Paleopedology of the Late Triassic Middle Passaic Formation, Newark Supergroup, Pottstown, Pa
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PALEOPEDOLOGY OF THE LATE TRIASSIC MIDDLE PASSAIC FORMATION, NEWARK SUPERGROUP, POTTSTOWN, PA A Thesis Submitted to the Temple University Graduate Board In Partial Fulfillment Of the Requirements for the Degree Master of Science By Steven Booty August 2013 ___________________________ Dr. Dennis O. Terry, Jr., Advisor ___________________________ Dr. Allison R. Tumarkin-Deratzian ___________________________ Dr. David E. Grandstaff ABSTRACT Cyclic stratigraphy has been recognized in the Newark Basin for many years. Each package, referred to as a Van Houten Cycle (VHC), generally has three divisions: shallow lake, deep lake, and subaerial exposure. Van Houten (1964) first proposed that Milankovitch orbital forcing was responsible for the manifestation of these ~21 kyr cycles. Although root traces have been observed in VHCs by others, no detailed paleopedological analysis has been performed that examines the relationship between individual VHCs, orbital forcing, and paleosol development. The Middle Passaic Formation of Late Triassic age is continuously exposed for over 30 meters along a railroad cut that follows Manatawny Creek near Pottstown, PA. Six VHCs were identified at this location and the upper most three were selected for detailed study due to their strong development. Three Van Houten Groups (VHGs), consisting of VHC Division 3, Division 1, and Division 2 respectively, were formed in order to group paleosol profiles (Division 3) with stratigraphically adjacent lacustrine units (Divisions 1 and 2) since the lakes directly affect the paleosurface through inundation and erosion. Petrographic analysis suggests that soils in this section only developed to the degree of Entisols or Protosols. Voids are lined with chalcedony and cored with calcite indicating diagenetic alteration. Molecular weathering ratio calculations proved unreliable due to diagenetic alteration of the strata. Magnetic susceptibility was measured on two intervals of the section, but is not well-suited to fractured, massive rock due to signal attenuation. ii Paleosol development is greater in instances where the overlying lake is poorly developed. Paleosols that are associated with a shallow lake or no lake likely have more time to develop than paleosols associated with deep lakes as the precipitation filling the lake would saturate the soil, hindering pedogenesis. The VHCs’ ~21 kyr interval forces time to be the limiting factor for pedogenesis in this section, ending in either sedimentation or inundation. However, time is also tied to climate as it modulates from relatively moist to relatively drier within a VHC. Orbital forcing is the ultimate controlling factor in soil formation since time, climate, insolation, and precipitation are all interrelated and influenced by it. Relief is independent of orbital forcing and a possible control on soil formation within the Basin. Soils that formed distal from the bounding fault may not have been subject to inundation due to their higher elevation. Further research is needed to establish paleocatenary relationships of soil within the Newark Basin. iii ACKNOWLEDGMENTS There are a lot of thanks to give regarding this project. Some people may require their own page, but I’ll try to paraphrase. Thanks to the Colebrookedale Railroad, especially Beanie, for allowing us on their land. I would like to thank all the professors for pushing me to make observations, not interpretations. DT, thank you for showing me the wonderful world of paleopedology and getting me started with fieldwork… and this project. It was puns of fun being your advisee. May the peanut butter joke forever live in infamy. G, when you weren’t making fun of New Jersey I suppose you may have taught me a thing or two about isotopes. Your straightforward advice was always worth the “Well, no…” that surely followed whatever question I had. But I got there! Allison… kitty! Also thank you for providing me background information for this project and helping me (and the rest of us) teach fossils to the evolutions kids. And sarcasm is cool or whatever. To my fellow graduate students: I literally could not have done this without you. Andrew, Joe, and Justin, you were all there from day one, dealing with herp, derp, kee, and other things I say that make no sense. Good on you guys, good on you. Thanks to Logan, your curiosity is surpassed by no one else I know. Keep on Logan-ing! Thanks to the chemistry kids: especially Mongo and Kate – always making sure I’m not hearing colors. Thanks to Nick for being a dog. Here is where I would thank Oest. Thank you Jesse for making this awkward and thanks to Stevie Pee and Dr. Myer for all the XRD help. Bill, thank you for being my ped-head mentor