Recognition and Significance of Bayhead Delta Deposits… 2014... · · 2015-01-14Volume 45 Number 1 September 2014 Page 1 Recognition and Significance of Bayhead Delta Deposits:

Volume 45 Number 1 September 2014 Page 1

Recognition and Significance of Bayhead Delta Deposits: Implications for Oil/Gas Exploration and Basin Dynamics

Jennifer Aschoff

Department of Geological Sciences, University of Alaska, Anchorage [email protected]

Detailed sedimentology and sequence-stratigraphic context of ancient bayhead delta (BHD) deposits in the Book Cliffs, UT provides insight into BHD development, and helps predict reservoir distribution using the transgressive tra-jectories they define. Estuaries are common features of transgressive coastlines with high preservation potential due to their position within incised valleys. Despite advances in estuarine facies models over the last 20 years, bayhead delta deposits are not widely recognized or utilized in the stratigraphic record, and their geometries/reservoir charac-teristics are not well known. Bayhead deltas develop at the innermost part of bays within wave-dominated and mixed-energy estuaries. Deposits of bayhead deltas can be important reservoirs for oil and gas. However, their true value is that they record the high-frequency turn-around from transgression to regression; in turn, this delineates the long-term trajectory of transgression and assists with facies prediction up- and down-dip of the estuarine facies tract. The follow-ing criteria for bayhead delta identification are herein proposed: (1) overall coarsening-up pattern, (2) presence of small-scale clinoforms (5-15 m height; 100-1000 m length) showing a down-clinoform decrease in grain-size and paleocurrent energy, (3) increasing abundance of mud interbeds toward the clinoform toe, (4) basinward- directed paleocurrents generated mainly by fluvial input with strong tidal overprint, (5) greatest tidal influence in the intertidal zones of the inactive delta front and better preservation of turbidites at clinoform toes, (6) brackish trace and body fos-sils and (7) located within a transgressive interval, especially near transgressive maximum. Recognition of bayhead delta deposits in the Book Cliffs, UT aided regional correlation and defined the transgressive trajectory within a retro-gradational sequence set. The rising transgressive trajectory defined herein helps to explain the high proportion of well-preserved tidal deposits within the middle Castlegate Sandstone and downdip equivalents. Utilization of bayhead delta deposits in other basin-scale studies provides a useful tool for reconstructing transgressive shoreline trajectories that can better predict reservoir distribution, and aids interpretation of long- and short-term drivers on clastic wedge development.

AGS Luncheon Date & Time: Sept. 18th, 11:30 am – 1:00 pm

Program: Recognition and Significance of Bayhead Delta Deposits: Implications for Oil/Gas Exploration and Basin Dynamics

Speaker: Jennifer Aschoff, Department of Geological Sciences, University of Alaska, Anchorage

Place: BP Energy Center

Reservations: Make your reservation before noon Tuesday, Sept. 16th, 2014

Cost: Seminar only, no meal: Free Reserve a box lunch: $15 Lunch with no reservation: On an “as-available” basis only


About the Speaker:

Jennifer Aschoff is currently associate professor of geology at the University of Alaska, Anchorage. The pri-mary focus of her academic research is the formation, fill, and economic resource potential of ancient sedi-mentary basins. She use an integrated approach using a range of datasets, including outcrop, seismic, well-log, core, and geochemical data to understand the linkages between tectonics, sedimentary process and basin dynamics. Her methods include detailed sedimentology, sequence stratigraphy typically integrating well logs, geologic mapping, provenance analysis, and paleocurrent analysis. Core research themes in-clude 1) understanding basin dynamics and their fill, especially the role of dynamic subsidence and 2) ap-plied stratigraphy and sedimentology as it pertains to the oil and gas industry

Jennifer held the positions of assistant professor of geology and geological engineering at Colorado School of Mines (2008-2011) and sedimentology/stratigraphy specialist with BP America (2011-2014). She re-ceived geology degrees from Montana State University (B.S., 2000), New Mexico State University (M.S., 2003) and University of Texas, Austin (Ph.D., 2008).

