The Geology of North-East Durham and South-East Northumberland
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THE GEOLOGY OF NORTH-EAST DURHAM AND SOUTH-EAST NORTHUMBERLAND. By DAVID WOOLACOTT, D.Sc., F.G.S. Read May 3rd, 1912. CONTENTS. PAGE I.-TABLE OF STRATA 87 II.-THE COAL MEASURES 88 II I.-IGNEOUS DYKES 9 1 I V.-THE PERMIAN SERIES 92 (a) The Yellow Sands . 93 (b) The Marl Slate . 94 (c) The Magnesian Limestone 94- V.-THE HIATUS 101 Vr.-THE GLACIAL A:;D POST-GLACIAL DEPOSITS. 101 This Paper was prepared for the use of the Members of the Association attending the Whitsuntide Excursion of 1912, and was issued as a Pamphlet. It is now reprinted with a few slight alterations. I.-TABLE OF STRATA. HE Strata which occur in this district belong to the following T divisions in descending order:- S U bm e r ged forest (Whitburn Bay). Deposits of sand and gravel with marine shells (found up to the 150 ft. contour). RECENT A:;D GLACIAL.· ~ Mounds of sand and gravel. Kaims, De r osits of sand, leafy clay and re-asserted boulder clay. lThe stony boulder clay. UPPER PERMIA:; OR Middlesbrough red beds with salt, gypsum THURINGIAN (Der anhydrite and thin fossi liferous magnesian Zechstein). limestonet 300 ft. The Magnesian Limestone up to 800 ft. (Kupferschiefer) The :\1arl Slate 3 ft. MlIllJLE PER~lIAN OR SAXO:<lIAN. The Yellow Sands 0 to ISO ft. LOWER P~:RMIA)l OR ARTINSKIA:; The Yellow Sands? UPPER COAL MEASURES (Not represented.) • The greatest thickness 0' these superficial depesits proved by borings In the Northumberland and Durham Coalfield is 233 ft. at Newton Hall, l'ramwellgate, ncar Durham. t Not seen in North-East Durham; only occurs in the South of Durham. 88 DAVID WOOLACOTT ON THE GEOLOGY OF MIDDLE COAL MEASURES A series of coal seams, sandstones, shales, OR WESTPHALIAN underclays, mussel-bands 1,500 ft. FOur dykes occur in the district.* The Tyne mouth, Hartley and Collywell exposed on IGNEOUS ROCKS. the coast of South-East Northumberland, and j one-the Hebburn-is found in the collieries of North-East Durham (e.g., Whitburn). II.-THE COAL MEASURES. The Coal Measures of Northumberland and Durham lie in the form of a syncline, and as the centre of the basin occurs in the neighbourhood of Sunderland, only the higher portions of these beds occur in the district under our notice. They belong entirely to the Middle Coal Measures (Westphalian), and contain the thickest and most productive seams. In South-Eastern Northumberland and in Durham, west of the Permian escarpment, they are buried beneath a variable thickness of superficial deposits, and are only exposed along the rivers and streams or where the thicker masses of sandstone rise to the sur face. These latter outcrops generally have villages perched upon them. Along the coast of South-Eastern Northumberland, between Tynemouth and Seaton Sluice, they can be examined in an almost continuous section.t They are here seen to' consist of a series of yellowish, brownish, reddish, or greyish-coloured sandstones and grits, often occurring in wedge-shaped masses, dark grey and blackish bituminous shales.j coal seams, underclays, and mussel bands. The mussel-bands are highly ferruginous,§ and other layers and nodules of clay ironstone occur. The seams exposed are the Low Main, Bensharn, Yard and Grey, but in the collieries lower seams-the Harvey (Beaumont) and the Brockwell-and a higher seam-the High main-are worked. Mr. S. R. Haselhurst has lately drawn up a correlation of the beds exposed in the Tyne mouth to Seaton Sluice sections II as follows :- SECTION EXPOSED FROM TYNEMOUTH TO SEATON SLUICE. HIGH MAIN Grey Shales. BLACK Red Sandstone. MIDDENS Yellow Shales with Micaceous Sandstone. TO GREY SEAM. SPANiSH Yellow Shales. ST. MARY'S BATTERY. Red and Brown Sandstones. IsLAND TO Yellow Shales. } CRAG Sandstones. POINT. * See note on page 92 regarding discovery of two new dykes. t A part of this section is shown in detail in Plate 27. Fig. I. t A shale exposed just north of St. Mary's Island has cone-in-cone structure developed in it. § One of these exposed at Whitley was worked as ironstone seme years ago. II University oj Durham. Phil. Soc., vol. iv, Pt. 3, p. 162. PROC. GEOL. Assoc., VOL. XXIV. PLATE 2 I. [Photo by 5. R. Haselhurst. A.-PSEliDO-STROMATlSM PRODUCED BY THE SHEARING OF SANDY SHALES BENEATH A MASSIVE SANDSTONE IN THE COAL MEASURES, WHITLEY. [Photo by D. Woolacott. B.-MAGNESIAN LIMESTONE, TROW ROCKS, SOUTH SHIELDS. Disturbed beds lying along the Major thrust plane between the Lower Bedded Limestone and the Brecciated Beds of the Middle Division (see page II). To face page 88. NORTH-EAST DURHAM AND SOUTH-EAST NORTHUMBERLAND 89 YARD SEAM. SHARPNESS P T. , AND C ULLERCOATS. Yellow Shales. Fire Clay. Brown Sand stone. TABLE ROCKS BENSHAM. SOUTHWARDS TOW.