Age, correlation, and origin of the type Lospe Formation (Lower Miocene), Santa Maria basin, central California
Richard G. StanleySamuel Y. JohnsonMichele L. TuttleJohn D. ObradovichMason 'Carl C. SwisherM.L.C. ThorntonD.R. VorkMark FilewiczRonald B. Cole
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Abstract:
The type Lospe Formation in the Casmalia Hills is an 800-m-thick sequence of sedimentary and minor volcanic rocks. The Lospe is entirely of early Miocene (Saucesian) age on the basis of palynomorphs, benthic foraminifers, and {sup 40}Ar/{sup 39}Ar ages of 17.70 {plus minus} 0.03 Ma (mean of seven determinations) and 17.39 {plus minus} 0.12 Ma (mean of six determinations). The {sup 40}Ar/{sup 39}Ar ages were measured on water-laid tuffs; these tuffs may have erupted from the same volcanic source as a welded tuff yielding an {sup 40}Ar/{sup 39}Ar age of 17.79 {plus minus} 0.10 Ma (mean of five determinations) from the Tranquillon volcanics on Tranquillon Mountain in the westernmost Transverse Ranges. Alluvial fan and fan-delta facies within the basal part of the Lospe are as thick as 200 m and consist mainly of conglomerate and sandstone derived from nearby fault-bounded uplifts of Mesozoic rocks. These coarse-grained facies grade upward into a sequence of interbedded sandstone and mudstone that accumulated in a shallow lake. Gypsum layers in the lake deposits contain sulfate depleted in {sup 34}S (0 to +3{per thousand}), suggesting that the sulfur had a hydrothermal origin. The uppermost 30 m of the Lospe consists of storm-deposited sandstone and mudstonemore » containing shallow-marine microfossils. The shallow-marine deposits are abruptly overlain by bathyal marine shale of the Point Sal Formation. The Lospe Formation records active faulting, volcanism, hydrothermal activity, and rapid subsidence during initial formation of the Neogene Santa Maria basin. These events may have resulted from crustal extension related to the beginning of clockwise rotation of the western Transverse Ranges about 18 to 17 Ma.« lessKeywords:
Conglomerate
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Fluvial, deltaic, and marine-shelf sediments were deposited in a 100 × 200 mi, north-south-oriented trough centered around Sydney where as much as 18,000 ft of strata accumulated during the Permo-Triassic. The trough is between and was filled by debris from two major blocks of older, deformed Paleozoic rocks. The northern block consists mainly of radiolarian chert, volcanic graywacke, and mudstone, intermediate-composition volcanics, and Permian granite. The southern and western block consists mainly of quartzose sediments, silicic volcanic rocks, quartzite, granite, and Permian basaltic rocks. Short transport distances and relatively slight reworking of these diverse rock types within the basin of deposition yielded a petrographically complex sequence but one in whi h contributions from southern, western, and northern sources can be distinguished readily. Lower Permian sediments apparently were derived mainly from the southern and western blocks and, except for small deltas in the nearshore area, were principally marine-shelf deposits having an abundant fauna of thick-shelled pelecypods, brachiopods, and bryozoans. Most of the marine sandstone and siltstone deposits contain a very large proportion of lithic fragments but some, apparently representing subaqueous bars, are mainly quartzose. During the Middle Permian the sequence was covered by a rapidly prograding sedimentary sequence derived from the northern block, which until Middle Triassic time provided most of the sediments to the trough. The principal sediment complexes derived from this northern system were two fluviatile wedges. One wedge each was deposited on either side of a b sement high, and the two wedges coalesced southward into a deltaic plain facing a shallow sea. Close borehole control within the fluvial system establishes the presence of channel-bar sandstone beds 50-200 ft thick. These grade laterally into levee and lacustrine siltstone and back-swamp coal beds. The alluvial deposits grade seaward into delta-plain deposits consisting of distributary-mouth bar sandstone beds 30-50 ft thick which interfinger laterally with interdistributary bay fills. Bay fill sequences generally grade from fine- to coarse-grained upward and commonly are overlain by intensely burrowed sandstone or root-clay and coal beds. Delta-front sandstone flanks the delta-plain deposits and merges with mottled gray siltstone of the open shelf. Several episodes of delta outbuilding separated by periods of marine transgression can be delineated. The last, most widespread progradation was followed in early Middle Triassic time by an equally extensive marine transgression. Fluvio-deltaic deposits which formed during this latest episode lack coal, and the sedimentary sequence is dominated by an orthoquartzitic barrier bar-tidal delta system, locally 1,000 ft thick, which grades laterally into marine red claystone and gray tidal-flat siltstone and fine-grained sandstone. The mineral composition of the latter sediments shows an increasing quantity of basaltic detritus from the south and a concurrent reduction of sediment influx from the north. End_of_Article - Last_Page 713------------
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The Type Section of the Kiowa crops out in southern Kansas (Kiowa County). Sedimentary, petrographic and paleontological analyses were conducted on outcrops in Kiowa County to determine environment of deposition and age of the formation. There are three main facies in the type Kiowa: a dark shale derived from current transported muds, sandstone from currents, and shell conglomerates that represent disturbed neighborhood assemblages or storm transported assemblages. XRD results show that the dark shale facies is dominated by illite, smectite and kaolinite clays. The sandstone is dominated by quartz, and the shell conglomerates by calcite with a matrix dominated by quartz. Paleontological analyses uncovered 11 different species of mollusks, 3 species of foraminifera and trace fossils of Fodinichina or Domichnia. The environment was determined to be a shallow marine setting near an opening to an estuarial bay or barrier bar in a shallow marine setting based on the presence of certain sedimentary structures, facies and differences of illite concentrations. The age of deposition is Late Albian ~102.5 Ma to ~101Ma based on correlation of similar units in North America and timing of transgressive events via sequence stratigraphy.
