Late Paleozoic Sedimentary Rocks Research Articles

Provenance of late Paleozoic sedimentary rocks in eastern Kazakhstan: Implications for the collision of the Siberian margin with the Kazakhstan collage

• The sedimentary provenance is different across the Char Shear Zone in eastern Kazakhstan. • The Char Shear Zone represents the suture between the Siberian margin and the Kazakhstan collage in eastern Kazakhstan. • The oceanic basin between the Siberian margin and the Kazakhstan collage was closed after 321 Ma. To unravel when, where, and how multiple arc systems were amalgamated is crucial for understanding the accretion processes of the Central Asian Orogenic Belt. Here we focus on the collision of the Siberian margin and the Kazakhstan collage along the Char Shear/Suture Zone in eastern Kazakhstan. We conducted U–Pb dating and Hf isotope analysis for detrital zircons of clastic rocks across the collisional zone of the Siberian margin (the Irtysh-Zaisan Complex) and the Kazakhstan collage (the Zharma-Saur Arc and the Char Zone). Our results show that the Irtysh-Zaisan Complex carries abundant early Paleozoic detrital zircons and minor Precambrian zircons, but there is a lack of such zircon populations in the Zharma-Saur Arc and the Char Zone. Devonian to Carboniferous detrital zircons appear in all sampling tectonic units, in which ε Hf (t) values of Carboniferous zircons from the Zharma-Saur Arc and the Char Zone are characterized by a narrow range (∼10–17) that is different from a relatively wider range of ε Hf (t) values of ∼5–18 for the Carboniferous zircons in the Irtysh-Zaisan Complex. The distinct sedimentary provenances of the Irtysh-Zaisan Complex and the Zharma-Saur Arc/Char Zone confirm that their tectonic boundary lies along the Char Shear Zone in eastern Kazakhstan. As the Late Carboniferous sedimentary rocks from the Zharma-Saur Arc and the Char Zone do not receive detritus from the Siberian margin, we consider that the Ob-Zaisan Ocean between the Siberian margin and the Kazakhstan collage was closed later than the deposition of these sedimentary rocks (<321 Ma).

Can magnetic fabric indicate the direction of a glacier movement? An example from Itararé Group and Aquidauana Formation, Paraná Basin, Brazil

Magnetic fabrics was determined on Late Paleozoic sedimentary rocks from Aquidauna Formation (50 sites) and Itararé Group (71 sites) that outcrop in Paraná Basin, applying both anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of anhysteretic remanence magnetization (AARM). Rock magnetism analyses reveal that magnetite, hematite, and paramagnetic matrix minerals are responsible for the magnetic susceptibility and AMS, while the magnetite is the carrier AARM. The AARM tensor is coaxial with AMS fabric. The analysis at the individual-site scale defines two AMS fabric types (A and B). The type A shows vertical AMS foliation pole (Kmin perpendicular to the bedding plane), while Kmax and Kint are scattered within the bedding plane itself. This fabric is usually interpreted as sedimentary-compactional. Type B shows the three well-clustered AMS axes with Kmin off-vertical, this fabric is the most important since it was found in the majority of the sites. This fabric is interpreted as indicative of sediment transport that could be inferred by the imbrication of AMS foliation (Kmin). The comparison of magnetic lineation (Kmax) for both Aquidauana Formation and Itararé Group with their respective glacial striae allow inferring that Kmax can be used as an indicator of glacier movement that was from SE towards NW, even though some variation or changes in the movement orientation could happen as found in the Itararé Group (from São Paulo and Paraná states), probably related to glacier advance and retreat or different glacier lobes.

Provenance and tectonic setting of late Paleozoic sedimentary rocks from the Alxa Tectonic Belt (NW China): Implications for accretionary tectonics of the southern Central Asian Orogenic Belt

