Geology of the eastern zone of the Sierra del Brezo (Palencia-Spain) BY J. Kanis Conten ts Pago Preface • 377 CHAPTER I Introduction 378 A. Nomenclature 379 CHAPTER II Geography and morphology 380 A. La Sierra del Brezo 380 B. Maps and aerial photographs 380 C. Morphology 381 1. Alluvial terraces 381 2. Piedmont alluvial plain 383 CHAPTER III Previous authors 385 CHAPTER IV Stratigraphy 389 A. Introduction 389 B. Devonian 392 1. Emsian 392 2. Couvinian 392 3. Prasnian 393 4. Other Devonian exposures 396 5. Final remarks 397 C. Carboniferous 398 1. Visean Upper and Lower Namurian 398 a. Radiolarian rock 398 b. Griotte 399 Caliza de e. Montaña 401 2. Namurian 403 3. Westphaliaii A 403 4. Westphalian B—C 405 5. Stephanian A 406 U. Mesozoic 407 CHAPTER V Paleontology 410 A. Introduction 410 B. Some notes paleontológica! 410 Page 1. Foramiiiifera 410 2. Radiolaria 412 3. Crinoidea 413 4. Pterinopeeteii rhytmieus Jackson 413 5. Palaeoxyii.s cf. appendieulata Lesqiikrkus 414 CHAPTER VI Paleobotany 416 A. Introduction 416 B. Westphalian IS—C 416 C. Stephanian A 417 CHAPTER VII Structure 423 A. Introduction 423 B. Structural units 423 1. Eastern of the Sierra del zone Brezo, sensu stricto 423 . a. Structure of the Devonian 423 b. Structure of the Caliza de Montaña series 426 .... 2. Namurian and Westphalian A structures 427 3. Structure of the Curavacas formation 428 4. Structures of the Carrion basin 428 5. Structure of the Mesozoic 429 C. Tectonic synthesis 430 D. The tectonic profiles 432 CHAPTER VIII Petrography . i 433 A. Introduction 433 B. Jntrusives of the investigated area 433 C. Conclusions 435 CHAPTER IX Mining 437 A. History of mining exploitation 437 The B. coal seams 437 The 1. reserves 437 C. The iron-bearing sandstone between Ventanilla and San Martin de los Herreros 438 1. and Origin composition of the ferruginous sandstone . 438 . 2. The reserves 439 1). The copper veins 439 1- Origin 440 Samenvatting 441 References 443 PREFACE The basis for this thesis is a field investigation in the northwestern part of the province Palencia (Spain) in the summers 1951—1954. The thesis is a summary of my Spanish paper, which will be published in about the Mallada" under a year by "Lucas Institute (Madrid) the auspices of the Consejo Superior de Investigaciones Científicas. In the thesis one will find a few figures, as well the appendices with edition. Spanish text, which were already prepared for the Spanish First of all I want to acknowledge the help of Prof. Dr. L. U. de Sitter, who showed his interest in all the problems which arose during the investig- ation and advice aid whose stimulating was a great to me. I am very grateful for the help and co-operation I had from the Consejo Superior de Investigaciones Científicas and from the President, Prof. 'Dr. San Miguel de la CaMARA and the Secretary, Prof. Dr. Bermudo Melóndez of the Instituto de Investigaciones Geológicas "Lucas Mallada". should like the N.V. Handels- I to express my gratitude to en Transport- maatschappij "Vulcaan" (Rotterdam) for their assistance during the fieldwork. felt Shirley whose My deeply thanks go to Dr. J. (Newcastle upon Tyne), kind assistance in the field and in the determination of the Devonian fauna contributed much to this thesis. I am indebted to Dr. C. L. Forbes (Cambridge) for identifying some of the well to Mr. R. H. Mr. J. A. Foraminifera, as my colleagues Wagner, van the Car- Hoeelaken and Mr. A. C. van Ginkel, who identified respectively boniferous plants, the Devonian brachiopods and the Lower Carboniferous Foraminifera, and to Mr. A. H. van der Veen for the many constructive discussions during the optical investigation of the dikes. I also appreciate the co-operation of the students A. Brants and B. N. Koopmans, during one summer fieldwork. Dr. John R. Gealy I want to express my gratitude to (Dallas, Texas) and Dr. R. van Vijoten (Mexico), who assisted me in correcting the English text. The illustrations and appendices were made by Miss C. Roest. Mr. J. Hoogendoorn handled the photograph material. Messrs. M. Deyn Sr. and Jr. made the thin sections. Mr. A. Verhoorn prepared some X-ray powder dia- Miss S. A. M. Vermeulen and Mrs. J. A. A. Zwaan—van Werkhoven grams. typed the manuscript. I am grateful to all for their co-operation. CHAPTER 1 INTRODUCTION The man for whom a rock is something valuable, will riches be surrounded by wherever he goes. PSLr Lac.ekkvkt "Lh-argen" In 1920 E. HERNáNDEZ-PACHEOo wrote a preface in a paper by Patac, intrincadas beginning: "La geología de la región asturiana es de lo más e interesantes de la Peninínsula Ibérica". Northwestern Palencia ,which I studied, is a part of this intricate and interesting "region asturiana". Much detailed investigation during the summers 1951—1954 was neces- to of the Devonian and Carboniferous sary come to a geological synthesis sediments