Evaporite Diapirs Research Articles

Evaporite diapirs in the La Popa basin, Nuevo León, Mexico

Reconnaissance mapping and stratigraphic work in the La Popa basin of Nuevo Leon, northern Mexico, has revealed two large structural features with cores of gypsum and anhydrite at the surface. These features are interpreted to be the surface expression of evaporite diapirs. They are exposed in folded sedimentary rocks belonging to the Potrerillos Formation of the Difunta Group of Maastrichtian age (Late Cretaceous). Sandstone units within the Potrerillos Formation pinch out toward the piercement features. Carbonate lentils composed of rudistid reefs and associated carbonate clastics flank the features and pinch out away from the features into marine shale members of the Potrerillos Formation. Most carbonate lentils occur in the immediate vicinity of the evaporite features and are interpreted to be genetically related to the diapirs. Syndiapiric sedimentary-facies patterns can be documented over 4,000 vertical feet (1,200 m) of section within the Potrerillos Formation. The large vertical extent of facies peculiarities near the piercement features indicates that the features were active for an extended period corresponding to at least two regressive-transgressive cycles during Maastrichtian time. A radial drainage pattern away from the northern feature indicates that the features are probably active today. A limestone inclusion from within one of the features has been dated as Kimmeridgian in age (Zuloaga or Smackover equivalent) and suggests that the evaporites are probably derived from the Jurassic Minas Viejas Formation. It is not known at present whether salt underlies the surface crust of gypsum and anhydrite. At the time that the first syndiapiric sediments of the Potrerillos Formation were deposited, the Minas Viejas Formation was buried at an estimated depth of 17,000 ft (5,200 m). The thick pre-Laramide cover, the pre-Laramide age of at least some of the syndiapiric sedimentary features, and the location of stocks away from major anticlines indicate that the emplacement of the diapirs is not related to Laramide compression. Geostatic loading is considered to be the most important mechanism for emplacement of the domes.

Evaporite Diapirism in the Sverdrup Basin: New Insights and Unsolved Problems

ABSTRACT Bipartite piercement domes and arcuate diapiric ridges in the western Sverdrup Basin are composed of a lower unit of rock salt and an upper unit of anyhydrite with limestone interbeds. As revealed by analogue models of buoyancy-driven diapirs, a thick unit of dense imporous anhydrite could not have risen actively together with the rock salt. Yet the anhydrite rocks have neither been attenuated nor pierced by the salt. Structural field evidence demonstrates unequivocally that the CaSO4 material (gypsum and/or anhydrite crystal mush) behaved as an active low-density medium in early states of diapirism. Apparently, the crystal water liberated by dehydration of buried sedimentary gypsum remained in the CaSO4 unit and preserved its low density for a limited period. Gradually, the light CaSO4 material turned into competent heavy anhydrite which formed a thick hood on the rising plugs and ridges of rock salt. After intensive shear along the flanks, the hood became a compact mass which was forced through the clastic overburden while breaking up internally. The competent anhydrite mass of at least one bipartite dome seems to have been exposed intermittently in the Upper Cretaceous. Some anhydrite cores of diapirs in the Eureka Sound fold belt, eastern Sverdrup Basin, behaved in the same way as those of the bipartite domes in the western Sverdrup Basin, and may have grown geostatically. Other large diapirs in the eastern Sverdrup Basin seem to be related to major faults, and may have risen under horizontal tectonic stress. It is not known to what extent these diapirs were actually driven by horizontal compression as opposed to differential buoyancy. Neither do we know which diapirs, if any, were initiated before the Eurekan Orogeny on eastern Axel Heiberg Island. Most of the outstanding problems cannot be solved completely until gravity studies have been made with the object of estimating the volume of low-density material below large structures like the North Mokka anticline, the Mokka Fiord dome or the Whitsunday Bay diapir.