AbstractThe Central Asian Orogenic Belt has long been considered the largest Phanerozoic accretionary orogen in the world; it developed through the subduction and final closure of the Paleo–Asian Ocean. However, the architecture and duration of the accretionary orogenesis of the Central Asian Orogenic Belt are still controversial despite decades of investigation. In this study, we present field, compositional, and stratigraphically controlled detrital zircon geochronological data for late Paleozoic sedimentary rocks from the Alxa Tectonic Belt to constrain their provenance, tectonic setting, and the overall tectonic configuration of the southern Central Asian Orogenic Belt. A Devonian sample yields a unimodal age peak (ca. 424 Ma) and broad late Mesoproterozoic ages. A Carboniferous sample has Early Silurian (ca. 438 Ma) and Late Devonian (ca. 382 Ma) peaks along with Neoproterozoic to Archean ages. The Permian samples are dominated by Ordovician–Devonian and Carboniferous–Permian ages. They yield maximum depositional ages ranging from ca. 291 Ma to 248 Ma and contain abundant zircon ages that are close to their depositional ages. These data reveal Ordovician–Silurian and Carboniferous–Permian magmatic flare-ups separated by a Devonian magmatic lull in the southern Central Asian Orogenic Belt. The arc terranes in southern Mongolia, central Beishan, and northern Alxa provided major detritus for the late Paleozoic sediments. An abrupt shift of zircon εHf(t) values at ca. 400 Ma reveals significant late Paleozoic crustal growth and excludes southern Alxa as a source. Oceanic basins prevented detritus from southern Alxa from reaching northern Alxa during Permian–Early Triassic time. A geological and provenance comparison of Permian basins in the southern Central Asian Orogenic Belt reveals the existence of two separate forearcs ascribed to bipolar subduction of the Paleo–Asian Ocean. Combined with recent paleomagnetic data, this leads us to advocate for an archipelago-style accretionary process induced by subduction retreat for the late Paleozoic tectonic evolution of the southern Central Asian Orogenic Belt, which continued into Late Permian–Early Triassic.

Convergence History of the Songliao and Jiamusi Blocks in the Eastern End of Central Asian Orogenic Belt: Evidence from Detrital Zircons of Late Paleozoic Sedimentary Rocks

Central Asian Orogenic Belt (CAOB) is one of the largest accretionary orogenic belts in the world. The eastern segment of CAOB is dominated by Paleozoic Paleo Asian Ocean tectonic regime, Mesozoic Paleo‐Pacific tectonic regime and Mongolian‐Okhotsk tectonic regime. The Songliao and Jiamusi blocks are located in the easternmost part of the CAOB and are the key region to solve the problem about overprinting processes of multiple tectonic regimes. It is generally believed that the Mudanjiang Ocean between the two blocks was finally closed in the Mesozoic, but the Paleozoic magmatism also developed along the Mudanjiang suture zone, while on both sides of the suture zone, there were comparable Paleozoic strata, indicating that the two blocks had converged during the Paleozoic, and the evolution history of the two blocks in the Late Paleozoic remains controversial. The Carboniferous‐Permian terrestrial strata mainly developed in Binxian, Wuchang and Tieli on Songliao Block, Baoqing and Mishan on Jiamusi Block. Samples from the Songliao and Jiamusi blocks in the Late Carboniferous‐Early Permian and Late Permian are collected for comparative analysis. The LA‐ICP‐MS zircon U‐Pb dating results show that the maximum depositional age of Middle Permian Tumenling Formation and Late Permian Hongshan Formation in Songliao Block is ∼260 Ma, while that of Tatouhe Formation and Carboniferous strata in Jiamusi Block are ∼290 Ma and ∼300 Ma, respectively, which supports the previous stratigraphic division scheme. The age peaks of ∼290–300 Ma, ∼400 Ma, ∼500 Ma appeared in the Late Carboniferous to Early Permian strata of Jiamusi Block and the Middle Permian strata of Songliao Block. The age peak of ∼500 Ma in the Middle Permian strata of Songliao Block may come from the Cambrian basement, Mashan Complex, of Jiamusi Block, while the age peaks of ∼420–440 Ma in the Carboniferous strata of Jiamusi Block may come from the Silurian magmatic arc in Zhangguangcai Range in the eastern margin of Songliao Block, reflects the history that they had been potential sources of each other, indicating that they may have combined in the Paleozoic. The Hongshan Formation of Songliao Block in the Late Permian lacks the age peak of ∼500 Ma, which indicate that Jiamusi Block was not the provenance of Songliao Block in the Late Permian, that is, there was a palaeogeographic isolation between the two blocks. Combined with the ∼210 Ma bimodal volcanic rocks developed along the Mudanjiang suture zone reported previously, we believe that the oceanic basin between the Songliao and Jiamusi blocks should have been connected in Late Permian and reopened during Late Permian to Late Triassic.

