摘要:

AbstractTwo unusual subaerial exposure horizons containing fibrous columnar calcite crystals are described from the (early Chadian) Lower Carboniferous of Portishead, near Bristol in southwest Britain. The lower horizon overlies the Courceyan Black Rock Limestone (mid‐ramp facies) and is separated from the upper horizon by the Sub‐Oolite Bed and is overlain by the Chadian Gully Oolite (both are inner ramp deposits).Regionally the Portishead Palaeosol Beds are interpreted as forming part of extensive emergent surfaces which developed along the southern margin of the Welsh–Brabant Massif. They correlate with similar subaerial exposure horizons in Belgium and southern Germany, and may be the product of a proposed major eustatic sea level fall at the end of the Cour

ISSN:0072-1050    

DOI:10.1002/gj.3350250102

出版商:John Wiley&Sons Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper determines, using simple mathematical models, maps of strain fields and foliation trajectories in the neighbourhood of plutonic bodies intruded into a region before, during, and after a lateral compression. The analyses reveal contrasting features for the three cases, which may be useful in distinguishing pre‐, syn‐, and post‐tectonic plutons in coaxially deformed terranes.The theoretically calibrated strain variation curve, along the regional shortening direction, around a pretectonic, rigid plutonic body shows a zone of strain increase (relative to the far‐field strain), whereas that around a syntectonic pluton shows a zone of strain decrease along with a zone of strain increase. The foliations deflect outward from a pretectonic pluton, but they bend towards a syntectonic pluton. The analysis also reveals that syntectonic plutons are likely to be elliptical in plan with axial ratio directly dependent on the ratio of the pluton's stress to the tectonic stress.Tectonic foliations deflect away from post‐tectonic plutons. However, the foliated area around a post‐tectonic pluton is systematically divided into two sets of zones one characterized by foliations showing compressional features, the other showing extension

ISSN:0072-1050    

DOI:10.1002/gj.3350250103

出版商:John Wiley&Sons Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe Moel‐y‐Golfa Andesite is a discordant intrusive body of porphyritic pyroxene andesite, 1 km across and at least 200 m thick. Textural variation defines a central facies and a marginal facies, the latter displaying well‐formed lobes, tubes, and pillows. The vertically stacked lobes, brecciated tubes, and elongate pillows of andesite intrude and locally enclose enclaves of altered host sediment and are cut by steeply dipping slide scars. The host sediments are locally strongly silicified and cut by numerous, anastomosed vertical and subvertical fissures. Fissures are filled by disrupted host sediment and fragments of brecciated andesite. The formation and filling of each fissure system was probably concomitant with the brecciation of an intrusive magma lobe. The complex relationship of igneous and sedimentary material indicates that the Moel‐y‐Golfa Andesite was emplaced into the host sediments whilst they were unconsolidated or only partly

ISSN:0072-1050    

DOI:10.1002/gj.3350250104

出版商:John Wiley&Sons Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractA sedimentological study of the lower Quaternary sediments in southern Shandong Province suggests that they were derived from a northern highland area of Archaean gneiss and Palaeozoic sediments. Diamond‐bearing kimberlites, intruded during the Ordovician, occur in the highland area and are a possible source of diamonds found in the Quaternary sediments. A warm and humid climate prevailed at the beginning of the Quaternary and braided rivers carried gravel and sand southeast towards the Yellow Sea. Cooler and drier conditions in Q2 times reconcentrated diamonds from the underlying Q1 gravels. Post‐Q2 faulting deflected the drainage to the south and subsequent erosion left only small remnants of diamondiferous Q2 gravel. A study of diamond shape characteristics suggests that the diamonds in the Quaternary sediments were derived from the known kimberlites to the north, although the possibility of undiscovered kimberlites occurring beneath the Quaternary sediments cannot be ruled

ISSN:0072-1050    

DOI:10.1002/gj.3350250105

出版商:John Wiley&Sons Ltd    

年代:1990

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350250106

出版商:John Wiley&Sons Ltd    

年代:1990

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350250108

出版商:John Wiley&Sons Ltd    

年代:1990

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350250101

出版商:John Wiley&Sons Ltd    

年代:1990

数据来源: WILEY