Basin Analysis.. Study Later

BASIN ANALYSIS

• BASIN ANALYSIS INVOLVES INTERPRETATION OF THE • FORMATION • EVOLUTION • ARCHITECTURE AND • FILL OF A SEDIMENTARY BASIN BY EXAMINING GEOLOGICAL VARIABLES ASSOCIATED WTH THE BASIN. • DONE BY USING THE TECHNIQUES OF • REVERSE MODELLING - INVOLVES ANALYSING FEATURES OF A BASIN IN ORDER TO DETERMINE THE MECHANISM WHICH PRODUCED THEM. • FORWARD MODELLING - INVOLVES PREDICTING HOW A BASIN WILL EVOLVE UNDER VARIOUS CIRCUMTANCES AND COMPARING THIS WITH THE ACTUAL BASIN.

• IT PROVIDES A FOUNDATION FOR EXTRAPOLATING KNOWN

INFORMATION INTO UNKNOWN REGIONS IN ORDER TO PREDICT THE NATURE OF THE BASIN WHERE EVIDENCE IS NOT AVAILABLE. •THE IMPORTANCE OF BASINS IN PETROLEUM INDUSTRY IS DECIDED BY ITS; i) GEOGRAPHICAL LOCATION ii) KIND OF BASIN iii) TECTONIC HISTORY iv) THE SEDIMENTARY HISTORY AND THE EFFECTS OF THERMAL CHANGES ON THESE SEDIMENTS

v) CONTENT, AGE, THICKNESS AND FACIES OF THE SEDIMENTS OF PRIMARY PETROLEUM CONCERN, SUCH AS THE RSERVOIR, CAP ROCK AND SOURCE BEDS.

• BASIN ANALYSIS ENCOMPASSES MANY TOPICS SINCE IT INTEGRATES SEVERAL FIELDS WITHIN GEOLOGY. THE MAJOR TOPICS INCLUDE;

• BASIN FORMATION AND CHARACTER, PLATE TECTONICS • BASIN FILL CHARACTERISTICS, PROCESSES AND EVOLUTION • BASIN ANALYSIS TECHNIQUES • DESCRIPTION AND CORRELATION OF STRATIGRAPHIC BASIN FILL (SEQUENCE STRATIGRAPHY) • PETROLEUM SYSTEM • PROSPECT GENERATION AND EVALUATION.

PURPOSE OF BASIN ANALYSIS • DETERMINE THE PHYSICAL CHRONOSTRATIGRAPHIC FRAMEWORK BY,

- INTERPRETING SEQUENCES, SYSTEM TRACTS AND PARASEQUENCES AND/ OR SIMPLE SEQUENCES ON OUTCROPS, WELL LOGS, SEISMIC DATA AND AGE DATA WITH HIGH RESOLUTION BIOSTRATIGRAPHY. • CONTRUCT GEOHISTORY, TOTAL SUBSIDENCE AND TECTONIC SUBSIDENCE CURVES ON SEQUENCE BOUNDARIES. • COMPLETE TECTONO- STRTIGRAPHIC ANALYSIS INCLUDING; • RELATE MAJOR TRANSGRESSIVE – REGRESSIVE FACIES CYCLES TO TECTONIC EVENTS

• RELATE CHANGES IN RATES OF TECTONIC SUBSIDENCE CURVES TO PLATE- TECTONIC EVENTS • ASSIGN A CAUSE TO TECTONICALLY ENHANCED UNCONFORMITIES • RELATE MAGMATISM TO TECTONIC SUBSIDENCE CURVES • MAP TECTONO- STRATIGRAPHIC UNITS • DETERMINE STYLE AND ORIENTAION OF STRUCTURES WITH TECTONO- STRATIGRAPHIC UNITS.

MECHANISM OF BASIN FORMATION MAJOR MECHANISMS FOR REGIONAL SUBSIDENCE/ UPLIFT; • ISOSTACTIC- CHANGES IN CRUSTAL OR LITHOSPHERIC THICKNESS • LOADING- BY THRUST SHEETS, VOLCANIC PILES, SEDIMENT • DYNAMIC EFFECTS- ASTHENOSPHERIC FLOW, MANTLE CONVENTION, PLUMPES

ISOSTACTIC PROCESS • CRUSTAL THINNING • EXTENTIONAL STRECHING, EROSION DURING UPLIFT, MAGMATIC WITHDRAWAL

• MANTLE- LITHOSPHERE THICKENING • COOLING OF LITHOSPHERE, FOLLOWING CESSATION OF STRETCHING OR CESSATION OF HEATING • CRUSTAL DENSIFICATION • DENSITY INCREASE DUE TO CHANGING PRESSURE/ TEMPERATURE CONDITIONS AND/ OR EMPLACEMENT OF HIGHER DENSITY MELTS INTO LOWER DENSITY CRUST LOADING • LOCAL ISOTATIC COMPENSATION OF CRUST AND REGINOL LITHOSPHERIC FLEXURE • DEPENDENT UPON FLEXURAL RIGITITY OF LITHOSPHERE • SEDIMENTARY OR VOLCANIC LOADING

• TECTONIC LOADING

• DURING OVERTHRUSTING AND / OR UNDERPULLING • SUBCRUSTAL LOADING • LITHOSPHERIC FLEXURE DURING UNDERTHRUSTING OF DENSE LITHOSPHERE