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The K-bentonite-rich interval of the Esopus Formation (eastern New York and northeastern Pennsylvania) overlies the coeval Oriskany/Glenerie/Ridgely Formations and ranges from 1 to 6.3 m in thickness. Six to seventeen soapy-feeling, yellow, tan, green, or gray clay to claystone beds (0.001 to 0.5 m-thick) interbedded with thin siltstone and chert beds (0.02--1 m-thick) characterize outcrops in eastern New York. Heavy mineral separates from these layers yield abundant uncorraded euhedral zircons and apatites, indicating that these are K-bentonites. In eastern Pennsylvania, the westernmost outcrop of the Esopus Formation displays a 2.3 m-thick massive, soapy-feeling clay to claystone-dominated interval. The presence of both coarse, highly abraded and small, fragile, pristine-appearing zircons and apatites from a 20 cm sampled interval may indicate a complex amalgamation/reworking history to the relatively thick, clay-dominated strata. Similar clay/claystone-rich strata have been found in the lower 0.15 to 1 m of the Beaverdam Member (Needmore Formation) in central Pennsylvania. Interbedded clays and claystones with or without minor siltstone beds characterize some outcrops. Other localities are clay-dominated, with minor amounts of quartz sand present in strata immediately overlying the Ridgely Sandstone. These newly discovered K-bentonite-rich strata mark a transition from shelfal orthoquartzites and carbonates to basinal black/dark gray shalesmore » similar to the overlying Middle Devonian Tioga ash interval. Deposition of ash-rich strata, associated with increased volcanic activity, coincided with subsidence of the foreland basin/relative sea level rise. These events were concurrent with a flush of siliciclastic sediments into the basin and are indicative of the onset of an early tectophase of the Devonian Acadian Orogeny.« less
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Deep marine low density turbidites of the Upper Cretaceous Tanjero Formation were studied in terms of their petrographic composition to deduce the provenance of the unit around Arbat, northeastern Iraq. Petrographic works based on modal analysis of the clastic rock fragments and released single minerals in silt, fine to coarse grained sandstone, and, in very small quantities, pebbly sandstone show that these turbidites are mainly composed of sedimentary rock fragments such as carbonate, microcrystalline and cryptocrystalline quartz bearing siliceous sedimentary cherts, Radiolaria bearing cherts, and released Radiolaria fossils from the cherts during a short distance transportation. Quartz and feldspar ratios in the whole thin sections are below two percent. The turbidite siltstones and sandstones are litharenite (calclithite) in composition, indicating sedimentary source rocks mainly consisting of carbonate rocks, Radiolaria, and chert-rich limestone. There is no significant petrographic variation across the clastic succession of the area. The composition of the clastic rocks suggests a recycled sedimentary source. Likewise, the QtFL ternary diagram suggests that the sediments are derived from a lithic recycled provenance, which indicates not only the Lower Cretaceous deep marine Qulqula (radiolarian) Formation as in the previous provenance works but also another deep marine unit, the Lower Cretaceous Balambo Formation, and a shallow water Lower Cretaceous Qamchuqa formation.
