Reef Rock Research Articles

Trace Element Distribution in Reef and Subreef Rocks of Jurassic Age in Britain and Switzerland

ABSTRACT Spectrographic analysis has shown that large regional variations in Sr, Ba, St, Al, Ti, Co, Mn, Fe and Ni, occur in Corallian reef and subreef rocks between exposures in Oxford, Yorkshire, and northern Switzerland. Vertical variations between reef and subreef are also marked. Strontium values for the majority of samples studied are markedly higher than previously reported for Jurassic rocks, and lower than in similar rock types of recent age. A correlation of diagenetic and geochemical data throws some light on the timing and nature of the mechanisms which produce a net loss of strontium within rocks. Diffractometer analysis has shown the presence of a low ordered silicate gel in rocks collected from Oxford localities. Mossbauer spectroscopy indicates that large quantities of iron (g 10,000 ppm) proxying for calcium, were introduced into these same rocks. This iron probably originated from an external source, and was introduced at the same time as the low ordered silica gel.

Uranium-Series Ages of Corals from the Red Sea

WE report here age determinations by the 230Th/234U method1–3 on corals from a Pleistocene littoral sequence along the Red Sea coast of Egypt. This coast is characterized by interbedded Pleistocene terrestrial gravel and coral reef rock, overlying with unconformity a gently tilted sequence of late Tertiary sediments. The Pleistocene sequence is indented by a number of benches; most are wave-eroded but some may be partly constructional. Each bench is encrusted with contemporary reef material and associated alluvial gravel (refs. 4–11, and unpublished work of R. G.).

Notes on late quaternary sea levels, Fiji and Rarotonga

Abstract Surveyed Holocene beach ridges near Taunova and Ndeumba, Fiji, have no accurate dates. Those at Ndeumba, where wind-blown sand may be absent, could represent high-spring-tide berms and they show that sea level has possibly fluctuated up to 3 ft above and 2 ft below the present within at least the later part of the Holocene. Radiocarbon dates for the 3 ft and 10 ft coral reefs at Rarotonga are 2,030 and 28,200 yr B.P. respectively, but because of recrystallisation these dates are most likely too young. A 6 ft terrace, probably younger than the 10 ft reef, is cut into older reef rock dated as greater than 48,900 yr B.P. A prograded strip of sand that almost completely encircles Rarotonga consists of storm ridges that are unsuitable for determining past sea levels. The oldest storm ridge has a radiocarbon date of 3,510 yr B.P. and is correlated with the oldest Holocene beach ridge in the Firth of Thames which has a radiocarbon date of 3,900 yr.

Fibrous Aragonite in Sealed Pliocene Glycymeris yessoensis: Postmortem: ABSTRACT

About 300 jointed bivalves of Glycymeris yessoensis were collected from a lenticle of an almost unispecific shell bed in the Onma Formation, central Japan. Most of the valves were partly open and completely infilled with the surrounding sandy silt; 5 were sealed and contained only a small amount of aragonite-cemented siltstone. The void in the chamber of the sealed valves is occupied with acicular needles of aragonite overgrown on the inner surface of the valves and on the surface of parasitic boreholes within the shells. The fibrous aragonite on the inner surface of the shells is in optical continuity with the aragonite crystals at both inner and outer structural layers. The fibrous aragonite indicates strong depletion of O18 and slight depletion of C13 UP> compared with the shell. A cold to temperate open sea comparable with that off the western coast of Hokkaido at present is zoogeographically indicated for the Onma molluscan fauna. These isotopic depletions differ from that of aragonite cement generally found in grapestone clusters, reef rocks, and beachrocks, all of which are typically tropical. The textural evidence suggests that precipitation of the aragonite postdated the partial infilling by sediments, but took place when the sediments were plastic; hence a freshwater origin of the aragonite is excluded. A plausible interpretation is aragonitic growth from a solution trapped and warmed within the chamber during an early stage of fossilization. Aragonite cementation may occur in a localized space such as a shell chamber in nontro ical seawater. End_of_Article - Last_Page 856------------