Report on the second meeting of the Canadian Tectonics Group held on 23–24 October 1982 at Gravenhurst, near Toronto

S OF PAPERS PRESENTED Diapirism of the Morin anorthosite; evidence from the petrofabrics o f quartz c-axes of surrounding granulites. C. Barraud and J. Mart ignole , D6par tement de G6ologie, Universit6 de Montr6al , C.P. 6128, Montr6al , P .Q. Canada H3C 3J7. Petrofabric analysis of quartz c-axes from supracrustal rocks in contact with the Morin anorthosite (Grenville Province) was used to establish the relationship between quartz microfabric and diapirism. Isotropic quartz fabric mainly occurs southwest of the anorthosite dome, in mesoperthite-bearing leucogranulites, close to the granite minimum and in granoblastic annealed granulites. Conversely, nonisotropic quartz fabric is interpreted as the result of stresses acting during or after the last crystallization or recrystallization. This fabric is characterized by a point maximum or a small girdle. The orientation of quartz c-axes is not related to the mesoscopic foliation, but tends to be oriented perpendicular to the contact of the Morin anorthosite. The absence of relationship between mesoscopic fabric and quartz axes suggests that the latter is due to a late strain. Inasmuch as quartz c-axes tend to be oriented according to the last strain increments, the radial strain pattern around the Morin anorthosite would be compatible with the ascent and spreading of the mass as a late event not followed by regional deformation and metamorphism. The presence of fairly large tracts of granulites with an almost isotropic quartz fabric shows that crystallization from anatectic melts or metamorphic recrystallization locally outlasted dynamic crystallization. Origin and deformation of the North Mokka anticline, a typical structure in the Western Eureka Sound fold belt, Axel Heiberg Island, Canadian Arctic. Jean van Berkel , Depar tment of Geology, Universi ty of Toronto , Toronto , Canada M5S 1A1. The North Mokka anticline on central eastern Axel Heiberg Island is one of numerous doubly-plunging anticlines in the Eureka Sound fold belt. Its southern nose is cut by a large second-order evaporite diapir, the Mokka Fiord diapir (Schwerdtner & Clark 1967). Structural evidence suggests that the anticline is not a buckle fold due to E-W compression (Thorsteinsson 1974) but a first-order diapiric ridge due to halokinesis (Trusheim 1960). The anticline comprises at least three coalescent domes that form a N-S chain. The middle dome has a teardrop shape with at, apex to the south, and contains a small second-order evaporite diapir in its core. A NNW-SSE to N-S trending fault with a steep westerly dip cuts the southern and middle domes and forms the southeastern contact of the Mokka Fiord diapir. It truncates the internal structure of the small diapir in the middle dome. The fault is regarded as a minor branch of the Stolz thrust zone, which trends NW-SE about 10 km southwest of the North Mokka anticline. Northeast and northwest trends in the Grenville Province-expressions of propagating shear-zones? N. G. Culshaw, Depar tment of Geology, University of Ottawa, Ottawa, Ontar io , Canada K1N 6N5. At the margins of ductile shear zones in the western Grenville Province, a fairly common feature is the juxtaposition of an unfolded foliation, bearing a down-dip stretching lineation, with an overor underlying zone of folding. Lineation in the unfolded foliation, often plunging moderately to the southeast, is commonly parallel to the fold axes. This feature may be present locally or on a regional scale. In the latter case large areas of NW-trending foliations may be truncated by the SE-dipping foliation of the shear zone, both areas bearing a moderately SE-plunging lineation. Ramsay & Allison (1979) have suggested that when a shear system is constrained in the Z direction, contraction may occur below the leading edge of a propagating ductile shear. If a passive layering, originally parallel to the shear plane, is introduced into their model, folds with their axes parallel to the stretching lineation may form in the zones of contraction. Consequently, when the shear plane dips moderately to the southeast parallel to the lineation, NW and NE trends may be formed simultaneously. Also the model predicts that locally, as the shear zone propagates, folds with NW-striking axial surfaces will be overprinted by those with NE-striking axial surfaces. Large-scale structural patterns in the central gneiss belt, Grenville Province of Ontario. A. Davidson, Geological Survey of Canada, 601 Booth Street, Ottawa, Ontar io , Canada K I A 0E8. Curvilinear zones of layered gneiss in the central gneiss belt, Ontario Grenville Province, are moderately to gently dipping, more than 1 km thick, and continuous for scores of kilometres. On the map they surround, wholly or partly, domains with internally complex, smaller scale structure and distinctive lithologies and metamorphism. Regionally, NE-trending zones truncate structure to the northwest, NWtrending zones truncate underlying structure. Conventional concepts, namely basement/cover unconformities, discordant plutonic contacts, and simple fault systems, do not adequately explain domain juxtapositions. Relative displacement of adjacent crustal segments can account for the observed relationships.