Detrital-zircon geochronology and Hf isotope of Paleozoic sedimentary rocks in the Jilin Province, NE China: tectonic significance for microcontinental blocks of eastern Central Asian Orogenic Belt

We undertook U-Pb-Hf isotope testing of detrital zircons from Late Paleozoic sedimentary rocks in the Jilin Province, NE China, with the aim of constraining the tectonic evolution of eastern Central Asian Orogenic Belt. The age populations of the detrital zircons from the sandstone of the Jiefangcun Formation in the Songliao Block are ~2234, ~1782, ~1030–921, ~817, ~540, and ~381–254 Ma, whereas those of the zircons from the greywacke of the Permian Kedao Formation in the Songliao Block yield are ~2436, ~1905, ~1692, 1146–1170, ~554–498, and ~342–255 Ma. Combined Hf isotope characteristics, these ages reveal that: (1) rocks from the Jiefangcun and Kedao formations were deposited after 254 and 255 Ma, respectively; (2) these formations were sourced mainly from the Songliao Block and the Jiamus Terrane in the eastern CAOB and to a lesser amount, from the northern margin of the NCC; and (3) it appears that several remnants of ancient Precambrian basement occur adjacent to these Late Paleozoic strata that occur within the microcontinental blocks. Detrital zircons from the silty sandstone of the Miaoling Formation in the western margin of the Khanka Terrane yield peak age populations of 508–476, 463–396, and 348–258 Ma, having similar eHf(t) values to those obtained from zircons within the Jiamusi Terrane. These data indicate that (1) deposition of the Miaoling Formation in the western margin of the Khanka Terrane had started by 258 Ma, and (2) these sediments were sourced mainly from the Jiamusi Terrane and local magmatic rocks. The widespread occurrence of detrital zircons with ages of 480–550 Ma and positive eHf(t) values within the Late Paleozoic strata in the Songliao Block and the Jiamusi–Khanka Terrane, indicates that the amalgamation of these blocks took place during the middle stage of the Paleozoic, probably after the Silurian, prior to the Late Permian.

The transition from a passive to an active continental margin in the Jiamusi Block: Constraints from Late Paleozoic sedimentary rocks

The eastern margin of the Jiamusi Block records the tectonic transition from a passive to an active continental margin during the Late Paleozoic- Early Mesozoic. Late Paleozoic sedimentary rocks from the Heitai and Zhenzishan formations along the eastern margin of the Jiamusi Block are a key to resolving these events. Major and trace element data (including REE) for 18 samples from late Paleozoic sedimentary rocks, with the characteristics of high SiO2, Al2O3, Na2O and K2O, low CaO, MgO and TiO2, enrichment in LREE and LILE, depletion in HFSE, and negative Eu anomalies, were plotted on various discrimination diagrams, indicating that the Heitai Formation formed in a passive continental margin setting, whereas the Zhenzishan Formation formed in an active continental margin setting. LA-ICPMS U-Pb dating of detrital zircon from two samples of the Heitai Formation and two samples from the Zhenzishan Formation indicates a range in age from 2735 ± 19 to 308 ± 3 Ma, showing similar populations to the Jiamusi Block. These detrital zircons not only indicate that the sedimentary material was derived from the Jiamusi Block, but also limit the depositional ages of the Heitai and Zhenzishan formations. The youngest zircon population of 374–384 Ma, with a peak at 382 Ma, from the Heitai Formation, together with evidence from paleontological studies, indicates the depositionol age of the Heitai Formation is Devonian (Givetian- Famennian), whereas the 308–318 Ma population, with a peak at 315 Ma, from the Zhenzishan Formation indicates that the depositionol age was late Carboniferous (post- Moscovian). This indicates that the transition from a passive to an active continental margin in the Jiamusi Block occurred between the Late Devonian and the late Carboniferous (380-310Ma) and was more likely related to the Mongol-Okhotsk oceanic subduction-accretion or Panthalassa Ocean, and not to the Paleo-Pacific Ocean or to the Paleo-Asian Ocean as previous considered.