• DYNAMIC EFFECTS

• ASTHENOSPHERE FLOW DESCENT OF DELAMINATION OF SUBDUCTED LITHOSPHERE • MANTLE CONVECTION • PLUMES

BASIN CLASSIFICATION AND ORIGIN

SEDMENTARY BASINS ARE COMMONLY CLASSIFIED IN TERMS OF THE FOLLOWING; • THE TYPE OF CRUST ON WHICH THE BASINS REST • THE POSITION OF THE BASINS WITH RESPECT TO PLATE MARGINS • FOR BASINS LYING CLOSE TO A PLATE MARGINS, THE TYPE OF PLATE INTERACTION OCCURING DURING SEDIMENTATION

INTERIOR BASINS, INTERCRATONIC RIFTS AND ALACOGENS INTERIOR BASINS • RELATIVELY LARGE, COMMONLY OVATE DOWNWARPS WITHIN THE INTERIORS OF STABLE CRATONIC

SHIELDS

• SOME INTERIOR BASINS – FILLED WITH MARINE SILICLASTIC, CARBONATE OR EVAPORITE SEDIMENT DEPOSITED FROM EPICONTINENTAL SEAS. OTHERS- NONMARINE SEDIMENTS. • VARIOUS MECHANISMS - SUBSIDENCE - COOLING AND SUBSIDENCE FOLLOWING A THERMAL EVENT (INTRUSION OF DENSE MATERIAL IN THE MANTLE)

- MANTLE PHASE CHANGES - MANTLE HOT SPOTS - SHALLOW SUBDUCTION

RIFTS • NARROW, FAULT- BOUNDED VALLEYS • RANGE IN SIZE FROM GRABENS A FEW KMs WIDE TO GIGANTIC RIFTS (EAST AFRICAN RIFT SYSTEM- 3000 KM LONG AND 30- 40 KM WIDE) • NO. OF SEDIMENTARY ENVIONMENTS CAN EXIST WITHIN RIFT - NONMARINE (FLUVIAL, LACUSTRINE, DESERT) TO - MARGINAL MARINES (DELTA, ESTUARINE, TIDAL FLAT) - AND MARINE (SHELF, SUBMARINE FAN) • DEPOSITES OF R.B INCLUDE, CONLOMERATES, S. STs, SHALES, TURBIDITES, COALS, EVAPORITES AND CARBONATES.

SURFACE CONFIGURATION OF EAST AFRICAN RIFT ZONE AND STAGES OF EVOLUTION OF THE RIFT.

AUALCOGNS • SPECIAL KIND OF RIFT, REFERRED AS FAILED ARMS OF A TRIPLE JUNCTION. • ONE ARM OF SPREADING RIFT SYSTEMSTOP SPREADING AFTER A FEW MILLION YEARS. • REST TWO ARMS OF THE RIFT CONTINUED TO SPREAD, SEPARATION OF THE CONTINENT AND DEVELOPMENT OF AN OCEAN. • LONG, NARROW TROUGHS THAT MAKE UP THE ARMS OF AUALCOGENS EXTEND INTO CONTINENTAL CRATONS. • DEPOSITES MAY INCLUDE NONMARINE (e.g. ALLUVIAL FAN) DEPOSITES,MARINE SHELF DEPOSITES AND DEEPER- WATER TURBIDITES. • CAMBAY BASIN, REELFOOT RIFT IN WHICH MISSIPPI RIVER FLOWS.

AUACOGENS NORTH OF BLACK AND CASPIAN SEA ON THE RUSSIAN PLATFORM

OCEANIC BASINS AND RISES OCEANIC BASINS • OCCUR IN VARIOUS PARTS OF DEEP OCEANIC FLOOR • CREATED BY RIFTING AND SUSIDENCE ACCOMPANING OPENING OF AN OCEAN- OWING TO CONTINENTAL RIFTING

• MAY INCLUDE OCEAN – FLOOR SAG BASINS, FAULT BOUNDED BASINS ASSOCIATED WITH RIDGE SYSTEM. • SEDIMENTS ARE MAINLY PELAGIC CLAYS, BIOGENIC OOZES, TURBIDITES. • SEDIMENTS ACCUMULATE IN THESE BASINS ADJACENT TO ACTIVE MARGINS MAY BE SUBDUCTED INTO A TRENCH AND CONSUMED DURING OCEAN CLOSING.

SUBDUCTION RELATED SETTING • FEATURES OF SEISMICALLY ACTIVE CONTINNTAL MARGINS • CHARACTERISED BY A DEEP- SEA TRENCH, AN ACTIVE VOLCANIC ARCH AND AN ARCH- TRENCH GAP • MOST IMPORTANT DEPOSITIONAL SITES ARE - DEEP- SEA TRENCH

- FORE- ARC BASINS (LIE WITHIN THE ARCH- TRENCH GAP) - BACK- ARCH OR MARGINAL BASINS • SEDIMENTS DEPOSITED ARE MAINLY, -SILICICLASTIC DEPOSITES DERIVED FROM VOLCAIN SOURCES IN THE VOLCANIC ARCH (SANDS AND MUDS ON THE SHELF, TURBIDITES IN DEEPER WATER IN SLOPE, BASIN AND TRENCH SETTING

• SEDIMENTS IN THE TRENCH, - TERRIGENOUS DEPOSITES TRNSPORTED BY TURBIDITY CURRENTS FROM LAND - TOGETHER WITH SEDIMENTS SCRAPED FROM A SUBDUCTING OCANIC PLATES- FORMING AN ACCRETIONARY COMPLEX

STRIKE- SLIP/ TRANSFORM- FAULT- RELATED SETTING • OCCUR ALONG - OCEAN SPREADING - TRANSFORM BOUNDARIES BETWEEN SOME MAJOR CRUSTAL PLATES - ON CONTINENTAL MARGINS AND - WITHIN CONTINENTS ON CONTINENETAL CRUST

• MOVEMENTS ALONG STRIKE- SLIP FAULTS – PRODUCE A VARITY OF PULL- APRT BASINS • MOST BASINS FORMED BY STRIKE- SLIP FAULTING ARE SMALL

• S- S BASINS OCCUR IN A VARITY OF SETTING- MAY BE FILLED BY EITHER MARINE OR NONMARINE SEDIMENTS.