Evolution of Sverdrup Basin, Arctic Canada

Sverdrup basin, a structural depression near the northern margin of the North American craton, contains a succession up to 13,000 m thick of Lower Carboniferous to Tertiary, marine and nonmarine sedimentary rocks, basalt flows, and gabbro dikes and sills. The basin evolved in five phases: (1) late Paleozoic, when evaporites and marine muds were deposited in the axial region and carbonates and mature sands on the margins; (2) early Mesozoic, when great thicknesses of siltstone and shale accumulated in axial parts of the basin; (3) middle Mesozoic, when terrigenous clastic deposits accumulated slowly; (4) late Mesozoic, when clastic deposits widely overstepped former basin margins; and (5) late Mesozoic-Cenozoic, when the basin underwent three stages of tectonism (Eurekan orogeny). Some evaporite diapirs in the basin developed halokinetically, beginning probably in the early Mesozoic; others were generated during Tertiary folding and faulting. Mafic volcanism and intrusion occurred episodically at times of basin foundering. Depending on the availability of imported terrigenous detritus, phases of mafic activity (and foundering) were accompanied by widespread marine transgression or by vigorous basin filling. The thick sedimentary fill masks the fundamental character of the basin. If acutely starved depositional conditions had prevailed through its Paleozoic and Mesozoic history, Sverdrup basin in the latest Cretaceous would have been a small ocean basin with steep sides, a basaltic floor about 3,500 m deep, and a thin succession of deep marine sediments--fundamental attributes of some modern small ocean basins.

Implications of coalification levels, Eureka Sound Formation, northeastern Arctic Canada

The rank of coal in the Eureka Sound Formation on Ellesmere and Axel Heiberg Islands ranges from brown coal to high volatile bituminous coal, based on reflectance determinations. Reflectance values from coals adjacent to the Stolz Fault, Axel Heiberg Island, are higher than in adjacent areas and may be related to abnormally high heat flows resulting from evaporite diapirism at depth, from the effect of overthrusting, or both. Regional reflectance values indicate that there is no correlation between the degree of coalification and the age of the strata, suggesting differing depths of burial and tectonic settings. Comparison of the coalification gradient at Fosheim Peninsula, Ellesmere Island, with that of the Téjon area of California permits estimation of a geothermal gradient which can be used for calculation of preorogenic sediment thickness. Maximum temperatures derived from the degree of coalification (100 °C at Fosheim) suggest that the sediments are within the zone of initial oil maturity.