Provenance analysis of the Late Paleozoic sedimentary rocks in the Xilinhot Terrane, NE China, and their tectonic implications

The Xilinhot Terrane is located in the eastern segment of the Central Asian Orogenic Belt in NE China, and is a key to a hotly debated issue on the Paleozoic tectonic evolution of this giant progenic belt. To constrain the tectonic evolution of the Xilinhot Terrane in the Late Paleozoic, we undertook zircon U–Pb dating and geochemical analyses of the Zhesi and Benbatu formations in the Suolun and Xi Ujimqin areas in the Xilinhot Terrane. Samples of the Benbatu Formation yield detrital zircon U–Pb ages ranging from 2659Ma to 316Ma, with four age populations at: 2659–1826Ma, 1719–963Ma, 590–402Ma, and 396–316Ma, whereas samples from the Zhesi Formation yield detrital zircon U–Pb ages ranging from 1967Ma to 250Ma, with four age populations at: 1967–1278Ma, 971–693Ma, 561–403Ma, and 399–250Ma. The age groups of both the Benbatu and Zhesi formations in the Xilinhot Terrane are similar to those in other parts of the Central Asian Orogenic Belt (CAOB). This evidence indicates that the Xilinhot Terrane is a microcontinent, and not an accretionary complex as previously thought. Furthermore, the youngest zircon grains in the Benbatu and Zhesi formations yield weighted mean 206Pb/238U ages of 322±12Ma (MSDW=0.12, n=4) and 257±2.8Ma (MSDW=1.6, n=8), respectively. Combined with fossil data, our new data suggest that the Benbatu and Zhesi formations in the Xilinhot Terrane were possibly deposited at ∼322Ma and ∼257Ma, respectively. Based on the provenance of the Carboniferous–Permian sandstones came from the blocks of NE China, we speculate that the Xilinhot Terrane is the western part of the Songliao block.

Detrital-zircon geochronology of Late Paleozoic sedimentary rocks in eastern Heilongjiang Province, NE China: Implications for the tectonic evolution of the eastern segment of the Central Asian Orogenic Belt

We undertook LA-ICP-MS U–Pb dating of detrital zircons from Late Paleozoic sedimentary rocks in eastern Heilongjiang Province, NE China, with the aim of constraining the tectonic evolution of the eastern segment of the Central Asian Orogenic Belt (CAOB). Detrital zircons from quartz sandstone of the Devonian Heilonggong Formation in the Zhangguangcai Range yield age populations of ∼ 2503, ∼ 1833, ∼ 903, ∼ 802, and 551–403 Ma. Zircons from quartz sandstone of the Devonian Baoquan Formation in the Lesser Xing'an Range yield age clusters at ∼ 2500, ∼ 800, and 489–425 Ma. These ages reveal that: (1) rocks from the Heilonggong and Baoquan formations were deposited after 391 and 413 Ma, respectively; (2) these rocks were sourced from regions with rocks as old as ∼ 2500 Ma, with dominant age populations of ∼ 2500, ∼ 1833, 903–800, and 551–403 Ma; and (3) in addition to new lower crust accreted during the Phanerozoic (as revealed by voluminous Phanerozoic granitoids with positive εNd values within the CAOB), it appears that several remnants of an ancient Precambrian basement occur adjacent to these Late Paleozoic basins (e.g., the Shangzhi, Tangyuan, and Baoqing basins) that occur within microcontinental massifs including the Songnen–Zhangguangcai Range, Xing'an, and Erguna massifs. Detrital zircons from quartz sandstone of the Devonian Heitai Formation on the eastern margin of the Jiamusi Massif yield peak age populations of 569, 542, 509, and 484 Ma, similar to those obtained from zircons within the Mashan Group of the Jiamusi Massif. These age data indicate that: (1) deposition of the Heitai Formation on the eastern margin of the Jiamusi Massif had started by 484 Ma, and (2) these sediments were sourced entirely from the Jiamusi Massif. The widespread occurrence of detrital zircons with ages of 480–550 Ma within Late Paleozoic basins in the Lesser Xing'an–Zhangguangcai Ranges and the Jiamusi Massif, combined with the presence of a Caledonian (445–499 Ma) I-type granitoid belt in the Lesser Xing'an–Zhangguangcai Ranges, indicates that amalgamation of the Songnen–Zhangguangcai Range and Jiamusi massifs took place before the Early Devonian, probably during the late stage of the Early Paleozoic (after ∼ 445 Ma).