over these past two years. You’ve helped me with my thesis more than these three sentences could possibly cover. Prrrrrrrttttttttt... iv I must give an extra special thanks to Shelah for making sure everything went as smooth as CST administrative malarkey would allow, and for always keeping the coffee pot full. Also thanks to Jim and Donald for keeping the department together. Thanks to the undergraduates that helped me with this project, either directly or indirectly. Danni, thanks for making thin sections like a boss. Leslee, tank you for keeping me from freaking out, and helping out when you could. Supreme thanks to Matt Enos for helping me with my field work, even when it was on weekends or got boring. Last, but not least, I want to thank my family for understanding/putting up with my decision to further my education and for their support. v TABLE OF CONTENTS Page ABSTRACT ………………………………………………………………………. ii ACKNOWLEDGMENTS ...……………………………………………………….. iv LIST OF FIGURES ………………………………………………………………... viii LIST OF TABLES …………....…………………………………………………… x CHAPTER 1. INTRODUCTION …………………………………………………………….. 1 2. BACKGROUND ……………………………………………………………… 8 2.1 Field Site ………………………………………………………………. 8 2.2 Background Geology ………………………………………………….. 8 2.3 Previous Work ………………………………………………………… 14 2.3.1 Newark Basin ……………………………………………….. 14 2.3.2 Paleosols …………………………………………………………….. 19 3. METHODS ……………………………………………………………………. 22 3.1 Field Work ……………………………………………………………. 22 3.1.1 Paleopedological Analysis ………………………………….. 22 3.1.2 Magnetic Susceptibility …………………………………….. 23 3.2 Laboratory Analysis …………………………………………………... 23 3.2.1 Depth Ranks ………………………………………………… 23 3.2.2 Soil Micromorphology ……………………………………… 23 3.2.3 Clay Mineralogy …………………………………………….. 24 3.2.4 X-Ray Fluorescence ………………………………………… 24 4. RESULTS ……………………………………………………………………... 26 4.1 Lower Van Houten Group …………………………………………….. 26 4.2 Middle Van Houten Group ……………………………………………. 31 4.3 Upper Van Houten Group …………………………………………….. 34 4.4 Clay Mineralogy ………………………………………………………. 35 4.5 Molecular Weathering Ratios …………………………………………. 38 5. DISCUSSION …………………………………………………………………. 47 5.1 Agents of Soil Formation ……………………………………………... 47 5.1.1 Climate ……………………………………………………… 47 5.1.2 Organisms …………………………………………………… 48 5.1.3 Parent Material ……………………………………………… 50 5.1.4 Relief ………………………………………………………... 51 5.1.5 Time …………………………………………………………. 53 vi 5.2 Molecular Weathering Ratios …………………………………………. 54 5.3 Magnetic Susceptibility ……………………………………………….. 54 5.4 Diagenesis ……………………………………………………………... 55 5.5 Lake Facies and Marl Units ……………………………………………. 57 5.6 Orbital Forcing ………………………………………………………... 61 5.7 Modern-Day Comparisons ……………………………………………. 64 5.8 Implications …………………………………………………………… 65 6. CONCLUSIONS ……………………………………………………………… 67 REFERENCES CITED ……………………………………………………............ 69 APPENDICES Appendix A. X-Ray Fluorescence Instrument Error Based On Bhvo Analyses …………………………………………………………………... 76 Appendix B. Composition Of Samples From Paleosols And Lacustrine Sediments In Weight Percent Of Oxides And Minor Elements (ppm)……. 77 Appendix C Magnetic Susceptibility Data ………………………………… 79 vii LIST OF FIGURES Page Fig. 1 – Geologic map of the Newark Basin……………………………………….. 2 Fig. 2 – Comparison of Triassic and modern day rift basins in Eastern Africa……. 3 Fig. 3 – The Van Houten Cycle model……………………………………………... 5 Fig. 4 – Exposures of various Triassic facies in the Newark Basin………………... 6 Fig. 5 – Aerial view of Pottstown, PA……………………………………………… 9 Fig. 6 – The Newark Basin as it was in the Late Triassic and today……………….. 11 Fig. 7 – Drill core data from the Newark Basin Coring Project……………………. 12 Fig. 8 – Cartoon representation of the three basic Milankovitch cycles…………… 17 Fig. 9 – Graphical representation of the hierarchy of sedimentary cycles…………. 18 Fig. 10 – Cross section of the Newark Basin Coring Project………………………. 20 Fig. 11 – Measured section of the exposure at Pottstown, PA…………………….. 27 Fig. 12 – Van Houten Cycle-scale measured section of the exposure at Pottstown.. 28 Fig. 13 – Photomicrographs of Unit 16…………………………………………….. 32 Fig. 14 – Photomicrographs of Unit 17…………………………………………….. 33 Fig. 15 – Photograph of Unit 19 and photomicrograph of clay fabric…………… 36 Fig. 16 – Photomicrographs of features within Unit 19……………………………. 37 Fig. 17 – Photomicrographs of Unit 20 and polished slabs from Units 29 and 30… 39 Fig. 18 – Photographs of various units within the middle Van Houten Cycle……... 40 Fig. 19 –.Photographs and photomicrographs of Unit 28………………………….. 41 Fig. 20 – Photomicrographs of Unit 30…………………………………………….. 42 Fig. 21 – X-Ray diffractogram of profiles………………………………………….. 43 viii Fig. 22 – Molecular weathering ratios of each of the selected paleosols…………... 44 Fig. 23 – Bioturbation features within the study section…………………………… 49 Fig. 24 – Schematic drawings of the various basin types…………………………..