Tertiary Beds Research Articles

Reconnaissance geophysical studies of the geothermal system in southern Raft River Valley, Idaho

Gravity, aeromagnetic, and telluric current surveys in the southern Raft River have been used to infer the structure and the general lithology underlying the valley. The gravity data indicate the approximate thickness of the Cenozoic rocks and location of the larger normal faults, and the aeromagnetic data indicate the extent of the major Cenozoic volcanic units. The relative ellipse area contour map compiled from the telluric current survey generally conforms to the gravity map except for lower values in the area of the geothermal system. An area of low apparent resistivity values defined by the audiomagnetotelluric (AMT) survey appears to outline the extent of the geothermal reservoir even though the reservoir is deeper than the penetration of the survey. Self‐potential anomalies relate to near surface hydrology. The Raft River Valley is underlain by about 2 km of Cenozoic rock, most of which is Tertiary sediments of the Salt Lake formation. On the west side of the valley the Tertiary rocks appear to be separated from the underlying Precambrian basement by a low angle fault along which the Tertiary rocks have slid off a buried basement dome. Subsequent normal faults displace both the basement surface and the Tertiary beds. The geothermal system occurs where these north‐trending faults intersect a poorly understood northeast‐trending zone that may be a basement shear zone. Apparently deep circulating water at a temperature of about 150°C rises in the area of this intersection and then spreads laterally in porous zones near the base of the Tertiary rocks to form the geothermal reservoir. Upward leakage from the reservoir produces shallower effects that were measured by the AMT survey.

Reservoir and Source-Bed History of Great Valley, California

The application of geochemical concepts and relations of porosity-permeability-depth helps focus exploratory efforts on the favorable parts of trends in partially explored basins. Porosity data from 165 producing ranging in age from Late Cretaceous to Pleistocene show that the best reservoirs lose porosity at a rate of approximately 1.52% per 1,000 ft (0.46% per 100 m) of burial. Reservoirs on the large-amplitude folds on the west side of the San Joaquin Valley have a more rapid porosity loss with depth. A crossplot of porosity-permeability indicates a best reservoir relation of a tenfold decrease in permeability for each decrease of seven porosity units. Within the Great Valley, four major depocenters are definable by use of isopach data. Each has had a different source-bed history. Continental margin sedimentary rocks of Late Cretaceous age contain organic material that generally is structured and is believed to be the source of gas in the Sacramento Valley. Although a Tertiary depocenter exists in the Delta area, subsidence has failed to place Paleocene and Eocene source beds into the thermal zone thought to be required for oil and gas generation. Gas trapped in Paleocene and Eocene reservoirs, therefore, must have migrated from more deeply buried Cretaceous source beds. Tertiary beds in the Buttonwillow and Tejon depocenters in the southern San Joaquin Valley contain large amounts of sapropelic organic material which is believed to be the source of the oil and gas found there. Source beds in the Buttonwillow depocenter have been in the thermal zone for generation for only about 5 m.y. In marked contrast, source beds in the Tejon depocenter started subsiding into the thermal zone more than 15 m.y. ago. Explorationists who recognize the best reservoirs and relate them to source, migration, and trap parameters in undrilled areas will be successful in finding future reserves of oil and gas and may avoid some unprofitable geologic successes that are economic failures.

Early maturation of organic matter and genesis of hydrocarbons as a result of heat from a shallow piercement salt dome

The Primrose Prospect lies 48 km east of Sable Island on the Scotian Shelf below 80 km of water. The subsurface geology is characterized by the presence of Jurassic salt that has pierced the early Cretaceous sediments and uplifted late Cretaceous and early Tertiary beds to provide localized structural closure, shale compaction, and anomalously high heat gradients in the younger sediments overlying the salt mass. The reservoir rocks interbedded with the compacted shales contain wet gas, condensate, and 31° API oil. The organic matter in these shales, which consists essentially of amorphous material, has undergone thermal alteration and maturation at a very shallow depth, a condition not apparent in coeval beds elsewhere in the area. This localized alteration of the organic matter is considered to have occurred in response to the thermal and pressure effects of the underlying halokinetic structure and could have resulted in the genesis of the mature hydrocarbons.

