestern Qaidam basin. Based on magnetostratigraphic dating, there was a hiatus in sedimentation in the Qaidam basin between 65 Ma and 54 Ma; this was confirmed by seismic profiles and borehole data, which show an unconformity between the Mesozoic Quanyagou Formation and the Lulehe Formation. Combined with an analysis of provenance, the detrital zircon young peak age and the sedimentary record revealed that the most significant regional uplift of the Altyn Tagh occurred during the Paleogene‐Early Eocene, almost coinciding with the collision of the Indian and Eurasian plates between 65 Ma and 44 Ma.

LANDSCAPE EVOLUTION, REGOLITH FORMATION AND NICKEL LATERITE DEVELOPMENT IN THE NORTHERN PART OF THE GREAT DYKE, ZIMBABWE

Research Article| December 01, 2013 LANDSCAPE EVOLUTION, REGOLITH FORMATION AND NICKEL LATERITE DEVELOPMENT IN THE NORTHERN PART OF THE GREAT DYKE, ZIMBABWE M.D. PRENDERGAST M.D. PRENDERGAST Guesachan, Shielhill Road, Kirriemuir, Angus, DD8 4PA, Scotland, United Kingdom, e-mail: marprend@hotmail.com Search for other works by this author on: GSW Google Scholar Author and Article Information M.D. PRENDERGAST Guesachan, Shielhill Road, Kirriemuir, Angus, DD8 4PA, Scotland, United Kingdom, e-mail: marprend@hotmail.com Publisher: Geological Society of South Africa First Online: 09 Mar 2017 Online ISSN: 1996-8590 Print ISSN: 1012-0750 © 2013 Geological Society of South Africa South African Journal of Geology (2013) 116 (2): 219–240. https://doi.org/10.2113/gssajg.116.2.219 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation M.D. PRENDERGAST; LANDSCAPE EVOLUTION, REGOLITH FORMATION AND NICKEL LATERITE DEVELOPMENT IN THE NORTHERN PART OF THE GREAT DYKE, ZIMBABWE. South African Journal of Geology 2013;; 116 (2): 219–240. doi: https://doi.org/10.2113/gssajg.116.2.219 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract The hilly northern part of the north-northeast-trending Great Dyke – the Mvukwe Range – comprises a 300 km2, elongate mass of exposed serpentinite displaying remnants of two principal erosion surfaces: an arealy-dominant upper surface and a subordinate lower surface confined to a northerly location. Both surfaces, assigned to successive phases of the composite, continent-wide, mid-Cretaceous to end-Oligocene, African Surface, are represented by variably-preserved table-lands of plateaus, mesas, buttes, and accordant summits. To the east and west, inselberg-bearing, granitic plains form a composite, Miocene, Post-African etch surface at contrasting lower elevations, resulting in eccentric dispositions of African erosion surfaces and Post-African internal valleys, all attributed to the varying maturity of the main drainage systems either side of the Mvukwe Range, a probable regional watershed since pre-Karoo times.The lower and upper African surfaces have present-day elevations of ca. 1525 m and (mostly) ca. 1620 m, respectively, although an original vertical separation of ca. 200 m is estimated in the north. Complex northward variations in preservation and elevation of the upper surface, plus a general northward increase in modal olivine in the serpentinised dunite protolith, point to significant regional uplift, probably associated with Tertiary displacement of the Zambezi Escarpment horst active since the Triassic at the northern extremity of the Great Dyke, as well as possible re-activation of Zambezi belt-related Proterozoic faults.Preserved African Surface regoliths comprise (cliff-forming) horizontally-fractured serpentinite overlain by a composite silica cap of horizontally-fractured serpentinite with sheeted silica veins below ferruginous silicified serpentinite. The predominantly, goethite-chrysotile African regoliths carry nickel enrichments of 1 to 2% Ni (or more) to depths of up to 10 m (or more) in the fractured serpentinite and sheeted silica vein zones; other nickel enrichments occur more sporadically within the protolith. Three principal mineralogical associations are postulated for the contained nickel: (1) discrete, fracture-related, ‘garnieritic’ minerals (in both regolith and protolith), (2) nickeloan serpentine within drusy vugs associated with silica veins, and, probably, (3) pervasive enrichments associated with goethite and/or chrysotile. Cobalt, concentrated towards the top of the preserved regolith profile, is most likely linked to goethite via a primary association with Mn.The geomorphological and geological features of Great Dyke nickel laterites are closely analogous to those of classic, saprolite-type nickel laterite deposits in Brazil. Both groups probably formed in fundamentally similar ways, the lower grade/thickness of the Great Dyke deposits attributable to the slightly differing climatological and geomorphological histories of northern Zimbabwe and of equatorial and tropical Brazil. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Paleoproterozoic gabbronoritic and granitic magmatism in the northern margin of the North China craton: Evidence of crust–mantle interaction

