Geochemical Characteristics of Oil and Source Rocks and Implications for Petroleum Systems, Talara Basin, Northwest Peru

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Geochemical characteristics AUTHORS Andrea Fildani Department of Geological of oil and source rocks and and Environmental Sciences, Stanford University, Stanford, California; present address: Chevron Energy Technology Company, 6001 Bollinger implications for petroleum Canyon Rd., San Ramon, California 94583; [email protected] systems, Talara basin, Andrea Fildani is a research geologist for the Quantitative Stratigraphy Team in San Ramon. He northwest Peru received his Laurea in geology from the University of Rome ‘‘La Sapienza’’ and his Ph.D. in geological Andrea Fildani, Andrew D. Hanson, Zhengzheng Chen, sciences from Stanford University. His research J. Michael Moldowan, Stephan A. Graham, and interests are in sequence stratigraphy, seismic stratigraphy, marine geology, and basin analysis. Pedro Raul Arriola Andrea is currently working on deep-water depositional systems reservoir characterization.

Andrew D. Hanson Department of Geo- ABSTRACT science, University of Nevada Las Vegas, 4505 South Maryland Parkway, Las Vegas, Nevada In the first comprehensive study of the Talara basin petroleum sys- 89154-4010; [email protected] tem of onshore and offshore northwest Peru, we test oil–source Andrew Hanson received his Ph.D. in geological rock correlation through molecular biomarker analysis of oil samples science from Stanford University in 1999. He then from wells scattered throughout the basin, as well as purported worked for Texaco’s deep-water Nigeria explora- source rocks. The new data presented in this manuscript suggest tion team as an exploration geoscientist. Hanson that the oils constitute one oil family, and that the source rock was is an assistant professor at the University of Ne- a predominant marine clay deposited in an oxic to suboxic envi- vada, Las Vegas, where his research focuses on ronment. Substantial relative amounts of oleanane in each oil sample China oil and source rock geochemistry, hydrocarbon migration issues associated with salt struc- indicate a notable input of terrestrial organic matter deposited in tures in the La Popa basin of Mexico, and exten- a mixed marine and terrestrial environment (probably deltaic). The sional basins of central and southern Nevada. high ratio of 24-norcholestanes to 27-norcholestanes and C25 highly branched isoprenoid (HBI) alkanes suggests a significant up- Zhengzheng Chen Department of Geological welling component in the source rock depositional environment. and Environmental Sciences, Stanford University, Stanford, California; present address: ConocoPhil- In addition, the high oleanane indices (oleanane/hopane) of the lips, 600 N. Dairy Ashford, Permian 3024, Houston, oils are not paralleled in any alternative source rock candidate in Texas, 77079; [email protected] this study. The values are as expected for Tertiary source rocks Zhengzheng Chen joined Upstream Technology of and are at levels that exceed any reported Cretaceous or older source ConocoPhillips in 2005. Currently, her work fo- rock or oil. This result, in concert with high nordiacholestane ratios, cuses on reservoir geochemistry in heavy-oil fields norcholestane ratios, and HBI concentrations, indicates a Tertiary in Venezuela and Alaska. She received her Ph.D. age source rock. in organic geochemistry from Stanford University Possible source rocks were selected and analyzed from different in 2004. Her thesis topics cover biomarker iso- outcrops and wells and compared with the oils. A negative correla- topes, characterizing biodegradation using biomarker acids, and petroleum systems in Saudi Arabia. tion suggests that Upper Cretaceous intervals of limestone, marl, and black shale previously believed to be important source rocks can be J. Michael Moldowan Department of Geo- discounted as an important contributor to Talara basin oils. Instead, logical and Environmental Sciences, Stanford the new data suggest a Tertiary source rock (Eocene–Oligocene[?]) University, Stanford, California 94305; [email protected] J. Michael Moldowan attained a Ph.D. in chemistry from the University of Michigan. After a postdoc- toral fellowship at Stanford University, he joined Copyright #2005. The American Association of Petroleum Geologists. All rights reserved. Chevron in 1974, where he developed fundamental Manuscript received September 11, 2004; provisional acceptance February 1, 2005; revised manuscript and applied technology related to petroleum received June 2, 2005; final acceptance June 30, 2005. DOI:10.1306/06300504094

AAPG Bulletin, v. 89, no. 11 (November 2005), pp. 1519–1545 1519 biomarkers. Since 1993, Michael has been a pro- comparable to that of the Progreso basin. However, no such source fessor (research) in Stanford University’s Depart- rock strata have yet been identified within the Talara basin. Certain ment of Geological and Environmental Sciences. Upper Cretaceous samples with good source potential could sup- He has published more than 90 articles in scientific journal and four books. port another petroleum system not yet identified in the coastal areas of Peru. Stephan A. Graham Department of Geologi- cal and Environmental Sciences, Stanford Uni- versity, Stanford, California 94305; INTRODUCTION [email protected]

Steve Graham is a professor in the School of Earth The presence of petroleum in coastal northwest Peru has been Sciences, Stanford University. He teaches courses in sedimentary geology, seismic interpretation, known for centuries. Original inhabitants used oil from natural sedimentary basin analysis, and petroleum reser- seeps for various purposes, and early Spanish colonists extracted voir characterization. His current research projects and refined tar from the La Brea seep south of the city of Talara include studies of sedimentary basins in eastern and used pitch to caulk their ships and to waterproof utensils. The Asia, South America, and western United States, first well in the basin was drilled in 1874, making Talara one of the as well as studies of the sedimentology and strati- first producing petroleum basins of South America (Travis, 1953). graphic architecture of deep-water deposits. Cumulative production from the basin exceeds 1.68 billion bbl of Pedro Raul Arriola Petrobras Energia S.A., oil and 1.95 tcf of gas from 42 oil and gas fields (Higley, 2004) Amador Merino Reyna 285 5tj piso San Isidro, (Figure 1). The U.S. Geological Survey estimated that mean recov- Peru; [email protected] erable oil, gas, and natural gas liquid resources from undiscovered Pedro Arriola graduated in 1997 with a degree fields in the basin sum up to 1.71 billion bbl of oil, 4.79 tcf of in geological engineering from the San Antonio gas, and 255 million bbl of natural gas liquids (Higley, 2004). This Abad University of Cusco, Peru. From 1999 to 2002, estimate is based on a combined Cretaceous–Tertiary source rock he worked for Perez Companc del Peru S.A. as a contribution. Gonzalez and Alarcon (2002), assuming only a Cre- development geologist. Pedro is currently working for Petrobras Energı´a Peru as a petroleum geologist taceous shale as the hydrocarbon source rock, calculated a total vol- 5 involved in reservoir studies in the Talara basin. ume of generated hydrocarbons of 2.75 10 MMBO and 2.25 104 tcf of gas and total trapped oil and gas of 2.48 105 MMBO and 2.03 103 tcf of gas. Their estimate of total volume of recoverable ACKNOWLEDGEMENTS hydrocarbons from the Talara basin province, including current The authors thank Perez Companc del Peru (now production, is 3.72 billion bbl of oil and 9.344 tcf of gas. Most Petrobras Energia S.A.) for support throughout importantly, Gonzales and Alarcon (2002) estimated the volume fieldwork, for access to data, and for oil samples. of remaining recoverable hydrocarbons (excluding current pro- In particular, Peter (Pedro) McGregor, Gerardo duction) to be 2.22 billion bbl of oil and 5.844 tcf of gas. Pozo, Juan Leyva, and Fabian Gutierrez were in- Despite the variable resource estimates based on different strumental in the oil-samples acquisition. Angela source rocks, agreement exists among authors that the mature M. Hessler and Gerardo Pozo helped in the field. We thank Jacob Waldbauer, Michael Hren, and Talara basin has been, and will continue to be, a significant petro- Page Chamberlain from the Stable Isotope Bio- leum province in the world energy panorama. Only in very recent geochemistry Laboratories at Stanford University years have secondary recovery programs been started in this basin, for helping us in d13C analyses. David Zinniker, which is still largely on primary production (Gutierrez and Arriola Fred Fago, and all the technicians at the Organic Ipenza, 2002), whereas the offshore of the basin is largely unex- Geochemistry Laboratories were very helpful and plored. For this reason, a more comprehensive study of the petro- supportive throughout the project development. leum system(s) of the Talara basin is crucial. The most compelling J. M. Moldowan is thankful to the Molecular Or- ganic Geochemistry Industrial Affiliates program problem about the Talara basin petroleum system is that very little for laboratory support. We also thank Debra is known about the source rock component. The supposed source Higley for providing access to an early version rock intervals have been sparsely drilled and sampled, and no of her work. A. Fildani thanks the Stanford biomarker-focused analytical work has yet been published. Project on Deep-Water Depositional Systems for Although petroleum systems include source, reservoir, and support throughout this project. This manuscript trap, the presence of a source rock is the most important factor benefited of reviews and comments from B. J. Katz, M. A. Smith, and AAPG Bulletin editor E. A. governing the accumulation of hydrocarbons (Dahl et al., 1994). Mancini. However, even after a cumulative production of 1.68 billion bbl of oil, the source rocks have not been rigorously documented, and

1520 The Petroleum System of Talara Basin Figure 1. Generalized map with limits of the Talara basin and major tectonic features of northwest Peru. Limits of the Talara basin are shown in short dashes; the area of oil production is highlighted with diagonal lines (modified from Mourier et al., 1988; Pillars de Zorritos location is from Kraemer et al., 1999).

different Upper Cretaceous intervals are cited as source leum systems are present in the basin? What are their rocks by various authors (Zun˜ iga-Rivero et al., 1999; relationships? Arispe, 2001a; Gonzales and Alarcon, 2002). Thus, Biomarkers are widely and successfully used in the many questions are still unanswered about the Talara petroleum industry to identify groups of genetically basin. Specific questions include the following. What related oils, to correlate oils with source rocks, and to is the source rock? What was its depositional environ- describe the probable source rock depositional environment? What age is the source rock? How many petro- ments for migrated oil of uncertain origin (Moldowan