K-Ar and fission-track dating of ash partings in coal beds from the Kenai Peninsula, Alaska: A revised age for the Homerian Stage–Clamgulchian Stage boundary

K-Ar and fission-track mineral ages determined from ash partings in upper Tertiary coal beds from the Kenai Peninsula, Alaska, establish an age of approximately 8 m.y. (late Miocene) for the Homerian Stage–Clamgulchian Stage boundary at the type section for the Homerian Stage and a late Miocene age for the early part of the Clamgulchian Stage. Our data do not support the concept that there is an “Arcto-Tertiary geoflora” which is different in age from similar floras at lower latitudes. This study demonstrates, for the first time, that volcanic ash partings contained wholly within coals are valuable for radiometric dating and stratigraphic correlation.

Cretaceous and lower Tertiary of Seine-Maritime, France: a guide to key localities

Representative sections in the Cretaceous and lower Tertiary sediments of Seine-Maritime, northern France, are described and a comparison made with the English south coast outcrops. In the Bec de Caux Aptian to lower Albian sandy and pebbly deposits, somewhat comparable to the Isle of Wight succession, rest non-sequentially upon Kimeridge Clay. The middle Albian marginal pebbly loams and local phosphatic nodule beds represent a less complete sequence than the Gault Clay of the Isle of Wight. The Gault farther east at Bully, Pays de Bray, shows lower Albian Douvilleiceras mammillatum Zone and basal middle Albian in clay facies. The upper Albian is represented within the Gault and Gaize of the Bec de Caux, corresponding with the highest Gault Clay and Upper Greensand of the Isle of Wight. Unlike the Cenomanian Lower Chalk of the Isle of Wight, the Craie Glauconieuse and Craie de Rouen contain conspicuous flint courses, reminiscent of higher horizons in south-west England. Palaeogene sediments rest unconformably on a locally irregular surface of mainly Santonian-Campanian Chalk. Surviving outcrops occur as scattered outliers standing above the level of the Chalk downland and as extensive sheets preserved in synclinal downwarps, especially north and east of Yvetot. Inland exposures are few but the large Varengeville outlier, west of Dieppe, shows fine cliff-sections. A marine transgressive sequence of early Sparnacian (lower Eocene) age, comparable to the Woolwich Bottom Bed of south-east England, passes up into regressive brackish and partly non-marine beds similar to the Woolwich Shell Beds of the Newhaven outlier but with greater lateral variation. Higher deposits, collectively termed Formation de Varengeville, include thick late Sparnacian marine sands strikingly akin to the Oldhaven Beds of Kent and a sandy Ypresian clay similar to the London Clay facies of Bognor Regis. Younger Tertiary beds are represented by small local outliers of marine sands and clays of (?) Helvetian date in the south and west of the Bec de Caux.

Petroleum Potential of Korean Offshore: ABSTRACT

Major offshore areas widely developed around the Korean Peninsula are in the Yellow Sea off the west coast, East China Sea off the south coast, and in narrow belts in the Japan Sea off the east coast. Geologic and geophysical surveys in these Korean offshore areas have been carried out since 1966 by the Geological and Mineral Institute of Korea (GMIK) and since 1969 by oil companies who obtained concessions on seven blocks from the Korean government. The GMIK has conducted reconnaissance seismic and magnetic surveys for general study of submarine geology. Oil companies have conducted preliminary and detail seismic, magnetic, and gravimetric surveys. Wildcat drilling was started in 1972 and four holes were drilled by three oil companies. Submarine geology of the offshore area can be summarized as follows. The Yellow Sea area has Tertiary sedimentary rocks with thicknesses of more than 1,000 m with several basin structures separated by uplifted basement or intrusive igneous rocks. The East China Sea and southern part of Japan Sea have Tertiary sedimentary rocks with thicknesses of more than 2,000 m with northeast-southwest zonal structure and folded and faulted structures in Tertiary beds. In the Japan Sea area Tertiary sedimentary rock in Pohang offshore area is less than 1,000 m thick and extends northward almost 100 km. Sedimentary rocks, more than 3,000 m thick and of probable Cenozoic age, are present on the continental slope. Petroleum potentials in offshore Tertiary strata must be studied further before final conclusions can be reached. Even so, rocks with high-organic content occur in the Yellow Sea area, and in the East China Sea and the Japan Sea areas good reservoir rock and potential structures for hydrocarbon accumulation have been detected. Further drilling work is recommended to discover hydrocarbons and to reevaluate the submarine geology and structure. End_of_Article - Last_Page 1445------------