underlying, this district of the province Palencia. and least Only by concientious study by mapping on a scale of at better into the and 1:25,000 can one get a insight geological structure history of the Asturian-Cantabric mountains. In recent years this type of investig- ation has been done by the "Servicio Geológico del Instituto de Estudios Asturianos" (cf. Lix)pjgs Libado 1954a) and by some geologists of the Geo- logical and Mineralogical Institute at Leiden, directed by Prof. Dr. L. U. de Sitter and under the auspices of the Consejo Superior de Investigaciones Científicas at Madrid. That detailed study yields valuable results is shown by the fact that Wagner (1955) could fix accurately the Asturian phase in the Barruelo de Santullán it to be than district, proving younger previously accepted (p. 175) : "La discordancia Astúrica de Barruelo es, sobre todo, notable por la oportuni- dad ofrece datar que para con gran precisión la fase orogénica aludida, ya que por el contacto inmediato entre el Estefaniense B—C discordante (paquete de la Peña Cilda) y las capas anteriormente plegadas del Estefaniense A (paquete de Barruelo) debe situarse al final del Estefaniense inferior". In the Sierra Brezo discussed del region, here, a very important post- Westphalian A phase, the Curavacas phase could be identified. Here the Curavacas B—C lies with formation, a conglomerate of Westphalian age, angular unconformity on Westphalian A or older rocks. This newly recognized orogenic phase is an important factor in the Paleozoic history of Palencia and no doubt it asserted its influence in Leon and Asturias also. The recognition of the Asturian and the Curavacas orogenic phases Paleozoic the opens new vistas for a structural interpretation of the of Asturian-Cantabric mountains. As the Devonian between Ventanilla and San Martin de los Herreros the rich in (on geological map indicated only as San Martin) is very fossils, a rather complete subdivision of the almost 600-metres-thick Devonian section 379 (cf. Appendix III) could be made. The beds range from Emsian to Famenian in age. In this section an economically valuable haematite-bearing sandstone was found; it is now being exploitated. In addition, the investigation contributes the Carrion basin to a better understanding of coal-containing (Stephanian A) which lies south of Cervera de Pisuerga and extends many tens of kilometres to the west. A. Nomenclature In describing the stratigraphy of an area misunderstandings can arise unless and defined. stratigraphie terms concepts are clearly In this paper I have used the terminology introduced by the American authors Kkumbein and Suoss (1951) and Pettijohn (1949). Among those are the terms and of and shelf concepts subgraywacke, orthoquartzite, epi- infraneritic, area, biohermal and biostromal limestone; their definitions of stratigraphie units has also been followed. The system of P. (1931, 1935) was used in the discussion of the intrusive rocks. CHAPTER II GEOGRAPHY AND MORPHOLOGY A. La Sierra del Brezo The central part of Spain, the Meseta Ibérica, is bordered in the north of by the Cordillera Cantábrica. The Paleozoic part the Asturian-Cantabric mountains is a Hercynian region, which is difficult to subdivide in physio- graphic units because of its involved geology and tectonics. One of the physiographic units is formed by the Sierra del Brezo, situated on the southern margin of the Asturian-Cantabric mountain belt, and therefore bordering on the Meseta. The eastern part of the Sierra del Fig. 1. Index map of the area mapped. The numbers are those of the sheets of the which used in topographic map (1: 50,000) were part. Brezo, which ends in the Pico Almonga (1511 m) and which includes Peña the As this is Redonda, is pictured on geological map (Appendix 1). the of the the "zona oriental la main part mapped area, name: de Sierra del Brezo" was chosen for this sheet. B. Maps and aerial photographs scale Topographic maps of the region exist in the of 1:50,000. Pig. 1 indicates the situation of the and which sheets of the area mapped topo- graphical map have served as partial base for the geological map (Appendix 1). The fieldwork during the last two seasons was facilitated because aerial photographs on a scale of 1:37,500 were placed at the author's disposal through the courtesy of the "Lucas Mallada" Institute of Madrid. Plate 1 a. The eastern part of the Sierra del Brezo looking north from Traspeña. In the foreground the Stephanien A basin, containing coal seams. b. View from the Mariserrana of the Vado de Cervera towards the other the eastern end of the Sierra del Brezo. top (east station) west, showing among things 381 C. Morphology There is a remarkable contrast in topography between the flat, Tertiary basin and Duero the steep mountains of the Sierra del Brezo, which rise about 700 metres above the plains.