SEISMIC PROFILE ACROSS A WRENCH FAULT

TYPES OF STRIKE- SLIP FAULT PATTERN AND RESULTING SEDIMENTARY BASINS A. B. C – BRAIDED FAULT D– FAULT TERMINATION E- EN ECHLON FAULT

COLLISION- RELATED SETTING • FORMED AS A RESULT OF CLOSING OF AN OECAN BASIN AND COLLISION BETWEEN CONTINENTS OR ACTIVE ARC SYSTEMS OR BOTH • COLLISION GENERATES COMPRESSIONAL FORECESDEVELOPMENT OF FOLD THRUST- BELTS AND ASSOCIATED FORELAND BASINS ALONG THE COLLISION SUTURE BELT. • MAY ALSO GIVE RISE TO STRIKE- SLIP MOVEMENT AND CREATION OF STRIKE BELT. • LANDMASSES TEND TO APPROACH EACH OTHER OBLIQUELY DURING COLLISION (OWING TO IRREGULAR SHAPE OF CONTINENTS AND ISLAND ARCS), PORTION OF AN OLD OCEAN MAY REMAIN UNCLOSED AFTER COLLISION OCCURS- SURVIVING EMBAYMENT ARE REMNANT BASINS- CHARACTERISED BY TUBIDITE SEDIMENTATION

• FORELAND BASINS CHARACTERISED BY NONMARINE GRAVELS, SANDS, AND MUDS (WHEN ISOLATED FROM THE OCEAN) • MAY CONTAIN CARBONATE, VAPORITES, AND/ OR TUBIDITES (IF HAVE CONNECTION WITH OCEAN)

TERMINOLOGY OF CONVERGENT MARGIN INVOLVING OVERRIDING PLATE

MODEL OF TECTONIC AND SEDIMENTARY EVOLUTION OF A SUTURE ZONE DEVELOPED BY IRREGULAR CONTINENTAL MARGINS

MAJOR ACTIVITIES IN BASIN ANALYSIS A. DECIPHERING THE REGIONAL TECTONIC FRAMEWORK OF THE BASIN •

LAND IMAGERY DATA

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TECTONIC FEATURES- LINEAMENTS, ZONE OF FRACTURES, FAULTS etc

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GEOMORPHIC ANOMALIES AND DRAINAGE PATTERN ANALYSIS

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STUD OF GRAVITY, MAGNETIC & AERRO- MAGNETIC DATA

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REGIONAL SEISMIC PROFILES AND DSS DATA- TO FIND OUT - BASEMENT CONFIGURATION - QUANTUM OF BASIN FILL - DEEP SEATED FAULT ZONES

PREPARATION OF TECTONIC & BASIN FILL MAPS.

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LINEAMENT MAP OF CAMBAY BASIN WITH PALEOCHANNELS

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MAGNETIC ANOMALY MAP ALSO SHOWS POSITIVE ANOMALIES OVER THE AREA OF CENTRAL GRAVITY HIGH.

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GEOLOGICAL SECTION ACROSS SANCHOR BLOCK

GEOLOGICAL SECTION ACROSS MEHSANA BLOCK

B. • PREPARATION OF ELECTROLOG CORRELATION OF THE PARAMETRIC/ EXPLORATORY WELLS • PREPARATION OF SEISMO- GEOLOGICAL SECTION ALONG AND ACROSS THE BASIN AT SUITABLE INTERVALS • DIVISION OF ENTIRE STRATIGRAPHIC SECTION INTO TIME/ ROCK UNITS • PREPARATION OF LAYOUT MAP SHOWING SEISMIC PROFILES ALONG AND ACROSS THE BASIN • STUDY OF SELECTED SEISMIC SECTIONS IN DIFFERENT PARTS OF THE BASIN

SEISMO- GEOLOGICAL SECTION ALONG 380-09 (MINDHOLA AREA), SOUTH CAMBAY BASIN

Geological section across Jaisalmer Basin (NNW- SSE)

C. SEQUENCE STRATIGRAPHY • STUDY OF TERMINATION CHARACTERS OF SEISMIC REFLECTORS • STUDY OF SEQUENCES OF BROAD SEISMIC FACIES PACKS • IDENTIFICATION OF MAJOR SEQUENCES/ PARASEQUENCES, UNCONFORMITIES etc • PREPARATION OF SYNTHETIC SEISMOGRAMS • STUDY OF TRANSGRESSIVE/ REGRESSIVE CYCLES WITH THE HELP OF SEA- LEVEL CURVES • SYSTEM TRACT ANALYSIS

INPUTS • KEY SEISMIC LINES • BIO & CHORNO- STRATIGRAPHIC DATA • VSP/ SONIC DATA OF KEY WELLS

RELATION OF STRATA TO THE UPPER BOUNDARY OF A DEPOSITIONAL SEQUENCE.

RELATIONSHIP OF STRATA TO THE LOWER BOUNDARY OF A DEPOSITIONAL SEQUENCE.

REGIONAL ELECTROLOG CORRELATION SHOWING VARIOUS SEQUENCES AND THEIR ASSOCIATED SYSTEM TRACTS.