Paleoproterozoic Xuwujia gabbronorites in the northern margin of the North China craton occur as dykes, sills and small plutons intruded into khondalite (aluminous paragneisses, sedimentary protoliths deposited at ca. 2.0–1.95 Ga), and as numerous entrained bodies and fragments of variable scales in the Liangcheng granitoids (ca. 1.93–1.89 Ga). These gabbronoritic dykes are present at all locations where ca. 1.93–1.92 Ga ultra-high-temperature metamorphism is recorded in the khondalite. A gabbronorite sample from the Hongmiaozi dyke gives zircon 207Pb/ 206Pb mean ages of 1954 ± 6 Ma (core domains) and 1925 ± 8 Ma (rim domains). These ages, as well as previously reported ages, constrain the age of mafic magmatism to be at ca. 1.96–1.92 Ga (∼1.93 Ga). One sample from the Xigou gabbro intruded by the Liangcheng granitoids gives a zircon 207Pb/ 206Pb mean age of 1857 ± 4 Ma, which is interpreted as the age of a metamorphic overprint. The Xuwujia gabbronorites comprise mainly gabbronorite compositions, as well as some norite, olivine gabbronorite, monzonorite, quartz gabbronorite, and quartz monzonorite. Chemically, they are tholeiitic and can be divided into two groups: a high-Mg group (6.2–22.9 wt.% MgO) and a relatively low-Mg group (2.2–5.7 wt.% MgO). The high-Mg group shows negative Eu-anomalies (Eu/Eu* = 0.53–0.72), slight light rare earth element enrichment (La/Yb N = 0.56–1.53), and small negative anomalies in high field-strength elements. The ɛNd ( t = 1.93 Ga) values vary from +0.3 to +2.4. The low-Mg group shows varied Eu-anomalies (Eu/Eu* = 0.48–1.05), and is enriched in light rare earth elements (La/Yb N = 1.51–11.98). The majority shows negative anomalies in high field-strength elements (e.g., Th, Nb, Zr, and Ti). Initial ɛNd (at 1.93 Ga) values for low-Mg gabbronorites vary from −5.0 to 0. The Xuwujia gabbronorites possibly experienced assimilation of crust, and fractional crystallization of initially olivine and hypersthene (the high-Mg group), and then olivine, clinopyroxene, and plagioclase (the low-Mg group). The slightly younger Liangcheng granitoids consist of garnet-bearing granite, granodiorite and quartz-rich granitic compositions. They are intermediate to felsic calc-alkaline rocks, thought to be derived from surrounding metasedimentary crust. Xigou gabbro could represent early cumulates. The granitoids have relatively high-Mg numbers (up to 54), and show some chemical affinities with the gabbronorites, which could have resulted from incorporation of gabbronoritic melts. The occurrence and chemical variations of the Xuwujia gabbronorites and Liangcheng granitoids can be interpreted to have resulted from crust–mantle interaction, with mingling and partial mixing of mantle (gabbronoritic) and crustal (granitic) melts. The Xuwujia gabbronorites originated from a mantle region with high potential temperatures (∼1550 °C), possibly associated with a plume or more likely a ridge-subduction-related mantle upwelling event. They could have had extremely high primary intrusion temperatures (up to 1400 °C). Emplacement of these magmas was likely responsible for the extensive crustal anatexis (Liangcheng granitoids) and the local ultra-high-temperature metamorphism. These sequences may have followed ca. 1.95 Ga continent–continent (arc?) juxtaposition and were themselves followed by significant regional uplift and exhumation in the northern margin of the North China craton.