Hydrocarbon Potential of Coastal Basins of Peru: ABSTRACT

Along the coast of Peru, the shelf between the Andes Mountains and the 100-fm isobath is narrow, about 100 km wide in a few places. Between lat. 6 and 14°S nearly all of it is a wide offshore shelf. This shelf has been the site of marine deposition throughout the Tertiary. Basement highs and irregularities define six subbasins. In the north, the mainly offshore Progreso basin extends into Peru from the Gulf of Guayaquil. It is filled with upper Tertiary shales, sands, and conglomerates with a maximum thickness of 6,000 m. The small abandoned Zorritos field was in this basin and some undeveloped oil and gas have been discovered recently. The basin has an estimated potential of 350 million bbl. The Talara basin, which has produced over 800 million bbl, is both onshore and offshore. Sedimentary rocks consist of Upper Cretaceous and lower Tertiary silicate clastic rocks with a maximum thickness of 8,000 m, but nearly all production comes from Eocene deltaic, fluvial, and turbidite sandstones. Intense block faulting, gravity sliding, and submarine slumping complicate development operations. The onshore part does not have large undiscovered potential, but the offshore is estimated to have a potential of one billion bbl. The Sechura basin is between the Andes and a discontinuous chain of low coastal mountains which separates it from the Talara basin. It is mostly onshore but extends southward onto the offshore. Up to 3,000 m of marine, brackish, and nonmarine sedimentary rocks, i cluding diatomite and phosphatic and tuffaceous elements, fill the basin. Most of the strata are upper Tertiary, but lower Tertiary and Cretaceous beds also are present. In the 1950s, 28 wildcat wells were drilled with the discovery of moderate reserves of gas. A total potential for the basin is estimated to be 100 million bbl. The Salaverry basin is the largest of the coastal basins. It is 500 km long and up to 100 km wide, is entirely offshore, and extends to within 100 km of Lima. It contains up to 3,000 m of Tertiary marine shales, silts, and calcareous sedimentary rocks with sandstones at the base. Two wells have been drilled in this basin and the estimated potential for the basin is 500 million bbl. The Pisco basin begins about 100 km south of Lima in the offshore, but southward splits into onshore and offshore parts. Up to 2,000 m of lower and upper Tertiary sedimentary rocks are present. The lower Tertiary is composed of conglomerates, sandstones, and calcareous shales. The upper Tertiary consists of sediments similar to those of the upper Tertiary in the Sechura basin. One well has been drilled in t e basin. The estimated potential for the basin is 100 million bbl. The Moquegua basin is a narrow onshore basin between the Andes and the coastal chain of mountains. Marine sediments are found only in the northern part and are of insufficient volume to have significant potential. The total potential of the coastal basins is estimated to be about two billion bbl. End_of_Article - Last_Page 1460------------

Sonneratioxylon from the Tertiary beds of Mohgaonkalan, M.P., India

A piece of fossil wood measuring 5 x 3·5cm from the Deccan Intertrappean Series was collected by one of US (T.S.M.) at Mohgaonkalan, Dist. Chhindwara, M.P., India. Anatomy of it showed strong resemblance with the anatomy of stem in the genus Sonneratia L. (family-Sonneratiaceae), to which it in all probability belongs and, therefore, has been named as Sonneratioxylon intertrappeum sp. novo A fossil fungus was obtained from this wood and it has been described separately elsewhere (Biradar & Mahabale, 1972).

Rice Valley Outlier—New Sequence of Cretaceous-Paleocene Strata in Northern Coast Ranges, California

Lower Cretaceous through Paleocene strata are exposed in a small outlier within the Eastern Belt of the Franciscan Complex (Berkland and others, 1972) near Rice Valley in the northern Coast Range of California. This outlier, and three others known in the region, are synclinally folded, downfaulted remnants of an upper thrust plate of Great Valley sequence rocks. The Rice Valley synclinal remnant is separated by faults from surrounding rocks of the Franciscan Complex. Two belts of serpentinized dunite and harzburgite, converging toward the south, border the Rice Valley sequence on the east, west, and south. The northern border is a reverse fault that brings blueschist facies metaclastic rocks of the Eastern Belt over unmetamorphosed, mildly deformed strata of the Rice Valley sequence. Basal beds of the sequence are Lower Cretaceous (Hauterivian) sandstone, shale, and limestone that are steeply tilted and faulted against the ultramafic rocks. About 3,500 ft of Cretaceous marine strata are unconformably overlain by more than 1,150 ft of shallow-marine lower Tertiary beds. Fossils are generally scarce throughout the sequence, but are abundant in limestone-rich horizons of Hauterivian and Cenomanian age as well as in a calcareous sandstone bed with more than 30 genera of late Paleocene (Meganos Stage) invertebrates. Special significance is attached to a 150-ft-thick bed of polished-pebble conglomerate which underlies the Paleocene fossils. The conglomerate is composed chiefly of Franciscan detritus, with pebbles of red radiolarian chert, lawsonitic metagraywacke, and serpentinite. This is the earliest known appearance of coarse Franciscan debris in an upper plate (Great Valley sequence) environment. Time restrictions on underthrusting and isostatic rebound of deeply subducted Franciscan rocks imply rapid rates of uplift and denudation during early Paleocene time. The suggested rate of 240 cm per 1,000 yrs is comparable with the highest known rates in the world today.