Vermetid Reefs and Coastal Development in the Ten Thousand Islands, Southwest Florida

Sediments which underlie the Ten Thousand Islands have been deposited over the past 5000 years, during a more or less continuous marine transgression. Maximum sediment thickness is approximately 25 feet. Both the macrofauna and microfauna were used to help interpret the depositional environment for these sediments. The clean, slightly peaty basal sand was deposited in a lagoon with very restricted tidal circulation. When more marine waters entered the area about 3000 years ago, a chain of gastropod reefs appeared along the coastline. During the ensuing sea level rise of about six feet, the reefs have grown in size and number to form a reef barrier which has greatly influenced sedimentation throughout the Ten Thousand Islands. Sand from the adjacent shallow shelf has been transported into the reef area by the abnormally high tides and violent wave action accompanying hurricanes. A complex of bay bottom sands and silts, tidal pass sands, oyster bars, and thick mangrove peats has accumulated behind the reef barrier. Reefs were formed by the sessile gastropod Vermetus (Thylaeodus) nigricans Dall. The wave resistant reef core consists of fused vermetid tubes in a matrix of calcareous silt. Talus deposits typically underlie portions of the reef core. Formation of reef rock was confined to the intertidal zone, a vertical distance of less than four feet. Reef cores, as much as nine feet thick, were built up during the period of sea level rise. The vermetid reefs are compared with post-Wisconsin serpulid reefs from Laguna Madre, Texas, and with rudistid reefs from the Edwards Limestone of Texas.

Growth and Dolomitization of Silurian Reefs, St. Clair County, Michigan

Pinnacle reefs in eastern Michigan were formed during a period of cyclic carbonate-evaporite deposition in latest Niagaran-early Salinan time. Reef sequences now have salt beds as their lateral equivalents. Restoration of evaporite sequences to their relative positions during deposition demonstrates, however, that this is the result of differential compaction of carbonate beds, rather than contemporaneous deposition of reef rock and evaporites. Compaction of carbonate mud during lithification, rather than cementation, also accounts for most porosity loss in the area. Where porosity is preserved, compaction-resistant framework is present, and the porosity is directly proportional to quantity of framework. The reef and surrounding carbonates are dolomitized. The pattern of dolomitization, quantity of dolomite in relation to bed thickness, position of the dolomite in relation to evaporite beds, and time of dolomitization suggest that dolomitization was caused by a continuous movement of large quantities of connate waters through the sediments. It cannot be shown that refluxion by highly concentrated brines during periods of evaporite deposition contributed substantially to dolomitization. Evaporite sequences overlying bodies of carbonate mud prevented the vertical escape of water during compaction. The water was forced to flow laterally to the reefs, and then vertically through them to the surface. This very large quantity of water was forced through a relatively small volume of rock in he reef area and supplied the magnesium for dolomitization. The outflow of water continued during intensely evaporitic cycles, altering evaporite deposition in the reef area, and preventing heavy brines from entering the porous reefs and destroying porosity.

Growth and Dolomitization of Silurian Reefs, St. Clair County, Michigan: ABSTRACT

Pinnacle reefs in eastern Michigan were formed during a period of cyclic carbonate-evaporite deposition in uppermost Niagaran-lower Salinan time. At present, reef sequences have salt beds as their lateral equivalents. Restoration of evaporite sequences to their relative positions during deposition demonstrates, however, that this is due to differential compaction of carbonate beds, rather than contemporaneous deposition of reef rock and evaporites. Compaction of carbonate muds during lithification, rather than cementation, also accounts for the majority of porosity loss in the area. Where porosity is preserved, compaction-resistant framework is present with the resulting porosity directly proportional to quantity of framework. The reef and surrounding carbonates are dolomitized. The pattern of dolomitization, quantity of dolomite in relation to bed thickness, position of the dolomites in relation to evaporite beds, and time of dolomitization suggest that dolomitization was caused by a continuous movement of large quantities of normal connate waters through the sediments. It cannot be shown that refluxion by highly concentrated brines during periods of evaporite deposition contributed substantially to dolomitization. Evaporite sequences overlying bodies of carbonate mud prevented the vertical escape of water during compaction, forcing this water to flow laterally to the reefs, and then vertically through them to the surface. This very large quantity of water was forced through a relatively small volume of ro k in the nearby reef area, supplying the magnesium for dolomitization. The outflow of water continued during intensely evaporitic cycles, altering evaporite deposition in the reef area, and preventing heavy brines from entering the porous reefs and destroying porosity. End_of_Article - Last_Page 534------------