Integrated petroleum systems and play fairway analysis in a complex Palaeozoic basin: Ghadames-Illizi Basin, North Africa

Abstract The Ghadames–Illizi Basin system is a highly productive petroleum province with a long exploration history in Algeria, Libya and Tunisia (from the late 1950s to present day). Ongoing exploration success in all three countries suggests that it will continue to provide attractive exploration targets in the future. The basin has a long (Cambrian to Plio-Pleistocene) and complex geological evolution characterized by multiple phases of subsidence punctuated by significant regional uplift events. Two ‘world-class’ petroleum source rocks of different geological age are present (Lower Silurian and Upper Devonian) with similar depositional environments and geochemical characters. Both source horizons have generated significant volumes of oil and gas. Migration is strongly influenced by the stratigraphic architecture of the basin fill, notably distribution of regional seals and the complex patterns of subcrop and onlap across regional unconformities. Multiple reservoir–seal combinations are presented by Late Ordovician glaciogenic sediments and younger Silurian through to Carboniferous paralic sequences. Integrating the stratigraphic relationships with the complex burial history of the basin (timing of uplift, degree of tilting, amount of section removed by erosion) is not a trivial task, but is key to exploration success in such a complex basin. With the aid of 3D basin reconstruction and fluid flow modelling software, we can attempt to capture the stratigraphic and structural complexity and make exploration predictions. If basin modelling techniques are to be optimally applied in such settings, a fully integrated and geologically realistic approach involving sedimentologists, structural geologists, geophysicists and geochemists is required. A modelling approach, workflow and some results are presented.

Structural expression of forearc crust uplift due to subducting asperity

New structural observations and mapping of reefal terraces, carried out both on the field and on satellite remote sensing data, indicate that Sumba Island is presently undergoing a large amount of extension, associated with a significant regional uplift. This crustal uplift may have been created by a major thrust emerging in the South of the island. The uplift, which partly accommodated the Australian plate–South West Banda Arc convergence, is associated with the general northeastward tilt of the island. The consequent anomalous positive topography along the southern coast of the island is being compensated by significant tectonic erosion along large-scale curvilinear normal faults in the southeastern half of the island. The most important expression of this gravitational collapse is located at the receding side of an advancing circular dome, showing striking similarities with accretionary wedges being affected by seamount subduction. The part of the forearc basin known as the Savu Basin is moderately deformed (mostly in its central part) and appears to act as a rigid buttress in the convergence between the Banda Arc and the Australian plate. As a result the convergence appears to be transferred northward within the actively-shortening back-arc domain, which goes from the north of the Flores Island to the southwest of the Timor block. The convergent plate boundary shows a transition between a stable domain (West of Sumba) and a tectonized domain (East of Sumba), the latter coinciding with the subduction of the outer Australian passive margin. The subduction of the ocean–continent boundary of the Austral-Indian plate below the Banda arc since the Lower Pliocene may have incorporated some crustal fragments in the plunging Benioff zone. Most likely, the integration of the stretched continental lithosphere in the subduction zone caused the uplift the entire forearc domain, exhibiting inherited structures of the upper plate.