Geology and Future Petroleum Potential, Ventura Basin, California: ABSTRACT

The Ventura basin is the western part of Transverse Ranges geomorphic province. It is a complex, highly folded and faulted synclinorium. Maximum thickness of sediments is 67,000 ft. The ages of formations range from Cretaceous through Holocene. In areal extent--including the onshore, the Santa Barbara Channel and the continental shelf--it is approximately 215 mi long, and averages 30 mi wide. Total volume of sediments is estimated at 40,000 cu mi. Despite its long history as an oil-producing basin, exploration of its ultimate potential is far from complete. Much of the thick sedimentary section has not been penetrated except in limited areas on the basin margins. Large volumes of marine lower Tertiary and Upper Cretaceous rocks are completely unexplored. Evaluation of the known profilic structures has rarely been carried below depths of 15,000 ft. In areas where the upper Tertiary beds are best developed, the obvious surface features have been drilled, and most are productive. Stratigraphic elements of entrapment occur in virtually all accumulations in the Ventura basin. Several primary stratigraphic accumulations are productive. It is believed that the greatest future potential of the basin lies in stratigraphic accumulations, and in the same general areas and measures which have been most productive to date. Estimates of 20-30 billion bbl of remaining oil in place do not appear unreasonable. Exploration for this potential awaits favorable future breakthroughs in economic, technologic, and political developments. End_of_Article - Last_Page 434------------

Two species of Foraminifera of the genus Turrilina with different wall structure

Two species of the foraminiferal genus Turrilina Andreae, 1844, occurring in the Tertiary beds of Denmark and Holland, can be distinguished by their wall structure only. In consequence it is recommended that the wall structure as a systematic character may in this and similar cases be of specific value only.

Exploration on Continental Shelf Off Northwest Australia: ABSTRACT

Exploration of a 144,000-sq mi rank wildcat area in offshore northwestern Australia began in 1964 with analog seismic surveys. Each year additional surveys have been carried out with a steady improvement in data quality due to advantage being taken of technological advances of the industry. Interpretation of these data and incorporation of available drilling results have permitted structural and depositional models to be rationalized for post-Paleozoic time-rock sequences. Improvements in drilling technology have allowed locations to be sited in greater water depths confirming depositional and structural models. End_Page 637------------------------------ To overcome seismic data problems associated with the high-speed Tertiary section, navigational problems due to the size of the area, drilling problems associated with geo-pressured shales and the highly porous Tertiary beds, new techniques constantly were required and introduced. To integrate the interpretation of the large volume of data and to apply the maximum amount of geologic rationalization require the cooperation and mutual support of competent geologists and geophysicists. Large areas to be mapped and steadily increasing volume of data from this area required the utilization of computer-assisted mapping. By mid-1971 approximately 40,000 mi of seismic data were in the files. At the same time wells 11 (Scott Reef No. 1) and 12 (North Rankin No. 1) were drilling and located what promise to be commercial accumulations of hydrocarbons. However, feasibility studies still are being evaluated and step-out wells have yet to be drilled. Since completion of these wells, other wildcats have been drilled resulting in several discoveries. Future potential in the area looks very bright with source, reservoir, and cap rocks in Triassic, Jurassic, and Cretaceous rocks. The potential of the Paleozoic section is as yet virtually unknown. End_of_Article - Last_Page 638------------