Geometry of Devonian Swan Hills Reef Complex--Alberta, Canada: ABSTRACT

End_Page 530------------------------------The Swan Hills reef complex is in the subsurface of west-central Alberta, 96 mi northwest of Edmonton. Early in 1957, Home Oil Company Limited discovered oil in these rocks at Virginia Hills and Swan Hills, and other discoveries in similar reservoirs within this complex soon followed. Before this, no commercial hydrocarbon production had been obtained from the rocks of this formation in Western Canada. By the end of 1966, the Swan Hills Formation ranked second in Western Canada in order of recoverable oil reserves. Between the year of discovery and the end of 1966, a total of 219,160,459 bbl of oil and 48 Bcf of gas have been recovered from 12 oil fields and 1 gas field. Total remaining recoverable reserves are estimated at 2,105,955,111 bbl of oil and 1,380 Bcf of gas. The oil is a paraffin-base crude with a gravity ranging from 38° to 45° API. Sulfur content of the crude may run as high as 0.42 percent but generally is less than 0.2 percent. Drilling depths differ considerably, depending on the position of the field relative to the regional dip, ranging from 6,950 ft in the northeast to 11,350 ft in the western parts of the producing area. The Swan Hills Formation is probably early Late Devonian in age and occupies a stratigraphic position low in the Beaverhill Lake Group. The reef complexes of this formation are situated along the edge of a broad carbonate platform south of the Peace River arch and east of the Western Alberta ridge. Continuing reef growth formed limestone mounds that consist largely of successive layers of superimposed atolls, each having an organic rim surrounding lagoon deposits. The resulting rocks form a complex pattern of porosity and permeability. The limestones of the reservoirs, with a few exceptions, have not been dolomitized. Stromatoporoids are the dominant organisms. The fields are simple stratigraphic traps, the oil and gas being held in the porous reef rocks by the surrounding impermeable rocks. In the productive area, the Swan Hills reefs are enclosed in a shale and dense limestone facies of the Beaverhill Lake Group. North and northeast of this area, in northern Alberta, a gradual lateral facies change to predominantly shale of the basin facies occurs. South and southeast in southern Alberta and Saskatchewan, there is a lateral facies gradation to dense limestone and dolomite, accompanied by a gradual thinning of the total thickness. A band of coarsely crystalline vuggy dolomite is present along the margin of this shelf. Farther south, anhydrite is interbedded with the dolomite and salt beds are present. End_of_Article - Last_Page 531------------

Geology and Origin of the Florida Keys

The Florida Keys form a crescentic chain of small limestone islands which extend from near Miami to Key West, a distance of about 150 miles. They are made of two main formations of Pleistocene age—the Key Largo Limestone and the Miami Limestone. The former, named and described by Sanford, is an elevated coral reef rock, and the latter, also described by Sanford, is an oolitic limestone in this area. The Key Largo Limestone is the surface rock of the Upper Keys, and the Miami Limestone covers the Lower Keys. A contact found at Big Pine Key shows that the oolitic limestone overlaps the Key Largo, and core borings show that the Key Largo underlies the oolitic cover for the entire area of the Lower Keys. The Key Largo, therefore, extends for the total length of the Keys. A core placed at Dry Tortugas, 70 miles west of Key West, encountered it at 30 feet below sea level. The Key Largo has a maximum thickness of over 200 feet. The fact that the Keys are located about 5 miles from the seaward edge of the Florida coral reef platform creates an interesting problem. They may be (1) remnants of an ancient outer reef similar to that found today bordering the living coral reef tract, or (2) they may have become established as a line of patch reefs in the back reef zone of a pre-existing platform which extended seaward some distance, possibly as far as the present platform. It is believed that the answer to this problem can be found through an understanding of what was happening seaward and leeward of the old reef at the time its corals were flourishing. Consequently, the composition and structure of the reef platform seaward of the Keys and the geologic history of the rocks of the Florida mainland immediately behind the Keys were studied. Information thus obtained plus observations on the composition, especially the coral content, of the Keys themselves have led the authors to believe that the Keys were formed as a line of patch reefs in a back reef area which was bordered on its seaward edge by an outer reef which has since been lowered, chiefly by erosion, and covered by more recent material.

