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Syndepositional events that affected fluvial, estuarine, and shallow-marine sediments of the units studied in southwest Colorado - the McCracken Sandstone Member of the Elbert Formation and the Ignacio Quartzite - included bioturbation, local formation of glaucony grains and phosphate crusts, local carbonate pedogenesis, and possibly silcrete pedog...
The Ignacio Quartzite - exposed in the San Juan Mountains of southwestern Colorado - is composed of red and brown arkose and subarkose sandstones and minor interbedded shales. The formation is newly divided here into the Tamarron Member (0-24 m) and the overlying Spud Hill Member (0-21 m). The Spud Hill Member has a greater abundance of sandstones...
The Eureka Sandstone is a quartzarenite 200 m thick that was deposited on the eastern shelf of the Cordilleran foreland basin from Canada to California. It has many characteristics of other lower Paleozoic quartzarenites in terms of its sheet-like geometry, mineralogical and textural maturity (99.5% detrital quartz, almost free of detrital clay), s...
In order to better understand the origin and controls of calcite cementation in marine sandstone we studied ten Tertiary lithostratigraphical units exposed in the northern Apennines, Italy, which display a variety of patterns of calcite cement. Five of the units studied were deposited in piggy-back (satellite) basins, and five were deposited in for...
Quartzarenite coastal sands extending from eastern Louisiana eastward to Apalachee Bay, Florida, are anomalous: their position 7° north of the Tropic of Cancer contrasts with most other known modern quartzarenites, most of which are in a tropical setting. To determine the origin of these quartzarenite beach sands, we compared the mineralogy of samp...
Giant spheroidal concretions (cannonball concretions; some nearly 6 m in diameter) in fluvial channel-fill sandstones at two localities of the Dakota Sandstone formed by import of cement constituents at a burial depth of <1 km. During cannonball concretion growth a self-organizational process restricted concretions to a relatively few but widely sp...
Two types of cavernous‐weathering features are exposed in the Oligocene Macigno Sandstone along 5 km of the Tuscan coast south of Livorno, Italy. Honeycomb cells (type 1 features) are typical closely spaced, more or less circular pits of centimetre scale that have been eroded 2 to 6 cm below the general surface of bedding planes or joints. ‘Aberran...
We have developed an interactive computer-based tutorial in sandstone petrology for undergraduate-level students. The goal of this tutorial is to provide students exposure to the highly visual subject matter of petrography outside the confines of organized laboratory exercises. This paper describes the architecture and development procedures of the...
Abstract Liesegang bands with apparent offset along fractures are common in some calcisiltite beds. Thin sections show, however, that primary laminations are not offset along the fractures. Following the development of fracture sets in the calcisiltite, the fractures were cemented by calcite. This formed polyhedral compartments of low-permeability...
Spheroidal (cannon ball) calcite-cemented concretions, some of gigantic size, were studied from three Cretaceous shelf sand- stone units: Ferron, Frontier, and Second Frontier. The concretions have diameters between 2 cm and 6 m; those larger than 40 cm in diameter in the Ferron and Frontier have septarian structure. Rare concretions in the Second...
Comparative anatomists since the time of Richard Owen ([1][1]) have observed that birds and crocodilians have a four-chambered heart and have speculated that such a heart was present in extinct archosaurs as well. Until recently, no direct evidence of the cardiovascular system had been reported in
A new, cost-efficient approach to teaching undergraduate-level sandstone petrography is being devised. The main goal of this multimedia tutorial is to provide a quantity of petrographic information sufficient to allow students to attain a high level of expertise in rock description. Development in digital format will permit effective delivery of th...
Highly elongate vertical and horizontal calcite-cemented concretions in Pleistocene shallow-marine and coastal eolian sand- stones are mixtures of terrigenous sand and carbonate biogenic grains cemented to various degrees by low-Mg calcite. Petrographic and sta- ble carbon and oxygen isotopic data support the earlier hypothesis of Mazzanti and Pare...
Temple Member of the Qasr El Sagha Formation contains spheroidal calcite-cemented concretions in sandstone ranging from 70 cm to 9 m in diameter, although most are 1 to 4 m in diameter. Most concretions are solitary, oblate spheroids, but some are prolate, coalesced (joined laterally), or are compound (enclose smaller concretions). Half the concret...
Bedding-parallel tafoni are well developed over much of the surface of the Tunnel Spring Tuff (Oligocene) exposed in 300-m-high Crystal Peak, an inselberg. The Tunnel Spring Tuff is a crudely stratified, non-welded rhyolite ash-flow tuff with > 30 per cent porosity. Clasts of Palaeozoic dolomite, limestone and quartzite make up 10 per cent of the t...
Chert nodules of the Drunka Formation (Lower Eocene) are mostly spherical, have diameters from 40 to 120 cm, are quasi-uniformly spaced 2–3 m apart in the plane of bedding, have concentric internal structure and, except for rare small (<6 cm) solid chert nodules, are less than 85% chertified. Nodules formed after moderate alteration of limestone by...