Geology of Tunisia and Adjacent Parts of Algeria and Libya

The southern part of the study area is part of the stable Saharan platform which, since the beginning of the Paleozoic, has been affected only by epeirogenic movements. Pre-Carboniferous Paleozoic strata are largely clastic, both continental and marine. Early invasions of the sea came from the west, but Carboniferous and younger transgressions came from a northerly (Tethyan) direction. Caledonian tectonic movements produced structural alignments and important regressions, but general uplift resulting from the Hercynian orogeny caused the major withdrawal of the sea. The dominant feature of post-Hercynian erosion in Algeria is a great T-shaped anticlinorium which projects into Tunisia. On the east, a projection of the Hercynian Nefusa uplift of Libya extends westward and c nnects with the anticlinorium. Just south of these positive areas is the Erg Oriental basin, which was connected during most of the Paleozoic with the Homra basin of western Libya. The former is bounded in the western part of the study area by the north-northeast-trending Hassi Touareg anticlinorium. Restriction of the western Tethys basin and post-Hercynian subsidence along the margin of the African landmass led to deposition of a thick series of Triassic and Liassic evaporites. Younger strata of the Saharan platform are relatively thin, and although continental sands were important during certain stages, lagoonal dolomite, evaporite, and shale are the dominant rock types. North of the platform was a subsident zone, the Jeffara flexure, where considerably thicker and more marine strata are characteristic. Associated with the flexure and extending beyond it is a complex series of faults. On the north and west, the principal later Mesozoic events consisted largely of epeirogenic uplifts with regression and local erosion, and transgressive downwarps. Frequent and more intense moveme ts characterized the early Cenozoic, and local deformation, marking the onset of Alpine orogeny, began in the Oligocene. Stronger orogenic pulses occurred at the end of the Miocene, but the last and most violent phase of the Tunisian Atlasic orogeny took place during the Pliocene-Pleistocene. In addition to the Saharan platform and Jeffara flexure, Mesozoic-Cenozoic tectonic features include stable shelves of the Pelagian craton in eastern and offshore Tunisia, and of Kasserine Island in central Tunisia. The latter was exposed during latest Cretaceous time and is bounded on the east by a series of north-south-trending faults and Jurassic horsts marking the eastern boundary of the Atlas zones. Between this axis and the Pelagian shelf and between the Saharan platform and Kasserine Island is a series of Cretaceous and Tertiary intracratonic basins, and in northern Tunisia are similar ones containing thick sections of Miocene-Pliocene clastic rocks. In northwestern Tunisia are many Triassic evaporite diapirs, and some thrust faults are present in a zone of very thick Oligocene flysch. Three hydrocarbon-productive trends are present in the study area: (1) Ypresian (early Eocene) carbonate rocks: facies change regionally southwestward from globigerinid mudstone (source beds) to dolomitized nummulitic calcarenite (reservoir) to evaporite (updip seal). Recent discoveries seem to be associated with small structures, but regional extent of the trend and attendant possibilities for stratigraphic entrapment suggest the potential for large reserves. (2) Paleozoic and Triassic sandstones: this trend contains the only proved, major reserves of Tunisia in the Triassic reservoir at El Borma field. Cambrian-Ordovician strata are productive at Rhourde El Baguel in Algeria, and sandstones of the Silurian-Lower Devonian Acacus Formation are capable of production in many Libyan well . Major fields are structurally controlled, but distribution of reservoir rocks is related to Hercynian uplift, which influenced erosion of Cambrian-Ordovician clastic strata and deposition of presalt Triassic detritus. Hydrocarbon source beds for both systems are believed to be Silurian euxinic shales. (3) Cretaceous shoreline: several small oil fields and one gas field currently are productive, mostly from bioclastic carbonate reservoirs of Aptian to early Senonian age. These accumulations are on surface anticlines in a foothills belt which is not deformed so severely as the main Atlas ranges.

Deltaic and Associated Facies of Difunta Group (Late Cretaceous to Paleocene), Parras and La Popa Basins, Coahuila and Nuevo Leon, Mexico: ABSTRACT

ABSTRACT The Difunta Group is gray calcareous mudstone, siltstone, and sandstone that interfingers with wedge-shaped redbed units. These complexly interfingered units are divided into 13 formations and numerous members, tongues, and lentils; the group has a thickness of 10,000 feet. Low sinuosity, high-bedload streams transported volcanic and sedimentary rock debris from the Sierra Madre Oriental eastward to the ancestral Gulf of Mexico. Separate rivers fed the Parras and La Popa basins. Sediment accumulated in arcuate, wave-dominated deltas that prograded slowly into water several hundred feet deep. Some sediment was transported by marine processes to shallow delta-flank environments. Delta-plain lake and interfluve deposits are bioturbated mudstone containing sparse leaves, charophyte oogonia, dinosaur bones, and oyster debris. Many beds were reddened by postdepositional oxidation of iron-bearing minerals. Delta-front sheet sands are 20 to 60 feet thick, well sorted, flat bedded, and have sparse Ophiomorpha. Delta-platform deposits are characterized by fantastic sequences of ball-and-pillow structure and a sparse molluscan fauna. Prodelta deposits are interbedded graded sandstone and bioturbated mudstone; the sandstone beds were deposited by turbidity currents generated at the delta front by hyperpycnal inflow. Carbonate banks up to 1000 feet thick developed in distal prodelta (shelf) environments on submarine highs that were sea-floor expressions of rising evaporite diapirs. At least four major regressive-transgressive cycles developed in response to episodic basin subsidence. In contrast to the Rocky Mountain Cretaceous transgressions, the Difunta accumulated sheet sandstone units 20 to 60 feet thick. Parts of the transgressive units are delta-destructional deposits, but many are coalesced progradational sheet sands.