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In the Lake Superior region, four sequences of sedimentary rocks reflect the tectonic-sedimentary framework before, during, and after the magmatic event that resulted in 10,000 m of dominantly basaltic volcanic rocks and large layered gabbroic intrusions. The oldest sequence includes four geographically separated, thin (100 m) pre-volcanic, white to pink, quartzose sandstone units that were deposited in braided alluvial plain-lacustrine environments within the shallow basin that was the initial manifestation of rifting. The second sedimentary sequence consists of immature sediment, largely derived from the volcanic sequence and deposited in alluvial fan, fluvial, and lacustrine environments during intervals between extrusive episodes. These red silty to conglomeratic units range from a few centimeters to hundreds of meters in thickness. The Oronto Group and the younger Bayfield Group and their equivalents are post-volcanic, dominantly red-bed sequences of siltstone, sandstone, and conglomerate, deposited in alluvial fan, fluvial, and lacustrine environments within the elongate basin. The Oronto Group (600 m) includes the Copper Harbor Conglomerate, the Nonesuch Shale (gray, carbonaceous, pyritiferous, and cupriferous argillaceous siltstone) and the Freda Sandstone. The Bayfield Group (2100 m) includes the Orienta Sandstone, the Devils Island Sandstone (100 m of orthoquartzite), and the Chequamegon Sandstone. Whereas volcanic detritus is dominantmore » in most of the Oronto Group and the equivalent Solor Church Formation, extrabasinal granitic detritus dominants in the Bayfield Group and its equivalents (Fond de Lac Formation, Hinckley Sandstone, and Jacobsville Sandstone). Paleocurrent data indicate a general basinward transport of sediment during deposition of the four sequences, 1100 Ma(.) to 950 Ma(.).« less
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Thick, massive beds of nonmarine limestone are exposed in the Elephant Mountain quadrangle, Brewster County, Texas. This Eocene carbonate ranges from 1 to 70 m (3 to 230 ft) in thickness, and is intercalated with the three lowermost formations of the Buck Hill volcanic group: the Pruett tuff, the Crossen Trachyte, and the Sheep Canyon Basalt. The Pruett Formation (Eocene), which is composed mainly of volcanic tuff and tuffaceous nonmarine limestone, uncomformably overlies the Boquillas limestone (Cretaceous). These interbedded tuffs, and intercalating lavas of the lower Buck Hill group represent several interruptions during the formation of this lacustrine deposit. The carbonate rocks consist primarily of pure to impure silty limestones with no appreciable dolomite or evaporite content. The unit contains charophytes, ostracodes, algal stromatolites, oncolites, possibly Equisetum, silicified wood, stromatolific tufa, and fresh-water gastropods. These features probably represent a shallow, low energy, sublittoral to littoral marginal facies which were deposited in a relatively humid environment. The thick lower beds of this nonmarine limestone were most likely deposited in a drainage basin formed by block faulting in the Late Cretaceous to early Tertiary. In contrast, the thinner beds in the upper portion of this deposit may have accumulated in local depressions formed in the surrounding volcanic flows. The true size of the lake basin is unknown due to the lack of exposure, but the Pruett tuff interbedded with limestone has been found in the subsurface approximately 90 km (56 mi) northwest of the study area. End_of_Article - Last_Page 464------------
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The mainly clastic Eureka Sound Group sediments on southern Ellesmere Island (Stenkul Fiord/Split Lake area) bear only few fossils, which allow the identification of particular stratigraphic stages. Recently, we found altered volcanic ash layers that could provide novel stratigraphic marker horizons in the coal–bearing estuarine and fluvial-deltaic sediments spanning the Paleocene/Eocene boundary. Two volcanic ash horizons, which are centimeter-thick and laterally traceable, were identified in fine-grained estuarine/coal swamp sediments of the Paleocene Mount Lawson Formation of the Eureka Sound Group north of Split Lake (fission track age ca. 60 Ma according to Grist & Zentilli 2005). The beige-brown layers are preserved as smectite-bentonites. A more whitish and several centimeter-thick layer was recovered from within a coal seam of the Late Paleocene to Early Eocene Margaret Formation south of Stenkul Fiord. The layer crops out just below the first occurrence of Eocene palynomorphs (Kalkreuth et al. 1996). It consists principally of the rare hydrated aluminium phosphate minerals Sr-crandallite or goyazite that are characteristic alteration products of volcanic ashes, which fell into coal swamps (e.g., Reinink-Smith 1990). Despite the diagenetic alteration, distinctive volcanic ash structures like columnar fragments, glass shards, and bubble-rich shards are preserved as pseudomorphs (identified by SEM). XRF and ICPMS analyses of all three samples were done in order to obtain the geochemical fingerprints of the original lava. The chondrite-normalized REE patterns of the smectitebentonite samples are comparable to those of alkaline volcanics. They fit well to the patterns of alkaline intercalations of the West-Greenland tholeiitic rift-related complex (Disko Island, absolute age 60 Ma, Larsen et al. 2003b) as well as to the patterns of bentonite layers in the Paleocene Basilika Formation on Spitsbergen. The REE pattern of the phosphate-rich sample is similar to the REE patterns of the Mo-clay volcanic ashes in Denmark (Larsen et al. 2003a), which have their origin in the strong volcanic activity on East-Greenland around 55 Ma (i.e., approximately at the Paleocene-Eocene boundary) during the opening of the North Atlantic. All samples yielded only a small quantity of zircon. Most of the zircon consists of rounded detrital grains yielding a wide variety of ages by LA-ICPMS that are representative of the Laurentian craton. A few euhedral grains were also found and these proved to be about 55 Ma in age but precision is limited by common Pb bias. The youngest grains identified by LA-ICPMS