Gold Deposits in Beishan Mountain, Northwestern China

Abstract. The Beishan Mountain spans three provinces ‐ Gansu, Xinjiang and Inner Mongolia, having an area of 120,000 km2 Tectonically, it transverses three different tectonic units, i.e. Siberia, Kazakhstan and Tarim plates, and is composed of nine ter‐rains with widely exposed Precambrian and Paleozoic strata, complex structures, intensive magmatic activities and widespread ore deposits. It is not only a main part of Tianshan‐Yinshan‐Great Hinggan metallogenic belt in China, but also a key to under‐stand the evolution of central‐Asian orogenic system.At present, more than 100 gold deposits and prospects have been discovered, explored and mined, among which Nanjinshan, Mazhuangshan, Liushashan, Jinwozi, Zhaobishan and Xiaoxigong are the most important ones. Based on the host rocks and the geological features, all these gold occurrences can be subdivided into three groups (or types): (1) hosted by Carboniferous or Permian volcanic or subvolcanic rocks; (2) hosted by or related to plutonic intrusions; and (3) hosted by Precambrian metamorphic rocks. The first group includes the Mazhuangshan gold deposit, which occurs in Hercynian quartz por‐phyry and rhyolite porphyry as gold‐bearing quartz veins. The second group is composed of the Liushashan, Nanjinshan Zhaobishan and Jinwozi gold deposits. Gold mineralization at these four deposits occurs within Hercynian granitoids intrusion: or late Paleozoic sedimentary rocks as quartz veins, veinlets and altered rocks. The Xiaoxigong gold deposit belongs to the third group, and is hosted by Precambrian schist, amphibolite and migmatite as quartz veins and altered rocks.Isotopic age dating data, geological and geochemical evidence suggest that most of the groups 1 and 2 gold deposits were generated during the emplacement of the Hercynian or partly Indosinian intrusions. These intrusions may provide both heat and metals for groups 1 and 2 deposits. In contrast, although the formation is closely related to the Hercynian magma‐tism, the ore‐forming materials of the group 3 deposits may not only come from the intrusions, but also from the Precambrian metamorphic rocks.

Separation mechanism in the formation of proximal and distal tin polymetallic deposits, Xinlu ore field, southern China; evidence from fluid inclusion data

The Xinlu tin polymetallic ore field in Guangxi Zhuang Autonomous Region, southern China is associated with the Mesozoic Guposhan granitic batholith, which intruded pre-Devonian metasedimentary rocks and late Paleozoic sedimentary rocks including large amounts of carbonates. Dikes of intermediate to granitic compositions similar in age to the granites are widespread. Five tin polymetallic deposits occur in the ore field; among them, the Dachong and Liuhe9ao deposits are located at the contact zone between the granitic intrusions and the Devonian sedimentary rocks and are therefore proximal deposits. The Baimianshan and Shimen deposits, classified as distal deposits, are located in the Devonian sedimentary rocks relatively far above the intrusions and are spatially related to dikes and/or fractures. The Muqiaomian deposit is situated in the sedimentary rocks not far from the contact zone, forming a transitional type between proximal and distal deposits. A correlation between the vertical distance from orebodies to iutrusion top surface and the depth of emplacement of the intrusions can be established: proximal deposits are found in the northern part of the ore field, where the granites were emplaced at relatively high levels, in contrast to the distal deposits which are found in the southern part of the ore field, where the granites were emplaced at deeper levels. Both proximal and distal deposits are mainly composed of sulfides, with pyrrhotite and sphalerite being the major components coexisting with cassiterite. The localization of the ore deposits does not appear to be controlled by a specific sedimentary bed at the ore field scale, nor can it be attributed to the effect of metal zonation.Fluid inclusions in cassiterite from proximal and distal ores and in quartz from granites associated with the proximal deposits have been studied. The chemical system of the ore-forming fluids is H 2 O-CO 2 (-other gases)-NaCl-CaCl 2 . The common coexistence of relatively CO 2 -rich gas inclusions (X (sub CO 2 ) = 0.07-0.18) and relatively saline liquid inclusions (NaCl + CaCl 2 = 17.1-44.5 wt %) in cassiterite indicates that fluid phase separation is probably an important mechanism of ore deposition. Homogenization temperatures of fluid inclusions are similar between proximal and distal deposits: 250 degrees to 450 degrees C for the Baimianshan deposit, 325 degrees to 450 degrees C for the Shimen deposit, and 350 degrees to 475 degrees C for the Liuhe9ao deposit. This indicates a small temperature gradient in the conduits of the ore-forming fluids. Fluid pressures estimated from isochores range from 70 to 546 bars for the ore deposits and from 123 to 2,822 bars for the granite at Liuhe9ao. The thickness of the overburden at the time of mineralization is estimated to be 3,900 m according to stratigraphic data, the corresponding hydrostatic and lithostatic pressures being 382 bars and 1,032 bars, respectively. Thus the fluid pressure data derived from fluid inclusion study indicate that there was probably a high-pressure contrast between the source of the fluids within the intrusions (approximated by lithostatic pressure) and the contact zone and conduits (approximated by hydrostatic pressure).A model is proposed to explain the separation of proximal and distal deposits in relation to the depth of emplacement of the intrusions. It is shown that the migration capacity and phase separation fields of the ore-forming fluids are associated with the change from a lithostatic pressure system within the intrusions to a hydrostatic pressure system outside the intrusions and in turn are related to the depth of emplacement of the intrusions. Therefore, when the intrusion is emplaced at high levels, mineralization tends to take place near the contact zone, forming proximal deposits, whereas when the intrusion is emplaced at deeper levels, mineralization is more likely to occur some distance from the intrusion, forming distal deposits.