Geology and Oil Potential of Canadian Arctic Islands: ABSTRACT

The Canadian Arctic Islands sedimentary basin covers an area of approximately 530,000 sq mi, has a land area of 306,000 sq mi, and contains an estimated 900,000 cu mi of sediment. Ultimate recoverable oil reserves are estimated to be 40 billion bbl. The area consists of 4 major structural provinces: (1) shield-bordering Precambrian shield areas with structural arches extending into the basin, (2) Central Stable region, (3) Innuitian region, and (4) the Arctic coastal plain. The Central Stable region includes several basins containing relatively flat-lying shelf carbonates of Ordovician-Silurian age, with thicknesses generally 5,000 ft within the basin areas thickening northward to a maximum of 15,000 ft. The Innuitian region is a mobile belt, characterized by thick sedimentation, that was tectonically active from the Paleozoic to the Tertiary. It is comprised of (a) the Franklinian fold belt, a gently folded early Paleozoic geosyncline, approximately 1,500 mi long, containing up to 16,000 ft of Ordovician and Silurian carbonate, evaporite, and shale; up to 6,000 ft of Lower Devonian clastics; and 16,000 ft of Middle and Upper Devonian strata ranging upward from marine carbonates and clastics to nonmarine clastics; and (b) Sverdrup basin, a NE-SW-trending basin, approximately 600 by 200 mi, containing up to 40,000 ft of post-Devonian to Tertiary strata. Permo-Pennsylvanian rocks are dominantly carbonate and evaporite. The Mesozoic to early Tertiary was dominated by heavy and continuous terrigenous clastic deposition, generally characterized by basinal marine-shale facies and marginal-sandstone facies. The axis of the basin is characterized by numerous evaporite diapirs. The Arctic coastal plain contains late Tertiary and Pleistocene strata, along the northwest edge of the Arctic Islands, bordering the Arctic Ocean in the position of the present-day continental shelf. The Arctic Islands sedimentary basin has all the necessary geologic elements conducive to the entrapment of hydrocarbons in prolific quantities. There is a very thick, lithologically varied, stratigraphic succession representing every geologic period, adequate source beds, and abundant potential rocks. There is an abundance of diversified traps--large anticlines, reefs, evaporite domes, faulted homoclines, unconformities, and facies changes. A wide range of hydrocarbon shows, including oil sands, seeps, stain, and bitumen, are present in a large area. The Arctic Islands is an area of outstanding potential for the discovery of large oil fields. End_of_Article - Last_Page 845------------