Fildani et al. 1521 et al., 1985; Peters and Moldowan, 1993; Peters et al., without considering interaction with at least two other 2005). We analyzed 30 oils for biomarkers and screened basins, the Progreso basin to the north and the Lan- possible source rocks suggested by previous workers. cones basin to the east (Figure 1). In particular, the Our results permit the characterization of the Talara geographic boundaries of the basin are unclear. For oil–source rock depositional environments, exclude cer- example, the southern end of the basin is poorly known, tain specific source rock candidates, and suggest the and the offshore (western) margin is largely unexplored. possibility of previously unsuspected oil sources. Spe- The onshore (eastern) margin is bounded by Paleozoic cifically, Talara oil biomarkers suggest a Cenozoic basement exposed in two areas: the Amotape Moun- source rock not yet identified in the basin, as well as tains and the Silla de Paita (Figure 1). The Amotape Upper Cretaceous source rock intervals of good po- Mountains extend at a 60j angle from the Andes and, tential, possibly linked to a Cretaceous-based petro- along with the Tamarindo high, separate the Talara leum system as yet unrecognized and unexploited in basin from the Lancones basin (Valencia and Uyen, the coastal area of Peru. 2002) (Figure 1). The southern limit of the onshore basin is the Paita high (Silla de Paita) (Figure 1), but no evident barriers are present in the offshore portion. The basin is bounded to the north by the Dolores– GEOLOGICAL BACKGROUND Guayaquil megashear and the Pillars de Zorritos, a subsurface granitic high penetrated by wells (Figure 1) The Talara basin has been exploited for petroleum for (Kraemer et al., 1999; Higley, 2004). The petroleum- more than a century but it remains a frontier basin in bearing Progreso basin developed in the late Oligo- terms of its geological and tectonic setting. Although cene and is filled by at least 6000 m (19,600 ft) of this study does not deal with the complex tectonic sediment (Kraemer et al., 1999). evolution of northwest Peru and the complicated basin The Talara basin covers at least 15,000 km2 history of Talara, a short description of the basin evo- (5800 mi2), less than half of which is onshore (Fil- lution sets the stage for the petroleum system. A more dani, 2004). The onshore sedimentary deposits range detailed account of basin evolution and sedimentary from Cretaceous to Eocene in age and consist of clastic successions can be found in Fildani (2004). fill that is in excess of 9000 m (29,500 ft) thickness The Talara basin sits astride the plate boundary (Carozzi and Palomino, 1993). In most of the forearc where the Chile–Peru trench and Ecuador trench are regions, tectonically driven subsidence in the mid- dissected by a transform fault that continues inland as dle Eocene permitted the accumulation of shallowing- the Dolores–Guayaquil megashear (Figure 1). The upward marine sequences resting unconformably on megashear represents a fundamental break in the Paleocene, Cretaceous, or older rocks (Ballesteros et al., crustal structure along the South American margin, 1988; Jaillard et al., 1995). Middle–late Eocene strata which influenced the sedimentary infill of northwest of the Talara basin record a more complex story with coastal Peru (Figure 1). The basement of western Ecua- a deepening trend and deposition of deep-water sys- dor, west of the megashear, is hypothesized to be Cre- tems. Periodic extension since the early Tertiary with taceous oceanic crust (Shepherd and Moberly, 1981), subsidence controlled by normal faulting was partially whereas the area south and east of the megashear is related to subduction erosion (sensu Von Heune and composed of metamorphic and granitic rocks. The Ta- Scholl, 1991; Fildani, 2004). The Talara basin sub- lara basin mainly overlies crust with continental affini- sided abruptly and was filled during the Paleocene– ties (Lonsdale, 1978). Different tectonic models have Eocene by siliciclastic material of multiple origins, been proposed for the coastal area of Ecuador and north- predominantly from the east and the northeast (Fildani, west Peru, reflecting the fact that the post-Paleozoic 2004). Limited carbonate facies are restricted to parts tectonic history of the area was complicated and not of the Cretaceous and Pliocene–Pleistocene sections simply related to subduction (Shepherd and Moberly, (Marsaglia and Carozzi, 1991; Carozzi and Palomino, 1981). One of the manifestations of activity along the 1993). Normal faulting affected the basin exten- Dolores–Guayaquil megashear was the formation of sively during and after deposition of the basin fill. the Gulf of Guayaquil (Progreso basin) north of the The deformation was prevalently postdeposition, and study area (Figure 1). the estimated total vertical displacement of base- The boundaries of the Talara basin are poorly de- ment is up to 10 km (6 mi) (Shepherd and Moberly, fined. It is impossible to describe the Talara basin 1981).

1522 The Petroleum System of Talara Basin The oldest formation in the region, the Amotape were visited and sampled (4j24036.400S, 80j5704.100 W). Formation (Figure 2), is exposed in the Amotape Moun- The Muerto Formation is overlain by a series of Cre- tains and consists of Paleozoic (Devonian to Permian) taceous and Paleocene siliciclastic units (Figure 2). Vari- low-grade metamorphic rocks (Shepherd and Moberly, ous authors have suggested that shale and limestone 1981). Mesozoic rocks are not well exposed in any part of the Cretaceous are the petroleum source rocks for of the basin; the few known outcrops are difficult to the Talara basin (mostly Muerto bituminous marl and access, and descriptions of these strata in the literature the Redondo black shale) (Zun˜ iga-Rivero et al., 1999; are incomplete. The Cretaceous Pananga and Muerto Arispe, 2001a; Gonzales and Alarcon, 2002). formations rest unconformably on the Amotape For- The Eocene strata are characterized by alternating mation and consist of limestone and bituminous marl. marine shale, sandstone, and conglomerate deposited The outcrops of the Pananga and Muerto formations almost continuously during the early Tertiary. Most

Figure 2. Simplified stratigraphic column with producing horizons (courtesy of Petrobras Energia P.A.) and potential source rock intervals sampled for this study.

Fildani et al. 1523 of the Eocene sandstone intervals are producing reser- regionally significant potential source rocks. Although voir horizons and are illustrated on the simplified strati- the Heath Formation is not recognized in the Talara graphic column of Figure 2 (Petrobras Energia S.A., area, Kraemer et al. (1999) indicated that the Heath 2001, personal communication; Higley, 2004). Formation is the primary source rock in the Progreso The coastline is marked by a series of raised Pleis- basin province (Figure 1). The Heath Formation was tocene marine terraces (tablazos) (DeVries, 1988). These deposited in the late Oligocene or early Miocene in a tablazos, composed of transgressive limestone and co- deltaic environment and has an average TOC of 1.6% quina beds, cover about 60% of the onshore basin and (Kraemer et al., 1999). have been a limitation for seismic exploration. Note In contrast, Perupetro (1999) asserted that poten- that there have been no studies of the pre-Cenozoic tial Tertiary hydrocarbon source rocks include shale of setting of the basin with regard to its relationship to the the Eocene San Cristobal Formation (lower Eocene of petroleum system(s). the Salina Group), the Chacra Group (lower Eocene Echinocyamus and Clavel (Parin˜ as) formations), the lower Talara (middle Eocene), and the Chira–Heath (upper Eocene–lower Oligocene) formations (Figure 2) PREVIOUS WORK ON PETROLEUM SOURCE (reported by Higley, 2004). Tertiary sediments in the ROCK AND OIL COMPOSITION deepest part of the basin are indicated as potential source rocks (Zun˜ iga-Rivero et al., 1998a). However, Published data on the Talara basin petroleum system Gonzales and Alarcon (2002) indicated that the Bal- are sparse and proprietary data sets are not easily ac- cones, as well as the Eocene Chira, Salina, and San cessible. Recently, the U.S. Geological Survey pub- Cristobal formations and different intervals in the Pa- lished an open-file report making available publicly, leocene were poor source rocks based on TOC and for the first time, a large database of oil analyses from hydrocarbon indices (Rock-Eval). the area (Higley, 2004). The American International Petroleum Company Pindell and Tabbutt (1995) indicated that five main evaluated the TOC of 151 samples of Tertiary shale Mesozoic–Cenozoic settings exist for source rock de- collected from outcrops and well cuttings throughout position and preservation in the Andean basins of the basin without identifying a good potential source South America. One of those five settings is within the rock interval (database reported by Higley, 2004). coastal environments of western South America, spe- Gonzales and Alarcon (2002) reported that the geo- cifically forearc basins. They noted that upwelling and chemical analyses of 13 shale and limestone samples attendant suboxic conditions concentrated organic mat- ranging in age from Early Cretaceous (Albian) to Oli- ter in the marine shale and cited the Upper Cretaceous gocene showed TOC contents ranging from 1.1 to 1.3%. Redondo Formation as one such rock unit that was de- Rodriguez and Alvarez (2001, personal communica- posited in this setting (Figure 2). tion), in an unpublished report for Perez Companc, Most of the data available for potential Talara indicated that, based on the analysis (Rock-Eval and source rocks are based on total organic carbon (TOC) TOC) of 135 samples from different wells through- and pyrolysis (Rock-Eval) and dispersed in proprietary out the basin from the Cretaceous to the upper Eo- reports. Total organic carbon values above 1% indicate cene, the Muerto Formation was the interval with the good to very good source rocks, whereas those below best source rock potential. This conclusion was based 1% have poor to fair source potential (Peters, 1986). on high (>2%) TOC results. Unfortunately, we had no Various authors postulated two separate formations as access to cuttings from this interval in our study. hydrocarbon source rocks in the Talara basin: the ma- Previously published oil data from the Talara rine shale of the Upper Cretaceous (Campanian) Re- basin province (reported by Higley, 2004) seem to dondo Formation and the Lower Cretaceous (Albian) suggest one oil family. The oils have median values of Muerto Formation, composed of marl and limestone 5.5 ppm for nickel (Ni) and 4.0 ppm for vanadium (V) (Figure 2) (Zun˜ iga-Rivero et al., 1998a, b; Arispe, (Higley, 2004). Based on the vanadium and nickel con- 2001a; Gonzales and Alarcon, 2002). Gonzales and tent and d13C values, Higley (2004) concluded that Alarcon (2002) proposed that the Cretaceous Re- the Talara basin province oils were from source rocks dondo Formation is the primary hydrocarbon source of similar origin, such as shale deposited in a marine rock in the basin and included the Cretaceous Muerto setting. Possible minor variations in oils were attributed Formation and upper Oligocene Heath Formation as to local differences in the same depositional system or

1524 The Petroleum System of Talara Basin from mixed nonmarine or marine-nonmarine shale that strate that the identification of Talara basin’s petro- contained a different ratio of nickel to vanadium (Higley, leum source rock(s) remains open. To address this 2004). Mixing of oils from several source rocks may also problem, we proceeded in three steps: (1) we col- have influenced the Ni and V contents of these oils lected all available published and unpublished data on (Higley, 2004). The oil samples reported by Higley the Talara basin petroleum system; (2) we performed (2004) are primarily from Eocene reservoirs. One oil oil biomarker analyses to define molecular characteris- sample listed is from a fractured interval from the Amo- tics of 30 oil samples; and (3) we analyzed selected po- tape Formation in the southern part of the basin (Port- tential source rocks to search for matches with our achuelo field; Figure 3). This oil shows the same geo- oil database. As a result, we were able to eliminate a chemical characteristics and groups with the other oils, series of previously postulated petroleum source rocks indicating that a late charge of old and fractured res- and redirect the focus toward a completely different ervoirs is possible in this basin. scenario for deposition of the basin’s source strata, These incomplete, conflicting, and generally broad opening new possibilities for exploration in the Talara prior studies (i.e., bulk geochemical analyses) demon- basin.