Figure 1. Ancient bayhead delta (BHD) deposits in the Book Cliffs, UT

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From the President’s Desk:

It is my great pleasure to welcome you to the 2014/2015 session of the Alaska Geological Society. As incoming president, I am very appreciative of the hard work done by the committee to organize the program of events for this session and in particular to Matt Frankforter, who served as past presi-dent of the society.

Those of you that have talked to me may be surprised to learn that I am not originally from Alaska. I spent my formative years in Scotland and had the opportunity as a young geology student to visit some of the classic localities described by Hutton, Murchison, Lapworth, Peache & Horne that shaped early geological theories. Most of these sites are conveniently situated within a short stroll of the highway, down the road from a comfortable bed & breakfast and within stumbling distance of the local pub, where a cold pint beckons at the end of a day of hard fieldwork. How different from work-ing in Alaska!

By compensation, the geology of Alaska is well worth the effort and hardships of getting into the field. Very few places on the planet earth provide the opportunity to observe so many active geological processes. It has been commented that the geology of Afghanistan has been mapped in greater de-tail than many areas of Alaska which serves to highlight the complexity of Alaska’s geology and the challenges of conducting field work in remote areas of the state. This session’s program will hopeful-ly add to our growing knowledge and understanding of the state’s geological riches.

~ Keith


My Pet Rock Matt Frankforter Hilcorp Alaska, LLC

Grain size transition in reservoir facies of the Hemlock formation, Trading Bay Unit, Cook Inlet, Alaska as represented by whole core. A: Jurassic Talkeetna “basement”, B: Hemlock conglomerate with fist size cobbles of Jurassic, C-E: Hemlock exhibiting various degrees of sorting and grain size transition from coarse conglomerate to gravelly pebble conglomerate, F-G: Conglomerate to coarse sandstone with bed-ding planes evident, H: Coarse sandstone.

The best reservoir quality is found in the coarse grained, well sorted sandstone where average porosities are 10-20% greater than in the conglomerates. For a given porosity, however, permeability tends to be higher in the conglomerates. Both facies have proven to be prolific reservoirs capable of producing at rates of 5,000-12,000 barrels of fluid per day.


ALASKA FOSSILS OF THE MONTH

RESURRECTING ANCIENT FOSSILS (“BRING OUT YOUR DEAD”) FROM THE MIDDLE JURASSIC OF TUXEDNI BAY, COOK INLET

by Robert B. Blodgett, Blodgett & Associates LLC, Consulting Geologist, 2821 Kingfisher Drive, Anchorage, Alaska 99502

Just a few weeks ago I had the fantastic experience of visiting the well-known Fossil Point area on the south shore of Tuxedni Bay (Fig. 1), west side of Cook Inlet, nearly due west of Ninilchik on the western shoreline of the Kenai Peninsula. This area is infamous for its exceedingly abundant and diverse Middle Jurassic invertebrate fossil fauna consisting primarily of bivalves [notably the large genus Retroceramus – see Blodgett (2012)] and ammonites. Despite having spent nearly my entire professional career working with Alaskan stratigraphy and paleontology, I had not had the opportuni-ty to visit the site until this summer, when in collaboration with several staff members of the National Park Service, we made a week-long excursion to conduct a baseline study of the paleontologic re-sources of this fossil paradise which occurs along the northern edge of the Lake Clark National Park & Preserve.

