Romanian Continental Plateau of the Black Sea. Tectonic-Sedimentary Evolution and Hydrocarbon Potential

CONTENTS

FOREWORD 9

INTRODUCTION 11

HYSTORY OF RESEARCHES 11

TECTONIC AND GEODYNAMIC FRAMEWORK OF THE CIRCUM-BLACK SEA AREAS 17
Balcanides 17
Srednogore 18
Pontides 18
Caucasus-Crimea 19
Scythian Platform 20
Northern Dobrogea 22
Moesian Platform 22
Kamcia Depression 23

CHRONOSTRATIGRAPHY OF THE FORMATIONS FROM THE ROMANIAN CONTINENTAL PLATEAU OF THE BLACK SEA, RESULTED FROM SEISMIC DATA 24
Megasequences and sequences on the Romanian shelf 24
Lower megasequence 25
Upper megasequence 30

STRUCTURE OF THE ROMANIAN CONTINENTAL PLATEAU OF THE BLACK SEA 33
Identifying the major tectonic units of the Romanian continental plateau of the Black Sea based on their image registered by seismic lines 34

PREOLIGOCENE STRUCTURE OF THE ROMANIAN CONTINENTAL PLATEAU OF THE BLACK SEA 36
Southern Unit 37
Structural elements of the Southern Unit 37
Vadu-Midia High 38
Corbu-Central-Midia depressional area 38
Constanta High 40
Agigea-East Neptun Block 41
Constanta depressional area-west of Lacu Rosu fault 42
Constanta depressional area-east of Lacu Rosu fault 43
The north-south faults system 43
Central Unit 44
Structural elements that compose the Central Unit 45
South-western flank 45
North-eastern flank 46
The north-south faults 50
Northern Unit 48
The north-south faults system 50
Observations upon the entire system of north-south faults from the Romanian continental plateau 51

CORRELATING THE PREOLIGOCENE STRUCTURE FROM THE ROMANIAN CONTINENTAL PLATEAU WITH THE STRUCTURE KNOWN FROM THE ONSHORE DOBROGEA 53
Southern Unit 53
Central Unit 54
Northern Unit 57

POST-EOCENE STRUCTURE OF THE ROMANIAN CONTINENTAL PLATEAU 59

POST-MIDDLE JURASSIC EVOLUTION OF THE ROMANIAN CONTINENTAL PLATEAU 62
Extensional period 62
Post-extensional period 64
Inversional and post-inversional periods 65

THE FRAMING OF THE ROMANIAN CONTINENTAL PLATEAU IN THE BLACK SEA BASIN GEODINAMICS 67

THE HYDROCARBON POTENTIAL OF THE ROMANIAN CONTINENTAL PLATEAU OF THE BLACK SEA 72
Traps 72
Reservoirs 73
Source rocks 74
Oligocene as source rock 76
Pre-Oligocene formations as source rocks 76
Hydrocarbon system 77

CONCLUSIONS 82

REFERENCES 86

FOREWORD

Dr. Ion Morosanu’s paper entitled „Romanian Continental Plateau of the Black Sea, Tectonic-Sedimentary Evolution and Hydrocarbon Potential” succeeds to fill in a gap in the knowledge of the geology of the Black Sea Basin, corresponding to the area from Romania.

The knowledge of the stratigraphy, tectonics and the paleogeography evolution of this area of the Black Sea was reduced as compared to that of the bordering sectors on the land: Dobrogea, Danube Delta and South of Moldavia.

As of 1969, the acquisition of seismic lines started on the Romanian continental plateau of the Black Sea, which within over twenty years exceeded fifty thousand kilometers. At the same time, the equipment necessary for this acquisition was continuously improved, passing from the analogic to the numeric recording. The main stratigraphyc sequences were made evident - Cretaceous, Paleogene, Neogene and the main tectonic lines that delimit the three great units which extend themselves from the onshore to the offshore.