Figure 3. Map showing the location of wells from which oil samples analyzed in this study were collected; inset shows detailed map with location of wells in Block X (courtesy of Pecom del Peru, now Petrobras del Peru).

Fildani et al. 1525 METHODS from freshly broken rocks probably helped to advertise this rock as the source rock of the northwest Peru ba- This work is based on 30 oils and 6 source rock ex- sins (Zun˜ iga-Rivero et al., 1999). We collected four sam- tracts collected during 2000 and 2001. To cover the ples from the Muerto Formation. Although the sam- entire basin, we collected oils from different wells from ples did not have elevated TOC values (Table 1), we fields onshore and offshore (Figure 3). Oils were fil- extracted and analyzed bitumens from one sample. tered to clean up impurities (such as sediments) and The Redondo Formation has been penetrated by separated using short-column chromatography, and satu- some wells in Block X, and Perez Companc (now Pe- rate and aromatic fractions were separated by high- trobras Energia S.A.) made four cuttings available for pressure liquid chromatography (HPLC) (Peters and bitumen extraction. The cuttings come from two wells Moldowan, 1993). Gas chromatography (GC), selected situated close to each other (Perez Companc wells EA ion-monitoring gas chromatrography–mass spectrome- 5927 and EA 2278 herein named simply wells 5927 and try (SIM-GCMS), and metastable reaction-monitoring 2278; Figure 3) and suggested the presence of pro- gas chromatography–mass spectrometry (MRM-GCMS) mising source rocks (Table 1). The black shale sample were performed on oils and possible source rock ex- named ‘‘Redondo’’ in Table 1 was taken from an un- tracts. The details of the implemented technical pro- specified core in the Upper Cretaceous interval. cedures are reported in Appendix 1. To create a broader source rock screening, we also sampled shale from different Eocene formations (Pozo, Ostrea, Lobitos, and Mogollon Medio formations; Table 1; Figure 2) that have been suggested as possible DATA PRESENTATION AND ANALYSIS source rocks by local geologists. To avoid the effects of outcrop weathering, we used samples from borehole Source Rock Geochemistry cores and cuttings when available. To complete our source rock collection, two Heath Because the published data, which include mostly Formation samples were taken from outcrops to the nonbiomarker parameters, are not specific about wells north in an area that some workers consider part of the and areal distribution of samples, it is currently not Progreso basin (3j43.1440S, 80j41.6310W). The samples possible to identify favorable depositional environments were collected from two different cliff exposures com- for potential source rocks or establish geochemical posed of shale and silty shale. They appear to be ther- correlations. Almost every shale interval in the Talara mally very immature, containing considerable organic basin has been indicated as a possible source of hy- material (leaves and stem material) consistent with depo- drocarbons (see list in Higley, 2004). The Cretaceous sition in a low-energy environment (possibly lagoonal). section, with the Muerto Formation and the Redondo Total organic carbon and Rock-Eval data indicate Formation, contains the favorite candidates (Zun˜ iga- that the samples collected from the Eocene section are Rivero et al., 1998a, b; 1999; Arispe, 2001a; Gonzales not favorable source rocks (Table 1). The best quality and Alarcon, 2002), but data presented to support Eocene samples contain type III kerogen and would this inference are insufficient. The Muerto Formation produce mostly dry gas (Figure 4) (Peters et al., 2005), was also indicated as the source rock when Perupetro yet no evidence of dry gas accumulation in the ba- advertised the bid round of 2000 (Perupetro, 1999; sin has ever been reported (Gonzales and Alarcon, Zun˜ iga-Rivero et al., 1999; Arispe, 2001b). 2002). Cretaceous source rocks have good liquid po- We targeted the Muerto Formation and the Re- tential with promising values of TOC and Rock-Eval dondo Formation to evaluate a match with the oils. (Table 1). However, TOC and Rock-Eval values indi- The Muerto Formation outcrop was examined and cate low-quality source rock for the Muerto Formation sampled, together with the underlying Pananga For- samples. The Muerto sample selected for biomarker mation on the west side of the Amotape Mountains analyses yielded a high C29/C30 hopane ratio and a very (Figure 1). The 2–3-m (6.6–10-ft)-thick limestone low diasterane/sterane value consistent with the ob- beds of the Pananga Formation comprising massive served carbonate depositional environment (Table 2; limestone with scattered ammonites are not a likely Figure 5). Cuttings from wells 5927 and 2278 are in- source. In contrast, the Muerto Formation is a thinly terpreted as having been deposited in the continuous bedded (10–20-cm; 4–8-in.), laminated marl with and laterally extended interval of Redondo Formation intercalated dark shales. The intense sulfurous smell that is reported as a basinal blanketing shale. These

1526 The Petroleum System of Talara Basin Table 1. Total Organic Carbon and Rock-Eval Data for Possible Source Rocks of Talara Basin

TOC and Rock-Eval Data* Interpretive Ratios** Sample

Identification Wells Depth (ft) Formation TOC S1 S2 S3 T max HI OI S2/S3 PI S1/TOC T Muerto 1 Outcrop Muerto 0.47 0.27 0.89 0.17 433 189 36 5.24 0.23 57 T Muerto 2 Outcrop Muerto 0.19 0.00 0.05 0.19 432 26 100 0.26 0.00 0 T Muerto 3 Outcrop Muerto 0.32 0.02 0.32 0.25 437 100 78 1.28 0.06 6

Well 2278 2278 7870–7880 Redondo 4.44 0.99 18.10 0.67 433 408 15 27.01 0.05 22 Well 2278 2278 7890–7910 Redondo 5.31 1.45 22.45 0.82 433 423 15 27.38 0.06 27

Well 5927 5927 8010 Redondo 2.82 0.37 9.40 0.53 433 333 19 17.74 0.04 13 Well 5927 5927 8060–8070 Redondo 1.61 0.10 2.88 0.31 433 179 19 9.29 0.03 6 Well 5927 5927 8080–8090 Redondo 1.95 0.11 3.35 0.33 435 172 17 10.15 0.03 6

Pozo 3265 Pozo 0.63 0.07 0.51 0.31 427 81 49 0.12 11 Ostrea 1 AA80 Ostrea 0.28 0.01 0.32 0.07 416 114 25 0.03 4 Ostrea 2 AX 11 Ostrea 2.41 0.09 1.41 0.48 430 59 20 0.06 4 Lobitos AA1768 Talara 0.45 0.01 0.39 0.08 439 87 18 0.03 2 Mogollon medio 1944 Mogollon 0.15 0.01 0.2 0.01 455 133 7 0.05 7

11/23/03 Redondo 1.31 0.17 2.51 0.27 435 192 21 0.06 13 11/8-6 Outcrop Heath 2.35 0.02 0.32 2.2 435 14 94 0.06 1 11/15-2 Outcrop Muerto 0.21 0 0.04 0.4 415 19 190 0.00 0 11/30-4 Outcrop Heath 0.34 0 0.05 0.35 383 15 103 0.00 0

*TOC = total organic carbon; S1,S2,S3 = Rock-Eval pyrolysis parameters that measure volatile organic compound (S1), organic compounds by cracking of kerogen (S2), and organic carbon dioxide (S3). **HI = hydrogen index; OI = oxygen index; PI = production index (S1/(S1 +S2)). All parameters are described in Peters (1986). samples are good potential source rocks based on bulk across the basin (Figure 3). Most of the wells produce geochemical measures (Table 1), but the two samples from multiple reservoirs, and the production is re- from well 2278 completely lack oleanane (Table 2; ported as combined. Talara oils vary in their GC patterns Figure 5), a compound related to terrestrial input mostly because of their different degrees of biodeg- (Moldowan et al., 1994). The sample from well 5927 radation (Figure 6). Oils of light biodegradation exhibit has oleanane (Figure 5), and a 24-norcholestane ratio full n-alkane (C15 + ) envelopes, whereas oils of severe and 24-nordiacholestane ratio (respectively, NCR and biodegradation (at least eight samples) are characterized NDR in Table 2). The values of NCR and NDR are by a large unresolved complex mixture with neither relatively high for this rock extract (well 5927, NCR = n-alkanes nor isoprenoids (Moldowan et al., 1992; Pe- 0.67, NDR = 0.53; see Table 2) for an Upper Creta- ters and Moldowan, 1993). Conventional biomarker ceous source rock where values lower than 0.6 and ratios are shown in Table 3 (steranes) and Table 4 0.5, respectively, are expected (Holba et al., 1998a, b). (hopanes). Sterane and homohopane distributions are Shale samples from wells 5927 and 2278 are probably similar for all the samples (Tables 3, 4). The oils have a from different intervals in the Redondo Formation. high C30 sterane index, suggesting a marine environment (Peters and Moldowan, 1993). The diasterane/ sterane ratio indicates a clay-rich environment (Hughes,