Sandstones from western Sinai which are entirely or partly of Carboniferous age were not buried more than 1.5 km until the Late Cretaceous and younger, when the lowermost rocks reached a depth of 2.5 km. The first diagenetic event was cementation by a trace to 4% of normal quartz overgrowths. Petrographic and O isotope data of the overgrowths are c...
In spite of their age, quartzose and feldspathic Lower Carboniferous sandstones deposited on the Arabian shield in western Sinai remain friable and porous (average of 19%, maximum of 25%) except for strongly cemented ferricretes and silcretes. These fluvial and shallow-marine sandstones were not buried more than 1.5 km until Late Cretaceous and you...
To add to the limited quantitative data on the rate loss of sand-size feldspar and rock fragments during transport in the beach zone, the abundance of QFR grain types was determined for 31 samples of beach sand from Padre Island, a barrier island 240 km long whose only source of river sand is from the Rio Grande at its southern end. Feldspar, volca...
The diagenetic influence on hydrocarbon reservoir quality was investigated for the Cambrian and Lower Carboniferous sandstones of southwestern Sinai. These quartzose and feldspathic Palaeozoic sandstones were not buried more than 1 to 1.5 km until Late Cretaceous and more recent times, when the most deeply buried rocks may have reached 25 km.Porosi...
Quartzose and feldspathic Cambrian and Lower Carboniferous sandstones (fluvial > marine > eolian) deposited on the Arabian shield in southwestern Sinai were not buried more than 1 to 1.5 km until Late Cretaceous and younger time, when the deepest rocks reached 2.5 km. Porosity was reduced by compaction to about 26%. Grain rearrangement was the main...
Calcite cement derived intraformationally in seven stratigraphic units of marine origin is distributed heterogeneously at the outcrop scale. Sandstone beds intercalated with calcareous shale older than Pliocene tend to be completely cemented, whereas stacked sandstone beds that lack shale interbeds have calcite cement in the form of tightly cemente...
Highly elongate, aligned, calcite-cemented concretions are present in exposed shallow-marine Pleistocene sands and gravels along the Basilicata coast of the Ionian Sea, southern Italy. Concretions are shaped like rods (pencils and cigars, 0.5-3 cm in diameter) and thin blades (031 cm thick and 1-5 cm wide). Most have aspect ratios greater than 5 an...
Compositional and textural characteristics of 13 calcite-cemented concretions are compared with those in adjacent but essentially uncemented host sandstones to test the belief that concretions better preserve original detrital compositions than do host rocks. Sandstones sampled are from five upper Eocene to Pliocene clastic units deposited in a pig...
We studied the composition and roundness of medium sand from 18 small beaches of Elba Island. Six are pocket beaches less than 100 m long; the longest is 1.3 km long. The drainage basins of streams that supply the beaches are all less than 25 km2; most are less than 5 km2. Beach sands range widely in composition owing to diverse source terrane. For...
Trichichnus, a thread-like burrow possibly the work of sipunculan worms, is widespread in Bouma E (turbidite claystone) and H (hemipelagic claystone) layers and some thin turbidite sandstone beds in basin-plain and outer fan-lobe deposits of the Marnoso-arenacea Formation. Trichichnus closely resembles that described elsewhere in chalk and marlston...
Sandstones of the marine Lower Cambrian Araba Formation and the overlying fluvial Upper Cambrian( ) Naqus Formation in Gebel Araba-Qabeliat, southwest Sinai (the eastern side of the Gulf of Suez) were studied to evaluate the major factors controlling potential hydrocarbon reservoir quality. The formations have a composite thickness of 873 m and ove...
Diagenetic trends near sandstone/shale contacts were studied in 12 cored sequences from four wells between depths of 5200 and 15,700 ft (1585 and 4785 m) to evaluate the heterogeneity of diagenetic processes on a local scale and to evaluate the hypothesis that reactive aqueous fluids and components for cements in sandstones were derived from adjace...
The porosity and packing of 174 samples of well-sorted surficial and shallowly buried (to 17 m), unconsolidated Holocene sands were determined by point counting the upper surface of thin sections of epoxy-impregnated samples in reflected light. Average depositional porosity for 124 surficial beach sands, river point-bar and braid-bar sands, and eol...
The total whole rock porosity lost by compaction for individual samples ranges from 9 to 31%. At all depths the amount of porosity lost by grain rearrangement (9 to 27%) is more than twice the amount of porosity lost by either measureable ductile grain deformation (0 to 8.3%) or pressure solution (0 to 7.3%). Depth and thermal maturation, the latte...
At the northern corner of El Zeit Range, 370 m of sandstone overlie Precambrian granite and underlie Cretaceous marine strata. The sandstones include the marine Lower Cambrian Araba Formation and the overlying dominantly fluvial Upper Cambrian( ) Naqus Formation The framework composition of both sandstones is almost entirely quartz with trace amoun...
Petrographic data have rarely been used in hydrogeologic studies, yet the aquifer's rocks record to varying extents the history of rock-water interaction in the aquifer. Recognition of paleohydrogeologic regimes can provide insights into porosity and permeability trends, groundwater chemistry, the formation of petroleum and mineral deposits, and th...