Origin and Timing of the Miocene-Pliocene Unconformity in Southeast Australia

An unconformity is present close to the Miocene-Pliocene boundary in the onshore and nearshore portions of the Otway, Port Phillip-Torquay, and Gippsland basins of southeast Australia. The unconformity is angular (generally < 1-5° angularity), with the underlying Miocene units having been deformed (gentle folding and reverse faulting) and eroded prior to deposition of the Pliocene succession. The unconformity also marks a change from Oligocene-Miocene deposition of cool-water carbonate sediments and brown coal-bearing successions to the accumulation of more siliciclastic-rich sediments in Pliocene time. The Miocene-Pliocene boundary therefore represents an interval of significant regional uplift in the southeast Australian basins. The amount of section removed is greatest around the Otway and Strzelecki ranges in Victoria, where up to a kilometer of section may have been removed. In most onshore sections of the Victorian basins hundreds of meters of section have been eroded. In distal offshore locations the boundary becomes conformable. The timing of uplift and erosion is best constrained in the Otway and Port Phillip basins, where late Miocene (N16 ∼ 10 Ma) sediments underlie the unconformity and earliest Pliocene (∼ 5 Ma) sediments overlie it. This timing coincides with a change in the dynamics of the Australian plate, beginning at around 12 Ma. Southeast Australia is currently under a NW-SE compressional regime, and this has probably persisted since the late Miocene. In the basins (as opposed to the basement-dominated highland areas), the late Miocene uplift event is more significant than later Pliocene-Recent uplift.

Oyu Tolgoi, Mongolia: Siluro-Devonian Porphyry Cu-Au-(Mo) and High-Sulfidation Cu Mineralization with a Cretaceous Chalcocite Blanket

The Oyu Tolgoi porphyry Cu-Au-(Mo) deposit is located in the Gobi Desert of southern Mongolia. The deposit consists of three main mineralized zones (North, Central, and South Oyu), interpreted to constitute at least two separate porphyry copper centers. Oyu Tolgoi is associated with a series of small, structurally controlled stocks and dikes of monzonitic and dioritic composition, which intrude a sequence of Siluro-Devonian volcanic and sedimentary rocks. Country rocks consist of pillow basalt and basaltic andesite interbedded with fine-grained clastic sedimentary horizons. The sequence is interpreted to have formed in a subaqueous island-arc volcanic environment, which formed part of the extensive Paleozoic Tuva Mongol arc. These island-arc rocks are covered by Carboniferous terrigenous sequences and are intruded by Carboniferous syenite and granite and Permian alkaline granite. Much of the area is covered by poorly consolidated Cretaceous sedimentary sequences. Central Oyu consists of a multiple-phase hydrothermal breccia crosscutting an altered fine-grained feldspar porphyry containing porphyry-type alteration and mineralization. The breccia underwent texture-destructive advanced argillic alteration characterized by several associations of quartz, alunite, dickite, pyrophyllite, sericite, and zunyite plus lesser svanbergite and fluorite. These associations overprint earlier formed K silicate and quartz-sericite-illite assemblages. Copper mineralization at Central Oyu is present in a supergene chalcocite blanket that formed at the expense of a pyrite-rich, hypogene chalcocite-covellite-tennantite (arsenosul-vanite, sulvanite, chalcopyrite, bornite) sulfide suite that accompanied the advanced argillic alteration event. At South Oyu, a feldspar-hornblende porphyry of monzonitic composition intrudes a sequence of fine grained andesite and basaltic andesite. Hypogene copper-gold mineralization occurs as early magnetite-rich, pyrite-poor quartz-chalcopyrite-bornite stockworks and sheeted veinlets. Hydrothermal alteration is composed of biotite and K feldspar with apatite and minor albite. Magnetite averages 7 to 10 vol percent, and copper and gold grades vary sympathetically. These early assemblages are overprinted by a sericite-chlorite event with ore-grade copper and erratic gold and molybdenum values and also by structurally controlled, pyrite-rich advanced argillic alteration. K-Ar ages show that the hypogene copper-gold mineralization at South Oyu is latest Silurian-earliest Devonian (411 ± 3 Ma) and that the entire district was intruded by postmineralization syenite during the Carboniferous (307 + 4 Ma). The supergene chalcocite blanket at Central Oyu formed in the Early Cretaceous-earliest Late Cretaceous, based on ages for supergene alunite of 117 ± 1 and 93 ± 1 Ma, which makes Central Oyu one of the oldest preserved chalcocite blankets in the world. Chalcocite blanket preservation was favored by climatic desiccation into the Late Cretaceous and the Tertiary. It is inferred that significant regional uplift took place at the Silurian-Devonian boundary. This synmineral-ization uplift and erosion may have been in part responsible for the telescoping of the hydrothermal systems at Oyu Tolgoi, including the superposition of epithermal-style associations over higher temperature, deeper seated assemblages typical of the porphyry environment.