The high density of the seismic lines, the quality of their majority, coroborated with geologic data obtained through the drilled wells allowed the author to precisely separate the main stratigraphic sequences, delimited by unconformities, grouped by the author in two megasequences separated by a regional unconformity between Eocene and Oligocene.

In the lower megasequence, with formations older than Oligocene, three sequences are separated corresponding to the stratigraphyc intervals Proterozoic-Paleozoic, Triassic-Jurassic and lower Cretaceous-upper Cretaceous-Eocene. In the upper megasequence, with tertiary formations, four seismic sequences are separated corresponding to the stratigraphyc intervals Oligocene, Badenian-Sarmatian, Pontian and Dacian-Romanian-Quaternary.

From the structural point of view, the three major units on the onshore are extended on the Romanian continental plateau of the Black Sea, representing the Moesian Platform, Northern Dobrogea and the Scythian Block. The identification of the three units was made on seismic lines only up to Eocene, after this age the Continental plateau evolving unitary from Oligocene up to Quaternary.

The author poins out the dominant role of the extensional tectonics in the evolution of the Continental plateau of the Black Sea during middle Jurassic-Albian.

Subsequently, during the Eocene-Oligocene period, the post-extensional and inversional tectonics of the Continental plateau determined the developed of the major structural configurations that allowed the author to individualize them in three tectonic units: Southern (Moesian Platform), Central (Histria Depression) and Northern (Scythian Block).

Through the detailed anlysis of the seismic lines, the author pointed out both the extensional-compressional tectonics and the different types of resulted structures, and the establishment of the major stratigraphyc-structural elements allowed him the correlation with the rest of the Black Sea Basin, as well as the tracking of the paleogeographyc evolution of the whole Black Sea Basin.

The author comes to the conlusion that the Black Sea was formed partially as a result of the extensional processes that affected the southern margin of the East European Platform and partially by the destruction of the Moesian Platform with the occurence of the Western Basin of the Black Sea as well as the Andrusow-Arhanghelski crest.

The discovery of the oil and gas fields in the offshore of the Black Sea, both in Romania and in the other riverside countries confirmed the existence of the favourable conditions of their generation, accumulation and preservation.

On the Romanian continental plateau of the Black Sea, the oil and gas fields are limited to Albian, Eocene and Oligocene formations. Gas shows are frequent in the Sarmatian and Pliocene formations, the characteristc elements for the gas collectors being frequent on the seismic lines.

Over the source rock of the hydrocarbon, the author makes an analysis of the existing data, resulted from the analysis of the samples taken from the wells by different companies, as well as from other studies, the Oligocene formations being considered on the first place, although the analyzed samples proved the existence of an immature thermal stage for oleogenesis. But the samples taken from deeper areas proved for these formations that they can also present maturity conditions, within the upper limit of the intreval.

The analysis of the samples from Jurassic and lower Cretaceous formations from the shelf, showed the oleogenetic potential and the maturity level corresponding to oleogenesis from these formations.

The potential of hydrocarbon of the Romanian continental plateau of the Black Sea seems to be not yet developed and a reassessment in the light of the new data included in this paper may still provide surprises.

Mr. Ion Morosanu’s paper may be considered a first complex synthesis of the knowledge accumulated up to now, suggesting the ways to be followed too. The richness of data, the compex analysis and the regional integration are a self-evident gain of the paper and of the author.

Dr. Oprea Dicea

ABOUT THE AUTHOR

Dr. Ion Morosanu studied petroleum geology at the Oil, Gas and Geology Institute from Bucuresti-Romania, where he obtained a Ph.D. degree.

The author began his work with Prospectiuni S.A. and now he has over 35 years experience in all aspects of the petroleum exploration in onshore (overthrust belts, foreland basins and platforms) and offshore (Black Sea).

In the last 20 years his intrest was focused to the decipher the stratigraphic and structural framework of the Romanian offshore of the Black Sea and finally to establishing its hydrocarbon potential.

In the same time, after 1990, his activity involved the consulting in oil exploration for different companies in the Romanian onshore and offshore.

This book is the result of the long time intrest in geology of the Black Sea basin and surrounding regions of the author.