Changes in packing and porosity resulting from compaction were studied in 38 Wilcox sandstones from 12 cores. Burial depths, adjusted for erosion in updip areas, range from 1100 to 14,500 ft. Neither quartz (/anti x/ = 5.6%) nor carbonate cement (/anti x/ = 2.9%) were introduced shallow enough or in sufficient abundance in the sandstones to signifi...
Quartz cement as syntaxial overgrowths is one of the two most abundant cements in sandstones. The main factors that control the amount of quartz cement in sandstones are: framework composition; residence time in the “silica mobility window”; and fluid composition, flow volume and pathways. Thus, the type of sedimentary basin in which a sand was dep...
Volumetric loss of detrital feldspar on the observed scale over such a short time span has major implications for provenance interpretations and for understanding the basin-wide mass balance of several major diagenetic components. The wide variation of feldspar content and composition at any given depth (temperature) attests to the premier signific...
Sandstones of the Pico and Repetto formations were studied to quantify the processes involved in compaction and to determine the porosity evolution of the beds during burial. The sandstones are mineralogically immature and, except for local carbonate-cemented beds, have insufficient cement to have prevented compaction. Stratigraphic studies and gra...
This chapter focuses on the diagenetic processes in northwestern Gulf of Mexico sediments. The northwestern Gulf of Mexico Basin has functioned as a natural laboratory for the exploration of many facets of geology. The thick Mesozoic and Cenozoic sediments of the Gulf Coast have been a focus for the study of diagenetic processes that typify large s...
White, elliptical, calcite-cemented concretion nuclei up to 2 m long contrast markedly in color, composition, and diagenetic history from more glauconite-rich concretion rinds and from dark green glaucarenite host rocks. Concretion nuclei are placers of loosely packed trilobite carapaces and minor quartz and glauconite tightly cemented with an aver...
Sandstones of the Pico and Repetto formations were studied to quantify the processes involved in compaction and to determine the porosity evolution of the beds during burial. The sandstones are mineralogically immature and, except for local carbonate-cemented beds, have insufficient cement to have prevented compaction. Stratigraphic studies and gra...
Pebbles and cobbles of Cretaceous carbonate rocks in Eocene and Neogene fluvial conglomerates and lag deposits derived from them have patterns of silicification that indicate most silicification occurred after deposition. This interpretation is supported by oxygen isotopic values of silica and by the absence of conchoidal fracture surfaces and perc...
White, elliptical, calcite-cemented concretion nuclei up to 1 m long contrast markedly in color, composition, and diagenetic history from more glauconite-rich concretion rinds and from dark-green glaucarenite host rocks. Concretion nuclei are loosely packed deposits of trilobite carapaces and minor quartz and glauconite that have intergranular volu...
Sandstones from three conventional cores between depths of 11,140 and 14,910 ft (3345 and 4545 m) currently have an average composition of QââFââRâ, but have lost approximately 5% feldspar to replacement by carbonates and to dissolution. Like other deeply buried Gulf Coast sandstones, plagioclase is being albitized and K-feldspar is dissolving. Pa...
LOCATION Roadcuts provide the only exposures of public access in the Marathon Uplift. However, roadcuts on U.S. 385 south of the town of Marathon and on U.S. 90 east of Marathon display spectacular features. Mileages to the first five stops in this guide are given from the junction of U.S. 385 south and U.S. 90 at the west edge of Marathon; mileage...
The Gulf of Mexico sedimentary basin is a natural laboratory for the study of on-going diagenetic and incipient metamorphic processes. Sediments and rocks of Eocene through Pleistocene age have been studied from the surface to depths in excess of 6 km. Sediments heated to temperatures above 100°C have been massively transformed by mechanical compac...
Fluvial-deltaic sands, which were subjected to calichification and other pedogenic processes, lost all macroporosity prior to burial. Most sands underwent compaction (average of 14% porosity loss), minor cementation by quartz and kaolinite, possibly during invasion of meteoric water introduced during a low stand of sea level, followed by extensive...
All detrital plagioclase that survived dissolution has been albitized. However, some K-feldspar, instead of dissolving, was stabilized by K + -rich brines derived from adjacent evaporites. This K-feldspar then developed extensive overgrowths. Fluvial red sandstone lost all initial porosity by the introduction of preburial pedogenic calcite and comp...
Sandstones of the Miocene Marnoso-arenacea Formation, a complex of slope, submarine-fan, and basin-plain deposits, were derived from several different Alpine and Apennine sources and have a remarkably diverse framework composition. Sandstones produce hydocarbons in the northern Apennines along the southern margin of the Po River valley. Reservoir q...
Diagenetic processes that alter the depositional composition of sands must be considered when making provenance interpretations. These modifying processes operate from the zone of weathering to the deep subsurface where diagenesis grades into metamorphism. Of greatest importance is the total dissolution of grains of feldspar, rock fragments, and he...
The reservoir quality of sandstone is almost entirely controlled by diagenetic events. The chemical and physical processes responsible for diagenesis are complex and they influence sands during all stages of burial and, in some basins, during subsequent uplift. Petrographic studies in the past ten years by many workers provide the basis for formula...