Preliminary Report on Some Pennsylvanian Reefs from Northwest Ellesmere Island: ABSTRACT

Pennsylvanian reefs as thick as 2,000 feet crop out nearly 10 miles along strike at Hare Fiord, Northwest Ellesmere Island. The reef flanks slope as much as 45°. There is no interfingering between the reefs and the overlying silty limestones. Stratification within the reefs is confined to planes parallel with the reef sides. In order of relative abundance, the reef fauna consists of crinoids, brachiopods, bryozoa, corals, gastropods, ammonites, trilobites, and fusulinids. Fenestellid bryozoans may have provided a reef framework, but no clear zonation into reef barrier and lagoon is apparent. A fore-reef is present, characterized by reef-derived conglomerates. A strange internal conglomerate, not readily explained as solution-breccia, is common. Recrystallization is widespread, particularly along intrusive dike margins. Porosity of the main reef rock is low, but the conditions leading to the formation of internal conglomerate may have produced porous localities in parts of the reef area other than the accessible cross section. The reefs probably formed in a climate not only warmer but also with more sunlight hours than that at the present latitude of northern Ellesmere Island. End_of_Article - Last_Page 518------------

Lithification of carbonate sediments in the Heron Island Reef, Great Barrier Reef

Abstract In this reef area lithification has resulted in the formation of beach rock at the surface and reef rock in the subsurface. The process of lithification which leads to the formation of beach rock is an unusual and interesting one, but does not play a major role in the consolidation of reef sediments. Beach rock results largely from the protective action of encrusting algae and to a less degree from carbonate precipitation from sea water. Because of the general lack of “fines” in reef flat and beach sands, matrix recrystallisation plays no part in beach rock formation. By contrast, the reef rock from the subsurface generally contains a higher percentage of fines and, below 100 feet, this material has been largely recrystallised to form a strong binding medium. The process of recrystallisation is apparently selective, those sediments with high matrix, high coral/algal ratio and low MgCO3 content showing the highest degree of recrystallisation. Depth of burial shows no direct relationship to this pr...

Shallow-Water Geology and Environments of Alacran Reef Complex, Campeche Bank, Mexico