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The Mesosaurus Inland Sea covered, in the Late Paleozoic, vast areas (~5 Mio km2) of the SW-Gondwanan continental interior. Major depocentres are represented by the Karoo basins of SW-Africa and the Parana Basin in South America. These areas were interconnected prior to the break-up of Gondwana and the subsequent opening of the South Atlantic Ocean. In Namibia and South Africa deposits of the Mesosaurus Inland Sea are preserved in the successions of the glacial Dwyka Group and the postglacial Ecca Group (Karoo Supergroup). These deposits comprise the major part of a 60-70 Ma depositional cycle and are the main focus of this study. The large-scale transgressive part of this cycle started in the Late Carboniferous with continental glacial deposits followed by marine glacial and postglacial inland sea deposits. During the Early Permian the Mesosaurus Inland Sea reached its greatest extent, which was accompanied by widespread deposition of Corg-rich sediments. The large scale regressive part is recorded by successions ranging from deep water offshore pelites and turbidite sandstones to shallow water shoreface and deltaic sandstones, deposited in a brackish environment. Shallow water inland sea sediments are in turn overlain by fluvio-lacustrine deposits, which are assigned to the Beaufort Group and form the upper part of the cycle. This successive change in the depositional environment from marine to brackish to freshwater is also reflected in the fossil record. During Dwyka times a marine association of the Gondwana faunal province was able to colonize parts of the Mesosaurus Inland Sea. Later, during lower Ecca times, the connection to the Panthalassan Ocean became insufficient to retain normal marine conditions, leading to strong faunal endemism in an isolated and brackish inland sea environ¬ment. The most well-known and widespread representatives of this endemic fauna are mesosaurid vertebrates and megadesmid bivalves. Numerous altered tuffs occur as interlayers within argillaceous sediments of the Dwyka and Ecca Group of southern Namibia. The vast majority of these altered tuffs are represented by soft and crumbly to hard and indurated, clay-mineral-rich, bentonitic layers. Another, much rarer type is represented by very hard, chert-like tuff layers, which are predominantly albitic in composition. Furthermore, tuff layers within the Gai-As Formation of the Huab area are rich in potassium feldspar and have a porcelain-like appearance. The diagenetically modified matrix is mainly crypto- to microcrystalline. Polished tuff specimen show, in some tuffs, plane lamination or bedding with two or more subunits forming a tuff layer. Some display a weakly developed lamination. Only in very rare cases were structures reminiscent of sedimentary micro-cross lamination observed. The sedimentary textures and structures of the tuffs indicate that they have been deposited mainly as distal ash-fall layers by suspension settling in water. Some may have also been deposited or modified under the influence of weak bottom currents. The primary, pyroclastic macro-components of the tuffs are mainly represented by crystals of quartz, plagio¬clase, and biotite. In some thin sections pseudo¬morphs after pyroxene or hornblende were observed. Euhedral zircon and apatite crystals were observed in almost every tuff. Vitric or formerly vitric macro-components are very rare. The matrix of the majority of the investigated tuffs is predominantly composed of clay minerals. However, the matrix of the tuffs originally consisted most probably of fine vitric ash particles. Soon after deposition the volcanic ash was diagenetically altered to smectitic clay minerals. At a later stage smectite was progressively replaced by illite under prograde conditions. Nowadays the matrix of the bentonitic tuffs is strongly illite-dominated and only in the softer tuff layers a minor smectite content can be detected. Both the primary macrocrystic components as well as the geochemistry of the altered tuffs indicate that their source magmas were mainly of intermediate composition. The abundance of splintery quartz and feldspar crystal fragments within the tuffs hints at a highly explosive plinian or phreatoplinian eruption style of the source volcanoes, which were most probably located within a subduction-related volcanic arc region along the southern margin of Gondwana. New single zircon U-Pb SHRIMP datings of tuff layers provide a much more reliable age control of the investigated sedimentary succession. U-Pb SHRIMP ages for tuff layers from the glaciogenic Dwyka Group in southwestern Africa range from 302.0 ± 3.0 to 297.1 ± 1.8 Ma. The basal part of the early post-glacial Prince Albert Formation is dated at around 290 Ma. SHRIMP ages for tuff layers from the upper part of the Prince Albert Formation, the Whitehill Formation, and the middle part of the Collingham Formation indicate that the Mesosaurus Sea reached its greatest extent at around 280 Ma.
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