SIMPLIFIED GLOBAL SEQUENCE CHART FOR PART OF THE TERTIARY AND QUARTERNARY.

A SIMULATED SEISMIC SECTION SHOWING SOME COMMON SEISMIC FACIES PATTERN THAT CAN BE IDENTIFIED FROM SEISMIC RECORDS.

TERMINOLOGY FOR RELATIONS THAT DEFINE UNCONFORMABLE BOUNDARIES OF A DEPOSITION SEQUENCE.

D. SEQUENCE ANALYSIS • STUDY OF SEISMIC SIGNATURES LEADING TO SEISMIC FACIES ANALYSIS FOR EACH SEQUENCE •ANALYSIS OF LOG MOTIFS FOR RECOGNITION OF SEDIMENTARY FACIES •WORKING OUT STRATAL PATTERN AND SEDIMENTARY FACIES MAPS • DECIPHERING GEOMETRY OF SAND BODIES, CARBONATE BUILDUPS etc • PREPARATION OF PALEOGEOGRAPHIC MAPS • PREPARATION OF PREPARATION OF FACIES, SAND/ SHALE RATIO MAP, PALEOCURRENT ANALYSIS etc

INPUTS • ALL AVAILABLE, NORMALLY PROCESSED/ REPROCESSED SEISMIC TO BE STUDIED • INTEGRATION OF SEISMIC ANALYSIS DATA •SYNTHESIS OF LITHOLOGICAL AND CORE DATA • INTEGRATION OF PALEONTOLOGICAL/ PALYNOLOGICAL DATA • STRATIGRAPHIC DIAGRAMES • STRATIGRAPHIC CROSS SECTION HUNG ON SHARED STRATIGRAPHIC FEATURES • FENCE DIAGRAME IS SERIES OF CROSS SECTION ON AN ISOMETRIC AMP

STRATIGRAPHIC MAPS • STRUCTURE CONTOUR MAP PLOTS THE SURFACE OF A SUBSURFACE LITHOLOGICAL UNIT • DETERMINE REGIONAL STRAUCTURAL ATTITUDE OF ROCKS, PRESENCE OF LOCAL STRUCTURAL FEATURES • POINT OF EQUAL ELEVATION ABOVE OR BELOW A DATUM ARE MAPPED AND CONTOURED • STRUCTURAL HIGHS (DOME/ ANTICLINE) & LOWS (BASINS/ SYNCLINES ARE OVIOUS • FULT INDICATED BY TIGHTLY BUNCHED CONTOURS ALONG A STRAIGHT LINE

STRUCTURE CONTOUR MAP DRAWN ON THE TOP OF FORMATION TOP

ISOPACH MAPS • POINTS OF EQUAL THICKNESS OF A ROCK UNIT ARE CONTOURED • REQUIRES DATA FOR TOP AND BOTTOM OF BED (THICKNESS) • ABNORMALLY THICK AREAS SUGGEST PRESENCE OF MAJOR DEPOSITIONAL CENTRES PALEOGEOGRAPHIC MAPS • PROVIDE MEANS TO ILLUSTRATE PALEODRAINAGE, PATTERS OF BASIN FILL, SHIFTED SHORELINES OR BURIAL OF PRE- EXITING TOPOGRAPHY • STRIPPED OFF ALL OVERLYING ROCKS TO A PARTICULAR UNIT ON WHICH THESE WERE DEPOSITED • MAP ON TOP OF EXPOSED UNIT (SUBCROP MAP) • MAP ON TOP OF OVERLYING ROCKS FROM BELOW (SUPERCROP MAP)

ISOPACH MAP OF KALOL FORMATION, CAMBAY BASIN

PALEOGEOGRAPHY DURING SEQ- II (KOPILI Fm. LATE EOCENE)

FACIES MAPS • ILLUSTRATES THE AERIAL VARIATION OF A STRATIGRAPHIC UNIT • VARIATIONS IN LITHOLOGICAL ASPECT AND ATTRIBUTESLITHOFACIES MAP • VARIATION IN FAUNAL/ FLORAL ASPECT- BIOFACIES MAP • TWO TYPES OF LITHOFACIES MAP • CLASTIC RATIO MAP - CONTOURS OF EQUAL CLASTIC RATIO (CONG+ S.St + SHALE) RATIO IS ---------------------------------(L.St + DOLO + EVAPOR. + COAL)

CLASTIC- RATIO MAP (CLASTIC/ NONCLASTIC)

FENCE DIAGRAM SHOWING INTERTONGUING FACIES RELATIONSHIPS BETWEEN MARINE AND NONMARINE DEPOSITES.

FACIES RELATIONSHIPS IN UPPER CRETACEOUS STRATA OF THE ROCKY MOUNTAIN

• THREE- COMPONET LITHOFACIES MAP

- SHOW BY MEANS OF PATTERNS OR COLORS THE RELATIVE ABUNDANCE, WITHIN A FORMATION/ STRATIGRAPHIC UNIT, OF THREE PRINCIPAL LITHOFACIES COMPONENTS SEISMIC STRATIGRAPHY • REFLECTION SEISMOLOGY RECORDS TIME FROM SOUNDING TO REFLECTION DETECTION • SOUND TRAVELS DOWNWARD, REFLECTED OFF SUBSURFACE STRAUCTURES, DETECTED BY GEOPHONE • RECORDED ON STRIP CHART WITH PULSE REPRESENTING TIME WHEN SOUND WAVE RETUNED • VERTICAL SCALE IS TWO- WAY TIME FOR MORE THAN ONE REFLECTED SURFACE ENCOUNTERED