Oil Geochemistry 1984). The relative abundance C27-C28-C29 of regular steranes of the oils exhibits small differences and does We sampled oils from different fields to have the not require different source rocks (Figure 7); the rather largest possible coverage of the basin and a regional uniform subequal abundances of the C27-C28-C29 ster- view sufficient to identify possible geochemical trends anes are typical of a marine algal flora. The stair-step

Fildani et al. 1527 Figure 4. Hydrogen index– oxygen index (Van Krevelen) plot indicating hydrocarbon- generative potential of source rocks sampled for this study (Peters, 1986). Type I = highly oil prone; type II = oil prone; type III = gas prone; type IV = gas prone to inert.

progression of C31 to C35 homohopanes is similar for The occurrence of diatomaceous intervals in the source all the samples and indicates an oxic or suboxic source rock of the oil has been confirmed by the presence of depositional environment (Figures 8, 9 with oil Talara 1) highly branched isoprenoid (HBI) alkanes detected in (Peters and Moldowan, 1991, 1993). Source rocks of the oil samples (mass/charge [m/z] 238; Table 5). Highly this type tend not to be prolifically productive and dis- branched isoprenoids are specifically related to rhizo- play relatively low to moderate TOC and HI values solenid diatom evolution and their diffusion and diver- (Peters and Moldowan, 1993). The almost total ab- sification after the late Turonian; the presence of large sence of C35 hopanes, normally associated with marine amounts of HBI is an age indicator (Sinninghe Damste´ carbonate and evaporite (Clark and Philp, 1989), ex- et al., 2004). Diatom-rich upwelling-related deposits cludes those lithologies from the source rock interval. are not well documented in the area, but evidence of

The C26 steranes (24-norcholestanes) and related paleo-upwelling is reported for Eocene and Miocene C26 diasteranes (24-nordiacholestane) are possibly de- strata preserved along the Peruvian coast (Marty et al., rived from a diatomaceous precursor (Holba et al., 1988; Dunbar et al., 1991) and from the modern Peru-

1998a). Their ratios to the nontaxon-specific C26 ster- vian marine slope (Aplin et al., 1992). The modern Pe- anes, 27-norcholestane and 27-nordiacholestane (NCR ruvian upwelling system is one of the most productive and NDR, respectively; Holba et al., 1998a) are in the areas of the oceans (Dunbar et al., 1991). The occur- high range of values reported for Tertiary source rocks. rence of diatomite and diatomaceous mudstone deposits

1528 The Petroleum System of Talara Basin Table 2. Sterane and Hopane Values Calculated for Selected Source Rock Extracts

Sterane

C29 Steranes C29 Steranes (aaa20R/aaa20R + (abb/aaa + Diasterane/ C30 Source Rocks Formations aaa20S) abb) Sterane C27 (%) C28 (%) C29 (%) Index NDR NCR Heath Formation 0.06 0.31 0.12 5 17 78 0.02 Redondo Formation 0.38 0.37 1.22 28 32 40 0.06 0.35 0.36 Muerto Formation 0.51 0.53 0.06 36 28 36 0.058 0 0.22 EA5927-8010 Redondo 0.26 0.39 0.65 32 28 40 0.086 0.53 0.67 Formation EA2278-7879 Redondo 0.46 0.45 0.48 29 35 35 0.081 0.28 0.39 Formation EA2278-7870 Redondo 0.47 0.41 0.40 32 34 34 0.077 0.28 0.41 Formation

Hopane

C30 hopane Tricyclic C32 22S/ ba/ Terpane/ Oleanane Source Rocks Formations Ts/(Ts +Tm)* (22S + 22R) (ab + ba)C29/C30 17a Hopane Index Heath Formation Redondo Formation 0.46 0.59 0.20 0.49 0 0.11 Muerto Formation 0.22 0.59 0.07 1.25 0 0 EA5927-8010 Redondo 0.41 0.56 0.10 0.49 0 0.14 Formation EA2278-7890 Redondo 0.58 0.64 0.08 0.35 0 0 Formation EA2278-7870 Redondo 0.57 0.67 0.06 0.36 0 0 Formation

*Ts =C27 18a(H)-trisnorhopane II; Tm =C27 17a(H)-trisnorhopane.

in the Chira Formation (late Eocene–early Oligocene) the subequal C27-C28-C29 sterane (algal) distribution, of the Talara basin suggests that it was deposited in an suggests a combination of marine and terrestrial sources upwelling oceanic margin (Dunbar et al., 1991). typical of a distal deltaic environment. The oils of the Talara basin show high relative In summary, the combination of high NDR and amounts of oleanane (Figure 8). Elsewhere, oleanane NCR, HBI, and the presence of oleanane in high rela- has been reported in Cretaceous and Tertiary source tive abundance (oleanane index > 0.2; Moldowan et al., rocks, where it is directly linked to flowering plants 1994) support the Tertiary-aged and mixed marine and (Moldowan et al., 1994). Oleanane can be used as a terrestrial input. In Talara oils, the moderate Pr/Ph ra- terrestrial input indicator (vascular plants) as well as tios (1.1–1.7; see Appendix 2), low diasterane/sterane an age indicator because its concentration can be rela- ratios (0.2–0.6, with the exception of AA9161 at 1.81), tively high in the Tertiary. All the Talara oils analyzed and the poor preservation of C34-C35 homohopane dis- have oleanane in the m/z 191 traces (Figure 8), with an tributions (Figure 9) suggest an oxic to suboxic depo- oleanane index (the ratio between oleanane and C30 sitional environment. homohopane) ranging from 0.2 to 1.2 (Table 4). The The Talara oils are of biodegradation degree 1–4, oleanane index suggests substantial higher plant input according to Peters et al. (2005). The impact of bio- (Moldowan et al., 1994). This character, coupled with degradation is most obvious in GC patterns of Talara

Fildani et al. 1529 1530 h erlu ytmo aaaBasin Talara of System Petroleum The

Figure 5. Examples of GCMS mass chromatograms for rock extracts from well cuttings, core, and outcrop. The Redondo rock and well 5927 (also sampled in the Redondo interval) yielded a detectable oleanane peak; the Muerto Formation sample does not have an oleanane peak. Note the high relative abundance of 30-norhopane for the Muerto Formation, typical of calcareous depositional environment. idn tal. et Fildani 1531 Figure 6. Gas-chromatogram traces for selected whole-oil samples from the Talara basin showing progressive biodegradation in the sample order AA5717 (rank 0), AA6529 (rank 2), EA8045 (rank 4), and EA878 (rank 5) based on the ranking scheme of Peters and Moldowan (1993). Notice the Pr/Ph relation typical of higher plant input. Table 3. Sterane Values Calculated for the Talara Basin Oils

C29 Steranes (aaa20S/aaa20R + C29 Steranes Diasterane/ Oil Samples aaa20S) (abb/aaa + abb) Sterane C27 (%) C28 (%) C29 (%) C30 Index NDR* NCR* Talara 1 0.56 0.58 0.44 0.27 0.34 0.39 0.031 0.55 0.68 Talara 2 0.54 0.57 0.33 29.28 34.52 36.20 0.032 0.53 0.66 Talara 4 0.53 0.58 0.31 30.74 34.55 34.71 0.032 0.51 0.66 Talara 6 0.56 0.59 0.32 31.47 35.08 33.46 0.030 0.53 0.66 Talara 7 0.52 0.55 0.21 33.09 33.30 33.60 0.032 0.52 0.66 Talara 10 0.54 0.58 0.31 31.35 34.94 33.71 0.030 0.48 0.63 Talara 14 0.57 0.60 0.34 30.50 34.50 35.00 0.030 0.53 0.67 Talara 15 0.51 0.55 0.25 30.18 34.84 34.99 0.033 0.52 0.66 Talara 17 0.54 0.58 0.28 30.00 34.00 36.00 0.030 0.48 0.66 Talara 20 0.53 0.60 0.33 26.89 36.42 36.69 0.030 0.50 0.66 Talara 21 0.56 0.59 0.32 31.40 33.00 35.60 0.032 0.51 0.66 Talara 26 0.58 0.58 0.49 28.54 35.66 35.80 0.038 0.52 0.65 Talara 30 0.53 0.59 0.30 30.00 35.00 35.00 0.033 0.52 0.67 AA 9174 0.58 0.59 0.47 31.00 33.00 36.00 0.032 0.53 0.68 EA 8054 0.59 0.60 0.48 31.00 33.00 36.00 0.033 0.50 0.68 EA 10519 0.57 0.59 0.40 31.00 34.00 35.00 0.032 0.53 0.71 EA8004 0.56 0.59 0.46 32.00 34.00 34.00 0.032 0.51 0.69 AA7874 0.59 0.58 0.40 28.49 33.27 38.24 0.030 0.56 0.72 EA9484 0.59 0.58 0.42 29.00 33.00 38.00 0.028 0.52 0.69 AA9161 0.62 0.58 1.47 24.00 35.00 41.00 0.057 0.54 0.65 EA878 0.54 0.60 0.42 31.00 35.00 34.00 0.029 0.57 0.69 AA5717 0.59 0.59 0.58 31.00 32.00 37.00 0.030 0.54 0.67 AA6982 0.56 0.58 0.43 29.00 35.00 36.00 0.031 0.56 0.70 EA7619 0.55 0.57 0.28 32.00 32.00 36.00 0.032 0.52 0.70 EA7931 0.57 0.60 0.43 32.00 35.00 34.00 0.030 0.52 0.70 AA2061 0.58 0.58 0.33 31.00 33.00 36.00 0.032 0.53 0.68 AA6592 0.58 0.60 0.49 33.00 31.00 36.00 0.027 0.50 0.69 EA1121 0.56 0.60 0.52 31.00 35.00 34.00 0.028 0.49 0.69