Alacran is an oval, shallow-water platform approximately 100 square miles in extent which rises above the general surface of the continental shelf 70 miles off the Yucatan Peninsula of Mexico. The reef complex includes the long, arcuate reef which forms the windward side of the platform, a deeper and less sharply defined belt of reef growth outlining the leeward margin, and a multitude of reefs of various shapes and sizes in the enclosed lagoon. Contemporary sedimentation at Alacran is resulting in three major types of accumulations: loose sediment, rigid frames, and non-rigid frames. The loose sediment, primarily skeletal debris in the form of silt, sand, and gravel, covers inter-reef parts of the lagoon bottom. The rigid frames are built by a succession of organic overgrowths during which new colonies spread over the in situ skeletons of their predecessors. Non-rigid frames are being built on the protected side of some rigid frames where branching colonies of coral or algae are so abundant on the loose sediment surface that the individual colonies nearly touch each other, or even intermesh, although they are not cemented to one another. In terms of their roles as geologic agents, the organisms of the area can be categorized as frame builders, cementing agents, sediment contributors, frame destroyers, inhibitors of reef growth, and sediment movers. Many non-fossilizable members of the fauna and flora have considerable influence on sediment character and on rate and place of sedimentation. Lateral changes in benthonic organisms and bottom character are prominent on and around the Alacran reefs. Reef surfaces are divisible into two and sometimes three zones based on distribution of species which build rigid frames. Two other zones are based on distribution of species which build non-rigid frames. Other zones, such as one recognizing prominence of sediment-binding plants, are differentiated in lagoonal areas between reefs. All the Alacran reefs appear to be thriving, or at least holding their own in relation to the destructive forces of wave action and burrowing organisms. The outward expansion of the reefs into deeper water seems to depend primarily on some of the massive corals which attain great size but do not require a hard substrate. Such species create the foundation of reef rock on which other frame builders can establish and to which they subsequently contribute. Several environmental factors influence the morphology of individual coral colonies. Change in colony form correlated with increase in water depth is well shown by one species of branching coral, and several other species illustrate the influence of wave action, sedimentation rate, and the presence of intruding organisms on colony morphology. The reefs which are exposed to the strongest wave action differ in several respects from those in more protected areas. Some of the major frame-building coral species on less protected reefs are absent or uncommon on most lagoonal reefs. Encrusting calcareous algae contribute to windward reef frames but are inconspicuous in lagoonal reefs. Study of reef surfaces suggests that cross sections of lagoonal reefs would show less tightly knit reef frames with larger pockets of loose sediment than would be the case in windward reefs.

Pilot Propane Project Completed in West Texas Reef

Abstract Injection of a 14,000-bbl "slug" of propane into a reef reservoir in an advanced stage of gas injection operations has resulted in miscible displacement of 100,000 bbl of stock-tank oil. Premature breakthrough of gas injected behind the slug is attributed to dilution of the propane slug, to unfavorable permeability distribution and to an insufficient amount of propane. Introduction The Millican field pilot propane project was intended to evaluate the applicability of the propane slug method to the Millican field (Fig. 1). A slug of 14,000 bbl of propane-butane mixture was injected in a single well followed by injected gas, and behavior of offset wells observed for two years. Recognized hazards were the high gas saturation due to the past history of gas injection and the non-uniformity of reef rock. Also, economic considerations limited the amount of propane which could be injected in a possible field-wide application. Favorable factors were a light oil containing a high proportion of intermediate hydrocarbons (see Table 1), gas injection facilities already in operation and a supply Of propane from a nearby gasoline plant. Despite the recognized hazards, project economics were considered favorable, since costs were low and any reduction in gas-oil ratio brought about by propane injection would be immediately reflected in increased oil production. History of Millican Field The Millican field, located in Coke County, Tex., produces from a Strawn reef limestone at 6,000 ft. Originally, the field had two small gas caps, and periodic material balance calculations indicate a closed reservoir. The oil was saturated at the original pressure of 2,540 psig at - 3,720 ft with 1,300 cu ft of gas per barrel and had a formation volume factor of 1.65. From core analyses, average porosity of the productive section of the reef is estimated at 6.6 per cent, connate water saturation at 20 per cent, and average permeability, 10 md. The field is completely unitized and produced gas has been returned since early in the history of the field.

Depositional Fabric in Permian Reef Limestones

Reef limestone in which primary textures have not been markedly altered by diagenetic changes is characterized by a distinctive fabric of both inorganic and organic constituents, and the more salient elements of the fabric are not primarily dependent on the particular kinds of organisms that make up reefs. The complex of reef-forming organisms has evolved markedly during geologic time, first one, then another group coming into prominence. For example, scleractinian corals and coralline algae, principal reef-formers today, were not responsible for formation of the Paleozoic reefs. In spite of this qualitative diversity among reefs of different geologic ages, all reefs are characterized by a common growth mode which is reflected in the fabric. Reference to the work on the Funafuti reef rock by Cullis (1904), the most complete study of its kind published to date, shows that there are many parallels betwen certain modern and Permian reef limestones. After formation of a reef frame by firmly attached calcareous organisms, relatively large primary voids are incrusted and even filled by deposits of fibrous calcium carbonate precipitated from sea water. Similar deposits form the cementing agent of beachrock. Probably these deposits are of great importance in consolidation of the reef rock. After burial, but before the voids are sealed, many of the incrusted cavities become filled with detritus. The sequential relationships of these late interstitial deposits demonstrate conclusively that the fibrous deposits are precipitated from freely circulating sea water. It appears, then, that the early history of reef limestone is marked by progressive reduction and loss of primary porosity. Secondary porosity is produced by selective leaching of aragonite and calcite constituents under gradually increasing pressures. It is this secondary porosity which is of interest in connection with petroleum reservoirs.