The Palaeoproterozoic Komatiite-Picrite Association of Finnish Lapland

The large range of chemical variation within intimately associated highly magnesian volcanic rocks in the Palaeoproterozoic Central Lapland Greenstone Belt prompted the construction of a new classification scheme for MgO-rich volcanic rocks, based on an [Al 2 O 3 ] vs [TiO 2 ] diagram where the axes are the Al 2 O 3 and TiO 2 contents (in mole proportions) of the rocks projected from the olivine composition. This diagram places the Lapland rocks in the fields of Ti-enriched komatiites and picrites. Komatiitic rocks are depleted in both light and heavy rare earth elements (LREE and HREE) relative to middle REE (MREE) and possess relatively high TiO 2 even in the most LREE-depleted varieties, whereas picritic rocks approach geochemically Hawaiian picrites. Seven clinopyroxene and whole-rock pairs analysed for Sm–Nd isotopes yield an average age of 2056 ± 25 Ma for the komatiites. Uncontaminated komatiites and picrites have similar positive e Nd values (+4) indicating generation from a mantle source with a long-term depletion in LREE relative to MREE. Geochemical characteristics of the komatiite–picrite association, including REE and Nb/Y–Zr/Y systematics, indicate chemical heterogeneities in the source region, which seem to have been created by complex depletion and enrichment processes shortly before or related to a dynamic melting process. The high MgO contents of the rocks coupled with chemical similarity between the Lapland and Hawaiian picrites supports a mantle plume model for their genesis. Nevertheless, the geotectonic evolution appears to have proceeded without significant regional uplift shortly before volcanism.

Shallow Oil in Northern Appalachian Basin: Evidence for Early Cretaceous Uplift from Fission Track Analysis: ABSTRACT

Apatite fission track data from Devonian and Carboniferous sandstones of eastern New York and Pennsylvania (e.g., Catskills, Anthracite belt) imply rapid cooling, presumably associated with significant uplift, in the Early Cretaceous (about 135 Ma). Maximum burial temperatures are unknown; however, temperatures immediately prior to uplift were greater than 130/sup 0/C, and limited zircon data suggest temperatures did not exceed 200/sup 0/C. In western New York and Pennsylvania, the data are similarly consistent with abrupt Early Cretaceous cooling, but from maximum temperatures not exceeding 105/sup 0/C. New apatite data from subsurface samples from western New York allow us to calculate a minimum geothermal gradient of approximately 22/sup 0/C/km, before the Early Cretaceous uplift. This calculation is compatible with shallow (200-600 m) Upper Devonian oil fields of the area, which have temperatures between 110/sup 0/ and 120/sup 0/C in the Cretaceous, the Oriskany gas field at 140/sup 0/C, Medina gas field at 150/sup 0/C, and Trenton gas field at 170/sup 0/C. These temperatures are compatible with oil- and gas-generation temperatures in other basins, and they provide a check for analysis. This minimum thermal gradient further implies that about 4 km of section must have been eroded from the region of these oilmore » fields. Thus, the fission track data suggest that oil fields between 200 and 600 m deep in the Upper Devonian sequences of southwestern New York and northeastern Pennsylvania contain fossil oil, which was generated prior to rapid cooling associated with significant regional uplift of the northern Appalachian basin during the Early Cretaceous.« less