*NDR = nordiacholestane ratio; NCR = norcholestane ratio. oils but does not impact biomarker analysis results. parameters to identify possible trends in the source The sterane and hopane distributions do not change rock distribution (Figure 10). Lacking knowledge of systematically with degrees of biodegradation. From the deep structure of Talara basin and with various au- GCMS analysis, we observed no destruction of steranes thors ascribing dominant vertical migration pathways and a consistent distribution of homohopane patterns in the basin (with minor lateral migration) (Sanz, 1988; (Figures 8, 9). Although oleanane is more resistant to Higley, 2004), the oleanane index and NDR of the oils biodegradation than C30 hopane (Peters et al., 2005, were plotted and contoured (Figure 10). In a verti- p. 665), oils of severe biodegradation degree (with cally drained basin, such as probably the small, highly pristane and phytane removed; i.e., EA878 trace in faulted Talara basin, progressive lateral changes in Figure 6) do not exhibit a higher oleanane/hopane source rock quality can be inferred in the variation of ratio than oils of light biodegradation degree. the geochemistry of migrated oils (Dahl et al., 1994). Variations in values of the biomarker parameters The oleanane index and the NDR distribution show suggest a source rock with local differences related to interesting differences (Figure 10). Contouring reveals facies variation of the source depositional environment. higher values along a roughly north-south axis for For this reason, we mapped variations in biomarker both parameters, flanked to the east and west by lower

1532 The Petroleum System of Talara Basin Table 4. Hopane Values Calculated for Talara Oils

Oil Ts/ C32 22S/ C30 Hopane Tricyclic Terpane/ Oleanane Samples (Ts +Tm)* (22S + 22R) ba/(ab + ba)C29/C30 17a Hopane Index Talara 1 0.66 0.55 0.12 0.44 0.00 0.69 Talara 2 0.60 0.55 0.12 0.44 0.00 0.36 Talara 4 0.62 0.57 0.11 0.45 0.00 0.39 Talara 6 0.65 0.58 0.10 0.44 0.00 0.33 Talara 7 0.52 0.55 0.11 0.46 0.00 0.26 Talara 10 0.65 0.55 0.10 0.44 0.00 0.44 Talara 14 0.62 0.53 0.11 0.44 0.00 0.39 Talara 15 0.57 0.57 0.11 0.46 0.00 0.30 Talara 17 0.58 0.56 0.11 0.45 0.00 0.34 Talara 20 0.55 0.56 0.10 0.48 0.00 0.50 Talara 21 0.62 0.55 0.12 0.45 0.00 0.36 Talara 26 0.64 0.54 0.13 0.47 0.00 0.69 Talara 30 0.63 0.49 0.10 0.45 0.00 0.37 AA 9174 0.73 0.65 0.11 0.48 0.00 0.69 EA 8054 0.72 0.63 0.10 0.50 0.00 0.67 EA 10519 0.71 0.65 0.11 0.51 0.00 0.54 EA8004 0.70 0.63 0.11 0.51 0.00 0.62 AA7874 0.69 0.63 0.10 0.45 0.00 0.57 EA9484 0.75 0.67 0.09 0.39 0.00 0.64 AA9161 0.73 0.62 0.17 0.60 0.00 1.00 EA878 0.66 0.67 0.10 0.48 0.00 0.49 AA5717 0.73 0.67 0.09 0.49 0.00 0.76 AA6982 0.71 0.67 0.09 0.47 0.00 0.58 EA7619 0.63 0.67 0.09 0.43 0.00 0.33 EA7931 0.69 0.65 0.09 0.44 0.00 0.46 AA2061 0.68 0.65 0.08 0.43 0.00 0.40 AA6592 0.75 0.67 0.09 0.42 0.00 0.63 EA1121 0.82 0.67 0.12 0.41 0.00 1.02

*Ts =C27 18a(H)-trisnorhopane II; Tm =C27 17a(H)-trisnorhopane. values. NDR shows a well-defined high in the center dex may have had more terrestrial input (river mouth?). of Block X, with the highest value reaching 0.57 Oils might be reflecting small differences in the source (Figure 10). The oleanane index shows two highs: rocks facies both stratigraphically and areally. one to the north and one to the south of Block X, with lower values offshore to the west. The mapped highs of Maturity Indicators and Biodegradation Effects the oleanane index and the NDR are almost compen- The Ts/(Ts +Tm) ratio is both maturity and source satory; the high of the NDR parameter sits between the dependent and is not an effective parameter for ma- highs of the oleanane index (Figure 10). The distribu- turity in Talara oils. Possible organic facies changes tion of these parameters suggests a nonhomogenous (as discussed above) dictate the changes in many bio- source rock with differences related to lateral facies marker parameters, such as Ts/(Ts +Tm) ratio, di- variation. The source depositional system was probably asterane/sterane ratio, and oleanane/C30 hopane ratio deposited along a north-south trend, which closely (Peters et al., 2005). The presence of C30 steranes, an mimics the modern coastline. The areas of higher NDR indicator for marine-source input (Moldowan et al., values suggest a more distal source facies possibly in- 1990), and oleanane, an indicator for terrestrial input, volved with upwelling (more algal, colder water, more point to a mixed-source input from both marine and nutrients), whereas the areas with a higher oleanane in- terrestrial organisms. The influence of organic facies

Fildani et al. 1533 Figure 7. Ternary plot of regular steranes for Talara oils and selected source rocks. Percentages of C27-C28-C29 steranes are based on GCMS analysis of mass/ charge (m/z) 217 peak areas of the saturates fraction. The ternary plot shows small differences and the uniform sub- regular C27-C28-C29 sterane distribution and can be interpreted as being indicative of a marine algal flora because of subequal C27-C28-C29 distribution.

change (marine vs. terrestrial) is supported by positive several oils show complete loss of isoprenoids by gas correlations observed between oleanane/hopane ratios chromatography–flame ionization detector (GC-FID) with source-indicative parameters, such as diasterane/ analysis (EA10519, EA8001, AA7874, EA9484, sterane ratios and Ts/(Ts +Tm) ratios (Figure 11). AA9161, EA878, and AA6982), rank 5. In these cases, Parameters from C29 steranes, 20S/(20S + 20R), and one might expect to observe samples that show some abb/(abb + aaa) ratios (averages about 0.55 and 0.58, biomarker biodegradation, although there appears to respectively; Table 3) are at or near their equilibrium be significant inertia between achieving total isopren- values (about 0.55 and 0.68, respectively; Seifert and oid biodegradation and effective biomarker alteration, Moldowan, 1986). This suggests that the oils have been which results in many oils being stuck at biodegrada- generated from the source rock in a narrow maturity tion rank 5. No obvious hints of biomarker alteration range at or near the peak of the oil window. appear in any of these oils, except sample AA9161 Biodegradation (reviewed by Peters et al., 2005) (Figure 11). Oil AA9161 shows elevated oleanane/ can alter biomarker ratios where one component of hopane and diasteranes/steranes ratios consistent with the ratio is more susceptible to bacterial attack than such alteration, and several of the other sterane parame- the other. Most of the studied oil shows a biodegra- ters (Table 3) are also deviant from the other oil samples, dation rank in the range 0–4 (ranging from intact suggesting alteration (Figure 11). Such alteration is evi- n-alkanes to complete n-alkane removal, but without dentbecausehopaneandsteranesaremorelabiletoward isoprenoid obliteration; Peters and Moldowan, 1993). biodegradation than oleanane and diasteranes, respec- At these biodegradation levels, oil generally does not tively, and these parameters are seen to respond accord- show alteration of polycyclic biomarkers. When iso- ingly with increased values for this sample (Table 3). prenoids are virtually removed (rank 5), biomarker alteration can become significant (ranks > 5). Oil is sometimes observed to contain n-alkanes and/or iso- OIL–SOURCE ROCK CORRELATION prenoids and shows significant biomarker alteration. These cases are commonly attributed to mixing in the Biomarker analyses of selected source rock extracts reservoir of multiple oil charges that have been de- from both subsurface and outcrop samples of the graded to different extents. Such cases have not been Talara basin were compared to the oils in an attempt observed in the Talara oils studied here. However, to establish oil–source rock correlation. The biomarker

1534 The Petroleum System of Talara Basin Figure 8. Example GCMS mass chromatograms for two oils from the Talara basin showing m/z 191. Notice the large oleanane peaks and the lack of preservation of the higher homohopanes. These data indicate a Cretaceous or younger source rock that was deposited in an oxic-suboxic setting and are similar to data for oils derived from other known deltaic settings.

Fildani et al. 1535 Figure 9. Homohopane distribution (C31 –C35) from Talara oil sample 1 (representative for all oils) indicates nonpreservation of the higher homohopanes, typical of suboxic bottom water during deposition.

parameters of the oils suggest a very specific depo- carbonate environment (C29/C30 hopanes) not encoun- sitional environment and age limitation for the source tered in the oils; it lacks oleanane and contains very low rock: a Tertiary age source deposited in a clay-rich ma- values of NCR and NDR. We therefore conclude that rine oxic to suboxic environment with terrestrial in- the bituminous marly limestone facies of the Muerto put. We infer that the source rock was deposited in Formation sampled for this study is not the source rock the offshore part of a deltaic environment where local for oils in the Talara basin. variation and interfingering of marine and terrestrial Samples from wells 5927 and 2278 are good source material occurred over short distances and through rocks based on their bulk geochemical measures (Table 1), time. Distal parts of deltaic systems tend to be clay but samples from well 2278 completely lack oleanane rich (Bhattacharya and Walker, 1992), and in an oceano- (Figure 5). Additionally, NDR and NCR values are graphic setting, such as what occurs along the Peruvian consistent with those typically recorded for Upper Cre- coast, diatom blooms are seasonally favored by up- taceous oils (Holba et al., 1998a) and are thus also welling, comparable to the modern Peruvian margin not a match for the Talara oils. The sample from well (Aplin et al., 1992). 5927 has oleanane (Figure 5) and 24-norcholestane The Cretaceous shale and marl have good poten- with values of NCR and NDR relatively high for an tial as source rocks (Figure 4) and, when plotted on a Upper Cretaceous source rock, where values lower

C27-C28-C29 ternary diagram, show a good potential than 0.6 and 0.5, respectively, are expected (Holba correlation with the oils (especially samples from well et al., 1998a, b). However, overall, the parameters for 2278; Figure 7). However, the Muerto Formation sam- sample well 5927 do not match well with the oils. This ple yielded biomarker parameter values typical of a sample initially appeared to be a possible candidate

Table 5. HBI* Values for Selected Oils

Samples Concentration Volume Spike** HBI HBI Standard HBI Sample weight (mg) (mg/mL) (mL) (mg) ppm GCMS area Area (ppm)

STD (Standard) 0.01326 50 0.663 CZ223 AA2061 14.4 0.01326 200 2.655 184.41 CZ225 115,067 29,161 727.6662 AA9161 14.3 0.01326 200 2.652 185.45 CZ226 No HBI EA1121 6 0.01326 100 1.326 221.00 CZ227 104,357 26,980 854.81457 EA7619 8.9 0.01326 100 1.326 148.99 CZ228 123,805 30,189 611.00248 Talara 1 1.3 0.01326 50 0.663 510.00 CZ229 105,594 26,414 2038.8029 Talara 10 1 0.01326 50 0.663 663.00 CZ230 33,119 23,611 929.9859 Talara 14 2.6 0.01326 50 0.663 255.00 CZ231 136,435 30,467 1141.9216 Talara 17 1.6 0.01326 50 0.663 414.38 CZ232 115,951 34,212 1404.396 Talara 20 0.7 0.01326 50 0.663 947.14 CZ233 51,489 28,284 1724.2059

*HBI standard concentration = 0.01333 mg/ml. Remaining HBI standard concentration = 0.01213. **Total spike solution used: 900.