Fossil Point is a prominent headland located along the south side of Tuxedni Bay on the west side of Cook Inlet, south-central Alaska (Figs. 1). The Middle Jurassic strata exposed at Fossil Point have long been known for their extremely prolific fossil invertebrate marine fauna (Blodgett and Santucci, 2014; Blodgett and Tainter, 2013; Detterman, 1963; Detterman and Hartsock, 1966; Imlay, 1961, 1964, 1984; Martin, 1926; Martin and Katz, 1912; Moffit, 1927; Stanton and Martin, 1905). Knowledge concerning the cornucopia of fossil materials available here extends back to the final days of Russian America. A significant fossil collection was made by the Russian mining engineer Peter Doroschin and sent to the Russian capital at St. Petersburg, where they were ultimately stud-ied and described by Eichwald (1871) (Fig. 2). Eduard von Eichwald (1795–1876) described many important Jurassic fossils from Alaska. His material was collected when Alaska was still part of the Russian Empire. Eichwald was one of Russia’s early and preeminent paleontologists. He was of German ancestry and was born in present-day Latvia, but spent much of his later career in St. Pe-tersburg. Most of his scientific articles were written in German, but appeared in various Russian pub-lications.

Three formations of the Middle Jurassic age Tuxedni Group are exposed in the headland of Fossil Point: Red Glacier Formation, Fitz Creek Siltstone, and the Cynthia Falls Sandstone. However, only two of these formations (Red Glacier and Fitz Creek) are highly fossiliferous, the Cynthia Falls bear-ing only a very limited fauna, mostly found in its uppermost beds. Both the Red Glacier and Fitz Creek contain abundant bivalves and ammonites, the latter group being the subject of studies by Ralph Imlay (1961, 1964, and 1984). Bivalves are the most common faunal group found in both the Red Glacier and Fitz Creek, but no serious faunal study has been conducted on them since Eichwald’s 1871 work, in which he recognized and described many species (most of which were nearly named by him).

Perhaps the most common bivalve species found in the Red Glacier Formation is the species deter-mined by Eichwald (1871) as Lyonsia aldiana Fischer (illustrated in his Pl. 15, figures 1-3 – see Fig-ure 3 below). (continued)


Specimens of his Lyonsia aldiana Fischer are abundant in the talus scree of shale and shaly silt-stone of the Red Glacier Formation at Fossil Point (see Fig. 4, 1-11), and none have been observed in the overlying Fitz Creek Siltstone, which is renowned for its large inoceramid bivalves belonging to the genus Retroceramus. Close comparison of this species with those found in more modern mono-graphic studies suggest that this species most probably should be reassigned to the genus Pleurom-ya. This genus also has 3-4 other species present in the same Red Glacier succession at Fossil Point, and another few species of the genus are present in even slightly older beds of the coeval Kialagvik Formation exposed further south at Wide Bay.

It is one of our priorities to revise the Middle Jurassic biostratigraphic distribution of bivalves of the Tuxedni Group of Cook Inlet and its counterpart, the Kialagvik Formation of the upper Alaska Penin-sula. In that the species have not been carefully studied (or illustrated) since 1871, it is obvious that probably the majority of the species will have to be reassigned to different genera. Our work will in-volve close collaboration with Russian paleontologists working with high-latitude Russian Arctic Ju-rassic faunas, notably ammonites, bivalves, and Foraminifera. Oil exploration is currently moving at a high pace in the Russian Arctic Jurassic, and our Russian colleagues have expressed great inter-ests in our findings and how their strata and those of southern Alaska will ultimately correspond both stratigraphically and faunally.

Hopefully in future postings we will keep you updated on our findings so close here in south-central Alaska.

REFERENCES

Blodgett, R.B., 2012, The bivalve genus Retroceramus Koshelkina, 1959: Alaska Geology (Newsletter of the Alaska Geological Society, Inc.), v. 42, no. 8, p. 5-8.

Blodgett, R.B., and Santucci, V.L., 2014. Fossil Point (Lake Clark National Park & Preserve): Alaska’s “Jurassic Park” for Middle Jurassic invertebrate fossils: Proceedings of the 10th Conference on Fossil Re-sources, Rapid City, South Dakota May 2014: Dakoterra, v. 6, p. 98-106.