Geologic Outline and Oil Fields of Sergipe Basin, Brazil

In the Sergipe basin of northeastern Brazil a Lower Cretaceous unconformity marks a change in general environment and tectonic style. Below this unconformity, Carboniferous to Lower Cretaceous beds are nonmarine, whereas the overlying Lower Cretaceous to Tertiary beds are dominantly marine. Intense normal faulting tectonic activity preceding the unconformity resulted in uplift and erosion which exposed Precambrian rocks in an area north of Aracaju while, in adjacent grabens, thick wedges of syntectonic conglomerates were deposited locally over older sediments. Irregularities on this unconformable surface were filled by the Carmopolis conglomerate and coarse sandstone member of the Muribeca Formation; the more extensive overlying Ibura Member evaporites of the same formati n also covered the areas where basement was still exposed. Neo-Cretaceous tectonism is characterized by small-scale faulting; the Riachuelo-Siririzinho and Vassouras-Carmopolis oil trends resulted from a combination of northwestward subsidence of basin-margin grabens and a regional southeastward tilting that started somewhat later. Oil production in this basin comes from the Carmopolis, Siririzinho, and Riachuelo fields, mostly from the Carmopolis Member. Some oil is produced also from Lower Cretaceous reservoirs in contact with the unconformity. Depth range of all reservoirs is 400-800 m. Favorable conditions for oil accumulation are the result of adequate structural evolution during Late Cretaceous time, presence of evaporites and probable oil source organic shales at the top of the reservoirs, and younger unconformities not reaching down to the trap. Locally, lateral permeability barriers or reservoir pinchouts complement the structural trap closure. The oil is of mixed base ranging from 24 to 30.5° API. Cumulative production to December 31, 1969, with Siririzinho and Riachuelo fields still being developed, was 23.65 × 106 bbl of oil. This production comes from 205 completed wells drilled in a 400-m grid.

Fossil woods from the tertiary of Burma

Fossil woods representing the genera Dipterocarpus and Shorea-Pentacme of Dipterocarpaceae, Gluta-Melanorrhoea of Anacardiaceae, Sterculia of Sterculiaceae, Acacia, Cynometra, Cassia and Afzelia-Intsia of Leguminosae, Lagerstroemia of Lythraceae, and a dicot wood of uncertain affinities have been investigated from the Tertiary beds of Burma. These woods are noteworthy owing to their fine structural preservation and from the standpoint of their palaeogeographical distribution. Modern comparable forms of these fossils are still found in the forests of Burma indicating thereby that there has been no appreciable change in the climatic conditions of this region since the existence of this flora, which flourished under the tropical, mesophytic conditions. An attempt has also been made to assign a precise age to the woods based on the floral assemblage.

Pre-hawera geology of the Kaka District, North-West Nelson

Abstract In the Kaka District the Cretaceous Separation Point Granite is unconformably overlain by Lower Tertiary sediments belonging to the Westhaven Group which is divided into four formations. The oldest formation, Motupipi, consisting of coal measures overlain by marine sands, is conformably overlain by algal limestone and sandstone of the Huia Formation. The Huia Formation is conformably overlain by massive fine-grained sediments of the Sherry River Formation which encloses a sequence of graded beds in the north, mapped as the Burmeister Formation. The contact of Lower Tertiary sediments and granite is depositional in the south, but in the north it is faulted along the Matariki Fault Zone. Faulting was preceded by folding of the Tertiary beds into two north-north-east trending folds, the Hope Anticline to the west and the Sherry Syncline to the east. Both the granite and Lower Tertiary rocks are unconformably overlain by non-marine beds belonging to the Tadmor Group. The Tadmor Group consists of the Upper Tertiary Glenhope Formation and the conformably overlying Lower Pleistocene Moutere Gravel. In the valleys a sequence of Upper Pleistocene aggradational gravels were deposited.

Geologic Outline and Oil Fields of Sergipe Basin, Brazil: ABSTRACT

In the Sergipe basin of northeastern Brazil a Lower Cretaceous unconformity marks a change in general depositional environment and tectonic style. Below this unconformity, Carboniferous to Lower Cretaceous beds are nonmarine, whereas the overlying Lower Cretaceous to Tertiary beds are dominantly marine. A period of intense normal faulting which preceded the unconformity resulted in an uplift which exposed Precambrian rocks in an area north of Aracaju, while in adjacent grabens thick wedges of syntectonic conglomerates were deposited locally over older sediments. Irregularities on this unconformable surface were filled by the Carmopolis Member of the Muribeca Formation, a conglomerate and coarse sandstone; the more extensive overlying Ibura Member evaporites of the same fo mation also covered the areas where basement was still exposed. Late Cretaceous tectonism is characterized by small-scale faulting; the Riachuelo-Siririzinho and Vassouras-Carmopolis oil trends resulted from a combination of northwestward subsidence of basin-margin grabens and a regional southeastward tilting that started somewhat later. Oil production in this basin from the Carmopolis, Siririzinho and Riachuelo fields comes mostly from the Carmopolis Member. Some oil is also produced from Lower Cretaceous reservoirs in contact with the unconformity. Depth range of all reservoirs is 400-800 m. Favorable conditions for oil accumulation are the result of adequate structural evolution during Late Cretaceous time, presence of evaporites and probable oil source organic shales at the top of the reservoirs, and younger unconformities not reaching down to the trap. Locally, lateral permeability barriers or reservoir pinchouts complement the structural trap closure. The oil is of mixed base ranging from 24 to 30.5° API. Cumulative production to December 31, 1969, with Siririzinho and Riachuelo fields still being developed, was 23.65 × 106 bbl of oil. This production comes from 205 completed wells drilled in a grid of 400 m. End_of_Article - Last_Page 353------------