1536 The Petroleum System of Talara Basin Figure 10. Distribution maps for oleanane index and NDR. Notice the compensatory aspect to their distributions, suggesting lateral facies changes in the source rocks. as Talara’s oil source, a dark shale deposited along an of oils (d13C) shows a trend of 13C enrichment with upwelling-related coastline, but the low oleanane and decreasing age that can be used to discriminate different the C27-C28-C29 sterane distribution indicate otherwise. oils (Chung et al., 1992; Andrusevich et al., 1998). Comparison of the biomarker parameters from the two Second, values of d13C for oils of the Talara basin hint wells (wells 5927 and 2278) suggests that the intervals at an undefined source rock that is younger than the sampled are not correlative, or the potential source rock Upper Cretaceous (Higley, 2004). We analyzed d13C interval has significant lateral variations (Figure 5). content of whole oil for nine samples from different We took additional analytical steps to isolate and fields in our possession (Table 6). The analyses were identify source units. Stable carbon isotopic compo- conducted at the Stable Isotope Biogeochemistry sition is considered important in oil-to-oil correlation Laboratories at Stanford University. Whole-oil d13C and oil-source correlation, as in fact they can be used to (versus Peedee belemnite [PDB]) isotope measure- identify negative correlation (Peters et al., 2005). Two ments of the nine oil samples yield a ratio near 21x considerations prompted us to collect stable carbon (Table 6; error of ±0.2x), suggesting a similar source isotopic data. First, stable carbon isotopic composition rock for each of the sampled Talara fields. Four d13C

Fildani et al. 1537 Figure 11. Correlation between Ts/(Ts +Tm) ratios, oleanane/ C30 hopane ratios, and diasterane/sterane ratio suggests that organic facies change is an in- fluential factor in the variation of biomarker parameters but not an issue for Talara oils. Divergent point in the upper right of each graph is sample AA9161, which has biodegraded biomarkers.

values from proprietary data from Perez Companc 5927 is isotopically too light to be the source of Talara show ratios near 21.5x(Table 6). oils. Age-discriminant biomarker parameters all suggest Our d13C analyses of kerogen extracted from the that Talara oil is from a Tertiary source rock interval. well 5927 sample yield an average value of 26.47x Figure 12 compares the parameter NCR with d13Cto (Table 6). This average value derived from kerogen reinforce the result of a Tertiary age for the oil. Fur- differs significantly from the average value of d13C for thermore, comparing the obtained d13C values with the Talara oils (21x). The sampled interval in well global values of carbon isotopes through time in crude

1538 The Petroleum System of Talara Basin 13 Table 6. d C Values for a Possible Source Rock and Oils tectonically complicated, remains burdened by unsub- from Talara Basin stantiated concepts. Biomarker parameters and d13C Formations Depth (ft) d13C(x) values indicate that where sampled, the Upper Creta- ceous strata are not the main source for Talara oil. Source Rock Thus, our findings contrast with the presumption of Well 5927 Redondo 8020–8030 26.142 source rocks in the Upper Cretaceous (Zun˜ iga-Rivero Well 5927 Redondo 8040–8050 26.332 et al., 1999; Arispe, 2001a; Gonzales and Alarcon, Well 5927 Redondo 8040–8050 26.95 2002; Valencia and Uyen, 2002). Published data showing the enrichment in d13C in the oils were interpreted Oils as a clear signature of a Tertiary source rock (Higley, EA1121 21.259 2004), thus contradicting the conventional belief that AA9161 20.741 the source rock is Late Cretaceous in age. Furthermore, EA7619 21.312 our analysis of potential source rock samples from AA2061 20.782 the Eocene interval failed to reveal any new possible Talara 10 20.711 source rocks, nor have any unpublished proprietary Talara 17 20.65 reports (Perez Companc, 2001, personal communi- Talara 20 22.056 cation) helped to unveil unreported sources. Talara 1 21.853 All available data suggest that Talara oils were Talara 14 21.483 generated from a younger source rock than previously believed, a source rock that might not even be present Oils (from Pecom del Peru) within the traditional boundaries of the Talara basin. Well 1531 Helico 21.1 Peters et al. (2005), from a limited database (reporting Well 1659 Ostrea 21.7 only few GCMS traces), suggested that the Heath For- Well 5167 Parinas 21 mation could be the source rock for both the Talara Well 5176 Bas. Salina 22.2 basin and the Progreso basin. A published chromatogram of a rock extract obtained from cuttings from the well Piedra Redonda C-13X (Peters et al., 2005) is a good oils (Chung et al., 1992; Andrusevich et al., 1998), the match with the oils from the Talara basin (Figure 13). value for the kerogen extracted by sample well 5927 is The sample is described as being from the Heath consistent with a Late Cretaceous system, whereas the Formation, and the chromatogram shows oleanane and oils suggest a younger source rock (maybe Oligocene or a pattern of tetracyclic terpanes similar to the oils from younger). The reason for the isotopic shift in the global Talara (Figure 13). Furthermore, Higley (2004) re- carbon budget that occurred in the late Tertiary is not ported that geochemical characteristics of two oils from completely understood, but it is believed to be related the Progreso basin are a good match with the observed to a sudden, rapid drop in the concentration of atmo- values of the Talara oils and concluded that the Talara spheric CO2 (Chung et al., 1992). The heavy isotopic and Progreso oils could be grouped in the same family, values of the Talara oils further suggest a prevalent ma- probably from the same source rock interval. Although rine input. Terrestrial organic matter is isotopically in- further analyses (for both biomarker and isotopes) are variant at about 25x(Chung et al., 1992). Although needed to unequivocally confirm this relationship, it the abundance of oleanane indicates that the source of appears that the potential source rocks could lie within the oil received higher land plant material, the heavy the deltaic system of the Heath Formation or a similar isotopic value of the oils suggests that marine algae depositional system. The Piedra Redonda well is located contributed the bulk of the organic matter to the source. north of the Talara basin in an area reported as part of the Progreso basin (Kraemer et al., 1999) (Figure 14). Because Oligocene and Miocene strata have not been IMPLICATIONS OF A TERTIARY SOURCE ROCK drilled in the Talara basin and the Heath Formation is only known to be present in outcrops north of Talara Talara basin oils present a dilemma with multiple per- basin, the upper Oligocene and early Miocene have been missible solutions inferable from the available data. overlooked as potential source rocks for oils in the Major effort is required to improve our understand- Talara basin. The presence of structural barriers (such ing of the petroleum system of a basin that, even if as the Pillars de Zorritos) and zones of intense faulting

Fildani et al. 1539 Figure 12. Comparative diagram showing (A) 24-norcholestane (NCR) vs. geologic age with white field indicating the variation of NCR with geologic age (modified from Holba et al., 1998a, b). (B) d13C variation through geologic time with fields being defined by diagonal lines (modified from Chung et al., 1992), and different average values represented by solid line with dots, from Andrusevich et al., (1998). For both figures the stars indicate average values. between the Progreso and the Talara basins have been riers became effective. In this scenario, lateral migra- considered obstacles for lateral migration. Unpublished tion of almost 100 km (62 mi) must be postulated to data from Perez Companc suggest that lateral migration account for the charge of the Eocene reservoir intervals is unlikely, especially to the north near the Progreso (Figure 14). The absence of oil in Oligocene deposits in basin, where the Oligocene has been drilled with no oil the north could be explained by the absence of traps at shows and where a series of dry wildcats were drilled the time of migration (Figure 14), with the implication south of the Pillars de Zorritos (Figure 1) (G. Pozo, 2004, of structural deformation after the late Oligocene. personal communication). This evidence seemingly pre- Another scenario depends critically on Paleogene cludes the possibility of lateral migration of oil from the extensional tectonism in the Talara basin (Fildani, 2004). upper Oligocene–lower Miocene Heath Formation, In this scenario, a Paleogene horst and graben setting which is present to the north, into Eocene Talara reser- would favor the development of basinal marine-source voirs, while leaving Oligocene reservoirs uncharged. facies and a thick accumulation of sediment, which Alternatively, we suggest three possible scenarios could have been sufficient to foster oil maturation. to account for Talara basin oil. For the first scenario, Sediments deposited in deep-water environments in the we assume that the Heath Formation main deposi- late Eocene crop out along the modern Peruvian coast tional area was located (as described) in the Progreso (Fildani, 2004). The Oligocene sedimentary rocks to basin, north of Talara. In this case, the Oligocene Heath the north are interpreted as having been deposited in Formation generated the oil that migrated to the deltaic environments, and the depositional systems of Eocene reservoirs of Talara before the structural bar- the Progreso basin are described as deltaic to shallow