HYPOTHETICAL THREE – COMPONENT MAP (S.St, SHALE, L.St) LITHOFACIES MAP

SEISMIC SECTION 380- 09 SHOWING STRUCTURAL INVERSION, MINDHOLA AREA

DEPOSITIONAL SEQUENCES AS DEFINEDFROM SEISMIC RECORDS

SEISMIC PROFILES • ALL SINGNALS FROM TRAVERSE COLLECTED, SCREENED BY COMPUTER, PRINTED OUT • REFLECTORS RESULT FROM ANY ABRUPT CHANGE IN SEISMIC VELOCITY • SUBSURFACE STRUCTURES AND GENETIC SEQUENCES • TEXTURES OF REFLECTIONS CAN BE MEANINGFUL • NON- MARINE BEDS TYPICALLY JAGGED REFLECTIOS • MARINE BEDS GENRALLY SMOTH, CONTINOUS, HOMOGENOUS

PALEOCURRENT ANALYSIS • USED TO DETERMINE THE FLOW DIRECTION OF ANCIENT CURRENTS- REFLECTS THE PALEOSLOPE. • ACCOMPLISHED BY MEASURING ORIENTATION OF DIRECTIONAL FEATURES SUCH AS SEDIMENTARY STRUCTURES (FLUTE CAST, RIPPLE MARKS, CROSS etc)

BEDS

• REVEALS THE DIRECTION IN WHICH THE SEDIMENT SOURCE AREA • AIDS IN UNDERSTANDING OF • GEOMETRY AND TREND OF LITHOLOGICAL UNITS • INTERPRETATION OF DEPOSITIONAL ENVIONMENTS

USE OF PALEOCURRENT DATA TO LOCATE SOURCE AREA

E. STRUCTURAL ANALYSIS • IDENTIFICATION OF FAULT SYSTEM, STRUCTURAL ELEMENTS

• PREPARATION OF STRUCTURE CONTOUR, ISOCHRON (TIME STRUCTURE MAP) AND ISOCHRONOPACH MAPS • TECTONO- STRATIGRAPHIC ANAYSIS • CONCEPTUAL GEOLOGICAL MODEL

• BASIN EVOLUTION HISTORY

PROPOSED LOCATION KKL- 1

TIME STRUCTURE MAP NEAR THE TOP OF SAND IN # K- 260

CONCEPTUAL GEOLOGICAL MODEL, OLPAD

F. PLAY ANALYSIS • ANALYSIS AND INTEGRATION OF • GEOCHEMICAL DATA • BASIN FILL MAPS (OR ISOPACH MAPS) • PALEO- STRUCTURAL MAPS, SUBSIDENCE CURVES • IDENTIFICATION OF SOURCE- RESERVOIR- CAP ROCK LOCALES AND RELATIONSHIP • IDENTIFICATION OF KITCHEN AREA AND PETOLEUM SYSTEM • IDENTIFICATION OF OIL AND GAS

G. PROSPECT EVALUATION • IDENTIFICATION AND EVALUATION OF STRUCTURAL, STRATIGRAPHIC AND COMBINATION TYPE OF PROSPECT • PREPARATION OF PROSPECT MAPS • TECHNO- ECONOMIC ANAYSIS • PROPOSAL FOR RELEASE OF EXPLORATORY LOCATIONS

SEQUENCE STRATIGRAPHY • IS DEFINED AS ‘THE STUDY OF ROCK RELATIONSHIP WITHIN A CHRONOSTRATIGRAPHY FRAMEWORK OF REPETITIVE , GENETICALLY RELATED STRATA, BOUNDED BY SURFACE OF EROSION OR NON- DEPOSITION, OR THEIR CORRELATIVE CONFORMITIES’. • SEQUENCE PROVIDES A TIME – STRATIGRAPHIC FRAMEWORK, BASED UPON THE GLOBAL EUSTATIC SEA LEVEL CYCLE CHART, CAN BE USE TO CORRELATE, DATE, MAP AND PREDICT SEDIMENTARY FACIES. DEPOSITIONAL SEQUENCE IS DEFINED AS A RELATIVELY CONFORMABLE SUCCESSION OF GENETICALLY RELATED STRATA, BOUNDED ABOVE AND BELOW BY UNCONFORMITIES OR THEIR CORRELATIVE CONFORMITIES.

Concept of depositional sequences.

CORRELATIVE CONFORMITY IS A BEDDING SURFACE SEPARATING YOUNGER FROM OLDER STRATA ALONG WHICH THERE IS NO EVIDENCE OF EROSION OR NON- DEPOSITION. GENETICALLY RELATED DESCRIBES THE SUIT OF SEDIMENTARY FACIES DEPOSITED OVER A SPECIFIC PERIOD OF TIME WITHIN THE DEPOSITIONAL ENVIRONMENT OF AN ENTIRE DRAINAGE BASIN, MAY INCLUDE BASIN’S HIGHLANDS, THE COASTLINE AND THE ABYSSAL DEPTHS.

RELATIVE SEA LEVEL COMPONENTS AND ACCOMODATION SPACE THE MARINE STRATIGRAPHIC RECORD IS COMPOSED OF DEPOSITIONAL SEQUENCES.