Mesozoic geology of the Jackson Mountains, northwestern Nevada

Research Article| March 01, 1984 Mesozoic geology of the Jackson Mountains, northwestern Nevada BRANCH J. RUSSELL BRANCH J. RUSSELL 1Department of Geological Sciences, Northwestern University, Evanston, Illinois 60201 Search for other works by this author on: GSW Google Scholar Author and Article Information BRANCH J. RUSSELL 1Department of Geological Sciences, Northwestern University, Evanston, Illinois 60201 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1984) 95 (3): 313–323. https://doi.org/10.1130/0016-7606(1984)95<313:MGOTJM>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation BRANCH J. RUSSELL; Mesozoic geology of the Jackson Mountains, northwestern Nevada. GSA Bulletin 1984;; 95 (3): 313–323. doi: https://doi.org/10.1130/0016-7606(1984)95<313:MGOTJM>2.0.CO;2 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 SocietyGSA Bulletin Search Advanced Search Abstract The Jackson Mountains Unit, a tectonostratigraphic unit in the Jackson Mountains, northwestern Nevada, includes the Upper Triassic pelagic, carbonate, and volcanogenic sedimentary rocks of the Boulder Creek beds, the Upper Triassic to Middle Jurassic volcanic and volcanogenic sedimentary rocks of the Happy Creek complex, and the Lower Cretaceous sedimentary rocks of the King Lear Formation. The lower Mesozoic rocks of the Jackson Mountains Unit record a transition from sedimentation on a starved lower slope–basinal margin, locally interrupted by prograding deposition from shoaled Mesozoic and possibly Paleozoic carbonate terranes, to the eruption of a proximal intraoceanic magmatic arc. This magmatic arc, represented by the Happy Creek igneous complex, erupted at the margin of North America that lay in northwestern Nevada during early Mesozoic and possibly later times.Between Middle Jurassic and mid-Cretaceous times, the Jackson Mountains Unit was subjected to multiple phases of deformation. Broad, open folding, probably resulting from shortening along a southwest-northeast axis (modern coordinates), affected the region between Middle Jurassic and Early Cretaceous times.During Early Cretaceous times, southeast-northwest shortening produced cleavage, thrusts, and folds. The second phase of shortening, orthogonal to the first, produced local intermountain basins in which the fluvial sediments of the Lower Cretaceous King Lear Formation were simultaneously deposited, on erosional unconformities above lower Mesozoic rocks of the Jackson Mountains Unit, and deformed. Also during the second phase of deformation, late Paleozoic sedimentary rocks were thrust over the Jackson Mountains Unit.A later phase of thrusting affected second phase structures between Early and mid-Cretaceous times. The absence of significant metamorphism and the development of only modest foliation, except near thrust faults, suggest that thrusting in the Jackson Mountains was thin skinned. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.