DUKE GEOLOGICAL LABORATORY Web: www.dukelabs.com E-Mail: [email protected] AIPG: TRIPS ON THE ROCKS Southern Central Park, New York 20 May 2009 Field Trip Notes by: Charles Merguerian, Ph.D. Duke Geological Laboratory 36 Fawn Lane Westbury, NY 11590 © 2009 CONTENTS CONTENTS..................................................................................................................................... i INTRODUCTION .......................................................................................................................... 1 HISTORICAL BACKGROUND.................................................................................................... 2 The History of Central Park........................................................................................................ 2 Rebuilding of the Zoo (1934): Robert Moses at his Finest........................................................ 5 History of Bedrock Geologic Investigations ............................................................................ 15 GEOLOGIC BACKGROUND..................................................................................................... 27 BEDROCK UNITS................................................................................................................... 27 Layer I: "Basement Complex" (Proterozoic Z and Y).......................................................... 27 Layers IIA and IIB: Cambro-Ordovician Strata ................................................................... 31 Bedrock Stratigraphy of New York City .................................................................................. 35 Geologic Structure--A Primer................................................................................................... 39 Folds...................................................................................................................................... 40 Faults..................................................................................................................................... 42 Surfaces of Unconformity..................................................................................................... 45 Sedimentary Structures ......................................................................................................... 46 Structures in Sedimentary- vs. Metamorphic Rocks ............................................................ 47 Tectonostratigraphic Units.................................................................................................... 48 Structural Geology of New York City...................................................................................... 48 Structure Sections ................................................................................................................. 49 The Geology of Cameron's Line............................................................................................... 50 Geology of Central Park ........................................................................................................... 52 Faults and Seismicity ................................................................................................................ 57 The Taconic Problem in New York City .................................................................................. 58 The Taconic Orogeny ............................................................................................................... 65 Post-Taconic Crustal Disturbances........................................................................................... 66 Plate-tectonic Interpretation...................................................................................................... 67 LAYER VII: QUATERNARY SEDIMENTS AND ASSOCIATED FEATURES ERODED BY GLACIERS ON BEDROCK SURFACES ........................................................................ 69 Features of Pleistocene Age.................................................................................................. 69 Features Made by Glacial Erosion of Bedrock..................................................................... 69 Striae and Grooves............................................................................................................ 70 Roche Moutonnées ........................................................................................................... 74 Drumlins (especially Rock Drumlins) .............................................................................. 75 Data from Indicator Stones ............................................................................................... 77 Pleistocene Sediments........................................................................................................... 77 Till..................................................................................................................................... 77 Outwash ............................................................................................................................ 77 Previous Interpretations of Glacial-flow-direction Indicators.............................................. 77 OBJECTIVES............................................................................................................................... 88 LIST OF LOCALITIES TO BE VISITED................................................................................... 88 DESCRIPTIONS OF INDIVIDUAL LOCALITIES ................................................................... 89 TABLES ....................................................................................................................................... 95 REFERENCES CITED............................................................................................................... 103 i DUKE GEOLOGICAL LABORATORY AIPG - TRIPS ON THE ROCKS Geology of Southern Central Park, New York 20 May 2009 Logistics: Departure from 59th Street and Central Park West @ 4:00 PM INTRODUCTION Today's walking trip to Central Park will cover only the southern part of this large area. We will begin near the zoo and swing around to the south and west, possibly ending opposite the American Museum of Natural History. In this guidebook, we review some of the history of the park itself, including its need and development, Robert Moses' reconstruction of the zoo in the mid-1930's as a tribute to his good friend, former Governor Alfred E. Smith, and many of the past geologic studies. We will depend considerably on CM's unpublished detailed studies carried out in 1982-1984. Geologically, we shall concentrate on the metamorphic bedrock of the Taconic Sequence and on the glacially eroded features on the bedrock surface. In the bedrock, we will examine the basis for CM's mapping of Cameron's Line within southern Central Park. We will be "going in and out the window," so to speak, as we pass back and forth between the middle unit of the Manhattan Schist (Waramaug or Hoosac Formation equivalent) beneath the Cameron's Line overthrust and the Hartland Formation, which composes the upper, overthrust sheet. The trip will provide an adequate basis for demonstrating CM's subdivisions of the various schist units of New York City formerly lumped together as the Manhattan Schist formation. In addition, we will focus on the glacial history of New York City as indicated by features developed on the crystalline bedrock by advancing Pleistocene ice. The rocky knolls within Central Park show dramatic effects of glacial erosion. The most-dominant features were caused by a thick glacier that flowed across Manhattan from about N30°W to S30°E. By careful study, however, it is possible to work out the effects of glacier(s) flowing from the NNE to SSW. 1 HISTORICAL BACKGROUND In this section, we review some of the circumstances surrounding the origin and construction of Central Park, Robert Moses' 1934 rebuilding of the zoo, and some of the previous geologic work both in the park and in the general vicinity of Manhattan Island. Central Park is rectangular in outline. It spans two and a half miles in length between 59th and 110th Streets and one-half mile in width between Fifth Avenue and Central Park West (Eighth Avenue). It covers roughly 840 acres in the midst of New York City, perhaps the most heavily engineered area in the world. According to the 1866 Guide to New York City (p. 31), "The Park was originally a bare, unwholesome suburb of the city, acres of it were naked of soil, and stagnant, marshy spots gathered the filth of bone-boiling establishments and pig-styes". Chronicles of the day reported that more than 5,000 squatters (outdoorsmen) lived on the terrain in shanties and hovels and that dog packs roved the area amidst the putrid smell of stables and the aforementioned pigsties and bone factories. Planned and constructed in the mid-1800s (Figure 1, on cover), Central Park rivals the well-known public parks of Europe and has provided an important rural aspect to recreational activities on Manhattan Island. The largest public park on the continent and known the world over for its natural botanical- and geological beauty and focus for a multitude of social- and cultural events since its construction, the story of Central Park is of historic interest to all students of our natural environment. As such, we here include a brief synopsis of the Park's unique story. The History of Central Park Drawing heavily from Cook (1869), the following section describes the planning and development of Central Park. In the early 1800s,