VARIABLES THAT CONTROL SEQUENCE FROMMATION

FORMATION OF THESE SEQUENCES IS CONTROLLED BY, • SEDIMENT SUPPLY IS A FUNCTION OF EROSION, RUNOFF AND FLUVIAL TRANSPORT LOADS AND PROCESSES, STRONGLY AFFECTED BY THE COMBINATION OF TECTONICS, CLIMATE AND DRAINAGE BASIN SIZE. • EUSTASY IS THE GLOBAL COMPONENT OF SEA LEVEL CHANGE CAUSED BY THE SUM OF CLIMATIC VARIABLE AND GLACIAL AND TECTONIC PROCESSES. • COMPACTION REDUCES THE VOLUME OF MARINE SEDIMENTS BY EXPELLING INTERSTITIAL PORE WATERS AND IS CAUSED EITHER BY DESICCATION OR OVERLYING SEDIMENT ACCUMULATION. • ACCOMMODATION SPACEIS SUM TOTAL OF TOTAL OF EUSTASY, SUBSIDENCE AND COMPACTION.

DEPOSITIONAL GEOMETRIES OF STRATIGRAPHIC SEQUENCES THE BALANCE BETWEEN SEDIMENT SUPPLY AND RELATIVE SEA- LEVEL CONTROLS OVERALL DEPOSITIONAL GEOMETRIES, WHICH ARE; PROGRADATIONAL (REGRESSION) GEOMETRIES • RESULT FROM A DOMINANCE OF SEDIMENT SUPPLY OVER ACCOMMODATION SPACE. • THIS SURPLUS CAUSES DEPOSITION TO MIGRATE BASIN WARD (WHERE SEDIMENTS HAVE SPACE). • PRODUCES STRATAL CLINOFORMS • REPRESENTS THE SHELF EDGE, SEPARATING COASTAL PLAIN AND NERITRIC FACIES FROM BATHYAL FACIES).

•AN UPWARD- COARSENING PROFILE OF SEDIMENTARY COMPONENTS ON WELL LOGS, CHARACTERISTIC OF SHELF MARGIN, HIGHSTAND AND PORTION OF THE LOWSTAND SYSTEMS.

AGGRADATIONAL GEOMETRIES • OCCUR WHEN SEDIMENT SUPPLY MATCHES THE INCREASE IN ACCOMMODATION SPACE AND PRODUCES VERTICALLY STACKED FACIES. • ELECTRICAL LOGS SHOW REPETITIVE UNITS OF UPWARD COARSENING OR MIXED COMPONENTS.

RETROGRADATIONAL (TRANSGRESSION) GEOMETRIES: • RESULT FROM EITHER SEDIMENT STARVATION OR NET INCREASE IN ACCOMMODATION SPACE (DUE TO A RELATIVE SEA LEVEL RISE) OVER SEDIMENT SUPPLY. • AN UPWARD SHIFT FROM COARSE- GRAINED, INNERNERITIC DEPOSITS TO DEEPER, PELAGIC DEPOSITIONAL ENVIRONMENTS (AS SEA LEVEL RISES AND SHORELINE MIGRATES). • PRODUCES FINING UPWARD ELECTRIC LOG PATTERNS. • ASSOCIATED PREDOMINANTLY WITH TRANSGRESSIVE SYSTEM TRACT DEPOSITION.

SEISMIC SEQUENCE ANALYSIS THE STRATA THAT MAKEUP A DEPOSITIONAL SEQUENCE MAY BE EITHER •

CONCORDANT ESSENTIALLY PARALLEL TO SEQUENCE BOUNDARY, OR

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DISCORDANT LACKING PARALLELISM WITH RESPECT TO SEQUENCE BOUNDARIES.

DISCORDANCE IS THE MOST IMPORTANT PHYSICAL CRITERION USED IN DETERMINING SEQUENCE BOUNDARIES.

TWO MAIN TYPES OF DISCORDANCE ARE; • TRUNCATION IS THE LATERAL TERMINATION OF STRATA CUT OFF FROM THEIR ORIGINAL DEPOSITIONAL LIMITS BY EROSION OCCURS AT THE UPPER BOUNDARY OF A SEQUENCE AND MAY BE EITHER LOCAL OR REGION EXTENT •LAPOUT IS THE LATERAL TERMINATION OF STRATA AGAINST A BOUNDARY AT THEIR ORIGINAL DEPOSITIONAL LIMIT.

RELATION OF STRATA TO THE UPPER BOUNDARY OF A DEPOSITIONAL SEQUENCE.

LAPOUT RELATIONSHIPS ARE FURTHER DIVIDED INTO TWO TYPES; • BASELAP AND • TOPLAP • BASELAP OCCURS AT THE LOWER BOUNDARY OF A DEPOSITIONAL SEQUENCE AND IS OF TWO TYPES, • ONLAP IS A BASELAP IN WHICH AN INITIALLY HORIZONTAL OR INCLINED STRATUM TERMINATES AGAINST A SURFACE OF GREATER INCLINATION. • DOWNLAP IS THE BASELAP IN WHICH AN INITIALLY INCLINED STRATUM TERMINATES DOWNDIP AGAINST AN INITIALLY HORIZONTAL OR INCLINED SURFACE.

ONLAP AND DOWNLAP INDICATE NONDEPOSITIONAL HIATUSES AND NOT EROSIONAL BREAKS IN DEPOSITION.

RELATIONSHIP OF STRATA TO THE LOWER BOUNDARY OF A DEPOSITIONAL SEQUENCE.

• TOPLAP IS LAPOUT AT UPPER BOUNDARY OF A DEPOSITIONAL SEQUENCE TOPLAP IS ALSO EVIDENCE OF A NONDEPOSITIONAL HIATUS.

TERMINOLOGY FOR RELATIONS THAT DEFINE UNCONFORMABLE BOUNDARIES OF A DEPOSITION SEQUENCE.

A SIMULATED SEISMIC SECTION SHOWING SOME COMMON SEISMIC FACIES PATTERN THAT CAN BE IDENTIFIED FROM SEISMIC RECORDS.

STRATAL UNITS WITHIN SEQUENCE INCLUDE,

DEPOSITIONAL SYSTEM IS A THREE DIMENSIONAL ASSEMBLAGE OF LITHOFACIES, GENETICALLY LINKED BY ACTIVE (MODERN) OR INFERRED (ANCIENT) PROCESSES AND ENVIRONMENTS (E.G. FLUVIAL, DELTAIC, BARRIER – ISLAND ETC).

SYSTEM TRACT - A SUBDIVISION OF A DEPOSITIONAL SYSTEM. FOUR KINDS ARE RECOGNIZED; I) A) LOWSTAND SYSTEM TRACT (LST) B) TRANSGRESSIVE SYSTEM TRACT (TST) C) HIGHSTAND SYSTEM TRACT (HST) D) SHELF MARGIN TRACT (SMST) II) PARASEQUENCE & PARASEQUENCE SET III) MARINE FLOODING SURFACE

SEQUENCE BOUNDARIES TWO TYPES OF SEQUENCES AND SEQUENCE BOUNDARIES HAVE BEEN IDENTIFIED; • TYPE- I SEQUENCE BOUNDARY • IS BOUNDED AT ITS BASE BY A TYPE- I SEQUENCE BOUNDARY, CHARACTERIZED BY SUBAERIAL EXPOSURE AND EROSION PRODUCED BY RELATIVE FALL IN SEA. • TYPE- I SEQ. BOUNDARY IS IDENTIFIED BY A BASINWARD SHIFT OF COASTAL FACIES AND FLUVIAL INCISION.

TYPE- I SEQUENCE CONSISTS OF THREE SYSTEM TRACTSA) LOWSTAND SYSTEM TRACT B) TRANSGRESSIVE SYSTEM TRACT AND C) HIGHLAND SYSTEM TRACT UNIT, BUT DOES NOT CONTAINED A SHELF MARGIN SYSTEM TRACT.

• MOST COMMONLY OBSERVED AND REPRESENT THE SETTING FOR THOSE EXPOSED PORTIONS OF THE CONTINENTAL SHELF DURING THE LOWER SEA LEVEL PHASE.

TYPE- II SEQUENCE BOUNDARY • HAS A TYPE- II SEQUENCE BOUNDARY AT ITS BASE AND EITHER A TYPE- I OR TYPE- II SEQUENCE BOUNDARY AT ITS TOP. • LACKS THE STRONG EROSINAL FEATURES ASSOCIATED WITH THE TYPE- I BOUNDARY AND THE BASINWARD SHIFT OF COASTAL FACIES. • CONSIDERED RARE WITHIN CLASTIC DEPOSITIONAL SEQUENCES.

SCHEMATIC ILLUSTRATION OF SYSTEM TRACTS AND PARASEQUENCES IN A TYPE- I AND A TYPE- II EQUENCE.

LOWSTAND SYSTEM TRACT • IS BOUNDED AT ITS BASE BY A TYPE- I SEQUENCE

BOUNDARY ON SHELF AND ITS CORRELATIVE COUNTERPART ABOVE THE CONDENSED SECTION IN DEEPER WATERS. • TOP IS MARKED BY TRANSGRESSIVE AND HST SURFACES. • DEPOSITED IN DEEPER BATHYAL ENVIRONMENTS DURING TIMES OF A FALL IN RELATIVE SEA LEVEL. • CONTINUE DURING THE SUBSEQUENT RISE IN SEA LEVEL. • DISPLAY CHARACTERISTIC INTERNAL GEOMETRIES DURING LST PHASE, INCISED VALLEYS AND CANYONS ARE ERODED ON THE SHELF. FILLED DURING SUBSEQUENT RISE IN SEA LEVEL AND ARE LABELED INCISED VALLEY FILL (IVF).

•DOWNSLOPE OF THESE FEATURES, THICKEST ACCUMULATIONS OF RESERVOIR QUALITY SANDS ARE DEPOSITED. • SEDIMENTARY BASINS WITH WELL- DEFINED SHELF EDGE PRODUCE WELL- DEFINED LST INTERNAL COMPONENTS , WHICH INCLUDE, - BASIN FLOOR COMPLEX (BFC) - SLOPE FAN COMPLEX (SFC) - PROGARDING COMPLEX (PC).

MODEL OF LOWSTAND SYSTEM TRACT

BASIN FLOOR COMPLEX (BFC) • COMPOSED OF TURBIDITE SANDS AND INTERLAYER SHALES OF SUBMARINE FANS. • SEISMIC REFLECTORS - DOWNLAP AND ONLAP TERMINATIONS. • CONTAINS EXCELLENT RESERVOIR QUALITY SANDS DISPLAY A BLOCKY PATTERN ON WELL LOGS. •BFC SANDS- HIGH PERMEABILITY AND POROSITIES, LIMITED CONTINUITY AND EXCELLENT SEALS WHEN CAPPED BY PELAGIC SHALES.

SLOPE FAN COMPLEX (SFC) • GRADES UPWARDS FROM PELAGIC SHALES INTO CHANNEL

TRANSPORT COMPLEXES • SANDS OF GOOD RESERVOIR POTENTIAL FOUND WITHIN CHANNEL AXES AND AS SHEET SANDS ON LEVEE FLANKS. • TYPICAL COARSENING- UPWARD PATTERN ON ELECTRICAL LOGS.