~RDS Black Shales and Sandstone. } CULLERCOATS. Red Sandstone. T able Rock Sandstone. Shales. Mussel-band. Shale. NORTH OF Sand stone. TABLE Shale. ROCKS. Sandstone. Shale. Black and Red Shales. Low MAI N. SMlTGGLERS' CAVJ':, SOUTH of Black Shales. CUL L ERCOA T S. Fire-day. The Series has been highly faulted by a number of cast and west faults which, throwing both to the north and south, often repeat the beds. The chief of these faults are the Brierdene "Dyke," which, with a downthrow to the north of some I 80 ft., shifts the outcrop of the High Main seam about two miles and cuts the coast in Whitley Bay to the south of St. Mary's Island, and the Ninety Fathom" Dyke," which is exposed on the coast to the south of Cullercoats Bay. It here throws the Yellow Sands, Marl Slate and Magnesi an Limestone against the Coal Measures in a most interesting section. This latter fault has a throw in the Coal Measures of some 600 to 1,000 ft., and is traceable from the coast to the south of Hexham, a distance of some twenty miles. Not only have these beds been faulted, but considerable hori zontal movements have taken place in them, so that the softer beds (shales and sandy shales) have been considerably disturbed (fractured, tilted and folded), and certain of the beds have had secondary structures developed in them, produced by the shear ing of the mass. These simulate flow-structure and false-bedding, and have lately been carefully examined by Mr. S. R. Haselhurst, who has shown that the strata between Seaton Sluice and Tynernouth have had" pseudo-stromatism" extensively developed in them.* Professor Lebour and Dr. Smythe have shown that one of the most mark ed of these horizontal movem ent s occurs at Whitley to the north of the Table Rock sandstone. H ere a series of shales and sandstones containing a mussel-band has been extensively disturbed by the movement. of a th ick compact sand stone bed over them, which has ploughed into them, faulting, folding and slickensiding them. t There is evidence to prove that these thrust-movements occurr ed after the post-Permian mo vemen t of the Ninety Fat hom Dyke, and they ap pear to be ... l} niv . Durham, P IJ il . Soc.. vel. iv , Pt . 3, page 167. t ..On a Case of Thrus t and Unconformity in the Coal Mea sures of Northumberland.' Qua rt. jaurn. Geol, Soc., volv lxii (1906), P. 530. PROe. GEOL. Assoc., VOL. XXIV, PART 2, 1913.J 7 9° DAVID WOOLACOTT ON THE GEOLOGY OF phenomena produced in the Coal Measures at the same time and by the same forces as the horizontal movements which will be shown to have occurred so extensively in the Permian. South of the Tyne the Coal Measures are no longer exposed on the coast; they sink beneath the Permian deposits. To the west of the Permian escarpment they rise to the surface, but are generally covered by a thick layer of superficial deposits. They lie beneath the east of Durham in a synclinal form, whose centre lies beneath Sunderland district; the dips within the area towards the centre of the basin being very low. This syncline is a dis tinct accentuation of the Coal Measure basin of Northumberland and Durham-a basin within a basin-hence the highest Coal Measures of the two northern counties possibly occur beneath the Magnesian Limestone in the east of Durham. The Hutton Seam is some 1,400 ft. beneath the base of the Permian at Sunderland, some 458 ft. at Marsden Colliery, four miles to the north, and 833 ft. at Horden Colliery, twelve miles to the south; this gives a small measure of the extensive denudation that must have occurred before the deposition of the Permian on the Coal Measures.* Several of the faults in the Coal Measures proved in the colliery workings do not cut the Permian strata above them, while some have a considerably smaller throw in the higher than the lower series. The Ninety Fathom "Dyke" is of the latter class. The major period of faulting was pre-Permian, although vertical movements of considerable displacement have occurred since Permian times. One of the most interesting features of the Coal Measures of this area are the beds-often highly ferruginous-containing remains of fresh or brackish water lamellibranchs. These bands, often entirely composed of Carbonicula aquilina, have been called mussel or anthracosia bands,t and are useful for purposes of correlation, but sufficient attention has not yet been paid to them. There appear to be six or seven such beds, those above the High Main and Low Main seams being most persistent. Besides these bands other layers with fossil mollusca occur. One of these strata that outcrops on the north bank of the Wear opposite Claxheugh, east of the fault that crosses the river, consists of a dark grey fissile shale containing three or four bands of clay ironstone.