Montmorillonite and zeolites in Mesozoic and Tertiary beds of southern England

Montmorillonite and zeolites in Mesozoic and Tertiary beds of southern England

Sedimentation and Thrusting of Late Mesozoic Rocks in the Coast Ranges near Clear Lake, California

South and southeast of Clear Lake, California, approximately 35,000 ft of clastic sedimentary strata of the Great Valley sequence ranging in age from Late Jurassic to Late Cretaceous crop out in irregular belts trending from northwest to southeast. Together with overthrust lower Tertiary beds, these rocks form a thrust complex that rests structurally upon the Franciscan assemblage of late Mesozoic age along the Soda Creek thrust and is overlain unconformably by late Cenozoic strata. A number of subsidiary thrusts, that are discordant to bedding, break the Great Valley sequence into at least three and possibly more than four successive thrust plates or slices. In all exposed cases, younger strata overlie older strata along the thrusts. The principal structurally intact stratigraphic components of the thrust complex are: A conformable Tithonian to Valanginian succession, 6900 ft, dominantly mudstone with 1600 ft of lithic sandstone and conglomerate in the upper part. Lower Cretaceous strata, 4500 ft, in part Aptian, dominantly thin-bedded quartzose sandstone and mterbedded mudstone. Three structurally isolated “mid”-Cretaceous successions, two of massive sandstone and one of mudstone, total of 5700 ft exposed. A conformable Upper Cretaceoussuccession, 17,500 ft, in large part Campanian, composed of five mappable units including massive sandstone (3700 ft), siltstonc (3600 ft), massive sandstone (4000 ft), mudstone (1000ft), and alternating sandstone and mudstone (5200 ft) in ascending order. A conformablemarine Paleocene and Eocene succession (5500 ft). The lithologic characteristics, petrologic variations, and paleocurrent indicators oi the strata in the Great Valley sequence near Clear Lake are comparable to those of correlative parts of the Great Valley sequence along the western side of the Sacramento Valley. Emplacement of the Great Valley sequence and the lower Tertiary beds above the Franciscan assemblage by regional thrusting was probably complete by Oligocene time from evidence elsewhere in the Northern Coast Ranges. The thrusts themselves and the strata of the thrust complex were later folded and cut by younger normal and reverse faults during Cenozoic deformations.

Fossil woods from the Tertiary of Hailakandi, Assam

Fossil woods representing Pometia of Sapindaceae, Mangifera of Anacardiaceae and Lagerstroemia of Lythraceae are described here from the Tertiary beds near Hailakandi, Assam. Petrified woods of Pometia and Lagerstroemia are known for the first time from India. These are of interest with regard to their palaeogeographical distribution.

The Paparoa Tectonic Zone

Abstract The Paparoa Tectonic Zone (new name) extends for 120 miles from the Alpine Fault at the Hokitika River to Kongahu Point, west Nelson, thus obliquely crossing the Paparoa Range. In the Late Tertiary and Quaternary, the zone was folded and fractured in a scissors movement, pivoting north-east of Greymouth, and up-faulting eastern blocks in the north and western ores in the south. A previous scissors movement along the same zone but in the opposite sense had occurred in late Cretaceous and early Tertiary times. The areas of down-faulting and thickest sedimentary fill are indicated by their coincidence with the highest ranks of the Brunner coals; and coarse breccias and conglomerates, extending outwards from the zone at several localities, were produced by vigorous faulting about uppermost Eocene times. Some Miocene faulting also occurred, perhaps accounting for the absence of lower Tertiary beds in the Kawhaka bore. Orogenic movements during the Miocene-Quaternary were accompanied by reverse faultin...