1540 The Petroleum System of Talara Basin Figure 13. Comparison between a representative oil from the Talara basin (Talara 1) and a published rock extract from the Piedra Redonda well (from Peters et al., 2005). Tetracyclic terpanes and homohopanes are labeled; the stars indicate an unknown tetracyclic terpane common to all the oils of Talara and to the Piedra Redonda sample. The rock extract comes from an interval of the late Oligocene Heath Formation.

marine (Kraemer et al., 1999). We suggest that the of the basin in the late Oligocene. Thrust faults are deposition of effective oil-source strata occurred off- present in outcrops in the Talara basin, and Serranne shore of the Talara basin in the late Eocene and Oli- (1987) reported phases of compressional tectonism gocene. These strata would be the southern equivalent based on structural analysis. Eocene proximal facies in of the Heath Formation. In this scenario, like the pre- the eastern part of the basin could have thrust over vious one, lateral migration of at least tens of kilo- equivalent distal offshore facies, as well as Oligocene meters must be assumed to account for the charge of strata, during basin inversion. This last scenario has not the Eocene reservoir intervals. Both scenarios 1 and 2 been tested by drilling, but it could be easily evaluated contrast with the currently proposed but unproven with good-quality regional seismic reflection profiles, vertical migration mechanism for reservoir charge in which presently are not available for the area. We the Talara basin (Sanz, 1988; Higley, 2004). cannot exclude a combination of different components A third alternative scenario retains the vertical mi- from these scenarios. Indeed, a strong possibility exists gration model in charging the Eocene reservoirs by that tectonism and structural architecture control mi- emphasizing the function of compressional inversion gration paths of the Talara petroleum system. The

Fildani et al. 1541 Figure 14. Location map of all the oil samples used in this study and for the Piedra Redonda well to the north where intervals of the Heath Formation were reached. The three different possible scenarios are described in the text. The arrows indicate possible migration paths for different scenarios.

mapped oil parameters of Figure 10 could be related to matter. An interpretation of a deltaic environment slight facies changes in source rock characteristics be- best explains the mix of marine and terrestrial com- cause they are quite systematic in their distribution and ponents, with a dominant marine component. Up- probably not coincidental. This implies the preserva- welling influences are clearly indicated by HBI, a bio- tion of oil characteristics throughout migration with marker compound directly related to the diffusion and only partial homogenization of oils. Thus, the areas of diversification of diatoms. Biomarker attribute map- effective source rock (kitchens) should be relatively ping shows that the upwelling deposits were located close, and only limited lateral migration is implied. in a more distal position in the deltaic system (prodelta or offshore). Based on a comparison with published data, we suggest that the Oligocene or younger shale de- CONCLUSIONS posits (such as the Heath Formation and/or its lateral equivalent) in the Talara offshore are the main source Biomarker parameters and the d13C signature of oil rocks for the oils of the Talara and Progreso basins. Al- samples from the Talara basin indicate that the oil was though the Upper Cretaceous strata of the Talara basin generated from a Tertiary source rock probably depos- contain potential petroleum source rock intervals, these ited in a marine upwelling setting (diatomaceous shale do not correlate with the biomarker signature of the intervals) with significant influx of terrestrial organic oils, and consequently, they are not the main source

1542 The Petroleum System of Talara Basin intervals of Talara oils analyzed. Nevertheless, Upper with an HP 6890 autoinjector. The injector was set at 325jC in the Cretaceous strata could provide the charge for an ad- splitless mode. The carrier gas was helium at 1.0 mL/min with a head pressure of 15.7 psi at 190jC. The column was a 60-m (197-ft) HP ditional petroleum system in northwest Peru yet to DB-1 column with 0.25 mm (0.009 in.) internal diameter and 0.25 be discovered. mm phase thickness. The GC oven temperature started at 140jC, stayed at this temperature for 1 min, rose to 325jCat3.5jC/min, and stayed at 325jC for 10 min. For the 2000 sample set, SIM-GCMS was conducted on a APPENDIX 1: LABORATORY PROCEDURES TrioVG instrument. The silicalited saturate cuts were diluted 10- fold with hexane, and 0.1 mL of the sample was injected on the HP AND TECHNIQUES 5890 Series II GC. The injector was set at 325jC in the splitless mode. The column was a 60-m (197-ft) HP DB-1 column with 0.25 mm Sample Separation (0.009 in.) internal diameter and 0.25 mm phase thickness. The oven GC temperature started at 130jC, then rose to 320jCat2jC/min, and stayed at 320jCfor20min. About 30 g of rock sample were pulverized and transferred to a po- rous thimble (Whatman cellulose extraction thimble, single thickness, 33 mm [1.3 in.] internal diameter, 80 mm [3.1 in.] external Metastable Reaction-Monitoring Gas length, and 35 mm [1.4 in.] external diameter), which was placed into a Soxtec extraction unit to extract soluble bitumen. A beaker Chromatography–Mass Spectrometry filled with extraction solvent (azeotropic mixture of toluene/ For the sample set collected in 2000, silicalited saturates were methylene chloride at a volume ratio of 2:1 with a boiling point analyzed using an HP 5890 Series II gas chromatograph connected of 63.8jC) was attached to the extractor and heated with an oil to an AutoSpecQ mass spectrometry. The GC oven temperature bath for 2 hr. Subsequently, the extract was transferred, solvent started at 140jC, stayed at this temperature for 1 min, then rose to evaporated, and weighed for cleanup and separation. 326jCat6jC/min, and stayed at 326jC for 15 min. Hydrogen was All rock extracts and oil samples were separated into saturates the carrier gas with a head pressure of 27 psi. The column was a 60-m and aromatic fractions at the Molecular Organic Geochemistry Labo- (197-ft) J&W DB-1 column with 0.25 mm (0.009 in.) internal di- ratories at Stanford University using the method described by Peters ameter and 0.25 mm phase thickness. The mass spectrometer was and Moldowan (1993). In brief, oils and rock extracts are absorbed set at EI+ ionization mode with a cycle time of 810 msec. onto an alumina column. The saturate-aromatic cut is rinsed from the Samples collected in 2001 were analyzed on the same column with methyl t-butyl ether/hexane (10:90 vol/vol). The cleaned- instrument, using a slightly different GC temperature program, up saturate-aromatic fraction of the oil or rock extract is separated which started at 150jC, then rose to 325jCat2jC/min, and stayed using a Waters model 590 HPLC pump equipped with a Whatman at 325jC for 20 min. Partisil 10 silica column (9.4 mm [0.37 in.] internal diameter 50 cm [20 in.]). The eluent is divided into three fractions: saturates, aromatics, and polar compounds. Molecular sieves (high Si/Al ZSM-5 zeolite, sili- ˚ calite, with pore size of 6 A) were used to remove n-alkanes (paraffins) APPENDIX 2: PRISTANE/PHYTANE RATIOS from saturates to increase the signals of more diagnostic biomarkers. Samples Pristane/Phytane

Instrumental Analysis AA2061 1.27 AA5717 1.65 AA6592 1.58 Gas Chromatography AA9174 1.68 AFMuerto, (rock extract) 1.06 Crude oils were analyzed using a Hewlett-Packard (HP) 5890 gas AFRedond, (rock extract) 1.96 chromatograph equipped with flame ionization detector and a 24-m EA1121 1.84 (78-ft) methyl silicone DB-1 column with 0.2 mm (0.008 in.) EA2278-7870 1.58 internal diameter and 0.33 mm phase thickness. Crude oils were EA2278-7890 1.29 diluted 40-fold with toluene, and 0.5 mL of the solution was injected EA5927-8010 0.17 onto the column. The injector was set at 325jC in the splitless EA7619 1.45 mode. Hydrogen was used as the carrier gas with a head pressure of EA7931 1.53 20 psi. The oven temperature was set to rise from 80 to 320jCat EA8054 1.29 10jC/min and to hold at 320jC for 20 min. Talara 1, B/C 1.70 Talara 2. B/C 1.68 Selected Ion-Monitoring Gas Talara 4, B/C 1.57 Chromatography–Mass Spectrometry Talara 7, B/C 1.52 Talara 10, B/C 1.48 Because of upgrades in instrumentation, two different instruments Talara 14, B/C 1.64 were used for samples collected in different years. Specifically, sam- Talara 15, B/C 1.49 ples collected in 2000 were analyzed with an SIM-GCMS, Trio I VG Talara 17, B/C 1.38 Masslab, whereas samples collected in 2001 were analyzed using an Talara 20, B/C 1.11 HP 5890 MSD. For the 2001 sample set, silicalited saturates were Talara 21, B/C 1.48 analyzed using HP 5890 Series II gas chromatograph connected to HP Talara 26, B/C 1.39 5972 Series mass selective detector. Silicalited saturate cuts were Talara 30, B/C 1.53 diluted 20-fold with hexane, and 0.5 mL of the solution was injected