LOG RESPONSES OF DIFFERENT SYSTEM TRACT ON SHELF AND SLOPE

PROGRADING COMPLEX (PGC) • COASTAL ONLAP ACROSS THE SHELF PRODUCES PGC AND RESULTS IN THE SUPPLY OF DISTAL SEDIMENTS TO THE LST COMPLEX • SAND DEPOSITION IS LIMITED TO SHORELINE AREAS ALONG THE OUTER SHELF, INCLUDE FLUVIAL AND SHOREFACE FACIES DISPLAY A COARSENING- UPWARD WELL LOG PATTERN. • THE PGC IS CAPPED BY DEEPWATER DISTAL DEPOSITS OF TST AND HST.

TRANSGRESSIVE SYSTEM TRACT • RISE IN RELATIVE SEA LEVEL AND TRANSGRESSION OF THE SHORELINE ACROSS THE SHELF, SEDIMENT SUPPLY TO LST COMPLEXES IS CUT OFF, EXCEPT FOR CONTINUED DISTAL ACCUMULATION . SEDIMENTS ACCUMULATE TO FORM THE TST. • CHARACTERIZED BY DIPPING STRATAL GEOMETRIES, DEFINES THE RETROGRADATIONAL ACCUMULATION OF SEDIMENTS ON TOP OF THE TRANSGRESSIVE SURFACE AND LST . • THE TOP OF THE TST WILL CONTAIN MFS AND CONDENSED SECTION, ONTO WHICH THE HST WILL THEN DOWN LAP.

MODEL FOR TRANSGRESSIVE SYSTEM TRACT

• ELECTROLOG REPONSE TST TEND TO FINING UPWARD. • BASINWARD, TST SEDIMENTS TEND TO THIN AND RECOGNIZED ON SEISMIC PROFILES BY APPARENT TRUNCATION SURFACE AT THEIR TOP. • RESERVOIR QUALITY SANDS WITHIN TST UNITS MAY INCLUDE BEACH AND SHORELINE FACIES.

HIGHSTAND SYSTEM TRACT • UPPERMOST UNIT OF A DEPOSITIONAL SEQUENCE AND OVERLIES THE PRECEDING TST PHASE AND IS CAPPED BY TYPE- I OR II SEQUENCE BOUNDARY. • RECOGNIZED ON SEISMIC PROFILES BY DOWNLAP ONTO MFS CONDENSED SECTION. • OCCURS WHEN THE SEDIMENT SUPPLY RATE EXCEEDS THE ACCOMMODATION SPACE, CAUSING PARASEQUENCE DEPOSITION AN UPWARD COARSENING OF SEDIMENTS. • RESERVOIR QUALITY SANDS, CHARACTERIZED BY RIBBONS OF SHEET SANDS PRODUCED BY SHORELINE FACIES.

Model for HST

SHELF MARGIN SYSTEM TRACT (SMST) • NOT FREQUENTLY DETECTED, SINCE THEY REPRESENT A RESTRICTED PERIOD OF DEPOSITION AT THE OUTER SHELF IN ASSOCIATION WITH A SMALL DROP AND SUBSEQUENT RISE IN SEA LEVEL. • FORMATION OF AN AGGRADATIONAL COMPLEX, WHICH DOWNLAPS ONTO A TYPE- II SEQ. BOUNDARY AT OUTER SHELF. • SMST COMPLEX MAY BE CAPPED BY EITHER A TYPE- I OR II SEQ. BOUNDARY.

MODEL OF SHELF MARGIN SYSTEM TRACT

PARASEQUENCE • A RELATIVELY CONFORMABLE SUCCESSION OF GENETICALLY

RELATED BEDS OR BED SETS (WITHIN PARASEQUENCE SET) BOUNDED BY MARINE FLOODING SURFACES OR THEIR CORRELATIVE SURFACES.

PARASEQUENCE SET • A SUCCESSION OF GENETICALLY RELATED PARASEQUENCES THAT FORM A DISTINCTIVE STACKING PATTERN THAT IS BOUNDED, IN MANY CASES, BY MAJOR MARINE- FLOODING SURFACES AND THEIR CORRELATIVE SURFACES. -.

MAXIMUM FLOODING SURFACE (MFS) • A MAXIMUM FLOODING SURFACE DEVELOPS DURING THE MAXIMUM LANDWARD INCURSION OF THE SHORE- LINE. CONDENSED SECTIONS, IN TURN, FORM WITHIN THE MFS. • MFS EXHIBITS PELAGIC DEPOSITION AND SEDIMENT STARVED ON THE SHELF AND SLOPE AND SEPARATES PHASES OF SHOREWARD RETROGRADATION (TRANSGRESSION) FROM THOSE OF BASINWARD PROGRADATION (REGRESSION). • THE MFS IS NOT AN UNCONFORMITY AND IS THEREFORE NOT A SEQUENCE BOUNDARY, IT REPRESENTS A FUNDAMENTAL DEPOSITIONAL SURFACE WITHIN A SEQUENCE. • IT CAN BE A PROMINENT AND USEFUL FEATURE IN SEISMIC INTERPRETATION. • MFS AND ASSOCIATED CONDENSED SECTION SOMETIMES PROVIDE A READILY DETECTABLE REFERENCE SURFACE ON SEISMIC RECORDS, WELL LOGS AND BIOSTRATIGRAPHIC DATA, CAN USE TO REGIONALLY CORRELATE STRATIGRAPHIC SEQUENCES

PARASEQUENCE STACKING PATTERN