Geology and Petroleum Potential of Canadian Arctic Islands: ABSTRACT

The Canadian Arctic Islands sedimentary basin covers an area of approximately 530,000 sq mi, with a land area of 306,000 sq mi, and contains an estimated 900,000 cu mi of sediment. The area consists of 4 major structural provinces. (1) The bordering Precambrian shield areas have structural arches that extend into the basin. (2) The central stable region consists of several basins containing relatively flat-lying shelf carbonates of Ordovician-Silurian age that generally are 5,000 ft thick within the basin and thicken northward to a maximum of 15,000 ft. (3) Inuitian region, a mobile belt characterized by thick sedimentary deposits, was tectonically active from the Paleozoic to the Tertiary. The region is comprised of the Franklinian fold belt and the Sverdrup basin. The Franklinian fold belt is a gently folded lower Paleozoic geosyncline, approximately 1,500 mi long. It contains up to 16,000 ft of Ordovician and Silurian carbonates, evaporites, and shale; up to ,000 ft of Lower Devonian clastic rocks, and 16,000 ft of Middle and Upper Devonian sedimentary rocks ranging from marine carbonates and clastics to nonmarine clastics. The Sverdrup basin, a NE-SW-trending basin approximately 600 by 200 mi contains up to 40,000 ft of post-Devonian to Tertiary rocks. Permo-Pennsylvanian strata are predominantly carbonate and evaporite. The Mesozoic to lower Tertiary are dominated by heavy and continuous terrigenous clastics, in general, basinal marine shale facies and marginal sandstone facies. The axis of the basin is characterized by numerous evaporite diapirs. (4) Arctic coastal plain province is along the northwest edge of the Arctic Islands, bordering the Arctic Ocean in the position of the present continental shelf. It contains late Tertiary and Ple stocene sedimentary rocks. The Arctic Islands sedimentary basin has all the necessary geologic elements conducive to the entrapment of hydrocarbons in prolific quantities. There is a very thick, lithologically varied, stratigraphic succession representing every geologic period with adequate source beds, and abundant potential reservoir rocks. There is an abundance of diversified traps--large anticlines, reefs, evaporite domes, faulted homoclines, unconformities, and facies changes. Hydrocarbon shows, including sands, seeps, stain, and bitumen are present in a large area and in a wide range of ages. The Arctic Islands is an area in which hydrocarbons shows have indicated outstanding potential for the discovery of large oil fields. End_of_Article - Last_Page 2478------------

Evidence for Evaporite Diapirism in Northeastern Mexico: GEOLOGICAL NOTES

Several authors have reported intrusive gypsum in northeastern Mexico. Salt diapirism also has been inferred. Recent evidence from cores indicates that the complete sequence of evaporites behaved as a mobile unit in response to tight folding. The salt (Jurassic) has a steeply dipping planar fabric in both Sierra del Fraile, where gypsum diapirism already has been documented, and in Sierra de Minas Viejas. The salt in Sierra de Minas Viejas is abnormally thick. It seems reasonable to conclude on this basis that Minas Viejas is also a true diapir. Because of the large scale of the mobility, however, it is of no great consequence whether or not actual piercement has occurred.

Cuban Evaporite Diapirs: ABSTRACT

At least five rock sequences occur in central Cuba: (1) an igneous-metamorphic basement of unknown age; (2) a Jurassic evaporite-redbed sequence; (3) a Portlandian-Turonian orthogeosynclinal suite; (4) a Turonian-Eocene series; and (5) a post-orogenic Eocene-Recent sedimentary cover. The Portlandian-Turonian orthogeosynclinal suite includes, from south to north, four facies belts: a eugeosynclinal suite, a transitional suite associated with the median welt, miogeosynclinal carbonates, and platform carbonates. During mid-Cretaceous and Eocene orogenies, the eugeosyncline was thrust northward, overriding the median welt and, locally, the miogeosyncline. The latter is deformed much more severely than the other belts. Only four evaporite diapirs are known in north Cuba. These lie north of the median welt in Matanzas and Camaguey Provinces, and are localized by deep faults. Two diapirs penetrate the eugeosynclinal rocks at or close to the surface. Exotic blocks in these two diapirs include fragments of eugeosynclinal, median welt, and miogeosynclinal facies. End_Page 350------------------------------ The following hypothesis is proposed to explain these facts: during orogenesis, the miogeosynclinal carbonates were detached from the underlying evaporites, crushed between the median welt and platform, and overridden locally by the eugeosyncline. After middle Eocene time, the diapirs intruded along deep faults and reached the surface with fragments from the overridden facies belts. The latest diapiric movements are post-Miocene. The small number of diapirs probably is related to the great competence of the thick, overlying post-evaporite carbonate section. End_of_Article - Last_Page 351------------