Fildani et al. 1543 REFERENCES CITED R. G. Schaefer, and H. Wilkes, eds., Advances in organic geochemistry: Part II. Biogeochemistry: Oxford, New York, Per- gamon, v. 29, p. 1269–1283. Andrusevich, V. E., M. H. Engel, J. E. Zumberge, and L. A. Brothers, Holba, A. G., E. W. Tegelaar, B. J. Huizinga, J. M. Moldowan, M. S. 1998, Secular, episodic chances in stable carbon isotope Singletary, M. A. McCaffrey, and L. I. P. Dzou, 1998b, 24-Nor- composition of crude oils: Chemical Geology, v. 152, p. 59– cholestane as age-sensitive molecular fossils: Geology, v. 26, 72. p. 783–786. Aplin, A. C., A. N. Bishop, C. J. Clayton, A. T. Kearsley, J. R. Hughes, W. B., 1984, Use of thiophenic organosulfur in character- Mossmann, R. L. Patience, A. W. G. Rees, and S. J. Rowland, izing crude oils derived from carbonate versus siliciclastic 1992, A lamina-scale geochemical and sedimentological study source, in J. G. Palacas, ed., Petroleum geochemistry and source of sediments from Peru margin (site 680, ODP Leg 112), in rock potential of carbonate rocks: AAPG Studies in Geology 18, C. P. Summerhayes, W. L. Prell, and K. C. Emeis, eds., Up- p. 181–196. welling systems: Evolution since the early Miocene: Geological Jaillard, E., M. Ordonez, S. Benitez, G. Berrones, N. Jimenez, G. Society (London) Special Publication 64, p. 131–149. Montenegro, and I. Zambrano, 1995, Basin development in an Arispe, A., 2001a, Peru offshore 1: Peru offers deep-water blocks accretionary, oceanic-floored forearc setting: Southern coastal south of Talara area: Oil & Gas Journal, v. 99, no. 8, p. 25–29. Ecuador during Late Cretaceous to late Eocene times, in A. J. Arispe, A., 2001b, Peru offshore 2: Tumbes–Talara blocks off Peru Tankard, R. Suarez Soruco, and H. J. Welsink, eds., Petroleum may signal deep-water play in turbidites: Oil & Gas Journal, basins of South America: AAPG Memoir 62, p. 597–613. v. 99, no. 7, p. 21–24. Kraemer, P., G. Weiner, and P. Alvarez, 1999, Evolucion tectono- Ballesteros, M. W., G. F. Moore, B. Taylor, and S. Rupert, 1988, estratigrafica de la cuenca de Tumbes–Progreso, offshore Peru: Seismic stratigraphic framework of the Lima and Yaquina fore- Ingepet-Perupetro, EXPR-1-PK-07. arc basins, Peru: Proceedings of the Ocean Drilling Program: Lonsdale, P., 1978, Ecuadorian subduction system: AAPG Bulletin, Initial Report, v. 112, p. 77–90. v. 62, p. 2454–2477. Bhattacharya, J. P., and R. J. Walker, 1992, Deltas, in R. G. Walker Marsaglia, K. M., and A. V. Carozzi, 1991, Depositional environ- and N. P. James, eds., Facies models, response to sea level ment, sand provenance, and diagenesis of the basal Salina For- change: Geological Association of Canada, p. 157–177. mation (lower Eocene), NW Peru: Journal South American Carozzi, A. V., and J. R. Palomino, 1993, The Talara forearc basin: Earth Sciences, v. 3, p. 253–267. Depositional models of oil-producing Cenozoic clastic sys- Marty, R., R. Dunbar, J. B. Martin, and P. Baker, 1988, Late Eocene tems: Journal of Petroleum Geology, v. 16, no. 1, p. 5–32. diatomite from the Peruvian coastal desert, coastal upwelling Chung, H. M., M. A. Rooney, M. B. Toon, and G. E. Claypool, in the eastern Pacific, and Pacific circulation before the 1992, Carbon isotope composition of marine crude oils: AAPG terminal Eocene event: Geology, v. 16, p. 818–822. Bulletin, v. 76, p. 1000–1007. Moldowan, J. M., W. K. Seifert, and E. J. Gallegos, 1985, Clark, J. P., and R. P. Philp, 1989, Geochemical characterization of Relationship between petroleum composition and depositional evaporite and carbonate depositional environments and corre- environment of petroleum source rocks: AAPG Bulletin, v. 69, lation of associated crude oils in the Black Creek basin, Alberta: p. 1255–1268. Canadian Petroleum Geologists Bulletin, v. 37, p. 401–416. Moldowan, J. M., F. J. Fago, C. Y. Lee, S. R. Jacobson, D. S. Watt, Dahl, J. E. P., J. M. Moldowan, S. C. Teerman, M. A. McCaffrey, N. E. Slougui, A. Jeganathan, and D. C. Young, 1990, Sedimen- P. Sundararaman, and C. E. Stelting, 1994, Source rock quality tary 24-n-propylcholestanes, molecular fossils diagnostic of ma- determination from oil biomarkers: I— New geochemical rine algae: Science, v. 247, p. 309–312. technique: AAPG Bulletin, v. 78, p. 1507–1526. Moldowan, J. M., P. Sundararaman, T. Salvatori, A. Alajbeg, B. DeVries, T. J., 1988, The geology of late Cenozoic marine terraces Gjukic, C. Y. Lee, and G. Demaisonn, 1992, Source correla- (tablazos) in northwestern Peru: Journal of South American tion and maturity assessment of select oils and rocks from the Earth Sciences, v. 1, p. 121–136. central Adriatic basin (Italy and Yugoslavia), in J. M. Moldowan, Dunbar, R. B., R. C. Marty, and P. A. Baker, 1991, Cenozoic marine P. Albrecht, and R. P. Phip, eds., Biological markers in sedi- sedimentation in the Sechura and Pisco basins, Peru: Palaeo- ments and petroleum: Englewood Cliffs, New Jersey, Prentice geography, Palaeoclimatology, Palaeoecology, v. 77, p. 235– Hall, p. 370–401. 261. Moldowan, J. M., J. E. Dahl, B. J. Huizinga, F. J. Fago, L. J. Hickey, Fildani, A., 2004, Analysis of two arc-associated basins and onset of T. M. Peakman, and D. Winship Taylor, 1994, The molecular their deep-water stages: Magallanes basin, Chile, and Talara fossil record of oleanane and its relation to angiosperms: basin, Peru: Ph.D. dissertation, Stanford University, Stanford, Science, v. 265, p. 768–771. California, 325 p. Mourier, T., C. Laj, F. Megard, P. Roperch, P. Mitouard, and A. Gonzales, E., and P. Alarcon, 2002, Potencial hidrocarburifero de la Farfan Medrano, 1988, An accreted continental terrane in cuenca Talara. Ingepet-Perupetro 2002 Seminar, Lima, Peru, northwestern Peru: Earth and Planetary Science Letters, v. 88, Nov. 6–8, 1 CD-ROM, EXPR-1-EG-07.pdf. p. 182–192. Gutierrez, F. E., and P. R. Arriola Ipenza, 2002, Analisis estrati- Perupetro, 1999, International bidding round — Offshore and grafico de los ciclos Talara-Verdun para la generacion de nuevas coastal blocks: Perupetro information booklet, Av. Luis oportunidades — Yacimento Carrizo – Cuenca Talara – Peru: Aldana, 320 San Borja, Lima, Peru, 47 p. Ingepet-Perupetro, EXPR-3-FG-33.pdf. Peters, K. E., 1986, Guidelines for evaluating petroleum source rock Higley, D., 2004, The Talara basin province of northwestern Peru: using programmed pyrolysis: AAPG Bulletin, v. 70, p. 318–329. Cretaceous–Tertiary total petroleum system: U.S. Geological Peters, K. E., and J. M. Moldowan, 1991, Effect of source, thermal Survey, e-bulletin B-2206a, 52 p.: http://pubs.usgs.gov/bul maturity, and biodegradation on the distribution and isomeri- /2206/A/. zation of homohopanes in petroleum: Organic Geochemistry, Holba, A. G., L. I. P. Dzou, W. D. Masterson, W. B. Hughes, B. J. v. 17, p. 47–61. Huizinga, M. S. Singletary, J. M. Moldowan, M. R. Mello, and Peters, K. E., and J. M. Moldowan, 1993, The biomarker guide; E. Tegelaar, 1998a, Application of 24-norcholestanes for con- interpreting molecular fossils in petroleum and ancient sedi- straining source age of petroleum, in B. Horsfield, M. Radke, ments: Englewood Cliffs, Prentice Hall, 363 p.

1544 The Petroleum System of Talara Basin Peters,K.E.,C.C.Walters,andJ.M.Moldowan,2005,Thebiomarker Sinninghe Damste´, J. S., et al., 2004, The rise of the rhizosolenoid guide, 2d ed.: Cambridge University Press, Cambridge, v. 1 and 2, diatoms: Science, v. 304, p. 584–587. 1155 p. Travis, R. B., 1953, La Brea-Parin˜ as oil field, northwest Peru: AAPG Pindell, J. L., and K. D. Tabbutt, 1995, Mesozoic–Cenozoic Bulletin, v. 37, p. 2093–2118. Andean paleogeography and regional controls on hydrocarbon Valencia, K., and D. Uyen, 2002, Cuenca Lancones: Interpretation systems, in A. J. Tankard, R. Suarez Soruco, and H. J. Welsink, geologica: Ingepet-Perupetro, EXPR-3-KV-18.pdf. eds., Petroleum basins of South America: AAPG Memoir 62, Von Heune, R., and D. W. Scholl, 1991, Observations at conver- p. 101–128. gent margin concerning sediment subduction erosion, and Sanz, V. R., 1988, Geologia y potencial hydrocarburifero de la the growth of continental crust: Review of Geophysics, v. 29, region Mancora–Tumbes: Ph.D. dissertation, Universidad Na- p. 279–316. cional Mayor de San Marcos, Lima, Peru, 119 p. Zun˜ iga-Rivero, F., J. A. Keeling, and H. Hay-Roe, 1998a, Peru’s Seifert, W. K., and J. M. Moldowan, 1986, Use of biological markers coastal basins: 2— Peru onshore deep-water basin should have in petroleum exploration, in R. B. Johns, ed., Methods in large potential: Oil & Gas Journal, v. 96 (September 7, 1998), geochemistry and geophysics: Amsterdam, Elsevier, p. 261– no. 36, p. 88–95. 290. Zun˜ iga-Rivero, F., J. A. Keeling, and H. Hay-Roe, 1998b, Peru’s coastal Serranne, M., 1987, Evolution tectono-sedimentaire du bassin de basin: 1— Attractive potential seen in 10 sub-basins off Peru: Oil Talara (nord-ouest du Perou): Bulletin de l’Institut Franc¸ais & Gas Journal, v. 96 (October 19, 1998), no. 42, p. 117–122. d’Etudes Andines, v. 16, no. 3–4, p. 103–125. Zun˜ iga-Rivero, F., H. Hay-Roe, and T. Vargas, 1999, Peru’s coastal Shepherd, G. L., and R. Moberly, 1981, Coastal structure of the basin— 5 (conclusion)— Potential untested under 50 million continental margin, NW Peru and SW Ecuador: Geological acres in Peru: Oil & Gas Journal, v. 97 (March 15, 1999), Society of America Memoir 154, p. 351–391. no. 11, p. 67–72.

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