LITHIFICATION OF PLEISTOCENE CLAY AT KAHUKU POINT, OAHU

Research Article| November 01, 1946 LITHIFICATION OF PLEISTOCENE CLAY AT KAHUKU POINT, OAHU RANDOLPH W CHAPMAN RANDOLPH W CHAPMAN THE JOHNS HOPKINS UNIVERSITY, BALTIMORE 18, MD. Search for other works by this author on: GSW Google Scholar GSA Bulletin (1946) 57 (11): 985–996. https://doi.org/10.1130/0016-7606(1946)57[985:LOPCAK]2.0.CO;2 Article history received: 15 Apr 1946 first online: 02 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 RANDOLPH W CHAPMAN; LITHIFICATION OF PLEISTOCENE CLAY AT KAHUKU POINT, OAHU. GSA Bulletin 1946;; 57 (11): 985–996. doi: https://doi.org/10.1130/0016-7606(1946)57[985:LOPCAK]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 At Kahuku Point, on the northern coast of Oahu, Territory of Hawaii, a layer of partially lithified clay rests unconformably on the irregular surface of an elevated marine bench of reef rock and beneath an overlying beach limestone and eolian limestone. The distribution, physical character, and chemical composition of this deposit reveal that it was washed in from areas having a lateritic soil development, deposited subaerially, and subsequently consolidated by calcium and magnesium carbonates leached from the overlying calcareous formations. Field relations indicate that the lithified clay is probably late Pleistocene. This content is PDF only. Please click on the PDF icon to access. 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.

Origin of coral reefs and islands

Dana interprets the previous work on coral reefs on Pacific islands as supporting Darwin9s (1842) theory of subsidence of coral reef islands. He states that the island of Hawaii, although growing little coral, has undergone more subsidence than the coral reef end of the chain, the volcanic activity more than keeping pace with the subsidence to yield a submarine continuation of the shield form as revealed by deep soundings fairly close to the island. These define a 4 degrees 309 slope, inferred to be that of a constructional shield. Dana emphasizes the distinctions that must be made to interpret coral deposits between porous beach deposits made by subaerial denudation, and the compact coral reef rock made underwater by living organisms. He suggests that firm evidence of subsidence could be obtained by identifying beach deposits underlying coral reef rock and suggests core drilling of atolls to find such evidence. In part 2, Dana considers the following objections to Darwin9s theory: I. Darwin9s insufficient knowledge of the facts bearing on the subject. II. Subsidence not ordinarily a fact because methods of producing barrier reefs and atolls have been brought forward that do not require its aid. III. The occurrence of cases of elevation in regions of atolls and barrier reefs inconsistent with the subsidence theory. IV. No ancient coral reefs in the geological series have the great thickness attributed by the subsidence-theory to modern reefs. V. Other methods of explanation and their supporting evidence. Under III, he cites Professor Karl Semper (1868, Zeitschrift Wissenschaft Zoologie, v. 13, p. 558), who objects to subsidence on islands that have reefs raised from 200 to 250 feet above sea level as "a cumbrous and entirely hypothetical series of upward and downward movements." Semper also argues that the strongest wind waves are too feeble to break off and lift large masses of reef, some 10 feet thick. Dana counters: "But the difficulty does not exist in fact: for earthquakes may have made the waves.," citing the proximity of the Pelew island to the tectonically and volcanically active areas to the west, including the Philippines and Krakatau. Dana concludes by evaluating all counter-claims to subsidence, finding none to irreconcilably conflict with Darwin, and much to support him.