Blodgett, R.B., and Tainter, A.W., 2013, Marine life in the Middle Jurassic of the Iniskin Peninsula, Lower Cook Inlet, south-central Alaska: Alaska Geology (Newsletter of the Alaska Geological Society, Inc.), v. 44, no. 4, p. 5-8.

Eichwald, Eduard Von, 1871, Die Miocän- und Kreideformation von Aläska und den aleutischen Inseln: Geognostisch-Palaeontologische Bermerkungen ber die Halbinsel Mangischlak und Aleutischen Inseln, p. 88-200, St. Petersburg.

Detterman, R.L., 1963, Revised stratigraphic nomenclature and age of the Tuxedni Group in the Cook Inlet region, Alaska: U.S. Geological Survey Professional Paper 475-C, p. C30-C34.

Detterman, R. L., and Hartsock, J.K., 1966, Geology of the Iniskin-Tuxedni region, Alaska: U.S. Geological Survey Professional Paper 512, 78 p.

Imlay, R.W., 1961. New genera and subgenera of Jurassic (Bajocian) ammonites from Alaska: Journal of Paleontology, v. 35, no. 3, p. 467-674.

Imlay, R.W., 1964, Middle Bajocian ammonites from the Cook Inlet region, Alaska: U.S. Geological Survey Professional Paper 418-B, p. B1-B61.

Imlay, R.W., 1984, Early and middle Bajocian (Middle Jurassic) ammonites from southern Alaska: U.S. Geo-logical Survey Professional Paper 1322, 38 p.

Magoon, L.B., Adkinson, W.L., and Egbert, R.M. 1976. Map showing geology, wildcat wells, Tertiary plant fos-sil localities, K-Ar age dates, and petroleum operations, Cook Inlet area, Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map I–1019, 3 sheets, scale 1:250,000.

Martin, G.C., 1926, The Mesozoic stratigraphy of Alaska: U.S. Geological Survey Bulletin 776, 493 p.

Martin, G.C., and Katz, F.J., 1912, A geologic reconnaissance of the Iliamna region, Alaska: U.S. Geological Survey Bulletin 485, 138 p.

Stanton, T.W., and Martin, G.C., 1905, Mesozoic section on Cook Inlet and Alaska Peninsula: Geological So-ciety of America Bulletin, v. 16, p. 391-410.


Figure 1. Geological map of part of the western side of Cook Inlet showing Fossil Point, Tuxedni Bay, and Chisik Island (modified from Magoon et al., 1976). The strata at Fossil Point are assigned to the Cynthia Falls Sandstone of the Tuxedni Group (shown in greenish-brown), to the west of which are shown outcrop-pings of the Fitz Creek Siltstone (shown in light-green color) and even further to west of which is the Red Glacier Formation (shown in dark green), both of the latter formations also belonging to the Tuxedni Group.

Figure 2. Cover of Eichwald’s 1871 classic paper in which the first taxonomic descriptions of marine invertebrates from Fossil Point were made

Figure 3. The three views (1-3) above are the origi-nal figures of Lyonsia aldiana Fischer of Eichwald, 1871, p. 172, Pl. 15, figs. 1-3. These originals were collected by Peter Doroschin when Alaska was still property of the Russian Empire. These specimens are deposited in St. Petersburg, Russia.


Figure 4. Bivalves from the Red Glacier Formation near Fossil Point, south shore of Tuxedni Bay, west side of Cook Inlet, south-central Alaska. 1-11 are of Lyonsia aldiana Fischer of Eichwald, 1871, p. 172, Pl. 15, figs. 1-3 [this is probably assignable to the genus Pleuromya]. 12-15 are of a second species, Panopaea aleutica Eichwald, 1871, p. 159, Pl. 12, figs. 7-8, possibly also belonging to a similar pleuromyid-like bivalve.

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Recognition and Significance of Bayhead Delta Deposits… 2014... · · 2015-01-14Volume 45 Number 1 September 2014 Page 1 Recognition and Significance of Bayhead Delta Deposits: